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:

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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

Momentum-integrated Elliptic Flow and Transverse Collision Geometry in Ultrarelativistic Nucleus-nucleus Collisions

Momentum-integrated Elliptic Flow and Transverse Collision Geometry in Ultrarelativistic Nucleus-nucleus Collisions
Author: Peter Kirk Walters
Publisher:
Total Pages: 164
Release: 2013
Genre:
ISBN:

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"Ultrareletivistic nuclear collisions at the Relativistic Heavy-Ion Collider have produced a high temperature, high energy density medium consisting of a strongly interacting plasma of quarks and gluons. This extreme state of matter provides a testing ground for quantum chromodynamics. Previous studies of gold-gold collisions over a wide range of beam energies revealed many properties of the produced medium. However, these studies were restricted to relatively large colliding systems which resulted in large collision volumes; it is therefore important to investigate what role the size of the collision volume plays in the evolution of the source, particularly as the source volume becomes vanishingly small. This can be achieved with symmetric copper-copper collisions, which offer access to a range of system sizes from [approximately] 10 participating nucleons up through volumes comparable to those created in gold-gold collisions. Collective behaviors of the produced particles in heavy-ion collisions can provide useful probes into the state of the medium produced, including its degree of thermalization and its properties. The elliptic flow, an anisotropy in the azimuthal distribution of the produced particles that is strongly correlated to the initial transverse geometry of the colliding nuclei, is one such collective motion that has proven to be a very useful observable for studying heavy-ion collisions. This is because it exhibits fairly large magnitudes in the systems being studied and is sensitive to the strength of the partonic interactions in-medium. The PHOBOS experiment, which can measure the positions of produced charged particles with high precision over nearly the full solid angle, is well-suited to study the elliptic flow and its evolution over an extended range along the beam direction. The elliptic flow from copper-copper collisions at center-of-mass energies of 22.4, 62.4, and 200GeV per nucleon pair are presented as a function of pseudorapidity and system size. The appearance of unexpected behaviors in the smaller system prompted a re-examination of the role of the collision geometry on the production of elliptic flow. Studies using Monte-Carlo Glauber simulations found that the fluctuating spatial configurations of the component nucleons in the colliding nuclei could result in significant variation of the shape of the nuclear overlap on an event-by-event basis, and that these fluctuations become important for small systems. The eccentricity, a quantity that characterizes the ellipticity of the nuclear overlap in the transverse plane, is redefined to account for these fluctuations as the participant eccentricity. It is found that the event-by-event fluctuations of the participant eccentricity are able to fully account for the observed elliptic flow in the smaller system. The participant eccentricity is used to normalize the measured elliptic flow across different colliding systems to a common initial geometry so that a direct comparison of the properties of the produced medium can be made. It is found that the produced medium evolves smoothly from systems of [approximately] 10 participant nucleons to systems involving more than 350 nucleons and for collision energies from 19.6 to 200GeV per nucleon pair. This smooth evolution of the elliptic flow is also observed as a function of pseudorapidity in all the systems studied. After accounting for the initial geometry, no indication of the identity of the original colliding system is observed"--Page vi-vii.

Studies of Nucleon-gold Collisions at 200 GeV Per Nucleon Pair Using Tagged D+Au Interactions

Studies of Nucleon-gold Collisions at 200 GeV Per Nucleon Pair Using Tagged D+Au Interactions
Author: Corey James Reed
Publisher:
Total Pages: 215
Release: 2006
Genre:
ISBN:

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(Cont.) Further, hadron production in p+Au interactions is compared to that of n+Au interactions. The single charge difference between a p+Au and a n+Au collision allows for a unique study of the ability of the interaction to transport the proton from the initial deuteron to mid-rapidity. However, no asymmetry between the positively and negatively charged hadron spectra of p+Au and n+Au interactions is observed at (qr) = 0.8. Collision centrality was determined using several different observables, including those based on the multiplicity in different regions of pseudorapidity and those based on the amount of nuclear spectator material. It is shown that measurements made on small collision systems in the mid-rapidity region are biased by centrality variables based on the mid-rapidity multiplicity. Despite this bias, a smooth evolution with centrality is observed in the Cronin enhancement of hadrons produced in d+Au collisions. It is shown that this smooth progression is independent of the choice of centrality variable when centrality is parametrized by the multiplicity measured near mid-rapidity.

Charged Hadron Transverse Momentum Spectra in Au+Au and D+Au Collisions at 200 GeV Per Nucleon Pair

Charged Hadron Transverse Momentum Spectra in Au+Au and D+Au Collisions at 200 GeV Per Nucleon Pair
Author: Jay Lawrence Kane
Publisher:
Total Pages: 235
Release: 2005
Genre:
ISBN:

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(Cont.) When ... is calculated for different rapidities, a suppression is seen as the rapidity in the deuteron fragmentation region increases. This has been predicted to be seen if a CGC does form in the colliding nuclei.

Predictions of Elliptic Flow and Nuclear Modification Factor from 200 GeV U+U Collisions at RHIC.

Predictions of Elliptic Flow and Nuclear Modification Factor from 200 GeV U+U Collisions at RHIC.
Author:
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Total Pages:
Release: 2010
Genre:
ISBN:

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Predictions of elliptic flow (v2) and nuclear modification factor (R{sub AA}) are provided as a function of centrality in U + U collisions at (square root)s{sub NN} = 200 GeV. Since the 238U nucleus is naturally deformed, one could adjust the properties of the fireball, density and duration of the hot and dense system, for example, in high energy nuclear collisions by carefully selecting the colliding geometry. Within our Monte Carlo Glauber based approach, the v2 with respect to the reaction plane v2{sup RP} in U + U collisions is consistent with that in Au + Au collisions, while the v2 with respect to the participant plane v2{sup PP} increases (almost equal to)30-60% at top 10% centrality which is attributed to the larger participant eccentricity at most central U + U collisions. The suppression of R{sub AA} increases and reaches (almost equal to)0.1 at most central U + U collisions that is by a factor of 2 more suppression compared to the central Au + Au collisions due to large size and deformation of Uranium nucleus.

Identified Particle Transverse Momentum Distributions from AU + AU Collisions at 62.4 GeV Per Nucleon Pair

Identified Particle Transverse Momentum Distributions from AU + AU Collisions at 62.4 GeV Per Nucleon Pair
Author: Conor Henderson
Publisher:
Total Pages: 322
Release: 2005
Genre:
ISBN:

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Transverse momentum (PT) distributions for pions, kaons, protons and antiprotons have been measured near mid-rapidity for Au+Au collisions at sNN = 62.4 GeV using the PHOBOS detector at the Relativistic Heavy-Ion Collider (RHIC) in Brookhaven National Laboratory. Particle identification is performed using the PHOBOS Time-of-Flight plastic scintillator walls and specific energy loss in the multi-layer silicon Spectrometer, which is also used for track reconstruction and momentum-determination. The spectra are corrected for all detector-dependent effects, including feed-down from weak decays. At PT 3 GeV/c, protons are measured to be the dominant species of charged hadrons and scale much faster with respect to collision centrality than mesons. This behaviour at 62.4 GeV is found to be remarkably similar to that observed in Au+Au collisions at 200 GeV, an interesting observation which should serve as an important constraint on the various mechanisms which have been proposed to describe particle production over this PT range. Baryon stopping, the transport of baryon number from intial beam rapidity, is explored through the net proton (p - p) yields at mid-rapidity. These results fill a large gap between the SPS and higher RHIC energies and as such form an important set of data for comparing to models of baryon transport mechanisms.