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Two-particle Azimuthal Correlations of High-pT Charged Hadrons at the CERN SPS

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 Added by Marek Szuba
 Publication date 2011
  fields
and research's language is English
 Authors Marek Szuba




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Two-particle azimuthal correlations of high-pT hadrons can serve as a probe of interactions of partons with the dense medium produced in high-energy heavy-ion collisions. First NA49 results on such correlations are presented for central and mid-central Pb+Pb collisions at 158A GeV beam energy, for different centrality bins and charge combinations of trigger and associate particles. These results feature a flattened away-side peak in the most central collisions, which is consistent with expectations of the medium-interaction scenario. A comparison with CERES Pb+Au results at the same energy, as well as with PHENIX Au+Au results at the top RHIC energy, is provided.



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Results on two-particle $DeltaetaDeltaphi$ correlations in inelastic p+p interactions at 20, 31, 40, 80, and 158~GeV/c are presented. The measurements were performed using the large acceptance NA61/SHINE hadron spectrometer at the CERN Super Proton Synchrotron. The data show structures which can be attributed mainly to effects of resonance decays, momentum conservation, and quantum statistics. The results are compared with the EPOS and UrQMD models.
A measurement of charged hadron pair correlations in two-dimensional $DeltaetaDeltaphi$ space is presented. The analysis is based on total 30 million central Be+Be collisions observed in the NA61/SHINE detector at the CERN SPS for incident beam momenta of 19$A$, 30$A$, 40$A$, 75$A$, and 150$A$ GeV/$c$. Measurements were carried out for unlike-sign and like-sign charge hadron pairs independently. The $C(Deltaeta,Deltaphi)$ correlation functions were compared with results from a similar analysis on p+p interactions at similar beam momenta per nucleon. General trends of the back-to-back correlations are similar in central Be+Be collisions and p+p interactions, but are suppressed in magnitude due to the increased combinatorial background. Predictions from the EPOS and UrQMD models are compared to the measurements. Evolution of an enhancement around $(Deltaeta,Deltaphi) = (0,0)$ with incident energy is observed in central Be+Be collisions. It is not predicted by both models and almost non-existing in proton-proton collisions at the same momentum per nucleon.
We present measurements of three-particle correlations for various harmonics in Au+Au collisions at energies ranging from $sqrt{s_{{rm NN}}}=7.7$ to 200 GeV using the STAR detector. The quantity $langlecos(mphi_1+nphi_2-(m+n)phi_3)rangle$ is evaluated as a function of $sqrt{s_{{rm NN}}}$, collision centrality, transverse momentum, $p_T$, pseudo-rapidity difference, $Deltaeta$, and harmonics ($m$ and $n$). These data provide detailed information on global event properties like the three-dimensional structure of the initial overlap region, the expansion dynamics of the matter produced in the collisions, and the transport properties of the medium. A strong dependence on $Deltaeta$ is observed for most harmonic combinations consistent with breaking of longitudinal boost invariance. Data reveal changes with energy in the two-particle correlation functions relative to the second-harmonic event-plane and provide ways to constrain models of heavy-ion collisions over a wide range of collision energies.
Two particle azimuthal correlations are studied in 4.2A GeV C+Ta collisions observed with the 2-m propane bubble chamber exposed at JINR Dubna Synchrophasotron. The correlations are analyzed both for protons and negative pions, and their dependence on the collision centrality, rapidity and rapidity difference is investigated. It is found that protons show a weak back-to-back correlations, while a side-by-side correlations are observed for negative pions. Restricting both protons to the target or projectile fragmentation region, the side-by-side correlations are observed for protons also. Using the two particle correlation function, the flow analysis is performed and intensity of directed flow is determined without event-by event estimation of the reaction plane.
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