Investigations of azimuthal asymmetry in semi-inclusive leptoproduction

We consider the azimuthal asymmetries in semi-inclusive deep inelastic leptoproduction arising due to both perturbative and nonperturbative effects at HERMES energies and show that the order corrections to and are significant. We also reconsider the results of perturbative effects for at large momentum transfers [1] using the more recent sets of scale-dependent distribution and fragmentation functions, which bring up to 18% difference in . In the same approach we calculate the as well. Received: 24 October 1997 / Revised version: 10 February 1998 / Published online: 30 March 1998     

Azimuthal asymmetry in polarized leptoproduction and spin-dependent structure functions

Asymmetry in azimuthal angle distribution of hadrons produced in polarized deep-inelastic lepton-nucleon scattering is discussed. Significant polarization effects are predicted. It is pointed out that such effects can be used as another method to measure the spin-dependent structure functions of the nucleons.     

Determination of an upper limit of the mass of the muonic neutrino from the pion decay in flight

An experiment has been performed to determine an upper limit on m_νμ from pion decay in flight in the forward direction. The kinematical analysis and the inherent calibrations lead to the result: 〈m_νμ²〉 = ?0.14 ± 0.20 (MeV/c²)² (68% CL), (90% CL).     

Dynamical aspects of photonuclear reactions below pion threshold

We study the reactions (γ,p), (γ,n), (γ,pp) and (γ,nn) below pion threshold in view of a systematic treatment of electromagnetic meson exchange currents. As a numerical example we calculate the integrated and differential cross sections for (γ,p) and (γ,n) on ⁴He.     

Single spin asymmetry in inclusive pion production,Collins effect and the string model

We calculated the single spin asymmetry in the inclusive pion production in the fragmentation region of transversely polarized proton-proton collisions. We generated the asymmetry at the level of fragmentation function (Collins effect) by the Lund coloured string mechanism. We compared our results to the presently available experimental data. We obtained a qualitative agreement with the data after assuming that the transverse polarizations of the u and the d quarks in the proton are +1 and ? 1, respectively, at x_B=1.     

A new beam asymmetry measurement from pion photoproduction on the neutron using CLAS

We present a preliminary analysis of the photon beam asymmetry observable （Z） from the pho- toproduction reaction channel γn → pπ in the invariant mass range 1.6--2.3 GeV. The measurement was obtained using the near-4π CEBAF Large Acceptance Spectrometer （CLAS） at Jefferson Laboratory, USA, employing a linearly polarised photon beam with an energy range 1.1 2.3 GeV, incident on a liquid deuterium target. The measurement will provide new data to address the poorly established neutron excitation spectrum and will greatly expand the sparse world data-set both in energy and angle.     

A new beam asymmetry measurement from pion photoproduction on the neutron using CLAS

We present a preliminary analysis of the photon beam asymmetry observable (Σ) from the pho-toproduction reaction channel γn→pπ~- in the invariant mass range 1.6-2.3 GeV. The measurement was obtained using the near-4π CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Laboratory, USA, employing a linearly polarised photon beam with an energy range 1.1-2.3 GeV, incident on a liquid deuterium target. The measurement will provide new data to address the poorly established neutron excitation spectrum and will greatly expand the sparse world data-set both in energy and angle.     

Symmetry aspects of finite-temperature confinement transitions

Analytical and numerical work on confinement phase transitions in finite-temperature Abelian and non-Abelian gauge theories is reviewed. These transitions are order-disorder transitions and their critical properties (if any) can be understood from the standard theory of critical phenomena. Strong coupling, large-N, and non-perturbative lattice methods are discussed. The role of matter fields as symmetry-breaking perturbations is noted as important to the eventual unraveling of the phase structure of quantum chromodynamics.     

General features of single-spin asymmetry in inclusive pion production in fixed-target experiments

Physics of Atomic Nuclei - The results of various experiments that measured a single-spin asymmetry in inclusive pion production are analyzed in the energy range between 13 and 200 GeV. The...     

The ππ total cross section: Its scale and massless pion limit

The question of the scale of the ππ total cross section is considered. We first give a simple intuitive argument for expecting cross sections in the massless chiral world to be finite. Assuming the universality of P-f Regge couplings, we give a simple dispersion theoretic evaluation of the asymptotic ππ total cross section, σ^ππ. We deduce an algebraic expression for σ^ππ and find that its scale is determined by 1/m_?² or, equivalently, 1/f_π² — just as Pagels conjectured. This relation has a smooth, finite limit as m_π tends to zero. Numerically, we obtain σ^ππ = 17 ± 4mb for physical mass pions and 14 ± 3mb for massless pions.     

New limit in the search for spontaneous pion emission from252Cf source

A new experiment was carried out at Modane (Laboratoire Souterrain de Modane, France) to determine the ratio \({{\Gamma _{\pi ^0 } } \mathord{\left/ {\vphantom {{\Gamma _{\pi ^0 } } {\Gamma _{SF} }}} \right. \kern-0em} {\Gamma _{SF} }}\) with a²⁵²Cf source. The very small cosmic ray rate measured on these premises allowed to assign an upper limit of 10^?12 at 95% confidence level to \({{\Gamma _{\pi ^0 } } \mathord{\left/ {\vphantom {{\Gamma _{\pi ^0 } } {\Gamma _{SF} }}} \right. \kern-0em} {\Gamma _{SF} }}\) .     

关于静电屏蔽上限的讨论

将导体壳放入外电场中,导体会在表面产生感应电荷,并达到静电平衡状态,导体壳腔内的电场处处为零,这就是静电屏蔽效应.然而,如果外电场极强,或者导体内部的自由电荷太少,以至于感应电场不能完全抵消外电场,则静电屏蔽效应将失效,这就是静电屏蔽的上限问题.本文从静电屏蔽的原理出发,将导体壳简化为一对平行金属平板的模型,定量的讨论了这一问题.通过计算我们发现,由于金属内存在大量的自由电子,在非极端问题中,宏观的导体装置都远远不会遇到静电屏蔽的上限问题.     

Final-state interaction in spin asymmetry and GDH sum rule for incoherent pion production on the deuteron

The contribution of incoherent single-pion photoproduction to the spin response of the deuteron, i.e., the asymmetry of the total photoabsorption cross-section with respect to parallel and antiparallel spins of photon and deuteron, is calculated over the region of the -resonance with inclusion of final-state NN and rescattering. Sizeable effects, mainly from NN rescattering, are found leading to an appreciable reduction of the spin asymmetry. Furthermore, the contribution to the Gerasimov-Drell-Hearn integral is explicitly evaluated by integration up to a photon energy of 550 MeV. Final-state interaction reduces the value of the integral to about half of the value obtained for the pure impulse approximation.Received: 14 February 2003, Revised: 10 April 2003, Published online: 1 July 2003PACS: 11.55.Hx Sum rules - 13.60.Le Meson production - 24.70.+s Polarization phenomena in reactions - 25.20.Lj Photoproduction reactionsE.M. Darwish: Present address: Physics Department, Faculty of Science, South Valley University, Sohag, Egypt.     

出人意料的电子电偶极矩上限

几十年来,实验物理学家都在尝试利用原子或分子束技术来测量电子的电偶极矩(EDM)。尽管还没有测出电子电偶极矩的具体大小,他们却不断地给出了更精确的电子电偶极矩上限值。这些实验通常在普通实验室的光学平台上进行,却对粒子物理研究有重要价值,而粒子物理实验通常是在巨大的粒子加速器上进行的。不少物理学家认为,EDM实验是用于研究超出粒子物理标准模型的新物理的最快和最廉价的手段。