Measurement of the Beam Asymmetry $Σ$ in the Forward Direction for pi0 Photoproduction
N. Sparks, V. Crede, A. V. Anisovich, J. C. S. Bacelar, R. Bantes, O. Bartholomy, D. Bayadilov, R. Beck, Y. A. Beloglazov, R. Castelijns, D. Elsner, R. Ewald, F… 展开作者
N. Sparks, V. Crede, A. V. Anisovich, J. C. S. Bacelar, R. Bantes, O. Bartholomy, D. Bayadilov, R. Beck, Y. A. Beloglazov, R. Castelijns, D. Elsner, R. Ewald, F. Frommberger, C. Funke, R. Gregor, A. Gridnev, E. Gutz, W. Hillert, P. Hoffmeister, I. Jaegle, J. Junkersfeld, H. Kalinowsky, S. Kammer, Frank Klein, Friedrich Klein, E. Klempt, M. Kotulla, B. Krusche, H. Loehner, I. V. Lopatin, S. Lugert, D. Menze, T. Mertens, J. G. Messchendorp, V. Metag, M. Nanova, V. A. Nikonov, D. Novinski, R. Novotny, M. Ostrick, L. M. Pant, H. Pee, M. Pfeiffer, A. Roy, A. V. Sarantsev, S. Schadmand, C. Schmidt, H. Schmieden, B. Schoch, S. Shende, V. Sokhoyan, A. Suele, V. V. Sumachev, T. Szczepanek, U. Thoma, D. Trnka, R. Varma, D. Walther, C. Wendel, A. Wilson
备注：
11 pages, 10 figures, published in Phys. Rev. C, included LEPS data and MAID 2007 predictions for comparison with our data
Photoproduction of neutral pions has been studied with the CBELSA/TAPS detector for photon energies between 0.92 and 1.68~GeV at the electron accelerator ELSA. The beam asymmetry~$Σ$ has been extracted for $115^\circ < θ_{\rm c.m.} < 155^\circ$ of the $π^0$~meson and for $θ_{\rm c.m.} < 60^\circ$. The new beam asymmetry data improve the world database for photon energies above 1.5~GeV and, by covering the very forward region, extend previously published data for the same reaction by our collaboration. The angular dependence of $Σ$ shows overall good agreement with the SAID parameterization.
The ALICE collaboration performed the first rapidity-differential measurement of coherent J/$ψ$ photoproduction in ultra-peripheral Pb-Pb collisions at a center-of-mass energy $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV. The J/$ψ$ is detected via its dimuon decay in the forward rapidity region ($-4.0 < y < -2.5$) for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 750 $μ$b$^{-1}$. The cross section for coherent J/$ψ$ production is presented in six rapidity bins. The results are compared with theoretic…
We report a new measurement of the beam-spin asymmetry $\boldsymbolΣ$ for the $\vecγ n \rightarrow K^+Σ^-$ reaction using quasi-free neutrons in a liquid-deuterium target. The new dataset includes data at previously unmeasured photon energy and angular ranges, thereby providing new constraints on partial wave analyses used to extract properties of the excited nucleon states. The experimental data were obtained using the CEBAF Large Acceptance Spectrometer (CLAS), housed in Hall B of the Thomas Jefferson National Accelerator Facility (JLab). The CLAS detector measured reaction products from a l…
The GlueX experiment is a photoproduction experiment located at Thomas Jefferson National Lab in Newport News, Virginia. GlueX is capable of making beam asymmetry ($Σ$) measurements using a tagged, linearly-polarized 9 GeV photon beam incident on a hydrogen target. Measurements of the beam asymmetry for the exclusive reactions $γp \rightarrow π^0 p$, $γp \rightarrow ηp$ and $γp \rightarrow η' p$ will provide insight into the meson production mechanisms. GlueX measurements are the first beam asymmetry results for the $η$ and $η'$ in this energy range and are expected to further constrain Regge …
In this paper we propose to investigate the transverse single spin asymmetry in the inelastic $J/Ψ$ photoproduction in $p^\uparrow p$ and $p^\uparrow A$ collisions at RHIC energies. At leading order this process probes the gluon Sivers function. We predict large values for the cross sections, which indicates that its experimental analysis is, in principle, feasible. The rapidity dependence of the single spin asymmetry is presented. We obtain that the asymmetry is strongly dependent on the model used for the gluon Sivers function and that it can be probed by the analysis of the $J/Ψ$ production…
The photoproduction of $ω$ mesons off the proton has been studied in the reaction $γp\to p\,ω$ using the CEBAF Large Acceptance Spectrometer (CLAS) and the frozen-spin target (FROST) in Hall B at the Thomas Jefferson National Accelerator Facility. For the first time, the target asymmetry, $T$, has been measured in photoproduction from the decay $ω\toπ^+π^-π^0$, using a transversely-polarized target with energies ranging from just above the reaction threshold up to 2.8 GeV. Significant non-zero values are observed for these asymmetries, reaching about 30-40% in the third-resonance region. New m…
The BGO-OD experiment at the ELSA accelerator facility uses an energy tagged bremstrahlung photon beam to investigate the internal structure of the nucleon. The setup consists of a highly segmented BGO calorimeter surrounding the target, with a particle tracking magnetic spectrometer at forward angles. BGO-OD is ideal for investigating low momentum transfer processes due to the acceptance and high momentum resolution at forward angles. This enables the investigation of strangeness photoproduction where $t$-channel exchange mechanisms play a dominant role. A detailed understanding of this low-m…
Exclusive dimuon production and coherent charmonium photoproduction at forward rapidity in ultra-peripheral Pb$-$Pb collisions at $\mathbf{\sqrt{s_{\rm NN}}=5.36}$ TeV
European Organization for Nuclear Research（欧洲核子研究中心）
Beam asymmetry for pi+ and pi0 photoproduction on the proton for photon energies from 1.102 to 1.862 GeV
用CEBAF大接收谱仪（CLAS）和能量为1.102 - 1.862 GeV的线偏振光子束测量了γ p -> p π 0和γ p -> n π +反应的束流不对称性。本文介绍了一种从实验数据中提取光束非对称性的傅里叶矩技术。这里报道的结果具有更高的精度和更精细的能量分辨率比以前的测量。我们的两个π介子反应的数据似乎有利于SAID和Bonn-Gatchina散射分析的老美因茨MAID预测。在将目前的光束不对称性集合并入世界数据库之后，用SAID分析进行的探索性拟合表明，与先前拟合相比的最大变化是针对Delta（1700）3/2-和Delta（1905）5/2+状态的性质。
The beam-helicity asymmetry was measured, for the first time, in photoproduction of $π^{0}η$ pairs on carbon, aluminum, and lead, with the A2 experimental setup at MAMI. The results are compared to an earlier measurement on a free proton and to the corresponding theoretical calculations. The Mainz model is used to predict the beam-helicity asymmetry for the nuclear targets. The present results indicate that the photoproduction mechanism for $π^{0}η$ pairs on nuclei is similar to photoproduction on a free nucleon. This process is dominated by the $D_{33}$ partial wave with the $ηΔ(1232)$ interm…
$K^+Λ(1405)$ photoproduction has been studied at the BGOOD experiment via the all neutral decay, $Λ(1405)\rightarrowΣ^0π^0$. The unique BGOOD experimental setup allows both the cross section and $Λ(1405)$ invariant mass distribution (line shape) to be measured over a broad $K^+$ polar angle range, extending to extreme forward $K^+$ angles unattainable at previous experiments. Evidence is provided for the role of a triangle singularity driven by the $N^*(2030)$ resonance, which appears to contribute significantly to $K^+Λ(1405)$ photoproduction. This is observed in both the angular distribution…
$γp \rightarrow K^+ Λ$ differential cross sections and recoil polarisation data from threshold for extremely forward angles are presented. The measurements were performed at the BGOOD experiment at ELSA, utilising the high angular and momentum resolution forward spectrometer for charged particle identification. The data discriminates between conflicting results in the world data set and enable extraction of the cross section as the minimum momentum transfer to the recoiling hyperon is approached.
We report a measurement of the $π^-$ photoproduction beam asymmetry for the reaction $\vecγ p \rightarrow π^- Δ^{++}$ using data from the GlueX experiment in the photon beam energy range 8.2--8.8 GeV. The asymmetry $Σ$ is measured as a function of four-momentum transfer $t$ to the $Δ^{++}$ and compared to phenomenological models. We find that $Σ$ varies as a function of $t$: negative at smaller values and positive at higher values of $|t|$. The reaction can be described theoretically by $t$-channel particle exchange requiring pseudoscalar, vector, and tensor intermediaries. In particular, this…
The BGO-OD experiment at the University of Bonn's ELSA accelerator facility in Germany is ideally suited to investigate photoproduction at extreme forward angles. It combines a highly segmented BGO electromagnetic calorimeter at central angles and an open dipole magnetic spectrometer in the forward direction. This allows the detection of forward going kaons, and complex final states of mixed charge from hyperon decays. Current projects at the BGO-OD experiment include strangeness production of $γp \rightarrow K^+ Λ/Σ^0$ at forward angles, $K^0Σ^0$ with a deuteron target and $K^+Λ(1405)$ line s…
Photoproduction of $Λ$ and $Σ^0$ hyperons using linearly polarized photons
背景：测量偏振可观的反应$\vecγ p \rightarrow K^+ Λ$和$\vecγ p \rightarrow K^+ Σ^0$已执行。这是为研究重子共振谱而设计的测量方案的一部分。目的：对几个偏振观测量的精确测量为唯象拟合提供了严格的约束条件。$\vecγ p \rightarrow K^+ Σ^0$反应的电子束反冲观测值以前还没有报道过。方法：测量是使用线性偏振光子束和CLAS探测器在托马斯杰斐逊国家加速器设施。计算结果的能量范围为1.71GeV，角范围为$<W<$.结果如下：两个反应提取的观测量是束不对称$Σ$，目标不对称$T$，和束反冲双偏振观测量$O_x$和$O_z$。结论：与理论拟合的比较表明，在以前没有数据存在的地区，新的数据包含重要的新信息，并加强了最新的Bonn-Gatchina拟合中使用的共振集的证据。
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…
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…
The GlueX experiment, located in experimental Hall D of Jefferson Lab, seeks to map the spectrum of light mesons in search of exotic hybrid mesons, a predicted class of hadronic states with explicit gluonic degrees of freedom. GlueX is a photoproduction experiment utilizing a linearly polarized photon beam at $E_γ=$ 8-9 GeV and a large acceptance spectrometer. The experiment has already collected orders of magnitude more data than previous experiments at similar energies. We show results on asymmetry measurements in the production of pseudoscalars mesons, which refine our understanding of prod…
The differential cross sections and decay angular distributions for coherent $ϕ$-meson photoproduction from helium-4 have been measured for the first time at forward angles with linearly polarized photons in the energy range $E_γ = \text{1.685-2.385 GeV}$. Thanks to the target with spin-parity $J^{P} = 0^{+}$, unnatural-parity exchanges are prohibited, and thus natural-parity exchanges can be investigated clearly. The decay asymmetry with respect to photon polarization is shown to be very close to the maximal value. This ensures the dominance ($> 94\%$) of natural-parity exchanges in this reac…
The BGO-OD experiment at the ELSA accelerator facility uses an energy tagged bremsstrahlung photon beam to investigate the excitation structure of the nucleon. The setup consists of a highly segmented BGO calorimeter surrounding the target, with a particle tracking magnetic spectrometer at forward angles. BGO-OD is ideal for investigating low momentum transfer processes due to the acceptance and high momentum resolution at forward angles. In particular, this enables the investigation of strangeness photoproduction where t-channel exchange mechanisms play an important role. This also allows acc…
We study tensor meson photoproduction outside of the resonance region, at beam energies of few GeVs. We build a model based on Regge theory that includes the leading vector and axial exchanges. We consider two determinations of the unknown helicity couplings, and fit to the recent a2 photoproduction data from CLAS. Both choices give a similar description of the a2 cross section, but result in different predictions for the parity asymmetries and the f2 photoproduction cross section. We conclude that new measurements of f2 photoproduction in the forward region are needed to pin down the correct …
