A non-monotonic energy dependence of the K + / pi + ratio with a sharp maximum close to 30 A GeV is observed in central Pb+Pb collisions. Within a statistical model of the early stage, this is interpreted as a sign of the phase transition to a QGP, which causes a sharp change in the energy dependence of the strangeness to entropy ratio. This observation naturally motivates us to study the production of multistrange hyperons (Xi, Omega) as a function of the beam energy. Furthermore it was suggested that the kinematic freeze-out of Omega takes place directly at QGP hadronization. If this is indeed the case, the transverse momentum spectra of the Omega directly reflect the transverse expansion velocity of a hadronizing QGP. In this report we show preliminary NA49 results on Omega - and Omega + production in central Pb+Pb collisions at 40 and 158 A GeV and compare them to measurements of Xi - and Xi + production in central Pb+Pb collisions at 30, 40, 80 and 158 A GeV

Collaboration, NA49

Mitrovski, Michael Kosta

English

Mitrovski, Michael K.

Alt, Christopher

Antičić, Tome

Baatar, B.

Barna, Daniel

Bartke, Jerzy

Behler, Matthias

Betev, Latchezar

Białkowska, Helena

Billmeier, Anja

Blume, Christoph

Boimska, Bożena

Botje, Michiel

Bracinik, Juraj

Bramm, Roland

Brun, René

Bunčić, Predrag

Cerny, Vladimír

Christakoglou, Panagiotis

Chvala, Ondrej

Cramer, John G.

Csató, Péter

Darmenov, Nikolay

Dimitrov, Anton

Dinkelaker, Peter

Eckardt, Volker

Filip, Peter

Fischer, Hans Gerhard

Flierl, Dominik Bernhard

Fodor, Zoltán

Foka, Panagiota

Freund, Peter

Friese, Volker

Gál, József

Gaździcki, Marek

Georgopoulos, George

Gładysz-Dziaduś, Ewa

Hegyi, Sándor

Höhne, Claudia

Kadija, Krešo

Karev, Alexandre

Kliemant, Michael

Kniege, Stefan

Kolesnikov, Vadim I.

Kollegger, Thorsten

Kornaś, Ewelina

Korus, Robert

Kowalski, Marek

Kraus, Ingrid

Kreps, Michal

Leeuwen, Marco van

Lévai, Péter

Litov, Leandr

Lungwitz, Benjamin

Makariev, Martin Vasilev

Malakhov, Aleksandr I.

Markert, Christina

Mateev, Matej D.

Mayes, Bill W.

Melkumov, Georgy L.

Meurer, Christine

Mischke, André

Molnár, József

Mrówczyński, Stanislaw

Pálla, Gabriella

Panagiotou, Apostolos D.

Panayotov, Dobromir

Perl, Katarzyna

Petridis, Athanasios

Pikna, Miroslav

Pinsky, Lawrence

Pühlhofer, Falk

Reid, Jeffrey G.

Renfordt, Rainer Arno Ernst

Retyk, Waldemar

Richard, Agnes Carol Joanna

Roland, Christof

Roland, Gunther

Rybczyński, Maciej

Rybicki, Andrzej

Sandoval, Andres

Sann, Hans

Schmitz, Norbert

Seyboth, Peter

Siklér, Ferenc

Sitar, Branislav

Skrzypczak, Ewa

Stefanek, Grzegorz

Stock, Reinhard

Ströbele, Herbert

Šuša, Tatjana

Szentpétery, Imre

Sziklai, János

Trainor, Thomas A.

Varga, Dezsö

Vassiliou, Maria

Veres, Gábor I.

Vesztergombi, György

Vranić, Danilo

Hochschulschriftenserver - Universität Frankfurt am Main

arXiv:nucl-ex/0312022 v1   29 Dec 2003Multistrange HyperonProduction in Pb+Pb collisionsat 30, 40, 80 and 158 A·GeVMichael Mitrovski for the NA49 Collaboration1Institut f¨ ur Kernphysik, August Euler Strasse 6,60486 Frankfurt, GermanyE–mail: Michael.Mitrovski@cern.chC. Alt9, T. Anticic21, B. Baatar8, D. Barna4,J. Bartke6, M. Behler13, L. Betev9, H. Bia  lkowska19,A. Billmeier9, C. Blume7, B. Boimska19, M. Botje1,J. Bracinik3, R. Bramm9, R. Brun10, P. Bunˇ ci´ c9,10,V. Cerny3, P. Christakoglou2, O. Chvala15,J.G. Cramer17, P. Csat´ o4, N. Darmenov18,A. Dimitrov18, P. Dinkelaker9, V. Eckardt14, P. Filip14,H.G. Fischer10, D. Flierl9,Z. Fodor4, P. Foka7,P. Freund14, V. Friese7, J. G´ al4, M. Ga´ zdzicki9,G. Georgopoulos2, E. G  ladysz6, S. Hegyi4, C. H¨ ohne13,K. Kadija21, A. Karev14, M. Kliemant9, S. Kniege9V.I. Kolesnikov8, T. Kollegger9, E. Kornas6,R. Korus12, M. Kowalski6, I. Kraus7, M. Kreps3,M. van Leeuwen1, P. L´ evai4, L. Litov18, B. Lungwitz9,M. Makariev18, A.I. Malakhov8, C. Markert7,M. Mateev18, B.W. Mayes11, G.L. Melkumov8,C. Meurer9, A. Mischke7, M. Mitrovski9, J. Moln´ ar4,St. Mr´ owczy´ nski12, G. P´ alla4, A.D. Panagiotou2,D. Panayotov18, K. Perl20, A. Petridis2, M. Pikna3,L. Pinsky11, F. P¨ uhlhofer13, J.G. Reid17, R. Renfordt9,W. Retyk20, A. Richard9 C. Roland5, G. Roland5,M. Rybczy´ nski12, A. Rybicki6,10, A. Sandoval7,H. Sann7, N. Schmitz14, P. Seyboth14, F. Sikl´ er4,B. Sitar3, E. Skrzypczak20, G. Stefanek12, R. Stock9,H. Str¨ obele9, T. Susa21, I. Szentp´ etery4, J. Sziklai4,T.A. Trainor17, D. Varga4, M. Vassiliou2, G.I. Veres4,G. Vesztergombi4, D. Vrani´ c7, S. Wenig10, A. Wetzler9,Z. W  lodarczyk12 I.K. Yoo16, J. Zaranek9, J. Zim´ anyi41NIKHEF, Amsterdam, Netherlands.2Department of Physics, University of Athens, Athens,Greece.3Comenius University, Bratislava, Slovakia.4KFKI Research Institute for Particle and NuclearPhysics, Budapest, Hungary.5MIT, Cambridge, USA.6Institute of Nuclear Physics, Cracow, Poland.7Gesellschaft f¨ ur Schwerionenforschung (GSI), Darm stadt, Germany.8Joint Institute for Nuclear Research, Dubna, Russia.9Fachbereich Physik der Universit¨ at, Frankfurt, Ger many.10CERN, Geneva, Switzerland.11University of Houston, Houston, TX, USA.12Institute of Physics ´ Swietokrzyska Academy, Kielce,1Presented at 25th International School of Nuclear Physics,Erice, ItalyPoland.13Fachbereich Physik der Universit¨ at, Marburg, Ger many.14Max Planck Institut f¨ ur Physik, Munich, Germany.15Institute of Particle and Nuclear Physics, CharlesUniversity, Prague, Czech Republic.16Department of Physics, Pusan National University,Pusan, Republic of Korea.17Nuclear Physics Laboratory, University of Washing ton, Seattle, WA, USA.18Atomic Physics Department, Soﬁa University St.Kliment Ohridski, Soﬁa, Bulgaria.19Institute for Nuclear Studies, Warsaw, Poland.20Institute for Experimental Physics, University ofWarsaw, Warsaw, Poland.21Rudjer Boskovic Institute, Zagreb, Croatia.A non monotonic energy dependence of the K+/π+ratio with a sharp maximum close to 30 A·GeV isobserved in central Pb+Pb collisions [1]. Withina statistical model of the early stage [2], this isinterpreted as a sign of the phase transition to a QGP,which causes a sharp change in the energy dependenceof the strangeness to entropy ratio. This observationnaturally motivates us to study the production ofmultistrange hyperons (Ξ,  ) as a function of thebeam energy.Furthermore it was suggested that the kinematicfreeze out of   takes place directly at QGP hadroniza tion. If this is indeed the case, the transversemomentum spectra of the   directly reﬂect thetransverse expansion velocity of a hadronizing QGP[3, 4].In this report we show preliminary NA49 results on  −and    + production in central Pb+Pb collisions at 40and 158 A·GeV and compare them to measurementsof Ξ− and   Ξ+ production in central Pb+Pb collisionsat 30, 40, 80 and 158 A·GeV.The NA49 detector [5] is a large acceptance hadronspectrometer at the CERN SPS, consisting of fourTPCs. Two of them, the Vertex TPCs (VTPC),are inside a magnetic ﬁeld for the determinationof particle momenta and charge. The ionisationenergy loss (dE/dx) measurements in the two MainTPCs (MTPC), which are outside the magnetic ﬁeld,are used for mass determination. Central collisionswere selected by a trigger using information from adownstream calorimeter (VCAL), which measures theenergy of the projectile spectator nucleons.In Fig.1 the NA49    +/ − and   Ξ+/Ξ− ratios asa function of the collision energy (√sNN) are shownand compared to results of NA57 [6, 7] and STAR[8, 9]. The NA49 and NA57 results measured at thesame energies are consistent. The data show a clearincrease of the    +/ − ratio from a value of about 0.4at SPS energies to about 1 at RHIC energies. The  Ξ+/Ξ− ratio also increases from SPS energies to about10.8 at RHIC energies.10 102 / y  (y=0)y00.20.40.60.811.21.4 NA49 - W / + W NA57- W /+ W STAR - W / + W NA49 X /+ X NA57 X /+ X STAR X /+ X (GeV) NN sFigure 1: The antihyperon/hyperon (  Y /Y ) ratio atmidrapidity in the SPS RHIC energy range.4 6 8 10 12 14 16 18 20 / B  (y=0)B10-310-210-11- W /+W- X /+XL / L/p p (GeV) NN sFigure 2: The antibaryon/baryon ratio (   B/B) atmidrapidity in the SPS energy range measured byNA49.The midrapidity    +/ − ratio is estimated to be0.46 ± 0.1 and 0.41 ± 0.18 for central Pb+Pb colli sions at 158 and 40 A·GeV, respectively. The valuesfor the midrapidity   Ξ+/Ξ− ratio are estimated tobe 0.13 ± 0.02, 0.065 ± 0.05 and 0.0049 ± 0.009 forcentral Pb+Pb collisions at 80, 40 and 30 A·GeV,respectively. In Fig.2 the antibaryon/baryon ratiosare shown as a function of the beam energy in the SPSenergy domain. In addition to   Ξ/Ξ and    /  ratiosthe results on   Λ/Λ [10] and   p/p [11] are shown. Theenergy dependence of   B/B ratios gets weaker withincreasing strangeness content.Fig. 3 shows the energy dependence of the midrapidity (GeV) NN s1 10 102 = 0)* (y-p / -X00.0020.0040.0060.0080.010.0120.0140.0160.0180.02) p  E895 (4 NA57 NA49 STAR (GeV) NN s1 10 102 = 0)* (y+p / +X00.0010.0020.0030.0040.0050.0060.0070.0080.0090.01 NA57 NA49 STARFigure 3: Energy dependence of the midrapidityΞ−/π− (left) and   Ξ+/π+ (right) ratio in centralPb+Pb and Au+Au collisions. (GeV) NN s1 10 102 = 0)* (y-p / -W00.00020.00040.00060.00080.0010.00120.00140.00160.00180.002 NA57 NA49 STAR (GeV) NN s1 10 102 = 0)* (y+p / +W00.00020.00040.00060.00080.0010.00120.00140.00160.00180.002 NA57 NA49 STARFigure 4: Energy dependence of the midrapidity −/π− (left) and    +/π+ (right) ratio in centralPb+Pb and Au+Au collisions.Ξ−/π− (left) and   Ξ+/π+ (right) ratio in centralPb+Pb and Au+Au collisions. The Ξ−/π− ratiosuggests that there is a non monotonic energy depen dence at SPS energies. The   Ξ+/π+ ratio increaseswith energy from SPS to RHIC energies. The  −/π−ratio shown in Fig. 4 seems to be energy independent,but the    +/π+ ratio shows again an increase fromSPS to RHIC energies.At 158 A·GeV, a high statistics data sample ofcentral Pb+Pb collisions is available, which allows usto obtain fully corrected spectra of  − and    +. Thetransverse mass spectra are ﬁtted by an exponentialfunction :1mtd2Ndmtdy= C · e−mt/T, (1)where the ﬁt parameters are a normalization factor Cand the inverse slope parameter T. The slope param eter is similar for  − and    + : T( −) = 276 ± 23MeV and T(   +) = 285 ± 39 MeV [11]. Our values2agree with those measured by the NA57 collaboration(T( −) = 280 ± 16 MeV and T(   +) = 324 ± 29 MeV)[12]. The large acceptance of the NA49 experiment al lows us to measure the  − (   +) spectra in a large ra pidity interval. The rapidity distributions for  − and   + are obtained by extrapolating pt spectra using theexponential. Both y spectra were ﬁtted by a Gaussian.The width of the  − distribution (σ( −) = 1.0 ± 0.2)seems to be larger than the one of the    + (σ( −) =0.7 ± 0.1). Mean multiplicities in full phase space wereestimated as integrals over measured points correctedfor the missing rapidity coverage using the Gaussianparametrisations. The resulting yields are < −> =0.47 ± 0.07 and <   +> = 0.15 ± 0.02, where the er rors are statistical only.AcknowledgmentsThis work was supported by the US Department ofEnergy Grant DE FG03 97ER41020/A000, the Bun desministerium fur Bildung und Forschung, Germany,the Polish State Committee for Scientiﬁc Research (2P03B 130 23, SPB/CERN/P 03/Dz 446/2002 2004, 2P03B 02418, 2 P03B 04123), the Hungarian ScientiﬁcResearch Foundation (T032648, T032293, T043514),the Hungarian National Science Foundation, OTKA,(F034707), and the Polish German Foundation.References[1] S. V. Afanasiev et al., (NA49 Collaboration),Phys. Rev. C66 (2002) 054902.[2] M. Ga´ zdzicki and M.I. Gorenstein, Acta Phys.Polon. B30 (1999) 2705 [arXiv:hep ph/9803462].[3] K.A. Bugaev, M. Ga´ zdzicki and M.I. Gorenstein,Phys. Lett. B544 (2002) 127.[4] D. Teaney, J. Lauret and E.V. Shuryak,arXiv:nucl th/0110037.[5] S. V. Afanasiev et al. (NA49 Collaboration), Nucl.Instrum. Meth. A 430 (1999) 210.[6] R. Caliandro et al., (WA97 Collaboration),J.Phys. G: Nucl.Part.Phys. 25 (1999) 171.[7] V. Manzari et al., (NA57 Collaboration), Nucl.Phys. A7 15 (2003) 140.[8] C. Suire et al., (STAR Collaboration), Nucl. Phys.A7 15 (2003) 470.[9] J. Castillio et al., (STAR Collaboration), Nucl.Phys. A7 15 (2003) 521.[10] A. Mischke et al., (NA49 Collaboration), Nucl.Phys. A7 15 (2003) 453.[11] M. van Leeuwen et al., (NA49 Collaboration),Nucl. Phys. A7 15 (2003) 161.[12] F. Antinori private communication.3

Acta Phys. Polon.

Antinori private communication.

Multistrange hyperon production in Pb + Pb collisions at 30, 40, 80 and 158 A GeV

Multistrange hyperon production in Pb + Pb collisions at 30, 40, 80 and 158 A GeV

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