Search

Information about the 3-dimensional description of the quark and gluon content of hadrons, described by the generalized parton distributions (GPDs), can be probed by exclusive processes in electron - proton ($ep$) collisions. In this letter, we investigate the timelike Compton scattering (TCS) in $ep$ collisions at the future electron - ion collider (EIC). Such process is characterized by the exclusive dilepton production through the subprocess $\gamma p \rightarrow \gamma^*p \rightarrow l^+ l^- p$, with the real photon in the initial state being emitted by the incoming electron. Assuming a given model for the GPDs, the TCS differential cross-section is estimated, as well the contribution associated to the interference between the TCS and Bethe - Heitler (BH) amplitudes. Predictions for the TCS, BH and interference contributions are presented considering the kinematical range expected to be covered by the EIC detectors. Moreover, the polarized photon asymmetry is also studied. Our results indicated that a future experimental analysis, considering photon circular polarizations, can be useful to probe the interference contribution and constrain the description of the GPDs for the proton., Comment: 8 pages and 9 figures. arXiv admin note: substantial text overlap with arXiv:2212.07657

Exclusive photoproduction of heavy $J/\psi$ meson is performed within handbag factorization method. The General Parton Distributions (GPDs) for gluons which are an essential ingredient here, are constructed using double distribution (DD) representation. The calculated cross section for few sets of gluon GPDs $H_g$ describe fine $J/\psi$ production experimental data from HERA to LHC energies. Based on this approach we estimate $J/\psi$ spin asymmetries determined by $E_g$ and $\tilde{H}_g$. The GPDs factorization approach can be employed to analyse heavy vector meson production in electron-proton scattering. Investigations of this reactions at future electron-ion colliders in USA and China can give an essential information on gluon GPDs., Comment: 13 pages, 17 figures

Gravitational form factors of hadrons provide information on mass and pressure distributions in the hadrons, and they have been investigated by generalized parton distributions (GPDs). The GPDs also contain information on internal compositions of hadron spins. Understanding on the origin of hadron masses, pressures, and spins is an important topic not only in hadron physics but also as fundamental physics, and it should be clarified by the GPD studies. The spacelike and timelike GPDs have been measured at charged-lepton accelerator facilities, for example, by the virtual Compton scattering and the two-photon process, respectively. In this work, we show the $\pi^\pm$ and $\pi^0$ production cross sections in neutrino (antineutrino) reactions $\nu \,(\bar\nu) + N \to \ell + \pi + N'$ for measuring the GPDs of the nucleon by using the theoretical formalism of Pire, Szymanowski, and Wagner. The $\pi^\pm$-production cross sections are useful for determining gluon GPDs, whereas the $\pi^0$ production probes quark GPDs. In particular, we show the roles of the pion- and rho-pole terms, the contribution from each GPD term ($H$, $E$, $\tilde H$, $\tilde E$), the effects of the gluon GPDs $H_g$ and $E_g$, and the effects of the reaction energy on the neutrino cross sections. The $\pi^0$-production cross section is sensitive to the quark GPDs including the pion- and rho-pole GPD terms in the Efremov-Radyushkin-Brodsky-Lepage region. These cross sections could be measured at Fermilab in future. The neutrino GPD studies will play a complementary role to the projects of charged-lepton and hadron reactions for determining the accurate GPDs., Comment: 15 pages, 14 figures

We investigate the exclusive $J/\psi$ production at the future Electron-ion collider in China by utilizing the eSTARlight event generator. We model the cross-section and kinematics by fitting to the world data of $J/\psi$ photoproduction. Projected statistical uncertainties on $J/\psi$ production are based on the design of a central detector, which consists of a tracker and vertex subsystem. The precision of the pseudo-data allows us to probe the near-threshold mechanism, e.g. the re-scattering effect. The significance of the forward amplitudes is discussed as well. The design and optimization of the detector enhance the potential for exploring the near-threshold region and the realm of high four-momentum transfer squared, which is of particular interest on several physics topics.., Comment: 11 pages, 11 figures

The General Parton Distributions (GPDs) are applied to study the hard Pseudoscalar Meson Production (PMP) at high energies. The PMP amplitudes are be obtained within the GPDs factorization. They are expressed in terms of GPDs convolution functions, which are most essential in PMP reactions. We show that these convolution functions can be extracted from the PMP data in future EIC of China (EicC). Predictions of $\pi^0$ and $\eta$ production at typical EicC energies are performed., Comment: Proceedings of the SPIN-2023 conference

Understanding the production mechanisms and utilizing them as probes to investigate the structure of exotic states represent some of the most actively studied research areas in particle physics. In this study, we present a theoretical analysis of the charmed meson $T^{-}_{cc}$ in the $\gamma{}p\to{}D^{+}T^{-}_{cc}\Lambda^{+}_{c}$ and $\gamma\gamma\to{}D^{+}T^{-}_{cc}D^{*0}$ reactions, considering $T^{+}_{cc}$ as a $DD^{*}$ molecule. The differential cross-section and total cross-section for the photoproduction of $T^{-}_{cc}$ in the $\gamma{}p\to{}D^+T^{-}_{cc}\Lambda^{+}_{c}$ and $\gamma\gamma\to{}D^{+}T^{-}_{cc}D^{*0}$ reactions are presented for nucleus-nucleus (nucleon-nucleon) ultraperipheral collisions at HL-LHC and RHIC, respectively. Taking into account the integrated luminosity per typical run and the luminosity of photons from the nucleus (nucleon), we observe a significant event count for $T^ {-} _{cc}$ production in p-p ultraperipheral collisions at HL-LHC., Comment: 7 pages,5 figures

The study of exclusive processes in photon - induced interactions allow us to probe the generalized parton distributions (GPDs), which provide information about the 3 dimensional description of the quark and gluon content of hadrons. In this paper we investigate the timelike Compton scattering (TCS) in ultraperipheral $pPb$ collisions at the LHC. Such process is characterized by the exclusive dilepton production through the subprocess $\gamma p \rightarrow \gamma^*p \rightarrow l^+ l^- p$, with the real photon in the initial state being emitted by the nucleus. Assuming a given model for the GPDs, the TCS differential cross section is estimated as well the contribution associated to the interference between the TCS and Bethe - Heitler (BH) amplitudes. Predictions for the TCS, BH and interference contributions are presented considering the kinematical range covered by the LHC detectors.

The exclusive $\eta$ and $\pi^0$ electroproduction is studied in the handbag approach based on Generalized Parton Distributions (GPDs) factorization. Predictions of $\pi^0$ and $\eta$ mesons are calculated for future Electron-Ion Collider of China (EicC) energy range using obtained cross sections we extract information on the transversity GPDs contributions to these processes.

The exclusive $\pi^0$ electroproduction is analyzed within the handbag approach based on Generalized Parton Distributions (GPDs) factorization. We consider the leading-twist contribution together with the transversity effects. It is shown that the transversity, $H_T$ and $\bar E_T$ GPDs are essential in the description of $\pi^0$ cross section. Predictions for future Electron-Ion Collider of China (EicC) energy range are done. It is found that transversity dominance $\sigma_T\gg\sigma_L$, observed at low energies is valid up to EicC energy range., Comment: 14 pages, 16 figures

The exclusive production of vector mesons and photons in $ep$ collisions is investigated considering three phenomenological saturation models based on distinct assumptions for the treatment of the dipole - hadron scattering amplitude. The latest high precision HERA data for the reduced and vector meson cross sections are used to update the saturation model proposed by Marquet - Peschanski - Soyez (MPS), which predicts that the saturation model is dependent of the squared momentum transfer $t$. The MPS predictions for the photon virtuality, energy and $t$ - dependencies of the exclusive $\rho$, $J/\Psi$ and DVCS cross sections are presented and a detailed comparison with the results derived using the impact parameter saturation models is performed. Our results indicate that a future experimental analysis of the $t$ - distribution $d\sigma/dt$ for exclusive processes in the kinematical range that will covered by the EIC and LHeC, considering the distinct photon polarizations and large values of $t$, will be able to discriminate between the distinct approaches for the QCD dynamics at high energies., Comment: 16 pages, 8 figures, 2 tables

Exclusive production of charmonium-like XYZ states in hadron-hadron ultraperipheral collisions(UPCs) and electron-proton scattering is studied employing effective Lagrangian method. Total cross sections and rapidity distributions of charmonium-like XYZ states are obtained in hadron-hadron UPCs and electron-proton scattering process. These predictions can be applied to estimate the observed event number of exclusive charmonium-like XYZ states in hadron-hadron UPCs and electron-proton scattering. The results indicate that it is significant to search $X(3872)$ and $Z^+_c(3900)$ in pA UPCs and Electron-Ion Collider in China will be an advantage platform to observe XYZ states in the future.

The exclusive $J/\Psi$ and $\Upsilon$ photoproduction in fixed - target collisions at the LHC and $ep(A)$ collisions at the Electron ion collider in China (EicC) is investigated considering different models for the treatment of the vector meson production at low energies, close to the threshold. Results for the total cross sections and associated distributions are presented. We predict a large number of $J/\Psi$ events at the LHC in the rapidity range covered by the LHCb detector. For the EicC, our predictions point out that a detailed analysis of the near threshold $J/\Psi$ and $\Upsilon$ photoproduction is feasible. Moreover, our results indicate that the modeling of the near threshold vector meson production can be constrained by future experimental analyzes at the LHC and EicC., Comment: 15 pages, 4 figures, 2 tables. Version published in EPJC

We present an analysis of the proton mass radius by studying the $t$-dependence of the differential cross sections of the vector meson photoproductions near the thresholds. At low energy, the photoproduction of a quarkonium off the proton is connected to the scalar gravitational form factor of the proton, which is sensitive to the proton mass distribution from the QCD trace anomaly. Under an assumption of the scalar form factor of dipole form, the proton mass radius is extracted via the near-threshold photoproduction data of J/$\psi$, $\phi$ and $\omega$ vector mesons. The average value of the proton mass radius is estimated to be $\sqrt{\left} = 0.67\pm0.03$ fm, with the dipole cutoff $m_{\rm s}=1.01\pm0.04$ GeV., Comment: 5 pages, 2 figures, minor modifications

We determine the leading Fock-state light front wave functions (LF-LFWFs) of the $\rho$ and J/$\psi$ mesons, for the first time from the Dyson-Schwinger and Bethe-Salpeter equations (DS-BSEs) approach. A unique advantage of this method is that it renders a direct extraction of LF-LFWFs in presence of a number of higher Fock-states. Modulated by the current quark mass and driven by the dynamical chiral symmetry breaking (DCSB), we find the $\rho$ and $J/\psi$ LF-LFWFs different in profile, i.e., the former are broadly distributed in $x$ (the longitudinal light-cone momentum fraction of meson carried by quark) while the latter are narrow. Moreover, the $\rho$ LF-LFWFs contribute less than 50% to the total Fock-state normalization, suggesting considerable higher Fock-states in $\rho$. We then use these LF-LFWFs to study the diffractive $\rho$ and $J/\psi$ electroproduction within the dipole picture. The calculated cross section shows general agreement with HEAR data, except for growing discrepancy in $\rho$ production at low photon virtuality. Our work provides a first dipole picture analysis on diffractive $\rho$ electroproduction that confronts the parton nature of the light (anti)quarks., Comment: 10 pages, 4 figures

In this paper we investigate the possibility of searching for the hidden-bottom pentaquark states in photon-induced interactions at the LHC. We consider the presence of the $P_b$ resonance in the $s$-channel of the $\gamma p \rightarrow \Upsilon p$ reaction and estimate its contribution for the exclusive $\Upsilon$ photoproduction in the fixed-target mode of the LHC. Predictions for the total cross sections, rapidity and transverse momentum distributions are derived using the STARlight Monte Carlo considering $Pb-p$, $Pb-He$ and $Pb-Ar$ fixed-target collisions at the LHC. Our results indicate that the presence of the $P_b$ resonance implies an enhancement in the rapidity distribution in the kinematical range covered by the LHCb detector. We demonstrate that the $P_b$ contribution for the $\Upsilon$ photoproduction becomes dominant if kinematical cuts are imposed on the rapidity and transverse momentum of the final state. These results indicate that an experimental analysis of the $\Upsilon$ photoproduction in fixed-target collisions can provide complementary and independent checks of the existence of these states, and help to understand their underlying nature., Comment: 10 pages, 3 figures, 1 table. arXiv admin note: text overlap with arXiv:1911.10886

The photoproduction of bottomonium-like states $Z_{b}(10610)$ and $Z_{b}(10650)$ via $\gamma p$ scattering is studied within an effectiv Lagrangian approach and the vector-meson-dominance model. The Regge model is employed to calculate the photoproduction of $Z_{b}$ states via $t$-channel with $\pi$ exchange.The numerical results show that the values of the total cross-sections of $Z_{b}(10610)$ and $Z_{b}(10650)$ can reach 0.09 nb and 0.02 nb, respectively, near the center of mass energy of 22 GeV. The experimental measurements and studies on the photoproduction of $Z_{b}$ states near energy region around $W\simeq 22$ GeV is suggested. Moreover, with the help of eSTARlight and STARlight programs, one obtains the cross-sections and event numbers of $Z_{b}(10610)$ production in electron-ion collision (EIC) and Ultraperipheral collisions (UPCs). The results show that a considerable number of events from $Z_{b}(10610)$ can be produced on the relevant experiments of EICs and UPCs. Also, one calculates the rates and kinematic distributions for $\gamma p\rightarrow Z_{b}n$ in $ep$ and $pA$ collisions via EICs and UPCs, and the relevant results will provide an important reference for the RHIC, LHC, EIC-US, LHeC, and FCC experiments to search for the bottomonium-like $Z_{b}$ states., Comment: 9 pages, 5 figures

The near-threshold photoproduction of $J/\psi$ is regarded as one golden process to unveil the nucleon mass structure, pentaquark state involving the charm quarks, and the poorly constrained gluon distribution of the nucleon at large $x$ ($>0.1$). In this paper, we present an analysis of the current experimental data under a two-gluon exchange model, which shows a good consistency. Using a parameterized function form with three free parameters, we have determined the nucleonic gluon distribution at the $J/\psi$ mass scale. Moreover, we predict the differential cross section of the electroproduction of $J/\psi$ as a function of the invariant mass of the final hadrons $W$, at EicC, as a practical application of the model and the obtained gluon distribution. According to our estimation, thousands of $J/\psi$ events can be detected per year on EicC near the threshold. Therefore, the relevant experimental measurements are suggested to be carried out on EicC., Comment: 6 pages, 7 figures

Ultraperipheral collisions (UPCs) of protons and nuclei are important for the study of the photoproduction of vector mesons and exotic states. The photoproduction of vector mesons in the pentaquark resonance channel in $p\mbox{-}Au$ UPCs at the Relative Heavy Ion Collider (RHIC) and $p$-$Pb$ UPCs at the Large Hadron Collider (LHC) is investigated by employing STARlight package. The cross sections of vector mesons via pentaquark state resonances channel are obtained using effective Lagrangian method. The pseudo-rapidity and rapidity distributions of $J/\psi $ and $\Upsilon(1S) $ are given for $p\mbox{-}Au$ UPCs at the RHIC and $p$-$Pb$ at the LHC. It is found that the RHIC is a better platform for discovering the pentaquark states than the LHC. Moreover, $P_{b}(11080)$ is easier to identify than $P_c(4312)$ because the background of $\Upsilon (1S)$ is weaker than $J/\psi$ in the $t$-channel at the RHIC., Comment: 9 pages, 5 figures

Inspired by the observation of the fully-charm tetraquark $X(6900)$ state at LHCb, the production of $X(6900)$ in $\bar{p}p\rightarrow J/\psi J/\psi $ reaction is studied within an effective Lagrangian approach and Breit-Wigner formula. The numerical results show that the cross section of $X(6900)$ at the c.m. energy of 6.9 GeV is much larger than that from the background contribution. Moreover, we estimate dozens of signal events can be detected by D0 experiment, which indicates that searching for the $X(6900)$ via antiproton-proton scattering may be a very important and promising way. Therefore, related experiments are suggested to be carried out., Comment: 4 pages, 2 figures

Electro-production of several pentaquark states is investigated in this paper. eSTARlight package is adapted to study the electro-production of $J/\psi$ and $\Upsilon (1S)$ via pentaquark $P_c$ and $P_b$ resonance channels in $e p \to e eJ/\psi p$ and $e p \to e\Upsilon(1S) p$ scattering processes at proposed electron-ion colliders (EICs). The results in this paper are compared to the non-resonance $t$-channels, which is described in pomeron exchange model in our studies. Some pseudo-rapidity distributions rapidity distributions of $J/\psi$ and $\Upsilon(1S)$ are presented for proposed EICs including EicC and EIC-US. It is found that EicC is a good platform to identify $P_b$ states in the future.

Due to the discovery of the hidden-charm pentaquark $P_c$ states by the LHCb collaboration, the interests on the candidates of hidden-bottom pentaquark $P_b$ states are increasing. They are anticipated to exist as the analogues of the $P_c$ states in the bottom sector and predicted by many models. We give an exploration of searching for a typical $P_b$ in the $\gamma p \to \Upsilon p$ reaction, which shows a promising potential to observe it at an electron-ion collider. The possibility of searching for $P_b$ in open-bottom channels are also briefly discussed. Meanwhile, the $t$-channel non-resonant contribution, which in fact covers several interesting topics at low energies, is systematically investigated., Comment: 18 pages,, publication version, references updated

Ultra-peripheral collisions (UPCs) of relativistic ions are an important tool for studying photoproduction at high energies. Vector meson photoproduction is an important tool for nuclear structure measurements and other applications. A future electron-ion collider (EIC) will allow additional studies, using virtual photons with a wide range of $Q^2$. We propose a significant expansion of the UPC and EIC photoproduction physics programs to include charged final states which may be produced via Reggeon exchange. We consider two examples: $a_2^+(1320)$, which is a conventional $q\overline q$ meson, and the exotic $Z_c^+(4430)$ state (modeled here as a tetraquark). The $Z_c^+(4430)$ cross-section depends on its internal structure, so photoproduction can test whether the $Z_c^+(4430)$ is a tetraquark or other exotic object. We calculate the rates and kinematic distributions for $\gamma p\rightarrow X^+n$ in $pA$ UPCs and $ep$ collisions at an EIC and in UPCs. The rates are large enough for detailed studies of these final states. Because the cross-section for Reggeon exchange is largest near threshold, the final state rapidity distribution depends on the beam energies. At high-energy colliders like the proposed LHeC or $pA$ collisions at the LHC, the final states are produced at far forward rapidities. For lower energy colliders, the systems are produced closer to mid-rapidity, within reach of central detectors., Comment: 5 pages with 3 figures

The measured electromagnetic form factors of $\Lambda$ hyperon in the time-like region are significantly deviated from pQCD prediction. We attribute the non-vanishing cross section near threshold to be the contribution of below-threshold $\phi$(2170) state, supporting its exotic structure. Above the threshold, we find significant role of a wide vector meson with the mass of around 2.34 GeV, which would be the same state present in $p\bar{p}$ annihilation reactions. As a result, we give a satisfactory description of the behavior of existing data without modifying pQCD expectation., Comment: 10 pages, 1 figure, published version

Photoproduction of vector mesons are computed in dipole model in proton-proton ultraperipheral collisions(UPCs) at the CERN Large Hadron Collider (LHC). The dipole model framework is employed in the calculations of vector mesons production in diffractive processes. Parameters of the bCGC model are refitted with the latest inclusive deep inelastic scattering experimental data. Employing the bCGC model and Boosted Gaussian light-cone wave function for vector mesons, we obtain prediction of rapidity distributions of $J/\psi$ and $\psi(2s)$ mesons in proton-proton ultraperipheral collisions at the LHC. The predictions give a good description to the experimental data of LHCb. Predictions of $\phi$ and $\omega$ mesons are also evaluated in this paper., Comment: arXiv admin note: text overlap with arXiv:1805.06210

Rapidity distributions of vector mesons are computed in dipole model proton-lead ultraperipheral collisions(UPCs) at the CERN Larger Hadron Collider(LHC). The dipole model framework is implemented in the calculations of cross sections in the photon-hadron interaction. The bCGC model and Boosted Gaussian wave functions are employed in the scattering amplitude. We obtain predictions of rapidity distributions of $J/\psi$ meson proton-lead ultraperipheral collisions. The predictions give a good descriptions to the experimental data of ALICE. The rapidity distributions of $\phi$, $\omega$ and $\psi(2s)$ mesons in proton-lead ultraperipheral collisions are also presented in this paper.

Incoherent rapidity distributions of vector mesons are computed in dipole model in PbPb ultraperipheral collisions at the CERN Large Hadron Collider (LHC). The IIM model fitted from newer data is employed in the dipole amplitude. The Boosted Gaussian and Gaus-LC wave functions for vector mesons are implemented in the calculation as well. Predictions for the $J/\psi$, $\psi(2s)$, $\rho$ and $\phi$ incoherent rapidity distributions are evaluated and compared with experimental data and other theoretical predictions in this paper. We obtain closer predictions of the incoherent rapidity distributions for $J/\psi$ than previous calculations in the IIM model.

The AdS/QCD holographic wave function of basis light-front quantization (BLFQ) for vector meson $J/\psi$ is applied in this manuscript. The exclusive production of $J/\psi$ in diffractive process is computed in dipole model with AdS/QCD holographic wave function. We use IP-Sat and IIM model in the calculation of the differential cross section of the dipole scattering off the proton. The prediction of AdS/QCD holographic wave function in BLFQ gives a good agreement to the experimental data.

The coherent cross section of $J/\psi$, $\rho$, $\phi$ are computed in dipole model in the ultraperipheral PbPb collisions, the IP-Sat and IIM model are applied in the calculation of the differential cross section of the dipole scattering off the nucleon, three kinds of forward vector meson wave functions are used in the overlap. The prediction of $J/\psi$ and $\rho$ is compared with the experimental data of the ALICE Collaboration, and the prediction of $\phi$ is also given in this paper.

We calculate the coherent and incoherent production of $J/\psi$ in PbPb ultraperipheral collisions. The production of $J/\psi$ in ultraperipheral collsions is product of photon flux distributions and cross section of photon-nucleus scatterings. The distributions of photon flux is computed in light-cone perturbation theory and the cross section of photon-nucleus scatterings is calculated in dipole model, we assume that the two gluons exchange contribution is the coherent cross section and the large-$N_c$ contribution is the incoherent cross section in photon-nucleus scattering. The numerical result of the rapidity distributions of $J/\psi$ production in PbPb ultraperipheral collisions at $\sqrt{s_{NN}}=2.76$TeV are compared with the experimental data measured by the ALICE collaboration.

We consider a gedanken experiment of the scattering of a current off a large nucleus to study the gluon saturation at the small-x limit and compute the Sudakov factor of this process through a one-loop calculation. The differential cross section is expressed in term of the Sudakov resummation, in which the collinear and the rapidity divergences are subtracted. We also discuss how to probe the Weizsaecker-Williams (WW) gluon distribution in the process of photon pair production in the pA collisions., Comment: 7 pages, 6 figures