Search

Differential cross section of the deuteron breakup reaction 1H(d,pp)n exhibits sensitivity to interaction dynamics components like three-nucleon force and/or Coulomb force. This sensitivity facilitates comprehensive testing of theoretical potential models that describe interactions within three-nucleon systems. An analysis of experimental data of the breakup reaction, conducted at a beam energy of 100 MeV, has been performed. The presented cross section results for selected configurations agree well with calculations based on meson exchange model potentials and on state-of-the-art results within the Chiral Effective Field Theory framework. [ABSTRACT FROM AUTHOR]

We discuss results of a simultaneous fit to the K−p reactions and πΣ photoproduction data employing an approach that combines tree level photoproduction amplitudes with πΣ − KN coupled channel model describing the meson-baryon rescattering in the final state. The achieved reproduction of the photoproduction mass distributions represents a significant improvement when compared with the parameter free predictions made earlier but remains inferior to more comprehensive models that employ much larger sets of adjustable parameters. [ABSTRACT FROM AUTHOR]

Hard Exclusive Meson Production (HEMP) and Deeply Virtual Compton Scattering (DVCS) are very promising reactions to access Generalized Parton Distributions (GPDs). Such exclusive measurements were performed at COMPASS in 2016 and 2017 at the M2 beamline of the CERN SPS using the 160 GeV muon beam scattering off a 2.5 m long liquid hydrogen target surrounded by a barrel-shaped time-of-flight system to detect the recoiling target proton. The scattered muons and the produced real photons were detected by the COMPASS spectrometer, which was supplemented by an additional electromagnetic calorimeter for the detection of large-angle photons. Exclusive π0 production is the main source of background for the DVCS measurement, while it provides complementary information for the parametrization of GPDs. We will report on preliminary results of the exclusive π0 production cross section and its dependence on the squared four-momentum transfer |t| and on the azimuthal angle ϕ between the scattering plane and the π0 production plane. The COMPASS data will provide further input to constrain GPDs, in particular chiral-odd ("transversity") GPDs. [ABSTRACT FROM AUTHOR]

This talk focuses on a recent work aiming at determining the composition of certain N* and Δ resonances, i.e. whether they are compact states formed directly by quarks and gluons, or composite generated from the mesonbaryon interaction. The information of the resonance poles is provided by a comprehensive coupled-channel approach, the Jülich-Bonn model. Thirteen states that are significant in this approach are studied. Two criteria for each state are adopted in this paper, the comparison thereof roughly indicates the model uncertainties. It is found that the conclusions for eight resonances are relatively certain: N(1535)1/2−,N(1440)1/2+,N(1710)1/2+, and N(1520)3/2− tend to be composite; whereas N(1650)1/2−, N(1900)3/2+, N(1680)5/2+, and Δ(1600)3/2+ tend to be compact. [ABSTRACT FROM AUTHOR]

The BGOOD photoproduction experiment accesses forward meson angles and low momentum exchange kinematics in the uds sector, which may be sensitive to molecular-like hadron structure. Recent results are presented, including strangeness photoproduction at forward meson angles, and π0π0 coherent photoproduction off the deuteron. [ABSTRACT FROM AUTHOR]

Recent lattice QCD calculations predict a multiplet of hybrid mesons, which are mesons with gluonic degrees of freedom. By mapping out the hybrid meson spectrum, we can gain insight into how the gluon contributes to the properties of bound states in QCD. The π1(1600) is a candidate for the lightest hybrid meson. This state has exotic quantum numbers of JPC = 1−+, which are forbidden for conventional mesons. The GlueX experiment has collected high statistics photoproduction data, which we are using to search for the π1(1600). These proceedings will summarize the search strategy for the π1(1600) at GlueX, including the most recent results in the ωππ, ηπ, and η′π final states. [ABSTRACT FROM AUTHOR]

In the domain of hadron spectroscopy, the investigation of meson resonances plays a pivotal role. This study focuses on the significance of twopion photoproduction as a prominent avenue for studying meson resonances in the ππ system. By employing the Regge formalism, our model incorporates the background contribution from the well-known "Deck Mechanism" and emphasizes the significant ρ(770) resonance, representing the P-wave contribution arising from pomeron and f2 exchanges. The model is extended by accounting for scalar mesons, namely σ, f0(980) and f0(1370), contributing to the S-wave behavior, as well as the tensor meson f2(1270) corresponding to the D-wave contributions, while also considering non-resonant P- and S-wave components. The model contains a number of free parameters, which are constrained from a global fit of the available experimental data for angular moments up to L = 2 for M = 0, ..., 2. The fitted angular moments are compared with experimental data obtained from CLAS. The key physical insights gained from the model are summarized. Furthermore, we extract the t-dependence of the Regge amplitude residue function for the subdominant exchanges, shedding light on their contribution to the overall dynamics. [ABSTRACT FROM AUTHOR]

The KLOE/KLOE-2 Collaboration ended its data taking in 2018, about 20 years after the detector was turned on. In two different periods of datataking about 8 fb−1 at the peak of the ϕ(1020) resonance have been collected. During the years many results of the study of the light mesons have been published. The analysis of this unique data sample continues and the results of the latest measurements concerning kaons, and vector and pseudoscalar mesons are presented in this paper. [ABSTRACT FROM AUTHOR]

In this analysis, the production of pseudoscalar η′ mesons via two virtual spacelike photons is studied (γ*γ* → η′). Double-tagged measurements are conducted at the BESIII experiment in Beijing, China, in which both virtual photons possess nonzero virtualities Q12 and Q22. The Monte Carlo generator Ekhara 3.0 is used to simulate the expected signal event distribution. By measuring the double differential cross section at BESIII, the transition form factor (TFF) can be determined for Q12, Q22 < 2 GeV2. The TFF of pseudoscalar mesons serves as essential input for calculating the hadronic light-by-light contribution to the theoretical Standard Model prediction of the anomalous magnetic moment of the muon aμ = (gμ − 2)/2. [ABSTRACT FROM AUTHOR]

NA66/AMBER has been approved by CERN in 2020 as a new multipurpose facility for experiments in meson and baryon physics. In a first beamtime in 2023, data have been taken for the determination of antiproton production cross-sections in proton-helium collisions, needed for the interpretation of cosmic antimatter observations. Preparations are ongoing for a measurement of the proton charge radius in high-energy muon-proton scattering. This measurement will feature substantially different systematics than other approaches and aims at clarifying the present discrepancies. Further, experiments to study the partonic structure of mesons in Drell-Yan processes and strange-meson spectroscopy are on the menu of AMBER. [ABSTRACT FROM AUTHOR]

Lattice QCD (LQCD) has proven to be an important tool in understanding the tension between the experimental value for the anomalous magnetic moment of the muon (g − 2)μ and its prediction from the standard model. The lattice provides a non-perturbative method for evaluating the hadronic contributions to (g − 2)μ, which contributes the largest amount to the uncertainty of the theoretical prediction. Among these the hadronic vacuum polarization aμHVP is the dominant contribution. In order to match the uncertainty of the experiment, lattice QCD needs to reach sub-percent precision. This requires the calculation of QED corrections to aμHVP, which are represented by additional Feynman diagrams. We present a lattice calculation of the UV-finite (2+2) diagram at the SU(3) flavor symmetric point and compare this to the pseudoscalar meson exchange model with a vector-meson dominance parametrization of the transition form factor. [ABSTRACT FROM AUTHOR]

In order to investigate few-particle hypernuclei within the framework of the Hyperspherical Function Method, it is necessary to obtain full wave functions that are anti-symmetric under particle interchange. These wave functions must include not only hyperspherical, but also spin-isospin parts. According to the Parentage Scheme of Symmetrization, N-particle hyperspherical functions (N=3,4,5,6...) symmetrized with respect to (N-1)-particles, can be obtained from the N-particle hyperspherical functions with arbitrary quantum numbers by the use of the transformation coefficients related with the permutations of the last two particles. This article explains how to obtain fully antisymmetrized wave functions consisting of spin-isospin and hyperspherical parts. It is demonstrated that there are sixteen possible combinations in (3+1) configuration and 12 possible combinations in (2+2) configuration when spin and isospin functions are represented by [4], [31], and [22] representations of the four-particle permutation group S4. A complete set of the fully antisymmetrized four-particle wave functions is obtained. It is demonstrated that proposed mathematical formalism can be easily generalized to obtain fully antisymmetrized wave functions for the systems of five and more particles. [ABSTRACT FROM AUTHOR]

The method and results of the first theory description of 4He Compton scattering at nuclear energies is presented, with a focus on figures. An upcoming publication [1] contains details and a comprehensive list of references. [ABSTRACT FROM AUTHOR]

The EM polarizabilities characterize a fundamental property of the proton that involves the system's response to an external electromagnetic (EM) field. They describe how easily the charge and magnetization distributions inside the system are distorted by the EM field, such as during the Compton scattering with a real photon. When the polarizabilities are generalized to finite momentum transfer by replacing the incoming real photon of the Compton scattering process with a space-like virtual photon, they map out the deformation of the quark densities in a proton subject to an EM field. Recent experimental measurements at Jefferson Lab have provided high precision data, that offer guidance and present significant challenges to nuclear theory. Future experiments aim to improve further these measurements, both by extending their kinematic range as well as by improving the level of the experimental precision. [ABSTRACT FROM AUTHOR]

We present results for the electromagnetic form factors of the proton and neutron computed on the (2 + 1)-flavor Coordinated Lattice Simulations (CLS) ensembles including both quark-connected and -disconnected contributions. The Q2-, pion-mass, lattice-spacing, and finite-volume dependence of our form factor data is fitted simultaneously to the expressions resulting from covariant chiral perturbation theory including vector mesons amended by models for lattice artefacts. From these fits, we determine the electric and magnetic radii and the magnetic moments of the proton and neutron, as well as the Zemach radius of the proton. To assess the influence of systematic effects, we average over various cuts in the pion mass and the momentum transfer, as well as over different models for the lattice-spacing and finite-volume dependence, using weights derived from the Akaike Information Criterion (AIC). [ABSTRACT FROM AUTHOR]

The 10 billion J/ψ decays collected with the BESIII experiment offer a unique opportunity to investigate the decays of η and η′ mesons produced in the radiative J/ψ → γη(′) transitions. Using this clean production mechanism, the BESIII experiment is making important contributions to precision studies of the strong and electromagnetic interactions in η(′) decays. Three papers are presented in which the decays η → π+π−π0, η → π0π0π0, η′ → ηπ0π0π0, and η′ → π+π−e+e− are studied to test C and CP symmetry, as well as the predictions of different effective field theories. [ABSTRACT FROM AUTHOR]

In electron-positron annihilations, the process of e+e− → χc1 can occur via the production of two virtual photons or through neutral current, therefore being suppressed with respect to the normal annihilation process via one virtual photon. Using a dedicated scan sample around the χc1 mass, the direct production of χc1 has been established for the first time in experiments. This provides a new approach for the study of the internal nature of hadrons. [ABSTRACT FROM AUTHOR]

In this talk we summarize the results we obtained for the partial decay widths of ϕ(2170) into two-body final states formed by a K̄ and a Kaonic resonance, like K(1460), K1(1270), as well as to final states constituted by a ϕ and an η/η´ mesons. The results obtained are compared with the values extracted from experimental data on the corresponding branching ratios, which were determined by the BESIII collaboration. A reasonable agreement is found, which together with the previous reproduction of the mass, width, and cross section for the process e+e− → ϕ f0 strongly indicates the molecular nature of ϕ(2170) as a ϕKK̄ system. [ABSTRACT FROM AUTHOR]

The study of heavy-flavour mesons and baryons in hadronic collisions provides unique access to the properties of heavy-quark hadronisation in the presence of large partonic densities, where new mechanisms of hadron formation beyond in-vacuum fragmentation can emerge. Performing these measurements in intervals of charged-particle multiplicities across different collision systems provides sensitivity to understand whether different hadronisation mechanisms are at play in small and large hadronic colliding systems. In this contribution, a selection of the latest charm and beauty production measurements in proton–proton (pp) collisions is presented, which can shed light on the modification of the heavy-quark hadronisation mechanisms with respect to leptonic collisions. New published results of the production of all prompt charm ground states in pp collisions at √S = 13 TeV, which allowed us to measure the charm fragmentation fractions and the total cc production cross section at midrapidity, will be shown. The new final measurement of non-prompt (i.e. originating from beauty-hadron decays) Λc+ baryons in the same collisions system will be discussed to provide a quantitative comparison between the hadronisation properties of beauty and charm hadrons. New measurements of Ξc0 production as a function of charged-particle multiplicity in pp collisions at √S = 13, and of Ξc0 production in p–Pb collisions at √SNN = 5.02 TeV, will be also presented, shedding further light on the hadronisation of charm-strange baryons in different colliding systems. [ABSTRACT FROM AUTHOR]

Heavy meson production in reactions with nuclei is an active new frontier to understand QCD dynamics and the process of hadronization in nuclear matter. Measurements in various colliding systems at RHIC and LHC, including Pb-Pb, Xe-Xe, O-O, p-Pb, and p-O, enable precision tests of the medium-size, temperature, and mass dependencies of the in-medium parton propagation and shower formation. We employ a coupled DGLAP evolution framework that takes advantage of splitting functions recently obtained in softcollinear effective theory with Glauber gluons (SCETG) and hard thermal loop (HTL) motivated collisional energy loss effects. With jet quenching effects constrained to the nuclear modification factor of charged hadrons in Pb-Pb collisions at 5.02 TeV, we present predictions for light and heavy-meson in Xe-Xe, O-O and p-Pb collisions at the LHC.We find that the nuclear modification scales non-trivially with the quark mass and medium properties. In particular, there can be sizeable collision-induced attenuation of heavy mesons in small systems such as oxygen-oxygen and high-multiplicity p-Pb events. Finally, we analyze the impact of different models of initial-state parton dynamics on the search for QGP signatures in small colliding systems. [ABSTRACT FROM AUTHOR]

We explore the consequences of gluonic hot spots inside the proton for the initial eccentricities in a proton-nucleus collision, and the constraints on the parameters describing these hot spots from coherent and incoherent exclusive vector meson production cross sections in deep inelastic scattering. We show that geometric fluctuations of hot spots inside the proton are the dominant source of eccentricity whereas color charge fluctuations only give a negligible correction. We find that the coherent cross section is sensitive to both the size of the target and the structure of the probe. The incoherent cross section is dominated by color fluctuations at small transverse momentum transfer |t|, by proton and hot spot sizes as well as the structure of the probe at medium |t| and again by color fluctuations at large |t|. [ABSTRACT FROM AUTHOR]

Heavy quarks, i.e. charm and beauty, are produced in the initial stage of heavy-ion collisions, on a time scale shorter than the medium formation time, and are sensitive to the large initial magnetic field produced perpendicular to the reaction plane, defined by the impact parameter direction and beam direction, in non-central heavy-ion collisions. In the presence of a large initial magnetic field, the charm quark can be polarised. The quark polarisation is then expected to be transferred to the hadron in the hadronisation process. We will present the first measurement of D*+ polarisation in Pb–Pb collisions at √SNN = 5.02 TeV, exploiting the large data sample collected by the ALICE Collaboration during the LHC Run 2 and we will compare these new results with the existing J/ψ polarisation measurements. [ABSTRACT FROM AUTHOR]

Within the Color Glass Condensate framework, we demonstrate that exclusive vector meson production at high energy is sensitive to the geometric deformation of the target nucleus and subnucleon scale fluctuations. Deformation of the nucleus enhances the incoherent cross section in the small |t| region. Subnucleon scale fluctuations increase the incoherent cross section in the large |t| region. In ultra-peripheral collisions (UPCs), larger deformation leads to a wider distribution of the minimal impact parameter Bmin required to produce a UPC. This, together with larger incoherent cross sections for larger deformation, results in smaller extracted radii. Our results demonstrate great potential for future studies of nuclear structure in UPCs and electron-ion collisions. [ABSTRACT FROM AUTHOR]

We present a unique signal of medium response to jet quenching: the enhancement of baryon-to-meson ratios for associated particles at intermediate transverse momentum around the triggered quenched jets. Since the lost energy from the jets can diffuse to large angles, we expect that such baryon-to-meson enhancement is stronger for larger distance with respect to the jet axis. Our prediction can be tested by future experiments. [ABSTRACT FROM AUTHOR]

Quasi-Particle Model (QPM) has been developed to study charm quark dynamics in ultra-relativistic heavy-ion collisions with good description of D mesons RAA(pT) and v2,3(pT) and leading to the evaluation of the spatial diffusion coefficient Ds(T). With an event-by-event full Boltzmann transport approach followed by a hybrid hadronization via coalescence plus fragmentation, we show RAA(pT), v2(pT) down to pT → 0 for D and B mesons. We find that QPM approach is able to correctly predict first available data on RAA(pT) and v2(pT) of single-electron from B mesons decays measured by ALICE. A significant breaking of the expected scaling of the thermalization time τth with MQ/T is found. Charm quark Ds(T) is about 50% larger than the asymptotic value for MQ → ∞, while the bottom Ds(T) is only 20% higher. In the infinite mass limit the Ds(T) is consistent with recent lQCD calculations with dynamical quarks. [ABSTRACT FROM AUTHOR]

Our investigation focuses on the rapidity-dependent directed flow, v1(y), of identified hadrons in Au+Au collisions across a broad range of √SNN from 7.7 to 200 GeV. Employing a (3+1)-dimensional hybrid framework, our study successfully reproduces the characteristic features of the measured v1(y) for both mesons and baryons across the considered beam energies. Notably, our analysis reveals the constraining power of baryonic v1(y) on the initial baryon stopping mechanism. Together with mesonic v1(y), the directed flow serves as a crucial tool for probing the equation of state governing dense nuclear matter at finite chemical potentials. [ABSTRACT FROM AUTHOR]

In these proceedings, we present new measurements from STAR of the global spin alignment(ρ00) of ϕ mesons in Au+Au collisions at √SNN = 19.6, 14.6 GeV using BES-II data and of J/ψ mesons in isobar collisions 4496Ru + 4496Ru and 4096Zr + 4096Zr at √SNN = 200 GeV. The energy-dependent spin alignment for ϕ mesons from BES-II data is consistent with that published from BES-I and showcases a significant improvement in precision. We performed a new measurement assessing the rapidity dependence of ϕ meson ρ00, and our findings are consistent with theoretical predictions. The global spin alignment of J/ψ mesons with respect to first order event plane aligns with a value of 1/3 within the statistical error. Additionally, we discuss the procedure of measuring the global spin alignment of ρ0 mesons at RHIC and provide the projection for errors. [ABSTRACT FROM AUTHOR]

In this work, the shape (temperature) of pt distributions of π− mesons is studied in dependence on the centrality and size of the system, using single-temperature Hagedorn and Boltzmann functions to approximate their soft (pt = 0.1-0.5 GeV/c) and hard (pt = 0.5-1.2 GeV/c) components separately. It is demonstrated that the shape and degree of overlap of the colliding nuclei affect the temperatures of the soft and hard components of the pt distributions of π− mesons. The degree of overlap of colliding nuclei and the concomitant rise in the number of participating protons cause the variations in temperature in the collision systems under study to increase. [ABSTRACT FROM AUTHOR]