We argue that features of hadron production in relativistic nuclear collisions, mainly at CERN-SPS energies, may be explained by the existence of three forms of matter: Hadronic Matter, Quarkyonic ...Matter, and a Quark–Gluon Plasma. We suggest that these meet at a triple point in the QCD phase diagram. Some of the features explained, both qualitatively and semi-quantitatively, include the curve for the decoupling of chemical equilibrium, along with the non-monotonic behavior of strange particle multiplicity ratios at center of mass energies near 10 GeV. If the transition(s) between the three phases are merely crossover(s), the triple point is only approximate.
The dependence of particle production on the size of the colliding nuclei is analyzed in terms of the thermal model using the canonical ensemble. The concept of strangeness correlation in clusters of ...sub-volume
V
c
is used to account for the suppression of strangeness. A systematic analysis is presented of the predictions of the thermal model for particle production in collisions of small nuclei. The pattern of the maxima of strange-particles-to-pion ratios as a function of beam energy is quite special, as they do not occur at the same beam energy and are sensitive to the system size. In particular, the
Λ
/
π
+
ratio shows a clear maximum even for small systems while the maximum in the
K
+
/
π
+
ratio is less pronounced in small systems.
The recently discovered sharp peak in the K+/π+ ratio in relativistic heavy-ion collisions 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 occurs at a temperature T=140 MeV and baryon chemical potential μB=410 MeV corresponding to an incident energy of sNN=8.2 GeV. The maximum in the Λ/π ratio is well reproduced by the statistical model, but the change in the K+/π+ ratio is much less pronounced than the one observed by the NA49 Collaboration. The calculated smooth increase of the K−/π− ratio and the shape of the Ξ−/π+ and Ω−/π+ ratios exhibiting maxima at different incident energies is consistent with the presently available experimental data. We conclude that the measured particle ratios with 20–30% deviations agree with a hadronic freeze-out scenario. These deviations seem to occur just in the transition from baryon-dominated to meson-dominated freeze-out.
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 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, Volume:
676
Journal Article
Peer reviewed
Open access
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.
The production of pions and kaons has been measured in 197Au+197Au collisions at beam energies from 0.6 to 1.5A GeV with the kaon spectrometer at SIS/GSI. The K+ meson multiplicity per nucleon is ...enhanced in Au+Au collisions by factors up to 6 relative to C+C reactions, whereas the corresponding pion ratio is reduced. The ratio of the K+ meson excitation functions for Au+Au and C+C collisions increases with decreasing beam energy. This behavior is expected for a soft nuclear equation-of-state.
In heavy ion reactions at energies around (1-2)A GeV the measured K- yields appear rather high as compared to pp collisions as shown by the KaoS Collaboration. Employing quantum molecular dy-namics ...simulations, we show that this is caused by the fact that the dominant production channel is not BB-->BBK+K- but the mesonic Lambda(Sigma)pi-->K-B reaction. Because the Lambda (Sigma) stem from the reaction BB-->Lambda(Sigma)K+B, the K+ and the K- yield are strongly correlated, i.e., the K(-)/K(+) ratio occurs to be nearly independent of the impact parameter as found experimentally. The final K- yield is strongly influenced by the K+N due to their production via the Lambda(Sigma) but very little by the K-N potential.
One of the most remarkable results to emerge from heavy-ion collisions over the past two decades is the striking regularity shown by particle yields at all energies. This has led to several very ...successful proposals describing particle yields over a very wide range of beam energies, reaching from 1A GeV up to 200A GeV, using only one or two parameters. A systematic comparison of these proposals is presented here. The conditions of fixed energy per particle, baryon+anti-baryon density, normalized entropy density as well as percolation model are investigated. The results are compared with the most recent chemical freeze-out parameters obtained in the thermal-statistical analysis of particle yields. The sensitivity and dependence of the results on parameters is analyzed and discussed. It is shown that in the energy range above the top energy of the BNL Alternating Gradient Synchrotron within present accuracies, all chemical freeze-out criteria give a fairly good description of the particle yields. However, the low energy heavy-ion data favor the constant energy per particle as a unified condition of chemical particle freeze-out. This condition also shows the weakest sensitivity on model assumptions and parameters.
PDF
