1,697 research outputs found
Heavy-to-light ratios as a test of medium-induced energy loss at RHIC and the LHC
The ratio of nuclear modification factors of high- heavy-flavored mesons
tolight-flavored hadrons (heavy-to-light ratio) is shown to be a sensitive tool
to test medium-induced energy loss at RHIC and LHC energies. Heavy-to-light
ratios of mesons at RHIC in the region GeV, and of and
mesons at the LHC in the region GeV, are proposed for such a test.
Finally, the different contributions to the nuclear modification factor for
electrons at RHIC are analyzed. Preliminary PHENIX and STAR data are compatible
with radiative energy loss provided the contribution of electrons from beauty
decays is small compared to that from charm.Comment: 5 pages, latex, 4 eps figs included using graphicx; to appear in the
proceedings of 18th International Conference on Ultrarelativistic
Nucleus-Nucleus Collisions: Quark Matter 2005 (QM 2005), Budapest, Hungary,
4-9 Aug 200
Nuclear Structure Functions and Heavy Flavour Leptoproduction Off the Nucleus at Small x in Perturbative QCD
Nuclear structure functions and cross-sections for heavy flavour production
in lepton-nucleus collisions are investigated in the low region accessible
now or in the near future. The scattering on a heavy nucleus is described by
the sum of fan diagrams of BFKL pomerons, which is exact in the high-colour
limit. The initial condition for the evolution at is taken from a
saturation model, which reproduces the experimental data on the proton. The
dependence of the structure functions is well described by a power factor
, with reaching values as low as 1/2 at extremely low .
The total cross-sections for heavy flavour production reach values of the order
of mb, and the corresponding transverse momentum distributions are sizeable up
to transverse momenta larger than the initial large scale .Comment: LaTeX2e, 16 pages, 6 eps figures included using epsfig; final
version, some comments added, results and conclusions unchange
Gluon distributions in nuclei at small x: guidance from different models
Different approaches to gluon shadowing at small x are reviewed. Some
available results relevant for RHIC and LHC are compared.Comment: 6 pages, LaTeX2e, uses enclosed cernrep.cls, one eps figure enclosed
using graphicx, contribution to the Yellow Report on Hard Probes in Heavy Ion
Collisions at the LH
Monte Carlo for Jet Showers in the Medium
The most commonly employed formalisms of radiative energy loss have been
derived in the high- energy approximation. In its present form, it is reliable
only for the medium modifications of inclusive particle spectra. Modifications
to this formalism are expected to be important for less inclusive measurements.
This is especially relevant for reconstructed jets in heavy-ion collisions,
which are becoming available only recently. We present some ideas to overcome
this limitation. Specifically, we show an implementation of radiative energy
loss within a jet parton shower. This implementation has been done within the
PYTHIA Monte Carlo event generator. We present the publicly available routine
Q-PYTHIA and discuss some of the obtained physics results.Comment: 4 pages, 1 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee. Final version
with minor typos correcte
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
Medium-Induced Gluon Radiation off Massive Quarks Fills the Dead Cone
We calculate the transverse momentum dependence of the medium-induced gluon
energy distribution radiated off massive quarks in spatially extended QCD
matter. In the absence of a medium, the distribution shows a characteristic
mass-dependent depletion of the gluon radiation for angles smaller than m/E,
the so-called dead cone effect. Medium-modifications of this spectrum are
calculated as a function of quark mass, initial quark energy, in-medium
pathlength and density. Generically, medium-induced gluon radiation is found to
fill the dead cone, but it is reduced at large gluon energies compared to the
radiation off light quarks. We quantify the resulting mass-dependence for
momentum-averaged quantities (gluon energy distribution and average parton
energy loss), compare it to simple approximation schemes and discuss its
observable consequences for nucleus-nucleus collisions at RHIC and LHC. In
particular, our analysis does not favor the complete disappearance of energy
loss effects from leading open charm spectra at RHIC.Comment: 27 pages LaTeX, 15 eps-figure
Nuclear Structure Functions at Small x from Inelastic Shadowing and Diffraction
Nuclear structure functions at small x and small or moderate are
studied using the relation with diffraction on nucleons which arises from
Gribov's Reggeon Calculus. A reasonable description of experimental data is
obtained with no fitted parameters. A comparison with other models and
predictions for future lepton-ion colliders are provided. Consequences for the
reduction of multiplicities in nucleus-nucleus collisions at energies of RHIC
and LHC are examined.Comment: LaTeX, 32 pages, 14 eps figures included using epsfig; 1 reference
update
Medium-induced emissions of hard gluons
We present a derivation of the medium-induced gluon radiation spectrum beyond
the current limitation of soft gluon emission. Making use of the path integral
approach to describe the propagation of high-energy particles inside a medium,
we study the limiting case of a hard gluon emission. Analytical and numerical
results are presented and discussed within the multiple soft scattering
approximation. An ansatz interpolating between soft and hard gluon emissions is
provided. The Landau-Pomeranchuk-Migdal effect is observed in the expected
kinematic region.Comment: 17 pages, 6 figures. Minor corrections, references updated. Accepted
by Phys. Lett.
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