831 research outputs found
Angular pattern of minijet transverse energy flow in hadron and nuclear collisions
The azimuthal asymmetry of minijet system produced at the early stage of
nucleon-nucleon and nuclear collisions in a central rapidity window is studied.
We show that in pp collisions the minijet transverse energy production in a
central rapidity window is essentially unbalanced in azimuth due to asymmetric
contributions in which only one minijet hits the acceptance window. We further
study the angular pattern of transverse energy flow generated by semihard
degrees of freedom at the early stage of high energy nuclear collisions and its
dependence on the number of semihard collisions in the models both including
and neglecting soft contributions to the inelastic cross section at RHIC and
LHC energies as well as on the choice of the infrared cutoff.Comment: 25 LaTeX pages, 11 figures embedded with epsf; expanded versio
ALICE potential for heavy-flavour physics
The Large Hadron Collider (LHC), where lead nuclei will collide at the
unprecedented c.m.s. energy of 5.5 TeV per nucleon-nucleon pair, will offer new
and unique opportunities for the study of the properties of strongly
interacting matter at high energy density over extended volumes. We will
briefly explain why heavy-flavour particles are well-suited tools for such a
study and we will describe how the ALICE experiment is preparing to make use of
these tools.Comment: 6 pages, 3 figures, prepared for the Proceedings of "Strange Quark
Matter 2007", Levoca, Slovaki
CGC and initial state effects in Heavy Ion Collisions
A brief review of the phenomenological studies in the field of heavy ion
collisions based on the Color Glass Condensate theory and, in particular, of
those relying in the use of the BK equation including running coupling effects
is presented.Comment: 6 pages, 5 figures. Contribution to the proceedings of the Hot Quarks
2010 Conference. June 21-26, La Londe Les Maures, Franc
Jets in 200 GeV p+p and d+Au collisions from the STAR experiment at RHIC
Full jet reconstruction in heavy-ion collisions is a promising tool for the
quantitative study of properties of the dense medium produced at RHIC.
Measurements of d+Au collisions are important to disentangle initial state
nuclear effects from medium-induced kT broadening and jet quenching. Study of
jet production and properties in d+Au in combination with similar studies in
p+p is an important baseline measurement needed to better understand heavy-ion
results. We present mid-rapidity inclusive jet pT spectra and di-jet
correlations (kT) in 200 GeV p+p and d+Au collisions from the 2007-2008 RHIC
run. We discuss the methods used to correct the data for detector effects and
for background in d+Au collisions.Comment: 4 pages, 5 figures. To appear in Hot Quarks 2010 conference
proceeding
From EMC- and Cronin-effects to signals of quark-gluon plasma
The EMC- and Cronin-effects are explained by a unitarized evolution equation,
where the shadowing and antishadowing corrections are dynamically produced by
gluon fusions. For this sake, an alternative form of the GLR-MQ-ZRS equation is
derived. The resulting integrated and unintegrated gluon distributions in
proton and nuclei are used to analyze the contributions of the initial parton
distributions to the nuclear suppression factor in heavy ion collisions. A
simulation of the fractional energy loss is extracted from the RHIC and LHC
data, where the contributions of the nuclear shadowing and antishadowing
effects are considered. We find a rapid crossover from week energy loss to
strong energy loss at a universal critical energy of gluon jet .Comment: 35 pages, 13 figures, to be published in Int. J. Mod. Phys.
Calculating Dilepton Rates from Monte Carlo Simulations of Parton Production
To calculate dilepton rates in a Monte Carlo simulation of ultrarelativistic
heavy ion collisions, one usually scales the number of similar QCD processes by
a ratio of the corresponding differential probabilities. We derive the formula
for such a ratio especially for dilepton bremsstrahlung processes. We also
discuss the non-triviality of including higher order corrections to direct
Drell-Yan process. The resultant mass spectra from our Monte Carlo simulation
are consistent with the semi-analytical calculation using dilepton
fragmentation functions.Comment: 14 pages in RevTex, 3 figures in uuencoded files, LBL-3466
Elliptic flow in nuclear collisions at the Large Hadron Collider
We use perfect-fluid hydrodynamical model to predict the elliptic flow
coefficients in Pb + Pb collisions at the Large Hadron Collider (LHC). The
initial state for the hydrodynamical calculation for central collisions
is obtained from the perturbative QCD + saturation (EKRT) model. The centrality
dependence of the initial state is modeled by the optical Glauber model. We
show that the baseline results obtained from the framework are in good
agreement with the data from the Relativistic Heavy Ion Collider (RHIC), and
show predictions for the spectra and elliptic flow of pions in Pb + Pb
collisions at the LHC. Also mass and multiplicity effects are discussed.Comment: 11 pages, 10 figure
Dynamical freeze-out condition in ultrarelativistic heavy ion collisions
We determine the decoupling surfaces for the hydrodynamic description of
heavy ion collisions at RHIC and LHC by comparing the local hydrodynamic
expansion rate with the microscopic pion-pion scattering rate. The pion
spectra for nuclear collisions at RHIC and LHC are computed by applying the
Cooper-Frye procedure on the dynamical-decoupling surfaces, and compared with
those obtained from the constant-temperature freeze-out surfaces. Comparison
with RHIC data shows that the system indeed decouples when the expansion rate
becomes comparable with the pion scattering rate. The dynamical decoupling
based on the rates comparison also suggests that the effective decoupling
temperature in central heavy ion collisions remains practically unchanged from
RHIC to LHC.Comment: 7 pages, 9 figure
On the theoretical and experimental uncertainties in the extraction of the J/psi absorption cross section in cold nuclear matter
We investigate the cold nuclear matter effects on production, whose
understanding is fundamental to study the quark-gluon plasma. Two of these
effects are of particular relevance: the shadowing of the parton distributions
and the nuclear absorption of the pair. If 's are not
produced {\it via} a process as suggested by recent theoretical
works, one has to modify accordingly the way to compute the nuclear shadowing.
This naturally induces differences in the absorption cross-section fit to the
data. A careful analysis of these differences however requires taking into
account the experimental uncertainties and their correlations, as done in this
work for Au collisions at \sqrtsNN=200\mathrm{GeV}, using several
shadowing parametrisations.Comment: 6 pages, 1 table, 3 figures, Submitted to J. Phys. G, talk given at
the International Conference on Strangeness in Quark Matter (SQM2009),
Buzios, Brasil, Sep. 27 - Oct. 2, 200
Constraining the Physics of Jet Quenching
Hard probes in the context of ultrarelativistic heavy ion collisions
represent a key class of observables studied to gain informations about the QCD
medium created in such collisions. However, in practice the so-called jet
tomography has turned out to be more difficult than expected initially. One of
the major obstacles in extracting reliable tomographic information from the
data is that neither the parton-medium interaction nor the medium geometry are
known with great precision, and thus a difference in model assumptions in the
hard perturbative Quantum Choromdynamics (pQCD) modelling can usually be
compensated by a corresponding change of assumptions in the soft bulk medium
sector and vice versa. The only way to overcome this problem is to study the
full systematics of combinations of parton-medium interaction and bulk medium
evolution models. This work presents a meta-analysis summarizing results from a
number of such systematical studies and discusses in detail how certain data
sets provide specific constraints for models. Combining all available
information, only a small group of models exhibiting certain characteristic
features consistent with a pQCD picture of parton-medium interaction is found
to be viable given the data. In this picture, the dominant mechanism is
medium-induced radiation combined with a surprisingly small component of
elastic energy transfer into the medium.Comment: 22 pages, 3 figures, 2 table
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