Photoproduction Processes Research Articles

NLO corrections to J/ψ+c+c¯ photoproduction

Based on the factorization framework of nonrelativistic quantum chromodynamics, we study the associated J/ψ+c+c¯ photoproduction process at next-to-leading order (NLO) in αs and leading order (LO) in the velocity expansion. The NLO (LO) total cross section for HERA is σtotHERA=0.118(0.074) nb and for EIC is σtotEIC=0.046(0.027) nb. The differential cross sections in pT2, W, and z are presented. The results indicate that the next-to-leading order corrections are substantial, and testable in experiment. Published by the American Physical Society 2024

Pion photoproduction of nucleon excited states with Hamiltonian effective field theory

We refine our previous calculation of multipole amplitude E0+ for pion photoproduction process, γN→πN. The treatment of final-state interactions is based upon an earlier analysis of pion-nucleon scattering within Hamiltonian effective field theory, supplemented by incorporating contributions from the N*(1650) and the KΛ coupled channel. The contribution from the bare state corresponding to the N*(1650) significantly enhances our results. Additionally, we also compute the multipole amplitude M1−, which is of direct relevance to the Roper resonance. The results are comparable with other dynamical coupled-channel models, even though the contribution from the bare state (interpreted as a 2s excitation) in this channel is small because of its large mass. Published by the American Physical Society 2024

Photoproduction of heavy QCD axions in supernovae

Compact stellar objects like supernovae and neutron stars are believed to cool by emitting axions predominantly via bremsstrahlung (NN→NNa), pion conversion (π−p+→Na), and photoproduction (γN→Na). In this paper, we study new contributions to the photoproduction channel pertaining to axions. We first point out the impact of anomaly-induced unavoidable Wess-Zumino-Witten term ∝εμναβFμν∂αaωβ in the photoproduction of such axions. We then perform a complementary data-driven study where the rate of photoproduction can be estimated from low-energy pion photoproduction data. We found that for such heavier axions, i.e., ma∼O(100) MeV, photoproduction processes can be dominant compared to the usual emission processes. In addition, the spectrum of these particles emitted in the process is significantly harder than those originating from bremsstrahlung. Published by the American Physical Society 2024

Probing nuclear structure via photoproduction processes in high energy nucleus-nucleus collisions

Probing nuclear structure via photoproduction processes in high energy nucleus-nucleus collisions

Distributions, sea-to-air fluxes, and biological consumption of carbon monoxide in the Bohai and Yellow Seas during winter

Carbon monoxide (CO) concentrations in the atmosphere and ocean are mainly influenced by anthropogenic inputs, abiotic photoproduction, biogenic sources, and bacterial consumption. This study, for the first time, investigated the distributions, sea-to-air fluxes, and microbial consumption rates of CO in the Bohai Sea (BS) and the Yellow Sea (YS) in winter to identify the main factors controlling CO distributions in both the atmosphere and seawater in colder temperature. Atmospheric CO mixing ratios ([CO]atm) and the concentrations of CO in surface seawater ([CO]surf) ranged from 176.8 to 1245.8 ppbv (mean value: 551.4 ± 214 ppbv) and from 0.49 to 3.1 nmol L−1 (mean value: 0.98 ± 0.55 nmol L−1), respectively. In addition, the spatial distribution of [CO]atm and [CO]surf showed that anthropogenic sources dominated the distribution of [CO]atm, but abiotic photoproduction processes were the main influencers of the distribution of [CO]surf. The surface water at most sampling stations was supersaturated with CO, with a mean saturation factor of 1.9, and the sea-to-air fluxes of CO were estimated to range from −13.88 to 123.88 nmol m−2 h−1 (12.59 ± 21.32 nmol m−2 h−1), suggesting that the BS and the YS were the source of atmospheric CO, and were estimated to contribute 0.009% to 1.4% to the global ocean emission. Microbial consumption experiments indicated that the microbial CO consumption rate constants (Kbio) ranged from 0.15 to 2.14 h−1, and showed that CO concentrations decreased exponentially with incubation time, suggesting that anaerobic CO consumption would limit CO accumulation in winter, thereby affecting the flux of [CO]surf to [CO]atm.

Constraining the chirally motivated [formula omitted] models with the πΣ photoproduction mass spectra

The paper presents a first time attempt on a combined fit of the K−p low-energy data and the πΣ photoproduction mass spectra, performed without fixing the meson-baryon rescattering amplitudes to a specific πΣ−K¯N coupled channels model obtained from fitting exclusively the K−p data. The formalism adopted to describe the photoproduction process is based on chiral perturbation theory and employs a limited number of free parameters. The achieved description of the photoproduction mass distributions is not quite satisfactory, leaving a room for improving the photo-kernel construction. Although the presented models tend to constrain the positions of the Λ(1405) poles it is difficult to draw any conclusions before accomplishing better data reproduction.

Helicity-flip transitions and the t-dependence of exclusive photoproduction of rho meson

We calculate the differential cross section dσ/dt for the diffractive photoproduction process γp → ρp and compare our results with experimental data. Our model is based on two-gluon exchange in the nonperturbative domain. We take into account both helicity conserving and often neglected helicity-flip amplitudes in the γ → V transition, which can contribute at finite t. The shape of the differential cross section as well as the role of helicity-flip processes is strongly related to the dependence of the unintegrated gluon distribution on transverse momenta in the nonperturbative region.

First global study of super dense gluonic matter with UPCs by ALICE

ALICE was the first experimental collaboration observing a moderate nuclear suppression down to low Bjorken-x in lead nuclei using coherent J/ψ photoproduction. In this contribution, we present new results extending the studies of the photonuclear cross section by covering the Bjorken-x interval of 1.1 · 10−5 < x < 3.3 · 10−2, corresponding to the photon-nuclear energies 17 < WγPb,n < 920 GeV. This is achieved by using multiple methods to extract the energy dependence, including new results on the forward neutron emission accompanying the coherent photoproduction process. These new results, combined with ALICE measurements of J/ψ off a proton target, probe the gluonic structure of the lead nuclei at the lowest Bjorken-x possible with any current experiment, challenging both gluon saturation and shadowing models to describe the data.

Photoproduction of P-wave doubly charmed baryon at future e+e− collider

The photoproduction of P-wave doubly charmed baryon (Ξcc) is investigated in the context of future high-energy and high-luminosity e+e− colliders. The direct photoproduction via the sub-process γ+γ→Ξcc+c¯+c¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\gamma +\\gamma \ o {\\Xi}_{cc}+\\overline{c}+\\overline{c} $$\\end{document} and the resolved channel γ+g→Ξcc+c¯+c¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\gamma +g\ o {\\Xi}_{cc}+\\overline{c}+\\overline{c} $$\\end{document} are considered. Within the framework of non-relativistic QCD, the calculation encompasses four P-wave (cc)-diquark configurations: cc3¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {(cc)}_{\\overline{\ extbf{3}}} $$\\end{document}[1P1], (cc)6[3P0], (cc)6[3P1] and (cc)6[3P2]. The two S-wave states, cc3¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {(cc)}_{\\overline{\ extbf{3}}} $$\\end{document}[3S1] and (cc)6[1S0], are also included for comparison. The cross sections, as well as the differential distributions involving transverse momentum, rapidity, and angular variables, have been computed. Numerical results reveal that the resolved photoproduction process plays a significant role and can provide dominant contributions. The photoproduction rate of the P-wave Ξcc is approximately one order of magnitude lower than that of the S-wave.

Reaction plane alignment with linearly polarized photon in heavy-ion collisions

The collective observables play critical roles in probing the properties of quark-gluon-plasma created in relativistic heavy-ion collisions, in which the information on initial collision geometry is crucial. However, the initial collision geometry, e.g., the reaction plane, cannot be directly extracted in the experiment. In this paper, we demonstrate the idea of determining the reaction plane via the feature of linear polarization of the coherent photoproduction process and discuss the advantages of the proposed approach in comparison with traditional methods.

Phi meson electroproduction at low transferred momentum

The electroproduction of phi meson is analyzed. The amplitude consist of two terms, the soft and the hard pomeron terms. it is assumed, that both pomerons are Regge poles. In the present approach, the two pomeron amplitude for the photoproduction processes is extended to construct an amplitude for the electroproduction processes by introducing the photon virtual mass ( . The residues of the two poles become functions of ( . These functions are extracted by fitting the differential cross section ( ) of the extended model at constant energy to the experimental data using the chi- square method. At each , the hard and the soft terms are multiplied by the factors and to match the data. The vertices of the pomeron coupling to the interacting particles are calculated by the dimensions of the vertices which are related to the masses of the interacting particles at each vertex.

Exclusive production of ρ meson in gamma-proton collisions: dσ/dt and the role of helicity flip processes

We calculate the differential cross section dσ/dt for the diffractive photoproduction process γp→ρp and compare to recent data extracted by the CMS collaboration from ultraperipheral proton-lead collisions. Our model is based on two-gluon exchange in the nonperturbative domain. We take into account both helicity conserving and often neglected helicity-flip amplitudes in the γ→V transition. The latter can contribute at finite t. The shape of the differential cross section as well as the role of helicity flip processes is strongly related to the dependence of the unintegrated gluon distribution on transverse momenta in the nonperturbative region.

Inclusive J/ψ photoproduction at the ILC within the framework of non-relativistic QCD

Based on the non-relativistic quantum chromodynamics factorization framework, we study the inclusive J/ψ photoproduction at the future high energy e+e− collider, International Linear Collider(ILC), where the initial photons come from the back-scattering of laser and electron (positron). The intermediate states, coverline{c} (3 {S}_1^{left[mathbf{1}right]} ,1 {S}_0^{left[mathbf{8}right]} ,3 {S}_1^{left[mathbf{8}right]} , 3 {P}_{0,1,2}^{left[mathbf{8}right]} ), and resolved photoproduction processes are considered. Numerical results show that the cross section of J/ψ photoproduction at the ILC could be very large, and the single resolved pro- cess via coverline{c} (3 {S}_0^{left[mathbf{8}right]} ) intermediate state dominates primarily the production. We also present various kinematic distributions for J/ψ photoproduction. Combining the high luminosity of the collision, J/ψ photoproduction at the ILC shall provide a good platform to test the NRQCD factorization.

Exotic Properties of N*(1895) and Its Impact on Photoproduction of Light Hyperons

In this work, we outline the findings of our recent study of the properties of $N^*(1895)$ and its consequential impacts on the cross sections of the photoproduction of $\Lambda(1405)$. Further, we discuss the possibility of the existence of an isovector state, with the mass similar to $\Lambda(1405)$, which we refer to as $\Sigma(1400)$. With the idea of motivating experimental investigations of $\Sigma(1400)$, we have studied its photoproduction process and determined the respective cross sections and polarization observables. We have studied also the coupling of $N^*(1895)$ to $K\Sigma(1400)$ and found that it gives an important contribution to the cross sections near the threshold. In the process, we have determined the branching ratios of the decay of $N^*(1895)$, to the final states involving $\Lambda(1405)$ and $\Sigma(1400)$, to be in the range of 6-7 MeV. Our findings can motivate consideration of alternative processes in partial wave analyses of experimental data, when studying the properties of $N^*(1895)$.

Calculations of differential momentum transfer spectra for J/ψ photoproduction in heavy-ion collisions * *Supported by the National Natural Science Foundation of China (12005220, 12175223) and MOST (2018YFE0104900)

Understanding the gluonic structure in nuclei is one of the most important goals in modern nuclear physics, for which J/ψ photoproduction is suggested as a powerful tool to probe the gluon density distribution. The experimental investigation of the photoproduction process is conventionally studied in ultra-peripheral heavy-ion collisions, and has recently been extended to hadronic collisions. However, theoretical efforts in hadronic heavy-ion collisions are still lacking in the literature. In this paper, we build up a phenomenological framework to calculate the differential momentum transfer spectra for J/ψ photoproduction in hadronic heavy-ion collisions based on a vector meson dominance model. For the first time, we include the effect of internal photon radiation in the calculations, and we find that the results with internal photon radiation could describe the experimental measurements from STAR very well.

Elastic and inelastic J/ψ photoproduction in p−p collisions at LHC energies: Features of the Weizsäcker-Williams approximation

The $J/\psi$ production originating from elastic and inelastic photoproduction processes in p-p collisions at LHC energies is investigated, where the fragmentation processes are involved. An exact treatment is performed, which adopts the Martin-Ryskin method to weight the contribution from different channels, and can return to Weizs\"{a}cker-Williams approximation (WWA) when $Q^{2}\rightarrow0$. The relevant kinematical relations are also achieved. We present a comprehensive analysis for the feature of WWA by comparing with the exact treatment. The results are expressed in $Q^{2}$, $y$, $z$, $p_{T}$, and $y_{r}$ (rapidity) distributions, and the total cross sections are also estimated. The numerical results indicate that, the incoherent-photon emission can provide the meaningful contribution to elastic photoproduction, and starts to play a very important role in the inelastic processes. The photoproduction and fragmentation processes can improve the contribution of $J/\psi$ production in $p$-$p$ collisions at LHC energies. Moreover, the WWA is only effective in very restricted domains, and the exact treatment is needed to deal accurately with the $J/\psi$ photoproduction, which can naturally avoid double counting and WWA errors.

X17 Discovery Potential in the γN→e^{+}e^{-}N Process at Electron Scattering Facilities.

We propose a direct search for the X17 particle, which was conjectured to explain the ATOMKI ^{8}Be and ^{4}He anomalies, through the dilepton photoproduction process on a nucleon in the photon energy range below or around the pion production threshold. For the scenarios of either pseudoscalar, vector, or axial-vector quantum numbers of the conjectured X17, we use existing constraints to estimate the X17 signal process. For dilepton invariant mass resolutions which have been achieved in previous experiments, a signal-to-background ratio of up to an order of magnitude is found for a neutron target, and, in particular, for the pseudoscalar and vector X17 scenarios.

Probing invisible vector meson decays with the NA64 and LDMX experiments

Electron beam fixed target experiments such as NA64 and LDMX use missing energy-momentum to detect the production of dark matter and other long-lived states. The most studied production mechanism is dark Bremsstrahlung through a vector mediator. In this work, we explore a complementary source of missing energy-momentum signals: Bremsstrahlung photons can convert to hard vector mesons in exclusive photoproduction processes, which then decay to dark matter or other invisible particles, such as neutrinos. We find that existing NA64 data can improve the leading constraints on invisible light vector meson decays, while a future run of LDMX could improve them by up to 5 orders of magnitude. For the examples of a dark photon and a $U(1{)}_{B}$ gauge boson mediator, accounting for meson decays substantially enhances these experiments' sensitivity, especially to thermal relic dark matter of mass ${m}_{\ensuremath{\chi}}\ensuremath{\gtrsim}0.1\text{ }\text{ }\mathrm{GeV}$.

Coherent photoproduction processes in hadronic heavy-ion collisions

Recently, significant abnormal enhancements in <i>J</i>/<i>ψ</i> and dilepton production have been observed in peripheral heavy-ion collisions at very low transverse momentum by the STAR, ALICE and ATLAS Collaborations. The observed excesses cannot be explained by hadronic production combined with the cold and hot medium effects, though it can be well described by coherent photoproduction calculations with nuclear overlap. These experimental and theoretical results provide evidence of coherent photoproduction in hadronic heavy-ion collisions, which suggest novel probes for detecting the properties of quark-gluon plasma (QGP). In this work, we review recent experimental and theoretical progress regarding coherent photoproduction in hadronic heavy-ion collisions.

Validity of equivalent photon spectra and the photoproduction processes in p-p collisions

Through a consistent analysis of the terms neglected in going from the accurate expression to the one of Weizsäcker-Williams approximation (WWA), the validity of equivalent photon spectra is studied, and a modified photon flux of proton is also derived. We take the photoproductions of photons and dileptons as examples, to provide the comparison between the exact results and the ones based on various photon fluxes. We present the results for the distributions in Q2 (virtuality of photons), y and pT, the total cross sections are also estimated. The numerical results show that the modified equivalent photon spectrum reproduces the exact result within less than one percent. And the corrections of photoproduction processes to the dileptons and photons productions are about 20%.