共查询到20条相似文献,搜索用时 31 毫秒
1.
Luís Silva 《Few-Body Systems》2013,54(7-10):1075-1078
2.
M. Vanderhaeghen 《The European Physical Journal A - Hadrons and Nuclei》2003,18(2-3):429-432
We discuss how generalized parton distributions (GPDs) enter in a variety of hard exclusive processes such as deeply virtual Compton scattering (DVCS) and hard meson electroproduction reactions on the nucleon. We show some key observables which are sensitive to the various hadron structure aspects of the GPDs, and discuss their experimental status.Received: 30 September 2002, Published online: 22 October 2003PACS:
13.60.Fz Elastic and Compton scattering - 13.60.Le Meson production - 12.38.Bx Perturbative calculations 相似文献
3.
Eric Weise 《Czechoslovak Journal of Physics》2005,55(1):A27-A34
COMPASS is a fixed target experiment at CERN studying nucleon spin structure in polarised deep inelastic muon nucleon scattering and hadron spectroscopy using hadron beams. The main goal of the COMPASS spin physics program is the measurement of the helicity contribution of the gluons to the nucleon spin, ΔG. This quantity is accessible via the photon-gluon-fusion process which can be selected by open charm production or production of hadron pairs with large transverse momenta. The spin physics program of COMPASS includes also measurements with a transversely polarised target. These allow to measure the transverse structure function.COMPASS has up to now successfully finished three runs with a muon beam of 160 GeV and a longitudinally polarized6LiD target in the years 2002, 2003 and 2004. An overview of the physics addressed by the muon program, with an emphasis on the ΔG/G measurement will be presented. The status of the analysis of the highpt hadron pairs, open charm, longitudinal and transverse asymmetries will be reviewed. 相似文献
4.
P. E. Reimer 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):593-596
The large ˉ(x)/ˉ(x) ratio observed by Fermilab E866/NuSea convincingly demonstrated that the sea is not simply a result of pQCD. Moreover, meson
cloud models also failed to explain fully the observed kinematic dependence. The Drell-Yan mechanism offers a unique, selective
probe of antiquarks in the nucleon. Fermilab has approved a new Drell-Yan experiment, E906, that will exploit this feature
to probe ˉ(x)/ˉ(x) by measuring the ratio of cross-sections for the proton-induced Drell-Yan process on hydrogen to deuterium. When the nucleon
is contained in a nucleus, the nucleon's parton distributions should to be modified; although this effect was not seen in
the sea quark distributions obtained by Fermilab E772 with Drell-Yan scattering. The upcoming E906 Drell-Yan experiment will
provide much more precise measurements over a wider kinematic range in order to guide and challenge the theoretical models. 相似文献
5.
A. Freund 《The European Physical Journal C - Particles and Fields》2003,31(2):203-214
In this paper, I will explain in as simple and intuitive physical terms as possible what generalized parton distributions are, what new information about the structure of hadrons they convey and therefore what picture of the hadron will emerge. To develop this picture, I will use the example of deeply virtual Compton scattering (DVCS) and exclusive meson electroproduction processes. Based on this picture, I will then make some general predictions for these processes.Received: 2 December 2002, Revised: 20 August 2003, Published online: 2 October 2003 相似文献
6.
B. Parsamyan 《Physics of Particles and Nuclei》2014,45(1):158-162
COMPASS is a fixed-target high energy physics experiment at the SPS at CERN [1]. One of the important objectives of the experiment is the exploration of the transverse spin structure of the nucleon via spin dependent azimuthal asymmetries in single-hadron production in deep inelastic scattering of polarized leptons off transversely polarized target. For this purpose a series of measurements were made in COMPASS, using 160 GeV/c longitudinally polarized muon beam and transversely polarized 6LiD (in 2002, 2003 and 2004) and NH3 (in 2007 and 2010) targets. Till now main attention was focused on Collins and Sivers asymmetries and obtained results play an important role in the general understanding of the three-dimensional nature of the nucleon and mechanism of SIDIS processes in terms of Transverse Momentum Dependent (TMD) Parton Distribution Functions (PDFs) and Fragmentation Functions (FFs). In addition to these two measured leading-twist effects, the SIDIS cross-section counts six more target transverse spin dependent azimuthal effects, which have their own well defined leading or higher-twist interpretation in terms of QCD parton model. So far COMPASS presented preliminary results for these asymmetries from deuteron [2, 3] and “proton-2007” data [4]. In this contribution we review the results obtained with the last “proton-2010” data sample. 相似文献
7.
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
8.
Light-front dynamics(LFD) plays an important role in the analyses of relativistic few-body systems. As evidenced from the recent studies of generalized parton distributions (GPDs) in hadron physics, a natural framework for a detailed study of hadron structures is LFD due to its direct application in Minkowski space as well as its distinct feature of accounting for the vacuum fluctuations in quantum field theories. In the last few years, however, it has been emphasized that treacherous points such as LF singularities and zero-modes should be taken into account for successful LFD applications to hadron phenomenology. In this paper, we discuss a typical example of the contemporary relativistic hadron physics in which the fundamental issues should be taken into account for the successful application of LFD. In particular, we focus on the kinematic issue of GPDs in deeply virtual Compton scattering (DVCS). Although this fundamental issue has been glossed over in the literature, it must be taken care of for the correct analysis of DVCS data. 相似文献
9.
Mazouz M Camsonne A Camacho CM Ferdi C Gavalian G Kuchina E Amarian M Aniol KA Beaumel M Benaoum H Bertin P Brossard M Chen JP Chudakov E Craver B Cusanno F de Jager CW Deur A Feuerbach R Fieschi JM Frullani S Garçon M Garibaldi F Gayou O Gilman R Gomez J Gueye P Guichon PA Guillon B Hansen O Hayes D Higinbotham D Holmstrom T Hyde CE Ibrahim H Igarashi R Jiang X Jo HS Kaufman LJ Kelleher A Kolarkar A Kumbartzki G Laveissiere G Lerose JJ Lindgren R Liyanage N Lu HJ Margaziotis DJ Meziani ZE 《Physical review letters》2007,99(24):242501
The present experiment exploits the interference between the deeply virtual Compton scattering (DVCS) and the Bethe-Heitler processes to extract the imaginary part of DVCS amplitudes on the neutron and on the deuteron from the helicity-dependent D(e,e'gamma)X cross section measured at Q2=1.9 GeV2 and xB=0.36. We extract a linear combination of generalized parton distributions (GPDs) particularly sensitive to E_{q}, the least constrained GPD. A model dependent constraint on the contribution of the up and down quarks to the nucleon spin is deduced. 相似文献
10.
P. N. Harriman 《Zeitschrift fur Physik C Particles and Fields》1992,55(3):449-453
We show that knowledge of thex 1 andx 2 dependence of the ratio of Drell-Yan cross-sections measured on heavy nuclei and deuterium can give us information about the origin of the EMC effect. Conversely, we show that an understanding of the EMC effect, together with (non-ratio) Drell-Yan data, can provide us with a way of discriminating between candidates for nucleon parton distributions. 相似文献
11.
G. Sbrizzai 《Physics of Particles and Nuclei》2014,45(1):167-169
The study of the spin structure of the nucleon and of the effects due to the quarks transverse momentum are part of the scientific program of COMPASS, a fixed target experiment at the CERN SPS. The azimuthal modulations which appear in the cross-section of SIDIS off unpolarised targets give insight on the intrinsic momentum structure of the nucleon and on the possible correlation between transverse spin and transverse momentum of the quarks. We present the results for the amplitudes of the cos(?), cos(2?), and sin(?) modulatuions (where ? is the azimuthal hadron angle in the gamma-nucleon system) obtained from the COMPASS data collected with a 160 GeV/c positive muon beam impinging on a deuteron target. The amplitudes are measured for both positive and negative hadrons, and the results on the dependence of the relevant kinematical variables obtained after a multi dimensional analysis are also presented. 相似文献
12.
13.
A. N. Sissakian O. Yu. Shevchenko A. P. Nagaitsev O. N. Ivanov 《Physics of Particles and Nuclei》2010,41(1):64-100
Effects of polarization of hadrons and constituent quarks in Drell-Yan processes are considered; they are one of the most
efficient tools for investigation of the quark structure of hadrons. Special attention is paid to such important parton distribution
functions as the transversity and T-odd Sivers and Boer—Mulders functions whose study is necessary for understanding the effects connected with the nonzero transverse
component of the quark momentum. An original method for direct extraction of transversity and Boer—Mulders function in the
proton from the data on Drell—Yan processes, in which a maximum of one hadron in the initial state is transversely polarized,
is presented. This method possesses a number of important advantages. The method is applied both to Drell—Yan processes with
a valence antiquark (antiproton-proton and pion-proton collisions) and with a sea antiquark (proton-proton, proton-deuteron,
and deuteron-deuteron collisions). Theoretical estimates of asymmetries and cross sections for setups at RHIC (BNL, US), NICA
(JINR, Russia), COMPASS (CERN, Switzerland), PAX (GSI, Germany), and J-PARC (Japan) are presented for evaluation of the measurability
of transversity and T-odd distributions. These theoretical estimates are accompanied by calculations of statistical uncertainties
for measured asymmetries using the new Monte Carlo generator of Drell—Yan events. The duality of Drell—Yan processes and those
of production of J/Φ resonance is studied, and it may allow one to considerably reduce statistical uncertainties of parton distributions. Kinematical
conditions, for which this duality can be observed, are evaluated. 相似文献
14.
M. Quaresma 《Physics of Particles and Nuclei》2014,45(1):333-335
The spin structure of the nucleon and its Parton Distribution Functions (PDFs) are important topics studied by the COMPASS experiment at CERN. So far, the transverse momentum dependent PDFs (TMD PDFs) of the proton and deuteron have been studied in Semi-Inclusive Deep Inelastic Scattering (SIDIS). The Drell-Yan (DY) process is a complementary way to access the TMD PDFs, using a transversely polarised target. Studying the angular distributions of dimuons from the DY events produced in the collisions of a π? beam with 190 GeV/c momentum off a transversely polarised proton target (NH3) we are able to extract the azimuthal spin asymmetries, which are generated by 4 out of the 8 TMD PDFs needed to describe the nucleon structure at leading order QCD. The expected sign change in Sivers and Boer-Mulders functions when accessed from DY and SIDIS will be checked [1]. The opportunity to study, in the same experiment, the TMD PDFs from both SIDIS and DY processes is unique at COMPASS. The COMPASS II Proposal [2] was approved by CERN including one year for polarised DY measurements; the beginning of the DY data taking is scheduled for 2014. The feasibility of the measurement was proven by several beam tests performed so far. 相似文献
15.
P. Kroll 《Physics of Particles and Nuclei》2013,44(6):915-919
Generalized parton distributions (GPDs) extracted from exclusive meson leptoproduction within the handbag approach are briefly reviewed. Only the GPD E is discussed in some detail. Applications of these GPDs to virtual Compton scattering (DVCS) and to Ji’s sum rule are also presented. 相似文献
16.
H.L. Lai J. Huston S. Kuhlmann J. Morfin F. Olness J.F. Owens J. Pumplin W.K. Tung 《The European Physical Journal C - Particles and Fields》2000,12(3):375-392
An up-to-date global QCD analysis of high energy lepton-hadron and hadron-hadron interactions is performed to better determine
the gluon and quark parton distributions in the nucleon. Improved experimental data on inclusive jet production, in conjunction
with precise deep inelastic scattering data, place good constraints on the gluon over a wide range of x; while new data on asymmetries in Drell-Yan processes contribute to better determine the d/u ratio. Comparisons with results of other recent global analyses are made, and the differences are described. Open issues
and the general problem of determining the uncertainties of parton distributions are discussed.
Received: 7 April 1999 / Published online: 21 December 1999 相似文献
17.
E.R. Cazaroto F. Carvalho V.P. Gonçalves M.S. Kugeratski F.S. Navarra 《Physics letters. [Part B]》2011
The exclusive processes in electron–ion (eA) interactions are an important tool to investigate the QCD dynamics at high energies as they are in general driven by the gluon content of the target which is strongly subject to parton saturation effects. In this Letter we compute the cross sections for the exclusive vector meson production as well as the deeply virtual Compton scattering (DVCS) relying on the color dipole approach and considering the numerical solution of the Balitsky–Kovchegov equation including running coupling corrections (rcBK). The production cross sections obtained with the rcBK solution and bCGC parametrization are very similar, the former being slightly larger. 相似文献
18.
Phenomenology of the notion of an unparticle U, recently perceived by Georgi, to describe a scale invariant sector with a nontrivial infrared fixed point at a higher energy scale is explored in details. Behaving like a collection of d(U) (the scale dimension of the unparticle operator O(U)) invisible massless particles, this unparticle can be unveiled by measurements of various energy distributions for the processes Z-->f f U and e- e+-->gammaU at e- e+ colliders, as well as monojet production at hadron colliders. We also study the propagator effects of the unparticle through the Drell-Yan tree-level process and the one-loop muon anomaly. 相似文献
19.
The quantitative impact of NLO-QCD corrections for searches of large and warped extra dimensions at hadron colliders are investigated
for the Drell-Yan process. The K-factor for various observables at hadron colliders are presented. Factorisation, renormalisation
scale dependence and uncertainties due to various parton distribution functions are studied. Uncertainties arising from the
error on experimental data are estimated using the MRST parton distribution functions.
相似文献
20.
D. Sokhan 《Physics of Particles and Nuclei》2014,45(1):170-172
Generalised Parton Distributions (GPDs) offer an insight into the three-dimensional structure of the nucleon and its internal dynamics, relating the longitudinal momentum of quarks to their transverse position. A very effective means of accessing GPDs is via measurements of cross-sections and polarisation-asymmetries in Deeply Virtual Compton Scattering (DVCS). In particular, the beam-spin asymmetry (BSA) in DVCS from the neutron is especially sensitive to angular momentum of the up- and down-quarks, and its measurement therefore has potential to shed important light on the puzzle of nucleon spin. We present a preliminary extraction of BSA from a recent experiment using a 6 GeV electron beam and the CLAS detector at Jefferson Laboratory and introduce the Central Neutron Detector to be integrated with CLAS12 for the exclusive measurement of neutron DVCS at 11 GeV, made possible by the Jefferson Lab upgrade. 相似文献