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A new SPS programme

Marek Gazdzicki — Thu, 14 Jun 2007 09:34:57 +0200

A new experiemntal program to study hadron production in hadron-nucleus and nucleus-nucleus collisions at the CERN SPS has been recently proposed by the NA49-future collaboration. The physics goals of the program are: (i) search for the critical point of strongly interacting matter and a study of the properties of the onset of deconfinemnt in nucleus-nucleus collisions, (ii) measurements of correlations, fluctuations and hadron spectra at high transverse momentum in proton-nucleus collisions needed as for better understanding of nucleus-nucleus results, (iii) measurements of hadron production in hadron-nucleus interactions needed for neutrino (T2K) and cosmic-ray (Pierre Auger Observatory and KASCADE) expriments. The physics of the nucleus-nucleus program is reviewed in this presentation.

Transparency, mixing and reflection of initial flows in relativistic nuclear collisions

Marek Gazdzicki; Mark I. Gorenstein — Wed, 14 Jun 2006 13:00:43 +0200

We propose to use the hadron number fluctuations in the limited momentum regions to study the evolution of initial flows in high energy nuclear collisions. In this method by a proper preparation of a collision sample the projectile and target initial flows are marked in fluctuations in the number of colliding nucleons. We discuss three limiting cases of the evolution of flows, transparency, mixing and reflection, and present for them quantitative predictions obtained within several models. Finally, we apply the method to the NA49 results on fluctuations of the negatively charged hadron multiplicity in Pb+Pb interactions at 158A GeV and conclude that the data favor a hydrodynamical model with a significant degree of mixing of the initial flows at the early stage of collisions.

Energy and system size dependence of chemical freeze-out in relativistic nuclear collisions

Francesco Becattini; Jaakko Manninen; Marek Gazdzicki — Wed, 14 Jun 2006 12:55:58 +0200

We present a detailed study of chemical freeze-out in p-p, C-C, Si-Si and Pb-Pb collisions at beam momenta of 158A GeV as well as Pb-Pb collisions at beam momenta of 20A, 30A, 40A and 80A GeV. By analyzing hadronic multiplicities within the statistical hadronization model, we have studied the parameters of the source as a function of the number of the participating nucleons and the beam energy. We observe a nice smooth behaviour of temperature, baryon chemical potential and strangeness under-saturation parameter as a function of energy and nucleus size. Interpolating formulas are provided which allow to predict the chemical freeze-out parameters in central collisions at centre-of-mass energies > 4.5 GeV and for any colliding ions. Specific discrepancies between data and model emerge in particle ratios in Pb-Pb collisions at SPS between 20A and 40A GeV of beam energy which cannot be accounted for in the considered model schemes.

Evidence for an exotic S=-2, Q=-2 baryon resonance in proton-proton collisions at the CERN SPS

Fri, 14 Oct 2005 17:29:24 +0200

Results of resonance searches in the Xi - pi -, Xi - pi +, Xi -bar+ pi -, and Xi -bar+ pi + invariant mass spectra in proton-proton collisions at sqrt[s]=17.2 GeV are presented. Evidence is shown for the existence of a narrow Xi - pi - baryon resonance with mass of 1.862±0.002 GeV/c2 and width below the detector resolution of about 0.018 GeV/c2. The significance is estimated to be above 4.2 sigma . This state is a candidate for the hypothetical exotic Xi --3/2 baryon with S=-2, I=3 / 2, and a quark content of (dsdsu-bar). At the same mass, a peak is observed in the Xi - pi + spectrum which is a candidate for the Xi 03/2 member of this isospin quartet with a quark content of (dsusd-bar). The corresponding antibaryon spectra also show enhancements at the same invariant mass.

Analysis of V0-events registered in the streamer spectrometer SKM-200

Marek Gazdzicki; K. Iovchev; E. Okonov; T. Tymieniecka — Tue, 04 Oct 2005 11:06:35 +0200

Analysis of Lambda and associative pion production in relativistic nucleus-nucleus collisions

M. Kh. Anikina; Marek Gazdzicki; A. Golokhvastov; et. al. — Tue, 04 Oct 2005 10:18:03 +0200

Experimental data on pi-mesons produced in inelastic and central nucleus-nucleus interactions at 4.5-Gev/C momentum per nucleon

M. Kh. Anikina; A. Abdurakhimov; V. Aksinenko; Marek Gazdzicki; et. al. — Tue, 04 Oct 2005 10:13:32 +0200

Study of the polarization for Lambda's produced in nucleus-nucleus interactions

Tue, 04 Oct 2005 10:06:05 +0200

Peculiarities of Lambda hyperon and Pi meson production in nucleus-nucleus collisions at high energies

Marek Gazdzicki; K. Iovchev; E. Kladnitskaya; E. Okonov; E. Skrzypczak — Tue, 04 Oct 2005 10:01:32 +0200

Charged particle spectra in central S+S collisions at 200 GeV/c per nucleon

Tue, 04 Oct 2005 09:53:11 +0200

The transverse momentum and rapidity distributions of negative hadrons and participant protons have been measured for central 32S+ 32S collisions at plab=200 GeV/c per nucleon. The proton mean rapidity shift < Delta y>~1.6 and mean transverse momentum ~0.6 GeV/c are much higher than in pp or peripheral AA collisions and indicate an increase in the nuclear stopping power. All pT spectra exhibit similar source temperatures. Including previous results for K0s Lambda , and Lambda -bar, we account for all important contributions to particle production.

A study of Lambda-production in central nucleus-nucleus interactions at a momentum of 4.5 GeV/c per incident nucleon

M. Kh. Anikina; A. Golokhvastov; L. Goncharova; Marek Gazdzicki; et. al. — Tue, 04 Oct 2005 09:31:20 +0200

Lambda hyperons produced in central nucleus-nucleus interactions at 4.5 GeV/c momentum per incident nucleon

Tue, 04 Oct 2005 09:20:48 +0200

Transverse momenta and rapidities of Lambda 's produced in central nucleus-nucleus collisions at 4.5 GeV/c·u (C-C,...,O-Pb) were studied and compared with those from inelastic He-Li interactions at the same incident momentum. Polarization of the Lambda hyperons was found to be consistent with zero ( alpha P=-0.06=0.11 for Lambda 's from central collisions). An upper limit of the Lambda -bar / Lambda production ratio was estimated to be less than 4.5 x 10-3. The experiment was performed in a triggered streamer chamber.

Difficulties of the thermodynamical model approach to pion production in relativistic ion collisions

Marek Gazdzicki; Stanislaw Mrówczynski — Tue, 04 Oct 2005 09:14:17 +0200

Thermodynamical models with various forms of partial transparency of nuclear matter are considered. It is shown that the introduction of transparency, however, significantly improves agreement with pion data concerning multiplicities and transverse momenta leads to a serious discrepancy with average rapidities of pions. Qualitative arguments are given that difficulties of the thermodynamical approach can be overcome if one assumes hydrodynamical expansion in the first stage of nuclear interactions.

Eksperimental'nye dannye po srednemu cislu provzaimodejstvovavšich protonov v neuprugich i zentral'nych jadro-jadernych vzaimodejstvijach pri energij 3.6 GeV/nuklon

M. Kh. Anikina; A. U. Abdurachimov; S. A. Avramenko; et. al.; Marek Gazdzicki — Tue, 04 Oct 2005 09:00:28 +0200

Comment on 'Strangeness enhancement in p+A and S+A interactions at energies near 200 A GeV"

Marek Gazdzicki; Ulrich Heinz — Tue, 04 Oct 2005 08:51:17 +0200

We argue that the recent analysis of strangeness production in nuclear collisions at 200 A GeV/c performed by Topor Pop et al. is flawed. The conclusions are based on an erroneous interpretation of the data and the numerical model results. The term "strangeness enhancement" is used in a misleading way.

Pion and strangeness puzzles

Marek Gazdzicki — Tue, 04 Oct 2005 08:27:52 +0200

The dependence of pion and strangeness production on the number of participant nucleons and collision energy is discussed for central A+A collisions. A possible interpretation of the experimental results assuming transition to QGP is sketched within a simple statistical approach.

Strangeness in Nuclear Collisions

Marek Gazdzicki; Dieter Röhrich — Tue, 04 Oct 2005 08:26:39 +0200

Data on the mean multiplicity of strange hadrons produced in minimum bias proton--proton and central nucleus--nucleus collisions at momenta between 2.8 and 400 GeV/c per nucleon have been compiled. The multiplicities for nucleon--nucleon interactions were constructed. The ratios of strange particle multiplicity to participant nucleon as well as to pion multiplicity are larger for central nucleus--nucleus collisions than for nucleon--nucleon interactions at all studied energies. The data at AGS energies suggest that the latter ratio saturates with increasing masses of the colliding nuclei. The strangeness to pion multiplicity ratio observed in nucleon--nucleon interactions increases with collision energy in the whole energy range studied. A qualitatively different behaviour is observed for central nucleus--nucleus collisions: the ratio rapidly increases when going from Dubna to AGS energies and changes little between AGS and SPS energies. This change in the behaviour can be related to the increase in the entropy production observed in central nucleus-nucleus collisions at the same energy range. The results are interpreted within a statistical approach. They are consistent with the hypothesis that the Quark Gluon Plasma is created at SPS energies, the critical collision energy being between AGS and SPS energies.

Observation of deconfinement phase transition in nucleus-nucleus collisions

Marek Gazdzicki — Fri, 30 Sep 2005 09:51:45 +0200

The main results obtained within the energy scan program at the CERN SPS are presented. The anomalies in energy dependence of hadron production indicate that the onset of deconfinement phase transition is located at about 30 A GeV. For the first time we seem to have clear evidence for the existence of a deconfined state of matter in nature. PACS numbers: 24.85.+p

Pion Suppression in Nuclear Collisions

Marek Gazdzicki; Mark I. Gorenstein; Stanislaw Mrowczynski — Fri, 30 Sep 2005 09:26:24 +0200

The pion multiplicity per participating nucleon in central nucleus-nucleus collisions at the energies 2-15 A GeV is significantly smaller than in nucleon-nucleon interactions at the same collision energy. This effect of pion suppression is argued to appear due to the evolution of the system produced at the early stage of heavy-ion collisions towards a local thermodynamic equilibrium and further isentropic expansion.

Pion and Strangeness Production as Signals of QCD Phase Transition

Marek Gazdzicki — Fri, 30 Sep 2005 09:25:46 +0200

It is shown that data on pion and strangeness production in central nucleus-nucleus collisions are consistent with the hypothesis of a Quark Gluon Plasma formation between 15 A GeV/c (BNL AGS) and 160 A GeV/c (CERN SPS) collision energies. The experimental results interpreted in the framework of a statistical approach indicate that the effective number of degrees of freedom increases by a factor of about 3 in the course of the phase transition and that the plasma created at CERN SPS energy may have a temperature of about 280 MeV (energy density $\approx$ 10 GeV/fm^3). Experimental studies of central Pb+Pb collisions in the energy range 20-160 A GeV/c are urgently needed in order to localize the threshold energy, and study the properties of the QCD phase transition.

On chemical equilibrium in nuclear collisions

Francesco Becattini; Marek Gazdzicki; J. Sollfrank — Fri, 30 Sep 2005 08:55:49 +0200

The data on average hadron multiplicities in central A+A collisions measured at CERN SPS are analysed with the ideal hadron gas model. It is shown that the full chemical equilibrium version of the model fails to describe the experimental results. The agreement of the data with the off-equilibrium version allowing for partial strangeness saturation is significantly better. The freeze-out temperature of about 180 MeV seems to be independent of the system size (from S+S to Pb+Pb) and in agreement with that extracted in e+e-, pp and p{\bar p} collisions. The strangeness suppression is discussed at both hadron and valence quark level. It is found that the hadronic strangeness saturation factor gamma_S increases from about 0.45 for pp interactions to about 0.7 for central A+A collisions with no significant change from S+S to Pb+Pb collisions. The quark strangeness suppression factor lambda_S is found to be about 0.2 for elementary collisions and about 0.4 for heavy ion collisions independently of collision energy and type of colliding system

On event-by-event fluctuations in nuclear collisions

Marek Gazdzicki; Andrei Leonidov; Gunther Roland — Fri, 30 Sep 2005 08:44:39 +0200

We demonstrate that a new type of analysis in heavy-ion collisions, based on an event-by-event analysis of the transverse momentum distribution, allows us to obtain information on secondary interactions and collective behaviour that is not available from the inclusive spectra. Using a random walk model as a simple phenomenological description of initial state scattering in collisions with heavy nuclei, we show that the event-by-event measurement allows a quantitative determination of this effect, well within the resolution achievable with the new generation of large acceptance hadron spectrometers. The preliminary data of the NA49 collaboration on transverse momentum fluctuations indicate qualitatively different behaviour than that obtained within the random walk model. The results are discussed in relation to the thermodynamic and hydrodynamic description of nuclear collisions.

A method to study "chemical" fluctuations in nucleus-nucleus collisions

Marek Gazdzicki — Fri, 30 Sep 2005 08:41:45 +0200

A method to study event-by-event fluctuations of the chemical (particle type) composition of the final state of high energy collisions is proposed.

Quark gluon plasma in a + a collisions at CERN SPS

Marek Gazdzicki — Fri, 30 Sep 2005 08:26:27 +0200

A brief review of a history of data collection and interpretation of the results on high energy A+A collisions is presented. Basic assumptions and main results of a statistical model of the early stage of the A+A collisions are discussed. It is concluded that a broad set of experimental data is in agreement with the hypothesis that QGP is created in central A+A (S+S and Pb+Pb) collisions at the SPS. Carefull experimental investigation of the A+A collisions in the energy region between top AGS and SPS energies is needed.

On the early stage of nucleus-nucleus collisions

Marek Gazdzicki; Mark I. Gorenstein — Fri, 30 Sep 2005 08:24:04 +0200

A statistical model of the early stage of central nucleus--nucleus (A+A) collisions is developed. We suggest a description of the confined state with several free parameters fitted to a compilation of A+A data at the AGS. For the deconfined state a simple Bag model equation of state is assumed. The model leads to the conclusion that a Quark Gluon Plasma is created in central nucleus--nucleus collisions at the SPS. This result is in quantitative agreement with existing SPS data on pion and strangeness production and gives a natural explanation for their scaling behaviour. The localization and the properties of the transition region are discussed. It is shown that the deconfinement transition can be detected by observation of the characteristic energy dependence of pion and strangeness multiplicities, and by an increase of the event--by--event fluctuations. An attempt to understand the data on J/psi production in Pb+Pb collisions at the SPS within the same approach is presented.