Protons and antiprotons at collider energies are a source of high energy Weizsäcker--Williams photons. This may open a possibility to study exclusive photoproduction of heavy vector mesons at energies much larger than possible at the HERA accelerator. Here we present a detailed investigation of the exclusive $J/ψ$ photoproduction in proton-proton (RHIC, LHC) and proton-antiproton (Tevatron) collisions. We calculate several differential distributions in $t_1, t_2, y, ϕ$, as well as transverse momentum distributions of $J/Ψ$'s. We discuss correlations in the azimuthal angle between outgoing protons or proton and antiproton as well as in the ($t_1, t_2$) space. Differently from electroproduction experiments, here both colliding beam particles can be a source of photons, and we find large interference terms in azimuthal angle distributions in a broad range of rapidities of the produced meson. We also include the spin--flip parts in the electromagnetic vertices. We discuss the effect of absorptive corrections on various distributions. Interestingly, absorption corrections induce a charge asymmetry in rapidity distributions, and are larger for $p p$ reactions than for the $p \bar p$ case. The reaction considered here constitutes an important nonreduceable background in recently proposed searches for odderon exchange.
Recent small-t ZEUS data for exclusive rho photoproduction are in excellent agreement with exchange of the classical soft pomeron with slope alpha'=0.25 GeV^{-2}. Adding in a flavour-blind hard-pomeron contribution, whose magnitude is calculated from the data for exclusive J/psi photoproduction, gives a good fit also to the ZEUS data for rho photoproduction at larger values of t, and to phi photoproduction.
We calculate differential cross sections for exclusive double diffractive (EDD) production of open charm in proton-proton and proton-antiproton collisions. Sizeable cross sections are found. The EDD contribution constitutes about 1 % of the total inclusive cross section for open charm production. A few differential distributions are shown and discussed. The EDD contribution falls faster both with transverse momentum of the $c$ quark/antiquark and the $c \bar c$ invariant mass than in the inclusive case.
{We investigate the photoproduction process $ p γ\rightarrow Λ_{c}^{+} \overline{D^{0}}$ within the handbag approach, which we assume to be the dominant mechanism at energies well above the production threshold and in the forward scattering hemisphere.
We report on a detailed investigation of exclusive J/psi production in proton--proton and proton-antiproton collisions. Predictions for Tevatron and LHC energies are included.
Exclusive photoproduction of heavy quarkonia at HERA is analyzed in the framework of the Regge-eikonal approach together with the nonrelativistic bound state formalism. Total and differential cross-sections for the process $γ+p\to (Q\bar{Q})_{1S}+p$ are calculated. The model predicts cross-sections of Exclusive Double Diffractive Events (EDDE) at TeVatron and LHC.
The amplitude for photoproduction gamma p -> Υp is calculated in a pQCD k_\perp-factorization approach. The total cross section for diffractive Υ's is compared to recent HERA data. The amplitude is used to predict the cross section for exclusive ppbar \to ppbar Υ(1S,2S) process in hadronic reactions at Tevatron energies. We also included absorption effects.
The cross section for exclusive $Υ$ ultraperipheral photoproduction at present and future colliders is determined using the low $x$ gluon PDF extracted from an analysis of exclusive $J/ψ$ measurements performed at HERA and the LHC. Predictions are given at next-to-leading order in collinear factorisation over a wide $γp$ centre-of-mass energy range, calculated assuming the non-relativistic approximation for the $Υ$ wave function, and with skewing corrections incorporated.
We present a simple interpretation of the recently observed near-threshold proton-antiproton enhancement. It is described by a set of low-energy parameters deduced from the analysis of NantiN experiments at LEAR. We predict a related effect in photoproduction reaction under study by CLAS collaboration.
Protons and antiprotons at collider energies are a source of high energy Weizsaecker--Williams photons. This opens up a possibility to study at the LHC exclusive photoproduction of heavy vector mesons at energies much larger than possible at the HERA accelerator. We present selected results of our detailed studies of various distributions for the production of heavy quarkonia (e.g. rapidity, transverse momenta, azimuthal angles). We give predictions for LHC energies. Our calculations are based on modelling the photoproduction amplitudes in a k_\perp-factorisation approach which is checked agai…
We present predictions for differential cross sections for the reaction $γp \to Φp$ and give an outlook to which extent our calculations may be generalized to the photoproduction of $J/Ψ$ mesons. Our results are obtained within perturbative QCD treating the proton as a quark-diquark system.
I study hard collisions between unpolarized protons and antiprotons where a lepton-antilepton pair is detected in coincidence with a final proton-antiproton pair, and no more particles are produced, in the regime 10 GeV^2 << s << 1000 GeV^2, M > 4 GeV, q_T < 3 GeV/c. The present work is centered on azimuthal asymmetries. Because of momentum conservation, a Boer-Mulders term in the momentum distribution of a quark implies a balancing effect in the momentum distribution of some spectators. This produces azimuthal asymmetries of the final hadrons. To analyze this, I have organized a parton-level …
A model based on a dipole Pomeron framework for vector meson exclusive photoproduction by real and virtual photons shows very good agreement with the experimental data. The model does not violate unitarity constrains and describes in a universal manner all the available data for $ρ$, $ω$, $ϕ$, $J/ψ$ and $Υ$ vector meson photoproduction in the region of energies $1.7\le W \le 250 GeV$ and photon virtualities $0 \le Q^2 \le 35 GeV^2$.
In this work we investigate the inclusive and exclusive photoproduction of dileptons, which is relevant for the physics programme to be studied in the proposed electron-proton collider, the LHeC. In the inclusive case, the process is sensitive to the parton distribution functions in the photon whereas the exclusive channel is connected to the small-$x$ QCD dynamics. For the latter, we investigate the role played by saturation physics at a very high energy scenario. The estimates for production cross sections and the number of events are presented.
We present predictions for the exclusive photoproduction of $Φ$-meson on Proton at large tranfer, where we use a quark-diquark structure model for the proton. Extrapolation from our results to lower tranfers is comparable in magnitude with available data in that range. This may support the diquark model in its ability to provide, for that process, an appropriate link between diffractive physics at low transfer and the standard semi-perturbative approach of hard exclusive processes at very large tranfer, where the proton recovers its three-quark structure.
The exclusive photoproduction of lepton pairs on nucleon and nucleus target is investigated within the high energy color dipole approach, where the main physical quantity is the dipole-target elastic scattering amplitude that captures the main features of the dependence on atomic number A, on energy and on momentum transfer t. These calculations are input in predictions for electromagnetic interactions in pp and AA collisions to be measured at the LHC.
We present a detailed computation of the fully exclusive cross section of p + antip --> W + photon + X with X = 0 and 1 jet in the framework of the factorization theorem and dimensional regularization. Order alpha-strong and photon bremsstrahlung contributions are discussed in the MS-bar mass factorization scheme. The resulting expressions are ready to be implemented numerically using Monte Carlo techniques to compute single and double differential cross sections and correlations between outgoing pairs of particles.
We discuss the potential to constrain the small-$x$ PDFs using the exclusive production of heavy vector mesons. The calculation of $J/ψ$ and $Υ$ photoproduction at NLO in collinear factorisation is described. The different behaviour of the NLO corrections for $J/ψ$ and $Υ$ is highlighted and we outline what might be expected from the inclusion of these processes in a PDF fit.
The forward photoproduction amplitude for gamma p to Upsilon p is calculated in a pQCD k_t-factorization approach with an unintegrated gluon distribution constrained by inclusive deep-inelastic structure functions. The total cross section for diffractive Upsilons is compared with a recent HERA data. We also discuss the 2S/1S ratio in diffractive Upsilon-production. The amplitude is used to predict the cross section for exclusive Upsilon production in hadronic reactions. Differential distributions for the exclusive p pbar to p Upsilon pbar process are calculated for Tevatron energies. We also s…
We calculate the leading-order perturbative contribution to $γp \to M_{V} p$, with $M_V$ being a $Φ$ or $J/Ψ$ meson, in the kinematic region of large energy and scattering angle.
In exclusive $J/ψ$ production by polarized photons incident on polarized protons, a finite polarization asymmetry arises because of $c\bar c$ Fermi-motion and binding-energy effects. The asymmetry depends on the polarized nonforward gluon distribution of the proton and thus gives information on gluon polarization in the proton. The analyzing power, however, is rather small.
We discuss exclusive $J/ψ$ photoproduction, initially in conventional collinear factorisation at NLO and then subsequently in a refined approach with a programme of low $x$ resummation and implementation of a crucial low $Q_0$ subtraction included. We compare and contrast predictions in both frameworks and remark about the possibility to constrain and ultimately determine the low $x$ and low scale gluon PDF, emphasising the significance of this for future global PDF analyses.
Exclusive photoproduction of dileptons, gamma p ->l+ l- p, will be measured in ultraperipheral collisions at LHC. The mechanism where the lepton pair comes from a heavy timelike photon radiated from a quark interferes with the pure QED process gamma gamma ->l+ l- As an analog of deeply virtual Compton scattering, this timelike Compton scattering is a way to study generalized parton distributions in the nucleon or the nucleus. High energy kinematics will enable to focus on gluon distributions. Nuclear effects may be scrutinized in heavy ion collisions.
The amplitude for $γp \to ϕp$ is calculated in a pQCD $k_{T}$ - factorization approach. The total cross section for this process is compared with HERA data. Total cross section, as a function of photon-proton energy and photon virtuality, is calculated. We also discuss the ratio of $σ_{L}$ / $σ_{T}$ and the dependence on the mass of the strange quark. The amplitude for $γp \to ϕp$ is used to predict the cross section for exclusive photoproduction of $ϕ$ meson in proton-proton collisions. Absorption effects are included. The results for RHIC, Tevatron and LHC energies are presented.
The photonuclear production of vector mesons in ultraperipheral heavy ion collisions is investigated within the collinear approach using different parameterizations for the nuclear gluon distribution. The integrated cross section and the rapidity distribution for the $AA \to V AA$ ($V = J/Ψ, Υ$) process are computed for energies of RHIC and LHC. A comparison with the recent PHENIX data on coherent production of $J/Ψ$ mesons is also presented. We demonstrate that the study of the exclusive quarkonium photoproduction can be used to constrain the nuclear effects in the gluon distribution.
We argue that coherent production of hard dijets by linearly polarized real photons can provide direct evidence for chirality violation in hard processes, the first measurement of the magnetic susceptibility of the quark condensate and the photon distribution amplitude. It can also serve as a sensitive probe of the generalized gluon parton distribution. Numerical calculations are presented for HERA kinematics.
The elastic differential and integrated total cross section for the exclusive $ρ^0$ photoproduction in electron-proton ($ep$) collisions are evaluated taking into account nonperturbative Pomeron exchange approach. By using three different models based on Regge phenomenology the results are compared to recent measurements by H1 Collaboration in $ep$ collisions and by the CMS collaboration from ultraperipheral proton-lead collisions. The analysis is expanded by calculating the coherent nuclear cross section, $σ(γA\rightarrow ρ^0 A)$, which is applied to $ρ^0$ production in ultraperipheral lead-l…
We derive the forward photoproduction amplitude for the diffractive $γp \to l^+ l^- p$ reaction in the momentum space. within the formalism of $k_\perp$- factorization. Predictions for the $γp \to l^+ l^- p$ reaction are given using unintegrated gluon distribution from the literature. We calculate the total cross section as a function of photon-proton center of mass energy and the invariant mass distribution of the lepton pair. We also discuss whether the production of timelike virtual photons can be approximated by continuing to the spacelike domain $ q^2 < 0$. The present calculation provide…
We provide predictions for the rapidity distributions of exclusive photoproduced J/psi and Upsilon mesons, and Z^0 bosons, at the Tevatron and LHC. We use the equivalent-photon approximation with the photon-proton cross sections given by the impact parameter dependent dipole saturation model, which has already been shown to give a good description of a wide variety of HERA data. We derive the quark-antiquark light-cone wave functions of timelike neutral electroweak bosons. An essential difference is pointed out between the amplitude for timelike heavy boson photoproduction and the amplitude fo…
We show how deviations from the dimensional scaling laws for exclusive processes may be related to a breakdown in the locality of quark-hadron duality, i.e. the "restricted locality". For exclusive reactions like meson photo- and electroproduction above the resonance region, we explore the effects arising from such a local duality breaking and propose that it can be a possible source for oscillations about the smooth quark counting rule predicted by pQCD in the 90-degree differential cross sections.
We summarize what is known about the transverse spatial distribution of gluons in the nucleon and its x-dependence from exclusive J/psi photo/electroproduction in e-p fixed-target and collider experiments (HERA H1 and ZEUS). This information can be used to predict the impact parameter dependence of the cross section for certain hard QCD processes (dijet production) in pbar-p and p-p collisions at the Tevatron and LHC.
In this work we investigate the coherent photoproduction of psi(1S), psi(2S) and Upsilon (1S) states in the proton-nucleus collisions in the LHC energies. Predictions for the rapidity distributions are presented using the color dipole formalism and including saturation effects that are expected to be relevant at high energies. Calculations are done at the energy 5.02 TeV and also for the next LHC run at 8.8 TeV in proton-lead mode. Discussion is performed on the main theoretical uncertainties associated to the calculations.
We study exclusive vector meson photoproduction, $γp \to V + p$ with $V=J/ψ$ or $Υ$, at NLO in collinear factorisation, in order to examine what may be learnt about the gluon distribution at very low $x$. We examine the factorisation scale dependence of the predictions. We argue that, using knowledge of the NLO corrections, terms enhanced by a large $\ln(1/ξ)$ can be reabsorbed in the LO part by a choice of the factorisation scale. (In these exclusive processes $ξ$ takes the role of Bjorken-$x$.) Then, the scale dependence coming from the remaining NLO contributions has no $\ln(1/ξ)$ enhanceme…
The reactions gamma p -> K+ Lambda and gamma p -> K* Lambda are analyzed within perturbative QCD, allowing for diquarks as quasi-elementary constituents of baryons. The diquark-model parameters and the quark-diquark distribution amplitudes of proton and Lambda are taken from previous investigations of electromagnetic baryon form factors and Compton-scattering off protons. Unpolarized differential cross sections and polarization observables are computed for different choices of the K and K* distribution amplitudes. The asymptotic form of the K distribution amplitude (proportional to x1 x2) is f…
The process of exclusive heavy vector meson photoproduction, gamma p -> V p, is studied in the framework of QCD factorization. The mass of the produced meson, V = Upsilon or J/Psi, provides a hard scale for the process. We demonstrate, that in the heavy quark limit and at the one-loop order in perturbation theory, the amplitude factorizes in a convolution of a perturbatively calculable hard-scattering amplitude with the generalized parton densities and the nonrelativistic QCD matrix element <O_1>_V. We evaluate the hard scattering amplitude at one-loop order and compare the data with theoretic…
We report on an attempt to describe hard exclusive photoproduction of $J/Ψ$ mesons, i.e. the reaction $γp \to J/Ψp$, by means of a modified version of the hard-scattering approach, in which the proton is treated as a quark-diquark rather than a three-quark system. In order to improve the applicability of the model at momentum transfers of only a few GeV we take into account constituent-mass effects in the calculation of the perturbative scattering amplitude. With a standard $J/Ψ$-meson distribution amplitude and diquark-model parameters adopted from preceding investigations of other photon-ind…
We present predictions for the rapidity-differential cross sections of exclusive $Υ$ photoproduction in ultraperipheral collisions (UPCs) of lead ions at the Large Hadron Collider (LHC). We work in the framework of collinear factorization at next-to-leading order (NLO) in perturbative QCD, modeling the generalized parton distributions (GPDs) through the Shuvaev transform of nuclear parton distribution functions (nPDFs). While the effects due to the GPD modeling turn out to be small, the direct NLO predictions still carry significant nPDF-originating uncertainties and depend strongly on the cho…
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 $J/ψ$ meson proton-lead ultraperipheral collisions. The predictions give a good descriptions to the experimental data of ALICE. The rapidity distributions of $ϕ$, $ω$ and $ψ(2s)$ mesons i…
We extend the k_\perp-factorization formalism for exclusive photoproduction of vector mesons to the production of electroweak Z^0 bosons. Predictions for the gamma p \to Z^0 p and p p \to p p Z^0 reactions are given using an unintegrated gluon distribution tested against deep inelastic data. We present distributions in the Z^0 rapidity, transverse momentum of Z^0 as well as in relative azimuthal angle between outgoing protons. The contributions of different flavours are discussed. Absorption effects lower the cross section by a factor of 1.5-2, depending on the Z-boson rapidity. We also discus…
The detection of exclusive processes induced by antiproton beams in the GeV range at PANDA(FAIR) opens possibilities for testing QCD predictions on the nucleon structure. In particular, the measurement of electromagnetic nucleon form factors through the proton-antiproton annihilation in a lepton pair can be studied. However, other processes, although interesting by themselves, play the role of background. We will focus on two examples: an 'electromagnetic process', the S-channel annihilation of proton and antiproton into a neutral pion and a virtual photon (followed by lepton pair emission) an…
We present results for total cross sections, single and double differential distributions and correlations between pairs of outgoing particles in the reactions p + antip --> W^+ + photon and p + antip --> W^+ + photon + jet at sqrt(S)=1.8 TeV. Order alpha-strong QCD corrections and leading logarithm photon bremsstrahlung contributions are included in the MS-bar mass factorization scheme for three experimental scenarios: 1) 2-body inclusive production of W^+ and photon, 2) exclusive production of W^+, photon and 1 jet and 3) exclusive production of W^+ and photon with 0 jet. The latest CTEQ par…
In this paper, we discuss the exclusive photoproduction of ground and excited states of $ψ(1S,2S)$ and $Υ(1S,2S)$ in ultraperipheral collisions (UPCs). Using the potential model in order to obtain the vector meson wave function, we find a good agreement of our calculations with data from the LHC and HERA colliders for $J/ψ(1S,2S) $ and $Υ(1S)$ in $γp$ collisions. We extend the calculations to the nuclear target case applying them to $AA$ UPCs with the use of the shadowing and finite coherence length effects fitted to the data. Our results are compared to the recent LHC data, in both incoherent…
In this contribution we report on the investigations of the exclusive production of J/psi and psi(2S) states in proton-proton and nucleus-nucleus reactions at the LHC using the theoretical framework of light-cone dipole formalism.
The exclusive photoproduction of vector mesons ($J/ψ$ and $ϕ$) are investigated by taking into account the next-to-leading order corrections in the framework of Color Glass Condensate. We confront the next-to-leading order modified dipole amplitude with the HERA data finding good agreement. Our studies show that the $χ^2/d.o.f$ from 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 differential cross section. The outcomes indicate that the higher-order corre…
The amplitude for $γp \to V p$, where $V$ is a $J/ψ$ or $Υ$ ground state or excited vector meson, is calculated in a pQCD $k_{T}$-factorization approach. We use this amplitude to predict the cross section for exclusive photoproduction of $J/ψ, ψ', Υ$ mesons in proton-proton collisions. Calculations are performed for a variety of unintegrated gluon distributions, and we compare our results to LHCb data. Here we especially focus on the possibilty of constraining saturation effects. Compared to earlier calculations we include both Dirac and Pauli electromagnetic form factors. We discuss the role …
We present a simple explanation for the recently observed near-threshold proton-antiproton enhancement. It is described by a set of low-energy parameters deduced from the analysis of NantiN experiments at LEAR. We predict a related effect in photoproduction reaction under study by CLAS collaboration.
We calculate the cross section and the beam asymmetry for exclusive photoproduction of charmed particles near threshold ($γ+p\to Λ_c^+ +\bar{D^0}$), in the framework of an effective Lagrangian model. We discuss the sensitivity of these observables to the magnetic moment of the $Λ_c$ baryon and of the coupling constant in the $pΛ_c D$ vertex. We show that exclusive measurements allow, in principle, to determine the magnetic moments of charmed baryons.
We present the first next-to-leading-order (NLO) perturbative QCD (pQCD) study of rapidity-differential cross sections of coherent exclusive photoproduction of $J/ψ$ mesons in heavy-ion ultraperipheral collisions (UPCs) at the LHC, $dσ/dy(\text{Pb} + \text{Pb} \rightarrow \text{Pb} + J/ψ+ \text{Pb})$. For this, we account for the photon-nucleon NLO cross sections at the forward limit, the $t$ dependence using a standard nuclear form factor, and the photon fluxes of the colliding nuclei. Approximating the generalized parton distributions with their forward-limit parton distribution functions (P…
The exclusive photoproduction of the $J/ψ$ state is investigated in peripheral AA collisions for the energies available at the LHC, $\sqrt{s}=2.76$ TeV and $\sqrt{s}=5.02$ TeV. In order to evaluate the robustness of the light-cone color dipole formalism, previously tested in the ultraperipheral regime, the rapidity distribution and the nuclear modification factor ($R_{AA}$) were calculated for three centrality classes: 30%-50%, 50%-70% and 70%-90%. In the peripheral regime, three scenarios were considered. In the scenario 1, a similar formalism adopted in the UPC regime is used; in the scenari…
We calculate the nuclear cross section for vector meson exclusive photoproduction within the QCD color dipole picture and in the Regge approach. For the former approach, we have considered the phenomenological saturation model, whereas for the latter we use a model based on the dipole Pomeron framework. Theoretical estimates for scattering on both light and heavy nuclei are given for a large range on energy.
Decays into two charged pions of the f0(1370) are the main source of an isolated structure localized between 1.2 and 1.5 GeV in the two charged pions mass spectrum measured in pp Central Exclusive Production (CEP) at 200 GeV at very low four momentum transfer ltl by the STAR experiment. These data confirm in the two charged pions decay channel the existence of the f0(1370) as an isolated well identified structure previously observed in K+K-, KsKs, 4 charged pions, two charged and two neutral pions and 4 neutral pions decays measured in antiproton annihilations at rest. The ensemble of these da…
First, I define generalized Bloom-Gilman duality and Bjorken-like scaling for inclusive photoproduction of pions, relating Quark-Parton Model description in the deep-inelastic region to the properties of exclusive resonance excitation. Secondly, connection between inclusive and exclusive processes is established in the formalism of Nonforward Parton Densities used here to predict deviations from dimensional scaling for a variety of observables: nucleon and pion elastic form factors, and pion Compton scattering.
We present the first study of rapidity-differential cross sections of coherent exclusive $J/ψ$ photoproduction in heavy-ion ultraperipheral collisions (UPCs) at the LHC, $\text{d}σ(\text{Pb}+\text{Pb}\rightarrow \text{Pb}+J/ψ+\text{Pb})/\text{d}y$, to NLO in collinear factorisation. Taking the generalised parton distributions as their forward limit counterparts, the NLO contributions in the cross sections are quantified and we show that the real part of the amplitude and quark-PDF contributions must not be neglected. We further evaluate the uncertainties arising from the scale-choice at both L…
The spin structure of the matrix element for the reactions $γ+ N\to Y_c +{D}^*$, where $Y_c=Λ_c^+(2285)$, $Σ_c(2455)$ are charmed baryons with spin 1/2, and $D^*(2010)$ is the vector charmed meson, can be parametrized, in collinear regime, in terms of three independent scalar amplitudes, which are functions of the photon energy $E_γ$, only. In framework of an effective Lagrangian approach generalized to charm photoproduction, we calculate the energy dependence of the differential cross section, the density matrix element of $\bar{D}^*$, $ρ_{11}$, the asymmetry $A_z$ in the collision of circula…
