Vector Meson Production Research Articles

Systematics of strong nuclear amplification of gluon saturation from exclusive vector meson production in high energy electron–nucleus collisions

We show that gluon saturation gives rise to a strong modification of the scaling in both the nuclear mass number A and the virtuality Q2 of the vector meson production cross-section in exclusive deep-inelastic scattering off nuclei. We present qualitative analytic expressions for how the scaling exponents are modified as well as quantitative predictions that can be tested at an Electron–Ion Collider.

Incoherent diffractive photoproduction of J/ψ and Υ on heavy nuclei in the color dipole approach

We calculate cross sections and transverse momentum distributions for the incoherent diffractive production of vector mesons $J/\psi$ and $\Upsilon$ on heavy nuclei. In distinction to coherent diffraction, the nucleus is allowed to break up, but except for the vector meson no new particles are produced in the reaction. Within the color dipole approach, we derive the multiple scattering expansion of the incoherent diffractive cross section as an expansion over quasielastic scatterings of the color dipole. We also compare our results to the measurement of the ALICE collaboration for incoherent $J/\psi$ production at $\sqrt{s_{\rm NN}} = 2.76 \, \rm {TeV}$ and show predictions at $\sqrt{s_{\rm NN}} = 5.02 \, \rm{TeV}$. We also briefly discuss a possible contribution to $J/\psi$ production in peripheral collisions in the $70 \div 90 \%$ centrality class.

Exclusive J/Ψ,ρ,ϕ and γ production at HERA and LHC within dipole models

We describe exclusive J/ψ,ρ,Φ and γ production at HERA and calculate cross sections and transverse momentum distributions for the incoherent diffractive production of vector mesons J/ψ and γ on heavy nuclei. Within the color dipole approach, we derive the multiple scattering expansion of the incoherent diffractive cross section as an expansion over quasielastic scatterings of the color dipole. We compare our results to the measurement of the ALICE (LHC) collaboration for incoherent J/ψ production

Color transparency in ρ0, ϕ, and J/Ψ mesons photoproduction

Employing the Feynman diagrams technique, the Golec–Biernat–Wustoff (GBW) model for performing nucleon–dipole interaction, and the Regge theory, a new approach for computing in a unique way (perturbative and nonperturbative) vector meson production is presented. The interaction between the color dipole created by the virtual photon and the nucleon is carried out by the exchange of two virtual gluons, which connect the color dipole with the gluonic sea inside the nucleon through a three‐gluon vertex. The model is explored in the production of ρ0, ϕ, and J/Ψ mesons.

Exclusive Charmonium Photo-Production at HERA and LHC with Color Glass Condensate**Supported by the National Natural Science Foundation of China under Grant Nos 11765005, 11305040, IRG11521064, 11775097 and 11465021, the Fund of Science and Technology Department of Guizhou Province under Grant No [2015]2114, and the Education Department of Guizhou Province under Grant No.KY[2017]004.

We calculate the exclusive charmonium photo-production in the framework of color glass condensate. To obtain a good description of the vector meson production experimental data at HERA, we introduce a vector meson mass dependent skewness factor into the skewness effect. Then we extend the skewness improved model to the LHC energies. The numerical results of our model are in good agreement with the J/ψ and ψ(2S) data in ultra-peripheral proton–proton collisions at LHC, which show the significance of the vector meson mass-dependent skewness factor. A prediction of the exclusive charmonium photo-production in ultra-peripheral nucleus–nucleus collisions is performed since it can provide a good way to test the effectiveness of the color glass condensate.

Proton structure fluctuations: constraints from HERA and applications to p + A collisions

We constrain proton structure fluctuations at small-x by comparing with the HERA diffractive vector meson production data, and find that large geometric fluctuations in the proton wave function are needed. Hydrodynamical simulations of proton-nucleus collisions including the fluctuating proton structure are found to be compatible with the momentum anisotropies measured at the LHC.

Photoproduction of heavy vector mesons in ultra-peripheral Pb–Pb collisions

Ultra-peripheral Pb-Pb collisions, in which the two nuclei pass close to each other, but at an impact parameter greater than the sum of their radii, provide information about the initial state of nuclei. In particular, heavy vector meson production, where the particle mass sets a hard scale, proceeds in such collisions by photon-gluon interactions, and gives access to nuclear PDFs. The ALICE collaboration has published measurements of J/ψ and ψ(2S) photoproduction in ultra-peripheral collisions in LHC Run 1 at forward (J/ψ) and mid-rapidity, and has obtained a substantially larger data set in 2015 from LHC Run 2, allowing much more detailed studies of the production mechanism to be performed. In particular, the increased energy and more detailed measurements in the forward region in Run 2 give access to significantly lower values of Bjorken-x than in previous studies. In this talk, the latest available results from Run 2 will be given.

Parton saturation scaling function for exclusive production of vector mesons and deeply virtual Compton scattering

We provide a universal expression of cross sections for the exclusive vector meson production and Deeply Virtual Compton Scattering (DVCS) in photon-proton and photon-nucleus interactions based on the geometric scaling phenomenon. The theoretical parameterization based on the scaling property depends only on the single variable $\tau_A = Q^2/Q_{\mathrm{sat}}^2$, where the saturation scale, $Q_{\mathrm{sat}}$, drives the energy dependence and the corresponding nuclear effects. This phenomenological result describes all available data from DESY-HERA for $\rho,\,\phi,\,J/\psi$ production and DVCS measurements. A discussion on the size of nuclear shadowing corrections on photon-nucleus interaction is also done.

Next-to-Leading Order Computation of Exclusive Diffractive Light Vector Meson Production in a Saturation Framework

We perform the first next-to-leading order computation of the γ^{(*)}→V (ρ,ϕ,ω) exclusive impact factor in the QCD shock-wave approach and in the most general kinematics. This paves the way to the very first quantitative study of high-energy nucleon and nucleus saturation beyond the leading order for a whole range of small-x exclusive processes, to be measured in ep, eA, pp, and pA collisions at existing and future colliders.

Constraints for proton structure fluctuations from exclusive scattering

We constrain the average density profile of the proton and the amount of event-by-event fluctuations by simultaneously calculating the coherent and incoherent exclusive diffractive vector meson production cross section in deep inelastic scattering. Working within the Color Glass Condensate picture, we find that the gluonic density of the proton must have large geometric fluctuations in order to describe the experimentally measured large incoherent cross section.

Imprints of fluctuating proton shapes on flow in proton-lead collisions at the LHC

Results for particle production in s=5.02TeV p+Pb collisions at the Large Hadron Collider within a combined classical Yang–Mills and relativistic viscous hydrodynamic calculation are presented. We emphasize the importance of sub-nucleon scale fluctuations in the proton projectile to describe the experimentally observed azimuthal harmonic coefficients vn, demonstrating their sensitivity to the proton shape. We stress that the proton shape and its fluctuations are not free parameters in our calculations. Instead, they have been constrained using experimental data from HERA on exclusive vector meson production. Including temperature dependent shear and bulk viscosities, as well as UrQMD for the low temperature regime, we present results for mean transverse momenta, harmonic flow coefficients for charged hadrons and identified particles, as well as Hanbury–Brown–Twiss radii.

Next-to-leading order corrections to deeply virtual production of pseudoscalar mesons

We complete the perturbative next-to-leading order corrections to the hard scattering amplitudes of deeply virtual meson leptoproduction processes at leading twist-two level by presenting the results for the production of flavor singlet pseudoscalar mesons. The new results are given in the common momentum fraction representation and in terms of conformal moments. We also comment on the flavor singlet results for deeply virtual vector meson production.

Investigating the impact of the gluon saturation effects on the momentum transfer distributions for the exclusive vector meson photoproduction in hadronic collisions

The exclusive vector meson production cross section is one of the most promising observables to probe the high energy regime of the QCD dynamics. In particular, the squared momentum transfer (t) distributions are an important source of information about the spatial distribution of the gluons in the hadron and about fluctuations of the color fields. In this paper we complement previous studies on exclusive vector meson photoproduction in hadronic collisions presenting a comprehensive analysis of the t-spectrum measured in exclusive ρ, ϕ and J/Ψ photoproduction in pp and PbPb collisions at the LHC. We compute the differential cross sections taking into account gluon saturation effects and compare the predictions with those obtained in the linear regime of the QCD dynamics. Our results show that gluon saturation suppresses the magnitude of the cross sections and shifts the position of the dips towards smaller values of t.

Recent results on diffractive and forward physics at HERA

Recent studies on diffractive processes in ep scattering at HERA are reviewed. Heavy quark production in diffractive processes was studied by tagging a D * meson in diffractive DIS events. The cross section for events with a prompt photon in the final state was also measured. The data are well reproduced by models using diffractive parton densities determined from inclusive diffractive DIS cross sections. Two studies were also made on exclusive vector meson production. The cross-section ratio σψ( (2S ))/σ (ψ (1S )), which reflects the difference in transverse shape of the charmonium wave functions, are compared to various models. Moreover, the diffractive ρ 0 photoproduction with a forward neutron, which has two vertices with small-pT recoil, were measured to study factorisation properties. The data show some indication of re-scattering.

Incoherent vector mesons production in PbPb ultraperipheral collisions at the LHC

The 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 calculations as well. Predictions for the J/ψ, ψ(2s), ρ and ϕ 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/ψ than previous calculations in the IIM model.

Next-to-leading order QCD corrections to paired Bc production in e+e− annihilation

We present theoretical analysis of paired Bc mesons production in e+e− annihilation at different energy scales taking into account full next-to-leading order QCD corrections. Both possible electroweak channels are considered: production via virtual photon and via virtual Z-boson. We study in detail the role of radiative QCD corrections, which were found to be significant especially at low energies. It is shown that the contribution from Z-boson is significant at high energies (s>MZ/2) especially in the case of paired production of pseudo-scalar and vector (Bc+Bc⁎) mesons. Azimuthal asymmetry induced by a P-violating weak interaction with Z-boson is also analyzed.

ϕ production at forward rapidity in pp, p–Pb and Pb–Pb collisions with ALICE

The ALICE experiment at the LHC measured vector meson production in p-Pb collisions at sNN=5.02 TeV, pp and Pb-Pb collisions at sNN=2.76 TeV. In pp collisions, the ϕ differential cross section as a function of pT was measured in the range 1<pT<5 GeV/c and compared with the calculations from PHOJET and PYTHIA. In p-Pb collisions, measurements of the ϕ yield and the nuclear modification factor in the rapidity ranges 2.03<y<3.53 (p-going direction) and −4.46<y<−2.96 (Pb-going direction) are shown. An asymmetry between the cross section at forward and backward rapidity is observed. Results are compared with the predictions provided by commonly used event generators. In Pb-Pb collisions, the ϕ yield and the nuclear modification factor are obtained as a function of centrality in the intermediate pT region (2<pT<5 GeV/c) and for 2.5<y<4. Differences are observed between these results and those measured in the same pT range at midrapidity in the KK channel.

Revealing proton shape fluctuations with incoherent diffraction at high energy

The differential cross section of exclusive diffractive vector meson production in electron proton collisions carries important information on the geometric structure of the proton. More specifically, the coherent cross section as a function of the transferred transverse momentum is sensitive to the size of the proton, while the incoherent, or proton dissociative cross section is sensitive to fluctuations of the gluon distribution in coordinate space. We show that at high energies the experimentally measured coherent and incoherent cross sections for the production of $J/\Psi$ mesons are very well reproduced within the color glass condensate framework when strong geometric fluctuations of the gluon distribution in the proton are included. For $\rho$ meson production we also find reasonable agreement. We study in detail the dependence of our results on various model parameters, including the average proton shape, analyze the effect of saturation scale and color charge fluctuations and constrain the degree of geometric fluctuations.

Diffractive ρ production at small x in future electron–ion colliders

The future electron–ion (eA) collider is expected to probe the high energy regime of the quantum chromodynamics (QCD), with the exclusive vector meson production cross section being one of the most promising observables. In this paper we complement previous studies of exclusive processes presenting a comprehensive analysis of diffractive ρ production at small x. We compute the coherent and incoherent cross sections taking into account non-linear QCD dynamical effects and considering different models for the dipole–proton scattering amplitude and vector meson wave function. The dependence of these cross sections on the energy, photon virtuality, nuclear mass number and squared momentum transfer is analysed in detail. Moreover, we compare the non-linear predictions with those obtained in the linear regime. Finally, we also estimate the exclusive photon, and ϕ production and compare with the results obtained for ρ production. Our results demonstrate that the analysis of diffractive ρ production in future electron–ion colliders will be important in understanding the non-linear QCD dynamics.

Evidence of Strong Proton Shape Fluctuations from Incoherent Diffraction.

We show within the saturation framework that measurements of exclusive vector meson production at high energy provide evidence for strong geometric fluctuations of the proton. In comparison, the effect of saturation scale and color charge fluctuations is weak. This knowledge will allow detailed future measurements of the incoherent cross section to tightly constrain the fluctuating geometry of the proton as a function of the parton momentum fraction x.