1,579 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
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
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
Study of the derivative expansions for the nuclear structure functions
We study the convergence of the series expansions sometimes used in the
analysis of the nuclear effects in Deep Inelastic Scattering (DIS) proccesses
induced by leptons. The recent advances in statistics and quality of the data,
in particular for neutrinos calls for a good control of the theoretical
uncertainties of the models used in the analysis. Using realistic nuclear
spectral functions which include nucleon correlations, we find that the
convergence of the derivative expansions to the full results is poor except at
very low values of
Relating high-energy lepton-hadron, proton-nucleus and nucleus-nucleus collisions through geometric scaling
A characteristic feature of small-x lepton-proton data from HERA is geometric
scaling -- the fact that over a wide range of x and Q^2 all data can be
described by a single variable , with all x-dependence
encoded in the so-called saturation momentum . Here, we observe
that the same scaling ansatz accounts for nuclear photoabsorption cross
sections and favors the nuclear dependence , . We then make the empirical finding
that the same A-dependence accounts for the centrality evolution of the
multiplicities measured in Au+Au collisions at RHIC. It also allows to
parametrize the high-p_t particle suppression in d+Au collisions at forward
rapidities. If these geometric scaling properties have a common dynamical
origin, then this A-dependence of should emerge as a consequence
of the underlying dynamical model.Comment: 4 pages, 3 postscript figure
Inclusive diffraction in future electron-proton and electron-ion colliders
We analyse the possibilities for the study of inclusive diffraction offered
by future electron--proton/nucleus colliders in the TeV regime, the Large
Hadron-electron Collider as an upgrade of the HL-LHC and the Future Circular
Collider in electron-hadron mode. Compared to collisions at HERA, we find
an extension of the available kinematic range in by a factor of order
and of the maximum by a factor of order for LHeC, while the FCC
version would extend the coverage by a further order of magnitude both in
and . This translates into a range of available momentum fraction of the
diffractive exchange with respect to the hadron (), down to
for a wide range of the momentum fraction of the parton with
respect to the diffractive exchange (). Using the same framework and
methodology employed in previous studies at HERA, considering only the
experimental uncertainties and not those stemming from the functional form of
the initial conditions or other ones of theoretical origin, and under very
conservative assumptions for the luminosities and systematic errors, we find an
improvement in the extraction of diffractive parton densities from fits to
reduced cross sections for inclusive coherent diffraction in by about an
order of magnitude. For , we also perform the simulations for the Electron
Ion Collider. We find that an extraction of the currently unmeasured nuclear
diffractive parton densities is possible with similar accuracy to that in .Comment: 24 pages, 16 figure
- …