共查询到20条相似文献,搜索用时 15 毫秒
1.
Airapetian A Akopov N Akopov Z Amarian M Andrus A Aschenauer EC Augustyniak W Avakian R Avetissian A Avetissian E Bacchetta A Bailey P Balin D Beckmann M Belostotski S Bianchi N Blok HP Böttcher H Borissov A Borysenko A Bouwhuis M Brüll A Bryzgalov V Capitani GP Cappiluppi M Chen T Ciullo G Contalbrigo M Dalpiaz PF Leo RD Demey M Nardo LD Sanctis ED Devitsin E Nezza PD Düren M Ehrenfried M Elalaoui-Moulay A Elbakian G Ellinghaus F Elschenbroich U Fabbri R Fantoni A Fechtchenko A Felawka L 《Physical review letters》2005,94(1):012002
Single-spin asymmetries for semi-inclusive electroproduction of charged pions in deep-inelastic scattering of positrons are measured for the first time with transverse target polarization. The asymmetry depends on the azimuthal angles of both the pion (phi) and the target spin axis (phi(S)) about the virtual-photon direction and relative to the lepton scattering plane. The extracted Fourier component sin((phi+phi(S))(pi)(UT) is a signal of the previously unmeasured quark transversity distribution, in conjunction with the Collins fragmentation function, also unknown. The component sin((phi-phi(S)(pi)(UT) arises from a correlation between the transverse polarization of the target nucleon and the intrinsic transverse momentum of quarks, as represented by the previously unmeasured Sivers distribution function. Evidence for both signals is observed, but the Sivers asymmetry may be affected by exclusive vector meson production. 相似文献
2.
L. L. Pappalardo 《The European Physical Journal A - Hadrons and Nuclei》2008,38(2):145-148
Transverse target single-spin asymmetries in semi-inclusive deep inelastic scattering allow to study the so-called Collins
and Sivers mechanisms. The first one connects the poorly known fundamental transversity distribution function, describing
the transverse spin-polarization of quarks in a transversely polarized proton, to the Collins fragmentation function, describing
spin-orbit correlations in the hadron formation process. The second one is sensitive to the Sivers function, which correlates
the intrinsic transverse momentum of quarks with the proton’s spin orientation and is related to the orbital angular momentum
of quarks. Preliminary results on azimuthal single target-spin asymmetries in semi-inclusive electro-production of pions and
kaons at the HERMES experiment are presented. The full data set collected with a transversely polarized hydrogen target was
analyzed providing the HERMES most precise results on the Collins and Sivers azimuthal moments.
Original article based on material presented at HADRON 2007. 相似文献
3.
Umberto D?Alesio Leonard Gamberg Zhong-Bo KangFrancesco Murgia Cristian Pisano 《Physics letters. [Part B]》2011,704(5):637-640
We study the process dependence of the Sivers function by considering the impact of color-gauge invariant initial and final state interactions on transverse spin asymmetries in proton-proton scattering reactions within the framework of the transverse momentum dependent (TMD), generalized parton model. To this aim, we consider the azimuthal distribution of leading pions inside a fragmenting jet as well as single inclusive jet asymmetry in polarized proton-proton collisions. In contrast to single inclusive pion production, in both cases we can isolate the Sivers contribution and thereby study its process dependence. The predictions for the Sivers asymmetry obtained with and without inclusion of color gauge factors are comparable in size but with opposite signs. We conclude that both processes represent unique opportunities to discriminate among the two approaches and test the universality properties of the Sivers function in hadronic scattering reactions. 相似文献
4.
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 xB=1. 相似文献
5.
J. Lajoie 《Physics of Particles and Nuclei》2014,45(1):91-92
The PHENIX MPC-EX detector is a Si-W preshower extension to the existing Muon Piston Calorimeters (MPC). The combined detectors will make possible a measurement of the prompt photon single spin asymmetry A N in 200 GeV transversely polarized p + p collisions, which will help elucidate the correlation of the transverse motion of valence partons in the proton with the proton spin. 相似文献
6.
Abelev BI Aggarwal MM Ahammed Z Anderson BD Arkhipkin D Averichev GS Bai Y Balewski J Barannikova O Barnby LS Baudot J Baumgart S Belaga VV Bellingeri-Laurikainen A Bellwied R Benedosso F Betts RR Bhardwaj S Bhasin A Bhati AK Bichsel H Bielcik J Bielcikova J Bland LC Blyth SL Bombara M Bonner BE Botje M Bouchet J Brandin AV Burton TP Bystersky M Cai XZ Caines H Calderón de la Barca Sánchez M Callner J Catu O Cebra D Cervantes MC Chajecki Z Chaloupka P Chattopadhyay S Chen HF Chen JH Chen JY 《Physical review letters》2007,99(14):142003
We report the first measurement of the opening angle distribution between pairs of jets produced in high-energy collisions of transversely polarized protons. The measurement probes (Sivers) correlations between the transverse spin orientation of a proton and the transverse momentum directions of its partons. With both beams polarized, the wide pseudorapidity (-1< or = eta < or = +2) coverage for jets permits separation of Sivers functions for the valence and sea regions. The resulting asymmetries are all consistent with zero and considerably smaller than Sivers effects observed in semi-inclusive deep inelastic scattering. We discuss theoretical attempts to reconcile the new results with the sizable transverse spin effects seen in semi-inclusive deep inelastic scattering and forward hadron production in pp collisions. 相似文献
7.
We investigate the Collins effect in single spin asymmetries (SSAs) of the
process by taking into account the transverse momentum dependence of the microscopic sub-process cross sections, with the transverse momentum in the Collins function integrated over. We find that the asymmetries due to the Collins effect can only explain the available data at best qualitatively, by using our choices of quark distributions in the quark-diquark model and a pQCD-based analysis, together with several options of the Collins function. Our results indicate the necessity to take into account contributions from other effects such as the Sivers effect or twist-3 contributions.Received: 21 June 2004, Revised: 26 November 2004, Published online: 15 February 2005PACS:
13.75.Cs, 13.85.Ni, 13.87.Fh, 13.88. + eJian-Jun Yang: Deceased on June 11, 2004. 相似文献
8.
P. Aurenche Rahul Basu M. Fontannaz 《The European Physical Journal C - Particles and Fields》2011,71(4):1616
We present a next-to-leading order calculation of prompt photon production in deep-inelastic scattering. The calculation involves
direct, fragmentation and resolved contributions. Inclusive as well as isolated photon production cross sections are presented.
The relevance of imposing a transverse momentum cut-off in the virtual-photon proton center-of-mass system rather than in
the laboratory frame is discussed. Whenever possible, a comparison of the theoretical results with recent HERA data is carried
out. 相似文献
9.
J. M. Friedrich 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):620-625
Results for the spin structure of the nucleon from the COMPASS data taking periods 2002 to 2004 are presented. The quark contribution
to the nucleon spin, following from a QCD fit to the new data, turns out to be significantly larger than it was derived from
the previous world data. The new data favour, on the other side, a comparatively small gluon polarisation in the range x
g ≈ 0.1. In the data taken with the deuteron target polarised transversely the related asymmetries are found to be small on
the level of accuracy reached so far, indicating a cancellation of the proton and neutron contributions. This is in agreement,
for both the Collins and the Sivers asymmetry, with recent theoretical calculations. Also, a step towards the understanding
of angular-momentum contributions with COMPASS is taken by the evaluation of asymmetries in exclusive vector meson production. 相似文献
10.
A. Gehrmann-De Ridder T. Gehrmann E. Poulsen 《The European Physical Journal C - Particles and Fields》2006,47(2):395-411
The production of final state photons in deep inelastic scattering originates from photon radiation off leptons or quarks
involved in the scattering process. Photon radiation off quarks involves a contribution from the quark-to-photon fragmentation
function, corresponding to the non-perturbative transition of a hadronic jet into a single, highly energetic photon accompanied
by some limited hadronic activity. Up to now, this fragmentation function was measured only in electron–positron annihilation
at LEP. We demonstrate by a dedicated parton-level calculation that a competitive measurement of the quark-to-photon fragmentation
function can be obtained in deep inelastic scattering at HERA. Such a measurement can be obtained by studying the photon energy
spectra in γ+(0+1)-jet events, where γ denotes a hadronic jet containing a highly energetic photon (the photon jet). Isolated
photons are then defined from the photon jet by imposing a minimal photon energy fraction. For this so-called democratic clustering
approach, we study the cross sections for isolated γ+(0+1)-jet and γ+(1+1)-jet production as well as for the inclusive isolated
photon production in deep inelastic scattering. 相似文献
11.
H. Gao J. P. Chen E. Cisbani X. Jiang J. C. Peng X. Qian L. Y. Zhu 《Few-Body Systems》2007,41(1-2):43-52
A first measurement of single target spin asymmetry (SSA) from semi-inclusive electroproduction of charged pions from a transversely
polarized 3He target in deep-inelastic-scattering kinematics will take data in Hall A at Jefferson Lab in 2008. Such SSA will allow for
an extraction of the much desired information on the Collins and Sivers asymmetry from the “neutron” in order to probe the
quark transversity distributions. The experiment will be a coincidence measurement with the BigBite spectrometer detecting
the scattered electrons and the left-arm HRS spectrometer detecting the charged pions. The prospect of future 11 GeV measurements
at Jefferson Lab in Hall A using a solenoid magnetic detector system is also discussed in this talk.
Correspondence: H. Gao, Department of Physics and the Triangle Universities Nuclear Laboratory, Duke University, Durham, NC
27708, USA 相似文献
12.
A. V. Efremov 《Czechoslovak Journal of Physics》2000,50(1):95-100
The perspectives of two new nonstandard methods of transverse quark polarisation measurement are considered: the jet handedness and the so-called “Collins effect” due to spin dependent T-odd fragmentation function responsible for the left-right asymmetry in fragmenting of transversely polarised quarks. Recent experimental indications in favour of the latter is observed. This makes us hope to use these effects in polarised DIS experiments for transversity measurement. The first estimation of transversity was done by using the azimuthal asymmetry in semi-inclusive DIS recently measured by HERMES and SMC. 相似文献
13.
Qian X Allada K Dutta C Huang J Katich J Wang Y Zhang Y Aniol K Annand JR Averett T Benmokhtar F Bertozzi W Bradshaw PC Bosted P Camsonne A Canan M Cates GD Chen C Chen JP Chen W Chirapatpimol K Chudakov E Cisbani E Cornejo JC Cusanno F Dalton MM Deconinck W de Jager CW De Leo R Deng X Deur A Ding H Dolph PA Dutta D El Fassi L Frullani S Gao H Garibaldi F Gaskell D Gilad S Gilman R Glamazdin O Golge S Guo L Hamilton D Hansen O Higinbotham DW Holmstrom T Huang M Ibrahim HF Iodice M Jiang X Jin G 《Physical review letters》2011,107(7):072003
We report the first measurement of target single spin asymmetries in the semi-inclusive (3)He(e,e'π(±))X reaction on a transversely polarized target. The experiment, conducted at Jefferson Lab using a 5.9 GeV electron beam, covers a range of 0.16 < x < 0.35 with 1.4 < Q(2) < 2.7 GeV(2). The Collins and Sivers moments were extracted from the azimuthal angular dependence of the measured asymmetries. The π(±) Collins moments for (3)He are consistent with zero, except for the π(+) moment at x = 0.35, which deviates from zero by 2.3σ. While the π(-) Sivers moments are consistent with zero, the π(+) Sivers moments favor negative values. The neutron results were extracted using the nucleon effective polarization and measured cross section ratios of proton to (3)He, and are largely consistent with the predictions of phenomenological fits and quark model calculations. 相似文献
14.
Leonard P. Gamberg 《Pramana》2009,72(1):55-68
The naive time reversal odd (‘T-odd’) parton distribution and fragmentation functions are explored. We use the spectator model
framework to study flavour dependence of the Boer-Mulders (h
1⊥ ) and Sivers (f
1T⊥) functions as well as the ‘T-even’ but chiral odd function h
1L⊥. These transverse momentum-dependent parton distribution functions are of significance for the analysis of azimuthal asymmetries
in semi-inclusive deep inelastic scattering, as well as for the overall physical understanding of the distribution of transversely
polarized quarks in unpolarized hadrons. In this context we also consider the Collins mechanism and the fragmentation function
H
1⊥. As a by-product of this analysis we calculate the leading twist unpolarized cos(2ϕ) asymmetry, and sin(2ϕ) single spin asymmetry for a longitudinally polarized target in semi-inclusive deep inelastic scattering.
相似文献
15.
Soffer J 《Physical review letters》2003,91(9):092005
For any inclusive reaction of the type A1(spin 1/2)+A2(spin 1/2)-->B+X, we derive new positivity constraints on spin observables and study their implications for theoretical models in view, in particular, of accounting for future data from the polarized pp collider at Brookhaven RHIC. We find that the single transverse spin asymmetry A(N), in the central region for several processes, for example, jet production, direct photon production, and lepton-pair production, is expected to be such that |A(N)| < or approximately 1/2, rather than the usual bound |A(N)|< or =1. 相似文献
16.
Hard photon emitted from energetic heavy ion collisions is of very interesting since it does not experience the late-stage nuclear interaction, therefore it is useful to explore the early-stage information of matter phase. In this work, we have calculated the impact parameter and beam energy dependence for azimuthal asymmetry, characterized by directed transverse flow parameter F and elliptic asymmetry coeffcient v2, of direct photons and the corresponding free protons in intermediate energy heavy-ion collisions. It is further shown the anti-correlated azimuthal asymmetry between direct photons and free protons. 相似文献
17.
The azimuthal distributions around the jet axis of leading pions produced in the jet fragmentation process in pp collisions are studied within the framework of the so-called generalized parton model. The observable leading-twist azimuthal asymmetries are estimated in kinematic configurations presently investigated at RHIC. It is shown how the main contributions coming from the Collins and Sivers effects can be disentangled. In addition, a test of the process dependence of the Sivers function is provided. 相似文献
18.
We consider photon pair production in hadronic collisions at large mass and small transverse momentum of the pair, assuming that factorization in terms of transverse-momentum dependent parton distributions applies. The unpolarized cross section is found to have azimuthal angular dependencies that are generated by a gluonic version of the Boer-Mulders function. In addition, the single transversely polarized cross section is sensitive to the gluon Sivers function. We present simple numerical estimates for the Boer-Mulders and Sivers effects in diphoton production at RHIC and find that the process would offer unique opportunities for exploring transverse-momentum dependent gluon distributions. 相似文献
19.
Avakian H Bosted P Burkert VD Elouadrhiri L Adhikari KP Aghasyan M Amaryan M Anghinolfi M Baghdasaryan H Ball J Battaglieri M Bedlinskiy I Biselli AS Branford D Briscoe WJ Brooks W Carman DS Casey L Cole PL Collins P Crabb D Crede V D'Angelo A Daniel A Dashyan N De Vita R De Sanctis E Deur A Dey B Dhamija S Dickson R Djalali C Dodge G Doughty D Dupre R El Alaoui A Eugenio P Fegan S Fersch R Forest TA Fradi A Gabrielyan MY Gavalian G Gevorgyan N Gilfoyle GP Giovanetti KL Girod FX Gohn W Gothe RW 《Physical review letters》2010,105(26):262002
We report the first measurement of the transverse momentum dependence of double-spin asymmetries in semi-inclusive production of pions in deep-inelastic scattering off the longitudinally polarized proton. Data have been obtained using a polarized electron beam of 5.7 GeV with the CLAS detector at the Jefferson Lab (JLab). Modulations of single spin asymmetries over the azimuthal angle between lepton scattering and hadron production planes ? have been measured over a wide kinematic range in Bjorken x and virtual photon squared four-momentum Q2. A significant nonzero sin2? single spin asymmetry was observed for the first time indicating strong spin-orbit correlations for transversely polarized quarks in the longitudinally polarized proton. 相似文献
20.
We show that a new beam–spin asymmetry appears in deep inelastic inclusive lepto-production at low transverse momenta when a hadron in the target fragmentation region is observed in association with another hadron in the current fragmentation region. The beam leptons are longitudinally polarized while the target nucleons are unpolarized. This asymmetry is a leading-twist effect generated by the correlation between the transverse momentum of quarks and the transverse momentum of the hadron emitted by the target. Experimental signatures of this effect are discussed. 相似文献