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Jets as a probe of dense matter at RHIC

Description: Jet quenching in the matter created in high energy nucleus-nucleus collisions provides a tomographic tool to probe the medium properties. Recent experimental results on jet production at the Relativistic Heavy-Ion Collider (RHIC) are reviewed. Jet properties in p+p and d+Au collisions have been measured, establishing the baseline for studying jet modification in heavy-ion collisions. Current progress on detailed studies of high transverse momentum production in Au+Au collisions is discussed, with an emphasis on dihadron correlation measurements.
Date: April 1, 2004
Creator: Filimonov, Kirill
Partner: UNT Libraries Government Documents Department

High p<sub partial> inclusive charged hadron distributions in Au+Au collisions at square root(s<sub NN>) = 130 Gev at RHIC

Description: This thesis reports the measurement of the inclusive charged particle (h{sup +} + h{sup -}) p{perpendicular} spectra for 1.7 < p{perpendicular} < 6 GeV/c at midrapidity (|{eta}| < 0.5) as a function of various centrality classes in Au+Au collisions at {radical}s{sub NN} = 130 GeV. Hadron suppression is observed relative to both scaled NN and peripheral Au+Au reference data, possibly indicating non-Abelian radiative energy loss in a hot, dense medium.
Date: July 1, 2003
Creator: Choi, Bum
Partner: UNT Libraries Government Documents Department

Chemical investigations of Element 108, Hassium (Hs)

Description: The basic aim of chemistry experiments of transactinide elements (TAN) is to establish their place in the periodic table of the elements, i.e. to determine if their chemical behavior is similar to the one of supposed homologs. In this contribution I will try to give an overview of all chemical experiments on element 108, hassium (Hs) that have been reported to date. Based on the systematics of the periodic table, Hs is expected to be a member of group 8 and therefore homologous to osmium (Os) and ruthenium (Ru). As a member of the transactinide series, its experimental investigation is complicated by low production cross-sections and short half-lives. It has therefore been successfully investigated only recently. Already in the seventies of the last century, several authors mentioned the tetroxides of the two heavier group 8 elements, Ru and Os, to be very outstanding compounds with respect to their unusually high volatility. A possible HsO{sub 4} was considered suitable for isolating Hs from unwanted by-products of the nuclear production reaction. While RuO{sub 4}4 is rather unstable, OsO{sub 4} is well-known to be a stable compound and is widely used in organic chemistry. Recent theoretical calculations on the electronic structure and properties of Hs [5,6] predict the formation of a stable HsO{sub 4} whose properties should be similar to the ones of OsO{sub 4}. This is in agreement with an extrapolation of the trend established in group 8 of the periodic table by Ru and Os [7]. All of the reported experiments on the chemistry of Hs therefore aimed at a formation of this compound. Hs was discovered in 1984, when Muenzenberg et al. reported the observation of a correlated decay-chain from {sup 265}Hs formed in the nuclear reaction {sup 58}Fe({sup 208}Pb; n) [8]. However, its half-life is only 1.55 ms, too ...
Date: July 3, 2003
Creator: Dullmann, Christoph E.
Partner: UNT Libraries Government Documents Department

Electron-positron production in ultra-peripheral heavy-ion collisions with the STAR experiment

Description: This thesis presents a measurement of the cross-section of the purely electromagnetic production of e{sup +}e{sup -} pairs accompanied by mutual nuclear Coulomb excitation AuAu {yields} Au*Au* + e{sup +}e{sup -}, in ultra-peripheral gold-gold collisions at RHIC at the center-of-mass collision energy of {radical}S{sub NN} = 200 GeV per nucleon. These reactions were selected by detecting neutron emission by the excited gold ions in the Zero Degree Calorimeters. The charged tracks in the e{sup +}e{sup -} events were reconstructed with the STAR Time Projection Chamber. The detector acceptance limits the kinematical range of the observed e{sup +}e{sup -} pairs; therefore the measured cross-section is extrapolated to 4{pi} with the use of Monte Carlo simulations. We have developed a Monte Carlo simulation for ultra-peripheral e{sup +}e{sup -} production at RHIC based on the Equivalent Photon Approximation, the lowest-order QED e{sup +}e{sup -} production cross-section by two real photons and the assumption that the mutual nuclear excitations and the e{sup +}e{sup -} production are independent (EPA model). We compare our experimental results to two models: the EPA model and a model based on full QED calculation of the e{sup +}e{sup -} production, taking the photon virtuality into account. The measured differential cross-section d{sigma}/dM{sub inv} (M{sub inv} - e{sup +}e{sup -} invariant mass) agrees well with both theoretical models. The measured differential cross-section d{sigma}/dp{sub {perpendicular}}{sup tot} (p{sub {perpendicular}}{sup tot} - e{sup +}e{sup -} total transverse momentum) favors the full QED calculation over the EPA model.
Date: August 1, 2003
Creator: Morozov, Vladimir Borisovitch
Partner: UNT Libraries Government Documents Department

Azimuthal anisotropy: The higher harmonics

Description: We report the first observations of the fourth harmonic (v{sub 4}) in the azimuthal distribution of particles at RHIC. The measurement was done taking advantage of the large elliptic flow generated at RHIC. The integrated v{sub 4} is about a factor of 10 smaller than v{sub 2}. For the sixth (v{sub 6}) and eighth (v{sub 8}) harmonics upper limits on the magnitudes are reported.
Date: March 12, 2004
Creator: Poskanzer, Arthur M. & Collaboration, STAR
Partner: UNT Libraries Government Documents Department

Dileptons from transport and hydrodynamical models

Description: Transport and hydrodynamical models used to describe the expansion stage of a heavy-ion collision at the CERN SPS give different dilepton spectrum even if they are tuned to reproduce the observed hadron spectra. To understand the origin of this difference we compare the dilepton emission from transport and hydrodynamical models using similar initial states in both models. We find that the requirement of pion number conservation in a hydrodynamical model does not change the dilepton emission. Also the mass distribution from the transport model indicates faster cooling and longer lifetime of the fireball.
Date: January 1, 2000
Creator: Huovinen, P. & Koch, V.
Partner: UNT Libraries Government Documents Department

Bottom production asymmetries at the LHC

Description: We present results on bottom hadron production asymmetries at the LHC within both the Lund string fragmentation model and the intrinsic bottom model. The main aspects of the models are summarized and specific predictions for pp collisions at 14 TeV are given. Asymmetries are found to be very small at central rapidities increasing to a few percent at forward rapidities. At very large rapidities intrinsic production could dominate but this region is probably out of reach of any experiment.
Date: January 1, 1999
Creator: Norrbin, E. & Vogt, R.
Partner: UNT Libraries Government Documents Department

Measurement of the beta-neutrino correlation in laser trapped {sup 21}Na

Description: Trapped radioactive atoms are an appealing source for precise measurements of the beta-neutrino correlation coefficient, a, since the momentum of the neutrino can be inferred from the detection of the unperturbed low-energy recoil daughter nucleus. Sodium-21 is produced on-line at the 88'' cyclotron at Lawrence Berkeley National Laboratory, and 8e5 atoms have been maintained in a magneto-optical trap. A static electric field draws daughter Neon-21 ions to a microchannel plate detector and betas are detected in coincidence with a plastic scintillator beta detector. The Neon-21 time-of-flight distribution determines the beta neutrino correlation coefficient, a. The resulting charge-state distribution is compared to a simple model based on the sudden approximation which suggests a small but important contribution from nuclear recoil-induced ionization. A larger than expected fraction of the daughters are detected in positive charge-states, but no dependence on either the beta or recoil nucleus energy was observed. We find a = 0.5243 plus or minus 0.0092, which is in 3.6 sigma disagreement with the Standard Model prediction of a = 0.559 plus or minus 0.003. Aside from a deviation from the Standard Model, a possible explanation for the discrepancy is that the branching ratio to the first excited state is in error.
Date: June 1, 2003
Creator: Scielzo, Nicholas David
Partner: UNT Libraries Government Documents Department

Anisotropic flow in the forward directions at {radical}s{sub NN} = 200 GeV

Description: The addition of the two Forward TPCs to the STAR detector allows one to measure anisotropic flow at forward pseudorapidities. This made possible the first measurement of directed flow at collision energies of {radical}s{sub NN} = 200 GeV. PHOBOS' results on elliptic flow at forward rapidities were confirmed, and the sign of v{sub 2} was determined to be positive for the first time at RHIC energies. The higher harmonic, v{sub 4}, is consistent with the recently suggested v{sub 2}2 scaling behavior.
Date: March 9, 2004
Creator: Oldenburg, Markus D.
Partner: UNT Libraries Government Documents Department

Anisotropic Flow in the Forward Directions

Description: The STAR Forward TPCs (FTPCs) extend the STAR acceptance for charged particles into the region 2.5 < |eta| < 4.0. We see the first signal of directed flow (v{sub 1}) at RHIC energies. While v{sub 1} is consistent with zero in the central rapidity region it rises up to 2 percent at pseudorapidities of +-4. With this signal we can verify that elliptic flow (v{sub 2}) is in-plane. The measurement of v{sub 2} in the FTPCs confirms the falloff by a factor of about 2 compared to mid-rapidity previously seen by PHOBOS [1]. In addition we look for higher harmonics (v{sub n}, n>2) where in the case of v{sub 4} a signal is seen in the STAR TPC. With the available statistics for the FTPCs we give an upper limit for these harmonics, since the results agree with zero within the errors. However, the falloff of v{sub 4} from mid-rapidity to forward-rapidities appears to be faster than for v{sub 2}.[1] B.B. Back. Phys. Rev. Lett. 89, 222301 (2002)
Date: March 9, 2004
Creator: Oldenburg, Markus D. & Putschke, Jorn
Partner: UNT Libraries Government Documents Department

Heavy Nuclei, From RHIC to The Cosmos

Description: Ultra-relativistic heavy ion collisions produce a high-temperature, thermalized system that may mimic the conditions present shortly after the big bang. This writeup will given an overview of early results from the Relativistic Heavy Ion Collider (RHIC), and discuss what we have learned about hot, strongly interacting nuclear systems. The thermal and chemical composition of the system will be discussed, along with observables that are sensitive to the early evolution of the system. I will also discuss the implications of the RHIC results for cosmic ray air showers.
Date: November 1, 2002
Creator: Klein, Spencer R.
Partner: UNT Libraries Government Documents Department

Second order Pseudo-gaussian shaper

Description: The purpose of this document is to provide a calculus spreadsheet for the design of second-order pseudo-gaussian shapers. A very interesting reference is given by C.H. Mosher ''Pseudo-Gaussian Transfer Functions with Superlative Recovery'', IEEE TNS Volume 23, p. 226-228 (1976). Fred Goulding and Don Landis have studied the structure of those filters and their implementation and this document will outline the calculation leading to the relation between the coefficients of the filter. The general equation of the second order pseudo-gaussian filter is: f(t) = P{sub 0} {center_dot} e{sup -3kt} {center_dot} sin{sup 2}(kt). The parameter k is a normalization factor.
Date: November 22, 2002
Creator: Beche, Jean-Francois
Partner: UNT Libraries Government Documents Department

Overview of results from the STAR experiment at RHIC.

Description: The Relativistic Heavy-Ion Collider (RHIC) provides Au+Au collisions at energies up to {radical}s{sub NN} = 200 GeV. STAR experiment was designed and constructed to investigate the behavior of strongly interacting matter at high energy density. An overview of some of the recent results from the STAR collaboration is given.
Date: June 20, 2003
Creator: Filimonov, Kirill & Collaboration, STAR
Partner: UNT Libraries Government Documents Department

The nuclear liquid-vapor phase transition: Equilibrium between phases or free decay in vacuum?

Description: Recent analyses of multifragmentation in terms of Fisher's model and the related construction of a phase diagram brings forth the problem of the true existence of the vapor phase and the meaning of its associated pressure. Our analysis shows that a thermal emission picture is equivalent to a Fisher-like equilibrium description which avoids the problem of the vapor and explains the recently observed Boltzmann-like distribution of the emission times. In this picture a simple Fermi gas thermometric relation is naturally justified. Low energy compound nucleus emission of intermediate mass fragments is shown to scale according to Fisher's formula and can be simultaneously fit with the much higher energy ISiS multifragmentation data.
Date: November 14, 2002
Creator: Phair, L.; Moretto, L.G.; Elliott, J.B. & Wozniak, G.J.
Partner: UNT Libraries Government Documents Department