1,270 research outputs found
Heavy-ion collisions at the Large Hadron Collider: a review of the results from Run 1
We present an overview of the results obtained in pPb and PbPb collisions at
the Large Hadron Collider during Run 1. We first discuss the results for global
characteristics: cross sections, hadron multiplicities, azimuthal asymmetries,
correlations at low transverse momentum, hadrochemistry, and femtoscopy. We
then review hard and electromagnetic probes: particles with high transverse
momentum, jets, heavy quarks, quarkonium, electroweak bosons and high
transverse momentum photons, low transverse momentum photons and dileptons, and
ultraperipheral collisions. We mainly focus on the experimental results, and
present very briefly the main current theoretical explanations.Comment: 33 pages, 29 figure
On correlations and discreteness in non-linear QCD evolution
We consider modifications of the standard non-linear QCD evolution in an
attempt to account for some of the missing ingredients discussed recently, such
as correlations, discreteness in gluon emission and Pomeron loops. The
evolution is numerically performed using the Balitsky-Kovchegov equation on
individual configurations defined by a given initial value of the saturation
scale, for reduced rapidities . We consider the
effects of averaging over configurations as a way to implement correlations,
using three types of Gaussian averaging around a mean saturation scale.
Further, we heuristically mimic discreteness in gluon emission by considering a
modified evolution in which the tails of the gluon distributions are cut-off.
The approach to scaling and the behavior of the saturation scale with rapidity
in these modified evolutions are studied and compared with the standard
mean-field results. For the large but finite values of rapidity explored, no
strong quantitative difference in scaling for transverse momenta around the
saturation scale is observed. At larger transverse momenta, the influence of
the modifications in the evolution seems most noticeable in the first steps of
the evolution. No influence on the rapidity behavior of the saturation scale
due to the averaging procedure is found. In the cut-off evolution the rapidity
evolution of the saturation scale is slowed down and strongly depends on the
value of the cut-off. Our results stress the need to go beyond simple
modifications of evolution by developing proper theoretical tools that
implement such recently discussed ingredients.Comment: 20 pages, LaTeX, 18 eps figures included using epsfig; changes in v3:
new kind of averaging added, 5 new plots, discussions and conclusions
extended, final versio
Employment in major cities in the district slumps relative to the rest of the country
Federal Reserve District, 8th ; Employment
High-enegy effective action from scattering of QCD shock waves
At high energies, the relevant degrees of freedom are Wilson lines - infinite
gauge links ordered along straight lines collinear to the velocities of
colliding particles. The effective action for these Wilson lines is determined
by the scattering of QCD shock waves. I develop the symmetric expansion of the
effective action in powers of strength of one of the shock waves and calculate
the leading term of the series. The corresponding first-order effective action,
symmetric with respect to projectile and target, includes both up and down fan
diagrams and pomeron loops.Comment: 15 pages, 10 eps figure
J/psi suppression at SPS and RHIC in the comovers approach
The NA50 collaboration data on the suppression are compared with the
results obtained in a comovers approach based on the Dual Parton Model (DPM).
Predictions for the suppression versus the charged multiplicity -
measured in the rapidity region of the dimuon trigger - are given for SPS and
RHIC energies.Comment: 4 pages, contribution to QM200
Anomalous suppression of production at large transverse momentum in Au + Au and d + Au collisions at 200 GeV
We propose a model of suppression of large -pions in heavy ion
collisions based on the interaction of the large pion with the dense
medium created in the collision. The model is practically the same as the one
previously introduced to describe suppression. Both the and the
centrality dependence of the data are reproduced. In deuteron-gold collisions,
the effect of the final state interaction with the dense medium turns out to be
negligibly small. Here the main features of the data are also reproduced both
at mid and at forward rapidities.Comment: 20 pages, latex, 3 postscript figures. Last version, to be published
in EJP
Correlations and the ridge in the Color Glass Condensate beyond the glasma graph approximation
We consider two-gluon production in dilute-dense collisions within the Color Glass Condensate framework, applicable to both proton-nucleus and heavy-light ion collisions. We go beyond the glasma graph approximation which is valid in the dilute-dilute limit and show the correspondence between the glasma graphs and the kT-factorized approach that we use in our calculation. We then identify the classical uncorrelated, and the Hanbury-Brown-Twiss (HBT) and Bose enhancement correlated contributions, with the Bose enhancement contribution being suppressed by the number of degrees of freedom with respect to the uncorrelated piece. We show that both the HBT and the Bose enhancement pieces survive the inclusion of higher order contributions in density and that they stem from the quadrupole piece of the two-gluon inclusive cross section. Finally, we illustrate the results using a toy model that allows a simple numerical implementation.The
work of TA is supported by Grant No. 2017/26/M/ST2/01074 of the National Science Centre,
Poland. The work of NA and DEW were supported by the European Research Council
grant HotLHC ERC-2011-StG-279579, Ministerio de Ciencia e Innovaci on of Spain under
project FPA2014-58293-C2-1-P and Unidad de Excelencia Mar a de Maetzu under project
MDM-2016-0692, Xunta de Galicia (Conseller a de Educaci on) within the Strategic Unit
AGRUP2015/11, and FEDER. This work has been performed in the framework of COST
Action CA15213 \Theory of hot matter and relativistic heavy-ion collisions" (THOR).S
J/ suppression at 200 GeV in the comovers interaction model
The yield of per binary nucleon-nucleon collision in and
collisions at GeV is computed in the framework of the
dual parton model, supplemented with final state interaction (comovers
interaction). For the latter we use the same value of the cross-section,
mb, which describes the anomalous suppression
observed at CERN-SPS energies. Several possibilities for the value of the
absorptive cross-section are considered. Shadowing is introduced in both the
comovers and the yields. A comparison with the results at CERN-SPS,
including a prediction for collisions, is also presented.Comment: 15 pages, 3 figure
Energy Dependence of the Cronin Effect from Non-Linear QCD Evolution
The non-linear evolution of dense partonic systems has been suggested as one
of the novel physics mechanisms relevant to the dynamics of hadron-nucleus and
nucleus-nucleus collisions at collider energies. Here we study to what extent
the description of Cronin enhancement in the framework of this non-linear
evolution is consistent with the recent observation in 200 AGeV d--Au
collisions at the Relativistic Heavy Ion Collider. We solve the
Balitsky-Kovchegov evolution equation numerically for several initial
conditions encoding Cronin enhancement. We find that the properly normalized
nuclear gluon distribution is suppressed at all momenta relative to that of a
single nucleon. Calculating the resulting spectrum of produced gluons in p-A
and A-A collisions, we establish that the nonlinear QCD evolution is unable to
generate a Cronin type enhancement, and that it quickly erases any such
enhancement which may be present at lower energies.Comment: 4 pages, Latex, 3 eps-figure
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