48 research outputs found
THERMUS -- A Thermal Model Package for ROOT
THERMUS is a package of C++ classes and functions allowing
statistical-thermal model analyses of particle production in relativistic
heavy-ion collisions to be performed within the ROOT framework of analysis.
Calculations are possible within three statistical ensembles; a grand-canonical
treatment of the conserved charges B, S and Q, a fully canonical treatment of
the conserved charges, and a mixed-canonical ensemble combining a canonical
treatment of strangeness with a grand-canonical treatment of baryon number and
electric charge. THERMUS allows for the assignment of decay chains and detector
efficiencies specific to each particle yield, which enables sensible fitting of
model parameters to experimental data.Comment: to be published in Computer Physics Communication
Strange Particle Production in pp Collisions at sqrt(s) = 0.9 and 7 TeV measured with the ALICE Experiment
Hadrons measured in proton-proton collisions at sqrt(s) = 0.9 and 7 TeV with
the ALICE detector have been identified using various techniques: the specific
energy loss and the time-of flight information for charged pions, kaons and
protons, the displaced vertex resulting from their weak decay for K0, Lambda
and Xi and the kink topology of decaying charged kaons. These various particle
identification tools give the best separation at different momentum ranges and
the results are combined to obtain spectra from pt = 100 MeV/c to 2.5 GeV/c.
This allows to extract total yields. In detail we discuss the K/pi ratio
together with previous measurements and we show a fit using a statistical
approach.Comment: 4 pages, 3 figures, Proceedings of the ICPAQGP2010 conference in Goa,
India, December 6th - 10th, 201
Transition from Baryonic to Mesonic Freeze-Out
The recently discovered sharp peak in the K+/pi+ ratio is discussed in the
framework of the statistical model. In this model a rapid change is expected as
the hadronic gas undergoes a transition from a baryon-dominated to a
meson-dominated gas. The transition happens at sqrt{s_{NN}} = 8.16 GeV,
temperature T = 140 MeV and baryon chemical potential mu_B = 410 MeV. The
maximum in the Lambda/pi ratio is well reproduced by the statistical model, but
the change in the K+/pi+ ratio is much less pronounced than the one observed by
the NA49 collaboration. Further experimental tests are proposed to clarify the
nature of the transition. In particular, the maxima expected in the statistical
model for the Xi/pi and Omega/pi ratios occur at slightly higher beam energies
than the maxima for the Lambda/pi and K+/pi+ ratios.Comment: 5 pages, 5 postscript figures, uses elsart.st
Statistical Model Predictions for Pb-Pb Collisions at LHC
The systematics of Statistical Model parameters extracted from heavy-ion
collisions at lower energies are exploited to extrapolate in the LHC regime.
Predictions of various particle ratios are presented and particle production in
central Pb-Pb collisions at LHC is discussed in the context of the Statistical
Model. The sensitivity of several ratios on the temperature and the baryon
chemical potential is studied in detail, and some of them, which are
particularly appropriate to determine the chemical freeze-out point
experimentally, are indicated. The impact of feed-down contributions from
resonances, especially to light hadrons, is illustrated.Comment: 5 pages, 2 figures, 1 table, SQM 2006 conference proceedings,
accepted for publication in J. Phys.
Multi-strange baryon production in pp, p-Pb and Pb-Pb collisions measured with ALICE at the LHC
Multi-strange baryons are of particular interest in the understanding of
particle production mechanisms, as their high strangeness content makes them
susceptible to changes in the hadrochemistry of the colliding systems. In
ALICE, these hyperons are reconstructed via the detection of their weak decay
products, which are identified through their measured ionisation losses and
momenta in the Time Projection Chamber. The production rates of charged
and baryons in proton-proton (pp), proton-lead (p-Pb) and lead-lead
(Pb-Pb) collisions are reported as a function of . A direct
comparison in the hyperon-to-pion ratios between the three collision systems is
made as a function of event charged-particle multiplicity. The recently
measured production rates in p-Pb interactions reveal an enhancement with
increasing event multiplicity, consistent with a hierarchy dependent on the
strangeness content of the hyperons. These results are discussed in the context
of chemical equilibrium predictions, taking into account the extracted
temperature parameter from a thermal model fit to the hadron yields in Pb-Pb
data
Transition from Baryon- to Meson-Dominated Freeze Out -- Early Decoupling around 30 A GeV?
The recently discovered sharp peak in the excitation function of the K+/pi+
ratio around 30 A GeV in relativistic heavy-ion collisions is discussed in the
framework of the Statistical Model. In this model, the freeze-out of an ideal
hadron gas changes from a situation where baryons dominate to one with mainly
mesons. This transition occurs at a temperature T = 140 MeV and baryon chemical
potential mu(B) = 410 MeV corresponding to an energy of sqrt(s) = 8.2 GeV. The
calculated maximum in the K+/pi+ ratio is, however, much less pronounced than
the one observed by the NA49 Collaboration. The smooth increase of the K-/pi-
ratio with incident energy and the shape of the excitation functions of the
Lambda/pi+, Xi-/pi+ and Omega/pi ratios all exhibiting maxima at different
incident energies, is consistent with the presently available experimental
data. The measured K+/pi+ ratio exceeds the calculated one just at the incident
energy when the freeze-out condition is changing.
We speculate that at this point freeze-out might occur in a modified way. We
discuss a scenario of an early freeze-out which indeed increases K+/pi+ ratio
while most other particle ratios remain essentially unchanged. Such an early
freeze-out is supported by results from HBT studies.Comment: 8 pages, 5 figures, SQM2006 conference, Los Angeles, March 200
Statistical Model Predictions for Particle Ratios at sqrt(s_NN) = 5.5 TeV
Particle production in central Pb-Pb collisions at LHC is discussed in the
context of the Statistical Model. Predictions of various particle ratios are
presented with the corresponding choice of model parameters made according to
the systematics extracted from heavy-ion collisions at lower energies. The
sensitivity of several ratios on the temperature and the baryon chemical
potential is studied in detail, and some of them, which are particularly
appropriate to determine the chemical freeze-out point experimentally, are
indicated. We show that the anti-p / p ratio is most suitable to determine the
baryon chemical potential while the Omega / K and Omega / pi ratios are best to
determine the temperature at chemical freeze-out.Comment: Submitted to Phys. Rev. C, 7 pages, 4 figure