Diffractive Vector Meson Production Research Articles

Exclusive vector meson production at high energies and gluon saturation

We systematically study exclusiv2 diffractive (photo)production of vector mesons ($J/\ensuremath{\psi}$, $\ensuremath{\psi}(2s)$, $\ensuremath{\phi}$, and $\ensuremath{\rho}$) off protons in high-energy collisions and investigate whether the production is a sensitive probe of gluon saturation. We confront saturation-based results for diffractive $\ensuremath{\psi}(2s)$ and $\ensuremath{\rho}$ production at HERA and $J/\ensuremath{\psi}$ photoproduction with all available data, including recent work from HERA, ALICE, and LHCb, finding good agreement. In particular, we show that the $t$ distribution of differential cross sections of photoproduction of vector mesons offers a unique opportunity to discriminate among saturation and nonsaturation models. This is due to the emergence of a pronounced dip (or multiple dips) in the $t$ distribution of diffractive photoproduction of vector mesons at relatively large, but potentially accessible $|t|$ that can be traced back to the unitarity features of color dipole amplitude in the saturation regime. We show that in saturation models the dips in $t$ distribution recede towards lower $|t|$ with decreasing mass of the vector meson, increasing energy or decreasing Bjorken-$x$, and decreasing virtuality $Q$. We provide various predictions for exclusive (photo)production of different vector mesons including the ratio of $\ensuremath{\psi}(2s)/J/\ensuremath{\psi}$ at HERA, the LHC, and future colliders.

Unifying “soft” and “hard” diffractive exclusive vector meson production and deeply virtual Compton scattering

A Pomeron model applicable to both "`soft" and "hard" processes is suggested and tested against the high-energy data from virtual photon-induced reactions. The Pomeron is universal, containing two terms, a "soft" and a "hard" one, whose relative weight varies with $\widetilde {Q^2}=Q^2+M_V^2$, where $Q^2$ is the virtuality of the incoming photon and $M_V$ is the mass of the produced vector particle. With a small number of adjustable parameters, the model fits all available data on vector meson production and deeply virtual Compton scattering from HERA. Furthermore, we attempt to apply the model to hadron-induced reactions, by using high-energy data from proton-proton scattering.

The dipole model Monte Carlo generator Sartre 1

We present the Monte Carlo generator Sartre for simulating diffractive exclusive vector meson production and DVCS in electron–proton, electron–ion, and hadron–hadron collisions. Program summaryProgram title: Sartre 1.0Catalogue identifier: AESP_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AESP_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: GNU General Public License, version 2No. of lines in distributed program, including test data, etc.: 703313No. of bytes in distributed program, including test data, etc.: 179406465Distribution format: tar.gzProgramming language: C/C++.Computer: Any with standard C/C++ compiler.Operating system: Tested on Linux and MacOS.Classification: 11.1, 11.2, 11.6.External routines: ROOT and GSL for numeric algorithms and other various tasks throughout the program. BOOST for multi-threaded integration (optional), GEMINI++ for nuclear break-up and CUBA for multi-dimensional numerical integration (the latter two supplied with the program package). Uses cmake for building and installing.Nature of the problem:Simulate diffractive exclusive vector meson and deeply virtual Compton scattering (DVCS) production in electron–nucleus scattering where the exchanged virtual photon interacts coherently with a large region of the nucleus. To calculate the cross section correctly it has to be averaged over all possible configurations of nucleon positions within the nucleus.Solution method:To make an arithmetic average of the quantum mechanical amplitude over nucleon configurations numerically and store the result in look-up tables.Implemented processes: The following processes can be simulated: e+p→e′+V+p′e+A→e′+V+A′p+p→p′+V+p′p+A→p′+V+A′(1)A+A→A′+V+A′ where V is a J/ψ,φ, or ρ vector meson, or a real photon (DVCS). All processes are mediated by a virtual photon and a pomeron. The present version is applicable for these processes at future electron–hadron colliders, such as the EIC and the LHeC, as well as HERA, RHIC, and the LHC.Restrictions:The program is reliable for process at xp<10−2, and large β=x/xp.Additional comments:The distribution file for this program is over 178 MB and therefore is not delivered directly when download or E-mail is requested. Instead an html file giving details of how the program can be obtained is sent.Running time:On a MacBook Pro with a 2.66 GHz Intel Core i7 processor, event generation takes ∼0.1 ms/event without correction and nuclear breakup, ∼0.2 ms/event with the recommended corrections switched on, and ∼6 ms/event when running with corrections and nuclear breakup.

Exclusive central diffractive production of scalar, pseudoscalar and vector mesons

We discuss exclusive central diffractive production of scalar ($f_{0}(980)$, $f_{0}(1370)$, $f_{0}(1500)$), pseudoscalar ($\eta$, $\eta'(958)$), and vector ($\rho^{0}$) mesons in proton-proton collisions. The amplitudes are formulated in terms of effective vertices required to respect standard rules of Quantum Field Theory and propagators for the exchanged pomeron and reggeons. Different pomeron-pomeron-meson tensorial (vectorial) coupling structures are possible in general. In most cases two lowest orbital angular momentum - spin couplings are necessary to describe experimental differential distributions. For the $f_{0}(980)$ and $\eta$ production the reggeon-pomeron, pomeron-reggeon, and reggeon-reggeon exchanges are included in addition, which seems to be necessary at relatively low energies. The theoretical results are compared with the WA102 experimental data, in order to determine the model parameters. For the $\rho^{0}$ production the photon-pomeron and pomeron-photon exchanges are considered. The coupling parameters of tensor pomeron and/or reggeon are fixed from the H1 and ZEUS experimental data of the $\gamma p \to \rho^{0} p$ reaction. We present first predictions of this mechanism for $pp \to pp \pi^{+} \pi^{-}$ reaction being studied at COMPASS, RHIC, Tevatron, and LHC. Correlation in azimuthal angle between outgoing protons and distribution in pion rapidities at $\sqrt{s} = 7$TeV are presented. We show that high-energy central production of mesons could provide crucial information on the spin structure of the soft pomeron.

Impact-parameter dependent color glass condensate dipole model and new combined HERA data

The Impact-Parameter dependent Color Glass Condensate (b-CGC) dipole model is based on the Balitsky-Kovchegov non-linear evolution equation and improves the Iancu-Itakura-Munier dipole model by incorporating the impact-parameter dependence of the saturation scale. Here we confront the model to the recently released high precision combined HERA data and obtain its parameters. The b-CGC results are then compared to data at small-x for the structure function, the longitudinal structure function, the charm structure function, exclusive vector meson (J/\psi, \phi, \rho) production and Deeply Virtual Compton Scattering (DVCS). We also compare our results with the Impact-Parameter dependent Saturation model (IP-Sat). We show that most features of inclusive DIS and exclusive diffractive data, including the Q^2, W, |t| and x dependence are correctly reproduced in both models. Nevertheless, the b-CGC and the IP-Sat models give different predictions beyond the current HERA kinematics, namely for the structure functions at very low x and high virtualities Q^2, and for the exclusive diffractive vector meson and DVCS production at high t. This can be traced back to the different power-law behavior of the saturation scale in x, and to a different impact-parameter b dependence of the saturation scale in these models. Nevertheless, both models give approximately similar saturation scale Q_S<1 GeV for the proton in HERA kinematics, and also both models lead to the same conclusion that the typical impact-parameter probed in the total \gamma^{*}p cross-section is about b\approx 2\div 3 GeV^{-1}. Our results provide a benchmark for further investigation of QCD at small-x in heavy ion collisions at RHIC and the LHC and also at future experiments such as an Electron-Ion Collider and the LHeC.

Exclusive diffractive processes in electron-ion collisions

We present a new technique to calculate the cross-section for diffractive vector meson production and DVCS in electron-ion collisions based on the dipole model. The measurement of these processes can provide valuable information on non-linear QCD phenomena, such as gluon saturation, and is the the only known way to gain insight into the spatial distribution of gluons in nuclei. We present predictions of differential cross-section distribution $d\sigma/dQ^2$ and $d\sigma/dt$ for $J/\psi$ and $\phi$ meson production for diffractive processes of heavy nuclei and demonstrate the feasibility of extracting the gluon source distribution of heavy nuclei, F(b), from coherent diffraction. We briefly introduce a new event generator based on our method that can be used for studying exclusive diffractive processes at a future electron-ion collider.

Reggeometry of Deeply Virtual Compton Scattering and Exclusive Vector Meson Production at HERA

A Reggeometric (Regge+Geometry) model, based on the observed proportionality between the forward slope of the differential cross section and the interaction radius, the latter depending on virtuality Q2 of the incoming virtual photon and on the mass M 2 of the produced particle, is constructed. The objective of this study is the dependence of the Regge-pole amplitude on the virtuality Q2 and masses of the external particles, which remains an open problem for the theory. The present analysis is based on the HERA data on Deeply Virtual Compton Scattering (DVCS) and exclusive diffractive Vector Meson Production (VMP). We treat each class of reactions separately, anticipating a further study that will include both a soft and a hard component of the unique pomeron.

On the Interplay between Q2 and t Dependences in Exclusive Diffractive Production of Real Photons and Vector Mesons in ep Collisions

We show how the familiar phenomenological way of combining the Q2 (photon virtuality) and t (squared momentum transfer) dependences of the scattering amplitude in Deeply Virtual Compton Scattering (DVCS) [1, 2] and Vector Meson Production (VMP) [2] processes can be understood in an off-mass-shell generalization of dual amplitudes with Mandelstam analyticity [3]. By comparingdifferent approaches, we managed also to constrain the numerical values of the free parameters.

Exclusive coherent production of heavy vector mesons in nucleus-nucleus collisions at energies available at the CERN Large Hadron Collider

Heavy nuclei at collider energies are a source of high energy Weizsaecker-Williams photons. This photon flux may be utilized to study high energy photon-nucleus interactions. Here we concentrate on the coherent diffractive production of heavy vector mesons on nuclear targets and show how it probes the unintegrated glue of the nucleus in the saturation domain. We present predictions for rapidity distributions of exclusive coherent J/Psi and Upsilon mesons which can be measured by the ALICE experiment at the LHC.

Exclusive diffractive production of real photons and vector mesons in a factorized Regge-pole model with nonlinear Pomeron trajectory

Exclusive diffractive production of real photons and vector mesons in ep collisions has been studied at HERA in a wide kinematic range. Here we present and discuss a Regge-type model of real photon production (Deeply Virtual Compton Scattering), as well as production of vector mesons (VMP) treated on the same footing by using an extension of a factorized Regge-pole model proposed earlier. The model has been fitted to the HERA data. Despite the very small number of the free parameters, the model gives a satisfactory description of the experimental data, both for the total cross section as a function of the photon virtuality Q2 or the energy W in the center of mass of the gamma\star-p system, and the differential cross sections as a function of the squared four-momentum transfer t with fixed Q2 and W.

Exclusive diffraction at HERA

Recent experimental results on diffractive vector meson production and deeply virtual Compton scattering from the H1 and ZEUS collaborations are reviewed.

Diffractive vector meson production at large t in coherent hadronic interactions at CERN LHC

The diffractive vector meson photoproduction with hadron dissociation in coherent hadron-hadron interactions at LHC energies is studied assuming that the color singlet $t$-channel exchange carries large momentum transfer. We estimate the rapidity distribution and total cross section for the processes $pp \rightarrow p V X$ and $PbPb \rightarrow Pb V X$ ($V = \rho$ or $\Upsilon$) considering the non-forward solution of the BFKL equation at high energy and large momentum transfer. Our results indicate that the experimental identification of these processes can be feasible at the LHC.

Exclusive production of heavy vector mesons in nucleus-nucleus collisions

Heavy nuclei at collider energies are a source of high energy Weizsäcker-Williams photons. This photon flux may be utilized to study high energy photon-nucleus interactions. Here we concentrate on the coherent diffractive production of heavy vector mesons on nuclear targets and show how it probes the unintegrated glue of the nucleus in the saturation domain.

Vector mesons and DVCS

Recent experimental results on diffractive vector meson (VM) production and deeply virtual Compton scattering (DVCS) from the H1 and ZEUS collaborations are reviewed. The data are compared with theoretical predictions.

Nonlinearity of vacuum Reggeons and exclusive diffractive production of vector mesons at HERA

The processes of exclusive photo- and electroproduction of vector mesons ${\ensuremath{\rho}}^{0}(770)$, $\ensuremath{\phi}(1020)$, and $J/\ensuremath{\psi}(3096)$ at collision energies $30\text{ }\text{ }\mathrm{GeV}&lt;W&lt;300\text{ }\text{ }\mathrm{GeV}$ and transferred momenta squared $0&lt;\ensuremath{-}t&lt;2\text{ }\text{ }{\mathrm{GeV}}^{2}$ are considered in the framework of a phenomenological Regge-eikonal scheme with nonlinear Regge trajectories in which their QCD asymptotic behavior is taken into account explicitly. By comparison of available experimental data from ZEUS and H1 Collaborations with the model predictions it is demonstrated that corresponding angular distributions and integrated cross sections in the above-mentioned kinematical range can be quantitatively described with use of two $C$-even vacuum Regge trajectories. These are the ``soft'' Pomeron dominating the high-energy reactions without a hard scale and the ``hard'' Pomeron giving an essential contribution to photo- and electroproduction of heavy vector mesons and deeply virtual electroproduction of light vector mesons.

Impact parameter dependent color glass condensate dipole model

We show that the color glass condensate dipole model of Iancu, Itakura, and Munier, improved to include the impact parameter dependence, gives a good fit to the total ${\ensuremath{\gamma}}^{*}p$ cross section measured at HERA if the anomalous dimension at the saturation scale, ${\ensuremath{\gamma}}_{s}$, is treated as a free parameter. We find that the optimum value of ${\ensuremath{\gamma}}_{s}=0.46$ is close to the value determined from numerical solution of the Balitsky-Kovchegov equation. The impact parameter dependent saturation scale is generally less than $0.5\text{ }\text{ }{\mathrm{GeV}}^{2}$ in the HERA kinematic regime for the most relevant impact parameters $b\ensuremath{\sim}2--3\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}1}$. We compare predictions of the model to data on the longitudinal and heavy flavour structure functions, exclusive diffractive vector meson production, and deeply virtual Compton scattering at HERA. The model is found to be deficient for observables sensitive to moderately small dipole sizes, where an alternative model with explicit Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution performs better. The energy dependence of exclusive diffractive processes is shown to provide an important discriminator between different dipole model cross sections.

Exclusive vector meson production at HERA from QCD with saturation

Following recent predictions that the geometric scaling properties of deep inelastic scattering data in inclusive ${\ensuremath{\gamma}}^{*}p$ collisions are expected also in exclusive diffractive processes, we investigate the diffractive production of vector mesons. Using analytic results in the framework of the Balitsky-Kovchegov (BK) equation at nonzero momentum transfer, we extend to the nonforward amplitude a QCD-inspired forward saturation model including charm, following the theoretical predictions for the momentum transfer dependence of the saturation scale. We obtain a good fit to the available HERA data and make predictions for deeply virtual Compton scattering measurements.

Exclusive diffractive processes at HERA within the dipole picture

We present a simultaneous analysis, within an impact parameter dependent saturated dipole model, of exclusive diffractive vector meson (J/psi, phi and rho) production, deeply virtual Compton scattering and the total gamma* p cross section data measured at HERA. Various cross sections measured as a function of the kinematic variables Q^2, W and t are well described, with little sensitivity to the details of the vector meson wave functions. We determine the properties of the gluon density in the proton in both longitudinal and transverse dimensions, including the impact parameter dependent saturation scale. The overall success of the description indicates universality of the emerging gluon distribution and proton shape.

Double diffractive meson production and the BFKL Pomeron ate+e−colliders

In this paper we study the double diffractive vector meson production in ${e}^{+}{e}^{\ensuremath{-}}$ collisions assuming the dominance of the BFKL pomeron exchange. We consider the nonforward solution of the BFKL equation at high energy and large momentum transfer and estimate the total cross section for the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}{V}_{1}{V}_{2}$ with antitagged ${e}^{+}$ and ${e}^{\ensuremath{-}}$, where ${V}_{1}$ and ${V}_{2}$ can be any two vector mesons (${V}_{i}=\ensuremath{\rho},\ensuremath{\omega},\ensuremath{\phi},J/\ensuremath{\Psi},\ensuremath{\Upsilon}$). The event rates for the future linear colliders are given.

Diffractive vector meson production

This is a brief introduction to diffractive vector meson production, both exclusive γ p → V p and large momentum transfer γ p → V X processes. I overview the theoretical basis for the perturbative description and some recent developments.