108 research outputs found
Medium-induced color flow softens hadronization
Medium-induced parton energy loss, resulting from gluon exchanges between the
QCD matter and partonic projectiles, is expected to underly the strong
suppression of jets and high- hadron spectra observed in
ultra-relativistic heavy ion collisions. Here, we present the first
color-differential calculation of parton energy loss. We find that color
exchange between medium and projectile enhances the invariant mass of energetic
color singlet clusters in the parton shower by a parametrically large factor
proportional to the square root of the projectile energy. This effect is seen
in more than half of the most energetic color-singlet fragments of
medium-modified parton branchings. Applying a standard cluster hadronization
model, we find that it leads to a characteristic additional softening of
hadronic spectra. A fair description of the nuclear modification factor
measured at the LHC may then be obtained for relatively low momentum transfers
from the medium
Jet physics in heavy-ion collisions
Jets are expected to play a prominent role in the ongoing efforts to
characterize the hot and dense QCD medium created in ultrarelativistic heavy
ion collisions. The success of this program depends crucially on the existence
of a full theoretical account of the dynamical effects of the medium on the
jets that develop within it. By focussing on the discussion of the essential
ingredients underlying such a theoretical formulation, we aim to set the
appropriate context in which current and future developments can be understood.Comment: 36 pages, 5 figures, few minor corrections, references added. Final
version published in IJMP
Rapidity and energy dependence of average transverse momentum and particle density in saturation models
Saturation models -- colour glass condensate and string percolation -- impose
a strict relation between the average transverse momentum, , and the
rapidity particle densities, dn/dy. By combining this relation with an
appropriate evolution equation for dn/dy, and imposing energy-momentum
conservation, we obtain a fair description of data, for generic AB collisions
(hadron-hadron, hadron-nucleus and nucleus-nucleus) at all rapidities and
(high) energies. Predictions are given for the LHC.Comment: 16 pages, 4 figures, 2 table
Forward-Backward rapidity correlations at all rapidities
We discuss forward-bacward rapidity correlations in the general situation of
asymmetrical collisions, asymmetric rapidity windows, higher rapidities and
higher energy. We give predictions for RHIC and LHC.Comment: 6 pages, 3 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
Nuclear size and rapidity dependence of the saturation scale from QCD evolution and experimental data
The solutions of the Balitsky-Kovchegov evolution equations are studied
numerically and compared with known analytical estimations. The rapidity and
nuclear size dependences of the saturation scale are obtained for the cases of
fixed and running coupling constant. These same dependences are studied in
experimental data, on lepton-nucleus, deuteron-nucleus and nucleus-nucleus
collisions, through geometric scaling and compared with the theoretical
calculations.Comment: 8 pages, 8 figures. Contribution based on talks given by J. G.
Milhano and C. A. Salgado to the proceedings of ``Hard Probes 2004'',
Ericeira (Portugal), November 4-10, 200
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