Non-photonic Electron at High Transverse Momentum in Au+Au Collisions and Bottom Quark Production in P+p Collisions at Sqrt(sNN)

Non-photonic Electron at High Transverse Momentum in Au+Au Collisions and Bottom Quark Production in P+p Collisions at Sqrt(sNN)
Author: Wenqin Xu
Publisher:
Total Pages: 172
Release: 2012
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A new form of matter with de-confined quarks and gluons, named the "Quark Gluon Plasma" (QGP), is predicted by Lattice Qutantum Chromodynamics to exist at high temperatures and/or high baryon density regions in the QCD phase diagram. Experimental evidence indicates that the QCD matter created in high energy Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC) in Brookhaven National Lab is a strongly-coupled Quark-Gluon Plasma. One of the central goals of heavy ion physics is to understand the QGP through quantitative comparisons between theoretical calculations and experimental measurements. Heavy flavor quarks are believed to be a unique probe for this task, because they are dominantly produced in the initial hard scatterings, where the production rate can be well calculated by perturbative-QCD(pQCD). When heavy favor quarks traverse the QGP medium, they bear the imprints of the medium via their interactions with the medium. Dynamical models have been developed to calculate the interactions between heavy quarks and the QGP medium to quantitatively extract the medium properties. This dissertation presents a series of experimental studies with the electrons produced in the semi-leptonic decays of heavy flavor quarks in Au+Au and p+p collisions, which serve as the proxies for heavy flavor quarks. These electrons are referred to as non-photonic electrons (NPE), to be differentiated from the main background of photonic electrons. The production of NPE at high pT is found to be highly suppressed in central and semi-central Au+Au collisions, compared to binary-collision scaled production in p+p collisions. The azimuthal anisotropy of NPE is found to be finite at high pT, and the azimuthal correlation between high pT NPE and low pT hadrons exhibits a broadening in the away-side, both of which strengthen the evidence for a strong coupling between heavy flavor quarks and the QGP medium. In addition, the bottom quark production cross-section in p+p collisions is obtained based on the measured spectrum of NPE and the ratio of bottom/charm decay electrons.

Correlations with Non-Photonic Electrons in 200 GeV Au+Au Collisions in STAR

Correlations with Non-Photonic Electrons in 200 GeV Au+Au Collisions in STAR
Author: Lloyd Edward Dunkelberger
Publisher:
Total Pages: 135
Release: 2016
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At sufficiently high temperatures and densities quarks and gluons exist in a deconfined state called Quark Gluon Plasma (QGP). QGP existed in the Universe shortly after the Big Bang, and today is created in accelerator based experiments which collide heavy nuclei at high energies. Results from these experiments point to a hot, dense and strongly interacting state of deconfined quarks and gluons. The study of heavy flavor probes (those originating from $c$ and $b$ quarks) is an active area of research in heavy ion collisions. Heavy quarks are produced in the initial hard scatterings of collisions and thus are sensitive to the entire evolution of the medium. They also potentially have different sensitivity to medium induced energy loss compared to light flavors. This dissertation investigates the interactions of heavy flavor quarks with the medium by studying correlations between electrons from heavy flavor decays and hadrons. At high transverse momentum, the direction of the electron is highly correlated with the direction of the parent heavy flavor meson. We look for evidence of energy loss in the QGP as well as jet induced effects on the medium. We present electron-hadron correlations from Au+Au collisions in a wide range of centrality bins as well as correlations from p+p. The datasets used are the best currently available due to high statistics and low material in the detector. We also investigate the dependence on the orientation of the trigger particle to the event plane to look for path length dependent effects on the correlation as well as non-flow contributions to electron electron $v_2$.

Influence of Bottom Quark Jet Quenching on Single ElectronTomography of Au+Au

Influence of Bottom Quark Jet Quenching on Single ElectronTomography of Au+Au
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Release: 2005
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High transverse momentum single (non-photonic) electrons are shown to be sensitive to the stopping power of both bottom, b, and charm, c, quarks in AA collisions. We apply the DGLV theory of radiative energy loss to predict c and b quark jet quenching and compare the FONLL and PYTHIA heavy flavor fragmentation and decay schemes. We show that single electrons in the p{sub T} = 5-10 GeV range are dominated by the decay of b quarks rather than the more strongly quenched c quarks in Au+Au collisions at (square root)s = 200 AGeV. The smaller b quark energy loss, even for extreme opacities with gluon rapidity densities up to 3500, is predicted to limit the nuclear modification factor, R{sub AA}, of single electrons to the range R{sub AA} (almost equal to) 0.5-0.6, in contrast to previous predictions of R{sub AA} (less-than or equal to) 0.2-0.3 based on taking only c quark jet fragmentation into account.

Scaling Properties of Hyperon Production in Au + Au Collisions at Sqrt SNN

Scaling Properties of Hyperon Production in Au + Au Collisions at Sqrt SNN
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Release: 2006
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We present the scaling properties of Lambda, Xi, and their anti-particles produced at mid-rapidity in Au+Au collisions at RHIC at psNN = 200 GeV. The yield of multi-strange baryons per participant nucleon increases from peripheral to central collisions more rapidly than the Lambda yield, which appears to correspond to an increasing strange quark density of matter produced. The value of the strange phase space occupancy factor gamma s, obtained from a thermal model fit to the data, approaches unity for the most central collisions. We also show that the nuclear modification factors, RCP, of Lambda and Xi are consistent with each other and with that of protons in the transverse momentum range2.0

Transverse Expansion in [sup 197] Au + [sup 197] Au Collisions at RHIC.

Transverse Expansion in [sup 197] Au + [sup 197] Au Collisions at RHIC.
Author:
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Total Pages: 4
Release: 2003
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Using the RQMD model, transverse momentum distributions and particle ratios are studied for 197Au + 197Au collisions at (square root)s{sub NN} = 200 GeV. In particular, they present results on the mean transverse momentum of charged pions, charged kaons, protons and anti-protons and compare with experimental measurements. They discuss an approach to study early partonic collectivity in high energy nuclear collisions.

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
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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.