Results 1 - 10 of 20183
Results 1 - 10 of 20183. Search took: 0.045 seconds
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[en] We present first results from our analysis of the most general quark-quark correlator of the nucleon, which can be parameterized in terms of so-called generalized transverse momentum dependent parton distributions. These results include the first complete parameterization of the nucleon GPDs and TMDs to all twists as well as new results on possible nontrivial relations between them.
[en] We present results on the system size dependence of high transverse momentum di-hadron correlations at √sNN = 200 GeV as measured by STAR at RHIC. Measurements in d+Au, Cu+Cu and Au+Au collisions reveal similar jet-like correlation yields at small angular separation (Δφ ∼ 0, Δη ∼ 0) for all systems and centralities. Previous measurements have shown that the away-side yield is suppressed in heavy-ion collisions. We present measurements of the away-side suppression as a function of transverse momentum and centrality in Cu+Cu and Au+Au collisions. The suppression is found to be similar in Cu+Cu and Au+Au collisions at a similar number of participants. The results are compared to theoretical calculations based on the parton quenching model and the modified fragmentation model. The observed differences between data and theory indicate that the correlated yields presented here will provide important constraints on medium density profile and energy loss model parameters.
[en] This text includes two papers which accompanied Mr. Della Nigra' paper on present experimental status. The first two chapters give an outline of the problem and intend to include this field of research inside a larger frame. Both following chapters develop a phenomenological analysis of these reaction mechanisms with emphasizing the present practical problems
[fr]Ce texte correspond a deux exposes qui accompagnaient celui de M. Della Negra sur la situation experimentale actuelle. Les deux premieres sections donnent une idee d'ensemble et tachent de placer ce domaine de recherches dans un cadre plus vaste. Les deux sections suivantes developpent l'analyse phenomenologique de ces mecanismes de reactions en insistant sur les questions pratiques actuelles
[en] The conclusions of this paper are: (1) It is possible to study the behavior of SIDIS structure functions at high and low transverse momentum; (2) Both calculations should be correct in the intermediate transverse momentum region; (3) For some structure functions, the two calculations describe the same mechanism and there is an exact matching; (4) For some structure functions, the two calculations describe two different mechanism that are simultaneously present and cannot match (expected mismatches); (5) For some structure functions, the two calculations should describe the same mechanism, but no exact matching is present (unexpected mismatch); (6) The last case indicates a violation of factorization with twist-3 TMD PDFs; and (7) The study has several phenomenological consequences.
[en] Samples of inclusive γ + 2 jet and γ + 3 jet events collected by the D0 experiment with an integrated luminosity of about 1 fb-1 in p(bar p) collisions at √s = 1.96 TeV are used to measure cross sections as a function of the angle in the plane transverse to the beam direction between the transverse momentum (pT) of the γ + leading jet system (jets are ordered in pT) and pT of the other jet for γ + 2 jet, or pT sum of the two other jets for γ + 3 jet events. The results are compared to different models of multiple parton interactions (MPI) in the pythia and sherpa Monte Carlo (MC) generators. The data indicate a contribution from events with double parton (DP) interactions and are well described by predictions provided by the pythia MPI models with pT-ordered showers and by sherpa with the default MPI model. The γ + 2 jet data are also used to determine the fraction of events with DP interactions as a function of the azimuthal angle and as a function of the second jet pT.
[en] Production of multi-hydrogen (mH) isotopes in the spallation of 200A GeV sulphur projectile using nuclear emulsion is reported. Yield of mH isotopes is studied and compared with that of the lowest energy (3.7A GeV) data. The two-source emission picture is used to describe the transverse momentum (P_T ) distribution of mH isotopes (with and without the effect of "3"2S (γ,p) "3"1P channel). The Rayleigh type P_T -distribution seems to be in agreement with the corresponding experimental data. The contributions of low and high temperature emission sources show a dependence on the photonuclear processes. (author)
[en] The 'pretzelosity' distribution is discussed. Theoretical properties, model results, and perspectives to access experimental information on this leading twist, transverse momentum dependent parton distribution function are reviewed. Its relation to helicity and transversity distributions is highlighted.
[en] The early parton momentum distribution is extracted by using the STAR collaboration data of ridge particles associated with a near-side jet in central A uAu collisions at √sNN = 200 GeV. The ridge particles are identified as medium partons kicked by the jet near the surface and they carry direct information on the parton momentum distribution at the moment of jet-parton collisions. The extracted parton momentum distribution has a thermal-like transverse momentum distribution but a rapidity plateau structure with a relatively flat rapidity distribution at mid-rapidities with sharp kinematic boundaries at large rapidities that depend on the transverse momentum.