312 research outputs found
Dissipation, noise and DCC domain formation
We investigate the effect of friction on domain formation in disoriented
chiral condensate. We solve the equation of motion of the linear sigma model,
in the Hartree approximation, including a friction and a white noise term. For
quenched initial condition, we find that even in presence of noise and
dissipation domain like structure emerges after a few fermi of evolution.
Domain size as large as 5 fm can be formed.Comment: 7 pages, 3 figure
How to Make Large Domains of Disoriented Chiral Condensate
Rajagopal and Wilczek have proposed that relativistic nuclear collisions can
generate domains in which the chiral condensate is disoriented. If sufficiently
large ({\it i.e.} nucleus sized), such domains can yield measurable
fluctuations in the number of neutral and charged pions. However, by numerical
simulation of the zero-temperature two-flavor linear sigma model, we find that
domains are essentially {\it pion} sized. Nevertheless, we show that large
domains can occur if the effective mesons masses are much lighter.Comment: 6 pages and 2 postscript figures, BNL-GGP-
The ZEPLIN II dark matter detector: data acquisition system and data reduction
ZEPLIN-II is a two-phase (liquid/gas) xenon dark matter detector searching
for WIMP-nucleon interactions. In this paper we describe the data acquisition
system used to record the data from ZEPLIN-II and the reduction procedures
which parameterise the data for subsequent analysis.Comment: 11 pages, 10 figure
The ZEPLIN II dark matter detector: data acquisition system and data reduction
ZEPLIN-II is a two-phase (liquid/gas) xenon dark matter detector searching
for WIMP-nucleon interactions. In this paper we describe the data acquisition
system used to record the data from ZEPLIN-II and the reduction procedures
which parameterise the data for subsequent analysis.Comment: 11 pages, 10 figure
Comparison of Hadronic Interaction Models at Auger Energies
The three hadronic interaction models DPMJET 2.55, QGSJET 01, and SIBYLL 2.1,
implemented in the air shower simulation program CORSIKA, are compared in the
energy range of interest for the Pierre Auger experiment. The model dependence
of relevant quantities in individual hadronic interactions and air showers is
investigated.Comment: Contribution to XII Int. Symp. on Very High Energy Cosmic Ray
Interactions, 4 pages, 8 figure
Kinetic description of hadron-hadron collisions
A transport model based on the mean free path approach to describe pp
collisions is proposed. We assume that hadrons can be treated as bags of
partons similarly to the MIT bag model. When the energy density in the
collision is higher than a critical value, the bags break and partons are
liberated. The partons expand and can make coalescence to form new hadrons. The
results obtained compare very well with available data and some prediction for
higher energies collisions are discussed. Based on the model we suggest that a
QGP could already be formed in the pp collisions at high energies
Directional detection as a strategy to discover Galactic Dark Matter
Directional detection of Galactic Dark Matter is a promising search strategy
for discriminating genuine WIMP events from background ones. Technical progress
on gaseous detectors and read-outs has permitted the design and construction of
competitive experiments. However, to take full advantage of this powerful
detection method, one need to be able to extract information from an observed
recoil map to identify a WIMP signal. We present a comprehensive formalism,
using a map-based likelihood method allowing to recover the main incoming
direction of the signal and its significance, thus proving its galactic origin.
This is a blind analysis intended to be used on any directional data.
Constraints are deduced in the () plane and systematic
studies are presented in order to show that, using this analysis tool,
unambiguous dark matter detection can be achieved on a large range of exposures
and background levels.Comment: 20 pages, 5 figures Final version to appear in Phys. Lett.
Can Disordered Chiral Condensates Form? A Dynamical Perspective
We address the issue of whether a region of disordered chiral condensate
(DCC), in which the chiral condensate has components along the pion
directions, can form. We consider a system going through the chiral phase
transition either via a quench, or via relaxation of the high temperature phase
to the low temperature one within a given time scale (of order ).
We use a density matrix based formalism that takes both thermal and quantum
fluctuations into account non-perturbatively to argue that if the linear
sigma model is the correct way to model the situation in QCD, then it is very
unlikely at least in the Hartree approximation, that a large ()
DCC region will form. Typical sizes of such regions are
and the density of pions in such regions is at most of order . We end with some speculations on how large DCC regions may be
formed.Comment: 21 pages LATEX, 12 figures available upon request via regular mail,
PITT-94-0
What it takes to measure a fundamental difference between dark matter and baryons: the halo velocity anisotropy
Numerous ongoing experiments aim at detecting WIMP dark matter particles from
the galactic halo directly through WIMP-nucleon interactions. Once such a
detection is established a confirmation of the galactic origin of the signal is
needed. This requires a direction-sensitive detector. We show that such a
detector can measure the velocity anisotropy beta of the galactic halo.
Cosmological N-body simulations predict the dark matter anisotropy to be
nonzero, beta~0.2. Baryonic matter has beta=0 and therefore a detection of a
nonzero beta would be strong proof of the fundamental difference between dark
and baryonic matter. We estimate the sensitivity for various detector
configurations using Monte Carlo methods and we show that the strongest signal
is found in the relatively few high recoil energy events. Measuring beta to the
precision of ~0.03 will require detecting more than 10^4 WIMP events with
nuclear recoil energies greater than 100 keV for a WIMP mass of 100 GeV and a
32S target. This number corresponds to ~10^6 events at all energies. We discuss
variations with respect to input parameters and we show that our method is
robust to the presence of backgrounds and discuss the possible improved
sensitivity for an energy-sensitive detector.Comment: 15 pages, 8 figures, accepted by JCAP. Matches accepted versio
Limits on spin-dependent WIMP-nucleon cross-sections from the first ZEPLIN-II data
The first underground data run of the ZEPLIN-II experiment has set a limit on
the nuclear recoil rate in the two-phase xenon detector for direct dark matter
searches. In this paper the results from this run are converted into the limits
on spin-dependent WIMP-proton and WIMP-neutron cross-sections. The minimum of
the curve for WIMP-neutron cross-section corresponds to 0.07 pb at a WIMP mass
of around 65 GeV.Comment: 12 pages, 2 figures, to be published in Physics Letters
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