279 research outputs found
A percolation transition in Yang-Mills matter at finite number of colours
We examine baryonic matter at quark chemical potential of the order of the
confinement scale, \mu_q\sim \lqcd. In this regime, quarks are supposed to be
confined but baryons are close to the ``tightly packed limit'' where they
nearly overlap in configuration space. We show that this system will exhibit a
percolation phase transition {\em when varied in the number of colours} :
at high , large distance correlations at quark level are possible even if
the quarks are essentially confined. At low , this does not happen. We
discuss the relevance of this for dense nuclear matter, and argue that our
results suggest a new ``phase transition'', varying at constant .Comment: Accepted for publication, Physical Review Letters. Title changed from
original, "Quarkyonic percolation at finite number of colors", at the request
of the edito
Photo-emission rate of sQGP at finite density
We calculate the thermal spectral function of SYM plasma with finite density
using holographic technique. We take the RN-AdS black hole as the dual gravity
theory. In the presence of charge, vector modes of gravitational and
electromagnetic perturbation are coupled with each other. By introducing master
variables for these modes, we solve the coupled system and calculate spectral
function. We also calculated photoemission rate of SYM plasma from spectral
function for light like momentum, AC conductivity and their density dependence.
The suppression of the conductivity in high density is noticed, which might be
yet another mechanism for the Jet quenching phenomena in RHIC experiment.Comment: 27 pages, 10 figure
The rapidity dependence of the proton-to-pion ratio in Au+Au and p+p collisions at sqrt(sNN) = 62.4 and 200 GeV
The BRAHMS measured proton-to-pion ratios in Au+Au and p+p collisions at
\rootsnn{62.4} and \rootsnn{200} are presented as a function of transverse
momentum and collision centrality within the pseudo-rapidity range 0 < eta <
3.8 The results for Au+Au at sqrt(sNN) = 200 GeV are compared with predictions
from models which incorporate hydro-dynamics, hadron rescattering and jet
production, in the eta interval covered. In Au+Au collisions at sqrt(sNN) = 200
GeV, eta ~ 2.2, and at sqrt(sNN) = 62.4 GeV, eta = 0, the bulk medium can be
characterized by the common value of \mi_B ~ 65 MeV. The p/pi ratios measured
for these two selections display a striking agreement in the pT range covered
(up to 2.2 GeV/c). At a collision energy of 62.4 GeV and at forward
pseudo-rapidity we found a crossing point of p/pi+ ratios measured in central
and semi-peripheral Au+Au and in p+p reactions. The crossing occurs in the
narrow eta bin around value of 3.2, simultaneously in the whole covered pT
range (0.3 GeV/c < pT < 2 GeV/c).Comment: 4 pages, 4 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee Included
corrections indicated in internal review report. Minor correction to Fig.
Rapidity-dependent chemical potentials in a statistical approach
We present a single-freeze-out model with thermal and geometric parameters
dependent on the position within the fireball and use it to describe the
rapidity and transverse-momentum spectra of pions, kaons, protons, and
antiprotons measured at RHIC at 200 GeV} by BRAHMS. THERMINATOR is used to
perform the necessary simulation, which includes all resonance decays. The
result of the fit to the data is the expected growth of the baryon and strange
chemical potentials with the spatial rapidity\alpha_\parallel. The value of the
baryon chemical potential at \alpha_\parallel ~ 3 is about 200 MeV, i.e. lies
in the range of the highest SPS energies. The chosen geometry of the fireball
has a decreasing transverse size as the magnitude of \alpha_\parallel is
increased, which also corresponds to decreasing transverse flow. The strange
chemical potential obtained from the fit to the K+/K- ratio is such that the
local strangeness density in the fireball is compatible with zero. The
resulting rapidity spectra of net protons are described qualitatively within
the statistical approach. As a result of our study, the knowledge of the
``topography'' of the fireball is acquired, allowing for other analyses and
predictions.Comment: 6 pages, tals at SQM 200
D^- mesic atoms
The anti-D meson self-energy is evaluated self-consistently, using unitarized
coupled-channel theory, by computing the in-medium meson-baryon T-matrix in the
C=-1,S=0 sector. The heavy pseudo-scalar and heavy vector mesons, anti-D and
anti-D^*, are treated on equal footing as required by heavy quark spin
symmetry. Results for energy levels and widths of D^- mesic atoms in 12C, 40Ca,
118Sn and 208Pb are presented. The spectrum contains states of atomic and of
nuclear types for all nuclei. anti-D^0--nucleus bound states are also obtained.
We find that, after electromagnetic and nuclear cascade, these systems end up
with the anti-D bound in the nucleus, either as a meson or as part of a exotic
anti-D N (pentaquark) loosely bound state.Comment: 22 pages, 4 figures, 5 table
Physics Revealed at Intermediate p_T
A review is given on the subject of hadron production at intermediate
in heavy-ion collisions. The underlying dynamical processes are inferred from
interpreting the data in the framework of recombination. Ridge formation with
or without triggers is found to play an important role in nearly all
observables in that region. Correlation data would be hard to interpret
without taking ridges into account. The semi-hard partons that create the
ridges may even be able to drive elliptic flow without fast thermalization.Comment: 8 pages, plenary talk given at Quark Matter 2008, Jaipur, Indi
Recent Results from the BRAHMS Experiment
We present recent results obtained by the BRAHMS experiment at the
Relativistic Heavy Ion Collider (RHIC) for the systems of Au + Au and Cu + Cu
at \rootsnn{200} and at 62.4 GeV, and p + p at \rootsnn{200}. Nuclear
modification factors for Au + Au and Cu + Cu collisions are presented. Analysis
of anti-particle to particle ratios as a function of rapidity and collision
energy reveal that particle populations at the chemical freeze-out stage for
heavy-ion reactions at and above SPS energies are controlled by the baryon
chemical potential. From the particle spectra we deduce significant radial
expansion ( 0.75), as expected for systems created with a large
initial energy density. We also measure the elliptic flow parameter
versus rapidity and \ptn. We present rapidity dependent ratios within
for Au + Au and Cu + Cu at \rootsnn{200}. \Raa is found to increase
with decreasing collision energy, decreasing system size, and when going
towards more peripheral collisions. However, \Raa shows only a very weak
dependence on rapidity (for ), both for pions and protons.Comment: 16 pages and 14 figures, proceedings for plenary talk at Quark Matter
2005, Budapest, Hungar
Jet Tomography in the Forward Direction at RHIC
Hadron production at high- displays a strong suppression pattern in a
wide rapidity region in heavy ion collisions at RHIC energies. This finding
indicates the presence of strong final state effects for both transversally and
longitudinally traveling partons, namely induced energy loss. We have developed
a perturbative QCD based model to describe hadron production in collision,
which can be combined with the Glauber -- Gribov model to describe hadron
production in heavy ion collisions. Investigating and collisions
at energy GeV at mid-rapidity, we find the opacity of the
strongly interacting hot matter to be proportional to the participant nucleon
number. Considering forward rapidities, the suppression pattern indicates the
formation of a longitudinally contracted dense deconfined zone in central heavy
ion collisions. We determine parameters for the initial geometry from the
existing data.Comment: 6 pages for Hot Quarks '06 Conferenc
How large is "large " for Nuclear matter?
We argue that a so far neglected dimensionless scale, the number of neighbors
in a closely packed system, is relevant for the convergence of the large
expansion at high chemical potential. It is only when the number of colors is
large w.r.t. this new scale (\sim \order{10}) that a convergent large
limit is reached. This provides an explanation as to why the large
expansion, qualitatively successful in in vacuum QCD, fails to describe high
baryo-chemical potential systems, such as nuclear matter. It also means that
phenomenological claims about high density matter based on large
extrapolations should be treated with caution.Comment: Proceedings of CPOD2010 conference, in Dubna. Results based on
Phys.Rev.C82, 055202 (2010), http://arxiv.org/abs/1006.247
Towards the critical behavior for the light nuclei by NIMROD detector
The critical behavior for the light nuclei with A has been
investigated experimentally by the NIMROD multi-detectors. The wide variety of
observables indicate the critical point has been reached in the disassembly of
hot nuclei at an excitation energy of 5.60.5 MeV/u.Comment: 4 pages, 2 figures; Proceeding of 18th Nuclear Physics Division
Conference of the Euro. Phys. Society (NPDC18) "Phase transitions in strongly
interacting matter", Prague, 23.8.-29.8. 2004. To be published in Nuclear
Physics
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