Cross Section For Vector Meson Production Research Articles

Scaling properties of exclusive vector meson production cross section from gluon saturation

It is already known from phenomenological studies that in exclusive deep-inelastic scattering off nuclei there appears to be a scaling behavior of vector meson production cross section in both nuclear mass number, $A$, and photon virtuality, $Q^{2}$, which is strongly modified due to gluon saturation effects. In this work we continue those studies in a realistic setup based upon using the Monte Carlo event generator Sar{\em t}re. We make quantitative predictions for the kinematics of the Electron-Ion Collider, focusing on this $A$ and $Q^{2}$ scaling picture, along with establishing a small region of squared momentum transfer, $t$, where there are signs of this scaling that may potentially be observed at the EIC. Our results are represented as pseudo-data of vector meson production diffractive cross section and/or their ratios, which are obtained by parsing data collected by the event generator through smearing functions, emulating the proposed detector resolutions for the future EIC.

Proton hot spots and exclusive vector meson production

We explore consequences of the existence of gluonic hot spots inside the proton for coherent and incoherent exclusive vector meson production cross sections in deep inelastic scattering. By working in the dilute limit of the Color Glass Condensate framework to compute the cross sections for Gaussian hot spots of fluctuating color charges and employing a non-relativistic vector meson wave function, we are able to perform large parts of the calculation analytically. 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 $t$. While the $t$-dependence of the cross section is well reproduced in our model, the relative normalization between the coherent and the incoherent cross sections points to the need for additional fluctuations in the proton.

Exclusive production of light vector mesons at next-to-leading order in the dipole picture

Exclusive production of light vector mesons in deep inelastic scattering is calculated at next-to-leading order in the dipole picture in the limit of high photon virtuality. The resulting expression is free of any divergences and suitable for numerical evaluations. The higher-order corrections are found to be numerically important, but they can be mostly captured by the nonperturbative fit parameters describing the initial condition for the small-$x$ evolution of the dipole scattering amplitude. The vector meson production cross section is shown to depend only weakly on the meson distribution amplitude and the factorization scale. We also present phenomenological comparisons of our result to the existing exclusive $\phi$ and $\rho$ production data from HERA and find an excellent agreement at high virtualities.

Scattering of Goldstone bosons and resonance production in a composite Higgs model on the lattice

We calculate the coupling between a vector resonance and two Goldstone bosons in SU(2) gauge theory with Nf = 2 Dirac fermions in the fundamental representation. The considered theory can be used to construct a minimal Composite Higgs models. The coupling is related to the width of the vector resonance and we determine it by simulating the scattering of two Goldstone bosons where the resonance is produced. The resulting coupling is gVPP = 7.8 ± 0.6, not far from gρππ ≃ 6 in QCD. This is the first lattice calculation of the resonance properties for a minimal UV completion. This coupling controls the production cross section of the lightest expected resonance at the LHC and enters into other tests of the Standard Model, from Vector Boson Fusion to electroweak precision tests. Our prediction is crucial to constrain the model using lattice input and for understanding the behavior of the vector meson production cross section as a function of the underlying gauge theory. We also extract the coupling {g}_{mathrm{VPP}}^{mathrm{KSRF}} = 9.4 ± 0.6 assuming the vector-dominance and find that this phenomenological estimate slightly overestimates the value of the coupling.

Coherent and incoherent vector meson electroproduction in the future electron - ion colliders: The hot - spot predictions

One of the more promising observables to probe the high energy regime of the QCD dynamics in the future Electron - Ion Colliders (EIC) is the exclusive vector meson production cross section in coherent and incoherent interactions. Such processes measure the average spatial distribution of gluons in the target as well the fluctuations and correlations in the gluon density. In this paper we present a comprehensive analysis of the energy, photon virtuality, atomic number and momentum transfer dependencies of the coherent and incoherent cross sections considering two different models for the nuclear profile function. In particular, we present the predictions of the hot - spot model, which assumes the presence of subnucleonic degrees of freedom and an energy-dependent profile. Our results indicate that the analysis of the ratio between the incoherent and coherent cross sections and the momentum transfer distributions in the future EIC can be useful to constrain the description of the hadronic structure at high energies.

Study of exclusive processes within the GPD approach

In this report, we analyze the exclusive meson production in leptonhadron and hadron processes to study Generalized Parton Distributions (GPDs). It is shown that in both reactions, the photoproduction mechanism of vector meson (VM) production predominates. We estimate the VM production cross section and spin observables. The possibility to study the exclusive VM production at NICA was analyzed. One can investigate different observables in ρ, ω and J/ψ productions to study quark and gluon GPDs. The other important process is the exclusive Drell-Yan (D-Y) production in the proton-proton reaction determined by two GPDs contributions. This reaction gives an important test of the GPD model and hopefully can be studied at NICA energies.

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.

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.

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.

Vector meson production in ultraperipheral collisions at the LHC

By using a Regge-pole model for vector meson production (VMP), successfully describing the HERA data, we analyse the correlation between VMP cross sections in photon-induced reactions at HERA and those in ultra-peripheral collisions at the Large Hadron Collider (LHC). Predictions for future experiments on production of $J/\psi$ and $\psi(2S)$ are presented.

Comparison of isoscalar vector meson production cross sections in proton–proton collisions

Abstract The reaction p p → p p ω was investigated with the TOF spectrometer, which is an external experiment at the accelerator COSY (Forschungszentrum Julich, Germany). Total as well as differential cross sections were determined at an excess energy of 93 MeV ( p beam = 2950 MeV / c ). Using the total cross section of ( 9.0 ± 0.7 ± 1.1 ) μb for the reaction p p → p p ω determined here and existing data for the reaction p p → p p ϕ , the ratio R ϕ / ω = σ ϕ / σ ω turns out to be significantly larger than expected by the Okubo–Zweig–Iizuka (OZI) rule. The uncertainty of this ratio is considerably smaller than in previous determinations. The differential distributions show that the ω production is still dominated by S-wave production at this excess energy, however higher partial waves clearly contribute. A comparison of the measured angular distributions for ω production to published distributions for ϕ production at 83 MeV shows that the data are consistent with an identical production mechanism for both vector mesons.

Dilepton production in proton–proton collisions at BEVALAC energies

The dilepton production in elementary pp → e+e−X reactions at BEVALAC energies Tlab = 1–5 GeV is investigated. The calculations include direct e+e− decays of the vector mesons ρ0, ω and ϕ, Dalitz decays of the π0-, η-, ρ-, ω- and ϕ-mesons and of the baryon resonances Δ(1232), N(1520),…. The subthreshold vector meson production cross sections in pp collisions are treated in a way sufficient to avoid double counting with the inclusive vector meson production. The vector meson dominance model for the transition form factors of the resonance Dalitz decays R → e+e−N is used in an extended form to ensure correct asymptotics which are in agreement with the quark counting rules. Such a modification gives a unified and consistent description of both R → Nγ radiative decays and R → Nρ(ω) meson decays. The effect of multiple pion production on the experimental efficiency for the detection of the dilepton pairs is studied. We find the dilepton yield in reasonable agreement with the experimental data for the set of intermediate energies whereas at the highest energy Tlab = 4.88 GeV, the number of dilepton pairs is likely to be overestimated experimentally in the mass range M = 300–700 MeV.

Inclusive Vector-Meson Production in the Dual Model

The cross section for the process $a+b\ensuremath{\rightarrow}\mathrm{vector}\mathrm{meson}+\mathrm{anything}$ in the central region at high energy is calculated in the dual resonance model. The model predicts that the total cross section for vector-meson production is down by about ${10}^{\ensuremath{-}3}$ from scalar-meson production at zero perpendicular momenta if the masses are those of the $\ensuremath{\rho}$ meson and pion. The vector meson is predicted to be polarized so that the decay pions tend to be emitted in the direction ${\stackrel{^}{p}}_{a}\ensuremath{-}{\stackrel{^}{p}}_{b}$ in the rest frame of the vector meson. Analytic approximations for the asymptotic dual amplitude, valid for all transverse momenta, are given for the first time.

Inclusive Production of Vector Mesons in the Dual-Resonance Model

The vector-meson inclusive distribution is considered by making use of the eight-point dual amplitude for which two of the external lines are regarded as the decay products of a single vector meson. We find that the vector-meson vertex is factorizable both in the fragmentation and central regions only for large values of $\ensuremath{\kappa}={{p}_{\ensuremath{\perp}}}^{2}+{m}^{2}$. Nonfactorizability for low values of $\ensuremath{\kappa}$ is due to the correlations between the beam-target system and the decay products. Explicit and yet simple expressions for the vertex function as well as the vectormeson production cross section are given to the leading order in $\ensuremath{\kappa}$ for the triple-Regge and pionization limits. They show that the vector-meson decays, in either of the kinematic regions, along the preferred beam direction with a ${cos}^{2}\ensuremath{\beta}$ dependence, in the rest frame of the vector meson, provided that the intercept of the leading vacuum trajectory takes the value unity. Furthermore, it is found that in the central region the states with helicity \ifmmode\pm\else\textpm\fi{}1 contribute dominantly to the decay correlations, while in the triple-Regge region the state with helicity zero is favored.

Application ofSU(6)Win a Model for Vector-Meson Production at High Energies

A double-Regge-pole model incorporating $\mathrm{SU}(3)$ symmetry, previously applied to pseudoscalar mesonbaryon exchange reactions, is extended to include certain vector-meson production reactions with $\mathrm{SU}{(6)}_{W}$ symmetry imposed at the forward direction. A large number of predictions for forward vector-meson production cross sections are obtained in terms of pseudoscalar-meson cross sections. These are compared where possible with the meager data available above 3 BeV/c, with generally favorable results.