Author: Prashanth Shanmuganathan
Publisher:
ISBN:
Category : Hadron interactions
Languages : en
Pages : 128

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Excited nuclear matter at high temperature and density results in the creation of a new state of matter called Quark Gluon Plasma (QGP). It is believed that the Universe was in the QGP state a few millionths of a second after the Big Bang. A QGP can be experimentally created for a very brief time by colliding heavy nuclei, such as gold, at ultra-relativistic energies. The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory consists of two circular rings, 3.8 km in circumference, which can accelerate heavy nuclei in two counter-rotating beams to nearly the speed of light (up to 100 GeV per beam). STAR (Solenoidal Tracker At RHIC) is one of two large detectors at the RHIC facility, and was constructed and is operated by a large international collaboration made up of more than 500 scientists from 56 institutions in 12 countries. STAR has been taking data from heavy ion collisions since the year 2000. An important component of the physics effort of the STAR collaboration is the Beam Energy Scan (BES), designed to study the properties of the Quantum Chromodynamics (QCD) phase diagram in the regions where a first-order phase transition and a critical point may exist. Phase-I of the BES program took data in 2010, 2011 and 2014, using Au+Au collisions at a center-of-mass energy per nucleon pair of 7.7, 11.5, 14.5, 19.6, 27 and 39 GeV. It is by now considered a well-established fact that the QGP phase exists. However, all evidence so far indicates that there is a smooth crossover when normal hadronic matter becomes QGP and vice versa in collisions at the top energy of RHIC (and likewise at the Large Hadron Collider at the CERN laboratory in Switzerland). At these very high energies, the net density of baryons like nucleons is quite low, since there are almost equal abundances of baryons and antibaryons. It is known that net-baryon compression increases as the beam energy is lowered below a few tens of GeV. Of course, if the beam energy is too low, then the QGP phase cannot be produced at all, so it has been proposed that there is an optimum beam energy, so far unknown, where phenomena like a first-order phase transition and a critical point might be observed. On the other hand, there also exists the possibility that a smooth crossover to QGP occurs throughout the applicable region of the QCD phase diagram. Experiments are needed to resolve these questions. In this dissertation, I focus on one of the main goals of the BES program, which is to search for a possible first-order phase transition from hadronic matter to QGP and back again, using measurements of azimuthal anisotropy. The momentum-space azimuthal anisotropy of the final-state particles from collisions can be expressed in Fourier harmonics. The first harmonic coefficient is called directed flow, and reflects the strength of the collective sideward motion, relative to the beam direction, of the particles. Models tell us that directed flow is imparted during the very early stage of a collision and is not much altered during subsequent stages of the collision. Thus directed flow can provide information about the early stages when the QGP phase exists for a short time. A subset of hydrodynamic and nuclear transport model calculations with the assumption of a first-order phase transition show a prominent dip in the directed flow versus beam energy. I present directed flow and its slope with respect to rapidity, for identified particle types, namely lambda, anti-lambda and kaons as a function of beam energy for central, intermediate and peripheral collisions. The production threshold of neutral strange particles requires them to be created earlier, and these particles have relatively long mean free path. Thus these particles may probe the QGP at earlier times. In addition, new Lambda measurements can provide more insight about baryon number transported to the midrapidity region by stopping process of the nuclear collision. It is noteworthy that net-baryon density (equivalent to baryon chemical potential) depends not only on beam energy but also on collision centrality. The centrality dependence of directed flow and its slope are also studied for all BES energies for nine identified particle types, lambda, anti-lambda, neutral kaons, charged kaons, protons, anti-protons, and charged pions. These detailed results for many particle species, where both centrality and beam energy are varied over a wide range, strongly constrain models. The measurements summarized above pave the way for a new round of model refinements and subsequent comparisons with data. If the latter does not lead to a clear conclusion, the BES Phase-II program will take data in 2019 and 2020 with an upgraded STAR detector with wider acceptance, greatly improved statistics, and will extend measurements to new energy points.

Author: Yang Wu
Publisher:
ISBN:
Category : Anisotropy
Languages : en
Pages : 0

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Author: Yadav Pandit
Publisher:
ISBN:
Category : Anisotropy
Languages : en
Pages : 160

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STAR (Solenoidal Tracker At RHIC) is one of two large detectors along the ring of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. Experiments that collide heavy nuclei at high energy have been taking data at RHIC since the year 2000. The main goal of RHIC has been to search for a new phase of matter called the Quark Gluon Plasma (QGP), and to determine its properties, including the phase diagram that governs the relationship between QGP and more conventional hadronic matter. This dissertation has a particular focus on analysis of STAR measurements of the anisotropy of particle emission over a range of colliding energies, and these particular measurements are made possible by a unique application of a detector subsystem called Beam-Beam Counters (BBCs), which are placed close to the beam lines on both sides of the collision region. This project has involved development of software that uses the hit pattern of charged particles in the BBCs to determine the collision reaction plane, for use in measurements of anisotropy. Anisotropic flow sheds light on the early partonic system, and according to models, is minimally distorted during the post-partonic stages of the collision. In this anisotropic flow analysis, the estimated reaction plane of each event is reconstructed using the BBC signals, which have a large rapidity gap between them. There is also a large rapidity gap between each BBC and the STAR Time Projection Chamber (the main STAR subsystem for measuring particle tracks). These large rapidity gaps allow us to measure correlations relative to the reaction plane with the least possible systematic error from what is known as "non-flow", i.e., background correlations unrelated to the reaction plane. Flow correlations are normally reported in terms Fourier coefficients, v1, v2, etc. Di- rected flow is quantified by the first harmonic (v1) in the Fourier expansion of the particle's azimuthal distribution with respect to the reaction plane. Elliptic flow is the name given to the second harmonic (v2), and triangular flow is the name for the third harmonic (v3). These harmonic coefficients carry information on the very early stages of the collision. The v1 component is emphasized in this dissertation, and the BBC information that is a unique feature of this work is especially important for v1 measurements. Until recently, higher-order odd harmonics were overlooked. These odd flow harmonics carry valuable information about the initial-state fluctuations of the colliding system. This dissertation includes a study of the flow harmonic related to dipole asymmetry and triangularity in the initial geometry.

Author: William Kenneth Wilson
Publisher:
ISBN:
Category : Anisotropy
Languages : en
Pages : 450

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Author: Fareha G. A. Atetalla
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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At the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL), Long Island, NY, the main goal of research into heavy-ion collisions has been to understand Quantum Chromo Dynamics (QCD) in conditions of extreme temperature and energy density. At ordinary temperatures, the quarks and gluons are confined within particles like protons and neutrons, but at very high temperatures and densities, a new deconfined phase of quarks and gluons is created. This new phase is known as Quark Gluon Plasma (QGP).Quarks with the quantum numbers "charm" and "bottom" are relatively massive and are produced only rarely, and this category is called heavy flavor. Heavy-flavor measurements deepen our understanding of the properties and nature of the excited QGP state. Heavy-flavor particles are unique probes for studies of the hot and dense QGP medium created in high-energy collisions, as they are produced early in the evolution of the collision.STAR (Solenoidal Tracker At RHIC) is now the last operational detector at the RHIC facility, and was constructed and is operated by a large international collaboration. The STAR collaboration is composed of 68 institutions from 14 countries, with a total of 743 collaborators. In 2014, STAR employed a new silicon pixel technology detector named the Heavy Flavor Tracker (HFT). The HFT has separate layers of silicon to guide tracks reconstructed in the main tracking detector of STAR (the Time Projection Chamber) down to a spatial resolution of around 30 [mu]m in the region near the center of STAR where the collisions occur, which allows particles with very short lifetimes (notably heavy flavor particles) to be identified.In this dissertation, I use the HFT to measure particles with the charm quantum number. This work also involves using a pair of calorimeter detectors at a polar angle of zero degrees to estimate the azimuthal angle of the reaction plane in each collision. About 2.2 billion collisions are in the dataset being studied. These measurements allow the azimuthal anisotropy (flow) of charmed particles to be studied. The results are compared to similar studies involving light quarks and the predictions of several theoretical models. My results show a surprisingly large first Fourier harmonic in the anisotropy for particles with charm compared with particles with lighter flavors (strange, up, down). Specifically, the signal for charm is about 30 times larger, and no model comes anywhere close to predicting this pattern.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 8

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The EOS experiment at the Bevalac has recently carried out exclusive event-by-event measurements of relativistic heavy ion collisions with a variety of projectile, target and beam energy combinations. The data was obtained using the EOS Time Projection Chamber. We present preliminary results on inclusive spectra, collective flow and azimuthal correlations obtained from a study of Au + Au reactions with beam energies covering 0.6 - 1.2 A GeV.

Author: Hildegard Meyer-ortmanns
Publisher: World Scientific
ISBN: 9814496278
Category : Science
Languages : en
Pages : 702

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Book Description
The phase structure of particle physics shows up in matter at extremely high densities and/or temperatures as they were reached in the early universe, shortly after the big bang, or in heavy-ion collisions, as they are performed nowadays in laboratory experiments. In contrast to phase transitions of condensed matter physics, the underlying fundamental theories are better known than their macroscopic manifestations in phase transitions. These theories are quantum chromodynamics for the strong interaction part and the electroweak part of the Standard Model for the electroweak interaction. It is their non-Abelian gauge structure that makes it a big challenge to predict the type of phase conversion between phases of different symmetries and different particle contents. The book is about a variety of analytical and numerical tools that are needed to study the phase structure of particle physics. To these belong convergent and asymptotic expansions in strong and weak couplings, dimensional reduction, renormalization group studies, gap equations, Monte Carlo simulations with and without fermions, finite-size and finite-mass scaling analyses, and the approach of effective actions as supplement to first-principle calculations.

Author: Martin David Partlan
Publisher:
ISBN:
Category :
Languages : en
Pages : 288

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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 5

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The azimuthal anisotropy of particle production is commonly used in high-energy nuclear collisions to study the early evolution of the expanding system. The prolate shape of uranium nuclei makes it possible to study how the geometry of the colliding nuclei affects final state anisotropies. It also provides a unique opportunity to understand how entropy is produced in heavy ion collisions. In this paper, the two- and four- particle cumulant v2 (v2{2} and v2{4}) from U+U collisions at √sNN = 193 GeV and Au+Au collisions at √sNN = 200 GeV for inclusive charged hadrons will be presented. The STAR Zero Degree Calorimeters are used to select very central collisions. Differences were observed between the multiplicity dependence of v2{2} for most central Au+Au and U+U collisions. The multiplicity dependence of v2{2} in central collisions were compared to Monte Carlo Glauber model predictions and it was seen that this model cannot explain the present results. (auth).

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Here, elliptic flow (v2) values for identified particles at midrapidity in Au + Au collisions measured by the STAR experiment in the Beam Energy Scan at the Relativistic Heavy Ion Collider at √sNN = 7.7-62.4 GeV are presented for three centrality classes. The centrality dependence and the data at √sNN = 14.5 GeV are new. Except at the lowest beam energies, we observe a similar relative v2 baryon-meson splitting for all centrality classes which is in agreement within 15% with the number-of-constituent quark scaling. The larger v2 for most particles relative to antiparticles, already observed for minimum bias collisions, shows a clear centrality dependence, with the largest difference for the most central collisions. Also, the results are compared with a multiphase transport (AMPT) model and fit with a blast wave model.