35 research outputs found
A heuristic description of high-pT hadron production in heavy ion collisions
Using a simplified model for in-medium dipole evolution accounting for color
filtering effects we study production of hadrons at large transverse momenta
in heavy ion collisions. In the framework of this model, several
important sources of the nuclear suppression observed recently at RHIC and LHC
have been analysed. A short production length of the leading hadron
causes a strong onset of color transparency effects manifested themselves as a
steep rise of the nuclear modification factor at large hadron
's. A dominance of quarks with higher leads to a weaker suppression
at RHIC than the one observed at LHC. In the RHIC kinematic region we include
an additional suppression factor steeply falling with , which is tightly
related to the energy conservation constraints. The latter is irrelevant at LHC
up to GeV while it causes a rather flat dependence of
the factor at RHIC c.m. energy GeV and even an
increasing suppression with at GeV. The calculations
contain only a medium density adjustment, and for an initial time scale =
1 fm we found the energy-dependent maximal values of the transport coefficient,
and 1.3 GeV/fm corresponding to
GeV and 2.76 TeV, respectively. We present a broad variety of predictions for
the nuclear modification factor and the azimuthal asymmetry which are in a good
agreement with available data from experiments at RHIC and LHC.Comment: 14 pages, 17 figures; extra clarifications added in Sects. II and III
(with additional Figs. 1-6) and in the extended Sect. V B (with additional
Fig.11), references added, conclusions unchange
Drell-Yan process in collisions: the exact treatment of coherence effects
In this work, we investigate production of Drell-Yan (DY) pairs in
proton-nucleus collisions in kinematic regions where the corresponding
coherence length does not exceed the nuclear radius, , and the quantum
coherence effects should be treated with a special care. The results for the
nucleus-to-nucleon production ratio available in the literature so far are
usually based on the assumption of a very long coherence length (LCL) . Since the onset of coherence effects is controlled by the coherence
length , we estimated its magnitude in various kinematic regions of the DY
process and found that the LCL approximation should not be used at small and
medium c.m. collision energies ( GeV) as well as at
large dilepton invariant masses. In order to obtain realistic predictions, we
computed for the first time the DY cross section using the generalised color
dipole approach based on the rigorous Green function formalism, which naturally
incorporates the color transparency and quantum coherence effects and hence
allows to estimate the nuclear shadowing with no restrictions on the CL. In
addition to the shadowing effect, we studied a complementary effect of initial
state interactions (ISI) that causes an additional suppression at large values
of the Feynman variable. Numerical results for the nuclear modification factor
accounting for the ISI effect and the finite are compared to the data
available from the fixed-target FNAL measurements and a good agreement has been
found. Besides, we present new predictions for the nuclear suppression as a
function of dilepton rapidity and invariant mass in the kinematic regions that
can be probed by the RHIC collider as well as by the planned AFTER@LHC and LHCb
fixed-target experiments.Comment: 14 pages, 10 figure
Heavy flavor production in high-energy collisions: color dipole description
We present a detailed study of open heavy flavor production in high-energy
collisions at the LHC in the color dipole framework. The transverse
momentum distributions of produced -jets, accounting for the jet energy
loss, as well as produced open charm and bottom mesons in distinct
rapidity intervals relevant for LHC measurements are computed. The dipole model
results for the differential -jet production cross section are compared to
the recent ATLAS and CMS data while the results for and mesons
production cross sections -- to the corresponding LHCb data. Several models for
the phenomenological dipole cross section have been employed to estimate
theoretical uncertainties of the dipole model predictions. We demonstrate that
the primordial transverse momentum distribution of the projectile gluon
significantly affects the meson spectra at low transverse momenta and
contributes to the largest uncertainty of the dipole model predictions.Comment: 22 pages, 9 figure
Theoretical uncertainties in exclusive electroproduction S-wave heavy quarkonia
In this work, we revise the conventional description of J/Psi(1S), Y(1S),
Psi'(2S) and Y'(2S) elastic photo- and electroproduction off a nucleon target
within the color dipole picture and carefully study various sources of
theoretical uncertainties in calculations of the corresponding
electroproduction cross sections. For this purpose, we test the corresponding
predictions using a bulk of available dipole cross section parametrisations
obtained from deep inelastic scattering data at HERA. Specifically, we provide
the detailed analysis of the energy and hard-scale dependencies of quarkonia
yields employing the comprehensive treatment of the quarkonia wave functions in
the Schroedinger equation based approach for a set of available c-\bar{c} and
b-\bar{b} interquark interaction potentials. Besides, we quantify the effect of
Melosh spin rotation, the Q^2-dependence of the diffractive slope and an
uncertainty due to charm and bottom quark mass variations.Comment: 43 pages of Latex including 29 figure
Multiple Scattering Theory for the Photoproduction of Vector Mesons off Nuclei
The integrated cross section for the incoherent photoproduction of vector
mesons on nuclei , , is calculated within Glauber
theory and as a function of the photon energy. The inverse of the longitudinal
momentum transfer is called coherence length and depends on the
virtuality and the energy of the photon. Nuclear transmission factors strongly
depend on ( is the nuclear radius) and this effect may interfere
with the search for color transparency effects.Comment: 9 pages, 1 Postscript figur
Drell-Yan phenomenology in the color dipole picture revisited
An extensive phenomenological study of the Drell-Yan (DY) process in
collisions at various energies is performed in the color dipole framework.
Besides previously studied production we have also included the
contribution relevant at large dilepton invariant masses. We investigate
the DY cross section differential in invariant mass, rapidity and transverse
momentum of the dilepton pair in collisions at RHIC and LHC. We consider
three different phenomenological models for the dipole cross section and found
a reasonable agreement with the available data. As a further test of the color
dipole formalism, we also study the correlation function in azimuthal angle
between the dilepton pair and a forward pion for different
energies, dilepton rapidites and invariant masses. The characteristic
double-peak structure of the correlation function around found for very forward pions and low-mass dilepton pairs is sensitive to
the saturation effects and can be tested by future DY measurements in
collisions.Comment: 16 pages, 12 figures; typos corrected, references added, conclusions
unchange
Spin rotation effects in diffractive electroproduction of heavy quarkonia
In this work we present for the first time the comprehensive study of the
Melosh spin rotation effects in diffractive electroproduction of S-wave heavy
quarkonia off a nucleon target. Such a study has been performed within the
color dipole approach using, as an example and a reference point, two popular
parametrizations of the dipole cross section and two potentials describing the
interaction between Q and bar{Q} and entering in the Schroedinger equation
based formalism for determination of the quarkonia wave functions. We find a
strong onset of spin rotation effects in 1S charmonium photoproduction which is
obviously neglected in present calculations of corresponding cross sections.
For photoproduction of radially excited Psi'(2S) these effects are even
stronger leading to an increase of the photoproduction cross section by a
factor of 2-3 depending on the photon energy. Even in production of radially
excited Y'(2S) and Y"(3S) they can not be neglected and cause the 20-30%
enhancement of the photoproduction cross section. Finally, we predict that the
spin effects vanish gradually with photon virtuality Q^2 following universality
properties in production of different heavy quarkonia as a function of Q^2 +
M_V^2.Comment: 23 pages of Latex including 10 figures. The version for resubmission
to European Physical Journal