28 research outputs found
Does HBT Measure the Freeze-out Source Distribution?
It is generally assumed that as a result of multiple scattering, the source
distribution measured in HBT interferometry corresponds to a chaotic source at
freeze-out. This assumption is subject to question as effects of multiple
scattering in HBT measurements must be investigated within a quantum-mechanical
framework. Applying the Glauber multiple scattering theory at high energies and
the optical model at lower energies, we find that multiple scattering leads to
an effective HBT density distribution that depends on the initial chaotic
source distribution with an absorption.Comment: 4 pages, talk presented at QM2004 Conference, January 11-17, 2004,
Oakland, California, USA, to be published in the Proceeding
HBT interferometry with quantum transport of the interfering pair
In the late stage of the evolution of a pion system in high-energy heavy-ion
collisions when pions undergo multiple scatterings, the quantum transport of
the interfering pair of identical pions plays an important role in determining
the characteristics of the Hanbury-Brown-Twiss (HBT) interference. We study the
quantum transport of the interfering pair using the path-integral method, in
which the evolution of the bulk matter is described by relativistic
hydrodynamics while the paths of the two interfering pions by test particles
following the fluid positions and velocity fields. We investigate in addition
the effects of secondary pion sources from particle decays, for nuclear
collisions at AGS and RHIC energies. We find that quantum transport of the
interfering pair leads to HBT radii close to those for the chemical freeze-out
configuration. Particle decays however lead to HBT radii greater than those for
the chemical freeze-out configuration. As a consequence, the combined effects
give rise to HBT radii between those extracted from the chemical freeze-out
configuration and the thermal freeze-out configuration. Proper quantum
treatments of the interfering pairs in HBT calculations at the pion multiple
scattering stage are important for our understanding of the characteristics of
HBT interferometry in heavy-ion collisions.Comment: 14 pages, 4 figure
Momentum Kick Model Analysis of PHENIX Near-Side Ridge Data and Photon Jet
We analyze PHENIX near-side ridge data for central Au+Au collisions at
\sqrt{s_{NN}}=200 GeV with the momentum kick model, in which a near-side jet
emerges near the surface, kicks medium partons, loses energy, and fragments
into the trigger particle and fragmentation products. The kicked medium partons
subsequently materialize as the observed ridge particles, which carry direct
information on the early parton momentum distribution and the magnitude of the
momentum kick. We find that the PHENIX ridge data can be described well by the
momentum kick model and the extracted early partons momentum distribution has a
thermal-like transverse distribution and a rapidity plateau structure. We also
find that the parton-parton scattering between the jet parton and the medium
parton involves the exchange of a non-perturbative pomeron, for jet partons in
momentum range considered in the near-side ridge measurements.Comment: 20 pages, 3 figure
Spatial coherence and density correlations of trapped Bose gases
We study first and second order coherence of trapped dilute Bose gases using
appropriate correlation functions. Special attention is given to the discussion
of second order or density correlations. Except for a small region around the
surface of a Bose-Einstein condensate the correlations can be accurately
described as those of a locally homogeneous gas with a spatially varying
chemical potential. The degrees of first and second order coherence are
therefore functions of temperature, chemical potential, and position. The
second order correlation function is governed both by the tendency of bosonic
atoms to cluster and by a strong repulsion at small distances due to atomic
interactions. In present experiments both effects are of comparable magnitude.
Below the critical temperature the range of the bosonic correlation is affected
by the presence of collective quasi-particle excitations. The results of some
recent experiments on second and third order coherence are discussed. It is
shown that the relation between the measured quantities and the correlation
functions is much weaker than previously assumed.Comment: RevTeX, 25 pages with 7 Postscript figure
Macroscopic superpositions of Bose-Einstein condensates
We consider two dilute gas Bose-Einstein condensates with opposite velocities
from which a monochromatic light field detuned far from the resonance of the
optical transition is coherently scattered. In the thermodynamic limit, when
the relative fluctuations of the atom number difference between the two
condensates vanish, the relative phase between the Bose-Einstein condensates
may be established in a superposition state by detections of spontaneously
scattered photons, even though the condensates have initially well-defined atom
numbers. For a finite system, stochastic simulations show that the measurements
of the scattered photons lead to a randomly drifting relative phase and drive
the condensates into entangled superpositions of number states. This is because
according to Bose-Einstein statistics the scattering to an already occupied
state is enhanced.Comment: 18 pages, RevTex, 5 postscript figures, 1 MacBinary eps-figur
Non-destructive optical measurement of relative phase between two Bose condensates
We study the interaction of light with two Bose condensates as an open
quantum system. The two overlapping condensates occupy two different Zeeman
sublevels and two driving light beams induce a coherent quantum tunneling
between the condensates. We derive the master equation for the system. It is
shown that stochastic simulations of the measurements of spontaneously
scattered photons establish the relative phase between two Bose condensates,
even though the condensates are initially in pure number states. These
measurements are non-destructive for the condensates, because only light is
scattered, but no atoms are removed from the system. Due to the macroscopic
quantum interference the detection rate of photons depends substantially on the
relative phase between the condensates. This may provide a way to distinguish,
whether the condensates are initially in number states or in coherent states.Comment: 26 pages, RevTex, 8 postscript figures, 1 MacBinary eps-figur
Systematic Measurements of Identified Particle Spectra in pp, d+Au and Au+Au Collisions from STAR
Identified charged particle spectra of , , and
\pbar at mid-rapidity () measured by the \dedx method in the
STAR-TPC are reported for and d+Au collisions at \snn = 200 GeV and for
Au+Au collisions at 62.4 GeV, 130 GeV, and 200 GeV. ... [Shortened for arXiv
list. Full abstract in manuscript.]Comment: 58 pages, 46 figures, 37 table