3,804 research outputs found
The physics programme of the ALICE experiment at the LHC
ALICE is the dedicated heavy-ion experiment designed to exploit the unique physics potential of nucleus-nucleus interactions at the LHC energies. ALICE will also study proton-proton and proton-nucleus collisions, which will provide reference data for the nucleus-nucleus collisions. In addition the pp data will allow for a number of genuine pp physics studies, especially in the low p t domain. In this paper we present the ALICE reach for a representative sample of measured observables, and we discuss how they test the properties of the matter created in heavy-ion collisions
Charmed hadron production in high-energy nuclear collisions
We present a new model for the description of heavy-flavor hadronization in
high-energy nuclear (and possibly hadronic) collisions, where the process takes
place not in the vacuum, but in the presence of other color charges. We explore
its effect on the charmed hadron yields and kinematic distributions once the
latter is applied at the end of transport calculations used to simulate the
propagation of heavy quarks in the deconfined fireball produced in nuclear
collisions. The model is based on the formation of color-singlet clusters
through the recombination of charm quarks with light antiquarks or diquarks
from the same fluid cell. This local mechanism of color neutralization leads to
a strong space-momentum correlation, which provides a substantial enhancement
of charmed baryon production -- with respect to expectations based on
collisions -- and of the collective flow of all charmed hadrons. We also
discuss the similarities between our model and recently developed mechanisms
implemented in QCD event generators to simulate medium corrections to
hadronization in the presence of other nearby color charges.Comment: 6 pages, proceedings of ICHEP-2022. arXiv admin note: substantial
text overlap with arXiv:2209.0423
Heavy-flavor transport and hadronization in pp collisions
Recent experimental results on the Lambda_c/D^0 ratio in proton-proton
collisions have revealed a significant enhancement compared to expectations
based on universal fragmentation fractions/functions across different colliding
systems, from e+e- to pp. This unexpected enhancement has sparked speculation
about the potential effects of a deconfined medium impacting hadronization,
previously considered exclusive to heavy-ion collisions. In this study, we
propose a novel approach that assumes the formation of a small, deconfined, and
expanding fireball even in pp collisions, where charm quarks can undergo
rescattering and hadronization. We make use of the same in-medium hadronization
mechanism developed for heavy-ion collisions, which involves local
color-neutralization through recombination of charm quarks with nearby opposite
color charges from the background fireball. Our model incorporates the presence
of diquark excitations in the hot medium, which promotes the formation of
charmed baryons. Moreover, the recombination process, involving closely aligned
partons from the same fluid cell, effectively transfers the collective flow of
the system to the final charmed hadrons. We show that this framework can
qualitatively reproduce the observed experimental findings in heavy-flavor
particle-yield ratios, -spectra and elliptic-flow coefficients. Our
results provide new, complementary supporting evidence that the collective
phenomena observed in small systems naturally have the same origin as those
observed in heavy-ion collision
The silicon multiplicity detector for the NA50 experiment at CERN
The design, operation and performance of the silicon strip Multiplicity Detector for the heavy-ion experiment NA50 at CERN are presented. The main features of the detector are high speed (50 MHz sampling frequency), high granularity (more than 13,000 strips), and good radiation resistance. The detector provided a measurement ofevent centrality in PbâPb collisions, as well as target identification and the measurement ofcharged particle pseudorapidity distributions as a function of centrality. r 2002 Elsevier Science B.V. All rights reserved. PACS: 29.4
The silicon Multiplicity Detector for the NA50 experiment
Abstract The operation and performance of the silicon strip Multiplicity Detector in the heavy-ion experiment NA50 at CERN are presented together with a selection of physics results. The main features of the detector are high speed (50 MHz sampling frequency), high granularity (more than 13,000 strips), and good radiation resistance. The detector provided a measurement of event centrality in PbâPb collisions, as well as target identification and the measurement of charged particle pseudorapidity distributions as a function of centrality
A new measurement of J/psi suppression in Pb-Pb collisions at 158 GeV per nucleon
We present a new measurement of J/psi production in Pb-Pb collisions at 158
GeV/nucleon, from the data sample collected in year 2000 by the NA50
Collaboration, under improved experimental conditions with respect to previous
years. With the target system placed in vacuum, the setup was better adapted to
study, in particular, the most peripheral nuclear collisions with unprecedented
accuracy. The analysis of this data sample shows that the (J/psi)/Drell-Yan
cross-sections ratio measured in the most peripheral Pb-Pb interactions is in
good agreement with the nuclear absorption pattern extrapolated from the
studies of proton-nucleus collisions. Furthermore, this new measurement
confirms our previous observation that the (J/psi)/Drell-Yan cross-sections
ratio departs from the normal nuclear absorption pattern for semi-central Pb-Pb
collisions and that this ratio persistently decreases up to the most central
collisions.Comment: 19 pages, 10 figures. Submitted to Eur. Phys. J.
J/psi azimuthal anisotropy relative to the reaction plane in Pb-Pb collisions at 158 GeV per nucleon
The J/ azimuthal distribution relative to the reaction plane has been
measured by the NA50 experiment in Pb-Pb collisions at 158 GeV/nucleon. Various
physical mechanisms related to charmonium dissociation in the medium created in
the heavy ion collision are expected to introduce an anisotropy in the
azimuthal distribution of the observed J/ mesons at SPS energies. Hence,
the measurement of J/ elliptic anisotropy, quantified by the Fourier
coefficient v of the J/ azimuthal distribution relative to the
reaction plane, is an important tool to constrain theoretical models aimed at
explaining the anomalous J/ suppression observed in Pb-Pb collisions. We
present the measured J/ yields in different bins of azimuthal angle
relative to the reaction plane, as well as the resulting values of the Fourier
coefficient v as a function of the collision centrality and of the
J/ transverse momentum. The reaction plane has been estimated from the
azimuthal distribution of the neutral transverse energy detected in an
electromagnetic calorimeter. The analysis has been performed on a data sample
of about 100 000 events, distributed in five centrality or p
sub-samples. The extracted v values are significantly larger than zero
for non-central collisions and are seen to increase with p.Comment: proceedings of HP08 conference corrected a typo in one equatio
Bottomonium and Drell-Yan production in p-A collisions at 450 GeV
The NA50 Collaboration has measured heavy-quarkonium production in p-A
collisions at 450 GeV incident energy (sqrt(s) = 29.1 GeV). We report here
results on the production of the Upsilon states and of high-mass Drell-Yan muon
pairs (m > 6 GeV). The cross-section at midrapidity and the A-dependence of the
measured yields are determined and compared with the results of other
fixed-target experiments and with the available theoretical estimates. Finally,
we also address some issues concerning the transverse momentum distributions of
the measured dimuons.Comment: 18 pages, 9 figures, to be published in Phys. Lett.
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