Meson Photoproduction Research Articles

Partial-wave analysis for photoproduction of pseudoscalar mesons with truncation in total angular momentum

Partial-wave analysis for photoproduction of pseudoscalar mesons with truncation in total angular momentum

Systematic investigation of trace anomaly contribution in nucleon mass

In this work, under the framework of the vector meson dominance model, the trace anomaly contribution value inside neutrons is extracted for the first time based on vector meson photoproduction data. Furthermore, we systematically compare and analyze the trace anomaly contributions of protons and neutrons. The results show that the trace anomaly contributions of protons and neutrons are close, which indirectly confirms that their internal structures and dynamic properties may have certain similarities. In addition, the main factors affecting the extraction of the trace anomaly contribution of nucleons are discussed in detail. This study not only provides a theoretical basis for us to better understand the source of nucleon mass but also makes a useful exploration and discussion on how to extract the trace anomaly contribution of nucleons more accurately in the future. Published by the American Physical Society 2024

Novel cross section ratios as possible signals of saturation in ultraperipheral collisions

We propose new cross section ratios in ultraperipheral A+A and p+A collisions (UPCs) as a potential experimental signal of saturation physics. We consider the ratio R1 of elastic vector meson photoproduction cross section to the inclusive hadron or jet photoproduction cross section. The ratio can be measured in the γ+A and γ+p collisions taking place in the UPCs. We label the ratios R1(A) and R1(p), respectively. Constructing the double ratio RUPC(A)=R1(A)/R1(p), and performing a small-x calculation both in the quasiclassical approximation and by including small-x evolution, we observe that RUPC(A) exhibits a markedly different dependence on the nuclear atomic number inside and outside the saturation region. This result indicates that RUPC(A) and R1(A) measurements in UPCs may help in the experimental searches for the evidence of saturation physics. Published by the American Physical Society 2024

$$\phi $$ Meson Photoproduction on the Nucleon and $${}^4$$He Targets

$$\phi $$ Meson Photoproduction on the Nucleon and $${}^4$$He Targets

Gravitational form factors of the proton from near-threshold vector meson photoproduction* *Supported by the National Natural Science Foundation of China (12065014, 12247101) and the Natural Science Foundation of Gansu province (22JR5RA266). We acknowledge the West Light Foundation of the Chinese Academy of Sciences (21JR7RA201)

We systematically analyze the quark and gluon gravitational form factors (GFFs) of the proton by connecting the energy-momentum tensor and near-threshold vector meson photoproduction (NTVMP). Specifically, the quark contributions of GFFs are determined by applying global fitting to the cross section of the lightest vector meson photoproduction. Combined with the gluon GFFs obtained from heavy quarkonium photoproduction data, the complete GFFs are obtained and compared with the experimental results and lattice quantum chromodynamics determinations. In addition, we use the resonance via Padé (RVP) method based on the Schlessinger point method to obtain a model-independent quark D-term distribution through direct analytical continuation of deeply virtual Compton scattering experimental data. If errors are considered, the results obtained with RVP are essentially consistent with those obtained by NTVMP. Moreover, the comprehensive information on GFFs helps to uncover the mass distribution and mechanical properties inside the proton. This study is not only an important basis for delving into the enigmatic properties of the proton, but also has significance for theoretically guiding future JLab and EIC experimental measurements.

Light vector mesons photoproduction and nuclear shadowing

AbstractIn this work, we study the photoproduction of mesons considering the proton and the nucleus as the target. Utilizing the dipole picture and the wave functions obtained via AdS/QCD, we were able to describe the HERA data and extend the formalism to the nuclear case considering the Glauber–Gribov model. The preliminary results obtained in the nuclear regime are compared to the recent LHC data and suggest the presence of a nuclear effect called shadowing.

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.

Entanglement-enabled spin interference in exclusive J/ψ photoproduction through ultra-peripheral collisions at STAR

In ultra-peripheral collisions (UPC), exclusive vector meson photoproduction, such as ρ0 and J/ψ, serves as a sensitive probe for studying the gluon structure in heavy nuclei. The linear polarization of the photons involved in these processes help to image the nucleus through the so-called entanglement-enabled spin interference in vector meson photoproductions. The photoproduced J/ψ has longer lifetime (2160 fm/c) and non-localized wave function which provides unique opportunity to study the entanglement between the photon and the Pomeron phases emitted from each nucleus. We present the first measurement of the interference pattern for the photoproduced J/ψ in Au+Au UPC at √sNN = 200 with the STAR experiment.

Probing the hidden-bottom pentaquark resonances in photonuclear bottomonium production near threshold: Differential observables

We study the near-threshold ϒ(1S) meson photoproduction from protons and nuclei by considering incoherent direct non-resonant (γp→ϒ(1S)p, γn→ϒ(1S)n) and two-step resonant (γp→Pbi+→ϒ(1S)p, γn→Pbi0→ϒ(1S)n, i=1, 2, 3; Pb1+,0=Pb+,0(11080), Pb2+,0=Pb+,0(11125), Pb3+,0=Pb+,0(11130)) bottomonium production processes with the main goal of clarifying the possibility to observe the non-strange hidden-bottom pentaquark states Pbi+,0 in this production via differential observables. 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 ϒ(1S) mesons on protons, on carbon and tungsten target nuclei at near-threshold incident photon beam energies by assuming the spin-parity assignments of the hypothetical hidden-bottom resonances Pb+,0(11080), Pb+,0(11125) and Pb+,0(11130) as JP=(1/2)−, JP=(1/2)− and JP=(3/2)− within four different realistic choices for the branching ratios of their decays to the ϒ(1S)p and ϒ(1S)n modes (0.125, 0.25, 0.5 and 1%) as well as for two options for the background contribution. We demonstrate that the measurements of these combined observables on proton and nuclear targets in the near-threshold energy region in future experiments at the planned high-luminosity electron-ion colliders EIC and EicC in the US and China should provide evidence for the existence of the above hidden-bottom pentaquark resonances as well as clarify their decay rates.

Ambiguities in partial wave analysis of two spinless meson photoproduction

Ambiguities in partial wave analysis of two spinless meson photoproduction

Exclusive Photo-production of J/Ψ and Ψ(2s) as a tool to explore the transition to high and saturated gluon densities at the LHC.


 
 
 We study the energy dependence of the cross-section for exclusive photo-production of vector mesons J/Ψ and Ψ(2s) and search for signs for the onset of non-linear QCD dynamics in this observable. Our study is based on two dipole models: the Golec-Biernat, Wuesthoff Model (GBW) and the Bartels, Golec-Biernat, Kowal- ski Model (BGK). We find that differences between linear and non-linear implementations of these models are relatively small in the kinematic region probed by both HERA and LHC experiments if the energy dependence of the photo-production cross-section is being considered. We however find that the ratio of both cross-sections grows with energy in the presence of non-linear effects, while it remains approximately constant in the linearized case. The ratio of photo-production cross-sections might therefore provide a suitable tool to characterize the size of non-linear QCD effects at current collider energies.
 
 

Top quark and vector meson production in heavy ion collisions at CMS

Heavy ion collisions are rich and complex systems that involve different aspects of QCD and electromagnetic phenomena. From head-on collisions to the case in which the nuclei miss each other, many of QCD and photo-induced probes are being actively investigated. In this contribution we briefly discuss both of these different topics and some of the CMS results on top quark production and vector meson photo-production, as well as the physics motivation to study these processes are presented.

Exclusive photo- and electroproduction of excited light vector mesons via holographic model

In this paper, we study total and differential observables of electro- and photoproduction of light rho , omega and phi mesons as functions of the center-of-mass energy of the gamma p collision and momentum transfer squared |t|. The corresponding vector mesons wave functions have been computed in the framework of relativistic AdS/QCD holographic approach. A satisfactory description of all available data on ground-state rho (1S), omega (1S) and phi (1S) mesons production cross sections has been achieved in the color dipole picture. Finally, the key observables of excited rho (2S), omega (2S) and phi (2S) states production in gamma ^{(*)} p collisions have been presented here using a common wave function formalism. This study reveals a large theoretical uncertainty coming from the modeling of the partial dipole amplitude in the nonperturbative kinematical domain. Hence, the latter could benefit from future measurements of photoproduction of the excited states.

Challenges to the Good-Walker paradigm in coherent and incoherent photoproduction

High-energy vector meson photoproduction is an important tool for studying the partonic structure of matter at low Bjorken$-x$. In the Good-Walker (GW) paradigm, the cross-section $d\sigma/dt$ for coherent production of vector mesons or other final states, depends the average transverse distribution of gluons, while the incoherent cross-section depends on fluctuations in the nuclear structure, due to variations in nucleon positions, and/or gluonic hot spots. However, predictions of the the GW paradigm seemingly conflict with data from multiple experiments which observe coherent production of vector mesons accompanied by nuclear excitation, or in peripheral relativistic heavy-ion collisions. These data are consistent with a simpler, semi-classical approach. We will discuss this contradiction and explore how and why GW fails. We will also contrast the significant differences in incoherent photoproduction on $^{197}$Au and $^{208}$Pb targets in the GW approach with the much smaller expected differences in their low$-x$ gluon content.

Vector meson photoproduction in UPCs with FoCal

We discuss the physics prospects of photon-induced measurements using the high-granularity FoCal detector to be installed at the ALICE experiment, covering the pseudorapidity interval 3.4 ≤ η ≤ 5.8. This new detector, scheduled to be in operation from Run 4, will explore the small Bjorken-x physics region in an unprecedented way. In this region the gluon ,saturation phenomenon is expected to be dominant. Combined with the rest of the ALICE subdetectors, including the zero degree calorimenters, FoCal will serve to reconstruct in a model-independent way the measured photoproduction cross sections for vectors mesons in a wide range of photon-target energies, down to x values of about 7 × 10−6 and 2 × 10−6 in ultra-peripheral photon–proton and photon–lead collisions, respectively.

Vector meson photoproduction in ALICE at the LHC

Ultra-peripheral collisions (UPC) of heavy ions provide unique opportunity to study vector meson (VM) photoproduction in ALICE. The recent results of analyses of coherent ρ0 photoproduction cross sections in Pb-Pb and Xe-Xe UPC at sNN=5.02 and 5.44 TeV, respectively are presented. Moreover, rapidity and |t| dependence of coherent J/ψ and rapidity dependence of ψ′ photoproduction cross section in Pb-Pb UPC at sNN=5.02TeV are shown. The most recent J/ψ photoproduction and exclusive dimuon cross section studies in p-Pb collisions at sNN=8.16TeV as well as perspectives for future measurements in Run 3 are also discussed in this paper.

Associated $$\phi $$ and $$J/\Psi $$ photoproduction in ultraperipheral PbPb collisions at the Large Hadron Collider and Future Circular Collider

In this paper we analyze the associated $\phi$ and $J/\Psi$ photoproduction in ultraperipheral $PbPb$ collisions through the double scattering mechanism for the energies of the Large Hadron Collider (LHC) and Future Circular Collider (FCC). Our results complement a previous analysis for the $\rho\rho$, $J/\Psi J/\Psi$ and $\rho J/\Psi$ production. We present our predictions for the total cross sections and rapidity distributions considering the rapidity ranges covered by the ALICE and LHCb detectors, which indicate that a future experimental analysis of $\phi J/\Psi$ final state is feasible. These results point out that the study of the double vector meson photoproduction in heavy ion collisions can be useful to constrain the double scattering mechanism and improve our understanding of the QCD dynamics at high energies.

First extraction of the proton mass radius and scattering length $$\vert\alpha_{\rho^{0}p}\vert$$ from ρ0 photoproduction

As it involves the lightest physical states excited from the vacuum by the vector quark current, near-threshold ρ0 photoproduction is considered a possible way to research the proton radius and the absolute value of the scattering lengths of the ρ0-proton interaction. In this study, under the assumption of a scalar form factor of dipole form, the value of the proton mass radius is calculated as (0.85 ± 0.06) fm by fitting the differential cross section of the γp → ρ0p reaction at near-threshold energy. For light vector meson photoproduction, because the exchange of a scalar quark-antiquark pair is not suppressed and should dominate the scalar gluon exchange, the radius we extract from ρ0 photoproduction is likely to represent the quark radius of the proton. This fact may explain why the value obtained in this study is very near the proton charge radius. Moreover, the absolute value of the ρ0-proton scattering length $$\vert\alpha_{\rho^{0}p}\vert=(0.31 \pm 0.06)$$ fm is obtained for the first time within the vector meson dominance model. This result disobeys the rule that the absolute value of the vector meson and proton scattering length $$\vert\alpha_{V_{p}}\vert$$ increases with the meson’s mass, which can be attributed to treating the ρ0 meson as a point in the analysis. These results provide useful theoretical information for an in-depth understanding of proton structure and the proton-vector meson interaction.

Exploration of trace anomaly contribution to proton mass based on light vector meson photoproduction

In the quantum chromodynamics, the mass source of the proton is decomposed into four parts by the energy momentum tensor: quark energy term, gluon energy term, quark mass term and trace anomaly term. And the trace anomaly term is the most crucial contribution for studying the internal structure of the proton. In this work, under the definition of the vector meson dominant model, the trace anomaly contribution of the proton is extracted from the experimental data of light vector mesons rho , omega and phi photoproduction at the near-threshold, which are (0.53pm 0.15)%, (1.47pm 0.48)% and (2.73pm 0.54)%, respectively. Further, combined with the results extracted from the heavy vector meson J/psi photoproduction, the distribution of the trace anomaly contribution with the vector meson mass is given for the first time. These results may provide important theoretical information for determining the range of the trace anomaly contribution and for further understanding the origin of the proton mass.

Pseudoscalar and scalar meson photoproduction interpreted by Regge phenomenology

We have evaluated pseudoscalar and scalar neutral pion photoproduction in $\stackrel{P\vec}{\ensuremath{\gamma}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}p$ and ${a}_{0}^{0}p$ above the resonance region and within Regge phenomenology. Our fit, including GlueX $\mathrm{\ensuremath{\Sigma}}$ pseudoscalar photoproduction data, shows that previous Stanford Linear Accelerator Center (SLAC) $\mathrm{\ensuremath{\Sigma}}$ measurements for $\stackrel{P\vec}{\ensuremath{\gamma}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}p$ above ${E}_{\ensuremath{\gamma}}=4\phantom{\rule{0.16em}{0ex}}\mathrm{GeV}$ vary substantially from SLAC data with more recent measurements made by GlueX in the vicinity of ${E}_{\ensuremath{\gamma}}=9\phantom{\rule{0.16em}{0ex}}\mathrm{GeV}$. The Regge model predicts that the beam polarization asymmetry $\mathrm{\ensuremath{\Sigma}}$ of the scalar meson is opposite to that of pseudoscalar meson photoproduction; however, the cross sections are similar. While the natural parity vector meson exchange is dominant in both cases, the contribution of the unnatural parity pseudovector meson exchange is very small. Using Regge phenomenology, we predicted high-energy behavior for double polarized observables $\mathbb{E}$, $\mathbb{F}$, $\mathbb{G}$, and $\mathbb{H}$ for the reactions $\ensuremath{\gamma}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}p$ and ${a}_{0}^{0}p$.