1,329 research outputs found

### Introduction to Low x Physics and Saturation

The idea of saturation of parton densities in small x physics is briefly
introduced. Some aspects of saturation are described, mainly focusing on the
status of our knowledge on the non-linear equations describing the high parton
density regime. Implications of saturation ideas on the description of nuclear
collisions at the Relativistic Heavy Ion Collider are discussed.Comment: 8 pages in LaTeX using enclosed appolb.cls, 3 eps figures included
using epsfig; minireview at the XXXIIIrd International Symposium on
Multiparticle Dynamics (Kracow, Poland, September 5th-11th 2003

### Predictions for the heavy-ion programme at the Large Hadron Collider

I review the main predictions for the heavy-ion programme at the Large Hadron
Collider (LHC) at CERN, as available in early April 2009. I begin by
remembering the standard claims made in view of the experimental data measured
at the Super Proton Synchrotron (SPS) at CERN and at the Relativistic Heavy Ion
Collider (RHIC) at the BNL. These claims will be used for later discussion of
the new opportunities at the LHC. Next I review the generic, qualitative
expectations for the LHC. Then I turn to quantitative predictions: First I
analyze observables which characterize directly the medium produced in the
collisions - bulk observables or soft probes -: multiplicities, collective
flow, hadrochemistry at low transverse momentum, correlations and fluctuations.
Second, I move to calibrated probes of the medium i.e. typically those whose
expectation in the absence of any medium can be described in Quantum
Chromodynamics (QCD) using perturbative techniques (pQCD), usually called hard
probes. I discuss particle production at large transverse momentum and jets,
heavy-quark and quarkonium production, and photons and dileptons. Finally,
after a brief review of pA collisions, I end with a summary and a discussion
about the potentiality of the measurements at the LHC - particularly those made
during the first run - to further substantiate or, on the contrary, disproof
the picture of the medium that has arisen from the confrontation between the
SPS and RHIC data, and theoretical models.Comment: 64 pages, 40 figures, 7 tables; invited review for "Quark-Gluon
Plasma 4"; v2: small changes, some predictions and references added, final
versio

### Nuclear Structure Functions at Small x in Multiple Scattering Approaches

A simple model for nuclear structure functions in the region of small $x$ and
small and moderate $Q^2$, is presented. It is a parameter-free extension, in
the Glauber-Gribov approach to nuclear collisions, of a saturation model for
the nucleon. A reasonable agreement with experimental data on ratios of nuclear
structure functions is obtained. The unintegrated gluon distribution and the
behavior of the saturation scale which result from this model are discussed.Comment: LaTeX2e, uses enclosed moriond.sty, 4 pages, 2 eps figures included
using epsfig, contribution to the XXXVIIIth Rencontres de Moriond: QCD and
Hadronic Interactions, Les Arcs, France, March 22nd-29th 200

### A simple model for nuclear structure functions at small $x$ in the dipole picture

A simple model for nuclear structure functions in the region of small x and
small and moderate $Q^2$, is presented. It is a parameter-free extension, in
the Glauber-Gribov approach to nuclear collisions, of a saturation model for
the nucleon. A reasonable agreement with experimental data on ratios of nuclear
structure functions is obtained. Nuclear effects in the
longitudinal-to-transverse cross section ratios are found to be small.
Predictions of the model for values of $x$ smaller than those available to
present experiments are given. The unintegrated gluon distribution and the
behaviour of the saturation scale which result from this model are shown and
discussed.Comment: LaTeX, 27 pages, 9 postscript figures included using epsfig; final
version: discussion on geometrical scaling clarified, comparison of gluon
densities with other approaches added, Fig. 8 redone, references added and
updated, some misprints corrected, results and conclusions unchange

### Jet quenching

Jet quenching studies play a prominent role in our current understanding of
ultra-relativistic heavy ion collisions. In this review I first present the
available formalism to compute medium-induced gluon radiation. Then I discuss
its effect on single particle spectra, with dedicated attention to the case of
the radiating parton being a massive quark. Next I examine more differential
observables like jet shapes and multiplicities, and the consequences of flow on
radiative energy loss. I conclude with some remarks.Comment: LaTeX, 8 pages, 7 eps figures, uses enclosed cjpsuppl.cls; invited
talk at Physics at LHC, Vienna, Austria, July 13th-17th 200

### 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 the long-range correlations in hadron-nucleus collisions

Long-range correlations between multiplicities in different rapidity windows
in hadron-nucleus collisions are analyzed. After recalling the standard results
in the probabilistic model, we study them in the framework of perturbative QCD.
Considering interacting BFKL pomerons in the form of fan diagrams coupled to a
dilute projectile, analytic estimates are done for very large rapidities. The
correlation strength results weakly depending on energy and centrality or
nuclear size, and generically greater than unity. Finally, we turn to the Color
Glass Condensate framework. For a saturated projectile and considering the most
feasible experimental situation of forward and backward rapidity windows
symmetric around the center-of-mass, the resulting correlation strength turns
out to be larger than unity and shows a non-monotonic behavior with increasing
energy, first increasing and then decreasing to a limiting value. Its behavior
with increasing centrality or nuclear size depends on the considered rapidity
windows.Comment: 17 pages, LaTeX, 6 eps figures included using graphicx; v2: error in
the CGC formula corrected, conclusions of the corresponding section changed
accordingl

### 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 $y=(\alpha_s N_c/\pi) Y<10$. 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

- â€¦