It is shown that the ratio of strange to nonstrange particle production in relativistic heavy-ion collisions is expected to reach a maximum at beam energies around 30
A
GeV in the lab frame. This ...maximum is unique to heavy-ion collisions, and has no equivalent in elementary particle collisions. The appearance of the maximum is due to the energy dependence of the chemical freeze-out parameters and is clearly seen as a pronounced peak in the Wroblewski factor as a function of the incident energy as well as in the behavior of the K
+/
π
+ ratio. Below
30
A
GeV
strange baryons contribute strongly because of the very large value of the chemical potential
μ
B
. As the energy increases, the decrease of the baryon chemical potential coupled with only moderate increases in the associated temperature causes a decline in the relative number of strange baryons above energies of about
30
A
GeV
leading to very pronounced maxima in the
Λ/
π
+ and
Ξ
−/
π
+ ratios.
The study of multiplicity distributions of identified particles in terms of their higher moments is at the focus of contemporary experimental and theoretical studies. In a thermalized system ...combinations of these moments are directly related to the Equation of State (EoS) through variations of the thermodynamic pressure with respect to changes in the chemical potential μQ, associated with a conserved charge Q. The ultimate goal of the experimental measurements in relativistic nuclear collisions is, by systematics comparison to the ab initio theoretical calculations, to probe the dynamics of genuine phase transitions between a hadron gas and the quark-gluon plasma. However, the comparison between experiment and theory is far from trivial, because several non-dynamical fluctuations need to be controlled prior to a meaningful comparison to theoretical predictions. In this report we present quantitative estimates for these non-dynamical contributions using the Canonical Ensemble (CE) formulation of the statistical mechanics. Together with the analytical formulas we provide also results from Monte Carlo simulations within the CE and compare our predictions with the corresponding measurements from the STAR experiment.
The PreAmplifier ShAper for the ALICE TPC detector Soltveit, H.K.; Stachel, J.; Braun-Munzinger, P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2012, Letnik:
676
Journal Article
Recenzirano
Odprti dostop
In this paper the PreAmplifier ShAper (PASA) for the Time Projection Chamber (TPC) of the ALICE experiment at LHC is presented. The ALICE TPC PASA is an ASIC that integrates 16 identical channels, ...each consisting of Charge Sensitive Amplifiers (CSA) followed by a Pole-Zero network, self-adaptive bias network, two second-order bridged-T filters, two non-inverting level shifters and a start-up circuit. The circuit is optimized for a detector capacitance of 18–25pF. For an input capacitance of 25pF, the PASA features a conversion gain of 12.74mV/fC, a peaking time of 160ns, a FWHM of 190ns, a power consumption of 11.65mW/ch and an equivalent noise charge of 244e+17e/pF. The circuit recovers smoothly to the baseline in about 600ns. An integral non-linearity of 0.19% with an output swing of about 2.1V is also achieved. The total area of the chip is 18mm2 and is implemented in AMS's C35B3C1 0.35μm CMOS technology. Detailed characterization tests were performed on about 48000 PASA circuits before mounting them on the ALICE TPC front-end cards. After more than two years of operation of the ALICE TPC with p–p and Pb–Pb collisions, the PASA has demonstrated to fulfill all requirements.
We explore net charge probability distributions in heavy ion collisions within the hadron resonance gas model. The distributions for strangeness, electric charge and baryon number are derived. We ...show that, within this model, net charge probability distributions and the resulting fluctuations can be computed directly from the measured yields of charged and multi-charged hadrons. The influence of multi-charged particles and quantum statistics on the shape of the distribution is examined. We discuss the properties of the net proton distribution along the chemical freeze-out line. The model results presented here provide a theoretical baseline in the search for a relation between the chemical freeze-out and the QCD cross-over line at RHIC and LHC energies.
We provide predictions for charmonium and open charm production in nuclear collisions at SPS/FAIR energies within the framework of the statistical hadronization model. The increasing importance at ...lower energies of Λc production is demonstrated and provides a challenge for future experiments. We also demonstrate that, because of the large charm quark mass and the different timescales for charm quark and charmed hadron production, possible modifications of charmed hadrons in the hot hadronic medium do not lead to measurable changes in cross sections for D-meson production. A possible influence of medium effects can be seen, however, in yields of charmonium. These effects are visible at all energies and results are presented for the energy range between charm threshold and RHIC energy.
We present the combined results on electron-pair production in 158 GeV/n Pb-Au (\(\sqrt{s}\) = 17.2 GeV) collisions taken at the CERN SPS in 1995 and 1996, and give a detailed account of the data ...analysis. The enhancement over the reference of neutral meson decays amounts to a factor of 2.31 \(\pm0.19 (stat.)\pm0.55 (syst.)\pm0.69 (decays)\) for semi-central collisions (28\(\%\)\(\sigma/\sigma_{geo}\)) when yields are integrated over m > 200 MeV/c2 in invariant mass. The measured yield, its stronger-than-linear scaling with \(N_{\rm ch}\), and the dominance of low pair pt strongly suggest an interpretation as thermal radiation from pion annihilation in the hadronic fireball. The shape of the excess centring at \(m\approx\) 500 MeV/c2, however, cannot be described without strong medium modifications of the \(\rho\) meson. The results are put into perspective by comparison to predictions from Brown-Rho scaling governed by chiral symmetry restoration, and from the spectral-function many-body treatment in which the approach to the phase boundary is less explicit.
We discuss the production of charmonium in nuclear collisions within the framework of the statistical hadronization model. We demonstrate that the model reproduces very well the available data at ...RHIC. We provide predictions for the LHC energy where, dependent on the charm production cross section, a dramatically different behavior of charmonium production as a function of centrality might be expected. We also discuss the case in elementary collisions, where clearly the statistical model does not reproduce the measurements.
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