Pion Interferometry in AuAu Collisions at a Center of Mass Energy Per Nucleon of 200 GeV

Pion Interferometry in AuAu Collisions at a Center of Mass Energy Per Nucleon of 200 GeV
Author: Mercedes López Noriega
Publisher:
Total Pages:
Release: 2004
Genre: Hadron interactions
ISBN:

Abstract: Quantum Chromodynamics predicts a phase transition from a state formed by hadrons to a plasma of deconfined quarks and gluons, the Quark Gluon Plasma, as a the energy density exceeds a critical value. This deconfined phase is believed to be the one in which the early universe existed in a time-scale [approx.] 10−5 s after the Big Bang. Ultrarelativistic Heavy Ion Collisions, like the ones that take place at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, reach energy densities above the critical value creating a deconfined phase of quarks and gluons that can be studied at the laboratory. This gives us the opportunity to study a phase of matter in the deconfined region of QCD, the properties of the strong interaction, the formation of hadronic matter and the interaction between hadrons. In the analysis presented in this thesis, the dynamical evolution of the particle emitting source and its space-time structure at freeze-out is studied using the two particle intensity interferometry technique. The expansion of the source is also studied. We find indications that this expansion may be caused by the initial pressure gradient generated in the initial stages of the collision through particle rescattering in a very dense medium.

Neutral Kaon Correlations in Au-au Collisions at Center of Mass Energy of 200 GeV Per Nucleon Pair

Neutral Kaon Correlations in Au-au Collisions at Center of Mass Energy of 200 GeV Per Nucleon Pair
Author: Selemon Bekele
Publisher:
Total Pages:
Release: 2004
Genre: Heavy ion collisions
ISBN:

Abstract: A few microseconds after the Big Bang, the universe is believed to have existed in the form of a plasma composed of strongly interacting particles known as quarks and gluons. Although the quarks and gluons behave as asymptotically free particles in a Quark Gluon Plasma (QGP), free quarks and gluons have never been discovered in the laboratory. Experiments at the Relativistic Heavy Ion Collider (RHIC) aim to create conditions similar to the early universe by colliding heavy ions at the highest energies possible in the hope of observing a phase transition from a QGP into hadronic degrees of freedom. The response of the space time structure of the hot reaction zone created in a heavy ion collision to a phase transition is one of the many observables being studied at RHIC. Making use of the techniques of two particle intensity interferometry, also known as the HBT effect, the RHIC experiments are studying the space-time structure and dynamical properties of the region from which particles are emitted. A large spatial size and long duration of particle emission are the predicted signals for a phase transition from a QGP to a hadronic phase. In this thesis we present results on the first measurement of one dimensional K0[subscript s] K0[subscript s] interferometry by the STAR experiment at RHIC in central (small impact parameter) Au-Au collisions at center of mass energy of 200 GeV per nucleon pair. The lambda parameter, which is a measure of the sources chaoticity, is found to be consistent with unity confirming the fact that the source is mostly chaotic as measured by STAR using three particle correlations. Without taking into account the effect of the strong interaction, the invariant radius R inv is found to be large for the mean transverse mass M [subscript t] of the pair, which is about 980 MeV/c, compared to expectations from charged pion correlations at the same M [subscript t]. Including the effect of the strong interactions makes the radius parameter for the K0[subscript s] K0[subscript s] system fall within the charged pion M [subscript t] systematics. Our result serves as a valuable cross-check of charged pion measurements which are mainly affected by contributions from resonance decays and final state interactions. This is also an important first step towards a full three dimensional analysis of neutral kaon correlations as high statistics data from RHIC will be available in the near future.

Pion Interferometry in Au+Au and Cu+Cu Collisions at Sqrt SNN

Pion Interferometry in Au+Au and Cu+Cu Collisions at Sqrt SNN
Author:
Publisher:
Total Pages:
Release: 2009
Genre:
ISBN:

We present a systematic analysis of two-pion interferometry in Au+Au collisions at (square root)sNN = 62.4 GeV and Cu+Cu collisions at (square root)sNN = 62.4 and 200 GeV using the STAR detector at RHIC. The multiplicity and transverse momentum dependences of the extracted correlation lengths (radii) are studied. The scaling with charged particle multiplicity of the apparent system volume at final interaction is studied for the RHIC energy domain. The multiplicity scaling of the measured correlation radii is found to be independent of colliding system and collision energy.

Two-Particle Interferometry of 200 GeV Au+Au Collisions at PHENIX.

Two-Particle Interferometry of 200 GeV Au+Au Collisions at PHENIX.
Author: M. Heffner
Publisher:
Total Pages: 8
Release: 2004
Genre:
ISBN:

The PHENIX experiment has measured pion-pion, kaon-kaon, and proton-proton correlations in Au+Au collisions at {radical}S{sub NN} = 200GeV. The correlations are fit to extract radii using both the Bowler Coulomb correction and full calculation of the two-particle wave function. The resulting radii are similar for all three species and decrease with increasing k{sub t} as expected for collective flow. The R{sub out} and R{sub side} radii are approximately equal indicating a short emission duration.

Elliptic Flow in Au+Au Collisions at 200 GeV Per Nucleon Pair

Elliptic Flow in Au+Au Collisions at 200 GeV Per Nucleon Pair
Author: Carla Manuel Vale
Publisher:
Total Pages: 154
Release: 2004
Genre:
ISBN:

The Relativistic Heavy Ion Collider (RHIC) has provided its experiments with the most energetic nucleus-nucleus collisions ever achieved in a laboratory. These collisions allow for the study of the properties of nuclear matter at very high temperature and energy density, and may uncover new forms of matter created under such conditions. This thesis presents measurements of the elliptic flow amplitude, v2, in Au+Au collisions at RHIC's top center of mass energy of 200 GeV per nucleon pair. Elliptic flow is interesting as a probe of the dynamical evolution of the system formed in the collision. The elliptic flow dependences on transverse momentum, centrality, and pseudorapidity were measured using data collected by the PHOBOS detector during the 2001 RHIC run. The reaction plane of the collision was determined using the multiplicity detector, and the azimuthal angles of tracks reconstructed in the spectrometer were then correlated with the found reaction plane. The v2 values grow almost linearly with transverse momentum, up to P[sub]T of approximately 1.5 GeV, saturating at about 14%. As a function of centrality, v2 is minimum for central events, as expected from geometry, and increases up to near 7% (for 0

Pion Production in 4.5 GeV Au + Au Collisions from the STAR Fixed-target Pilot Run

Pion Production in 4.5 GeV Au + Au Collisions from the STAR Fixed-target Pilot Run
Author: Kathryn Carson Meehan
Publisher:
Total Pages:
Release: 2018
Genre:
ISBN: 9780438930698

The RHIC Beam Energy Scan (BES) Program was proposed to look for the turn-off of signatures of the quark gluon plasma (QGP), search for a possible QCD critical point, and study the nature of the phase transition between hadronic and partonic matter. The first phase of the BES program (BES-I) took place from 2010-2016. Several interesting observables studied in BES-I, including the net-proton higher moments and the directed flow of protons, show interesting behavior below 20 GeV and could suggest a transition to a hadron dominated regime. Data from energies lower than 7 GeV could help determine whether these behaviors are indicative of phase transitions or criticality. The goal of the STAR Fixed-Target (FXT) Program is to extend the collision energy range in BES-II to lower energies than is feasible with colliding beams. In order for this program to be approved, it was necessary to demonstrate that STAR could successfully perform measurements in a fixed-target geometry. In this dissertation we present results from the fixed-target pilot run data set collected in 2015 with the STAR detector. The pilot run consisted of 4.5 GeV per nucleon center-of-mass energy Au + Au collisions. The [pi]− spectra and rapidity density are measured from the top 5% most central collisions and found to be comparable to previous results at similar energies from the AGS experiments. Additionally the 4[pi] yield is extracted and found to be 153 +/- 15 (stat) +/- 29 (sys). Together, these and additional results measured by other analyzers from multiple institutions in STAR, demonstrated that STAR can successfully reproduce many physics results from the AGS experiments. This helped convince the Brookhaven Program Advisory Committee (PAC) to include an official FXT program in BES-II, to be conducted in 2019-2021. Specifically, the PAC approved the collection of 100 million events each taken at eight different energies with STAR operating in the fixed-target configuration. This will extend BES-II to center-of-mass energies as low as 3.0 GeV per nucleon, nearly doubling the [mu][subscript B] reach of the BES program and thus broadening our search for interesting transition features in the phase diagram.

Neutral Pion Production in Nucleus-nucleus Collisions at 158 and 200 GeV/nucleon

Neutral Pion Production in Nucleus-nucleus Collisions at 158 and 200 GeV/nucleon
Author:
Publisher:
Total Pages: 11
Release: 1998
Genre:
ISBN:

Two years ago, at the 12th Winter Workshop on Nuclear Dynamics held here in Snowbird, the authors presented WA80 limits on direct photon production in 200-GeV 32S + Au collisions. It was found that the results were consistent (within 1[sigma]) with the absence of an excess of photons over those that can be accounted for by the two-photon decay branches of [pi]° and [eta] mesons and by the small photon contributions from other radiative decays. They are in the process of finalizing the direct-photon production results from collisions of lead nuclei at 158 GeV/nucleon. The author briefly discusses the status of the analysis and gives some preliminary results at the end of this talk. However, most of this presentation is concerned with a very different aspect of the photon measurements: distributions of neutral pions. In contrast to direct photons which probe initial collision conditions, hadrons, such as neutral pions, interact strongly and decouple late in the reaction evolution and, thus, provide information concerning the system at freeze out. Transverse momentum spectra at low and intermediate p{sub T} relate to thermodynamic and hydrodynamic descriptions of the hot, dense systems. In addition, the high-p{sub T} region reflects the hard-scattering regime and may help one understand initial-state particle production by forming a bridge to proton-proton and proton-nucleus results. It follows that it is essential that the [pi]° measurements cover a large p{sub T} range.