It has recently been proven that the invariance of observables with respect to angle dependent phase rotations of reaction amplitudes mixes multipoles changing also their relative strength [1]. All contemporary partial wave analyses (PWA) in $η$ photoproduction on protons, either energy dependent (ED) [2-5] or single energy (SE) [6] do not take this effect into consideration. It is commonly accepted that there exist quite some similarity in the $E0+$ multipole for all PWA, but notable differences in this, but also in remaining partial waves still remain. In this paper we demonstrate that once this phase rotations are properly taken into account, all contemporary ED and SE partial wave analysis become almost identical for the dominant $E0+$ multipole, and the agreement among all other multipoles becomes much better. We also show that the the measured observables are almost equally well reproduced for all PWA, and the remaining differences among multipoles can be attributed solely to the difference of predictions for unmeasured observables. So, new measurements are needed.
New high-precision total and differential cross sections for $η$ and $η'$ photoproduction on the proton obtained by the A2 Collaboration at the Mainz Microtron are presented. The data for $η$ photoproduction demonstrate a cusp at the energy W$\sim$1.9~GeV. Furthermore, we present a new version of the $η$MAID model for $η$ and $η'$ photoproduction. The model includes 23 nucleon resonances parametrized with Breit-Wigner shapes. The background is described by vector and axial-vector meson exchanges in the $t$ channel using the Regge phenomenology. Parameters of the resonances were obtained from a…
Photoproduction of eta mesons from nucleons can provide valuable information about the excitation spectrum of the nucleons. The angular dependence of photoproduction in the photon-induced reaction is investigated in the multi-source thermal model. The results are compared with experimental data from the decay mode. They are in good agreement with the experimental data. It is shown that the movement factor increases linearly with the photon beam energies. And, the deformation and translation of emission sources are visually given in the formalism.
In this work, the cross sections of $ϕ$ photoproduction are systematically investigated with the two gluon exchange model and the pomeron model. The results obtained show that the theoretical values of the two models agree well with the experimental data. Since the mass radius and mechanical properties of the proton are encoded in the scalar gravitational form factor of the momentum energy tensor, based on the differential cross sections of $ϕ$ photoproduction at near-threshold predicted by the two gluon exchange model, the average mass radius of the proton is derived as $\sqrt{\left\langle r^…
SAID Analysis of Meson Photoproduction : Determination of Neutron and Proton EM Couplings
我们提出了一个概述的GW SAID组的努力，分析新的π介子光生质子和中子的目标。数据库的主要贡献来自最近的CLAS和MAMI非极化和极化测量。从脉冲近似（IA）中的费米运动效应以及超出IA的NN和piN效应的新测量中提取过程gamma n --> pi-p的微分截面。EM耦合的结果进行了比较，其他最近的研究。
Pion photoproduction off the proton in a gauge-invariant chiral unitary framework
我们在一个明显规范不变的手征么正扩展的手征微扰理论中研究质子光生π介子。在第一步中，我们考虑介子重子散射考虑到所有的次主导级接触相互作用。得到的低能常数由s波π-核子散射和反应pi- p --> eta n的低能数据拟合确定。为了评估理论上的不确定性，我们执行两种不同的拟合策略。在确定了低能常数后，我们分析了π介子和η光生的s波多极振幅E0+的数据。这些都是无参数的预测，因为两个新的低能常数是由中子和质子的磁矩决定的。
As it involves the lightest physical states excited from the vacuum by the vector quark current, near-threshold $ρ^0$ photoproduction is considered a possible way to research the proton radius and the absolute value of the scattering lengths of the $ρ^0$--proton interaction. In this work, under the assumption of a scalar form factor of dipole form, the value of the proton mass radius is calculated as $0.85\pm 0.06 \text{ fm }$ by fitting the differential cross section of the $γp \rightarrow ρ^0 p$ reaction at near-threshold energy. For light vector meson photoproduction, because the exchange o…
We study the inclusive J/psi production at large transverse momenta at lepton-hadron colliders in the limit when the exchange photon is quasi real, also referred to as photoproduction. Our computation includes the leading-P_T leading-v next-to-leading alpha_s corrections. In particular, we consider the contribution from J/psi plus another charm quark, by employing for the first time in quarkonium photoproduction the variable-flavour-number scheme. We also include a QED-induced contribution via an off-shell photon which remained ignored in the literature and which we show to be the leading cont…
We apply the nuclear model with explicit mesons to photoproduction of neutral pions off protons at the threshold. In this model the nucleons do not interact with each other via a potential but rather emit and absorb mesons that are treated explicitly on equal footing with the nucleons. We calculate the total cross section of the reaction for energies close to threshold and compare the calculations with available experimental data. We show that the model is able to reproduce the experimental data and determine the range of the parameters where the model is compatible with the experiment.
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…
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 datas of light vector mesons $ρ$, $ω$ and $ϕ$ photoproduction at the near-threshold, which are ($1.15\pm0.08$)$\%$, ($2.70\pm0.04$)$\%$ a…
A review of our works providing a theoretical description of incoherent pion photoproduction on the deuteron is presented. The existing $γd\toπNN$ data are analysed, especially those obtained more recently by the CLAS Collaboration at JLab, the A2 Collaboration at MAMI at Mainz, and the PION@MAX-lab Collaboration at Lund. A procedure, which accounts for the final state interactions (FSI), is applied to extract $γn\toπN$ differential cross sections from the deuteron data. The role of FSI is discussed. We also comment on the results of other works in connection with some discrepancies seen in co…
Spin-observables in pseudoscalar meson photoproduction is discussed. This work is complementary to the earlier works on this topic. Here, the reaction amplitude is expressed in Pauli-spin basis which allows to calculate all the observables straightforwardly. We make use of the fact that the underlying reflection symmetry about the reaction plane can be most conveniently and easily exploited in this basis to help finding the non-vanishing and independent observables in this reaction. The important issue of complete experiments is reviewed. By expressing the reaction amplitude in Pauli-spin basi…
In this paper we investigate the photoproduction of QED bound states in proton -- proton, proton -- nucleus and nucleus -- nucleus collisions at RHIC, LHC and FCC energies considering an accurate treatment of the absorptive corrections and for the nuclear form factor. The total cross sections for the production of singlet and triplet $(l^+ l^-)$ states, with $l = e,\, μ, \, τ$, are estimated and a detailed analysis of the photoproduction of singlet QED bound states is performed considering the rapidity ranges covered by central and forward detectors. The impact of the Coulomb corrections on th…
Partial wave amplitudes of meson photoproduction reactions are an important source of information in baryon spectroscopy. We investigate a new approach in single-energy partial wave analyses of these reactions. Instead of using a constraint to theoretical models in order to achieve solutions which are continuous in energy, we enforce the analyticity of the amplitudes at fixed values of the Mandelstam variable $t$. We present an iterative procedure with successive fixed-$t$ amplitude analyses which constrain the single-energy partial wave analyses and apply this method to the $γp \to ηp$ reacti…
We report on a theoretical study of the hidden charm $N^*_{c \bar{c}}$ states in the $γp \to \bar{D}^{*0} Λ^+_c$ reaction near threshold within an effective Lagrangian approach. In addition to the contributions from the $s$-channel nucleon pole, the $t$-channel $D^0$ exchange, the $u$-channel $Λ^+_c$ exchange and the contact term, we study the contributions from the $N^*_{c \bar{c}}$ states with spin-parity $J^P = 1/2^-$ and $3/2^-$. The total and differential cross sections of the $γp \to \bar{D}^{*0} Lambda^+_c$ reaction are predicted. It is found that the contributions of these $N^*_{c \bar…
We revisit inclusive J/psi and Upsilon photoproduction at lepton-hadron colliders, namely in the limit when the exchanged photon is quasi real. Our computation includes the next-to-leading-order (NLO) alpha_s corrections to the leading-order contributions in v. Similarly to the case of NLO charmonium-hadroproduction processes, the resulting cross sections obtained in the MS-bar factorisation scheme are sometimes found to be negative. We show that the scale-fixing criteria which we derived in a previous study of eta(c) production successfully solves this problem from the EicC all the way up to …
