1,379 research outputs found
Jet reconstruction in heavy ion collisions (emphasis on Underlying Event background subtraction)
A modification of the internal structure of jets is expected due to the
production of a dense QCD medium, the Quark Gluon Plasma, in heavy-ion
collisions. We discuss some aspects of jet reconstruction in p+p and A+A
collisions and emphasize the dramatically increased contribution of the
underlying event in nucleus-nucleus collisions as compared with the vacuum
case. We conclude with its consequences on the full jet spectrum and
fragmentation function extraction at LHC.Comment: 10 pages, talk given at First International Workshop on Multiple
Partonic Interactions at the LHC, "MPI@LHC'08", Perugia, Italy, October 27-31
200
Jet fragmentation Monte Carlo study in vacuum and in medium in the ALICE experiment at the LHC
The production of jets in proton+proton (p + p) and heavy ion collisions (HIC) is of great interest to study perturbative quantum chromodynamics (pQCD) in vacuum and in medium. In particular, jets yield information on the way
partons radiate inside them (and how the radiation is modified in the medium) and then fragment into hadrons. For clear understanding of the in-medium modifications, it is first mandatory to have a good control of the measurements in p + p collisions in the ALICE experiment. After a discussion on the expected jet reconstruction performances, the results of a MC-based analysis on intrajet radiations are shown. An attempt to estimate the background contamination from the collisions is presented
Multi-strange baryon production in Au+Au collisions at top RHIC energy as a probe of bulk properties
We report STAR preliminary results on multi-strange baryon production in
Au+Au collisions at sqrt(s_NN)=200 GeV at RHIC. Its implication for the
formation of a new state of matter is discussed. The system size dependence on
the production of strange baryons is investigated to study the onset of strange
quark equilibration in the medium. The nuclear modification factor of Lambda,
Xi and Omega is also presented. Its suppression at p_T>3 GeV/c supports the
formation of a dense interacting medium at RHIC. The spectra of multi-strange
baryons reveal that within a hydro-inspired model, they may decouple prior than
lighter particles and that their flow may be mostly developed at a partonic
level. This idea is emphasized by the measurement of the v_2 of Xi+AntiXi and
Omega+AntiOmega whose behaviour is close to the Lambda+AntiLambda baryon
elliptic flow in the intermediate p_T region where a constituent quark scaling
of v_2 is observed.Comment: 8 pages, 8 figures, Strange Quark Matter 2004 conference proceeding
Decomposition of fractional quantum Hall states: New symmetries and approximations
We provide a detailed description of a new symmetry structure of the monomial
(Slater) expansion coefficients of bosonic (fermionic) fractional quantum Hall
states first obtained in Ref. 1, which we now extend to spin-singlet states. We
show that the Haldane-Rezayi spin-singlet state can be obtained without exact
diagonalization through a differential equation method that we conjecture to be
generic to other FQH model states. The symmetry rules in Ref. 1 as well as the
ones we obtain for the spin singlet states allow us to build approximations of
FQH states that exhibit increasing overlap with the exact state (as a function
of system size). We show that these overlaps reach unity in the thermodynamic
limit even though our approximation omits more than half of the Hilbert space.
We show that the product rule is valid for any FQH state which can be written
as an expectation value of parafermionic operators.Comment: 22 pages, 8 figure
New antineutrino energy spectra predictions from the summation of beta decay branches of the fission products
In this paper, we study the impact of the inclusion of the recently measured
beta decay properties of the Tc, Mo, and
Nb nuclei in an updated calculation of the antineutrino energy spectra
of the four fissible isotopes U, and Pu. These
actinides are the main contributors to the fission processes in Pressurized
Water Reactors. The beta feeding probabilities of the above-mentioned Tc, Mo
and Nb isotopes have been found to play a major role in the component
of the decay heat of Pu, solving a large part of the
discrepancy in the 4 to 3000\,s range. They have been measured using the Total
Absorption Technique (TAS), avoiding the Pandemonium effect. The calculations
are performed using the information available nowadays in the nuclear
databases, summing all the contributions of the beta decay branches of the
fission products. Our results provide a new prediction of the antineutrino
energy spectra of U, Pu and in particular of U for
which no measurement has been published yet. We conclude that new TAS
measurements are mandatory to improve the reliability of the predicted spectra.Comment: 10 pages, 2 figure
Effects of inclusion of spray-dried porcine plasma in lactation diets on sow and litter performance.
Antineutrino emission and gamma background characteristics from a thermal research reactor
The detailed understanding of the antineutrino emission from research
reactors is mandatory for any high sensitivity experiments either for
fundamental or applied neutrino physics, as well as a good control of the gamma
and neutron backgrounds induced by the reactor operation. In this article, the
antineutrino emission associated to a thermal research reactor: the OSIRIS
reactor located in Saclay, France, is computed in a first part. The calculation
is performed with the summation method, which sums all the contributions of the
beta decay branches of the fission products, coupled for the first time with a
complete core model of the OSIRIS reactor core. The MCNP Utility for Reactor
Evolution code was used, allowing to take into account the contributions of all
beta decayers in-core. This calculation is representative of the isotopic
contributions to the antineutrino flux which can be found at research reactors
with a standard 19.75\% enrichment in U. In addition, the required
off-equilibrium corrections to be applied to converted antineutrino energy
spectra of uranium and plutonium isotopes are provided. In a second part, the
gamma energy spectrum emitted at the core level is provided and could be used
as an input in the simulation of any reactor antineutrino detector installed at
such research facilities. Furthermore, a simulation of the core surrounded by
the pool and the concrete shielding of the reactor has been developed in order
to propagate the emitted gamma rays and neutrons from the core. The origin of
these gamma rays and neutrons is discussed and the associated energy spectrum
of the photons transported after the concrete walls is displayed.Comment: 14 pages, 11 figures, Data in Appendix A and B (13 pages
Hard and soft probe - medium interactions in a 3D hydro+micro approach at RHIC
We utilize a 3D hybrid hydro+micro model for a comprehensive and consistent
description of soft and hard particle production in ultra-relativistic
heavy-ion collisions at RHIC. In the soft sector we focus on the dynamics of
(multi-)strange baryons, where a clear strangeness dependence of their
collision rates and freeze-out is observed. In the hard sector we study the
radiative energy loss of hard partons in a soft medium in the multiple soft
scattering approximation. While the nuclear suppression factor does
not reflect the high quality of the medium description (except in a reduced
systematic uncertainty in extracting the quenching power of the medium), the
hydrodynamical model also allows to study different centralities and in
particular the angular variation of with respect to the reaction
plane, allowing for a controlled variation of the in-medium path-length.Comment: 5 pages, 4 figures, Quark Matter 2006 proceedings, to appear in
Journal of Physics
First measurements with a new -electron detector for spectral shape studies
The shape of the spectrum corresponding to the electrons emitted in
decay carries a wealth of information about nuclear structure and fundamental
physics. In spite of that, few dedicated measurements have been made of
-spectrum shapes. In this work we present a newly developed detector for
electrons based on a telescope concept. A thick plastic scintillator is
employed in coincidence with a thin silicon detector. First measurements
employing this detector have been carried out with mono-energetic electrons
from the high-energy resolution electron-beam spectrometer at Bordeaux. Here we
report on the good reproduction of the experimental spectra of mono-energetic
electrons using Monte Carlo simulations. This is a crucial step for future
experiments, where a detailed Monte Carlo characterization of the detector is
needed to determine the shape of the -electron spectra by deconvolution
of the measured spectra with the response function of the detector. A chamber
to contain two telescope assemblies has been designed for future -decay
experiments at the Ion Guide Isotope Separator On-Line facility in
Jyv\"askyl\"a, aimed at improving our understanding of reactor antineutrino
spectra
High pT and jet physics from RHIC to LHC
The observation of the strong suppression of high pT hadrons in heavy ion
collisions at the Relativistic Heavy Ion Collider (RHIC) at BNL has motivated a
large experimental program using hard probes to characterize the deconfined
medium created. However what can be denoted as ``leading particle physics''
accessible at RHIC presents some limitations which motivate at higher energy
the study of much more penetrating objects: jets. The gain in center of mass
energy expected at the Large Hadron Collider (LHC) at CERN will definitively
improve our understanding on how the energy is lost in the system opening a new
major window of study: the physics of jets on an event-by-event basis. We will
concentrate on the expected performance for jet reconstruction in ALICE using
the EMCal calorimeter.Comment: 14 pages, 14 figures, Proceedings of the Workshop on Relativistic
Nuclear Physics (WRNP) 2007, Kiev, Ukraine. Conference Info:
http://wrnp2007.bitp.kiev.ua/. Final version published in "Physics of Atomic
Nuclei
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