A Study of Jets at the STAR Experiment at the Relativistic Heavy Ion Collider Via Two-particle Correlations PDF Download
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Languages : en
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Jets have been studied in high energy heavy ion collisions by measuring the angular correlation between particles at high transverse momentum. Differences in the yield and shape of the angular correlations as a function of system size give information on the medium produced in the collision. Such modifications can be used to infer the presence of a Quark-Gluon Plasma phase, wherein parton degrees of freedom are manifest over nuclear rather than nucleonic scales. In the present work, two-particle correlations were studied in \(d+Au\) and \(Au+Au\) collisions at \(\sqrt{s_{NN}}\) = 200 GeV measured by the STAR experiment at RHIC. The technique was extended to include pseudo-rapidity, permitting jets to be characterised in two-dimensions, and enabling the jet shape to be studied in greater detail. Corrections were developed for the incomplete detector acceptance and finite two-track resolution. Both unidentified and identified particle correlations were studied, using charged tracks and neutral strange particles \(\Lambda, \overline{\Lambda}\), and \(K^0_{Short}\) reconstructed from their characteristic \(V\)0 decay topology. The focus of the analysis was the correlation peak centred at zero azimuthal separation, which is significantly enhanced in central \(Au+Au\) collisions compared to lighter systems. The modified peak was found to comprise a jet-like peak broadened in the pseudo-rapidity direction, sitting atop a long range pseudo-rapidity correlation. The former is suggestive of jet modification by the medium, and the latter may indicate a medium response to jets. Correlations with identified particles indicated the modified same side peak may in part be formed from particles originating from the underlying event.
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Languages : en
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Jets have been studied in high energy heavy ion collisions by measuring the angular correlation between particles at high transverse momentum. Differences in the yield and shape of the angular correlations as a function of system size give information on the medium produced in the collision. Such modifications can be used to infer the presence of a Quark-Gluon Plasma phase, wherein parton degrees of freedom are manifest over nuclear rather than nucleonic scales. In the present work, two-particle correlations were studied in \(d+Au\) and \(Au+Au\) collisions at \(\sqrt{s_{NN}}\) = 200 GeV measured by the STAR experiment at RHIC. The technique was extended to include pseudo-rapidity, permitting jets to be characterised in two-dimensions, and enabling the jet shape to be studied in greater detail. Corrections were developed for the incomplete detector acceptance and finite two-track resolution. Both unidentified and identified particle correlations were studied, using charged tracks and neutral strange particles \(\Lambda, \overline{\Lambda}\), and \(K^0_{Short}\) reconstructed from their characteristic \(V\)0 decay topology. The focus of the analysis was the correlation peak centred at zero azimuthal separation, which is significantly enhanced in central \(Au+Au\) collisions compared to lighter systems. The modified peak was found to comprise a jet-like peak broadened in the pseudo-rapidity direction, sitting atop a long range pseudo-rapidity correlation. The former is suggestive of jet modification by the medium, and the latter may indicate a medium response to jets. Correlations with identified particles indicated the modified same side peak may in part be formed from particles originating from the underlying event.
Author: Léon Gaillard
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Languages : en
Pages : 182
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Author: Essam Othman Elhalhuli
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Languages : en
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This work has studied the particle composition of jets by determining the ratios p±/p± and K±/p± in Au + Au and d + Au collisions at vsNN = 200 GeV measured by the STAR experiment at RHIC. Jets were found by measuring the angular azimuthal correlation between particles at high transverse momentum. Jets were then identified by their back-to-back correlation. A technique was developed to identify charged particles using their specific ionisation measured in the STAR Time Projection Chamber (TPC). This thesis contains one of the first implementations of using direct photons to tag jets in heavy ion collisions. An attempt was made to extract a trigger sample rich in direct photons from neutral triggers. The hadron ratios were calculated from the jet yields as a function of transverse momentum in each collision system. Although the away side yield is suppressed in central Au + Au, there is no evidence that the relative particle yields are changed. The hadron ratios for the three systems were found to be consistent with simulated p + p events generated using the Pythia Monte Carlo event generator. This reinforces the conclusion that the fragmentation process is unchanged by interactions with the medium.
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Languages : en
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Author: Essam Othman Elhalhuli
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Category :
Languages : en
Pages : 142
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Author: Elizabeth Wingfield Oldag
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Category :
Languages : en
Pages : 320
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For over a decade studies of the strong interaction in extremely dense nuclear environments have been done at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. It is hypothesized that colliding two beams of Au nuclei at relativistic speeds creates an environment of hot dense nuclear matter where the quarks and gluons inside the nucleus, which are normally confined within the protons and neutrons, become deconfined into a soup called the quark-gluon plasma. Since direct observation of this short-lived phase is impossible, many sophisticated analysis techniques attempt to study the early interactions via the final state particles. What has emerged from analyses of the data are two, contradictory paradigms for understanding the results. On the one hand the colliding quarks and gluons are thought to strongly interact and reach thermal equilibrium. The other view is that primary parton-parton scattering leads directly to jet fragmentation with little effect from re-scattering. It is in principle possible to distinguish and perhaps falsify one or both of these models of relativistic heavy ion collisions via the analysis of two-particle correlations among all charged particles produced in [mathematical symbols] = 200 GeV Au+Au collisions at the STAR experiment at RHIC. This dissertation presents studies of two-particle correlations, whose derivation can be traced back to Pearson's correlation coefficient, in transverse momentum and angular space. In momentum space a broad peak is observed extending from 0.5-4.0 GeV/c which, as a function of nuclear overlap, remains at a fixed position while monotonically increasing in amplitude. Comparisons to theoretical models suggests this peak is from jet fragmentation. In a complementary study the momentum distribution of correlations in ([eta],[phi]) space is investigated. The momentum distribution of correlated pairs that contribute to the peak near the origin, commonly associated with jet fragmentation, is peaked around 1.5 GeV/c and does not soften with increased centrality. These measurements present important aspects of the available six dimensional correlation space and provide definitive tests for theoretical models. Preliminary findings do not appear to support the hypothesis of a strongly interacting QGP where back-to-back jets are expected to be significantly suppressed.
Author: Eric Vazquez
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Languages : en
Pages :
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Measurements at the Relativistic Heavy Ion Collider (RHIC) have provided indirect measurements of jets in a heavy ion environment using the two- particle correlation method in the presence of a high-pT particle. These measurements have offered insight into the formation of a new state of dense nuclear matter called the Quark-Gluon Plasma (QGP) through the observation of jet quenching. However, the two-particle methodology has also shown to be biased towards di-jet production near the surface of the medium being created. Here, a detailed study using the PHENIX detector is provided, in an attempt to measure a more accurate jet-induced two-particle correlation measurement than previously published and to reduce the bias observed in two-particle correlation measurements. The reduction in surface bias emission is performed via the requirement of two antipodal high-pT particles (a.k.a. "2+1" correlation) in an attempt to control the production point of the di-jet. The measurements made in Au+Au collisions when compared to p+p collisions show that the method provides additional sensitivity to the jet quenching previously observed in two-particle correlation method.
Author: Li Yi
Publisher: Springer
ISBN: 1493964879
Category : Science
Languages : en
Pages : 97
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This thesis covers several important topics relevant to our understanding of quark-gluon plasma. It describes measurement of the third-order harmonic flow using two-particle correlations and isolation of flow and non-flow contributions to particle correlations in gold-gold collisions. The work also investigates long-range longitudinal correlations in small systems of deuteron-gold collisions. The former is related to the hydrodynamic transport properties of the quark-gluon plasma created in gold-gold collisions. The latter pertains to the question whether hydrodynamics is applicable to small systems, such as deuteron-gold collisions, and whether the quark-gluon plasma can be formed in those small-system collisions. The work presented in this thesis was conducted with the STAR experiment at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, where the center-of-mass energy of both collision systems was a factor of 100 larger than the rest mass of the colliding nuclei. The results contained in this thesis are highly relevant to our quest for deeper understanding of quantum chromodynamics. The results obtained challenge the interpretation of previous works from several other experiments on small systems, and provoke a fresh look at the physics of hydrodynamics and particle correlations pertinent to high energy nuclear collisions.
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Languages : en
Pages : 8
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An overview of the STAR experiment at the Relativistic Heavy Ion Collider is presented. The experiment will concentrate on the measurement of particle production and jet production at midrapidity in a search for the Quark-Gluon Plasma. These hadronic observables will be studied on an event-by-event basis to determine the thermodynamics of single events and to identify special and unusual events. The physics addressed by STAR is discussed.
Author: Abinash Pun
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Category : Heavy ions
Languages : en
Pages :
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The possible presence of Quark-Gluon Plasma (QGP), the new state of matter created at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) in Au+Au and Pb+Pb collisions, is currently under investigation for smaller collisions systems such as light-heavy ions and even p+p. Long range angular correlations of particles produced in p+Pb, p+Au, d+Au, and 3He+Au, show evidence of QGP collective flow, but another signature, QGP-induced jet energy loss effects has not been identified. To address this situation, in this dissertation, a recently introduced observable RI is employed in light-heavy ion collisions. RI is derived from two-particle correlation method commonly used to study jet modification from energy loss in Au+Au.
