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# J-FUTURE

Europe/Paris
Jefferson Lab / Messina University

#### Jefferson Lab / Messina University

Polo Papardo, edificio SBA, Viale Ferdinando Stagno d'Alcontres 31, Messina (Italy)
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Description

While the Jefferson Lab 12 GeV program is running, it is already time to plan the future developments for the facility. A new round of upgrades to CEBAF are under technical development. One of these is a potential energy upgrade to 24 GeV using novel magnet designs in the existing recirculation arcs. Another is a potential for intense polarized beams of electrons or positrons, which would allow for new measurements in nucleon tomography, provide precision extraction of contributions from higher order electromagnetic currents, and allow new tests of the standard model. In addition, it is possible to open new research lines using secondary beams.

The objective of the workshop is to gather theorists and experimentalists to discuss the physics opportunities and technical options for each of the possible upgrade scenarios.

For in-person participants, proof of COVID-19 vaccination is mandatory to access the university buildings.

Participants
• Abir Saidi
• Alessandro Bacchetta
• Alessandro Pilloni
• Alex Bogacz
• Alexandre Camsonne
• Andrea Signori
• Andrea Sofia Triolo
• Annalisa D'Angelo
• Antonina Rosano
• Antonino Fulci
• Ashot Gasparian
• Axel Schmidt
• Bill Briscoe
• Bryan McKinnon
• Cesar Fernandez-Ramirez
• Chandrasekhar Akondi
• Christopher Dilks
• Daniel Carman
• David Dean
• David Flay
• David Mack
• Derek Glazier
• Dien Nguyen
• Douglas Higinbotham
• Elena Santopinto
• Eric Voutier
• Fabio Mauceri
• Fabio Risitano
• Florian Hauenstein
• Gerassimos Petratos
• Giuseppe Mandaglio
• Glòria Montaña
• Gordan Krnjaic
• Gordan Krnjaic
• Hamlet Mkrtchyan
• Harut Avakian
• Igor Strakovsky
• Jay Benesch
• Jiwan Poudel
• Joseph Grames
• Justin Stevens
• Kai-Thomas Brinkmann
• Katheryne Price
• Lamiaa El Fassi
• Laura Anoldo
• Letterio Biondo
• Luca Marsicano
• Marco Battaglieri
• Mariangela Bondì
• Mark Baker
• Mark Jones
• Matteo Cerutti
• Michael Wood
• Narbe Kalantarians
• Nunzio Randazzo
• Ole Hansen
• Or Hen
• Patrizia ROSSI
• Paul Brindza
• Pete Markowitz
• Peter Pauli
• Prajwal MohanMurthy
• Rafayel Paremuzyan
• Raffaella De Vita
• Raphaël Dupré
• Reza Kazimi
• Robert Edwards
• Robert Kaminski
• Sean Dobbs
• Sebastian E. Kuhn
• Sebastiano Ettore Spoto
• Silvia Niccolai
• Silviu Covrig Dusa
• Simone Vallarino
• simonetta liuti
• Stefan Diehl
• Stefano Grazzi
• Stepan Stepanyan
• Sylvester Joosten
• Vincent Mathieu
• virgilio vecchio
• Volker Burkert
• Wenliang Li
• Xiaochao Zheng
• Yuri Gotra
• Zainab Dahrouch
• Monday, March 28
• 2:00 PM 5:00 PM
Physics
• 2:00 PM
The Jefferson Lab of the Future 30m
Speaker: Patrizia Rossi (JEFFERSON LAB)
• 2:30 PM
Nucleon-structure studies with exclusive reactions at a future upgraded JLab 30m

Understanding the multi-dimensional partonic structure of the nucleon via the measurement of Generalized Parton Distribution (GPDs) is one of the central goals of the scientific program of Jefferson Lab. While the 12-GeV program progresses, various upgrade scenarios open up perspectives to expand the measurable observables for Deeply Virtual Compton Scattering (DVCS) and other exclusive reactions giving access to GPDs, as well as to reach unexplored kinematical regimes.
This talk will present the experimental program, proposed for JLab, to measure DVCS ($eN \to eN \gamma$) on both the proton and the neutron, with the CLAS12 spectrometer and polarized positron and electron beams of 10.6 GeV. The proposed measurement of Double Deeply Virtual Compton Scattering (DDVCS, $eN \to eN \ell^+\ell^-$) with the SOLID spectrometer will also be presented. These experimental configurations will provide a direct access to the real parts of combinations of Compton Form Factors (CFFs), which are, in turn, connected to GPDs. The combination of DVCS observables on neutron and proton targets is a necessary step to perform the flavor decomposition of the real parts of the $H$ and $E$ CFFs. DDVCS will provide the unique possibility to disentangle the $x$ (average momentum fraction carried by the initial-final quark) dependence of the CFFs. The perspectives for the physics of GPDs that would open up with a possible doubling of the CEBAF accelerator energy will be also presented.

Speaker: Silvia Niccolai (IJCLab Orsay)
• 3:00 PM
Theory of deeply virtual exclusive processes 30m

I will review the status of current theoretical progress on deeply virtual exclusive processes and of the extraction of observable from experiment.

Speaker: Simonetta Liuti
• 3:30 PM
Coffee break 30m
• 4:00 PM
Opportunities for semi-inclusive studies at high-energy (theory) 30m

In this talk I will briefly review where we stand with hadron structure and hadronization studies with semi-inclusive processes, in particular SIDIS.
I will also highlight the fundamental role of the present and future experimental facilities for the advancement of the field.

Speaker: Andrea Signori (University of Pavia and Jefferson Lab)
• 4:30 PM
Opportunities for semi-inclusive studies at high-energy (experiment) 30m

The quark-gluon dynamics manifests itself in a set of non-perturbative functions describing all possible spin-spin and spin-orbit correlations. Recent studies of correlated hadron pairs, including the pairs created in target and current fragmentation region, indicate significant correlations in hadron fragmentation process. Their understanding is becoming increasingly important in the interpretation of pion electroproduction data in general, and hadronization process of quarks, in particular. More significant, than originally anticipated, fraction of pions coming from correlated di-hadrons, indicated by recent measurements at JLab, and supported by various realistic models describing the hadronization process, may have a significant impact on various aspects of data analysis, including the modeling, composition, and interpretation of semi-inclusive DIS data, as well as calculations of radiative corrections. Detailed studies in multi-dimensional space, of various multiplicities and different azimuthal modulations in single and di-hadron case as a function of transverse momentum of involved hadrons and the $Q^2$, will be needed to sort out all disagreements with theory predictions and improve the phenomenology of 3D PDFs.
In this contribution, we will present ongoing studies and some proposed future measurements with hadrons in electroproduction at large $Q^2$, with current CLAS12 detector at Jefferson Lab, and discuss opportunities with JLab energy upgrade to 24 GeV.

Speaker: Harut Avagyan (Jefferson Lab)
• 5:00 PM 6:00 PM
• 5:00 PM
Instrumentation for high luminosity upgrade of CLAS12 30m

The CLAS12 detector located in the Hall-B of the Thomas Jefferson National Accelerator Facility has been designed to operate at the nominal luminosity of $10^{35} \text{cm}^{-2} \text{s}^{-1}$, assuming a unitary particle reconstruction efficiency. Improving the performance of CLAS12 in terms of luminosity times the reconstruction efficiency will significantly enhance the physics reach of experiments in Hall B, allowing not only to conclude the approved physics program in a timely schedule, but also to access physics processes still unexplored due to limited statistics.
The possible upgrades of the CLAS12 instrumentation for efficient operation at an increased luminosity up to a factor ten are discussed.

Speaker: Annalisa D'Angelo (University of Rome Tor Vergata and INFN Roma Tor Vergata)
• 5:30 PM
From CLAS to CLAS12 and CLAS24 30m
Speaker: Volker Burkert (Jefferson Lab)
• 6:00 PM 6:30 PM
Break 30m
• 6:30 PM 7:30 PM
Discussion
• 6:30 PM
Nucleon and Nuclear structure 1h
Speakers: Alessandro Bacchetta (University of Pavia and INFN Pavia) , Harut Avagyan (Jefferson Lab) , Raphaël Dupré (IJCLab, Paris-Saclay U.)
• Tuesday, March 29
• 2:00 PM 4:15 PM
Physics
• 2:00 PM
Spectroscopy (theory) 30m
Speaker: Vincent Mathieu (JLab)
• 2:30 PM
Spectroscopy (experiment) 30m

Upgrading the energy of CEBAF would open the door for many important spectroscopy measurements. In particular the recently discovered and apparently exotic states collectively know as $XYZ$ mesons will become accessible. This presentations uses models constructed by the JPAC collaboration to estimate rates and kinematics for some key reactions. Although the production mechanism modeled is via low $Q^2$ electroproduction, parallels to real photoproduction are drawn. Some generic toy high acceptance or high luminosity style detectors are then considered as an intitial investigation into what an optimal approach to detecting the final states might look like.

Speaker: Derek Glazier (University of Glasgow)
• 3:00 PM
Opportunities beyond hadron physics: the physics case 30m

Although its main focus is hadron physics, Jefferson Lab (JLab) features a significant experimental program dedicated to beyond Standard Model (BSM) physics, including the search for new light particles possibly explaining the Dark Matter problem. Experiments such as APEX,HPS and BDX-mini, aim to exploit CEBAF unique capabilities to produce and detect Dark Photons, hypothetical bosons acting as a "portal" to a new Dark Sector of particles. In a future perspective, secondary beams at JLab can be exploited to further explore scenarios beyond hadron physics: intense muon and neutrino beams could in fact be extracted from the beam-dumps of the laboratory and put to use. Future upgrades of the facility offer even more opportunities, such as the possibility to run light Dark Matter experiments using dedicated positron beams.
After an overview of the addressed physics scenarios, my talk will briefly review BSM experimental efforts currently running at JLab and will present new opportunities arising from the use of secondary beams and future CEBAF upgrades.

Speaker: Luca Marsicano (INFN Genova)
• 3:30 PM
Prospects of testing electroweak physics using a positron beam at Jefferson Lab 30m

Electron scattering has provided some of the cornerstone experiments for the establishment of the electroweak (EW) sector of the Standard Model, in particular in its neutral-current (NC) sector. With the addition of a positron beam, one could expand such studies but in order to maximize the physics impact, our focus is not to measure the charge-counterpart observables as for electron scattering, but rather to study new observables that arise from comparing $e^+$ and $e^-$ scatterings. In this talk, I will discuss ideas about using a possible positron beam at JLab to measure lepton-charge asymmetry $A_{e^+e^-}$, the possibility of extracting the axial-axial electron-quark effective coupling $g^{eq}_{AA}$, and the level of control for both experimental systematic effects and QED higher-order corrections that is needed for such EW physics study.

Speaker: Xiaochao Zheng
• 4:00 PM
u-Channel Physics Observables at Future CLAS 15m

The recent measurements on exclusive backward-angle electroproduction of mesons from Jefferson Lab electron-proton fixed-target scattering experiments above the resonance region, hint on a new domain of applicability of QCD collinear factorization framework in the special u-channel kinematics regime. Within this kinematics, the collinear factorized description of hard exclusive meson electroproduction reactions involves a new class of non-perturbative quantities known as the nucleon-to-meson Transition Distribution Amplitudes (TDAs). These TDAs share common features both with generalized parton distributions (GPDs) and baryon distribution amplitudes (DAs) and encode valuable new information on hadronic structure. Thanks to the pioneering experimental efforts, the interest of studying hadron structure through u-channel meson production observables have grown significantly.
In this presentation, a brief overview of the theoretical status of the TDA framework will be given along with the experimental measurements from CLAS and CLAS12 that demonstrated its success; a later section will describe the future u-Channel opportunities associated with the upgrades to CLAS12 and CLAS24 program.

Speaker: Wenliang Li (William & Mary)
• 4:15 PM 4:45 PM
Break 30m
• 4:45 PM 6:15 PM
• 4:45 PM
24 GeV CEBAF FFA energy upgrade 30m

Encouraged by recent success of CBETA, a proposal was formulated to increase the CEBAF energy from the present 12 GeV to 22-24 GeV by replacing the highest-energy arcs (Arc 7-10) with Fixed Field Alternating Gradient (FFA) arcs, where beams with energies spanning a factor of two or more, can be simultaneously transport through the same array of combined function magnets. The new pair of FFA racetrack configured with permanent magnets would provide eight (4 + 4) new beam passes, allowing the energy to be nearly doubled using the existing CEBAF SRF cavity system. One of the immediate accelerator design tasks is to develop a proof-of-principle FFA arc lattice adiabatically matched to the linacs. We also examine a possibility of accommodating positrons into the new accelerator complex.

Speaker: Alex Bogacz (Jefferson Lab)
• 5:15 PM
Ce+BAF : Considerations and Prospects for Polarized (and unpolarized) Positron Beams 30m

While conventional electron-driven positron sources have been built and operated at accelerator facilities producing unpolarized positron beams, we are at Jefferson Lab in a unique positron to provide also positrons with a high degree of spin polarization. The Polarized Electrons for Polarized Positrons (PEPPo) experiment demonstrated a very efficient means to produce highly spin polarized positron beams from electrons beams like we have at CEBAF today.

In this presentation I will describe considerations and prospects for producing both polarized (and unpolarized) positrons beams at CEBAF and accelerating them to high energies. In particular, I will focus on two technical challenges to realize the positron injector, an intense polarized electron source and an efficient high power positron production target. Additionally, I will comment on the injection of positrons into CEBAF, their transport to the end stations, and considerations for orienting the spin polarization of the positron beams.

Speaker: Joe Grames (JLab)
• 5:45 PM
Luminosity: CEBAF Beam Power Limits 30m

In 1998 when planning for the 12 GeV upgrade got underway, the maximum beam power was specified as 960 kW, consistent with the original 1 MW limit. While the Environmental Assessment (EA) conducted in 2007 allowed 1 MW each to Halls A and C, the 12 GeV upgrade project kept the original power limit specification. The C100 cavities were designed with high input impedance, emphasizing gradient over current capability ($P=V^2/R + I^2R$). The C75 cavity was designed to the same specification in 2017. Both types are limited to about 450 μA summed over all passes and Halls. The EA of 2007 gives an opportunity to consider doubling the beam power. In this talk the limitations and possibilities of various systems are discussed. The intermediate heat exchanger in the shared beam dump cooling system is specified at 1.1 MW. The JLab Facilities organization is beginning planning for
heat exchanger upgrade. All JLab safety documentation specifies 1 MW maximum and the changes in the documentation to match the 2007 EA are expected by year-end. Eight stub tuners which may be used to alter the C100 cavity impedance seen by the RF source are on order and will be installed this spring. Beam tests to determine the highest power than can be delivered with the system as it exists are planned by year-end. If the stub tuners are successful they will be installed on all C100 cavities as funding permits. It is hoped that by mid-decade it will be possible to deliver 70 μA fifth pass simultaneously to Halls A and C, total beam power ~1.6 MW. Hall A and C beam dumps are rated at 1 MW each. Hall D beam dump is rated at 100 kW. Hall B will soon install a 100 kW dump. These power limits will remain even if beam energy is increased. The A and C beam dumps have been evaluated to 16 GeV; all four will have to be re-evaluated if energy is increased beyond that.

Speaker: Jay Benesch (JLab)
• 6:15 PM 6:45 PM
Break 30m
• 6:45 PM 7:45 PM
Discussion
• 6:45 PM
Speakers: Adam Szczepaniak (Indiana Univeristy/JLab) , Bryan McKinnon (University of Glasgow) , Gordan Krnjaic (KICP) , Raffaella De Vita (INFN - Genova)
• Wednesday, March 30
• 2:00 PM 5:00 PM
Physics
• 2:00 PM
Positrons at Jefferson Lab and the Goal of Understanding Two Photon Exchange 30m

Two-photon exchange (TPE), a small contribution to electron scattering amplitudes, can occasionally, if not properly accounted for, have a big impact. For example, neglected TPE corrections may be the cause of the significant discrepancy between polarization-transfer and Rosenbluth-separation determinations of the proton's form factors at large momentum transfer. Though theoretical calculations of TPE corrections are necessarily model-dependent, TPE can be isolated experimentally through differences between electron scattering and positron scattering in a number of observables. The effort to quantify TPE is one of the primary motivations for adding the capability of accelerating positrons at Jefferson Lab. While the flagship measurements would compare electron-proton and positron-proton cross section ratios with the goal of resolving the proton form factor discrepancy, other measurements, such as target-normal single-spin asymmetries, polarization transfer, and nuclear-elastic scattering would provide new and independent constraints of TPE models. In this talk, I review the previous experimental and theoretical efforts and present how the future positron program at Jefferson Lab can significantly advance our understanding of TPE.

Speaker: Axel Schmidt (George Washington University)
• 2:30 PM
Probing the partonic structure of nuclei and bound nucleons 30m

Physics possibilities at JLab and its complementarity with the EIC

Speaker: Or Hen (MIT)
• 3:00 PM
Spin at high-x 30m

Nucleon valence quark structure at very high values of the scaling variable $x$ is sensitive to the mechanism of SU(6) breaking. In particular the valence quark polarizations $\Delta u/u$ and $\Delta d/d$ can be predicted by quark models, perturbative QCD, and other approaches, with significantly different expected
results. Present data are not sufficiently precise in the high-$x$ region to stringently test these predictions. New experiments at Jefferson Lab with 12 GeV beam will significantly improve our knowledge of these quantities out to $x \approx 0.8$, albeit with significant remaining sensitivity to models and assumptions used in their extraction from experimental results. In my talk, I will lay out the present situation and expected results for the 12 GeV program, and address the question what improvements we can expect from a higher luminosity, 24 GeV electron beam at Jefferson Lab.

Speaker: Sebastian Kuhn (Old Dominion University)
• 3:30 PM
The MARATHON experiment with a 24 GeV JLab beam 30m

The possibility of extending the measurements of the Jefferson Lab (JLab) MARATHON experiment to higher values of the squared four-momentum transfer $Q^2$ and of the Bjorken scaling variable x will be presented. The first part of the presentation will summarize results from the MARATHON experiment based on data from electron deep inelastic scattering from the tritium and helium-3 mirror nuclei. The second part will summarize i) the requirements for a possible new JLab experiment using existing apparatuses in the Hall C Facility of the Lab, and ii) selected projected results, mainly on the ratio of the proton and neutron nucleon $F_2^n/F_2^p$ structure functions, and on the isoscalar EMC effect of the $A=3$ nucleus.

Speaker: Gerassimos Petratos
• 4:00 PM
Coffee break 30m
• 4:30 PM
The psi' with SOLID 30m
Speaker: Sylvester Joosten (Argonne National Laboratory)
• 5:00 PM 6:00 PM
Infrastructure and detectors: Infrastructure
• 5:00 PM
Opportunities beyond hadron physics: muon and neutrino beams 30m

High intensity extracted electron/positron beams are a precious source of secondary beams. A muon beam (up to $10^9\mu/$s in the energy range 1-6 GeV) and a neutrino beam (up to $10^{18}\nu/$m$^2/$year with energy mainly below 100 MeV) are generated by the interaction of the primary CEBAF 12 GeV (or 20 GeV) electron (positron) beam with the beam dump. Several processes (A-sstralhung, resonant and non-resonant annihilation) are also expected to produce an intense Light Dark Matter beam, if it exist, to be used in scattering experiments such as BDX. In this contribution we will review the simulation results for beams of muon, neutrino and LDM produced by the interaction of the primary electron beam with Hall-A beam dump demonstrating that the unique features of JLab secondary beams will be able to complement and extend the current physics program at Jefferson Lab.

Speakers: Antonino Fulci (Messina U.) , Marco Battaglieri (JLab/INFNGE)
• 5:30 PM
Opportunities beyond hadron physics: BDX, nuBDX, JPOS 30m

Upgrades of the CEBAF accelerator can turn JLAB into the reference lepton-beam facility at intensity frontier opening new research opportunities beyond hadron physics. The upgraded machine will add new capabilities including positron beams and high intensity secondary beams of muons, neutrinos and, if exists, light dark matter particles.
To take advantage of these opportunities new and/or modified infrastructures in terms of civil constructions and detectors are required. This contribution aims to give an overview of the several experiments that can exploit the secondary beams available in the future at JLAB, providing for each of them, a description of the necessary infrastructures and an indicative timeline for their realization.

Speaker: Mariangela Bondi (INFN)
• 6:00 PM 6:30 PM
Break 30m
• 6:30 PM 7:30 PM
Discussion
• 6:30 PM
Summary 1h
Speakers: Alessandro Pilloni (INFN Roma) , Eric Voutier (CNRS/IN2P3/IPNO - UPS) , Marco Battaglieri (JLab/INFNGE)