Light Cone 2018

May 14, 2018, 8:00 AM → May 18, 2018, 6:00 PM US/Eastern

Jefferson Lab - CEBAF Center

Andrea Signori (Jefferson Lab), Chueng R. Ji (North Carolina State University), Raul Briceno (Jefferson Lab), Wally Melnitchouk (Jefferson Lab)

===============================================================

To attend the talks remotely via Bluejeans, please click here (meeting ID: 311 536 872)

If the link does not direct you automatically to the meeting, please follow these instructions.

Parallel sessions, Thursday May 17:
- session 3A-4A (Auditorium) : click here (meeting ID: 615 342 749)
- session 3B-4B (F113) : click here (meeting ID: 616 186 559)

===============================================================

Light Cone 2018 is the latest in the series of conferences that, beginning in 1991, have played an important role in promoting research towards a rigorous description of hadrons and nuclei based on light cone quantization methods. A strong relation with experimental developments represents an important commitment of the light cone community, so it is timely that Light Cone 2018 will be held at Jefferson Lab. As with earlier conferences in the series, the aim of this meeting will be to create a scientific program that will stimulate developments in research at the forefront of nuclear, hadron and particle physics research.

In particular, Light Cone 2018 will focus on the following physics topics and methodologies:

Physics Topics

   hadronic structure
   meson and baryon spectroscopy
   parton physics
   finite temperature and density QCD
   few- and many-body physics

Methodologies

   light-front field theories
   lattice field theory
   effective field theories 
   phenomenological models
   present and future facilities

 

Deadline for abstract submission: April, 25th 2018

Monday, May 14

Registration Opens

A

Convener: Wally Melnitchouk (Jefferson Lab)

1 Welcome

Speaker: Stuart Henderson (Argonne National Lab/Jefferson Lab)

2 Nuclear Physics at Jefferson Lab

Speaker: Robert McKeown (Jefferson Lab)

Slides BMCK_LC2018_v1.pptx

3 Mesons and Baryons in Basis Light Front Quantization

Speaker: Prof. James Vary (Iowa State University)

Slides LC2018_Vary_JLAB.pdf

4 Overview of Hadron Structure from Lattice QCD

Speaker: Prof. Martha Constantinou (Temple University)

Slides Light_Cone_2018_MConstantinou.pdf

coffee break

B

Convener: Dr David Richards (Jefferson Lab)

5 x-dependent hadron structure from lattice QCD

Speaker: Dr Christopher Monahan

Slides cjmonahan_lc2018.pdf

6 Pseudo-PDFs and quasi-PDFs structure

Speaker: Anatoly Radyushkin (ODU/JLab)

Slides Radyushkin_LC18_05_14.pdf

7 A lattice QCD computation of quark distributions at the pysical point

Speaker: Dr Fernanda Steffens

Slides LC_2018.pdf

8 Full nucleon structure functions from the lattice

Speaker: G. Schierholz

Slides lightcone18.pdf

lunch break

C

Convener: Nobuo Sato (UConn)

9 TMDs and SIDIS

Speaker: Ted Rogers (ODU/JLab)

Slides lightconerogers.pdf

10 Relating TMD and collinear factorization

Speaker: Prof. Leonard Gamberg (Penn State Berks)

Slides gamberg_LC18fx.pdf

11 Classical binding of hadrons

A perturbative expansion for bound states starts with a lowest order approximation that has a non-perturbative wave function, with all powers in the coupling $\alpha$. The distinction between lowest and higher orders is blurred since contributions of finite order in $\alpha$ may be assigned to either one. A criterion beyond powers of $\alpha$ is needed to fully define a perturbative expansion for bound states. I consider the criterion that the gauge field should satisfy the classical field equations at lowest order. This corresponds to lowest order in $\hbar$, but all orders in $\alpha$, and ensures that the expansion starts from a configuration with stationary action. Poincare invariance as well as unitarity is expected to hold at each order in the fundamental constant $\hbar$. Higher order corrections are defined by an expression for the S-matrix similar to the Interaction Picture, but with in- and out-states that are eigenstates of a Hamiltonian that includes the classical gauge field. The formal derivation and higher order terms of this "Potential Picture" remain to be studied. When applied to non-relativistic QED atoms the classical criterion leads to lowest order atoms described by the Schrödinger equation. The Schrödinger equation cannot be derived from QED based only on a power expansion in $\alpha$, for reasons stated in the beginning. The QCD scale $\Lambda_{QCD}$ can arise through a boundary condition on the classical gluon field equations. The homogeneous solution for the classical gluon field that satisfies basic physical requirements appears to be unique, up to an overall scale. It is of O($\alpha_s^0$) and leads to a strictly linear potential for mesons and a related one for baryons. Meson wave functions may be found iteratively, corresponding to an expansion in $1/N_c$. At lowest order in $1/N_c$ there is no string breaking and the states lie on linear Regge trajectories for vanishing quark mass $m$. The overlap of these states determine decays and meson loop corrections, as required by unitarity at higher orders in $1/N_c$. There are massless solutions which allow to include the effect of spontaneous chiral symmetry breaking when $m=0$. The massless $0^{++}$ sigma state can mix with the perturbative vacuum without breaking Poincare invariance. A chiral transformation of such a condensate creates massless pions. For a small quark mass $m \neq 0$ the $0^{-+}$ pion gains a mass $M \propto \sqrt{m}$ and is annihilated by the axial vector current as expected for a Goldstone boson.

Speaker: Prof. Paul Hoyer (University of Helsinki)

Slides Hoyer_LC2018.pdf

12 Lattice field theory in real time

Speaker: P. Bedaque

Slides BedaqueLC2018.pdf

coffee break

D

Convener: Robert Edwards (Jefferson Lab)

13 Recent results from GlueX

Speaker: Justin Stevens (College of William and Mary)

Slides lightcone_gluex.pdf

14 Recent results in lattice QCD spectroscopy

Speaker: B. Hoerz

Slides hoerz.pdf

15 Exotic Meson Spectroscopy: Challenges and Prospects

Speaker: Dr Vincent Mathieu (JLab)

Slides LightCone-May18.pdf

16 Quarks and Mesons in the Covariant Spectator Theory

Speaker: E. Biernat

Slides Biernat_LC2018.pdf

reception

Tuesday, May 15

E: vacuum / 1

Convener: Dr Jianwei Qiu (Jefferson Lab)

17 Correspondence between IFD and LFD: Vacuum and related issues

Speaker: Chueng R. Ji (North Carolina State University)

Slides LC2018-Ji.pdf

18 Contrasting light-front and canonical representations of quantum field theory

Speaker: W. Polyzou

Slides lc_2018_talk.pdf

19 Non-triviality of the vacuum in light-front quantization

Speaker: John Collins

Slides Collins-LC2018.pdf

20 Physics on the Light Front: The Light-Front Vacuum and Light-Front Holography

Speaker: Prof. Stanley Brodsky (SLAC National Accelerator Laboratory, Stanford Univsersity)

Slides SJB_LC2018_May_15,_2018__.pdf

coffee break

E: vacuum / 2

Convener: Dr Jianwei Qiu (Jefferson Lab)

21 Chirally constraining the proton light-cone wavefunction

Speaker: S. Beane

Slides JLab2018silasbeane.pdf

22 What ET thinks of the LF vacuum

Speaker: J. Hiller

Slides hiller-lc2018.pdf

23 discussion

Slides

• Ben-Bakker.pdf
• martinovic_vac.pdf
• Paul-Hoyer.pdf
• Qiu-Discussion-Intro.pdf
• Stan-Glazek.pdf

lunch break

Parallel session 1A

Convener: W. Broniowski

24 Progress on Calculation of Pion Valence Distribution form Hadronic Lattice Cross Sections

Recently, it has been shown that a class of coordinate-space-separated non-local hadronic matrix elements, computable directly in lattice QCD, can be factorized into parton distribution functions with calculable coefficients, in the same manner as the hadronic cross sections measured in an experiment [Phys.Rev.Lett. 120 (2018) no.2, 022003]. The pion and kaon, the lightest pseudo scalar mesons, provide an excellent theatre in which to explore these ideas. Furthermore, the pion is of inherent theoretical interest and plays a vital role in the understanding the nucleon and in nuclear structure. In this talk, we describe progress at understanding the valence quark distribution of the pion using configuration-space separated gauge-invariant hadronic currents.

Speaker: Raza Sufian (Jefferson Lab)

Slides Raza_LCSs.pdf

25 First Monte Carlo Global QCD Analysis of Pion Parton Distributions

Pions have long been associated with being the lightest bound state made of quarks, antiquarks and gluons (partons), as well as being the Goldstone boson produced from the breaking of effective chiral symmetry. In previous works, its parton distribution function (PDF) has been determined only by $\pi A$ Drell-Yan (DY) experiments such as E615 and NA10 done at Fermilab and CERN, respectively. In the DY process, two hadrons collide, with one donating a quark and the other donating an antiquark, eventually producing a dimuon pair. Since the initial annihilation provides enough energy to create a heavy lepton pair, the quark/antiquark must have high momentum. Thus, the DY process can only resolve the high momentum fraction ($x_\pi \gt 0.2$) region of the pion’s parton distribution, which constrains only the valence PDFs. To more accurately determine the pion PDF at lower $x_\pi$, we must include data from leading neutron (LN) electroproduction experiments such as H1 and Zeus done at HERA at DESY. Here, a target proton struck with an electron transforms into a detected neutron, a process which at forward angles, is dominated by the one-pion exchange model. Inherently, the theory has some model dependence (albeit relatively weak) coming from the splitting function’s regularization prescription, of which we test five. This process probes much smaller momentum fraction as $x_\pi \sim 10^{-3}$, where the sea and gluon dominate, providing an unseen constraint on the sea quark and gluon PDFs. In practice, we fit the parton distributions to all existing DY and LN datasets using a Monte Carlo (MC) method based on nested sampling. The method uniquely calculates the likelihood function at various positions in vector space to nest around the global maximum likelihood value. The MC nature allows us to rigorously quantify the uncertainty in the PDFs. We successfully have determined the pion PDFs at both the high-$x_\pi$ and low-$x_\pi$, and in doing so, we obtain a $\chi^2$ of $0.96 – 1.04$ over the five models. The PDFs we obtain reveal that at the input scale, the gluon carries a significant fraction of the pion momentum $\sim 30\%$, which is higher than predicted with only the DY data, and the sea carries $\sim 15\%$ of the momentum fraction of the pion. We can also describe the $\bar{d}-\bar{u}$ asymmetry in the proton by using the determined pion PDF and the same pion splitting functions as used in the LN process.

Speaker: Mr Patrick Barry (North Carolina State University)

Paper https://arxiv.org/abs/1804.01965

Slides Barry_Light_Cone_2018.pdf

26 Pion Model inspired by Lattice QCD

We study a pion Bethe-Salpeter (BS) amplitude model in Minkowski space inspired by Lattice QCD results for the quark self-energy for space like momentum. The model is based on the assumption of the Godstone boson nature of the pion and the pseudoscalar BS vertex is chosen to match the scalar part of the self-energy. The model allows a Nakanishi representation of the BS ampliude and produce reasonable results for the form-factor and decay constant. In addition it is discussed how the model can be used to study, PDFs, TMDs and the elementary fragmentation function. Work in collaboration with: Clayton de Mello, João Pacheco BC de Melo, Wayne de Paula and Rômulo Moreira Moita.

Speaker: Prof. Tobias Frederico (Instituto Tecnologico de Aeronautica)

Slides FREDERICO_LC2018.pdf

27 Pion off-shell electromagnetic form factors

\documentclass[12pt]{article} \begin{document} \pagestyle{empty} Pion off-shell electromagnetic form factors J.~P.~B.~C.~de~Melo$^1$,~Tobias Frederico$^2$ and C.-R.~Ji$^3$ $^1$Laborat\'orio de F\'{\i}sica Te\'orica e Computacional-LFTC \newline Universidade Cruzeiro do Sul, 01506-000, S\~ao Paulo, Brazil \\ $^2$Departamento de F\'\i sica, Instituto Tecnol\'ogico de Aeron\'autica, Centro T\'ecnico Aeroespacial $^3$Department of Physics, North Carolina State University,~NCSU, USA \\ The light mesons, like pion, play special rules in try to understanting QCD, between another motivation, the pion is the Goldstone boson, and, is central to symmetry breaking and partial current conservation (PCAC). The most general way to take informations about the hadronic substructure, i.e.; in terms of the degrees of freedom from QCD, quarks and gluons, are the study of the electromagnetic form factors. The electromagnetic form factors play also, fundamental importance in order to studing processes involving hadrons and virtual photons. Because the pion have spin zero, and, with the time-reverse invariance, we need only one electromagnetic form factor to describe the pion. Still, general approaches about electromagnetic form factors for pseudoscalar particles, not take in account off-shell effects. But in order to be more consistent, and go beyond on-shell, the off-shell effects is need be included at the electromagnetic interactions. The possible on-shell effects, also appear in meson pion exchange current [1], because in that case, the exchanged pion is not on-mass shell. The most general electromagnetic description for the pion, need two electromagnetic form factors, $F_1(q^2,t)$, and, $F_2(q^2,t)$, wich are related the Ward-Takahashi identity [2]. Ward-Takahashi identity was explore some years ago for the boson case in the reference [3] with the light-front approach. The electromagnetic off-shell form factors was been calculated for the boson bound state, and, in that work, is realized, the zero modes inclusion is crucial to preserve the Ward-Takahashi indentities with the Light-front Field Theory. However, microscopic model is not already made to incorpore off-shel effects at the vertex, and extract the off-shell form factors. In the present work, we explore the electromagnetic off-shell effects for the pion meson and extract the off-shell electromagnetic form factors, $F_1(q^2,t)$ and $F_2(q^2,t)$, from experimental electroproduction cross section data [4,5]. However, the extraction of the electromagnetic form factor with the reaction $^1H(e,e',\pi^+)n$, need some model for the $G_{\pi NN}(t)$ form factor, here, we explore some possibilities for this form factor. The differents models are explored, in order to see the power predictions for that models, with respect the pion observables, like, electromagnetic form factors, electromagnetic radius and, also, the pion electroweak decay constant. \\ References 1. F.Gross and D. O. Riska, Phys. Rev. C36, 1928 (1987). 2. Lewis H. Ryder, Quantum Field Theory, Cambridge University Press. 3. H. W. L. Naus, J. P. B. C. de Melo and T.Frederico, Few Body Syst. 24, 99 (1998). 4. H. P. Blok et al., [Jefferson Lab Collaboration], Phys. Rev. C78, 045202 (2008). 5. G. M. Huber et al., [Jefferson Lab Collaboration], Phys. Rev. C78, 045203 (2008). \end{document}

Speaker: Dr Joao Pacheco de Melo (Laboratório de Fisica Teórica e Computacional, LFTC, UCS)

Slides talklc2018v16.pdf

28 Light Quark Flavor asymmetry and EMC effect studies at the Fermilab E906/SeaQuest experiment

The Fermilab E906/SeaQuest is an experiment aimed at studying the anti-quark distributions in nucleons and nuclei. The experiment uses a 120 GeV proton beam extracted from the Main Injector at Fermilab to collide with various liquid and cryogenic targets to study a variety of physics topics ranging from light quark flavor asymmetry to the EMC effect in the nucleon sea. It takes advantage of the Drell-Yan process to probe the anti-quark structure. In the Drell-Yan process, a quark from one hadron annihilates with an anti-quark from another hadron, producing a virtual photon which eventually decays into a dilepton pair. The SeaQuest forward spectrometer is optimized for detecting such di-muon pairs. The overall status of the experiment and recent results regarding dbar/ubar ratio and EMC effect studies will be presented in this talk.

Speaker: Arun Tadepalli (Rutgers University)

Slides Light_Cone_2018_Tadepalli.pptx

Parallel session 1B

Convener: O. Gonzalez

29 Convergence of the light-front coupled-cluster method

We explore the convergence of the light-front coupled-cluster (LFCC) method in the context of two-dimensional quenched scalar Yukawa theory. This theory is simple enough for higher-order LFCC calculations to be relatively straightforward. The quenching is to maintain stability; the spectrum of the full theory with pair creation and annihilation is unbounded from below. The basic interaction in the quenched theory is only emission and absorption of a neutral scalar by the complex scalar. The LFCC method builds the eigenstate with one complex scalar and a cloud of neutrals from a valence state that is just the complex scalar and the action of an exponentiated operator that creates neutrals. The lowest order LFCC operator creates one; we add the next order, a term that creates two. At this order there is a direct contribution to the wave function for two neutrals and one complex scalar and additional contributions to all higher Fock states. Results for the lowest order and this new second order approximation are compared with those obtained with standard Fock-state expansions.

Speaker: Dr Sophia Chabysheva (University of Minnesota-Duluth)

30 Recursion relations for off-shell amplitudes on the light-front and Wilson lines

In this presentation we will discuss some interesting properties of the off-shell scattering amplitudes in the framework of the light-front perturbation theory. It is shown that certain recursion relation between tree level off-shell amplitudes in this formalism actually resums whole classes of graphs into a Wilson line. More precisely, we demonstrate a correspondence between the light-front methods for the computation of the off-shell amplitudes and the approach which makes use of the matrix elements of straight infinite Wilson lines, which are manifestly gauge invariant objects and satisfy Ward identities. In addition, we demonstrate that such structure is helicity independent and emerges from analytic properties of matrix elements of Wilson line operators, where the slope of the straight gauge path is shifted in a certain complex direction. This is similar to the procedure leading to the Britto-Cachazo-Feng-Witten (BCFW) recursion, with the difference that a complex shift is applied to the Wilson line slope instead of the external momenta.

Speaker: Prof. Anna Stasto (Penn State)

Slides anna_stasto_lc18.pdf

31 The MHV Lagrangian and hidden Wilson lines

The MHV Lagrangian is the Yang-Mills Lagrangian quantized on the light cone, where the two transverse gluonic degrees of freedom have been canonically transformed to a set of new fields, in which the vertices become a series of the maximally helicity violating (MHV) amplitudes continued off-shell. The usage of the MHV vertices to construct amplitudes is also known as the Cachazo-Svrcek-Witten (CSW) method. After a review of these ideas I will discuss properties of the transformation leading to the MHV Lagrangian, in particular I will argue that the solution to the field transformation has a form of certain Wilson line. I will also discuss some consequences of that fact.

Speaker: Piotr Kotko (Institute of Nuclear Physics, PAN)

Slides LC2018_Kotko_1.pdf

32 Energy-momentum tensor for unpolarized proton target

The expectation value of the quantum energy-momentum tensor (EMT) for an unpolarized proton target in the Breit frame can be matched with an anisotropic perfect fluid EMT. This matching offers the possibility of interpreting the EMT form factors in terms of the internal energy and transverse/radial pressure inside an unpolarized proton target. The generalization of this result to a more general class of frames leads to additional terms in the anisotropic fluid EMT, which can be related to the rotation and spin of proton. We illustrate these results using current phenomenological knowledge of the EMT form factors.

Speaker: Dr Arkadiusz Trawinski (CEA-Saclay)

Slides Trawinski, A. - LC2018

33 Fermion-antifermion phenomenology in Minkowski space

The advent of approaches based on the Euclidean space for studying hadron observables, such as lattice QCD and Schwinger-Dyson equations, has been remarkable and responsible to produce important understanding on the non-perturbative dynamical regime. However, the quantum field theory formulation in Minkowski space has subtle and essential signatures as, e.g., the ones related to the spin degrees of freedom, that require to be evaluated in a theoretical framework developed in the physical space, where the dynamical processes take place. One important tool is the Fock space expansion, which allows one to construct a probabilistic description of hadrons and to explore relativistic effects on the dynamics as, e.g., through the analysis of the electromagnetic (EM) form factors beyond the impulse approximation [1]. In recent years, studies based on actual solutions of the homogeneous Bethe-Salpeter equation directly in Minkowski space have becoming available. This achievement makes feasible to start phenomenological investigations of the hadron structure, shedding light on the intrinsic dynamics that is formally and conceptually connected with the physical space, i.e. the Minkowski one [2,3]. The new framework for solving the Bethe-Salpeter equation has a main ingredient given by the the so-called Nakanishi Integral Representation of the Bethe-Salpeter amplitude that allows one to explicitly deal with its analytic structure, without resorting to the Wick rotation. In order to illustrate the phenomenological potential of the aforementioned framework we explore the $0^-$ quark-antiquark bound state, by the solution of the coupled integral equations. The study is done in the ladder approximation, based on the suppression of the cross-ladder contribution found for bosonic systems [2]. By taking the constituents and exchanged-boson masses from, e.g., lattice calculations, dynamical observables like the light-cone momentum distributions are predicted. The decay constant $f_\pi$ is also computed, as well as the electromagnetic form factors. Such a preliminary investigation of the phenomenology of what we call mock pion will allow to settle the framework where one can develop more and more realistic description in Minkowski space. [1] V. Gigante, J. H. Alvarenga Nogueira, E. Ydrefors, C. Gutierrez, V. A. Karmanov and T. Frederico, Phys. Rev. D 95, 056012 (2017) [2] J. H. Alvarenga Nogueira, Chueng-Ryong Ji, E. Ydrefors and T. Frederico, Phys. Lett. B 777, 207-211 (2018)] [3] W. de Paula, T. Frederico, G. Salmè, M. Viviani, R. Pimentel, %Fermionic bound states in Minkowski space: light-cone singularities and structure, Eur. Phys. J. C 77, 764 (2017)

Speaker: Mr Jorge Henrique De Alvarenga Nogueira (Instituto Tecnológico de Aeronáutica & 'La Sapienza' Università di Roma & INFN, Sezione di Roma)

Slides bse_LC_JN.pdf

coffee break

Parallel session 2A

Convener: Dr Christopher Monahan (Institute for Nuclear Theory)

34 Evaluation of Parton Distribution Functions and Generalized Parton Distributions from their Moments and Ioffe Time Behavior

Electromagnetic interactions probe the Fourier transform of the quark-quark correlation function measuring the light cone distance traveled by the struck quark during the interaction, also known as Ioffe time. The small distance behavior of the correlation function can be determined by the first few moments calculated on the lattice while its large distance behavior, exceeding the proton size, is regulated by Regge type terms. I will show how this characteristic dependence of the correlation function can be used to extract the Bjorken x dependence of the u and d quark generalized parton distributions in the proton. I will also present a study of QCD evolution in the transverse space coordinate for the recently introduced pseudo-pdfs using a phenomenological model.

Speaker: Prof. simonetta liuti (university of virginia)

Slides liuti_LC18.pdf

35 The dressed quark propagator and new TMD sum rules

A new set of TMD sum rules is derived by relating integrals of the semi-inclusive quark-quark correlator to the fully dressed quark propagator. A complete set of momentum sum rules is obtained for the quark-quark TMDs up to twist-3 level, and for quark-gluon-quark TMDs up to twist-2. The technique is then extended to di-quark TMDs. Applications to inclusive DIS and semi-inclusive electron-positron annihilation will be discussed.

Speaker: Alberto Accardi (Hampton U. and Jefferson Lab)

Slides Accardi_-_New_sum_rules-expanded.pdf

36 Nucleon PDFs in small boxes

It has been recently proposed that PDFs can be studied directly using lattice QCD. Such studies require the evaluation of matrix of non-local operators. Since this was first proposed, there has been an intense investigation of all possible systematics except for the effects associated with the fact that lattice QCD is necessarily defined in a finite spacetime. In this talk, I present the first attempt to assess these systematics, and I show that these matrix elements might suffer of large finite-volume artifacts.

Speaker: Mr Juan Guerrero (Hampton University/Jefferson Lab)

Slides LC_2018_Juan_Guerrero.pdf

37 Pseudo Distributions from Lattice QCD

The Direct calculation of x-dependent parton distribution functions (PDFs) are not possible using ab initio Euclidean-space Lattice QCD, due to their definitions in terms of light-cone coordinates. I present the recent Lattice QCD calculation of pseudo PDFs, a Lorentz invariant generalization of light cone PDFs. These Lorentz invariant functions can be calculated on a Euclidean lattice and related to light cone PDFs in the proper limits. I will discuss the applicability of perturbative formula to the lattice data. I will also discuss methods of extracting the PDF from lattice data over a limited range of momenta and Euclidean-space separations.

Speaker: Joseph Karpie (College of William and Mary)

Slides Lightcone_(2018)_Pseudo-PDFs_on_the_Lattice.pdf

38 Direct calculation of slope of form factors in lattice QCD.

The charge radius of the nucleon can be related to the slope of the electromagnetic form factors at zero momentum transfer. Calculations of the form factors using lattice QCD are typically obtained for a discrete set of momenta $Q^2$, from which the charge radius can be inferred. We present a method to compute the slope of electromagnetic form factors directly, including at $Q^2 = 0$, by computing the coordinate-space moments of current matrix elements. We begin by describing the formalism, and then apply it to the calculation of the isovector form factor of the nucleon.

Speaker: Dr David Richards (Jefferson Lab)

Slides lightcone2018.pdf

39 -

Parallel session 2B

Convener: Prof. Stanley Brodsky (SLAC National Accelerator Laboratory, Stanford Univsersity)

40 Generalized parton distributions in light-front holographic QCD

The structure of generalized parton distributions is determined from light-front holographic QCD up to a universal reparametrization function $w(x)$ which incorporates Regge behavior at small $x$ and inclusive counting rules at $x \to 1$. A simple ansatz for $w(x)$ which fulfills these physics constraints with a single-parameter results in precise descriptions of both the nucleon and the pion quark distribution functions in comparison with global fits. The analytic structure of the amplitudes leads to a connection with the Veneziano model and hence to a nontrivial connection with Regge theory and the hadron spectrum.

Speaker: Dr Tianbo Liu (JLab & Duke)

Slides liu_lc2018.pdf

41 Non-perturbative constraints on the matrix elements of the energy-momentum tensor

The structure of the hadronic matrix elements of the energy-momentum tensor play an important role in determining the properties of the corresponding form factors which appear in the Lorentz covariant decomposition of these objects. In this talk I will discuss a non-perturbative approach to constraining the low energy limit of these form factors, and its relevance in interpreting the vanishing of the anomalous gravitomagnetic moment.

Speaker: Dr Peter Lowdon (SLAC)

Slides LC2018_Lowdon.pdf

42 Collisions of gluon strings in scattering of leptons and hadrons

The ridge effect observed in high multiplicity events in proton-proton scattering at LHC can be due to the collisions of flux tubes in the projectiles which are in turn related to the fundamental physics of color confinement. We discuss observable effects due to gluon string collisions in electron-proton and peripheral proton-proton scattering related to scattering of photons. In the former case, the final-state ridges are expected to exhibit maximal multiplicity when the elliptic flow is aligned with the electron scattering plane. In the second example, the final-state multiplicity and elliptic flow are maximal when the proton scattering planes are aligned. Variation of these observables with azimuthal angle between projectile scattering planes is estimated to be on the order of several percent.

Speaker: Stanislaw D. Glazek (Faculty of Physics, University of Warsaw)

Slides SDGlazek-Strings-LC2018-20180515.pdf

43 Single-Transverse-Spin-Asymmetry Studies in the Fixed-Target Mode using the LHC Beams (AFTER@LHC)

I will review the physics opportunities offered by the use of the multi-TeV proton LHC beam in the fixed-target mode with a polarised target.

Speaker: Jean-Philippe Lansberg (IPN Orsay - CNRS/IN2P3 - Paris-Saclay U.)

Slides AFTER-LC2108.pdf

44 Study of the gluon and charm content of the deuteron

We evaluate the gluon and charm parton distribution functions (PDFs) of the deuteron using light-front quantization together with the impulse approximation. We use a nuclear wave function obtained by solving the nonrelativistic Schrödinger equation with the realistic Argonne v18 nuclear force; it is then convoluted with the proton PDF. The resulting gluon distribution in the deuteron (per nucleon) is smaller than that of the proton by a few percent close x = 0.4, whereas it is enhanced at x larger than 0.6. We discuss the applicability of our computation and comment on how to extend it to x as large as two. We also analyze the charm distribution of the deuteron within the same approach by considering perturbatively and non-perturbatively (intrinsic) generated charm inside the deuteron. In particular, we note that the intrinsic charm content in the deuteron may be enhanced for 6-quark configurations.

Speaker: Dr Nodoka Yamanaka (IPN Orsay)

Slides 2018.05.15_yamanaka.pdf

45 -

Wednesday, May 16

F

Convener: F. Steffens

46 How PDF fits became precision physics

Speaker: Z. Kassabov

Slides talk.pdf

47 Collinear Distributions from Monte Carlo QCD Analyses

Speaker: Jacob Ethier (College of William and Mary/Jefferson Lab)

Slides Ethier_Light_Cone_2018.pdf

48 Partonic quasi- and pseudo-distributions of the pion from a chiral quark model

Speaker: W. Broniowski

Slides Broniowski_LC18.pdf

49 Quark model results for the PDFs and quasi-distributions of nucleons and mesons

Speaker: Dr Timothy Hobbs (Southern Methodist University)

Slides LC18_HOBBS.pdf

coffee break

G

Convener: Prof. Matthias Burkardt (NMSU)

50 The proton charge radius and the PRad experiment

Speaker: Haiyan Gao (Duke University)

Slides PRad-HGao-LightCone2018.pdf

51 Orbital angular momentum in the nucleon's chiral periphery

We study the transverse spatial distribution of orbital angular momentum (OAM) in the nucleon at peripheral distances b∼1/Mπ. Chiral EFT is used to compute the form factors of the energy-momentum tensor and their peripheral transverse densities, including the density associated with light-front orbital angular momentum. This density is represented in first–quantized form, as overlap integral of chiral light–front wave functions describing the transition of the nucleon to soft pion–nucleon intermediate states. We identify the operator generating OAM densities in transverse coordinate space and argued that under a fist-quantized framework interpretation, it properly describes the structure of OAM contributions in the nucleon’s periphery.

Speaker: Dr Carlos Granados (The George Washington University)

Slides LC18slides.pdf

52 Parton distributions from nonlocal chiral SU(3) effective theory

Speaker: P. Wang

Slides 2018LC_PingWang.pdf

53 Timelike form factors on the light front

Speaker: H.-M. Choi

Slides LC2018-Choi-May16.pdf

lunch break

Excursion

Thursday, May 17

C

Convener: Andrea Signori (Jefferson Lab)

54 Recent developments in nucleon spin decomposition

Speaker: Y. Hatta

Slides 2018JlabHatta.pdf

55 Large transverse momentum in semi-inclusive deeply inelastic scattering beyond the lowest order

Speaker: Nobuo Sato (UConn)

Slides slides.pdf

56 TMD phenomenology

Speaker: Osvaldo Gonzalez-Hernandez

Slides gonzalez_LightCone2018.pdf

57 Accessing dihadron fragmentation functions in e^+e^- and SIDIS

Speaker: Dr Hrayr Matevosyan (CSSM, University of Adelaide)

Slides Hrayr_Matevosyan-LightCone-2018_JLab_Talk.pdf

coffee break

H

Convener: Dr Anuradha Misra (University of Mumbai)

58 Abnormal relativistic states

Speaker: V. Karmanov

59 Approximate three-quark Hamiltonian in heavy flavor QCD

Hamiltonian for baryons in heavy-flavor QCD is approximately evaluated using the renormalization group procedure for effective particles (RGPEP). The calculation yields Hamiltonian terms up to second order in the strong coupling constant. The renormalized Hamiltonian eigenvalue problem is reduced to the Fock sector of only three quarks using assumption that effective gluons develop a mass. The resulting effective three-quark interaction Hamiltonian consists of the Coulomb and harmonic oscillator terms. The oscillator terms depend on the coupling constant, quark masses and the RGPEP scale, but they do not depend on the gluon mass ansatz. Masses of ground and excited states of triply heavy baryons are estimated by evaluating expectation values of the Coulomb terms in the harmonic oscillator three-quark eigenstates. This very crude approximation produces spectra that are in qualitative and in many cases also in quantitative agreement with quark model predictions and lattice QCD calculations, especially for bbb and ccc systems. In ccb systems, the cc pair forms a tight diquark circling around the quark b. Our results for baryons are obtained with no free parameters, except the renormalization scale for ccb and cbb systems, because the coupling constant and quark masses are fixed in the same theory by comparison with the known spectra of heavy quarkonia. These results suggest that heavy-flavor QCD is suitable for realistic studies of the dynamics of gluons in the presence of stable color sources using the front form of Hamiltonian dynamics. The RGPEP that we use here in second order, can be extended to fourth order and inclusion of nonperturbative solutions to the evolution equation for effective particles. These extensions are needed to verify our gluon mass ansatz in theory.

Speaker: Mr Kamil Serafin (University of Warsaw)

Slides kserafinLC2018.pdf

60 Probing small-x gluon in high energy nucleus collisions

Speaker: G. Chen

Slides smallBjx.pdf

61 Positronium on the light-front

Speaker: X. Zhao

Slides Lightcone2018_Xingbo_Zhao_180512.pdf

lunch break

Parallel session 3A

Convener: Prof. Leonard Gamberg (Penn State Berks)

62 transverse force tomography

Twist-3 Generalized Parton Distributions may provide an alternative source of information on quark orbital angular momentum. Additionally, twist-3 GPDs embody information on the spatial distribution of quark-gluon correlations and thus provide information about the transverse position dependence of forces that act on the active quark in a DIS experiment. We discuss both the connection between twist-3 GPDs and transverse forces as well as general features of twist-3 GPDs.

Speaker: Prof. Matthias Burkardt (NMSU)

Slides LC18.pdf

63 3D Partonic Struture of Nucleons and Nuclei

A wealth of information on the structure of matter lies in the correlations between the momentum and spatial distributions of the fundamental constituents of matter: quarks and gluons. These correlations are accessible via the study of generalized parton distributions (GPDs). The deeply-virtual Compton scattering (DVCS) is the preferred probe of GPDs and has been used to study the proton in a number of experiments at HERA, CERN, and JLab, yielding the first 3D partonic images of the proton. New groundbreaking measurements of exclusive DVCS from the He-4 nucleus are a critical step towards providing similar 3D pictures of the quark structure of nuclei, and provide a new approach to understanding the modification of protons and neutrons within the dense environment of a nucleus. Studies of He-4 are particularly important, as their partonic structure is encoded within a single GPD. The new measurements provided the first beam-spin asymmetry data on exclusive DVCS from He-4 using a highly-polarized electron beam from the Continuous Electron Beam Facility (CEBAF) at JLab. Scattering from a pressurized He-4 target was measured in the CEBAF Large Acceptance Spectrometer (CLAS) with the addition of a new Radial Time Projection Chamber (RTPC). From the azimuthal dependence of the beam-spin asymmetry the real and imaginary parts of the He-4 Compton form factor, which is directly sample the nuclear GPD, were extracted in a model-independent way. This data proved the experimental feasibility of measuring such nuclear exclusive reactions and led the way to the approval of a next generation nuclear measurements. In this talk, I will present the recent results and the future measurements will be discussed.

Speaker: Dr Mohammad Hattawy (Argonne National Lab)

Slides LC2018_MHattawy.pdf

64 GPDs from charged current meson production in ep experiments

We suggest that generalized parton distributions can be probed in charged current meson production process, $ep\to \nu_e\pi^{-}p$. In contrast to pion photoproduction, this process is sensitive to the unpolarized GPDs $H,E$, and for this reason has a very small contamination by higher twist and Bethe-Heitler type contributions. Since all produced hadrons are charged, we expect that the kinematics of this process could be easily reconstructed. We estimated the cross-sections in the kinematics of upgraded 12 GeV Jefferson Laboratory experiments and found that thanks to large luminosity the process can be measured with reasonable statistics. The talk is partially based on our recent publication [Phys. Rev. D 96, 096006][1]. [1]: http://dx.doi.org/10.1103/PhysRevD.96.096006

Speaker: Dr Marat Siddikov (Universidad Santa Maria)

Slides Siddikov_CCDVMP_LightCone2018.pdf

65 Controlling excited-state contributions to nucleon charges g_A, g_T and g_S in lattice QCD calculations

The axial charge of the nucleon remains a quantity of phenomenological importance as it relates to nuclear beta decay and the degree of chiral symmetry breaking in QCD. Defined simply as the axial vector form factor at zero momentum transfer, the axial charge of the nucleon has long been a benchmark calculation in Lattice Field Theory. The bulk of Lattice determinations of the nucleon axial charge have, however, historically differed from the world average by roughly 10%. This systematic discrepancy is today mainly attributed to excited-state contamination. The variational method and the Jacobi smearing technique have seen extensive use in lattice calculations in the hopes of taming excited-state contributions to nuclear properties. By employing a basis of several interpolators, including some of hybrid character, and utilizing the quark smearing algorithm Distillation, we demonstrate an earlier onset of a plateau region in extracted nucleon matrix elements with reduced statistical uncertainties, when compared to analyses using just the variational method or single smeared interpolators. This presentation will highlight our methodology and results for the isovector axial charge of the nucleon on two isoclover lattice ensembles, in good agreement with experiment. Having demonstrated an effective reduction in excited-state effects, we extend our presentation to include precision determinations of the isovector scalar and tensor charges of the nucleon. If constrained precisely, these results will provide useful theoretical input to the ongoing experimental search for BSM physics.

Speaker: Mr Colin Egerer (William and Mary)

Slides egererLC2018.pdf

66 Prospects for studying the structure of the excited states via lattice QCD

The non perturbative nature of QCD at low energies poses a challenge in obtaining the properties of hadrons. LQCD has proven to be a useful tool for studying the structure of states that are stable under the strong interactions, which are a small fraction of the states present in QCD. In this talk, I will present efforts to study the structure of the majority of QCD states, which are either unstable or bound states of other hadrons. I will consider the simplest non-trivial case represented by the rho meson and illustrate an approach to extract its electromagnetic form factors. To this end I will present the status of the numerical implementation of recently proposed formalism that allows for the extraction of electromagnetic scattering amplitudes from which one may then extract the form factors of the rho.

Speaker: Alessandro Baroni (University of South Carolina)

Slides LC_18.pdf

Parallel session 3B

Convener: Prof. James Vary (Iowa State University)

67 Dynamical observables for a J=1/2 system within a fully Poincare'-covariant framework

The formalism based on the Poincare' covariant spin-dependent spectral function, recently introduced [1] within the light-front (LF) Hamiltonian dynamics, allows one to develop a phenomenological tool for investigating three-fermion bound systems, in particular their dynamical observables. As it is well-known, several and quite relevant efforts are underway at JLAB with the aim of getting information on both the nucleon transverse-momentum distributions [2] and $^{\rm 3}$He and $^{\rm 3}$H structure functions [3]. In this contribution, it will be presented some new relations among the six T-even leading-twist transverse-momentum distributions (TMDs) of a three-fermion system, e.g. the nucleon in valence approximation. Such relations can be formally obtained once the valence contribution to the correlator for a J=1/2 bound system is expressed in terms of the spin-dependent spectral function, whose diagonal terms yield the probability distributions to find a constituent with given spin and LF momentum. Moreover, within the same framework, some preliminary results of the EMC effect for the three-nucleon system will be also provided. The spin-dependent spectral function is defined through the overlaps between the ground state wave function of the three-body system and the states given by a Cartesian product of a plane wave of LF momentum $\tilde{ \kappa}$ (describing the struck particle in the intrinsic reference frame of the cluster [1,(23)]) and a state describing the intrinsic motion of a fully interacting two-particle spectator subsystem. As an example of the rich wealth of information one can extract and check against the experimental outcomes, one could mention the decomposition of the spin-dependent momentum distributions, obtained after properly integrating the spectral function on the relative intrinsic momentum $k_{23}$ of the interacting spectator pair, viz $$ n^\tau_{\sigma \sigma '}(x,{\bf k}_{\perp};{\cal M},{\bf S}) ~ = ~ {2 (-1)^{{\cal M} + 1/2} \over (1- x)}~ \int d { k}_{23}~ %k^2_{23} ~{E_{23}~E({\bf k_1})\over k^+_1}~ \left \{ ~{\cal Z}_{\sigma \sigma'}(k_{23}, L=0) ~ + ~ {\cal Z}_{\sigma \sigma'}(k_{23}, L=2) ~ \right \} ~ $$ where $L$ is the orbital angular momentum of the one-body off-diagonal density matrix. By exploiting a similar result, but for the T-even leading twist TMDS, it will be shown that the linear relations proposed in Ref. [4] between the transverse parton distributions, i.e. $$ \Delta f(x, |{\bf p}_{\perp}|^2 )= \Delta'_T f(x, |{\bf p}_{\perp}|^2 ) ~ + ~ {|{\bf p}_{\perp}|^2 \over 2 M^2}~ h^{\perp}_{1T}(x, |{\bf p}_{\perp}|^2 ) \quad \quad g_{1T}(x, |{\bf p}_{\perp}|^2 ) = - h^{\perp}_{1L}(x, |{\bf p}_{\perp}|^2 ) $$ exactly hold in valence approximation when the contribution to the transverse momentum distributions from the angular momentum $L=2$ is absent. **References** [1] A. Del Dotto, E. Pace, G. Salme', S. Scopetta, Phys. Rev. C **95**, 014001 (2017). [2] Hall A, H. Gao et al, PR12-09-014: Target Single Spin Asymmetry in Semi-Inclusive Deep-Inelastic $(e, e' \pi^\pm)$ Reaction on a Transversely Polarized $^{3}$He Target; J.P. Chen et al, PR12-11-007: ``Asymmetries in Semi-Inclusive Deep-Inelastic $(e, e' \pi^\pm)$ Reactions on a Longitudinally Polarized $^{3}$He Target''. [3] MARATHON Coll., P. Gerassimov et al E12-10-103: ``MeAsurement of the $F_{2n}/F_{2p}$, d/u Ratios and A=3 EMC Effect in Deep Inelastic Electron Scattering Off the Tritium and Helium MirrOr Nuclei''. [4] R. Jacob, P.J. Mulders, and J. Rodrigues, Nucl. Phys. A **626,** 937 (1997); B. Pasquini, S. Cazzaniga, S. Boffi, Phys. Rev. D **78**, 034025 (2008); C. Lorce', B. Pasquini, Phys. Rev. D **84**, 034039 (2011).

Speaker: Dr Giovanni Salme' (Istituto Nazionale di Fisica Nucleare -)

Slides GS_LC018.pdf

68 Basis Light-Front Quantization Approach to Proton

Basis Light-front Quantization (BLFQ) has been proposed as a nonperturbative framework for solving quantum field theory. Based on the resulting light-front wave function obtained within the BLFQ framework, we investigate the several aspects of the nucleon properties such as electromagnetic form factors, generalized parton distributions (GPDs) etc.. In the effective Hamiltonian, we implement a confining potential in the transverse direction inspired by the light-front holography as well as a longitudinal confinement potential for the completeness. The one-gluon exchange interaction has also been included in the effective Hamiltonian for generating the spin structure. The obtained results in BLFQ formalism are compared with the light-front quark-diquark model constructed from the soft-wall AdS/QCD prediction.

Speaker: Dr Chandan Mondal (Institute of Modern Physics, Chinese Academy of Sciences)

Slides Chandan_LC2018.pdf

69 Basics light front quantization for the light mesons

We propose an effective Hamiltonian for the valance Fock sectors of mesons to implement the chiral quark condensate based on the Nambu-Jona-Lasinio model. Such a term allows us to generalize the basis light front quantization framework with the longitudinal confinement ansatz and the one-gluon exchange potential to the pi and rho mesons. The multi-flavor version of the effective Hamiltonian is expected to account for the valence quark flavor mixing of the eta and eta prime mesons.

Speaker: Dr Shaoyang Jia (Department of Physics and Astronomy, Iowa State University)

Slides LC2018_SJ.pdf

70 Radiative transitions between 0-+ and 1-- heavy quarkonia on the light front

We present calculations of radiative transitions between vector and pseudoscalar quarkonia in the light-front Hamiltonian approach. The light-front wavefunctions of heavy quarkonia are obtained from the Basis Light-Front Quantization (BLFQ) approach in a holographic basis. We study the transition form factor with both the traditionally used ``good current'' $J^+=J^0+J^z$ and the transverse current $J^R=J^x+i J^y$. This allows us to investigate the role of rotational symmetry by considering vector mesons with different magnetic projections ($m_j=0,\pm 1$). We use the longitudinally polarized state ($m_j=0$) of the vector meson to obtain the transition form factor, since this procedure employs the dominant components of the light-front wavefunctions and is more robust in practical calculations. While the transverse polarizations ($m_j=\pm 1$) are also examined, transition form factors depend on the subdominant components of the light-front wavefunctions and are less robust in consequnce. In addition, we apply the transverse current to calculate the decay constant of vector mesons where we obtain consistent results between $m_j=0$ and $m_j=1$. This consistency provides evidence for features of rotational symmetry within the model. Transitions between states below the open-flavor thresholds are computed, including those for excited states. Comparisons are made with the experimental measurements as well as with Lattice QCD and quark model results.

Speaker: Meijian Li (Iowa State University)

Slides LC2018_MeijianLi.pdf

71 Light-front Hadronic Models

A class of Phenomenological models of hadronic systems motivated by QCD that have dual representations as a theory of quarks interacting with gluons and hadrons exchanging mesons are investigated. The model is formulated as a fully relativistic model with a light-front kinematic symmetry. The bare meson wave functions and production vertices are determined by the underlying QCD degrees of freedom and can all be calculated analytically. The bare meson exhibits linear confinement and the mass fall in Regge trajectories. The simplicity of the model facilitates the investigation of sea quark contribution to the meson spectrum and wave functions. The hadronic spectrum, lifetimes, cross section, vertex strength and sea quark effects are calculated using quark masses and one strength parameter.

Speaker: sirajudheen Kuthini Kunhammed (The University of Iowa)

Slides lcon.pdf

coffee break

Parallel session 4A

Convener: Dr Cedric Lorce (Ecole polytechnique)

72 Power corrections to TMD factorization for particle production

A typical factorization formula for production of a particle with a small transverse momentum in hadron-hadron collisions is given by a convolution of two TMD parton densities with cross section of production of the final particle by the two partons. For practical applications at a given transverse momentum, though, one should estimate at what momenta the power corrections to the TMD factorization formula become essential. In this talk I present the results of calculation of first power corrections to TMD factorization formula for Z-boson production and Drell-Yan process in high-energy hadron-hadron collisions. At the leading order in $N_c$ power corrections are expressed in terms of leading power TMDs by QCD equations of motion.

Speaker: Prof. Ian Balitsky (JLab/ODU)

Slides LiCo18a.pdf

73 Generalized TMDs in hadronic collisions

Being the "mother distributions" of all types of two-parton correlation functions, generalized TMDs (GTMDs) have garnered a lot of attention. We address the important question of how to access GTMDs in physical processes. Recently, we have shown that quark GTMDs can in principle be probed through the exclusive pion-nucleon double Drell-Yan process, where the focus was on two particular GTMDs only. We now present new results concerning access to the remaining quark GTMDs in the same process. Extending our analysis, we also show that GTMDs for gluons can be explored via exclusive double $\eta_c$ production in hadronic collisions.

Speaker: Ms Shohini Bhattacharya (Temple University)

Slides Shohini_LC2018.pdf

74 Non-perturbative study of the three-body system within the Bethe-Salpeter approach

From a general point of view, understanding the interaction in terms of the fundamental degrees of freedom is very important for nuclear and particle non-perturbative physics. Since that is a very difficult problem, simple models are of great value for understanding the crucial qualitative features of the solution with more realistic kernels. Understanding the properties of relativistic three-body systems is important, in particular, for the perspective of hardron physics, e.g. for the modeling of the nucleon. Furthermore, it is well-known that in the non-relativistic approach the binding energy of this system is not bounded from below, what is known as Thomas collapse. As it was discovered in the light-front dynamics (LFD) [1,2], the relativistic repulsion prevent the Thomas collapse in the non-relativistic sense. The Bethe-Salpeter equation provides a convenient approach to perform non-perturbative studies of few-body systems in Minkowski space. Calculations of that type is important in order to access dynamical observables, such as space-like and time-like form factors. In this contribution we discuss some recent progress regarding the solution of the bound-state Bethe-Salpeter equation (BSE) for a system of three bosons interacting through a zero-range interaction. We compare the results for the binding energy and transverse amplitude computed by two different methods: 1. Solution in Minkowski space by direct integration of the BSE, by taken care of the singularities. The adopted is thus similar to the one introduced by Carbonell and Karmanov for the two-body system in Ref. [3]. 2. Solution in Euclidean space by Wick rotation of the integration contour. Our results show that, at least for moderate three-body binding energies, a fair agreement is found between the two methods, both for the binding energy and the modulus of the transverse amplitude. This is encouraging since the calculations based on direct integration of the BSE present many challenges, due to the singularities of the kernel and the Bethe-Salpeter amplitude. As our calculations in Euclidean space show [4], the contributions from higher Fock components, which are not included in the LFD treatment are very significant, both for the binding energies and the tranverse amplitudes. This can be explained in terms of an effective three-body force of relativistic origin. [1] T. Frederico, Phys. Lett. B 282 (1992) 409 [2] J. Carbonell and V. A. Karmanov, Phys. Rev. C 67 (2003) 037001 [3] J. Carbonell and V. A. Karmanov, Phys. Rev. D 90 (2014) 056002 [4] E. Ydrefors et al, Phys. Lett. B 770 (2017) 131.

Speaker: Dr Emanuel Ydrefors (Instituto Tecnologico de Aeronautica)

Slides threebody_ydrefors.pdf

75 Trident pair production in lightfront quantization

High-intensity lasers currently attract a great deal of interest due to the prospects of using them to study unexplored regimes of fundamental physics. Trident pair production is a basic process in this field, where an electron collides with a laser and produces an electron-positron pair. One part of this is a two-step process where the initial electron emits a real, on-shell photon that subsequently decays into an electron-positron pair, and the rest is referred to as a one-step process. We have [1] studied the split between these one- and two-step processes using lightfront quantization, motivated by the facts that in this formalism all particles are on-shell and the Hamiltonian has instantaneous terms. Apart from providing new insights into trident, this formalism has also allowed us to calculate important terms that have previously been neglected. Reference [1] V. Dinu and G. Torgrimsson, ``Trident pair production in plane waves: Coherence, exchange, and spacetime inhomogeneity'', Phys. Rev. D 97 (2018) 036021

Speaker: Dr Greger Torgrimsson (Theoretisch-Physikalisches Institut Friedrich-Schiller-Universität Jena; Helmholtz Institute Jena)

Slides TridentLightCone.pdf

76 Light-Front Simulations of the True Muonium

A light-front quantization study of the nonperturbative spectrum of the bound state $(\mu^+\mu^-)$, true muonium, has been performed. Using Pad\'{e} approximants, it has been possible to extract continuum and infinite-cutoff limits for the singlet and triplet states for a range of coupling constants $\alpha$. This allows for an investigation of the $\alpha$ dependence of the light-front spectra, the results of which are compared to standard calculations. Decay constants have also been obtained. Improved calculations have been undertaken for the energy shifts due to the presence of a second, lighter flavor ($e$). Finally, initial results for three-flavor ($e$, $\mu$, $\tau$) calculations are presented.

Speaker: Dr Henry Lamm (University of Maryland)

Slides Lamm_Presentation.pdf

77 -

Parallel session 4B

Convener: Dr Carlos Granados (The George Washington University)

78 Constrained Degrees of Freedom of Fermion in Light-Front Dynamics

The fermion degrees of freedom in light-front dynamics (LFD) carry the unique constraint component distinguished from the ordinary equal-time fermion degrees of freedom. The constraint component of the fermion degrees of freedom in LFD results in the instantaneous contribution to the fermion propagator distinguished from the ordinary equal-time forward and backward propagation of relativistic fermion degrees of freedom. The helicity of the on-mass-shell fermion spinors in LFD is also distinguished from the ordinary Jacob-Wick helicity in the instant form dynamics (IFD) with respect to whether the helicity depends on the reference frame or not. To exemplify these distinguished features of the fermion degrees of freedom in LFD, we have computed the annihilation process of the fermion and anti-fermion pair interpolating the fermion degrees of freedom between the IFD and the LFD. In this talk, we present the helicity amplitudes of the pair production of two scalar particles in the electron and positron annihilation process. We present the whole landscape of the helicity amplitudes between the IFD and the LFD with respect to the scattering angle and center-of-momentum in the annihilation/production process. Our analysis clarifies any conceivable confusion in the prevailing notion of the equivalence between the IFD at infinite momentum frame (IMF) and the LFD.

Speaker: Ms Bailing Ma (North Carolina State University)

Slides LC2018BailingMa.pdf

79 Vacuum and 1-particle states in equal-time vs. light-front quantization

In the canonical quantization procedure the quantum field operators are smeared with a test function of Schwartz class for coordinates on the quantization hypersurface, with a sharp dependence on the temporal parameter. Such quantum operators when acting on the vacuum state produce smeared 1-particle states and higher number particles states. These states, provided their norm is finite, form the Fock space of states. For the equal-time quantization procedure one needs to diagonalize the Hamiltonian operator, which can be exactly done mostly only for a free field dynamics. When one imposes the spectral condition that the spectrum of the Hamiltonian operator is non-negative for the Fock space states, then one obtains the definition of the vacuum state and the smeared creation and annihilation operators. This leads to 1-particle states, with a sharp dependence on time parameter, which have a finite, mass dependent norm, so they belong to the Fock space. For the light-front quantization procedure the conditions that the LF Hamiltonian P^{-} and the longitudinal translation kinematic generator P^{+} have non-negative spectra lead only a restriction on the longitudinal momentum variable k^{+} > 0. Thus the 1-particle states appear with no dependence on mass but with an infinite norm, so they do not belong to the Fock space. However one may evolve these 1-particle states in the light front time by means of the unitary operator and then smear the light front time dependence with a test function. This extra smearing produces 1-particle states with a finite norm, which therefore belong to the Fock space of states. Evidently these final states have mass dependence, from the temporal evolution with the Hamiltonian operator, but the vacuum state remains simple with no reference to the Hamiltonian. Accordingly the 1-particle states are drastically different within the equal time and the light front formulations, though they lead to the same physical results. For the interacting models, where the Hamiltonian operator changes number of particles, one cannot diagonalize it in the basis of Fock states without introducing some truncation. Thus the equal time approach is bound to be a perturbative formulation. On the contrary the light front procedure gives exact basis for 1-particle states, which then needs to be evolved in light front time - where the perturbation calculation enters. Again the light front vacuum state remains simple.

Speaker: Dr Jerzy Przeszowski (University of Białystok)

Slides ET-vs-LF.pdf

80 Equivalence of Light - Front and Covariant QED and the Form of the Gauge Boson Propagator

An important issue in establishing the equivalence of light-front QED in light cone gauge and the Covariant QED is the question of whether to use the two term or the three term propagator for the gauge boson. In this talk, we elaborate on this issue and show, by way of examples, that the equivalence cannot be achieved without including the third term in the photon propagator.

Speaker: Dr Anuradha Misra (University of Mumbai)

Slides AMisra_LC2018.pdf

81 Non-vanishing of vacuum diagrams in light-cone perturbation theory

Recently, J. Collins has pointed out that vacuum diagrams are, contrary to the general belief, non-vanishing in light-front field theory. In our contribution, we first recall the old (forgotten) arguments by Chang and Ma and by Yan, why this should be so. Then we apply the argument of analyticity of the self-energy diagrams in \lambda\phi^3 and \lambda \phi^4 two-dimensional models in light-front (LF) perturbation theory to calculate the vacuum bubbles explicitly as p=0 values of the appropriate self-energy diagrams. The results are non-zero and agree with the usual Feynman-diagram calculation. Surprisingly, the light-front bubbles are non-vanishing NOT due to LF zero modes. This is confirmed by the DLCQ calculations, where the mode with n=0 (the LF zero mode k^+ =0) is manifestly absent, but the results still converge to the continuum values for increasing "harmonic resolution" K. Generalization to realistic 3+1 dimensional case and to e.g. Yukawa theory is straightforward. *) work done in collaboration with A. Dorokhov, BLTP JINR Dubna

Speaker: Lubomir Martinovic (Institute of Physics SAS, Bratislava and BLTP JINR Dubna)

Slides martinovic_lc18.pdf

82 Electron scattering from a deeply bound nucleon on the light-front

We calculate the cross section of the electron scattering from a bound nucleon within light-front approximation. The advantage of this approximation is the possibility of systematic account for the off-shell effects which become essential in high energy electro-nuclear processes aimed at probing the nuclear structure at small distances. We derive a new dynamical parameter which allows to control the extend of the "off-shellness" of electron - bound-nucleon cross section for different regions of momentum transfer and initial light-cone momenta of the bound nucleon. The derived cross section is compared with the results of other approaches treating the off-shell effects in electron-nucleon scattering.

Speaker: Frank Vera (Florida International University)

Slides GeN_LF.pdf

83 Light-front methods in next-generation nuclear DIS at EIC

Measurements of deep-inelastic scattering (DIS) on polarized light ions (deuteron, 3He, ...) address important physics topics such as the spin structure of the neutron, nuclear modifications of parton densities, and coherent effects at small x. Detection of the nuclear breakup state ("spectator tagging") reveals the nuclear configurations present during the high-energy process and permits a controled theoretical treatment of nuclear effects. Such measurements could be performed at a future Electron-Ion Collider (EIC) with suitable forward detectors. We report about recent progress in developing the theoretical framework for DIS on the polarized deuteron with spectator tagging at EIC. This includes (a) calculation of the final-state interactions in tagged DIS on the deuteron at large x using methods of light-front quantization [1]; (b) extraction of free neutron spin structure from tagged DIS using on-shell extrapolation; (c) novel studies of nuclear shadowing in diffractive tagged DIS at small x. We present suggestions for future theoretical studies and experimental simulations for the EIC.

Speaker: Christian Weiss (Jefferson Lab)

Slides weiss18_lc2018.pdf

Banquet

Friday, May 18

I

Convener: Prof. Tobias Frederico (Instituto Tecnologico de Aeronautica)

84 Spatial distribution of Jaffe-Manohar and Ji's angular momenta

Speaker: Dr Cedric Lorce (Ecole polytechnique)

Slides LC2018.pdf

85 GPDs and LFWFs : crossing the $|x| = |\xi|$ line

In the very few years after the introduction of Generalised Partons Distributions (GPDs), various authors have made attempts to compute the latter through the use of an overlap of Lightfront Wave Functions (LFWFs). However, contrary to Parton distribution functions (PDFs) or transverse momentum dependent functions (TMDs), GPDs are defined according to different overlaps on their definition domain. More precisely, while on the so-called DGLAP region, the GPDs can be computed as an overlap of LFWFs with the same number of constituent, on the ERBL region $|x|<\xi$, they can be seen as an overlap of LFWFs with a different number of constituent. This property have led the models built this way (except in few specific cases) to violate one of the fundamental aspect of GPDs called the polynomiality. In this talk, I will detail the new systematic method we have introduced to tackle this issue.

Speaker: Dr Cédric Mezrag (INFN Sezione di Roma)

Slides mezrag_LC_2018.pdf

86 Lorentz invariance and QCD equation of motion relations for partonic orbital angular momentum

Speaker: Abha Rajan (University of Virginia)

Slides AR_LightCone.pdf

87 GPD phenomenology

Speaker: Adam Freese (Florida International University)

Slides FreeseSlides.pdf

coffee break

I

88 The GPD program at Jefferson Lab

Speaker: Latifa Elouadrhiri (Jefferson Lab)

Slides LC2018-Latifa-LE-Final.pptx

89 Virtual Compton scattering on a scalar target: the need for a complete set of Compton form factors

Speaker: B. Bakker

Slides LC2018.pdf

90 Nucleon structure in a light-front quark-diquark model

Speaker: Mr Tanmay Maji (Indian Institute of Technology Kanpur, Kanpur 208016, India)

Slides Tanmay_LC18.pdf

91 Recent results and prospects for hadronic physics at Belle and Belle II

Speaker: Dr Anselm Vossen (Duke University)

Slides Lightcone2018_Vossen.pdf Lightcone2018_Vossen.pptx

lunch break

G

Convener: Raul Briceno (Jefferson Lab)

92 Baryon spectroscopy and structure with functional methods

Speaker: G. Eichmann

Slides eichmann-2018-lightcone.pdf

93 Mesons as relativistic bound states in a Minkowski-space approach

Speaker: S. Leitao

Slides LC2018_Sofia_Leitao.pdf

94 Few-nucleon systems from lattice QCD

Speaker: William Detmold (MIT)

Slides Detmold_LightCone2018.pdf

95 New developments in nuclear lattice simulations

Speaker: D. Lee

Slides DLee_LightCone2018.pdf

coffee break

A: closing remarks

Convener: Chueng R. Ji (North Carolina State University)

96 A percent level determination of the nucleon axial charge from lattice QCD

Speaker: Andre Walker-Loud (LBNL)

Slides Walker-Loud_gA_lightcone.pdf

97 Total decay and transition rates from lattice QCD

Speaker: D. Robaina

Slides Robaina_LC2018.pdf

98 Entanglement on the Light Front

Speaker: Piet Mulders (Vrije Universiteit Amsterdam, NIKHEF)

Slides 2018-LC2018-Mulders.pdf

99 From JLab12 to the EIC

Speaker: Rikutaro Yoshida (Jefferson Lab)

Slides Light_Cone_2018_Yoshida.pptx