本文报道了$e p \to e' p π^{+} π^{-} $过程的微分截面和完全积分截面上获得的最全面的数据集。这些数据是用杰斐逊实验室的CLAS探测器收集的。测量进行了迄今未探索的运动学区域的光子虚拟0.2 $<$ $Q^{2}$ $<$ 0.6 GeV $^{2}$和不变质量的最终强子系统$W$从1.3到1.57 GeV。第一次，在测量所覆盖的$W$和$Q^{2}$的每个箱中确定了9个独立的1倍微分截面。对数据的现象学分析使我们能够建立起对反应起作用的最重要的机制。非共振机制占截面的主要部分。然而，我们发现敏感性的s-通道激发低质量核子共振，特别是$N(1440)P_{11}$和$N(1520)D_{13}$状态的运动学依赖的1倍微分截面。
英文摘要：
This paper reports on the most comprehensive data set obtained on differential and fully integrated cross sections for the process $e p \to e' p π^{+} π^{-} $. The data were collected with the CLAS detector at Jefferson Laboratory. Measurements were carried out in the so-far unexplored kinematic region of photon virtuality 0.2 $<$ $Q^{2}$ $<$ 0.6 GeV$^{2}$ and invariant mass of the final hadron system $W$ from 1.3 to 1.57 GeV. For the first time, nine independent 1-fold differential cross sections were determined in each bin of $W$ and $Q^{2}$ covered by the measurements. A phenomenological analysis of the data allowed us to establish the most significant mechanisms contributing to the reaction. The non-resonant mechanisms account for a major part of cross-sections. However, we find sensitivity to s-channel excitations of low-mass nucleon resonances, especially to the $N(1440)P_{11}$ and $N(1520)D_{13}$ states in kinematical dependencies of the 1-fold differential cross-sections.
Impressive progress achieved in the past decade in experimental studies of exclusive meson photoproduction off protons and global multi-channel amplitude analyses has resulted in the discovery of several long-awaited new nucleon resonances, with a decisive impact from the results of $KΛ$ and $KΣ$ photoproduction measured with the CLAS detector at Jefferson Lab. Further extension of these efforts towards combined studies of exclusive meson photo- and electroproduction data off protons will be presented. A new excited state of the nucleon, the $N'(1720)3/2^+$, discovered from combined analyses o…
Exclusive $π^+π^-p$ photo- and electroproduction data from CLAS have considerably extended the information on the spectrum and structure of nucleon resonances. The data from the $π^+π^-p$ and $Nπ$ channels have provided results on the electrocouplings of most resonances in the mass region up to 1.8 GeV and at photon virtualities up to 5.0 GeV$^2$. The recent CLAS data on $π^+π^-p$ photoproduction have improved knowledge on the photocouplings of nucleon resonances in the mass range of 1.6 GeV $<$ $M_{N^*}$ $<$ 2.0 GeV and on their decays to the $πΔ$ and $ρp$ final hadron states. For the first t…
The results on the photo- and electroexcitation amplitudes of most nucleon resonances in the mass range up to 2.0 GeV determined from the CLAS experimental data on exclusive $π^+π^-p$ photo-/electroproduction off protons in collaboration between the Jefferson Lab and Moscow State University are presented. The first and only available results on electroexcitation amplitudes from CLAS in a wide range of photon virtualities $Q^2$ $<$ 5.0 GeV$^2$ revealed the nucleon resonance structure as a complex interplay between the inner core of three dressed quarks and external meson-baryon cloud. These res…
The exclusive electroproduction process $ep \rightarrow e'p'π^{0}$ was measured in the range of photon virtualities $Q^{2} = 0.4 - 1.0$~GeV$^{2}$ and the invariant mass range of the $pπ^{0}$ system of $W = 1.1 - 1.8$~GeV. These kinematics are covered in exclusive $π^{0}$ electroproduction off the proton with nearly complete angular coverage in the $pπ^{0}$ center-of-mass system and with high statistical accuracy. Nearly 36000 cross section points were measured, and the structure functions $σ_T+εσ_L$, $σ_{LT}$, and $σ_{TT}$, were extracted via fitting the $ϕ_{π^{0}}$ dependence of the cross sec…
The first results on the $σ_{LT'}$ structure function in exclusive $π^0p$ electroproduction at invariant masses of the final state of 1.5 GeV $<$ $W$ $<$ 1.8 GeV and in the range of photon virtualities 0.4 GeV$^2 < Q^2 < 1.0$ GeV$^2$ were obtained from data on beam spin asymmetries and differential cross sections measured with the CLAS detector at Jefferson Lab. The Legendre moments determined from the $σ_{LT'}$ structure function have demonstrated sensitivity to the contributions from the nucleon resonances in the second and third resonance regions. These new data on the beam spin asymmetries…
We report on a Rosenbluth separation using previously published data by the CLAS collaboration in Hall B, Jefferson Lab for exclusive $π^{0}$ deeply virtual electroproduction (DVEP) from the proton at a mean $Q^{2}$ of $\approx$ 2 (GeV/c)$^{2}$. The central question we address is the applicability of factorization in $π^0$ DVEP at these kinematics. The results of our Rosenbluth separation clearly demonstrate the dominance of the longitudinal contribution to the cross section. The extracted longitudinal and transverse contributions are in agreement with previous data from Hall A at Jefferson La…
Backward-angle electroproduction of $η'$ mesons off protons at $W=2.13~\text{GeV}$ and $Q^{2}=0.46~\left(\text{GeV}/c\right)^{2}$
Tohoku University（东北大学）；Nuclear Physics Institute, CAS（中国科学院近代物理研究所）；Kyoto University（京都大学）；Osaka University（大阪大学）；The University of Tokyo（东京大学）；Hampton University（汉普顿大学）；Virginia Military Institute（弗吉尼亚军事学院）；Thomas Jefferson National Accelerator Facility（托马斯·杰斐逊国家加速器设施）；University of Virginia（弗吉尼亚大学）；University of Zagreb（萨格勒布大学）；California State University, Los Angeles（加州州立大学洛杉矶分校）；The College of William and Mary（威廉与玛丽学院）；University of Tennessee, Knoxville（田纳西大学诺克斯维尔分校）；INFN, Sezione di Roma（意大利国家核物理研究所罗马分部）；Mississippi State University（密西西比州立大学）；Florida International University（佛罗里达国际大学）；Michigan State University（密歇根州立大学）
Pion electroproduction off the proton is analyzed in a new framework based on a general parametrization of transition amplitudes, including constraints from gauge invariance and threshold behavior. Data with energies $1.13~{\rm GeV}<W<1.6~{\rm GeV}$ and $Q^2$ below $6~{\rm GeV}^2$ are included. The model is an extension of the latest Jülich-Bonn solution incorporating constraints from pion-induced and photoproduction data. Performing large scale fits ($\sim10^5$ data) we find a set of solutions with $χ^2_{\rm dof}=1.69-1.81$ which allows us to assess the systematic uncertainty of the approach.
The $^{1}H$($e,e^\prime K^+$)$Λ$ reaction was studied as a function of the Mandelstam variable $-t$ using data from the E01-004 (FPI-2) and E93-018 experiments that were carried out in Hall C at the 6 GeV Jefferson Lab. The cross section was fully separated into longitudinal and transverse components, and two interference terms at four-momentum transfers $Q^2$ of 1.00, 1.36 and 2.07 GeV$^2$. The kaon form factor was extracted from the longitudinal cross section using the Regge model by Vanderhaeghen, Guidal, and Laget. The results establish the method, previously used successfully for pion ana…
TWOPEG: An Event Generator for Charged Double Pion Electroproduction off Proton
已经开发了用于通道$e p \rightarrow e' p' π^{+} π^{-}$的新事件生成器TWOPEG。它使用了先进的方法与权重的事件生成，并采用五倍微分结构函数从最近版本的JM模型适合所有结果带电双π光子和电截面从CLAS（已公布的和初步的）。在CLAS测量数据所覆盖的区域，TWOPEG成功地再现了现有的集成和单差双π截面。为估计数据未涵盖区域的截面，采用了专门的外推程序。EG目前覆盖了从0.0005 GeV $^2$开始的$Q^2$和从反应阈值到4.5 GeV的$W$中的运动学区域。TWOPEG允许从生成的分布中获得截面值并模拟辐射效应。提供了代码的链接。TWOPEG已用于CLAS数据分析和PAC提案准备，并设计用于CLAS12时代。
We report on the first measurement of cross sections for exclusive deeply virtual pion electroproduction off the proton, $e p \to e^\prime n π^+$, above the resonance region at backward pion center-of-mass angles. The $φ^*_π$-dependent cross sections were measured, from which we extracted three combinations of structure functions of the proton. Our results are compatible with calculations based on nucleon-to-pion transition distribution amplitudes (TDAs) and shed new light on nucleon structure.
The analysis of the nine 1-fold differential cross sections for the $γ_{r,v} p \to π^+π^-p$ photo- and electroproduction reactions obtained with the CLAS detector at Jefferson Laboratory was carried out with the goal to establish the contributing resonances in the mass range from 1.6~GeV to 1.8~GeV. In order to describe the photo- and electroproduction data with $Q^2$-independent resonance masses and hadronic decay widths in the $Q^2$ range below 1.5~GeV$^2$, it was found that an $N'(1720)3/2^+$ state is required in addition to the already well-established nucleon resonances. This work demonst…
We investigate $ϕ$-meson electroproduction off the proton target, i.e., $γ^* p \to ϕp$, by employing a tree-level effective Lagrangian approach in the kinematical ranges of $Q^2$ = (0$-$4) $\mathrm{GeV}^2$, $W$ = (2$-$5) GeV, and $|t| \leq 2\,\mathrm{GeV}^2$. In addition to the universally accepted Pomeron exchange, we consider various meson exchanges in the $t$ channel with the Regge method. Direct $ϕ$-meson radiations in the $s$- and $u$-channels are also taken into account. We find that the $Q^2$ dependence of the transverse ($σ_{\mathrm{T}}$) and longitudinal ($σ_{\mathrm{L}}$) cross secti…
Background: Measurements of exclusive meson production are a useful tool in the study of hadronic structure. In particular, one can discern the relevant degrees of freedom at different distance scales through these studies. Purpose: To study the transition between non-perturbative and perturbative Quantum Chromodyanmics as the square of four momentum transfer to the struck proton, -t, is increased. Method: Cross sections for the $^1$H(e,e'$π^+$)n reaction were measured over the -t range of 0.272 to 2.127 GeV$^2$ with limited azimuthal coverage at fixed beam energy of 4.709 GeV, Q$^2$ of 2.4 Ge…
Pion and eta electroproduction data are jointly analyzed for the first time, up to a center-of-mass energy of 1.6 GeV. The framework is a dynamical coupled-channel model, based on the recent Jülich-Bonn-Washington analysis of pion electroproduction data for the same energy range. Comparisons are made to a number of single-channel eta electroproduction fits. By comparing multipoles of comparable fit quality, we find some of these amplitudes are well determined over the near-threshold region, while others will require fits over an extended energy range.
New Results from the Studies of the $N(1440)1/2^+$, $N(1520)3/2^-$, and $Δ(1620)1/2^-$ Resonances in Exclusive $ep \to e'p' π^+ π^-$ Electroproduction with the CLAS Detector
