Total Photoproduction Cross Section Research Articles

Investigating exclusive ρ0 photoproduction within the Regge phenomenology approach

The elastic differential and integrated total cross section for the exclusive ρ0 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→ρ0A), which is applied to ρ0 production in ultraperipheral lead-lead and xenon-xenon collisions. The predictions are compared to the measurements performed by ALICE Collaboration. Aspects of the theoretical uncertainties and limitations of the formalism are scrutinized.

Towards clarifying the possibility of observation of the LHCb hidden-charm pentaquarks [formula omitted], [formula omitted], [formula omitted] and [formula omitted] in near-threshold charmonium photoproduction off protons and nuclei

We study the near-threshold J/ψ meson photoproduction from protons and nuclei by considering incoherent direct non-resonant (γp→J/ψp, γn→J/ψn) and two-step resonant (γp→Pci+→J/ψp, γn→Pci0→J/ψn, i=1, 2, 3, 4; Pc1+,0=Pc+,0(4312), Pc2+,0=Pc+,0(4337), Pc3+,0=Pc+,0(4440), Pc4+,0=Pc+,0(4457)) charmonium production processes. We calculate the absolute excitation functions, energy and momentum distributions for the non-resonant, resonant and for the combined (non-resonant plus resonant) production of J/ψ mesons on protons as well as, using the nuclear spectral function approach, on carbon and tungsten target nuclei at near-threshold incident photon energies by assuming the spin-parity assignments of the hidden-charm resonances Pc+,0(4312), Pc+,0(4337), Pc+,0(4440) and Pc+,0(4457) as JP=(1/2)−, JP=(1/2)−, JP=(1/2)− and JP=(3/2)− within three different realistic scenarios for the branching ratios of their decays to the J/ψp and J/ψn modes (0.25, 0.5 and 1%). We show that will be very hard to measure the Pci+ pentaquark states through the scan of the J/ψ total photoproduction cross section on a proton target in the near-threshold energy region around the resonant photon energies of 9.44, 9.554, 10.04 and 10.12 GeV if these branching ratios ∼ 1% and less. We also demonstrate that at these photon beam energies the J/ψ energy and momentum combined distributions considered reveal distinct sensitivity to the above scenarios, respectively, at “low” J/ψ total energies and momenta, which implies that they may be an important tool to provide further evidence for the existence of the pentaquark Pci+ and Pci0 resonances and to get valuable information on their decay rates to the J/ψp and J/ψn final states. The measurements of these distributions could be performed in the future at the 12 GeV CEBAF facility.

Possibility of observation of hidden-bottom pentaquark resonances in bottomonium photoproduction on protons and nuclei near threshold

We study the meson photoproduction on protons and nuclei at near-threshold center-of-mass energies below 11.4 GeV (or at the corresponding photon laboratory energies below 68.8 GeV). We calculate the absolute excitation functions for the nonresonant and resonant photoproduction of mesons off protons at incident photon laboratory energies of 63-68 GeV by considering direct ( ) and two-step ( , , ) production channels within different scenarios for the nonresonant total cross section of the elementary reaction and for branching ratios of the decays , , and . We also calculate an analogous function for the photoproduction of mesons on the 12C and 208Pb target nuclei in the near-threshold center-of-mass beam energy region of 9.0-11.4 GeV by considering the respective incoherent direct ( ) and two-step ( , , and , , ) ) production processes using a nuclear spectral function approach. We demonstrate that a detailed scan of the total photoproduction cross section on proton and nuclear targets in the near-threshold energy region in future high-precision experiments at the proposed high-luminosity electron-ion colliders EIC and EicC in the US and China should provide a definite result for or against the existence of the nonstrange hidden-bottom pentaquark states and ( =1, 2, 3) as well as clarify their decay rates.

Double neutral pion photoproduction off the proton with FOREST at ELPH

Total cross section for the double neutral pion photoproduction off the proton is presented in the incident photon energy range of 0.58 to 1.15 GeV. The data were accumulated in the years 2009–2010, recorded by a 4π EM calorimeter at ELPH, named FOREST. The number of recorded events obtained during this period is 1.6×109 for a hydrogen target. Two neutral pions are reconstructed via detecting their decay products, four gammas (2π 0 → 4γ ). Compared to the previous results obtained by other groups, our data are in good agreement with theirs within error bars.

Photoproduction total cross section and shower development

The total photoproduction cross section at ultra-high energies is obtained using a model based on QCD minijets and soft-gluon resummation and the ansatz that infrared gluons limit the rise of total cross sections. This cross section is introduced into the Monte Carlo system AIRES to simulate extended air-showers initiated by cosmic ray photons. The impact of the new photoproduction cross section on common shower observables, especially those related to muon production, is compared with previous results.

Diffractive photoproduction of J/ψ at LHC energies

In this work we calculate the rapidity distribution and the total cross section for the diffractive photoproduction of J/ψ in PbPb collisions in LHC energies. We use the color dipole formalism and different models for the forward dipole-proton scattering amplitude (N) which take into account nonlinear effects. Using always the same model for the wave function of the vector meson, we estimate the theoretical uncertainty related to the choice of the model for N. We compare our results with available data from ALICE [1, 2] and present our prediction for higher enegies.

Photoproduction models for total cross section and shower development

A model for the total photoproduction cross section based on the ansatz that resumma- tion of infrared gluons limits the rise induced by QCD minijets in all the total cross-sections, is used to simulate extended air showers initiated by cosmic rays with the AIRES simulation program. The impact on common shower observables, especially those related with muon production, is analysed and compared with the corresponding results obtained with previous photoproduction models.

Comparing AdS/CFT dipole model to HERA F2 data

We apply an AdS/CFT-inspired color-dipole model which contains only three free parameters to describe the HERA data for the inclusive structure function F2 at small Bjorken-x and virtuality. We found that the saturation scale in our AdS/CFT-based parameterization varies in the range of 1 ÷ 3 GeV becoming independent of energy/Bjorken-x at very small x. This leads to the prediction of x-independence of the structure functions at very small x. With the fitted parameters in our model, the predictions for F2, longitudinal structure function, charm structure function and total photo-production cross-sections in the kinematic regions of future experiments can be given.

Total photoproduction cross section at very high energy

In this paper we apply to photoproduction total cross-section a model we have proposed for purely hadronic processes and which is based on QCD mini-jets and soft gluon re-summation. We compare the predictions of our model with the HERA data as well as with other models. For cosmic rays, our model predicts substantially higher cross-sections at TeV energies than models based on factorization but lower than models based on mini-jets alone, without soft gluons. We discuss the origin of this difference.

Diffractive photoproduction at the LHC

In this contribution we analyze the electromagnetic interactions present in hadron-hadron collisions at the LHC energy. In particular, we summarize our estimate for the total cross sections for the diffractive photoproduction of Z 0 and vector mesons in the h h → h X h process ( X = Z 0 , J / Ψ , ϒ ), which are characterized by two rapidity gaps in the final state. The study of these processes is feasible considering the proton tagging detectors (Roman Pots) already planned for the initial start-up of the LHC.

Photoproduction of π 0 ω off protons for E γ ≤3 GeV

Differential and total cross-sections for photoproduction of gamma proton to proton pi0 omega and gamma proton to Delta+ omega were determined from measurements of the CB-ELSA experiment, performed at the electron accelerator ELSA in Bonn. The measurements covered the photon energy range from the production threshold up to 3GeV.

ANALYSIS OF HIGH ENERGY K+K- PHOTOPRODUCTION ON HYDROGEN

We have analyzed the γp→pK+K- reaction in the K+K- effective mass region around the mass of the ϕ(1020) meson. The interference of the S-wave contribution with the P-wave has been studied. Both scalar resonances f0(980) and a0(980) have been taken into account. We obtained a good description of the available experimental data, in particular the mass distributions and the moments of the kaon angular distribution. Our calculations give values of the integrated S-wave total photoproduction cross section between 4 and 7 nb for the K+K- effective mass range around the ϕ(1020) mass and at the laboratory photon energy near 5 GeV. These numbers favor lower experimental estimates obtained at DESY.

Sum rule for a difference of proton and neutron total photoproduction cross sections

Starting from very high-energy inelastic electron-nucleon scattering with a production of a hadronic state $X$ to be moved closely to the direction of the initial nucleon, then utilizing analytic properties of parts of forward virtual Compton scattering amplitudes on proton and neutron, one obtains the relation between nucleon form factors and a difference of proton and neutron differential electroproduction cross sections. In particular, for the case of small transferred momenta, one finally derives sum rule, relating Dirac proton mean square radius and anomalous magnetic moments of proton and neutron to the integral over a difference of the total proton and neutron photoproduction cross sections.

Large logarithms in the beam normal spin asymmetry of elastic electron-proton scattering

We study a parity-conserving single-spin beam asymmetry of elastic electron-proton scattering induced by an absorptive part of the two-photon exchange amplitude. It is demonstrated that excitation of inelastic hadronic intermediate states by the consecutive exchange of two photons leads to logarithmic and double-logarithmic enhancement due to contributions of hard collinear quasireal photons. The asymmetry at small electron scattering angles is expressed in terms of the total photoproduction cross section on the proton and is predicted to reach the magnitude of 20--30 ppm. At these conditions and fixed 4-momentum transfers, the asymmetry is rising logarithmically with increasing electron beam energy, following the high-energy diffractive behavior of total photoproduction cross section on the proton.

Collinear photon exchange in the beam normal polarization asymmetry of elastic electron–proton scattering

The parity-conserving single-spin beam asymmetry of elastic electron–proton scattering is induced by an absorptive part of the two-photon exchange amplitude. We demonstrate that this asymmetry has logarithmic and double-logarithmic enhancement due to contributions of hard collinear quasi-real photons. An optical theorem is used to evaluate the asymmetry in terms of the total photoproduction cross section on the proton, predicting its magnitude at 20–30 parts per million for high electron beam energies and small scattering angles. At fixed 4-momentum transfers, the asymmetry is rising logarithmically with increasing electron beam energy, following the high-energy diffractive behavior of total photoproduction cross section on the proton.

New sum rules for nucleon and trinucleon total photoproduction cross-sections

Two new sum rules are derived relating Dirac radii and anomalous magnetic moments of the considered strongly interacting fermions with the convergent integral over a difference of the total proton and neutron, as well as $He^3$ and $H^3$, photoproduction cross-sections.

Quarkonium photoproduction at next-to-leading order

We present the calculation of O( α s 2 α em) corrections to heavy-quarkonium total photoproduction cross sections. Results are given for the colour-octet component of S and P waves. The calculation is performed using covariant projectors in dimensional regularization. A phenomenological study of the results, including a discussion of the high-energy behaviour of the cross sections, is presented. For γp energies up to few hundred GeV the NLO corrections significantly reduce the scale dependence of the production rates relative to the Born-level results. Large small- x corrections arise at higher energies, making the predictions strongly dependent on the shape of the gluon density and on the choice of factorization scale.

Photoproduction of neutral pion pairs in the Coulomb field of the nucleus

The total cross section for Coulomb photoproduction of neutral pion pairs in the reaction is estimated within the effective chiral Lagrangian approach. The amplitude of with one off-shell photon is calculated at in the momentum expansion; in addition, nuclear absorption is taken into account. Besides its experimental feasibility, the results of the calculation demonstrate that the reaction is a powerful source of information on the process close to threshold.

Study of photon dissociation in diffractive photoproduction at HERA

Diffractive dissociation of quasi-real photons at a photon-proton centre of mass energy of W >> 200 GeV is studied with the ZEUS detector at HERA. The process under consideration is {gamma}{rho}{yields} XN, where X is the diffractively dissociated photon system of mass MX and N is either a proton or a nucleonic system with mass MN < 2 GeV. The cross section for this process in the interval 3 < MX < 24 GeV relative to the total photoproduction cross section was measured to be s{sup partial}D/s{sub tot} = 6.2 {+-}0.2 (stat) {+-}1.4 (syst)%. After extrapolating this result to the mass interval of mf2 < MX2 < 0.05W2 and correcting it for proton dissociation, the fraction of the total cross section attributed to single diffractive photon dissociation, {gamma}{rho}{yields}, is found to be s{sub SD}/s{sub tot} = 13.3 {+-}0.5 (stat){+-}3.6(syst)%. The mass spectrum of the dissociated photon system in the interval 8 < MX < 24 GeV can be described by the triple pomeron (PPP) diagram with an effective pomeron intercept of {alpha}{sub P}(0)=1.12{+-}0.04(stat) {+-}0.08(syst). The cross section for photon dissociation in the range 3 < MX < 8 GeV is significantly higher than that expected from the triple pomeron amplitudemore » describing the region 8 < MX < 24 GeV. Assuming that this discrepancy is due to a pomeron-pomeron-reggeon (PPR) term, its contribution to the diffractive cross section in the interval 3 < MX < 24 GeVis estimated to be f{sub PPR}=26{+-} 3(stat) {+-} 12(syst).« less

AssociatedJ/ψ+γphotoproduction as a probe of the color-octet mechanism

The associated production of a J/psi and a photon in photon-hadron collisions is considered, and shown to be a good probe of the presence of colour-octet mediated channels in quarkonia production, as predicted by the factorization approach within NRQCD. Total and differential cross sections for photoproduction at fixed target experiments and at HERA are presented. Associated J/psi + gamma production at hadron colliders is briefly discussed.