Elliptic flow in Au+Au collisions at sqrt sNN = 130 GeV

Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at sqrt[sNN] = 130 GeV using the STAR Time Projection Chamber at the Relativistic Heavy Ion Collider. The elliptic flow signal, v2, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependence of elliptic flow are also presented.alle Autoren: K. H. Ackermann19, N. Adams28, C. Adler12, Z. Ahammed27, S. Ahmad28, C. Allgower13, J. Amsbaugh34, M. Anderson6, E. Anderssen17, H. Arnesen3, L. Arnold14, G. S. Averichev10, A. Baldwin16, J. Balewski13, O. Barannikova10,27, L. S. Barnby16, J. Baudot14, M. Beddo1, S. Bekele24, V. V. Belaga10, R. Bellwied35, S. Bennett35, J. Bercovitz17, J. Berger12, W. Betts24, H. Bichsel34, F. Bieser17, L. C. Bland13, M. Bloomer17, C. O. Blyth4, J. Boehm17, B. E. Bonner28, D. Bonnet14, R. Bossingham17, M. Botlo3, A. Boucham30, N. Bouillo30, S. Bouvier30, K. Bradley17, F. P. Brady6, E. S. Braithwaite2, W. Braithwaite2, A. Brandin21, R. L. Brown3, G. Brugalette34, C. Byrd2, H. Caines24, M. Calderón de la Barca Sánchez36, A. Cardenas27, L. Carr34, J. Carroll17, J. Castillo30, B. Caylor17, D. Cebra6, S. Chatopadhyay35, M. L. Chen3, W. Chen3, Y. Chen7, S. P. Chernenko10, M. Cherney9, A. Chikanian36, B. Choi31, J. Chrin9, W. Christie3, J. P. Coffin14, L. Conin30, C. Consiglio3, T. M. Cormier35, J. G. Cramer34, H. J. Crawford5, V. I. Danilov10, D. Dayton3, M. DeMello28, W. S. Deng16, A. A. Derevschikov26, M. Dialinas30, H. Diaz3, P. A. DeYoung8, L. Didenko3, D. Dimassimo3, J. Dioguardi3, W. Dominik32, C. Drancourt30, J. E. Draper6, V. B. Dunin10, J. C. Dunlop36, V. Eckardt19, W. R. Edwards17, L. G. Efimov10, T. Eggert19, V. Emelianov21, J. Engelage5, G. Eppley28, B. Erazmus30, A. Etkin3, P. Fachini29, C. Feliciano3, D. Ferenc6, M. I. Ferguson7, H. Fessler19, E. Finch36, V. Fine3, Y. Fisyak3, D. Flierl12, I. Flores5, K. J. Foley3, D. Fritz17, N. Gagunashvili10, J. Gans36, M. Gazdzicki12, M. Germain14, F. Geurts28, V. Ghazikhanian7, C. Gojak14, J. Grabski33, O. Grachov35, M. Grau3, D. Greiner17, L. Greiner5, V. Grigoriev21, D. Grosnick1, J. Gross9, G. Guilloux30, E. Gushin21, J. Hall35, T. J. Hallman3, D. Hardtke17, G. Harper34, J. W. Harris36, P. He5, M. Heffner6, S. Heppelmann25, T. Herston27, D. Hill1, B. Hippolyte14, A. Hirsch27, E. Hjort27, G. W. Hoffmann31, M. Horsley36, M. Howe34, H. Z. Huang7, T. J. Humanic24, H. Hümmler19, W. Hunt13, J. Hunter17, G. J. Igo7, A. Ishihara31, Yu. I. Ivanshin11, P. Jacobs17, W. W. Jacobs13, S. Jacobson17, R. Jared17, P. Jensen31, I. Johnson17, P. G. Jones4, E. Judd5, M. Kaneta17, M. Kaplan8, D. Keane16, V. P. Kenney23*, A. Khodinov21, J. Klay6, S. R. Klein17, A. Klyachko13, G. Koehler17, A. S. Konstantinov26, V. Kormilitsyne7,26, L. Kotchenda21, I. Kotov24, A. D. Kovalenko10, M. Kramer22, P. Kravtsov21, K. Krueger1, T. Krupien3, P. Kuczewski3, C. Kuhn14, G. J. Kunde36, C. L. Kunz8, R. Kh. Kutuev11, A. A. Kuznetsov10, L. Lakehal-Ayat30, J. Lamas-Valverde28, M. A. C. Lamont4, J. M. Landgraf3, S. Lange12, C. P. Lansdell31, B. Lasiuk36, F. Laue24, A. Lebedev3, T. LeCompte1, W. J. Leonhardt3, V. M. Leontiev26, P. Leszczynski33, M. J. LeVine3, Q. Li35, Q. Li17, Z. Li3, C.-J. Liaw3, J. Lin9, S. J. Lindenbaum22, V. Lindenstruth5, P. J. Lindstrom5, M. A. Lisa24, H. Liu16, T. Ljubicic3, W. J. Llope28, G. LoCurto19, H. Long7, R. S. Longacre3, M. Lopez-Noriega24, D. Lopiano1, W. A. Love3, J. R. Lutz14, D. Lynn3, L. Madansky15§, R. Maier19, R. Majka36, A. Maliszewski33, S. Margetis16, K. Marks17, R. Marstaller19, L. Martin30, J. Marx17, H. S. Matis17, Yu. A. Matulenko26, E. A. Matyushevski10, C. McParland17, T. S. McShane9, J. Meier9, Yu. Melnick26, A. Meschanin26, P. Middlekamp3, N. Mikhalin7,26, B. Miller3, Z. Milosevich8, N. G. Minaev26, B. Minor17, J. Mitchell15, E. Mogavero3, V. A. Moiseenko11, D. Moltz17, C. F. Moore31, V. Morozov17, R. Morse17, M. M. de Moura29, M. G. Munhoz29, G. S. Mutchler28, J. M. Nelson4, P. Nevski3, T. Ngo7, M. Nguyen3, T. Nguyen3, V. A. Nikitin11, L. V. Nogach26, T. Noggle17, B. Norman16, S. B. Nurushev26, T. Nussbaum28, J. Nystrand17, G. Odyniec17, A. Ogawa25, C. A. Ogilvie18, K. Olchanski3, M. Oldenburg19, D. Olson17, G. A. Ososkov10, G. Ott31, D. Padrazo3, G. Paic24, S. U. Pandey35, Y. Panebratsev10, S. Y. Panitkin16, A. I. Pavlinov26, T. Pawlak33, M. Pentia10, V. Perevotchikov3, W. Peryt33, V. A Petrov11, W. Pinganaud30, S. Pirogov7, E. Platner28, J. Pluta33, I. Polk3, N. Porile27, J. Porter3, A. M. Poskanzer17, E. Potrebenikova10, D. Prindle34, C. Pruneau35, J. Puskar-Pasewicz13, G. Rai17, J. Rasson17, O. Ravel30, R. L. Ray31, S. V. Razin10,13, D. Reichhold9, J. Reid34, R. E. Renfordt12, F. Retiere30, A. Ridiger21, J. Riso35, H. G. Ritter17, J. B. Roberts28, D. Roehrich12, O. V. Rogachevski10, J. L. Romero6, C. Roy30, D. Russ8, V. Rykov35, I. Sakrejda17, R. Sanchez7, Z. Sandler7, J. Sandweiss36, P. Sappenfield28, A. C. Saulys3, I. Savin11, J. Schambach31, R. P. Scharenberg27, J. Scheblien3, R. Scheetz3, R. Schlueter17, N. Schmitz19, L. S. Schroeder17, M. Schulz3,19, A. Schüttauf19, J. Sedlmeir3, J. Seger9, D. Seliverstov21, J. Seyboth19, P. Seyboth19, R. Seymour34, E. I. Shakaliev10, K. E. Shestermanov26, Y. Shi7, S. S. Shimanskii10, D. Shuman17, V. S. Shvetcov11, G. Skoro10, N. Smirnov36, L. P. Smykov10, R. Snellings17, K. Solberg13, J. Sowinski13, H. M. Spinka1, B. Srivastava27, E. J. Stephenson13, R. Stock12, A. Stolpovsky35, N. Stone3, R. Stone17, M. Strikhanov21, B. Stringfellow27, H. Stroebele12, C. Struck12, A. A. P. Suaide29, E. Sugarbaker24, C. Suire14, T. J. M. Symons17, J. Takahashi29, A. H. Tang16, A. Tarchini14, J. Tarzian17, J. H. Thomas17, V. Tikhomirov21, A. Szanto de Toledo29, S. Tonse17, T. Trainor34, S. Trentalange7, M. Tokarev10, M. B. Tonjes20, V. Trofimov21, O. Tsai7, K. Turner3, T. Ullrich36, D. G. Underwood1, I. Vakula7, G. Van Buren3, A. M. VanderMolen20, A. Vanyashin17, I. M. Vasilevski11, A. N. Vasiliev26, S. E. Vigdor13, G. Visser5, S. A. Voloshin35, C. Vu17, F. Wang27, H. Ward31, D. Weerasundara34, R. Weidenbach17, R. Wells17, R. Wells24, T. Wenaus3, G. D. Westfall20, J. P. Whitfield8, C. Whitten, Jr.7, H. Wieman17, R. Willson24, K. Wilson35, J. Wirth17, J. Wisdom7, S. W. Wissink13, R. Witt16, J. Wolf17, L. Wood6, N. Xu17, Z. Xu36, A. E. Yakutin26, E. Yamamoto7, J. Yang7, P. Yepes28, A. Yokosawa1, V. I. Yurevich10, Y. V. Zanevski10, J. Zhang17, W. M. Zhang16, J. Zhu34, D. Zimmerman17, R. Zoulkarneev11, and A. N. Zubare

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

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

Lambda production near threshold in central nucleus-nucleus collisions

Lambda 's produced in central collisions of 40Ar+KC1 at 1.8-GeV/u incident energy were detected in a streamer chamber by their charged-particle decay. For central collisions with impact parameters b<2.4 fm the Lambda production cross section is 7.6±2.2 mb. A calculation in which Lambda production occurs in the early stage of the collision qualitatively reproduces the results but underestimates the transverse momenta. An average Lambda polarization of -0.10±0.05 is observed. PACS numbers: 25.70 B

Energy dependence of multi-pion production in high-energy nucleus-nucleus collisions

Exclusive pi - and charged-particle production in collisions of Ar+KCl is studied at incident energies from 0.4 to 1.8 GeV/u. Complete disintegration of both nuclei is observed. The correlation between pi - and total charge multiplicity shows no islands of anomalous pion production. For constant numbers of proton participants the pi - multiplicity distributions are Poissons. For central collisions increases smoothly and to first order linearly with the c.m. energy. Disagreement with the firestreak model is found. Pacs numbers: 25.70.Hi, 24.10.D

Charged-particle exclusive analysis of central Ar + KCl and Ar + Pb reactions at 1.8 and 0.8 GeV/nucleon

An event by event analysis is carried out for all charged particles observed in central collisions of 40Ar + KCl and 40Ar + Pb at 1.808 and 0.772 GeV/nucleon, respectively. Total transverse energy is used for impact parameter selection within the central trigger condition. The central Ar + KCl reaction exhibits a forward-backward oriented momentum flux. The flux distribution of the most central Ar + Pb events is approximately isotropic in the fireball center of mass

Stopping power and collective flow of nuclear matter in the reaction Ar+Pb at 0.8 GeV/u

Charged-particle exclusive data for Ar+Pb collisions at 0.772 GeV/u are analyzed in terms of collective variables for the event shapes in momentum space. Semicentral collisions lead to sidewards flow whereas nearly head-on collisions have spherical shapes in the c.m. frame, resulting from complete stopping of projectile motion. The hydrodynamical model predictions agree qualitatively with the data whereas the standard cascade model disagrees, lacking in stopping power and collective flow

Collective motion in nucleus-nucleus collisions at 800 MeV/nucleon

Semicentral Ar+KCl, La+La, and Ar+Pb collisions at 800 MeV/nucleon were studied using a streamer chamber. The results are analyzed in the framework of the transverse momentum analysis and in terms of the average sphericity matrix. A critical examination of the analysis procedures, both experimental and theoretical, is given. New procedures are described to account for overall momentum conservation in the reaction, and to correct for azimuthal variations in the detection efficiency. Average transverse momenta per nucleon in the reaction plane are presented for deuterons emitted in the forward hemisphere, as these provide the most reliable information. A Vlasov-Uehling-Uhlenbeck calculation with a stiff equation of state gives a good fit to the momenta in the Ar+Pb reaction. Flow effects parametrized further using the sphericity tensor are found stronger than in the cascade model and consistently weaker than predicted by hydrodynamics. Parameters from the sphericity tensor exhibit a larger variation as a function of multiplicity than do the average momenta per nucleon

Compression effects in relativistic nucleus-nucleus collisions

The negative-pion multiplicity is measured for central collisions of 40Ar with KCl at eight energies from 0.36 to 1.8 GeV/nucleon and for 4He on KCl and 40Ar on BaI2 at 977 and 772 MeV/nucleon, respectively. A systematic discrepancy with a cascade-model calculation which fits proton- and pion-nucleus cross sections but omits potential-energy effects is used to derive the energy going into bulk compression of the system. A value of the incompressibility constant of K=240 MeV is extracted in a parabolic form of the nuclear-matter equation of state

Collective motion in Ar+Pb collision at beam energies between 400 and 1800 MeV/nucleon

The energy dependence of rapidity distributions and flow effects was studied in central Ar+Pb collisions at 400, 800, and 1800 MeV/nucleon using a streamer chamber. Rapidity distributions for proton and pions are found to have a Gaussian shape whereas those for deuterons exhibit a two-peak structure at the two higher energies. The average in-plane transverse momentum per/nucleon and per/event shows saturation of flow around 800 MeV/nucleon for this asymmetric system. The aspect ratio of the sphericity tensor is closely correlated with the flow angle. This correlation appears to be independent of beam energy. The number of participating nucleons in central collisions varies from 213 at 400 to 135 at 1800 MeV/nucleon indicating that at the lowest energy almost the entire target nucleus participates in the collision.weitere Autoren