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The International Workshop on Partial Wave Analyses and Advanced Tools for Hadron Spectroscopy (PWA13/ATHOS8) is a joint meeting combining the 13th International Workshop on Pion-Nucleon Partial Wave Analysis and the Interpretation of Baryon Resonances (PWA) and the 8th Workshop on Partial Wave Analysis Tools for Hadron Spectroscopy (ATHOS). It will take place at William & Mary in Williamsburg, Virginia, in proximity to the Thomas Jefferson National Accelerator Facility (Jefferson Lab). Previous editions were held at University of Bristol (2021), CBPF in Rio de Janeiro (2019), IHEP in Beijing (2018), George Washington University (2017), and University of Bonn (2015).
The purpose of this workshop series is to bring together experimental and theoretical groups working in hadron spectroscopy. The emphasis of the scientific program is on methods and tools for data analysis, addressing challenges that are common in the study of excited baryons, mesons, and the recently discovered exotic hadrons in the light- as well as in the heavy-quark sector. For the planned workshop, a special focus will be put on the application of innovative statistical methods like artificial intelligence and machine learning (AI/ML) to the field of amplitude analysis. An active participation of early-career scientists (students and postdoctoral researchers) in the discussions is encouraged.
Recent work on a model computation of light hybrid properties are summarized and compared to lattice field theory. Applications to decay, production, and flavor mixing will be discussed.
Quantum Chromodynamics (QCD) provides a theoretical framework for understanding interactions among quarks and gluons within hadrons. However, the influence of gluonic excitations on hadron characteristics and structure remains uncertain. Recent discoveries of potentially ex- otic hadrons underscore the need for precise spectroscopic measurements to decipher the strong force. This discussion focuses on ongoing analy- ses using photoproduction data from the GlueX experiment at Jefferson Lab, with emphasis on η(′)π systems. Specifically, we explore the produc- tion mechanisms of the a2(1320) mesons in these channels, a step toward unveiling exotic quantum-number hybrid mesons. Furthermore, the dis- cussion will cover the application of an amplitude analysis utilizing the polarized photon beam of the GlueX experiment, to identify the lightest hybrid mesons.
The GlueX experiment at Jefferson Lab has collected an unprecedented amount of data and will continue to do so on the production of light mesons with a polarized photon beam. These data can provide detailed insights into the photoproduction mechanisms, but their interpretation requires a parallel theoretical effort. In the high energy regime studied by GlueX, the photoproduction of single mesons can be explained in terms of Regge exchanges. Although it is well known that pion exchange dominates at low momentum transfer in charge-exchange reactions, the precise determination of its contribution in high energy peripheral production has never been satisfactorily established. The high precision data from photoproduction reactions at GlueX will certainly help in this regard. In this talk I will focus on the pion photoproduction reaction, which offers a clean probe of the pion exchange mechanism. I will discuss the role of gauge invariance in pion exchange, relevant to approach its reggeization in an appropriate way. I will also present a novel strategy to reggeize the pion pole which considers explicitly the exchange in the t-channel of all the mesons in the pion trajectory. Each of these exchanges contributes with a pole in spin, known as a Regge pole. I will demonstrate that the summation of these poles can be performed analytically, and I will compare the outcomes of this approach with other commonly used reggeization prescriptions [1].
[1] G. Montana, et al. (JPAC Collaboration) (in preparation)
The GlueX experiment at Jefferson Lab probes the spectrum of light hadrons with a $6-12\text{ GeV}$ linearly polarized beam. We study the $\gamma p\to K_S K_S p$ channel at GlueX to investigate the production of light flavorless mesons with even spin, namely the $f$ and $a$ mesons. The $f_0$ states in the $1-2\text{ GeV}/c^2$ mass range are particularly interesting, as there are too many for them to all be $q\bar{q}$ mesons. One possible explanation is that these states mix with the lightest scalar glueball, which has the same quantum numbers as the $f_0$ mesons ($J^{PC}=0^{++}$) and is predicted by lattice simulations to be in the same mass range. The GlueX data from this channel that will be shown contains evidence of multiple overlapping states. We decompose the spin states using two methods of partial-wave analysis, mass-independent amplitudes and a K-matrix model. This analysis uses highest-statistics dataset for this channel in photoproduction to date, even when restricted to the most-polarized energy range of $\sim8-9\text{ GeV}$.
The COMPASS experiment is a multi-purpose two-stage spectrometer located at the CERN SPS. One of its main goals is the investigation of the excitation spectrum of light mesons in diffractive reactions. One of the final states produced at COMPASS is $K_S^0 K^-$, in which only selected resonances, the $a_J$ states with even $J$, can appear at COMPASS’ high beam energies. Performing a partial-wave analysis of the COMPASS data allows a very selective study of these states and enables us to probe their intrinsic $s\bar{s}$ content, due to the two strange mesons. However, in two-body final states such as $K^0_S K^-$, one complication arises: mathematical ambiguities in the partial-wave decomposition result in different combinations of amplitude values describing the same intensity distribution.
Using the so-far largest dataset of $K_S^0 K^-$ events, we are able to search for new resonances and measure states with high precision. We will discuss the ambiguity issue and present the results of the partial-wave analysis, which shows several clear resonance signals.
The discovery of the pentaquark candidate in the amplitude analysis of Lb -> J/psi p K decays in 2015 has ignited an interest in heavy hadron spectroscopy at the LHCb experiment. This has lead to further discoveries of more pentaquark candidates at the LHCb experiment, notably in Bs -> J/psi p pbar and B -> J/psi Lambda p decays. A majority of these experimental discoveries rely heavily on amplitude analyses to study the properties and confirm the existence of pentaquark candidates. This talk would present the latest update from the LHCb experiment on heavy hadron spectroscopy of pentaquark candidates, with a focus on challenges encountered by the ongoing amplitude analysis of Lb -> J/psi p K with the full LHCb Run 1 + 2 dataset.
In the helicity formalism the task of calculating the correct roations between two systems is non trivial. While it can be done in an analytical manner for three body decays, this is not the case for decays involving more particles. To reassure consistent treatment of quantization axes for particles with spin, a series of boosts and rotations has to be translated into one set of angles known as the Wigner rotation.
This work introduces an efficient Python-based implementation for calculating Wigner rotations in multi-particle decay processes, utilizing NumPy and JAX for numerical computations.
Addressing the complexity of Lorentz transformations, our method leverages both SO(3,1) and SU(2) representations to compute rotation angles for any given particle within n-body decays accurately. This approach overcomes traditional challenges of sensitivity to $2\pi$ rotations and angle extraction, providing a robust tool for the computational analysis of complex decay phenomena in high-energy physics.
B^{\pm} \to DK^+{\pm}, D—>K_S pi+ pi- and related decay modes provide an exceptionally precise way to measure the CP violating parameter gamma, one of the key measurements at LHCb and BELLE II. In order to avoid the theory uncertainties related to the description of the multi body D decay, model-independent methods are used - these use charm threshold (CLEO-c / BESIII data) to constrain the phase difference between D and anti-D amplitudes to the same point in phase space. These analyses usually average over bins of the D decay’s phase space, with the inevitable information loss that such averaging entails. This talk presents a new method that does not rely on such binning but instead corrects the phase of the charm amplitude model based on threshold information. This does not only lead to a more precise measurement of gamma, but also to a model-independent phase correction of the amplitude model that could be used to test models. (This will be based on JHEP 09 (2023) 007, https://inspirehep.net/literature/2660852 plus several additional, new results.)
We present the first calculation in lattice QCD of the process $\gamma K \to K\pi$ in which the narrow $K^*$ vector resonance appears. Using a lattice on which the pion has a mass of 284 MeV, we determine the transition amplitude at 128 points in the $(Q^2, E_{K\!\pi})$ plane, and find suitable resonant scattering descriptions. We demonstrate the need to account for $S$--wave $K\pi$ elastic scattering when converting the finite-volume matrix elements computed in lattice QCD to the physically relevant infinite-volume matrix elements, even when we are primarily interested in the $P$--wave amplitude. Analytically continuing parameterizations of the $\gamma K \to K\pi$ amplitude to the $K^*$ resonance pole, we obtain the $K^{*+} \to K^+ \gamma$ transition form-factor, and compare the $Q^2=0$ value to the corresponding value extracted from the experimental partial decay width.
A precise and complete measurement of the excitation spectrum of light mesons allows us to study QCD in the non-perturbative regime and is an important input to other studies, e.g., of $B$ meson decays. While the non-strange light-meson spectrum is already mapped out rather well, the strange-meson spectrum may hold many surprises, as almost no new data have been available for the last 20 years.
The $190\,\mathrm{GeV}/c$ negative hadron beam at CERN's M2 beam line contains a $K^-$ component, which allows us to study the spectrum of strange mesons with the COMPASS experiment, a two-stage magnetic spectrometer. The flagship channel is the $K^-\pi^-\pi^+$ final state, for which COMPASS has acquired the so-far world's largest data set. We performed a partial-wave analysis in order to disentangle the produced mesons by their spin-parity quantum numbers. In this talk, we will discuss major challenges of this analysis such as the treatment of incoherent backgrounds and report on properties of excited strange mesons with various spin-parity quantum numbers.
The reproducibility of complex amplitude models from published papers poses a significant challenge in high-energy physics, hindering progress and reliability. If these models were readily reproducible, it would standardize verification, enhance community reanalysis, and improve the utility of MC generators. We propose a solution involving the serialization of amplitude models into a lightweight, human-readable format, starting with three-body decay analyses. Our approach aims to bridge the gap in model accessibility and reproducibility, utilizing JSON for model descriptions. Early efforts are in progress with ThreeBodydDecays.jl
, COMPWA
, and TFAnalysis
implementations, and we see potential for broader adoption, including a possible extension to ROOT via the HS3 initiative. Success in this endeavor requires active community support and collaboration with developers of leading frameworks, ensuring widespread adoption and the advancement of transparent, reproducible research in our field.
Electroproduction reactions reveal the structure of light baryon resonances. Recent results of a simultaneous analysis of $\pi N$, $\eta N$, and $K\Lambda$ electroproduction data with the Juelich-Bonn-Washington (JBW) approach are presented. The extraction of multipoles and their uncertainties is discussed, and preliminary results for transition form factors at the resonance poles are shown.
The exploration of nucleon structure and electromagnetic transitions from ground state to excited state is a cornerstone of nuclear physics research. Meson electro-production experiments have opened new avenues for investigating these phenomena, particularly in the 12 GeV era at Jefferson Lab with the CLAS12 spectrometer. The $\eta N$ final states, accessible only through isospin $I = 1/2$ resonances, provide a unique tool for studying nucleon excitations. By simplifying the analysis and enabling a cleaner extraction of resonance properties compared to the extensively studied $\pi N$ final states, $\eta$ electro-production offers a complementary approach to unraveling the structure of excited nucleons. This work presents the first-ever measurement of the beam spin asymmetry (BSA) in exclusive $\eta$ electro-production, covering a previously unexplored kinematic region with $1.6 \leq W \leq 2.2$~GeV. The BSA is extracted from the CLAS12 data using a comprehensive analysis framework that carefully considers the statistical limitations of the data set. The results are compared to predictions from theoretical models, such as the J"{u}lich-Bonn-Washington (JBW) and MAID, as well as compared to previously published cross-section and spin observable results from CLAS, and SLAC. Notably, the extracted BSA exhibits discrepancies with the model predictions, highlighting the potential for refining theoretical descriptions of nucleon resonances and their electromagnetic couplings through the incorporation of these new data. The high-precision data obtained in this previously unmeasured kinematic region now serve as valuable input for refining models.
In order to connect theoretical predictions for the baryon spectrum in the non-perturbative energy regime to experimental data, coupled-channel approaches are the method of choice. In those approaches a simultaneous partial-wave analysis of multiple reactions with different initial and final states are performed.
I will present the framework of the Juelich-Bonn dynamical coupled-channel model as well as recent updates and preliminary fit results for newly included $\pi$-photoproduction data from CLAS and $\eta$-photoproduction data from LEPS.
Nowadays, experimentally observed states that are often assigned to the light meson or charmonium sector might indicate an exotic nature. Such exotic particles include glueballs, hybrids, and tetraquarks. Not only do these states pose a theoretical challenge, but experimentally it is often difficult to distinguish exotic and non-exotic matter and to characterise their nature. In such cases, it helps to compare different production mechanisms and decay patterns. This provides additional constraints and allows for a coupled channel partial wave analysis to describe the different spectra simultaneously, respecting unitarity and analyticity. Therefore, gluon-poor two-photon fusion events and gluon-rich hadronic reactions as e.g. radiative J/ψ decays can be used to disentangle the highly populated light meson spectrum.
The BESIII experiment has collected world leading high statistic data samples in the charmonium region and further allows to study two-photon events. Therefore, BESIII offers great opportunities to combine different reactions and to shed light onto the light meson regime.
The talk will discuss recent experimental results from coupled channel analyses as well as recent PWA results from BESIII. Special emphasise will be on the models used and the associated software tools.
We extend the scope of the extraction of the electromagnetic form factor of the pion, $f_\pi$, from lattice QCD.
In the past, the calculation of electroweak induced transitions to two hadron states has been restricted to the elastic region.
We implemented the technology required to calculate $f_\pi$ beyond the first inelasticity, specifically in a lattice with heavier than physical pions into the coupled channel region of $\pi\pi/K\overline{K}$.
Additionally, this method determines the isovector timelike kaon form factor.
Furthermore, we also study a dispersive representation of $f_\pi$ to constrain the spacelike and timelike data extracted from the lattice with a unified approach.
This work lays the foundation to study the internal structure, and potentially the nature, of resonances that decay into multiple channels, e.g. the exotic $\pi_1$ meson.
The sustainable use of energy should be fulfilled as well in the field of particle physics, especially considering that it has additional advantages. Over recent decades, the continuous increase of experimental data in high energy physics applications has led to a significant computational demand. In particular, time-consuming coupled channel analyses require sometimes fits with a hundred free parameters that extend over several weeks, are an area where such optimisation is of great value. To address this need, we are currently integrating various AI tools into PAWIAN (PArtial Wave Interactive ANalysis), a software package developed at Ruhr-University Bochum for conducting partial wave analysis even more efficiently. PAWIAN's architecture enables the simultaneous analysis of data from various hadron physics experiments and supports sophisticated dynamical models as K-matrix formalism or tensor formalism. The current project includes efficiency improvements within the minimisation procedures by moving from numerical methods towards automatic differentiation for the intermediate derivative computations. Additionally, augmenting the gradient descent algorithm with a velocity term aims to address issues such as local minima, instabilities, and prolonged computation time. Furthermore, we are working on pseudo-event binning, where events are grouped to optimise the number of function evaluations without losing precision. Preliminary results of these efforts and specific benchmark cases regarding the implementation of these AI techniques will be presented.
The talk will discuss amplitude analyses techniques employed to study the spectrum of heavy mesons at LHCb.
Rare B meson decays like B->K mu mu provide highly sensitive probes of physics beyond the standard model. Recent results show intriguing indications of discrepancies between standard-model prediction and observation. PWA techniques play a crucial role in these analyses, especially those related to the angular distribution of B->K( * ) mu mu. They are critical in understanding and properly taking into account hadronic effects that might otherwise emulate physics beyond the standard model. In addition, rescattering in B->K tau tau -> K mu mu also provides a probe of B->K tau tau that is currently more precise that the direct B->K* tau tau measurement. This talk will present recent developments and results.
The next generation of experimental facilities promises to extend current heavy spectroscopy efforts to electro- and photoproduction. I will summarize recent efforts from the JPAC collaboration in this sector which include predicting expected production rates for many exotic candidate XYZ states and amplitude analysis of conventional charmonium photoproduction. I will focus on interesting open questions in this sector and the potential impact of new data at future experiments.
The GlueX experiment has produced the world's largest data sample for peripheral photoproduction of mesons with a goal to expand our understanding of the strong interaction and search for hybrid mesons. The experiment at the Thomas Jefferson National Accelerator Facility utilizes the GlueX detector and a tagged linearly polarized photon beam that peaks between 8 - 9 GeV incident on a liquid hydrogen target. Multiple partial-wave analyses are ongoing in the collaboration, and some exhibit ambiguous behavior in their result. We will present the mathematical nature of these ambiguities and tools to help diagnose if either the model or data will exhibit these ambiguities. Lastly, we will introduce tentative solutions to help address these obstacles.
Partial wave analysis (PWA) is often performed in one of two regimes: either the data is kinematically binned to remove assumptions about the dynamics, or parameterized models like Breit-Wigner functions are used to encode physical dynamics. The ability to bridge these regimes can provide additional flexibility in describing the underlying physics.
NIFTy[1], a probabilistic programming framework developed for astrophysics, has recently been adapted to be used for PWA at COMPASS[2]. A non-parametric model, described as a correlated field, is used to characterize kinematically smooth complex binned amplitudes. Parametric models can also be mixed in. This technique is being explored for the analysis of the GlueX polarized photoproduction data. Preliminary studies will be shown along with a highlight on the future direction.
[1] G. Edenhofer, P. Frank, J. Roth, R. H. Leike, M. Guerdi, L. I. Scheel-Platz,
M. Guardiani, V. Eberle, M. Westerkamp, and T. A. Enßlin. Re-Envisioning
Numerical Information Field Theory (NIFTy.re): A Library for Gaussian
Processes and Variational Inference, 2024.
[2] F. M. Kaspar, J. Beckers, and J. Knollm ̈uller. Progress in the Partial-Wave
Analysis Methods at COMPASS. EPJ Web Conf., 291:02014, 2024.
In scattering experiments, meson resonances have for many decades been studied in a 2-step procedure. First, the spin-density matrix has been non-parametrically extracted using the isobar model. From this, the resonance parameters have been determined in the second step. The latter requires detailed modeling of all amplitudes and thus could typically be performed simultaneously for few waves only and was restricted to a limited range of the spectral mass distribution. We will report on a new method that allows us to combine a parametric and non-parametric model in a single analysis step and that uses the information of the full mass spectrum. We successfully applied this method to a PWA model with over 336 partial waves.
We present a partial-wave analysis of $\tau^-\to \pi^-\pi^-\pi^+ \nu_\tau$ decays using the world's largest sample of these decays from the Belle experiment at KEK, Japan.
We discuss the employed covariant tensor formalism and the treatment of large incoherent backgrounds in our sample.
We give preliminary results on light-meson resonances appearing in the $\pi^-\pi^-\pi^+$ system, including $a_1(1420)$, and in the $\pi^-\pi^+$ subsystem, measured using the so-called freed-isobar method; and we give prospects for measurements at Belle II.
Accessing the hadron spectrum from Quantum ChromoDynamics (QCD) poses several challenges given its non-perturbative nature and the fact that most states couple to multi-particle decay modes. Although challenging, advances in both theoretical and numerical techniques have allowed us to determine few-body systems directly from QCD. A synergistic approach between lattice QCD and scattering theory offers a systematic pathway to numerically compute properties such as the hadron spectrum from first principles. I will present an overview of this program, and discuss developments in determining three-hadron scattering processes using lattice QCD. These techniques allow us to push the boundaries of resolving the few-body problem in spectroscopy from first-principles.
Scattering of three pions is relevant for the analysis of axial resonances that can be studied on the lattice and in experiment. Conceptual developments of a finite-volume formalism (FVU) for the analysis of lattice data are presented, including coupled channels. Progress for infinite-volume coupled-channel systems and the effect of rescattering effects is reported, as well.
This talk presents study cases of the decay and production of hadrons with $c$-quark content from the point of view of effective field theories. A theoretical review of the $D^{+}_S\rightarrow K^+K^-K^+$ and $B\rightarrow H(c\bar{c})\;X$ decays is shown. The $D^{+}_S\rightarrow 3K$ $W$-radiation topology, also known as external $W$-emission, is introduced and visualized using Dalitz plots. Then, the talk continues with a review of non-relativistic quantum chromodynamics (NRQCD) factorization for charmonium production to finish with a fitting of the long-distance matrix elements (LDMEs) present in the inclusive decay rate of $B$ mesons into $\chi_{c}$ states, employing literature results at next to leading order (NLO) in QCD and theoretical uncertainties management. The resulting amplitude for the $D^{+}_S\rightarrow 3K$ decay coincides with the decay channel phenomenological knowledge, by the presence of the tail of $f_0(980)$ at the beginning of the phase space and the dominance of the $\phi(1020)$ resonant structures. Additionally, the model implemented has the freedom to be adjusted with future fittings. For the $B\rightarrow H(c\bar{c})\;X$ decay is performed a fitting on the LDMEs present in $\chi_{c}$ states production using the experimental value of their branching fractions. A similar procedure is performed with the ratio of the branching fractions, however, a proper way of constraining the experimental data and handling the theoretical predictions is still needed. This talk is based on the eponymous master's thesis disserted in January 2024 at the Universidad Nacional de Colombia.
During the talk, I will discuss progress in applying the relativistic three-particle scattering formalism to systems of non-degenerate mesons of arbitrary angular momenta. For concreteness, I will focus on the $DD\pi$ system in the charm $C = 2$ and isospin $I = 0$ sectors, where the doubly charmed tetraquark $T_{cc}(3875)^+$ should appear as a pole in the elastic $3\to3$ scattering amplitude. After a short overview of the $T_{cc}^+$ physics, finite-volume results, and the three-body formalism, I will describe solutions to integral equations describing this three-body process. I will focus on systems with heavier than physical pion masses and present several simple models of $T_{cc}^+$ proposed to explain the available and future lattice data. In particular, I will advocate for the importance of partial $S$- and $D$-wave mixing in this system and describe its implications for the finite-volume $DD\pi$ energy levels.
Ideally, we describe amplitude models with recognizable mathematical expressions and directly fit those models to large data sample with high performance. The ComPWA project achieves this by formulating models with a Computer Algebra System and using its symbolic expression trees as a code generation template for fast, computational back-ends like JAX.
We present the latest features that have been implemented symbolically, in particular spin alignment for three-body decays using Dalitz-Plot Decomposition and K-matrix parametrizations for coupled channels, with interactive visualizations of Riemann sheets and resonance poles. These features illustrate how the symbolic approach results in a transparent, self-documenting workflow that is well-suited for performing high-performance computations such as amplitude analysis fits.
The BESIII experiment is collecting e+e- annihilation data in the tau-charm region. A large number of datasets above the open-charm threshold with center-of-mass energies of up to 5 GeV allows detailed studies of both conventional charmonia and charmonium-like states. In this contribution, recent highlights and future plans for the spectroscopy of charmonium(-like) states will be presented.
The $\eta(1295)$ and $\eta(1405/1475)$ are assumed to be the candidates of the first radially-excited states of $\eta-\eta'$ and even the pseudo-scalar glueball. Ragarding to the recent BESIII $J/\psi\rightarrow\gamma K^0_S\bar{K}^0_S\pi^0$, we perform a dispersive analysis in the Khuri-Trieman framework which incoporates both the two- and three-body unitarity in the final state interactions. And then, the invariant mass spectrums are learned to shed light on the nature of these pseudo-scalar states.
Single-energy partial wave analysis has often been applied as a way to fit data with minimal model dependence. However, remaining unconstrained, partial waves at neighboring energies will vary discontinuously because the overall amplitude phase cannot be determined through single-channel measurement. This problem can be mitigated with the use of a constraining penalty function based on an associated energy-dependent fit. However, the weight given to this constraint results in a biased fit to the data. In this paper, for the first time, a constraining function which does not influence the fit to data is explored. The constraint comes from the overall phase found in multi-channel fits which, in the present study, are the Bonn-Gatchina and Juelich-Bonn multi-channel analyses. The data are well reproduced and weighting of the penalty function does not influence the result. The method is applied to KΛ photoproduction data and all observables can be maximally well reproduced. While the employed multi-channel analyses display very different multipole amplitudes, we show how this can be related to the overall phase.
The talk will cover the application of the Bayesian parameter-inference method to a truncated partial-wave analysis in pseudoscalar meson photoproduction. As an example, a dataset from the photoproduction of eta mesons is examined. The basics of the method as well as its possible limitations will be discussed.
A reliable determination of the pole parameters and residues of nucleon resonances is notoriously challenging, given the required analytic continuation into the complex plane. We provide a comprehensive analysis of such resonance parameters accessible with Roy-Steiner equations for pion-nucleon scattering - a set of partial-wave dispersion relations that combines the constraints from analyticity, unitarity, and crossing symmetry - most prominently of the $\Delta(1232)$ resonance. Further, we study the Roper, $N(1440)$, resonance, which lies beyond the strict domain of validity, in comparison to Padé approximants, comment on the role of subthreshold singularities in the $S$-wave, and determine the residues of the $f_0(500)$, $\rho(770)$, and $f_0(980)$ resonances in the $t$-channel process $\pi\pi\to\bar NN$. The latter allows us to test - for the first time fully model independently in terms of the respective residues - universality of the $\rho(770)$ couplings and the Goldberger-Treiman relation expected if the scalars behaved as dilatons, in both cases revealing large deviations from the narrow-resonance limit.
Machine learning offers many tools that can be exploited to understand physics. In this talk I will present how neural networks can help understanding the hadron spectrum, its properties and the underlying dynamics that leads to the formation of resonances.
Artificial Intelligence (AI) generative models have been successfully used in several field. In this contribution I will present results of the A(I)DAPT (AI for Data Analysis and Data PreservaTion) working group. Our objective is to develop AI-based tools to address the main challenges in Nuclear Physics and High Energy Physics measurements: unfold detector effects and preserve multi-dimensional correlations when working on large datasets.
In this contribution I will present a first closure test performed on pseudo-data matched on CLAS g11 experiment kinematics, where generative models were able to unfold detector effects on data and reproduce multi-differential contribution in data. I will also show the current progress in expanding this study towards more complex processes and detector layout, such as CLAS12 two pion electroproduction.
Resonances are characterized uniquely by their complex pole location and the
corresponding residues. On the other hand experimentally resonances
are typically identified as structures in amplitudes - in particular
branching ratios of resonances are determined as ratios of count rates. To make contact
between these quantities it is necessary to connect line shapes and resonance
parameters.
In this work we provide such a connection and illustrate the formalism
on the examples of $\rho(770)$ and $f_0(500)$.
From those line shapes, expressions for partial widths and branching ratios are derived
and compared to other approaches proposed
in the literature.
We determine, from Lattice QCD, the elastic $\pi\pi$ scattering amplitude in the three possible isospin channels for various quark masses. We observe that, once the $\sigma$ becomes an unstable particle, its pole position is very noisy. By performing a full dispersive analysis, we drastically reduce the systematic uncertainties associated with model extractions, constrain the low energy scattering region, and determine the pole position with accuracy.
The GlueX experiment at Jefferson Lab uses linearly polarized photoproduction to study the light quark meson spectrum and search for spin-exotic mesons. The linear polarization of the beam allows separation of the natural and unnatural production mechanisms in $t$-channel production. The production mechanisms of the axial vector $b_1(1235)$ meson can be measured via amplitude analysis of the $\omega\pi$ channel. This amplitude analysis procedure will be described for the charge exchange reaction $\gamma p\to\omega\pi^-\Delta^{++}$, and the production mechanisms of the charged $b_1^-$ at low momentum transfer will be presented and compared with those of the neutral $b_1^0$.
Contrary to the general notion that the background part of resonant scattering amplitude must be large and complicated for broad resonances, we show that the size of background depends only on the geometry, more precisely, on the angle at which the resonant pole is "seen" from the threshold. We use an approximation which treats the threshold as a simple zero instead of a branch point [1,2], and it works perfectly not only for mostly elastic meson and baryon resonances, but also for the highly inelastic Z boson. It enables us to connect the background to the complex residue phase, an elusive resonant parameter from the world of nucleon resonances, and it equals twice the background phase shift. To include the Z boson in this picture we study two separate definitions of resonant mass and width: as pole, and Breit-Wigner parameters. We clarify that the two different definitions come from two ways of combining the total phase shift from resonant and background terms: the sum of tangents, or the tangent of the sum. Using all this, we show that the infamous non-Breit-Wigner meson resonance f_0(500) has the same shape as any broad Breit-Wigner resonance with the mass close to the threshold [3].
[1] Model-Independent Extraction of the Pole and Breit-Wigner Resonance Parameters, S. Ceci, M. Korolija, and B. Zauner, Phys. Rev. Lett. 111, 112004 (2013)
[2] Fundamental properties of resonances, S. Ceci, M. Hadzimehmedovic, H. Osmanovic, A. Percan & B. Zauner
Scientific Reports volume 7, Article number: 45246 (2017)
[3] The strangest non-strange meson is not so strange after all, Sasa Ceci, Marin Vuksic, and Branimir Zauner, https://arxiv.org/abs/2005.11564v3
In this talk, we perform a comprehensive amplitude analysis on photon-photon scattering into pion&\eta and kaon pairs within the isovector channels. The coupled channel scattering of \pi\eta-K\bar{K}-\pi\eta' are taken into account, and the photon-photon reaction amplitudes are constrained based on the Au-Morgan-Pennington method, where the final states interaction theorem is imposed. The decays of \eta'/\eta-->\pi\gamma\gamma are included in an overall analysis. Constraints from chiral effective field theory, dispersion relations, and the experimental data are considered, too. Finally, a high-quality solution is obtained, and we can extract the scalars involved in these processes. These amplitudes are helpful for further study of Light-by-Light sum rules.
The ALICE detector at the LHC has undergone a major upgrade in the long shutdown 2019-2022 to be able to take data at much higher rates in Run 3 and beyond. I will present the various challenges of this upgrade, and will show first results of pion and kaon pairs in double gap events taken in pp collisions in Run 3. I will discuss the prospects of developing a partial wave analysis for these pairs.
The intense photon fluxes of relativistic nuclei provide an opportunity to study photonuclear interactions in ultra-peripheral collisions. Exclusive final states of vector mesons can be studied in the process $\gamma$ + A → meson + A. The measurement of photoproduced $\pi^+\pi^− \pi^+ \pi^−$ final states in ultra-peripheral Pb–Pb collisions at √sNN = 5.02 TeV is presented for the first time. The cross section, d$\sigma$/dy, times the branching ratio is measured in the rapidity interval |y| < 0.5 and compared to recent theoretical predictions. The invariant mass distribution is not well described with a single Breit-Wigner resonance, so the production of two independent excited resonances, $\rho$(1450) and $\rho$(1700), and their interference is considered. The values of the masses and widths of the resonances are found to be in a good agreement with the PDG values. The mixing angle between the two resonances is also extracted from the fits to the invariant mass spectra.
Commissioned in 2017, the CLAS12 spectrometer is the flagship detector system in Hall B at Jefferson Lab, replacing the previous spectrometer, CLAS, which operated from 1997 until 2012. CLAS12 enables large acceptance studies of electron-induced reactions using the now energy-doubled CEBAF electron beam, with access to quasi-real photoprodcution processes via the low-Q2 Forward Tagger. The Forward Tagger is able to determine the properties of the photon, such as polarisation, on an event-by-event basis, offering notable advantages over both real photon beams and hadronic beam experiments, where most experimental data exists.
The MesonEx experiment seeks to address fundamental questions in our understanding of QCD by probing the spectrum of mesons, searching for exotic states and making precise determination of masses and properties. The existence of exotic states, suggested by both quark models and lattice calculations, would allow gluonic degrees of freedom to be explored, and may help explain the role played by gluons in the QCD interaction. This talk will showcase recent progress in MesonEx analyses, and outline our approaches and prospects for partial wave analysis of several multi-particle final states.
I report the preliminary results of the Regge model study of the spin density matrix elements (SDMEs) of the $\Delta(1232)$ in the photoproduction reaction ${\vec\gamma} p \to \pi^-\Delta^{++}$. This reaction is being studied by GlueX in its ongoing efforts to understand the spectrum the light hybrid mesons. The intensity profile of the photoproduction of resonance(s) from a polarized photon is governed by the SDMEs of the resonance(s) produced. While the line shapes provide information about the decay of the unstable states, the SDMEs tell us about their production mechanism. I present the results of the ongoing efforts at the JPAC to model the photoproduction of mesons along with the $\Delta$, the insights derived from the properties of the SDMEs and briefly discuss their implications for higher spin states. I also discuss the effects of transformation to different bases.
A lattice QCD computation of the I=0 and S=-1 coupled channel \pi \Sigma - K N scattering amplitudes in the Λ(1405)region is detailed. We use a single ensemble of gauge field configurations with N_f = 2+ 1 dynamical quark flavors where the mass of the pion is around 200 MeV. Hermitian correlation matrices using both single baryon and meson-baryon interpolating operators for a variety of different total momenta and irreducible representations are used. Several parametrizations of the two-channel scattering K-matrix are utilized to obtain the scattering amplitudes from the finite-volume spectrum. I will discuss the results obtained for the complex scattering amplitudes in this calculation and the strategies utilized to verify the two-pole nature of the Lambda(1405) resonance.