Helicity-dependent cross sections for the photoproduction of $π^0$ pairs from nucleons

质子外光生双π的束流螺旋度不对称性

Beam-Helicity Asymmetries in Double Pion Photoproduction off the Proton

在美因茨的MAMI加速器上，在三个同位旋通道$\vecγp\to π^{+}π^0n$、$\vecγp\to π^{0}π^0p$和$\vecγp\to π^{+}π^{-}p$中测量了束流螺旋度不对称性。用格拉斯哥磁谱仪标记由纵向极化电子的韧致辐射产生的圆极化光子。利用$~4π$电磁量能器，结合晶体球探测器和TAPS探测器，测量了带电π介子和$π^0$介子的衰变光子。精确测量的不对称性对生产过程的细节非常敏感，因此是反应动力学建模中的关键观测量。

Measurement of the helicity dependence for single $π^{0}$ photoproduction from the deuteron

The helicity-dependent single $π^{0}$ photoproduction cross section on the deuteron and the angular dependence of the double polarisation observable $E$ for the quasi-free single $π^0$ production off the proton and the neutron have been measured for the first time from the threshold region up to the photon energy 1.4 GeV. The experiment was performed at the tagged photon facility of the MAMI accelerator and used a circularly polarised photon beam and longitudinally polarised deuteron target. The reaction products were detected using the large acceptance Crystal Ball/TAPS calorimeter, which cov…

第一和第二共振区的介子光生

Meson photoproduction in the first and second resonance region

本文讨论了在核介质中通过介子与自由质子和核子的光生反应研究重子共振。特别强调中性介子的产生，由于非共振背景的抑制，中性介子特别适合于核子激发态的研究。在过去的十年中，在美因茨微波加速器（MAMI）上用TAPS探测器进行的实验对详细研究低位核子共振P33（1232），D13（1520）和S11（1535）做出了非常重要的贡献。最新的结果，从单和双π介子生产和η-photoregulation进行了总结。

First measurement of helicity-dependent cross sections in pi0-eta photoproduction from quasi-free nucleons

The helicity-dependent cross sections for the photoproduction of $π^0η$ pairs have been measured for the first time. The experiment was performed at the tagged photon facility of the Mainz MAMI accelerator with the combined Crystal Ball - TAPS calorimeter. The experiment used a polarized deuterated butanol target and a circularly polarized photon beam. This arrangement allowed the $σ_{1/2}$ (photon and target spin antiparallel) and $σ_{3/2}$ (parallel spins) components to be measured for quasi-free production of $π^0η$ pairs off protons and neutrons. The main finding is that the two helicity c…

从螺旋度相关的截面研究中子光生{ \boldmath{$η$} }的窄结构

Insight into the narrow structure in {\boldmath{$η$}}-photoproduction on the neutron from helicity dependent cross sections

测量了准自由质子和中子光生$η$的双极化可观测$E$和螺旋度依赖的截面$σ_{1/2}$和$σ_{3/2}$。在美因茨MAMI加速器的A2实验的圆偏振标记光子束与纵向偏振氘代丁醇靶组合使用。Crystal Ball和TAPS的$4π$探测器设置非常适合探测来自$η\rightarrow 2γ$和$η\rightarrow 3π^0$的反冲核子和衰变光子。结果表明，以前在$η$光生中子中观察到的窄结构仅在$σ_{1/2}$中明显，因此，最有可能与自旋-1/2振幅有关。在$η$产生中对该分波有贡献的核子共振只有$N1/2^-$（$S_{11}$）和$N1/2^+$（$P_{11}$）。此外，提取的Legendre系数的角分布$σ_{1/2}$是在最近的反应模型预测假设一个狭窄的共振，在$P_{11}$波作为起源的这种结构是很好的协议。

基于中性π介子光生新极化数据的N（1520）3/2螺旋度振幅的能量无关多极分析

The N(1520) 3/2- helicity amplitudes from an energy-independent multipole analysis based on new polarization data on photoproduction of neutral pions

本文报道了反应$γp \to pπ^0$的极化观测量T、P和H的新数据。结果提取时，横向偏振丁醇目标和线性偏振光子束的方位角不对称性。这些数据是在波恩电子展宽加速器ELSA上用CBELSA/TAPS探测器获得的。这些和早期的数据被用来执行截断的能量独立的分波分析在切片能量箱。这种能量无关的分析相比，从能量依赖的分波分析的结果。

具有π介子光生双极化观测量的核子共振研究

Study of Nucleon Resonances with Double Polarization Observables of Pion Photoproduction

利用Capstick和Roberts预言的共振参数，研究了核子共振在π介子光生双极化观测中的作用.作为一个例子，我们表明，不能很好地确定的两星共振N $^{-}_{3/2}$（1960），可以通过执行实验的光束反冲极化在大角度检查。

介子光生非奇异重子共振研究

Study of Non-Strange Baryon Resonances with Meson Photoproduction

光生介子是研究核子共振态的一个很好的工具。作为对π介子诱导反应的补充，自由质子的光生有助于确定核子共振的基本性质，如激发能、衰变宽度、自旋和与光子的耦合。轻核，特别是氘核的光生反应揭示了核子电磁激发的同位旋结构。在过去几年中，这一领域取得了重大进展。新的加速器设施与最先进的探测器技术相结合，将实验推向了前所未有的灵敏度和精度。实验的进展伴随着反应模型的新发展，这是提取核子态性质所必需的，现代强子模型试图将这些性质与QCD联系起来。这篇评论的重点在于实验方面，并侧重于实验，旨在精确的研究低的核子共振。

Nucleon dissociation and incoherent $J/ψ$ photoproduction on nuclei in ion ultraperipheral collisions at the CERN Large Hadron Collider

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…

轻子对光生中核子的横截性和光子分布振幅的探讨

The nucleon's transversity and the photon's distribution amplitude probed in lepton pair photoproduction

本文提出了一种利用横向极化靶上光生轻子对来计算质子中手征奇横向部分子分布的新方法。基本成分是贝特-海特勒或德雷尔-杨振幅与过程振幅的干涉，其中光子通过其扭转2手征奇分布振幅耦合到夸克。这种方法允许在实验上扫描核子中的横向分布的形状以及光子分布幅度。

Eta and Etaprime Photoproduction on the Nucleon with the Isobar Model EtaMAID2018

The isobar model EtaMAID has been updated with new and high precision data for eta and etaprime photoproduction on protons and neutrons from MAMI, ELSA, GRAAL and CLAS. The background is described in a recently developed Regge-cut model, and for the resonance part the whole list of nucleon resonances has been investigated with 21 N* states contributing to eta photoproduction and 12 N* states contributing to etaprime photoproduction. A new approach is discussed to avoid double counting in the overlap region of Regge and resonances. A comparison is done among four newly updated partial waves ana…

$ηn$ photoproduction and nucleon resonances

We present results of a recent work on the reaction mechanism of $ηn$ photoproduction off the neutron in the range of $ \sqrt{s} \approx 1.5 - 1.9$ GeV and discuss the role of various nucleon resonances listed in the Particle Data Group (PDG). We make use of an effective Lagrangian approach combining with a Regge method. The total and helicity-dependent cross sections $σ_{1/2},\,σ_{3/2}$ are computed and the numerical results are in good agreement with the A2 experimental data.

Photoproduction of $J/ψ$ in d+Au ultraperipheral collisions at the BNL Relativistic Heavy Ion Collider

We argue that the STAR data on $J/ψ$ photoproduction in $d+Au$ ultraperipheral collisions (UPCs) at the momentum transfer $t \neq 0$ primarily probes elastic and possibly nucleon-dissociative $J/ψ$ photoproduction on quasi-free nucleons, while being essentially insensitive to expectedly weak nuclear modifications of the gluon distribution in the deuteron. Analyzing the STAR detector capabilities for selection of UPC events, we explore the possibility that the contribution of nucleon-dissociative $J/ψ$ photoproduction is negligibly small and obtain a very good description of the $t$ dependence …

$K^0Λ$ photoproduction off the neutron with nucleon resonances

We investigate kaon photoproduction off the neutron target, i.e., $γn \to K^0 Λ$, focusing on the role of nucleon resonances given in the Review of Particle Data Group in the range of $\sqrt{s} \approx 1600 - 2200$ MeV. We employ an effective Lagrangian method and a Regge approach. The strong couplings of nucleon resonances with $KΛ$ vertices are constrained by quark model predictions. The numerical results of the total and differential cross sections are found to be in qualitative agreement with the recent CLAS and FOREST experimental data. We discuss the effects of the narrow nucleon resonan…

Effects of nucleon resonances on $η$ photoproduction off the neutron reexamined

We investigate $η$ photoproduction off the neutron target, i.e., $γn \to ηn$, employing an effective Lagrangian method combining with a Regge approach. As a background, we consider nucleon exchange in the $s$-channel diagram and $ρ$- and $ω$-meson Regge trajectories in the $t$ channel. The role of nucleon resonances given in the Review of Particle Data Group in the range of $W \approx 1500 - 2100$ MeV and the narrow nucleon resonance $N(1685,1/2^+)$ is extensively studied. The numerical results of the total and differential cross sections, double polarization observable $E$, and helicity-depen…

核子外标量介子$f_0(500)$和$f_0(980)$的光生

Photoproduction of the scalar mesons $f_0(500)$ and $f_0(980)$ off the nucleon

我们研究光生标量介子的核子，使用有效的拉格朗日和Regge方法。我们首先研究了$f_0(980)$的光生作用，用Regge传播子代替费曼传播子，研究了$t$ -通道中的$ρ$ -介子交换。通过再现微分截面上的实验数据来确定模型参数。然后，我们将相同的方法应用于$f_0(500)$或$σ$的光生，具有相同的参数的Regge传播。由于产生$f_0(500)$的阈值能量相当低，所以$N^*$共振可以在$s$ -通道中发挥作用，该共振可以衰变为处于等序态和标量态的核子和两个π介子。为了检查$N^*$共振的影响，我们建立了两个模型来研究$N^*$共振的各自贡献。我们发现特别是$N^*(1440)$和$N^*(1680)$在$f_0(500)$光产生中起重要作用。我们讨论了目前的结果的物理意义。

核子上前向角度π介子光生反应的Regge现象学

Regge phenomenology of pion photoproduction off the nucleon at forward angles

本文提出了一种基本无参数的Regge模型用于核子前向π介子光生反应，通过经验衰变宽度或SU(3)关系确定交换介子耦合常数，无需拟合即可更好地描述截面和自旋极化不对称性实验数据。

K ~* λ（1116）光生与核子共振

K*Lambda(1116) photoproduction and nucleon resonances

考虑到核子共振的贡献，我们研究了阈值附近质子靶光生K* λ（1116）的反应机制。在树水平玻恩近似下，采用有效拉格朗日方法，我们研究了D13（2080）和D15（2200）的作用。我们发现，D13起着至关重要的作用，再现实验数据以及在前向散射区在低能量。我们还提出了理论预测的单光子束的不对称性，以及能量和角度的依赖性的截面的反应。

轻子对光生中核子的横截性和光子分布振幅的探讨

Probing the nucleon's transversity and the photon's distribution amplitude in lepton pair photoproduction

本文描述了一种通过光生轻子对来获得质子中手征奇横观部分子分布的新方法。基本成分是通常的贝特·海特勒或德雷尔-杨振幅与过程振幅的干涉，其中光子通过其手征奇分布振幅耦合到夸克，该振幅归一化为QCD真空的磁化率。一个有前途的现象学的单，双自旋观测出现从这个振幅的不寻常的功能。

$η$ photoproduction off the deuteron and low-energy $η$-nucleon interaction

We study $η$ photoproduction off the deuteron ($γd\toηpn$) at a special kinematics: $\sim 0.94$ GeV of the photon beam energy and $\sim 0^\circ$ of the scattering angle of the proton. This kinematics is ideal to extract the low-energy $η$-nucleon scattering parameters such as $a_{ηN}$ (scattering length) and $r_{ηN}$ (effective range) because the $η$-nucleon elastic scattering is significantly enhanced. We show that if a ratio $R$, the $γd\toηpn$ cross section divided by the $γp\toηp$ cross section convoluted with the proton momentum distribution in the deuteron, is measured with 5% error, ${\…

利用离子超周边碰撞中高能相干矢量介子光生研究重核中的横核子和胶子分布

Accessing transverse nucleon and gluon distributions in heavy nuclei using coherent vector meson photoproduction at high energies in ion ultraperipheral collisions

本文利用已获得的关于在LHC运行1中Pb-Pb超周边碰撞（UPC）中轻、重矢量介子的$t$积分相干光生数据的理论方法，计算了在LHC运行2中$ρ$和$J/ψ$矢量介子的动量转移分布.我们证明了核遮蔽不仅抑制了截面的绝对值，而且使动量转移分布向更小的动量转移值$|t|$移动。这一结果可以解释为：在$ρ$情况下，核内有效核子密度的碰撞参量空间加宽了14%，在$J/ψ$情况下，核内胶子分布加宽了$5-11$ %.

$K^0Λ$ Photoproduction with Nucleon Resonances

We investigate the reaction mechanism of $K^0 Λ$ photoproduction off the neutron target, i.e., $γn \to K^0 Λ$, in the range of $W\approx 1.6-2.2$ GeV. We employ an effective Lagrangian method at the tree-level Born approximation combining with a Regge approach. As a background, the $K^*$-Reggeon trajectory is taken into account in the $t$ channel and $Λ$ and $Σ$ hyperons in the $u$-channel Feynman diagram. In addition, the role of various nucleon resonances listed in the Particle Data Group (PDG) is carefully scrutinized in the $s$ channel where the resonance parameters are extracted from the …

核子外η光生中窄N（1685）共振的证据

Evidence for a narrow N(1685) resonance in eta photoproduction off the nucleon

本文对GRAAL自由质子光生η的σ束流不对称性进行了修正分析。新的分析揭示了W ~1.685 GeV附近的窄结构。我们通过量子数为P_{11}或P_{13}或D_{13}的窄共振的贡献来描述这种结构。结合最近在W~1.68 GeV中子准自由eta光生中观察到的类似凸点的结构，这一结果为窄（γ < 25 MeV）N*（1685）共振提供了证据。这种可能的新核子态的性质，即质量，窄的宽度，和更强的光耦合到中子，是类似于那些预测的奇异重子的反夸克非奇异成员。

基于CLAS阈值光产生测量的ρ介子-核子散射长度

rho-Meson Nucleon Scattering Length from CLAS Threshold Photoproduction Measurements

本研究利用CLAS阈值光产生数据和介子-重子反应模型，测定ρ介子-核子散射长度，发现其远小于强子尺寸及ω核子散射长度，为强子结构理论研究提供了新的实验依据。

$N(2000)\, 5/2^+$、$N(2060)\,5/2^-$、$N(2120)\,3/2^-$和$N(2190)\,7/2^-$对$K^*Λ$光产生的影响

Effects of $N(2000)\, 5/2^+$, $N(2060)\,5/2^-$, $N(2120)\,3/2^-$, and $N(2190)\,7/2^-$ on $K^*Λ$ photoproduction

我们重新调查的$K^*Λ(1116)$光生的核子目标，有效的拉格朗日方法的基础上。我们包括更高的核子共振，如$N(2000)\, 5/2^+$，$N(2060)\,5/2^-$，$N(2120)\,3/2^-$和$N(2190)\,7/2^-$，其中的数据取自2012年版的粒子物理评论，除了$t$通道图（$K$，$K^*$和$κ$），$s$通道核子和$u$通道超子（$Λ$，$Σ$和$Σ^*$）的贡献。我们发现，$N(2120)\,3/2^-$和$N(2190)\,7/2^-$共振是必不可少的，在描述新的CLAS数据带电$K^*$光生。另一方面，它们很少影响中性PDMATHAMT光生成。

Dynamical model of $ϕ$ meson photoproduction on the nucleon and $^4He$

We investigate $ϕ$ meson photoproduction on the nucleon and the \nuclide[4]{He} targets within a dynamical model approach based on a Hamiltonian which describes the production mechanisms by the Pomeron-exchange, meson-exchanges, $ϕ$ radiations, and nucleon resonance excitations mechanisms. The final $ϕN$ interactions are included being described by the gluon-exchange, direct $ϕN$ couplings, and the box-diagrams arising from the couplings with $πN$, $ρN$, $KΛ$, and $KΣ$ channels. The parameters of the Hamiltonian are determined by the experimental data of $γp \to ϕp$ from the CLAS Collaboration…

$η$ and $η'$ photoproduction with EtaMAID including Regge phenomenology

We present a new version of the EtaMAID model for $η$ and $η'$ photoproduction on nucleons. The model includes 23 nucleon resonances parameterized with Breit-Wigner shapes. The background is described by vector and axial-vector meson exchanges in the $t$ channel using the Regge cut phenomenology. Parameters of the resonances were obtained from a fit to available experimental data for $η$ and $η'$ photoproduction on protons and neutrons. The nature of the most interesting observations in the data is discussed.

Pomeron, nucleon-resonance, and $(0^+,0^-,1^+)$-meson contributions in $ϕ$-meson photoproduction

We investigate the reaction mechanism of the $ϕ$-meson photoproduction off the proton target, i.e., $γp\toϕp$, up to $\sqrt{s}=2.8$ GeV. For this purpose, we employ an effective Lagrangian approach in the tree-level Born approximation, and we employ various experimental and theoretical inputs. As a theoretical setup, the vectorlike Pomeron ($C=+1$) is taken into account as a parameterized two-gluon exchange contribution. We also consider $f_1(1285)$ axial-vector-meson, ($π,η$) pseudoscalar-meson, and ($a_0,f_0$) scalar-meson exchanges in the $t$ channel, in addition to the experimentally confi…

$Λ$碎裂过程中核子和$Λ$ -超子的螺旋度和横截度分布

Helicity and Transversity Distribution of Nucleon and $Λ$-Hyperon from $Λ$ Fragmentation

结果表明，极化核子靶上带电轻子深度非弹性散射（DIS）中的$Λ$ -超子碎裂可以提供有关夸克螺旋度和核子及$x$中$Λ$ -超子横度分布的敏感信息.在SU（6）夸克-旁观者-双夸克模型和微扰QCD（pQCD）模型下，分别计算了靶核子纵向极化和横向极化时产生的$Λ$的自旋转移，并计算了核子和$Λ$的夸克分布.计算结果还表明，质子和中子靶的自旋转移行为不同，这可以为大$x$质子的$d$价夸克的夸克螺旋度和横度分布的不同预测提供灵敏的检验.