902 research outputs found
Quarkonia measurements in heavy-ion collisions in CMS
The production of quarkonia is one of the most promising signals at the LHC for the study of the production properties of Quark Gluon Plasma. In addition to the J/psi, the extent to which upsilon is suppressed should give much insight into the new state of matter. The large muon acceptance and the high precision tracker make the CMS detector ideal for studies of this physics. In this note, the performance of the CMS detector for quarkonia measurements in heavy-ion collisions in the dimuon channel is presented. Dimuon reconstruction efficiencies and mass resolution are calculated using detailed detector simulation. Mass spectra and signal to background ratios are estimated with a fast Monte Carlo program. Results obtained with the fast Monte Carlo are compared with more detailed simulations
Charmonium dynamics in heavy ion collisions
Applying the HSD transport approach to charmonium dynamics within the
'hadronic comover model' and the 'QGP melting scenario', we show that the
suppression pattern seen at RHIC cannot be explained by the interaction with
baryons, comoving mesons and/or by color screening mechanism. The interaction
with hadrons in the late stages of the collision (when the energy density falls
below the critical) gives a sizable contribution to the suppression. On the
other hand, it does not account for the observed additional charmonium
dissociation and its dependence on rapidity. Together with the failure of the
hadron-string models to reproduce high v2 of open charm mesons, this suggests
strong pre-hadronic interaction of c-cbar with the medium at high energy
densities.Comment: 6 pages, 2 figures, talk presented at the international conference on
"Strangeness in Quark Matter", 24-29 June 2007, Levoca, Slovaki
Observation des états excités des hypernoyaux de masse 4
voir fichier pd
Heavy Ion Physics at the LHC
The ion-ion center of mass energies at the LHC will exceed that at RHIC by
nearly a factor of 30, providing exciting opportunities for addressing unique
physics issues in a completely new energy domain. Some highlights of this new
physics domain are presented here. We briefly describe how these collisions
will provide new insights into the high density, low momentum gluon content of
the nucleus expected to dominate the dynamics of the early state of the system.
We then discuss how the dense initial state of the nucleus affects the lifetime
and temperature of the produced system. Finally, we explain how the high energy
domain of the LHC allows abundant production of `rare' processes, hard probes
calculable in perturbative quantum chromodynamics, QCD. At the LHC, high
momentum jets and bound states, the family, will be
produced with high statistics for the first time in heavy ion collisions.Comment: 10 pages, 2 figures, proceedings of INPC 04 in Goteborg, Sweden, July
2004, includes conference style fil
J/psi Absorption in Heavy Ion Collisions
We present a new calculation of the pi-J/psi dissociation cross sections
within the Constituent Quark-Meson Model recently introduced. To discuss the
absorption of J/psi in heavy-ion collisions, we assume the J/psi to be produced
inside a thermalized pion gas, as discussed by Bjorken, and introduce the
corrections due to absorption by nuclear matter as well. We fit the absorption
length of the J/psi to the data obtained at the CERN SPS by the NA50
Collaboration for Pb-Pb collisions. Collisions of lower centrality allow us to
determine the temperature and the energy density of the pion gas. For both
these quantities we find values close to those indicated by lattice gauge
calculations for the transition to a quark-gluon plasma. A simple extrapolation
to more central collisions, which takes into account the increase of the energy
deposited due to the increased nucleon flux, fails to reproduce the break in
J/psi absorption indicated by NA50, thus lending support to the idea that an
unconfined quark-gluon phase may have been produced. This conclusion could be
sharpened by analysing in a similar way, as a function of centrality, other
observables such as strange particle production.Comment: 12 pages, 7 figure
Charm and beauty of the Large Hadron Collider
With the acceleration of lead nuclei in the LHC, heavy-ion physics will enter
a new energy domain. One of the main novelties introduced by the 30-fold
energy-jump from RHIC to the LHC is the abundant heavy-quark production. After
discussing a few examples of physics issues that can be addressed using heavy
quarks, we present a selection of results on the expected experimental
capability of ALICE, the dedicated heavy-ion experiment at the LHC, in the
open-heavy-flavour sector.Comment: 10 pages, 5 figures. Invited talk at Strangeness in Quark Matter
(SQM) 2004, Cape Town, South Africa, 15-20 September 2004. Submitted to J.
Phys.
Heavy-quarkonium interaction in QCD at finite temperature
We explore the temperature dependence of the heavy-quarkonium interaction
based on the Bhanot-Peskin leading order perturbative QCD analysis. The Wilson
coefficients are computed solving the Schrodinger equation in a screened
Coulomb heavy-quark potential. The inverse Mellin transform of the Wilson
coefficients then allows for the computation of the 1S and 2S heavy-quarkonium
gluon and pion total cross section at finite screening/temperature. As a
phenomenological illustration, the temperature dependence of the 1S charmonium
thermal width is determined and compared to recent lattice QCD results.Comment: 14 pages, 5 figures. Clarification added, published versio
Estimation of Collision Impact Parameter
We demonstrate that the nuclear collision geometry (i.e. impact parameter)
can be determined with 1.5 fm accuracy in an event-by-event analysis by
measuring the transverse energy flow in the pseudorapidity region with a minimal dependence on collision dynamics details at the LHC
energy scale. Using the HIJING model we have illustrated our calculation by a
simulation of events of nucleus-nucleus interactions at the c.m.s energy from 1
up to 5.5 TeV per nucleon and various type of nuclei.Comment: 6 pages, 3 figure
Pt-imbalance in dimuon+jet production as a signal of partonic energy loss in heavy ion collisions at LHC
We consider a hard jet production tagged by a muon pair in ultrarelativistic
heavy ion collisions. The process cross section is calculated by the CompHEP
Monte-Carlo generator taking into account full gamma*/Z interference pattern at
LHC energies. We have found that reasonable statistics, ~1000 events per 1
month of LHC run with lead beams, can be expected for realistic geometrical
acceptance and kinematic cuts. The transverse momentum imbalance due to
interactions of jet partons in the medium is evaluated for mu+mu-pair+jet
correlation, as well as for the correlation between mu+mu- pair and a leading
particle in a jet. Theoretical and experimental uncertainties of these
observables are discussed.Comment: 17 pages in LaTeX including 5 eps-figure
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