Electroproduction of exclusive $ϕ$ vector mesons has been studied with the CLAS detector in the kinematical range $1.4\leq Q^2\leq 3.8$ GeV$^{2}$, $0.0\leq t^{\prime}\leq 3.6$ GeV$^{2}$, and $2.0\leq W\leq 3.0$ GeV. The scaling exponent for the total cross section as $1/(Q^2+M_ϕ^2)^n$ was determined to be $n=2.49\pm 0.33$. The slope of the four-momentum transfer $t'$ distribution is $b_ϕ=0.98 \pm 0.17$ GeV$^{-2}$. Under the assumption of s-channel helicity conservation (SCHC), we determine the ratio of longitudinal to transverse cross sections to be $R=0.86 \pm 0.24$. A 2-gluon exchange model is able to reproduce the main features of the data.
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…
This work is a pioneering study of backward-angle omega cross sections through the exclusive 1H(e,e'p)omega reaction using the missing mass reconstruction technique. The extracted cross sections are separated into the transverse (T), longitudinal (L), and LT, TT interference terms. The analyzed data were part of experiment E01-004 (Fpi-2), which used 2.6-5.2GeV electron beams and HMS+SOS spectrometers in Jefferson Lab Hall C. The primary objective was to detect coincidence pion in the forward-angle, where the backward-angle omega events were fortuitously detected. The experiment has central Q2…
The study of the spectrum and structure of excited nucleon states employing the electroproduction of exclusive reactions is an important avenue for exploring the nature of the non-perturbative strong interaction. The CLAS detector in Hall~B has provided the dominant part of the available world data on most relevant meson electroproduction channels off the nucleon in the resonance region for $Q^2$ up to 5~GeV$^2$. Analyses of CLAS data for the exclusive channels $πN$, $ηN$, and $π^+ π^- p$ on a proton target have provided the only results available on the $Q^2$ evolution of the electro-excitati…
Beam-recoil transferred polarizations for the exclusive electroproduction of $K^+Λ$ and $K^+Σ^0$ final states from an unpolarized proton target have been measured using the CLAS12 spectrometer at Jefferson Laboratory. The measurements at beam energies of 6.535~GeV and 7.546~GeV span the range of four-momentum transfer $Q^2$ from 0.3 to 4.5~GeV$^2$ and invariant energy $W$ from 1.6 to 2.4~GeV, while covering the full center-of-mass angular range of the $K^+$. These new data extend the existing hyperon polarization data from CLAS in a similar kinematic range but from a significantly larger datas…
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…
Target and beam-target spin asymmetries in exclusive pion electroproduction for $Q^2>1$ GeV$^2$. II. $e p \rightarrow e π^0 p$
测量了专用$π^0$电生成反应$γ^* p \to p π^0$的束靶双自旋不对称性和靶单自旋不对称性，扩展了来自同一实验的$γ^* p \to n π^+$反应的分析。这些结果是用杰斐逊实验室的CEBAF大型接收谱仪从6 GeV的纵向极化电子与纵向极化质子的散射中得到的。所涵盖的运动学范围是$1.1<W<3$ GeV和$1<Q^2<6$ GeV $^2$。在$W$、$Q^2$、\cthcm和$ϕ^*$中获得了约5700个箱的结果。发现波束-目标不对称性通常大于零，具有相对适度的\phicmsp依赖性。靶不对称性表现出非常强的\phicmsp依赖性，与$π^+$电产生相反，在低$W$和高$W$下的结果之间发生符号变化。合理的协议，发现与现象学适合以前的数据$W<1.6$ GeV，但显着差异，在较高的$W$。当结合横截面测量，以及$π^+$观测值，目前的结果将提供强大的约束在中等和大的$Q^2$值的核子共振振幅，共振质量高达2.4 GeV。
We propose to use the High Momentum Spectrometer of Hall C combined with the Neutral Particle Spectrometer (NPS) to perform high precision measurements of the Deeply Virtual Compton Scattering (DVCS) cross section using a beam of positrons. The combination of measurements with oppositely charged incident beams is the only unambiguous way to disentangle the contribution of the DVCS$^2$ term in the photon electroproduction cross section from its interference with the Bethe-Heitler amplitude. This provides a stronger way to constrain the Generalized Parton Distributions of the nucleon. A wide ran…
Probing hard/soft factorization via beam-spin asymmetry in exclusive pion electroproduction from the proton
University of Regina（里贾纳大学）；Thomas Jefferson National Accelerator Facility（托马斯·杰斐逊国家加速器设施）；Catholic University of America（美利坚天主教大学）；University of York（约克大学）；Florida International University（佛罗里达国际大学）；Ohio University（俄亥俄大学）；Research Institute of Basic Sciences, Korea Aerospace University（韩国航空大学基础科学研究院）；Department of Physics, Yonsei University（延世大学物理系）
We present precision measurements of the target and beam-target spin asymmetries from neutral pion electroproduction in deep-inelastic scattering (DIS) using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. We scattered 6-GeV, longitudinally polarized electrons off longitudinally polarized protons in a cryogenic $^{14}$NH$_3$ target, and extracted double and single target spin asymmetries for $ep\rightarrow e^\primeπ^0X$ in multidimensional bins in four-momentum transfer ($1.0<Q^2<3.2$ GeV$^2$), Bjorken-$x$ ($0.12<x<0.48$), hadron energy fraction ($0.4<z<0.7$), transverse pion …
