We study the influence of a strong laser field on the Bethe-Heitler photoproduction process by a relativistic nucleus. The laser field propagates in the same direction as the incoming high-energy photon and it is taken into account exactly in the calculations. Two cases are considered in detail. In the first case, the energy of the incoming photon in the nucleus rest frame is much larger than the electron's rest energy. The presence of the laser field may significantly suppress the photoproduction rate at soon available values of laser parameters. In the second case, the energy of the incoming photon in the rest frame of the nucleus is less than and close to the electron-positron pair production threshold. The presence of the laser field allows for the pair production process and the obtained electron-positron rate is much larger than in the presence of only the laser and the nuclear field. In both cases we have observed a strong dependence of the rate on the mutual polarization of the laser field and of the high-energy photon and the most favorable configuration is with laser field and high-energy photon linearly polarized in the same direction. The effects discussed are in principle measurable with presently available proton accelerators and laser systems.
It is shown that birefringence effect influences on production of particles with the spin S greater or equal then 1 at collisions of high energy particles.
With the advent of new photon tagging facilities and novel experimental technologies it has become possible to perform photoproduction cross section measurements of pseudoscalar mesons on nuclei with a percent level accuracy. The extraction of the radiative decay widths from these measurements at forward angles is done by the Primakoff method, which requires theoretical treatment of all processes participating in these reactions at the same percent level. In this work we review the theoretical approach to meson photoproduction amplitudes in the electromagnetic and strong fields of nuclei at fo…
We consider photoproduction of $ω$ mesons off complex nuclei to study interactions of transversely and longitudinally polarized vector mesons with nucleons. Whereas the total cross section for interactions of the transversely polarized vector mesons with nucleons $σ_T=σ(V_TN)$ can be obtained from coherent photoproduction, measurements of vector meson photoproduction in the incoherent region provide a unique opportunity to extract the total cross section for longitudinally polarized mesons interacting with nucleons $σ_L=σ(V_LN)$, which has not yet been measured and strongly depends on theoreti…
We study the photoproduction of scalar mesons close to the threshold of f_0(980) and a_0(980) using a unitary chiral model. Peaks for both resonances show up in the invariant mass distributions of pairs of pseudoscalar mesons. A discussion is made on the photoproduction of these resonances in nuclei, which can shed light on their nature, a subject of continuous debate.
We calculate inclusive photoproduction cross-sections for both proton and nuclei targets, using a saturation model derived from an approximate solution to the Balitsky-Kovchegov nonlinear evolution equation. This paper extends our hypothesis, that one can successfully use the dipole picture and saturation models to describe soft processes, instead of the soft Pomeron Regge parametrization. Our fit is compatible with our previous fit to DIS data, and utilizes the same phenomenological parameters as in our paper devoted to soft hadronic interactions. Using the Glauber formalism, and no additiona…
The recent studies is reported of the neutrino photoproduction on nuclei, gamma + Ze -> Ze + gamma + nu + anti-nu, in a strong magnetic field. It is shown that the catalyzing influence of the field on the process decreases essentially because of the modification of the photon dispersion properties in a strong magnetic field. Therefore, at any field magnitude, neutrino photoproduction cannot compete with the URCA processes. This conclusion contradicts a recent statement in the literature.
The nuclear enhancement observed in inelastic photoproduction of $J/Ψ$ should not be interpreted as evidence for an increased gluon density in nuclei. The nuclear suppression of the production rate due to initial and final state interactions is calculated and a novel two-step color exchange process is proposed, which is able to explain the data.
Threshold neutral pion photoproduction on light nuclei is studied in the framework of baryon chiral perturbation theory. We obtain a general formula for the electric dipole amplitude in the special case of neutral pion photoproduction on a nucleus. To third order in small momenta, the amplitude is a sum of 2- and 3-body interactions with no undetermined parameters. With reasonable input from the single nucleon sector, our result for neutral pion photoproduction on the deuteron is in agreement with experiment.
High energy photoproduction off nuclear targets is studied within the Glauber-Gribov approximation. The photon is assumed to interact as a $q\bar{q}$-system according to the Generalized Vector Dominance Model and as a ``bare photon'' in direct scattering processes with target nucleons. We calculate total cross sections for interactions of photons with nuclei taking into account coherence length effects and point-like interactions of the photon. Results are compared to data on photon-nucleus cross sections, nuclear shadowing, and quasi- elastic $ρ$-production. Extrapolations of cross sections a…
In a transport model that combines initial state interactions of the photon with final state interactions of the produced particles we present a calculation of inclusive photoproduction of mesons in nuclei in the energy range from 1 to 7 GeV. We give predictions for the photoproduction cross sections of pions, etas, kaons, antikaons, and $π^+π^-$ invariant mass spectra in ^{12}C and ^{208}Pb. The effects of nuclear shadowing and final state interaction of the produced particles are discussed in detail.
We demonstrate how the elementary amplitudes $γN\to ΨN$, the amplitude of the nondiagonal $J/ψN\Leftrightarrow ψ' N$ transition, and the total $J/ψN$ and $ψ' N$ cross sections can be determined from measurements of the coherent $J/ψ$ and $ψ'$ photoproduction off light nuclei at moderate energies. For this purpose we provide a detailed numerical analysis of the coherent charmonium photoproduction off silicon within the generalized vector dominance model (GVDM) adjusted to account for the physics of charmonium models and color transparency phenomenon.
Recent advances in the photon tagging facilities together with the novel, high resolution fast calorimetry made possible to perform photoproduction cross section measurements of pseudoscalar mesons on nuclei with a percent level accuracy. The extraction of the radiative decay widths, needed for testing the symmetry breaking effects in QCD, from these measurements at small angles is done by the Primakoff method. This method requires theoretical treatment of all processes participating in these reactions at the same percent level. The most updated description of general processes, including the …
We calculate the coherent charmonium photoproduction at intermediate energies accounting for the physics of the charmonium bound states and the dependence of the cross section on the region occupied by color using a correspondingly adjusted generalized vector dominance model (GVDM). In the photon energy domain where the coherence lengths are comparable to the average internucleon distances in nuclei and the nuclear radii we found that significant oscillations of the total and forward photoproduction cross sections governed by the longitudinal nuclear form factor are strongly modified by the ch…
The questions on the presense and quantitative role of the constant terms in the real part of the high-energy photon-nucleon and photon-nucleus amplitudes representing the contribution of the non-Regge (the fixed j=0-pole) singularities in the finite-energy sum rules (FESR) for the photoabsorption cross sections on nucleons and the lightest atomic nuclei are discussed and new testable relations are presented for relevant combinations of the Compton scattering amplitudes.
The integrated cross section for the incoherent photoproduction of vector mesons on nuclei $γ^* A \to VX$, $X\not=A$, is calculated within Glauber theory and as a function of the photon energy. The inverse of the longitudinal momentum transfer is called coherence length $l_c$ and depends on the virtuality and the energy of the photon. Nuclear transmission factors strongly depend on $l_c/R_A$ ($R_A$ is the nuclear radius) and this effect may interfere with the search for color transparency effects.
High energy multiparticle photoproduction off nuclear targets is studied. The photon is assumed to interact in direct scattering processes or as a resolved $q\bar{q}$-state according to the Generalized Vector Dominance Model. In the description of resolved interactions multiple soft and hard processes in each $q\bar{q}$--nucleon interaction are taken into consideration. The model, formulated within the framework of the two-component Dual Parton Model, is shown to agree with hadron production data from real and weakly virtual photon-nucleus interactions. Differences between multiparticle produc…
We investigate inclusive omega photoproduction off complex nuclei, concentrating on the feasibility to examine a possible in-medium change of the omega meson properties by observing the pi^0 gamma invariant mass spectrum. The simulations are performed by means of a BUU transport model including a full coupled-channel treatment of the final state interactions. In-medium changes of the omega spectral density are found to yield a moderate modification of the observables as compared to the situation in free space. Also the effects of a momentum dependence of the strong omega potential are discusse…
We study photon-induced coherent production of Upsilon in ultraperipheral heavy ion collisions at LHC and demonstrate that the counting rates will be sufficient to measure nuclear shadowing of generalized gluon distributions. This will establish the transition from the regime of color transparency to the regime of perturbative color opacity in an unambiguous way. We argue that such measurements will provide the possibility to investigate the interaction of ultra-small color dipoles with nuclei in QCD at large energies, which are beyond the reach of the electron-nucleon (nucleus) colliders, and…
In the present paper we investigate pi0 pi0 and pi(+/-)pi0 photoproduction off complex nuclei at incident beam energies of 400-460 MeV. Simulations of two pion photoproduction on protons and nuclei are performed by means of a semi-classical BUU transport model including a full coupled-channel treatment of the final state interactions. Elastic scattering of the final state pions with the nucleons in the surrounding nuclear medium is found to yield a downward shift of the pi pi invariant mass distribution. We show that the target mass dependence of the pi0 pi0 invariant mass spectrum as measured…
We study the photoproduction of vector mesons off proton and off nuclear targets. We work within the colour dipole model in an approach that includes subnucleon degrees of freedom, so-called hot spots, whose positions in the impact-parameter plane change event-by-event. The key feature of our model is that the number of hot spots depends on the energy of the photon--target interaction. Predictions are presented for exclusive and dissociative production of $ρ^{0}$, $\mathrm{J/}ψ$, and $Υ(1S)$ off protons, as well as for coherent and incoherent photoproduction of $ρ^{0}$ off nuclear targets, whe…
Investigations of the quasifree reaction A$(γ, K Y)$B are presented in the distorted wave impulse approximation (DWIA). For this purpose, we present a revised tree-level model of elementary kaon photoproduction that incorporates hadronic form factors consistent with gauge invariance, uses SU(3) values for the Born couplings and uses resonances consistent with multi-channel analyses. The potential of exclusive quasifree kaon photoproduction on nuclei to reveal details of the hyperon-nucleus interaction is examined. Detailed predictions for the coincidence cross section, the photon asymmetry, an…
First quasiclassical correction to the differential cross section of high-energy electron-positron photoproduction in the electric field of a heavy atom is obtained with the exact account of the field. This correction is responsible for the charge asymmetry ${\cal A}$ in this process. When the transverse momentum of at least one of the produced particles is much larger than the electron mass $m$, the charge asymmetry can be as large as tens percent. We also estimate the contribution $\tilde{\cal A}$ to the charge asymmetry coming from the Compton-type diagram. For heavy nuclei, this contributi…
Using the general notion of cross section fluctuations in hadron--nucleus scattering at high energies, we derive an expression for the cross section of incoherent $J/ψ$ photoproduction on heavy nuclei $dσ_{γA \to J/ψY}/dt$, which includes both elastic $dσ_{γp \to J/ψp}/dt$ and proton-dissociation $dσ_{γp \to J/ψY}/dt$ photoproduction on target nucleons. We find that with good accuracy, $dσ_{γA \to J/ψY}/dt$ can be expressed as a product of the sum of the $dσ_{γp \to J/ψp}/dt$ and $dσ_{γp \to J/ψY}/dt$ cross sections, which have been measured at HERA, and the common nuclear shadowing factor, wh…
We consider $J/ψ$ photoproduction in ion--ion ultraperipheral collisions (UPCs) at the LHC and RHIC in the coherent and incoherent quasielastic channels with and without accompanying forward neutron emission and analyze the role of nuclear gluon shadowing at small $x$, $x=10^{-4}-10^{-2}$, in these processes. We find that despite the good agreement between large nuclear gluon shadowing and the ALICE data in the coherent channel, in the incoherent channel, the leading twist approximation predicts the amount of nuclear suppression which is by approximately a factor of $1.5$ exceeds that seen in …
We present the photoproduction of an intermediate mass Higgs (IMH) boson associated with a $W$ boson at the future electron-proton colliders using bremsstrahlung photon beam or laser backscattered photon beam. With bremsstrahlung photon beam the search for the IMH boson is unfavorable because of the small signal rate. But with laser photon beam the search is viable due to a much larger rate, and provided that the $B$-identification is efficient and $m(b\bar b)$ measurement has a good resolution.
Rho photoproduction on complex nuclei is re-examined using a generalised vector dominance model which succesfully predicts the observed nuclear shadowing in real photoabsorption and deep inelastic scattering. This model is shown to give a good fit to rho photoproduction data on both nucleons and complex nuclei, in which the well-known disagreement between the measured gamma-rho coupling and the gamma-rho coupling required by the simple vector dominance model is eliminated. The rho N total cross-sections required are similar to those predicted by the additive quark model; and the magnitude of t…
By using the theoretical approaches describing well the available data on $t$-integrated coherent photoproduction of light and heavy vector mesons in Pb-Pb ultraperipheral collisions (UPCs) at the Large Hadron Collider (LHC) in Run 1, we calculate the momentum transfer distributions for this process for $ρ$ and $J/ψ$ vector mesons in the kinematics of Run 2 at the LHC. We demonstrate that nuclear shadowing not only suppresses the absolute value of the cross sections, but also shifts the momentum transfer distributions toward smaller values of the momentum transfer $|t|$. This result can be int…
We calculate cross sections and transverse momentum distributions for the incoherent diffractive production of vector mesons $J/ψ$ and $Υ$ 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 $J/ψ$ produ…
We make predictions for the cross section of coherent $J/ψ$ photoproduction in Pb-Pb and O-O ultraperipheral collisions (UPCs) at the LHC as a function of the $J/ψ$ rapidity $y$ in the framework of collinear factorization and next-to-leading order (NLO) perturbative QCD. We quantify the strong scale dependence and significant uncertainties due to nuclear PDFs and show that our approach provides a reasonable description of the LHC data on coherent $J/ψ$ photoproduction in Pb-Pb UPCs. We demonstrate that these uncertainties are reduced by approximately a factor of 10 in the scaled ratio of the O…
We make predictions for the cross sections of coherent photoproduction of $ρ$, $ϕ$, $J/ψ$, $ψ(2S)$, and $Υ(1S)$ mesons in Pb-Pb ultraperipheral collisions (UPCs) at $\sqrt{s_{NN}}=5.02$ TeV in the kinematics of run 2 at the Large Hadron Collider extending the approaches successfully describing the available Pb-Pb UPC data at $\sqrt{s_{NN}}=2.76$ TeV. Our results illustrate the important roles of hadronic fluctuations of the photon and inelastic nuclear shadowing in photoproduction of light vector mesons on nuclei and the large leading twist nuclear gluon shadowing in photoproduction of quarkon…
In this paper, we calculate the cross-section for the photoproduction of quark-antiquark pairs in the peripheral collision of ultra-relativistic nuclei, by treating the color field of the nuclei within the Color Glass Condensate model. We find that this cross-section is sensitive to the saturation scale $Q_s^2$ that characterizes the model. In particular, the transverse momentum spectrum of the produced pairs could be used to measure the properties of the color glass condensate.
The resonant photoproduction of ultrarelativistic electron-positron pairs (PPP) in a nuclear field and a weak laser field is theoretically studied. Under resonance conditions, the intermediate virtual electron (positron) in the laser field becomes a real particle. As a result, the initial process of the second order in the fine structure constant in the laser field effectively reduces into two successive processes of the first order: single-photon production of electron-positron pair in a laser field (laser-stimulated Breit-Wheeler process) and laser-assisted process of electron (positron) sca…
The differential cross section of coherent photo-production of heavy quarkonia on nuclear targets is calculated within the QCD color dipole formalism. The higher-twist nuclear shadowing corresponding to the $\bar QQ$ Fock component of the photon, is calculated including the correlation between dipole orientation $\vec r$ and impact parameter of a collision $\vec b$, which is related to the transverse momentum transfer via Fourier transform. We also included the leading twist gluon shadowing corresponding to higher Fock components of the photon containing gluons, which have specifically short c…
In this work we investigate the photoproduction of radially excited vector mesons off nuclei in heavy ion relativistic collisions. In particular, we analyze the exclusive photoproduction of psi(2S) off nuclei, evaluating the coherent and the incoherent contributions to that process. The theoretical framework used in the present analysis is the light-cone dipole formalism and predictions are done for PbPb collisions at the CERN-LHC energy of 2.76 TeV. The theoretical uncertainties are analyzed and comparison is also done to the recent ALICE Collaboration data for the psi(1S) state photoproducti…
The nonlinear Breit-Wheeler process is studied in the presence of strong and short laser pulses. We show that for a relativistically intense plane-wave laser field many features of the momentum distribution of the produced electron-positron pair like its extension, region of highest probability and carrier-envelope phase effects can be explained from the classical evolution of the created particles in the background field. To this end an intuitive semiclassical picture based on the local constant-crossed field approximation applied on the probability-amplitude level is established and compared…
We study the $Υ(1S)$ meson photoproduction on protons and nuclei at the near-threshold center-of-mass energies below 11.4 GeV (or at the corresponding photon laboratory energies $E_γ$ below 68.8 GeV). We calculate the absolute excitation functions for the non-resonant and resonant photoproduction of $Υ(1S)$ mesons off protons at incident photon laboratory energies of 63--68 GeV by accounting for direct ($γp \to {Υ(1S)}p$) and two-step ($γp \to P^+_b(11080,11125,11130) \to {Υ(1S)}p$) $Υ(1S)$ production channels within different scenarios for the non-resonant total cross section of elementary re…
The strong electromagnetic fields associated with high energy protons and nuclei may lead to exclusive photoproduction of vector mesons in proton-proton and nucleus-nucleus collisions at the LHC. This paper will discuss the expected cross sections and rapidity and transverse momentum distributions.
The variation of the coherence length $l_c=2ν/(Q^2+m_V^2)$ in virtual photoproduction of vector mesons off nuclei as a function of the photon energy $ν$ or virtuality $Q^2$ results in dramatic changes in the values of the nuclear transparency. Color transparency effects can be easily mixed up with the effects of the coherence length in incoherent photoproduction on nuclei.
We argue that study of the cross section of coherent photo(electro) production of vector mesons off nuclear targets provides an effective method to probe the leading twist hard QCD regimes of color transparency and perturbative color opacity as well as the onset of black body limit (BBL) in the soft and hard QCD interactions. In the case of intermediate energies we use the Generalized Vector Dominance Model to take into account coherence effects for two distinctive limits - the soft interactions for production of $ρ$ and $ρ'$-mesons and the color transparency regime for production of charmoniu…
Tunneling electron-positron pair production is studied in a new setup in which a strong low-frequency and a weak high-frequency laser field propagate in the same direction and collide head-on with a relativistic nucleus. The electron-positron pair production rate is calculated analytically in the limit in which in the nucleus rest frame the strong field is undercritical and the frequency of the weak field is below and close to the pair production threshold. By changing the frequency of the weak field one can reduce the tunneling barrier substantially. As a result tunneling pair production is s…
We study the inclusive photoproduction of $T_{{\bar c}{\bar c}}(3875)^-$ mesons (which are the antiparticles of the doubly charmed tetraquarks $T_{cc}(3875)^+$ discovered recently by the LHCb Collaboration) from nuclei in the near-threshold energy region within the nuclear spectral function approach by considering incoherent direct ($γp(n) \to D^+(D^0){T_{{\bar c}{\bar c}}(3875)^-}Λ^+_c$) photon--nucleon $T_{{\bar c}{\bar c}}(3875)^-$ creation processes as well as five possible different scenarios for their internal structure with the main goal of clarifying the possibility to decipher this st…
We extend our recent study of dilepton invariant-mass spectra from the decays of rho mesons produced by photon reactions off nuclei. We specifically focus on experimental spectra as recently measured by the CLAS Collaboration at the Thomas Jefferson National Accelerator Facility using carbon and iron nuclei. Building on our earlier work we broaden our description to a larger set of observables in order to identify sensitivities to the medium effects predicted by microscopic calculations of the rho spectral function. We compute mass spectra for several target nuclei and study the spectral shape…
Based on accurate calculations of the flux of equivalent photons of the proton and heavy nuclei and the pQCD framework for the gluon distribution in the proton and nuclei, we analyze the rapidity and momentum transfer distributions of coherent $J/ψ$ photoproduction in ultraperipheral proton-Pb collisions at the LHC. We demonstrate that unlike the case of proton-proton UPCs marred by certain theoretical uncertainties and experimental limitations, after a cut excluding the region of small momentum transfers, ultraperipheral proton-Pb collisions offer a clean way to study the gluon distribution i…
The exclusive $Υ$ photoproduction in ultraperipheral proton-nucleus and nucleus-nucleus collisions at LHC energies is being investigated using pQCD framework which constrain the gluon distribution in the proton and nuclei at low $x$. Rapidity distributions of $Υ$ photoproduction with different gluon distribution parameterization and gluon shadowing for nuclear PDFs including photon flux suppression for strong interaction, are being presented at LHC energies. Predictions done for ultraperipheral collisions at $\sqrt s$=$8.16$ TeV in pPb, and at $\sqrt s$=$5.02$ TeV in PbPb collisions which are …
This work investigates the exclusive photoproduction of $ψ(2S)$ meson off nuclei evaluating the coherent and the incoherent contributions. The theoretical framework used in the present analysis is the light-cone dipole formalism and predictions are done for PbPb collisions at the CERN-LHC energy of 2.76 TeV. A comparison is done to the recent ALICE Collaboration data for the $ψ(1S)$ state photoproduction.
We compare the coherent and quasielastic J/psi photoproduction in the peripheral heavy ion collisions in kinematics of RHIC. Our improved estimate of the total coherent cross section is a factor of two smaller than the earlier ones. We find that the counting rate of quasielastic J/psi photoproduction tagged by neutrons emitted due to cascading of the recoiled nucleon within the residual nucleus exceeds the rate of the coherent events. We argue that measurements of this process can be used to learn about the dynamics of color dipole-nucleon interactions in nuclei in the wide effective range of …
We study the near-threshold inclusive photoproduction of $Ξ^-$ hyperons off $^{12}$C and $^{184}$W target nuclei within a first-collision model relying on the nuclear spectral function and including incoherent $Ξ^-$ production in direct elementary $γp \to K^+{K^+}Ξ^-$ and $γn \to K^+{K^0}Ξ^-$ processes. The model takes into account the impact of the nuclear effective scalar $K^+$, $K^0$, $Ξ^-$ and their Coulomb potentials on these processes as well as the absorption of final $Ξ^-$ hyperons in nuclear matter, the binding of intranuclear nucleons and their Fermi motion. We calculate the absolute…
We discuss the photoproduction of $Υ$ and $J/ψ$ at high energy $\bar{p}p$, $pp$ and heavy ion colliders. We predict large rates in $\bar{p}p$ interactions at the Fermilab Tevatron %and in heavy-ion interactions at the CERN LHC. These reactions can be and in $pp$ and heavy-ion interactions at the CERN LHC. The $J/ψ$ is also produced copiously at RHIC. These reactions can be used to study the gluon distribution in protons and heavy nuclei. We also show that the different CP symmetries of the initial states lead to large differences in the transverse momentum spectra of mesons
We argue that with an increase of the collision energy, elastic photoproduction of $ρ$ mesons on nuclei becomes affected by the significant cross section of photon inelastic diffraction into large masses, which results in the sizable inelastic nuclear shadowing correction to $σ_{γA \to ρA}$ and the reduced effective $ρ$-nucleon cross section. We take these effects into account by combining the vector meson dominance model, which we upgrade to include the contribution of high-mass fluctuations of the photon according to QCD constraints, and the Gribov-Glauber approximation for nuclear shadowing…
