共查询到20条相似文献,搜索用时 9 毫秒
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A forward dispersion calculation is implemented for the spin polarizabilities γ1,,γ4 of the proton and the neutron. These polarizabilities are related to the spin structure of the nucleon at low energies and are structure-constants of the Compton scattering amplitude at
. In the absence of a direct experimental measurement of these quantities, a dispersion calculation serves the purpose of constraining the model building, and of comparing with recent calculations in heavy baryon chiral perturbation theory. 相似文献
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本文主要介绍对核子纵向自旋结构函数的实验研究进展。首先简要介绍核子自旋结构的部分理论模型,包括朴素的部份子模型和QCD中的夸克一部份子模型,同时简要介绍标度律和标度律的破坏及其原因;接着介绍实验研究的理论基础,包括弱作用和轻子一核子的深度非弹散射中轴流的作用和几个关于核子自旋结构的求和规则和它们的QCD修正;且简要介绍深度非弹散射实验的研究方法,包括单举测量、半单举和遍举测量。最后,详细介绍实验研究进展,包括对质子和。中子的纵向自旋结构函数的测量,国际上几个主要实验室在不同的能量下,在用不同的靶、不同的束流对不同范围的Bjorken变量x和不同的四动量转移范围Q2下的实验、特点及其结果。最后简略介绍了我国实验物理工作者在该领域的国际合作组的部分工作。 相似文献
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O. Yu. Shevchenko R. R. Akhunzyanov V. Yu. Lavrentyev 《The European Physical Journal C - Particles and Fields》2011,71(8):1713
The first moments of the polarized valence parton distribution functions (PDFs) truncated to the wide Bjorken x region 0.004<x<0.7 are directly (without any fitting procedure) extracted in the next to leading order (NLO) QCD from both COMPASS and HERMES
data on pion production in polarized semi-inclusive DIS (SIDIS) experiments. The COMPASS and HERMES data are combined in two
ways and two scenarios for the fragmentation functions (FFs) are considered. Two procedures are proposed for an estimation
of light sea quark contributions to the proton spin. Both lead to the conclusion that these contributions are compatible with
zero within the errors. 相似文献
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A. V. Efremov K. Goeke P. Schweitzer 《The European Physical Journal C - Particles and Fields》2003,32(3):337-346
Predictions are made for single spin azimuthal asymmetries due to the Collins effect in pion production from semi-inclusive deeply inelastic scattering off transversely and longitudinally polarized targets for the HERMES and COMPASS experiments. The x-dependence of the asymmetries is evaluated using the parton distribution functions from the chiral quark-soliton model. The overall normalization of the predicted asymmetries is determined by the information on the Collins fragmentation function extracted from previous HERMES data on azimuthal asymmetries
from a longitudinally polarized target. The single spin asymmetries A
UT from the transversely polarized proton target are found to be about
for positive and neutral pions both at HERMES and COMPASS. For a longitudinally polarized target we obtain for COMPASS
and
.Received: 18 September 2003, Published online: 26 November 2003 相似文献
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D. Lhuillier 《Progress in Particle and Nuclear Physics》2008,61(1):183-197
We present an introduction to accurate measurements of the weak neutral current in the elastic scattering of longitudinally polarized electrons off hadronic targets, and show how they can provide new and stringent limits on the contribution of strange quarks to the nucleon form factors. Such a contribution is of particular interest for the study of nucleon structure, since strange quarks do not contribute to the valence state and give us a direct insight into the dynamics of quark-antiquark fluctuations. We discuss the latest published results of Happex and G0 experiments as well as the perspectives of high precision measurements of parity violating asymmetries. 相似文献
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G.K.Mallot 《中国物理C(英文版)》2010,34(9)
The Compass experiment at CERN is studying the nucleon spin structure with a 160 GeV polarized muon beam and polarized targets as well as hadron structure with 190 GeV pion, kaon and proton beams. The paper gives an overview of the results for the helicity and transverse spin structure of the nucleon. A first result from the spectroscopy experiments, the observation of a resonance with exotic JPC = 1- + quantum numbers at 1660 MeV is also presented. The paper ends with an outlook to future measurements. 相似文献
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G. K. Mallot 《中国物理 C》2010,34(9):1269-1274
The Compass experiment at CERN is studying the nucleon spin structure with a 160 GeV polarized muon beam and polarized targets as well as hadron structure with 190 GeV pion,kaon and proton beams.The paper gives an overview of the results for the helicity and transverse spin structure of the nucleon.A first result from the spectroscopy experiments,the observation of a resonance with exotic J P C = 1-+ quantum numbers at 1660 MeV is also presented.The paper ends with an outlook to future measurements. 相似文献
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H. E. Jackson 《中国物理 C》2010,34(9):1247-1253
Results are presented from the Hermes experiment which uses semi-inclusive deep inelastic lepton scattering to study the flavor structure of the nucleon.Data have been accumulated for pion and kaon double spin asymmetries,single-spin azimuthal asymmetries for meson electroproduction,deep virtual Compton scattering (DVCS),and meson multiplicities.These results provide information on the properties of the strange sea in the proton,constraints on transverse momentum dependent quark parton distributions,and demonstrate the promise of DVCS for isolating the total angular momentum carried by the quarks in the proton. 相似文献
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H.E.Jackson 《中国物理C(英文版)》2010,34(9)
Results are presented from the Hermes experiment which uses semi-inclusive deep inelastic lepton scattering to study the flavor structure of the nucleon. Data have been accumulated for pion and kaon double spin asymmetries, single-spin azimuthal asymmetries for meson electroproduction, deep virtual Compton scattering (DVCS), and meson multiplicities. These results provide information on the properties of the strange sea in the proton, constraints on transverse momentum dependent quark parton distributions, and demonstrate the promise of DVCS for isolating the total angular momentum carried by the quarks in the proton. 相似文献
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Qinghua Xu 《Frontiers of Physics》2015,10(6):101402
Both the PHENIX and STAR experiments at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory are running polarized proton–proton collisions at s = 200 and 500 GeV. The main goal of the RHIC spin physics program is to gain deeper insight into the spin structure of the nucleon. We will give an overview of recent spin results from RHIC, particularly the study of gluon polarization via jet/hadron production and sea quark polarization via W boson production in longitudinally polarized proton–proton collisions. 相似文献
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E. Zemlyanichkina 《Physics of Particles and Nuclei》2014,45(1):176-178
We present new results on longitudinal inclusive double-spin asymmetry A 1,p (x) in deep-inelastic muon-proton scattering and proton spin-dependent structure function g 1 p (x, Q 2). New COMPASS data on longitudinal polarised NH3 target were collected during the year 2011 with beam of positive muons with energy E = 200 GeV. Kinematical threshold Q 2 ≥ 1 (GeV/c)2 and the fractional energy 0.1 < y < 0.9 allow us to cover low x region down to 0.025. 相似文献
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Several theoretical aspects in leading (1-loop) and higher (2-loop) order as well as various approaches of extracting leading
twist-2 parton distributions from structure function measurements are discussed and summarized. Their implications for the
small-x region (x⩽10−2) are analyzed and compared with alternative approaches where higher twist contributions (‘fans’) are added to the twist-2
LO terms in the evolution equations. The second part of these lectures deals with longitudinally polarized parton distributions
related to the structure functiong
1, in particular with various scenarios to explain the total spin structure of nucleons, including the gluon anomaly as well.
Specific (realistic) tests for discriminating between these alternatives are discussed as well asx-dependent expectations, in particular for neutron targets in connection with the Bjorken sum rule. Furthermore, various theoretical
expectations and sum rules for the transverse (chiral-even) structure functiong
2 are presented and very recent developments of transverse chiral-odd (‘transversity’) distributions are briefly discussed. 相似文献
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The first moments of polarized valence parton distribution functions truncated to the wide Bjorken x region 0.004 < x < 0.7 are directly (without any fitting procedure) extracted in the NLO QCD from combined semi-inclusive DIS data of COMPASS and HERMES collaborations. Two scenarios for fragmentation functions are considered. Applying the proposed original procedure to these results we estimate the contributions of sea u and d quarks to the proton spin, which turn out to be simply zero within the errors. 相似文献
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O. Yu. Shevchenko R. R. Akhunzyanov V. Yu. Lavrentyev 《Physics of Particles and Nuclei》2013,44(3):490-493
The first moments of polarized valence PDFs, responsible for the respective contributions to the nucleon spin, are extracted in NLO QCD from the data of COMPASS and HERMES collaborations on the semi-inclusive difference asymmetries. To this end the new method of QCD analysis (alternative to the usual global fit analysis) is applied. Using the obtained results on valence PDFs the first moments of polarized sea PDFs are reconstructed. They turn out surprisingly small: compatible with zeros within the errors. 相似文献
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