Recoil polarization and beam-recoil double polarization measurement of ηelectroproduction on the proton in the region of the S_{11}(1535) resonance
H. Merkel, P. Achenbach, C. A. Ayerbe Gayoso, J. C. Bernauer, R. Böhm, D. Bosnar, B. Cheymol, M. O. Distler, L. Doria, H. Fonvieille, J. Friedrich, P. Janssens,… 展开作者
H. Merkel, P. Achenbach, C. A. Ayerbe Gayoso, J. C. Bernauer, R. Böhm, D. Bosnar, B. Cheymol, M. O. Distler, L. Doria, H. Fonvieille, J. Friedrich, P. Janssens, M. Makek, U. Müller, L. Nungesser, J. Pochodzalla, M. Potokar, S. Sánchez Majos, B. S. Schlimme, S. Širca, L. Tiator, Th. Walcher, M. Weinriefer
The beam-recoil double polarization P_{x'}^h and P_{z'}^h and the recoil polarization P_{y'} were measured for the first time for the p(\vec{e},e'\vec{p})ηreaction at a four-momentum transfer of Q^2=0.1 GeV^2/c^2 and a center of mass production angle of θ= 120^\circ at MAMI C. With a center of mass energy range of 1500 MeV < W < 1550 MeV the region of the S_{11}(1535) and D_{13}(1520) resonance was covered. The results are discussed in the framework of a phenomenological isobar model (Eta-MAID). While P_{x'}^h and P_{z'}^h are in good agreement with the model, P_{y'} shows a significant deviation, consistent with existing photoproduction data on the polarized-target asymmetry.
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…
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…
Electroproduction of p π^{+} π^{-} off protons at 0.2<Q^{2}<0.6 GeV^{2} and 1.3<W<1.57 GeV with CLAS
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。
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…
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…
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 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…
We present first measurements of the double ratio of the polarization transfer components $(P^{\prime}_{\!x} \!/ P^{\prime}_{\!z} )_p/ (P^{\prime}_{\!x} \!/ P^{\prime}_{\!z} )_s$ for knock-out protons from $s$ and $p$ shells in $^{12}{\rm C}$ measured by the $^{12}{\rm C}(\vec{e},{e}'\vec{p}\,)$ reaction in quasi-elastic kinematics. The data are compared to theoretical predictions in relativistic distorted-wave impulse approximation. Our results show that differences between $s$- and $p$-shell protons, observed when compared at the same initial momentum (missing momentum) largely disappear whe…
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…
Absolute measurements of neutron fluence are an essential prerequisite of neutron-induced cross section measurements, neutron beam lines characterization and dosimetric investigations. The H(n,p) elastic scattering cross section is a very well known standard used to perform precise neutron flux measurements in high precision measurements. The use of this technique, with proton recoil detectors, is not straightforward below incident neutron energy of 1 MeV, due to a high background in the detected proton spectrum. Experiments have been carried out at the AIFIRA facility to investigate such back…
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…
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
We study the response of EJ-301 liquid scintillator to monochromatic 244.6 $\pm$ 8.4 keV neutrons, targeting the 10-100 keV proton recoil energy interval. Limited experimental information exists for proton light yield in this range, for this or any other organic scintillator. Our results confirm the adequacy of a modified Birks' model, common to all organic scintillator formulations, predicting a marked increase in quenching factor as proton energy approaches the few keV regime. The relevance of this behavior within the context of searches for low-mass particle dark matter is mentioned.
Absolute measurements of neutron flux are an essential prerequisite of neutron-induced cross section measurements, neutron beam lines characterization and dosimetric investigations. A new gaseous detector has been developed for measurements of 0.2 to 2 MeV neutron flux based on proton-recoil process. The detector, consisting of two segmented ionization chambers read by Micromegas technology, has beed conceived to provide quasi-absolute neutron flux measurements with an accuracy of \simeq3%. The gas pressure flexibility makes the telescope non sensitive to γ and electrons background, and theref…
The KOALA experiment measures the differential cross section of (anti)proton-proton elastic scattering over a wide range of four-momentum transfer squared 0.0008 < |t| < 0.1 (GeV/c)$^2$ . The forward scattering parameters and the absolute luminosity can be deduced by analyzing the characteristic shape of the differential cross-section spectrum. The experiment is based on fixed target kinematics and uses an internal hydrogen cluster jet target. The wide range of |t| is achieved by measuring the total kinetic energy of the recoil protons near 90° with a recoil detector, which consists of silicon…
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.
We calculate the contributions of weak magnetism and proton recoil of order O(E^2_e/m^2_N)~10^{-5}, i.e. to next-to-next-to-leading order in the large nucleon mass expansion, to the neutron lifetime and correlation coefficients of the neutron beta decay, where E_e and m_N are the electron energy and the nucleon mass, respectively. We analyze the electron-energy and angular distribution for the neutron beta decay with a polarized neutron, a polarized electron and an unpolarized proton. Together with Wilkinson's corrections (Nucl. Phys. A 377, 474 (1982) and radiative corrections of order O(alph…
Recoil Proton Telescopes and Parallel Plate Avalanche Counters for the $^{235}$U(n,f) cross section measurement relative to H(n,n)H between 10 and 450 MeV neutron energy
