共查询到20条相似文献,搜索用时 0 毫秒
1.
The HERMES Collaboration has recently published a set of (correlated) beam charge, beam spin and target spin asymmetries for
the Deeply Virtual Compton Scattering (DVCS) process. This reaction allows in principle to access the Generalized Parton Distributions
(GPDs) of the nucleon. We have fitted, in the QCD leading-order and leading-twist handbag approximation, but in a model-independent
way, this set of data and we report our results for the extracted Compton form factors. In particular, we are able to extract
constrains on the H GPD. 相似文献
2.
We investigate the possibility to acquire information of nuclear generalized parton distribution (GPD) H by studying the deeply virtual Compton scattering (DVCS) off several nuclear targets at the HERMES group (Hadron Electron Ring Accelerator Measurement of Spin). Two different models are used and developed to demonstrate the leading asymmetry amplitude.A^sinФ LU for coherent-enriched and incoherent-enriched parts with both statistical and systematic uncertainties estimated. It is found that a clear enhancement of ratio of nuclear asymmetry A ^AsinФ to free proton asymmetry A^H,sinФ LU in the coherent-enriched region is expected by both models,and a decrease of the ratio in incoherent-enriched region; both give the information about nuclear modifications. It is also possible to distinguish between those two models even under the limited statistics. 相似文献
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一个新的强子态的实验证据在2?7.6GeV正电子轰击氘靶产生的虚光子产物中被发现.HERMES通过分析衰变道K0sp→π+π–p,在K0sp不变质量谱上质量1528±2.6(stat.)±2.1(sys.)MeV处观察到共振峰.该共振峰可以被解释为理论预言的五夸克强子态Θ+(uudds).而K+p不变质量谱上未能观察到共振预示Θ+很可能是同位旋单态. 相似文献
5.
H. Fonvieille V. A. Karmanov 《The European Physical Journal A - Hadrons and Nuclei》2009,42(2):287-298
Contrary to the reaction \( \bar{{p}}\) p \( \rightarrow\) e + e - with a high-momentum incident antiproton on a free target proton at rest, in which the invariant mass M of the e + e - pair is necessarily much larger than the \( \bar{{p}}\) p mass 2m , in the reaction \( \bar{{p}}\) d \( \rightarrow\) e + e - n the value of M can take values near or below the \( \bar{{p}}\) p mass. In the antiproton-deuteron electromagnetic annihilation, this allows to access the proton electromagnetic form factors in the timelike region of q2 near the \( \bar{{p}}\) p threshold. We estimate the cross-section \(d\sigma _{\bar pd \to e^ + e^ - n} /d\mathcal{M}\) for an antiproton beam momentum of 1.5GeV/c. We find that near the \( \bar{{p}}\) p threshold this cross-section is about 1pb/MeV. The case of heavy-nuclei target is also discussed. Elements of experimental feasibility are presented for the process \( \bar{{p}}\) d \( \rightarrow\) e + e - n in the context of the \( \overline{{{\rm P}}}\) ANDA project. 相似文献
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S. B. Dubovichenko 《Physics of Atomic Nuclei》2000,63(5):734-738
The deuteron form factors and tensor polarizations in elastic ed scattering are considered for four versions of the Nijmegen nucleon-nucleon potentials. The numerical deuteron wave functions in these potentials are approximated by a series of Gaussian functions with the result that it can be used in any computations of integrated characteristics. The quality of this approximation of the wave function is exemplified by comparing the results that it produces for the momentum distributions, the quadrupole moment, the D-state probability, and the deuteron radius with the results of the corresponding precise calculations. 相似文献
9.
W. Deconinck 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):653-655
An experimental search for the Θ(1540)- and Λ(1520)-resonance was performed in quasi-real photoproduction on deuterium at the HERMES experiment. While evidence for Θ(1540) was found in the decay channel pK
0
S→pπ
+
π
-, no evidence for the corresponding anti-particle was found. In some models it is expected that the Θ(1540) and the Λ(1520) have similar production mechanisms. The photoproduction cross-sections for the Λ(1520) in the decay channel Λ(1520)→pK
- and the corresponding anti-particle are determined. The partial photoproduction cross-sections for Λ(1520) and ˉ(1520) are obtained as σ
Λ(1520) = 65.3±8.8(stat)±6.9(syst)nb and σ
ˉ(1520) = 9.8±2.6(stat)±0.9(syst)nb, corresponding to a ratio R
Λ(1520) = σ
ˉ(1520)/σ
Λ(1520) = 0.15±0.05(stat)±0.02(syst). 相似文献
10.
Using deeply virtual Compton scattering as a tool to study the structure of hadrons in an exclusive process, one expresses the amplitudes in terms of invariant quantities: the Compton form factors. In this paper the sensitivity of the hadronic part of the cross section to the Compton form factors is determined. 相似文献
11.
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
12.
指出了某些教材中康普顿散射示意图画法的不妥之处,并严格推导了康普顿散射中反冲电子的散射角,给出了正确的康普顿散射示意图. 相似文献
13.
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
14.
Photon emission by an electron embedded in a strong external field of general form is studied theoretically. The external
field considered is a plane-wave electromagnetic field of any number of components, period and polarisation. Exact, Volkov
solutions of the Dirac equation with the 4-potential of the general external field are obtained. The photon emission is considered
in the usual perturbation theory using the Volkov solutions to represent the electron. An expression for the transition probability
of this process is obtained after the usual spin and polarisation sums, trace calculation and phase space integration. The
final transition probability in the general case contains a single sum over contributions from external field photons, an
integration over one of the phase space components and the Fourier transforms of the Volkov phases. The validity of the general
expression is established by considering specific external fields. Known specific analytic forms of the transition probability
are obtained after substitution of the 4-potential for a circularly polarised and constant crossed external field. As an example
usage of the general result for the transition probability, the case of two circularly polarised external fields separated
by a phase difference is studied both analytically and numerically. 相似文献
15.
《Nuclear Physics A》1986,455(3):550-560
Methods for the numerical calculation of form factors for many-nucleon transfer reactions are reviewed with the aim of discussing different approximations commonly used. A new procedure is introduced that avoids some of the shortcomings of the previous methods, to which it is compared. 相似文献
16.
Li Ning Liu Chao-Chen Wu Ya-Jie 《The European Physical Journal A - Hadrons and Nuclei》2020,56(9):1-14
The European Physical Journal A - The application of the Point-by-Point treatment to numerous fission cases (i.e. 74 cases including many actinides fissioning spontaneously or induced by thermal... 相似文献
17.
G. Karyan 《Physics of Particles and Nuclei》2014,45(1):85-87
The HERMES collaboration has measured charge-separated pion and kaon multiplicities in semi-inclusive deep inelastic scattering using a 27.6 GeV electron or positron beam scattering off a hydrogen or deuterium target. The results are presented as a function of the Bjorken variable x B , the negative squared four-momentum transfer Q 2, the hadron fractional energy z and it’s transverse momentum P h ⊥. These data will be very useful to understand the quark-fragmentation process in deep-inelastic hadron electro-production and will serve as crucial input in the understanding of spin asymmetries in polarized semi-inclusive deep-inelastic scattering. 相似文献
18.
Ng KL 《Physical review D: Particles and fields》1993,47(11):5187-5190
19.
C. F. Perdrisat 《Physics of Particles and Nuclei》2013,44(6):942-946
There has been much activity in the measurement of the elastic electromagnetic proton and neutron form factors in the last decade, and the quality of the data has been greatly improved by performing double-polarization experiments, in comparison with with previous unpolarized cross section data. Here we will review the experimental data base in view of the new results for the proton and the neutron, obtained at MIT-Bates, JLab and MAMI. The rapid evolution of phenomenological models triggered by these high-precision experiments will be discussed. In particular, the possibility that the proton is non-spherical in its ground state, and that the transverse charge density are model independently defined in the infinite momentum frame. Likewise, flavor decomposition of the nucleon form factors into dressed u and d quark form factors, may give information about the quark-diquark structure of the nucleon. The current proton radius “crisis” will also be discussed. 相似文献
20.
M. Ostrick 《The European Physical Journal A - Hadrons and Nuclei》2006,30(1):81-108
Dynamical and thermal characterizations of excited nuclear systems produced during the collisions between two heavy ions at
intermediate incident energies are presented by means of a review of experimental and theoretical work performed in the last
two decades. Intensity interferometry, applied to both charged particles (light particles and intermediate mass fragments)
and to uncharged radiation (gamma rays and neutrons) has provided relevant information about the space-time properties of
nuclear reactions. The volume, lifetime, density and relative chronology of particle emission from decaying nuclear sources
have been extensively explored and have provided valuable information about the dynamics of heavy-ion collisions. Similar
correlation techniques applied to coincidences between light particles and complex fragments are also presented as a tool
to determine the internal excitation energy of excited primary fragments as it appears in secondary-decay phenomena. 相似文献