Photoproduction Of Vector Mesons Research Articles

Exclusive ϒ and ρ(770)0 photoproduction in pPb at [formula omitted] with CMS

The first measurements of exclusive ϒ and ρ(770)0 vector meson photoproduction with the CMS detector at LHC in ultraperipheral proton-lead collisions at sNN=5.02TeV are presented. The ϒ(1S) cross section, which has been measured in the dumuon channel, is consistent with the updated ZEUS ep results at HERA. A fit of function A(Wγp[GeV]/400)δ to the CMS pPb measurement together with HERA ep and LHCb pp data gives the δ value, consistent with J/ψ photoproduction results. The obtained result provides a new insight for low-x gluon distribution in protons in an energyrange previously less constrained. The cross section for exclusive photoproduction of ρ(770)0 has been measured where ρ(770)0 decays to two pions. The obtained pomeron slope parameter, α′ = 0.28 ± 0.11(stat) ± 0.12(syst)GeV−2, is consistent with the ZEUS result and with the Gribov-Regge theory expectation.

Nuclear form factor of xenon from photoproduction of vector mesons in Xe-Xe ultraperipheral collisions at the LHC

Using the Gribov-Glauber model for photon-nucleus scattering and a generalization of the vector meson dominance model for the hadronic structure of the photon, we calculate cross sections of light and heavy vector meson photoproduction in ultraperipheral Xe-Xe collisions at 5.44 TeV at the Large Hadron Collider. Analyzing the momentum transfer distribution in this process, we examine the feasibility to extract the nuclear isoscalar form factor of Xe isotopes, which are needed in searches for dark matter with Xenon-based detectors.

Production of vector mesons in pentaquark state resonance channel in p-A ultraperipheral collisions * *Supported by the National Natural Science Foundation of China (11705076, 11975278, 11405222), the Strategic Priority Research Program of Chinese Academy of Science (XDB34030301). This work is partly supported by HongLiu Support Funds for Excellent Youth Talents of Lanzhou University of Technology

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- UPCs at the Relative Heavy Ion Collider (RHIC) and p- UPCs at the Large Hadron Collider (LHC) is investigated by employing the STARlight package. The cross sections of vector mesons via the pentaquark state resonance channel are obtained using the effective Lagrangian method. The pseudo-rapidity and rapidity distributions of and are given for p- UPCs at the RHIC and p- UPCs at the LHC. It is found that the RHIC is a better platform for discovering pentaquark states than the LHC. Moreover, is easier to identify than because the background of is weaker than that of in the t-channel at the RHIC.

The cos 2\u03d5 azimuthal asymmetry in \u03c10 meson production in ultraperipheral heavy ion collisions

We present a detailed study of vector meson photoproduction in ultraperipheral heavy ion collisions (UPCs). Using the dipole model, we develop a framework for the joint impact parameter and transverse momentum dependent cross sections. We compute the unpolarized cross section and cos 2ϕ azimuthal angular correlation for ρ0 photoproduction with ϕ defined as the angle between the ρ0’s transverse momentum and its decay product pion meson’s transverse momentum. Our result on unpolarized coherent differential cross section gives excellent description to the STAR experimental data. A first compari- son between theoretical calculation and experimental measurement on the cos 2ϕ azimuthal asymmetry, which results from the linearly polarized photons, is performed and reasonable agreement is reached. We find out the characteristic diffractive patterns at both RHIC and LHC energies and predict the impact parameter dependent cos 2ϕ azimuthal asymmetries for ρ0 photoproduction by considering UPCs and peripheral collisions. The future experimental measurements at RHIC and LHC relevant to our calculations will provide a tool to rigorously investigate the coherent and incoherent production of vector meson in UPCs, as well as to probe the nuclear structure in heavy ion collisions.

Photoproductions of f1(1285) and η′(958) from the analysis of CLAS data with the Primakoff effect at high energies

We investigate photoproduction of axial vector meson $f_1(1285)$ based on the CLAS experiment $\gamma p\to pf_1(1285)\to p\eta\pi^+\pi^-$ using the Regge model for $\rho^0+\omega$ exchanges. The combined analysis of $\gamma p\to p\eta'\to p\eta\pi^+\pi^-$ reaction including $\eta(1295)$ is accompanied to evaluate the decay mode $\eta(1295)\to \eta\pi^+\pi^-$ from the potential overlap with the $f_1$ reaction. The predominance of $\rho^0(770)$ exchange over the $\omega(782)$ with the coupling constant $\gamma\rho^0f_1$ extracted from the CLAS experiment leads to a good description of the measured cross sections for $f_1$, while the scale of the cross section is corrected by the branching fraction $\eta'\to\eta\pi^+\pi^-$, and $f_1\to\eta\pi^+\pi^-$, respectively. As an extension to study the nonmesonic production mechanism, the Primakoff effect by the virtual photon exchange is investigated in the exclusive reaction $\gamma p\to pf_1$ up to $\sqrt{s}\approx50$ GeV, finding that it plays a similar role to the Pomeron in the vector meson photoproduction at high energies. Such an unique role of the virtual photon exchange similar to the $f_1$ case is identified up to $\sqrt{s}\approx250$ GeV in the $\gamma p\to p\pi^0$ and $\gamma p\to p\eta$ as well as $\gamma p\to p\eta'$ reaction.

Exclusive photoproduction of vector meson at next-to-leading order from color glass condensate * * Supported by the National Natural Science Foundation of China (11765005, 11947119, 11305040, 11847152, 11775097), the Fund of Science and Technology Department of Guizhou Province ([2018]1023, [2019]5653), the Education Department of Guizhou Province (KY[2017]004), Qian Kehe Platform Talents ([2017]5736-027), the National key research and development program of

The exclusive photoproduction of vector mesons ( and ) is investigated by considering the next-to-leading order corrections in the framework of the color glass condensate. We compare the next-to-leading order modified dipole amplitude with the HERA data, finding a good agreement. Our studies show that the from the leading order, running coupling, and collinearly improved next-to-leading order dipole amplitudes are 2.159, 1.097, and 0.932 for the elastic cross-section, and 2.056, 1.449, and 1.357 for the differential cross-section, respectively. The results indicate that the higher-order corrections contribute significantly to the vector meson productions, and the description of the experimental data is dramatically improved once the higher order corrections are included. We extend the next-to-leading order exclusive vector meson production model to LHC energies using the same parameters obtained from HERA. We find that our model provides a rather good description of the and data in proton-proton collisions at 7 TeV and 13 TeV in LHCb experiments.

Coherent photoproduction of \u03c10 vector mesons in ultra-peripheral Pb-Pb collisions at sqrt{{mathrm{s}}_{mathrm{NN}}} = 5.02 TeV

Cross sections for the coherent photoproduction of ρ0 vector mesons in ultra-peripheral Pb-Pb collisions at sqrt{{mathrm{s}}_{mathrm{NN}}} = 5.02 TeV are reported. The measurements, which rely on the π+π− decay channel, are presented in three regions of rapidity covering the range |y| < 0.8. For each rapidity interval, cross sections are shown for different nuclear-breakup classes defined according to the presence of neutrons measured in the zero-degree calorimeters. The results are compared with predictions based on different models of nuclear shadowing. Finally, the observation of a coherently produced resonance-like structure with a mass around 1.7 GeV/c2 and a width of about 140 MeV/c2 is reported and compared with similar observations from other experiments.

Exclusive vector meson photoproduction at high energies using the discrete BFKL approach

A phenomenological study of the exclusive vector meson photoproduction within the discrete BFKL approach is performed. We estimate the BFKL amplitude in terms of a discrete set of eigenfunctions and use the HERA [Formula: see text] data to constrain the free parameters of the model. As a consequence, we derive a parameter free prediction of the energy dependence of the exclusive vector meson cross section. We demonstrate that the HERA and LHCb data for the exclusive [Formula: see text] and [Formula: see text] photoproduction are quite well describe in a large energy range. However, the model overestimates the precise LHCb data for the smallest values of [Formula: see text], which can be interpreted as an indication of the onset of nonlinear (saturation) effects in the QCD dynamics.

D-wave effects in diffractive electroproduction of heavy quarkonia from the photon-like Vrightarrow Q{bar{Q}} transition

We analyse the validity of a commonly used identification between structures of the virtual photon gamma ^*rightarrow Qbar{Q} and vector meson Vrightarrow Q{bar{Q}} transitions. In the existing studies of S-wave vector-meson photoproduction in the literature, such an identification is typically performed in the light-front (LF) frame while the radial component of the meson wave function is rather postulated than computed from the first principles. The massive photon-like Vrightarrow Q{bar{Q}} vertex, besides the S-wave component, also contains an extra D-wave admixture in the Q{bar{Q}} rest frame. However, the relative weight of these contributions cannot be justified by any reasonable nonrelativistic Q{bar{Q}} potential model. In this work, we investigate the relative role of the D-wave contribution starting from the photon-like quarkonium Vrightarrow Q{bar{Q}} transition in both frames: in the Q{bar{Q}} rest frame (with subsequent Melosh spin transform to the LF frame) and in the LF frame (without Melosh transform). In both cases, we employ the same radial wave functions found in the potential approach. We show that the photon-like transition imposed in the Q{bar{Q}} rest frame, with subsequent boosting to the LF frame, leads to significant discrepancies with the experimental data. In the second case, i.e. imposing the photon-like transition straight in the LF frame, we find that the corresponding total J/ psi (1S) photoproduction cross sections are very close to those obtained with the “S-wave only” Vrightarrow Q{bar{Q}} transition, both leading to a good description of the data. However, we find that the “S-wave only” transition leads to a better description of photoproduction data for excited (e.g. psi '(2S)) heavy quarkonium states, which represent a more effective tool for study of D-wave effects. Consequently, the predictions for production of excited states based on the photon-like structure of Vrightarrow Q{bar{Q}} transition should be treated with a great care due to a much stronger sensitivity of the D-wave contribution to the nodal structure of quarkonium wave functions.

Ultra-peripheral Vector Meson Photoproduction in Heavy-ion Collisions in CMS

Ultra-peripheral Vector Meson Photoproduction in Heavy-ion Collisions in CMS

Coherent J/ψ photoproduction in ultra-peripheral Pb–Pb collisions with ALICE at the LHC

There are several predictions for the behaviour of the gluon distribution in nuclei at small Bjorken-x and experimental data are needed to choose among them. This is achieved by measuring the cross section of processes specially sensitive to this parton distribution.The high flux of photons from lead ions at the LHC allows us to study photon-induced reactions in ultra-peripheral collisions of Pb–Pb nuclei, in particular of those producing a J/ψ meson exclusively. The study of these collisions, where projectiles do not overlap, provides information about the initial state of nuclei.The newest ALICE results on vector meson photoproduction are presented. The increased statistics and higher collision energy of of Run 2 allow us to put new constraints on available models.

Photoproduction of charged final states in ultraperipheral collisions and electroproduction at an electron-ion collider

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.

QCD evolution based evidence for the onset of gluon saturation in exclusive photo-production of vector mesons

We investigate photo-production of vector mesons J/Ψ and ϒ measured both at HERA and LHC, using 2 particular fits of inclusive unintegrated gluon distributions, based on non-linear Balitsky-Kovchegov evolution (Kutak-Sapeta gluon; KS) and next-to-leading order Balitsky-Fadin-Kuraev-Lipatov evolution (Hentschinski-Sabio Vera-Salas gluon; HSS). We find that linear next-to-leading order evolution can only describe production at highest energies, if perturbative corrections are increased to unnaturally large values; rendering these corrections to a perturbative size, the growth with energy is too strong and the description fails. At the same time, the KS gluon, which we explore both with and without non-linear corrections, requires the latter to achieve an accurate description of the energy dependence of data. We interpret this observation as a clear signal for the presence of high gluon densities in the proton, characteristic for the onset of gluon saturation.

Exclusive ρ and J/Ψ photoproduction in ultraperipheral pA collisions: Predictions of the gluon saturation models for the momentum transfer distributions

In this letter we complement previous studies on exclusive vector meson photoproduction in hadronic collisions presenting a comprehensive analysis of the t-spectrum measured in exclusive ρ and J/Ψ photoproduction in pA collisions at the LHC. We compute the differential cross sections considering two phenomenological models for the gluon saturation effects and present predictions for pPb and pCa collisions. Moreover, we compare our predictions with the recent preliminary CMS data for the exclusive ρ photoproduction. We demonstrate that the gluon saturation models are able to describe the CMS data at small – t. On the other hand, the models underestimate the few data point at large – t. Our results indicate that future measurements of the large – t region can be useful to probe the presence or absence of a dip in the t-spectrum and discriminate between the different approaches to the gluon saturation effects.

Vector Meson Photoproduction in Hadronic Collisions: Recent Results and Prospects

Vector Meson Photoproduction in Hadronic Collisions: Recent Results and Prospects

Overview of ALICE results on ultra-peripheral collisions

Lead nuclei, accelerated at the LHC, are sources of strong electromagnetic fields which can be used to measure photon-induced interactions in a new kinematic regime. These interactions can be studied in ultra-peripheral p–Pb and Pb–Pb collisions where impact parameters are larger than the sum of nuclear radii and hadronic interactions are strongly suppressed. Heavy quarkonium photoproduction is of particular interest since it is sensitive to gluon distributions in target hadrons. An overview of ALICE results on vector meson photoproduction in ultra-peripheral Pb–Pb and p–Pb collisions will be presented. Implications to study gluon density distributions and nuclear gluon shadowing will be discussed.

Heavy Vector Meson Photoproduction in Ultra-peripheral Collisions at the LHC

Heavy Vector Meson Photoproduction in Ultra-peripheral Collisions at the LHC

Exclusive vector meson photoproduction in fixed-target collisions at the LHC

The exclusive rho , omega and J/Psi photoproduction in fixed-target collisions at the LHC is investigated. We estimate, for the first time, the rapidity and transverse momentum distributions of the vector meson photoproduction in pHe, pAr, PbHe and PbAr fixed-target collisions at the LHC using the STARlight Monte Carlo and present our results for the total cross sections. Predictions for the kinematical range probed by the LHCb detector are also presented. Our results indicate that the experimental analysis of this process in fixed-target collisions at the LHC is feasible. Such future analysis will probe the QCD dynamics in a kinematical range complementary to that studied in the collider mode.

Mass dependence of vector meson photoproduction off protons and nuclei within the energy-dependent hot-spot model

We study the photoproduction of vector mesons off proton and off nuclear targets. We work within the colour dipole model in an approach that includes subnucleon degrees of freedom, so-called hot spots, whose positions in the impact-parameter plane change event-by-event. The key feature of our model is that the number of hot spots depends on the energy of the photon–target interaction. Predictions are presented for exclusive and dissociative production of ρ0, J/ψ, and ϒ(1S) off protons, as well as for coherent and incoherent photoproduction of ρ0 off nuclear targets, where Xe, Au, and Pb nuclei are considered. We find that the mass dependence of dissociative production off protons as a function of the energy of the interaction provides a further handle to search for saturation effects at HERA, the LHC and future colliders. We also find that the coherent photonuclear production of ρ0 is sensitive to fluctuations in the subnucleon degrees of freedom at RHIC and LHC energies.

Coherent and incoherent production of vector mesons in ultraperipheral collisions of xenon ions within the QCD parton saturation approach

In this paper, we analyze the exclusive vector meson photoproduction in the recent run using xenon ions at energy of 5.44 TeV performed by the Large Hadron Collider. We focus on the ultraperipheral collisions and provide theoretical predictions for coherent and incoherent cross sections within the color dipole approach and gluon saturation framework. The rapidity distribution is investigated in both cases and comparison to other approaches available in the literature is completed. We show that the expected yields are enough to perform reliable cross section measurements for light mesons as ${\ensuremath{\rho}}^{0}$ and $\ensuremath{\phi}$.