81 research outputs found
Photon-tagged correlations in heavy-ion collisions: kinematic requirements and a case study
Photon-tagged correlations may be useful to determine how the dense partonic
medium produced in heavy-ion collisions affects the fragmentation of
high-energy quarks and gluons into a leading hadron. In these proceedings, I
discuss the kinematic requirements for the hadron and the prompt photon
transverse momentum cuts. A case study at LHC energy, tagging on p_T > 20 GeV
and p_T > 50 GeV photons, is then briefly examined.Comment: 4 pages, 2 figures. To appear in the proceedings of the 19th
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions
(QM2006), Shanghai, China, 14-20 November 200
Quarkonium suppression in heavy-ion collisions from coherent energy loss in cold nuclear matter
The effect of parton energy loss in cold nuclear matter on the suppression of
quarkonia (J/psi, Upsilon) in heavy-ion collisions is investigated, by
extrapolating a model based on coherent radiative energy loss recently shown to
describe successfully J/psi and Upsilon suppression in proton-nucleus
collisions. Model predictions in heavy-ion collisions at RHIC (Au-Au, Cu-Cu,
and Cu-Au) and LHC (Pb-Pb) show a sizable suppression arising from the sole
effect of energy loss in cold matter. This effect should thus be considered in
order to get a reliable baseline for cold nuclear matter effects in quarkonium
suppression in heavy-ion collisions, in view of disentangling hot from cold
nuclear effects.Comment: 20 pages, 9 figure
Heavy-quarkonium suppression in p-A collisions from parton energy loss in cold QCD matter
The effects of parton energy loss in cold nuclear matter on heavy-quarkonium
suppression in p-A collisions are studied. It is shown from first principles
that at large quarkonium energy E and small production angle in the nucleus
rest frame, the medium-induced energy loss scales as E. Using this result, a
phenomenological model depending on a single free parameter is able to
reproduce J/psi and Upsilon suppression data in a broad xF-range and at various
center-of-mass energies. These results strongly support energy loss as the
dominant effect in heavy-quarkonium suppression in p-A collisions. Predictions
for J/psi and Upsilon suppression in p-Pb collisions at the LHC are made. It is
argued that parton energy loss scaling as E should generally apply to hadron
production in p-A collisions, such as light hadron or open charm production.Comment: 41 pages, 21 figures, 4 tables. v2: Model corrected at small and
negative xF (section 3.1), conclusions unchange
Quarkonium suppression from coherent energy loss in fixed-target experiments using LHC beams
Quarkonium production in proton-nucleus collisions is a powerful tool to
disentangle cold nuclear matter effects. A model based on coherent energy loss
is able to explain the available quarkonium suppression data in a broad range
of rapidities, from fixed-target to collider energies, suggesting cold energy
loss to be the dominant effect in quarkonium suppression in p-A collisions.
This could be further tested in a high-energy fixed-target experiment using a
proton or nucleus beam. The nuclear modification factors of J/ and
as a function of rapidity are computed in p-A collisions at
GeV, and in p-Pb and Pb-Pb collisions at GeV.
These center-of-mass energies correspond to the collision on fixed-target
nuclei of 7 TeV protons and 2.76 TeV lead nuclei available at the LHC.Comment: 7 pages, 2 figure
Coherent medium-induced gluon radiation in hard forward partonic processes
We revisit the medium-induced coherent radiation associated to hard and
forward (small angle) scattering of an energetic parton through a nuclear
medium. We consider all hard forward processes (, ,
and ), and derive the energy spectrum of induced coherent
radiation rigorously to all orders in the opacity expansion and for the
specific case of a Coulomb scattering potential. We obtain a simple general
formula for the induced coherent spectrum, which encompasses the results
corresponding to previously known special cases.Comment: 35 pages, 10 figures; title changed, introduction developed and
references added, detailed discussion added in Section VI, all results
unchanged; version v2 corresponds to the published versio
J/psi suppression in p-A collisions from parton energy loss in cold QCD matter
The effects of energy loss in cold nuclear matter on J/psi suppression in p-A
collisions are studied. A simple model based on first principles and depending
on a single free parameter is able to reproduce J/psi suppression data at large
xF and at various center-of-mass energies. These results strongly support
energy loss as a dominant effect in quarkonium suppression. They also give some
hint on its hadroproduction mechanism suggesting color neutralization to happen
on long time-scales. Predictions for J/psi and Upsilon suppression in p-Pb
collisions at the LHC are made.Comment: 4 pages, 4 figure
Depletion of atmospheric neutrino fluxes from parton energy loss
The phenomenon of fully coherent energy loss (FCEL) in the collisions of
protons on light ions affects the physics of cosmic ray air showers. As an
illustration, we address two closely related observables: hadron production in
forthcoming proton-oxygen collisions at the LHC, and the atmospheric neutrino
fluxes induced by the semileptonic decays of hadrons produced in proton-air
collisions. In both cases, a significant nuclear suppression due to FCEL is
predicted. The conventional and prompt neutrino fluxes are suppressed by in their relevant neutrino energy ranges. Previous estimates of
atmospheric neutrino fluxes should be scaled down accordingly to account for
FCEL.Comment: 5 pages, 4 figure
Higher-Twist Dynamics in Large Transverse Momentum Hadron Production
A scaling law analysis of the world data on inclusive large-pT hadron
production in hadronic collisions is carried out. A significant deviation from
leading-twist perturbative QCD predictions at next-to-leading order is
reported. The observed discrepancy is largest at high values of xT=2pT/sqrt(s).
In contrast, the production of prompt photons and jets exhibits the scaling
behavior which is close to the conformal limit, in agreement with the
leading-twist expectation. These results bring evidence for a non-negligible
contribution of higher-twist processes in large-pT hadron production in
hadronic collisions, where the hadron is produced directly in the hard
subprocess rather than by gluon or quark jet fragmentation. Predictions for
scaling exponents at RHIC and LHC are given, and it is suggested to trigger the
isolated large-pT hadron production to enhance higher-twist processes.Comment: 5 pages, 4 figures. Extended introduction, additional reference
Single inclusive pion pT-spectra in proton-proton collisions at sqrt(s) = 22.4GeV: data versus perturbative QCD calculations
We compare the inclusive transverse momentum spectra of single pions above pT
= 3 GeV/c measured in proton-proton (p-p) collisions at sqrt(s) = 21.7 - 23.8
GeV, with next-to-leading order (NLO) perturbative QCD (pQCD) predictions using
recent parametrizations of the parton densities and parton-to-pion
fragmentation functions. Although the dependence on the theoretical scales is
large, the calculations can reproduce the experimental results both in
magnitude and shape. Based on the existing data and on a pQCD
-rescaling of the measured spectra, we provide a practical
parametrization of the baseline p-p pion transverse momentum spectrum to be
compared to nucleus-nucleus collisions data at sqrt(s_NN) = 22.4 GeV.Comment: 16 pages, 7 figure
- …