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Lambda and Antilambda reconstruction in central Pb+Pb collisions using a time projection chamber
(1997)
Yates, Tim A. ; Afanasiev, Sergey V. ; Alber, Thomas ; Appelshäuser, Harald ; Bächler, Joachim ; Bailey, Stephen John ; Barnby, Lee Stuart ; Bartke, Jerzy ; Białkowska, Helena ; Blyth, Charles O. ; Bock, Rudolf ; Bormann, Christian ; Brady, Franklin Paul ; Brockmann, Robert ; Buncic, Nenad ; Bunčić, Predrag ; Caines, Helen Louise ; Cebra, Daniel A. ; Chan, P ; Cooper, Glenn E. ; Cramer, John G. ; Cramer, Pauline B. ; Csató, Péter ; Dietz, Oliver ; Dunn, Jason ; Eckardt, Volker ; Eckhardt, Frank ; Ferguson, M. I. ; Fischer, Hans Gerhard ; Flierl, Dominik Bernhard ; Fodor, Zoltán ; Foka, Panagiota ; Freund, Peter ; Friese, Volker ; Fuchs, M ; Gabler, Frank ; Gál, József ; Gaździcki, Marek ; Gładysz-Dziaduś, Ewa ; Grebieszkow, Jaroslaw ; Günther, Jörg ; Harris, John W. ; Hegyi, Sándor ; Henkel, Torsten ; Hill, L. A. ; Huang, Isaac ; Howe, Mark A. ; Hümmler, Holm Gero ; Igo, George J. ; Irmscher, Detlef ; Jacobs, Peter Martin ; Jones, Peter Graham ; Kadija, Krešo ; Kolesnikov, Vadim I. ; Kowalski, Marek ; Lasiuk, Brian ; Lévai, Péter ; Malakhov, Aleksandr I. ; Margetis, Spyridon ; Markert, Christina ; Melkumov, Georgy L. ; Mock, Andreas ; Molnár, József ; Nelson, John M. ; Odyniec, Grazyna Janina ; Pálla, Gabriella ; Panagiotou, Apostolos D. ; Petridis, Athanasios ; Piper, Andreas ; Porter, R. Jefferson ; Poskanzer, Arthur M. ; Poziombka, Stefan ; Prindle, Duncan J. ; Pühlhofer, Falk ; Rauch, Wolfgang Hans ; Reid, Jeffrey G. ; Renfordt, Rainer Arno Ernst ; Retyk, Waldemar ; Ritter, Hans Georg ; Röhrich, Dieter ; Roland, Christof ; Roland, Gunther ; Rudolph, Heinrich ; Rybicki, Andrzej ; Sakrejda, Iwona ; Sandoval, Andres ; Sann, Hans ; Semenov, Alexei Yu. ; Schäfer, Erich ; Schmischke, Dirk ; Schmitz, Norbert ; Schönfelder, Stefan ; Seyboth, Peter ; Seyerlein, Jürgen ; Siklér, Ferenc ; Skrzypczak, Ewa ; Squier, Gordon Thomas Anderson ; Stock, Reinhard ; Ströbele, Herbert ; Szentpétery, Imre ; Sziklai, János ; Toy, Milton Y. ; Trainor, Thomas A. ; Trentalange, Stephen ; Ullrich, Thomas ; Vassiliou, Maria ; Vesztergombi, György ; Vranić, Danilo ; Wang, Feipeng ; Weerasundara, Dhammika D. ; Wenig, Siegfried ; Whitten, Charles A. ; Wienold, Thomas ; Wood, Lindsay ; Zimányi, József ; Zhu, X Z ; Zybert, Ryszard
The large acceptance time projection chambers of the NA49 experiment are used to record the trajectory of charged particles from Pb + Pb collisions at 158 GeV per nucleon. Neutral strange hadrons have been reconstructed from their charged decay products. To obtain distributions of Λ, and Ks0 in discrete bins of rapidity, y, and transverse momentum, pT, calculations have been performed to determine the acceptance of the detector and the efficiency of the reconstruction software as a function of both variables. The lifetime distributions obtained give values of cτ = 7.8 ± 0.6 cm for Λ and cτ = 2.5 ± 0.3 cm for Ks0, consistent with data book values.
Wolf, Kevin L. ; Gutbrod, Hans Herbert ; Meyer, W. G. ; Poskanzer, Arthur M. ; Sandoval, Andres ; Stock, Reinhard ; Gosset, Jean ; King, Chuck ; King, George ; Sen, Nguyen Van ; Westfall, Gary D.
Pion-production cross sections have been measured for the reaction 40Ar+40Ca--> pi ++X at a laboratory energy of 1.05 GeV/nucleon. A maximum in the pi + cross section occurs at mid-rapidity, which is anomalous relative to p+p and p+nucleus reactions and compared to many other heavy-ion reactions. Calculations based on cascade and thermal models fail to fit the data.
Pion production and charged-particle multiplicity selection in relativistic nuclear collisions
(1982)
Wolf, Kevin L. ; Gutbrod, Hans Herbert ; Meyer, W. G. ; Poskanzer, Arthur M. ; Sandoval, Andres ; Stock, Reinhard ; Gosset, Jean ; Jourdain, Jean Claude ; King, Chuck ; King, George ; Sen, Nguyen Van ; Westfall, Gary D.
Spectra of positive pions with energies of 15-95 MeV were measured for high energy proton, 4He, 20Ne, and 40Ar bombardments of targets of 27Al, 40Ca, 107,109Ag, 197Au, and 238U. A Si-Ge telescope was used to identify charged pions by dE / dx-E and, in addition, stopped pi + were tagged by the subsequent muon decay. In all, results for 14 target-projectile combinations are presented to study the dependence of pion emission patterns on the bombarding energy (from E / A=0.25 to 2.1 GeV) and on the target and the projectile masses. In addition, associated charged-particle multiplicities were measured in an 80-paddle array of plastic scintillators, and used to make impact parameter selections on the pion-inclusive data. NUCLEAR REACTIONS U(20Ne, pi +), E / A=250 MeV; U(40Ar, pi +), Ca(40Ar, pi +), U(20Ne, pi +), Au(20Ne, pi +), Ag(20Ne, pi +), Al(20Ne, pi +), U(4He, pi +), Al(4He, pi +). E / A=400 MeV; Ca(40Ar, pi +), U(20Ne, pi +), U(4He, pi +), U(p, pi +), E / A=1.05), GeV; U(20Ne, pi +), E / A=2.1 GeV; measured sigma (E, theta ), inclusive and selected on associated charged-particle multiplicity.
Wienhard, Klaus ; Schneider, R. K. M. ; Ackermann, K. ; Bangert, Kurt ; Berg, Ulrich Emil Paul ; Stock, Reinhard
The 16O ( gamma ,p0) reaction has been studied with linearly polarized bremsstrahlung photons in and below the giant E1 resonance. The parity of the absorbed radiation was determined from the observed azimuthal asymmetry of the emitted protons. Combined with unpolarized measurements the polarized results determine the proton decay amplitudes of the M1 resonance at Ex=16.2 MeV in 16O. The shape of the unpolarized 16O ( gamma ,p3) angular distribution in the giant E1 resonance was derived from the measured analyzing power. NUCLEAR REACTIONS 16O( gamma ,p), E=15-25 MeV; measured analyzing power theta =90° linearly polarized bremsstrahlung; 16O dipole levels deduced pi ; 16.2 MeV 1+ resonance deduced p0 decay amplitudes; 16O GEDR deduced p3 angular distribution.
Wienhard, Klaus ; Ackermann, K. ; Bangert, Kurt ; Berg, Ulrich Emil Paul ; Bläsing, Carola ; Naatz, W. ; Ruckelshausen, A. ; Rück, D. ; Schneider, R. K. M. ; Stock, Reinhard
The parities of eleven J=1 levels in 208Pb were determined by nuclear resonance fluorescence scattering of linearly polarized photons. A new 1+ level at Ex=5.846 MeV with Gamma 02 / Gamma =1.2±0.4 eV was found. This level can probably be identified with the theoretically predicted isoscalar 1+ state in 208Pb. All other bound dipole states below 7 MeV with Gamma 02 / Gamma >1.5 eV have negative parity. The 1- assignment to the 4.842-MeV level is of special significance because of previous conflicting results about its parity.
Wickert, Helmut ; Ackermann, K. ; Bangert, Kurt ; Berg, Ulrich Emil Paul ; Bläsing, Carola ; Naatz, W. ; Ruckelshausen, A. ; Schennach, Stefan ; Stock, Reinhard
Nuclear resonance fluorescence experiments with linearly polarized bremsstrahlung were performed to determine parities of strong dipole transitions in 40Ar. A total of 14 transitions—ten of them previously unknown—in the energy range from 4.7 to 10.2 MeV could be identified. From this experiment it is evident that the main dipole strength to bound states is due to E1 excitations. An upper limit of B(M1) [up arrow] <0.5 µN2 was found for individual magnetic dipole excitations in 40Ar in the energy region below neutron threshold.
Westfall, Gary D. ; Gosset, Jean ; Johansen, P. J. ; Poskanzer, Arthur M. ; Meyer, W.G ; Gutbrod, Hans Herbert ; Sandoval, Andres ; Stock, Reinhard
A simple model is proposed for the emission of nucleons with velocities intermediate between those of the target and projectile. In this model, the nucleons which are mutually swept out from the target and projectile form a hot quasiequilibrated fireball which decays as an ideal gas. The overall features of the proton-inclusive spectra from 250- and 400-MeV/nucleon 20Ne ions and 400-MeV/nucleon 4He ions interacting with uranium are fitted without any adjustable parameters.
Ströbele, Herbert ; Brockmann, Robert ; Harris, John W. ; Riess, F. ; Sanodoval, Andres ; Stock, Reinhard ; Wolf, Kevin L. ; Pugh, Howel G. ; Schroeder, Lee S. ; Renfordt, Rainer Arno Ernst ; Tittel, Klaus ; Maier, M.
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.
Stock, Reinhard ; Jahnke, U. ; Hendrie, D. L. ; Mahoney, J. ; Maguire, C. F. ; Schneider, W. F. W. ; Scott, D. K. ; Wolschin, G.
Angular distributions for elastic and inelastic transitions in 20Ne + 16O scattering have been measured at E(20Ne)=50 MeV. For the 0+, 2+, and 4+ members of the 20Ne ground-state rotational band, the angular distributions exhibit pronounced backward peaking characteristic of an alpha -cluster exchange mechanism. The analysis of the ground-state transition in the first-order elastic transfer model yields no satisfactory fit although microscopic cluster form factors and full recoil corrections are employed. A coupled channels calculation for the 0+, 2+, and 4+ transitions reveals very strong coupling effects, indicating that the coherent superposition of first-order optical model and distorted-wave Born-approximation amplitudes may not be an adequate model for these reactions. NUCLEAR REACTIONS 16O(20Ne, 16O) and 16O(20Ne, 20Ne), elastic and inelastic transfer; E=50MeV; measured sigma (Ef , theta ); optical model + DWBA, and CCBA analyses.
Stock, Reinhard ; Gutbrod, Hans Herbert ; Meyer, W. G. ; Poskanzer, Arthur M. ; Sandoval, Andres ; Gosset, Jean ; King, Chuck ; King, George ; Lukner, Christian ; Sen, Nguyen Van ; Westfall, Gary D. ; Wolf, Kevin L.
Proton emission in relativistic nuclear collisions is examined for events of low and high multiplicity, corresponding to large and small impact parameters. Peripheral reactions exhibit distributions of protons in agreement with spectator-participant decay modes. Central collisions of equal-size nuclei are dominated by the formation and decay of a fireball system. Central collisions of light projectiles with heavy targets exhibit an enhancement in sideward emission which is predicted by recent hydrodynamical calculations.
Stock, Reinhard ; Gaul, G. ; Santo, R. ; Bernas, M. ; Harvey, B. ; Hendrie, D. ; Mahoney, J. ; Sherman, J. ; Steyaert, J. ; Zisman, M.
The elastic alpha scattering to backward angles has been studied for 40,42,44,48Ca between 40.7 and 72.3 MeV. The cross sections for 40Ca are larger than those for the higher isotopes up to the highest energies. They show backward increases that disappear above 50 MeV. The enhancement factor for 40Ca over 42,44Ca varies smoothly with energy. 48Ca does also show a backward cross-section enhancement over 42,44Ca. alpha -cluster rotational bands in the 44Ti compound state, four-nucleon correlations in 40Ca, and the l-dependent optical model are discussed as approaches to understand the anomaly. The rotator model appears to agree qualitatively with the experimental data. It involves rotational bands extending at least up to J=16 in 44Ti.
Stock, Reinhard ; Bock, Rudolf ; Brockman, R. ; Harris, John W. ; Sandoval, Andres ; Ströbele, Herbert ; Wolf, Kevin L. ; Pugh, Howel G. ; Schroeder, Lee S. ; Maier, M. ; Renfordt, Rainer Arno Ernst ; Dacal, Ángel ; Ortiz, Maria Esther
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.
In high multiplicity nucleus-nucleus collisions baryon-antibaryon annihilation and regeneration occur during the final hadronic expansion phase, thus distorting the initial equilibrium multiplicity ratios. We quantify the modifications employing the hybrid UrQMD transport model and apply them to the grand canonical partition functions of the Statistical Hadronization Model(SHM). We analyze minimum bias and central Pb+Pb collision data at SPS and LHC energy. We explain the Pion to Proton ratio puzzle. We also reproduce the deuteron to proton ratio at LHC energy by the SHM, and by UrQMD after attaching a phase space coalescence process. We discuss the resulting (T,μB) diagram.
Stock, Reinhard ; Becattini, Francesco ; Bleicher, Marcus ; Kollegger, Thorsten ; Schuster, Tim ; Steinheimer-Froschauer, Jan
We analyze hadrochemical freeze-out in central Pb+Pb collisions at CERN SPS and LHC energies. Employing the UrQMD hybrid transport model we study the effects of the final hadron/resonance expansion phase on the hadron multiplicities established at hadronization. The bulk meson yields freeze out directly at hadronization whereas the baryon-antibaryon sector is subject to significant alterations, due to annihilation and regeneration processes. We quantify the latter changes by survival factors for each species which are applied to modify the statistical model predictions for the data. The modified SM analysis recovers the hadronization points, which coincide with the recent lattice QCD predictions of the parton-hadron transition line at finite baryochemical potential.
Strangeness enhancement is discussed as a feature specific to relativistic nuclear collisions which create a fireball of strongly interacting matter at high energy density. At very high energy this is suggested to be partonic matter, but at lower energy it should consist of yet unknown hadronic degrees of freedom. The freeze-out of this high density state to a hadron gas can tell us about properties of fireball matter. The hadron gas at the instant of its formation captures conditions directly at the QCD phase boundary at top SPS and RHIC energy, chiefly the critical temperature and energy density.
A steep maximum occurs in the Wroblewski ratio between strange and non-strange quarks created in central nucleus-nucleus collisions, of about A=200, at the lower SPS energy square root s approximately equal to 7 GeV. By analyzing hadronic multiplicities within the grand canonical statistical hadronization model this maximum is shown to occur at a baryochemical potential of about 450 MeV. In comparison, recent QCD lattice calculations at finite baryochemical potential suggest a steep maximum of the light quark susceptibility, to occur at similar mu B, indicative of "critical fluctuation" expected to occur at or near the QCD critical endpoint. This endpoint hat not been firmly pinned down but should occur in the 300 MeV < mu c B < 700 MeV interval. It is argued that central collisions within the low SPS energy range should exhibit a turning point between compression/heating, and expansion/cooling at energy density, temperature and mu B close to the suspected critical point. Whereas from top SPS to RHIC energy the primordial dynamics create a turning point far above in epsilon and T, and far below in mu B. And at lower AGS energies the dynamical trajectory stays below the phase boundary. Thus, the observed sharp strangeness maximum might coincide with the critical square root s at which the dynamics settles at, or near the QCD endpoint.
A selection of recent data referring to Pb+Pb collisions at the SPS CERN energy of 158 GeV per nucleon is presented which might describe the state of highly excited strongly interacting matter both above and below the deconfinement to hadronization (phase) transition predicted by lattice QCD. A tentative picture emerges in which a partonic state is indeed formed in central Pb+Pb collisions which hadronizes at about T = 185 MeV, and expands its volume more than tenfold, cooling to about 120 MeV before hadronic collisions cease. We suggest further that all SPS collisions, from central S+S onward, reach that partonic phase, the maximum energy density increasing with more massive collision systems.
Hadronic yields and yield ratios observed in Pb+Pb collisions at the SPS energy of 158 GeV per nucleon are known to resemble a thermal equilibrium population at T=180 +/- 10 MeV, also observed in elementary e+ + e- to hadron data at LEP. We argue that this is the universal consequence of the QCD parton to hadron phase transition populating the maximum entropy state. This state is shown to survive the hadronic rescattering and expansion phase, freezing in right after hadronization due to the very rapid longitudinal and transverse expansion that is inferred from Bose-Einstein pion correlation analysis of central Pb+Pb collisions.
With new data available from the SPS, at 40 and 80 GeV/A, I review the systematics of bulk hadron multiplicities, with prime focus on strangeness production. The classical concept of strangeness enhancement in central AA collisions is reviewed, in view of the statistical hadronization model which suggests to understand strangeness enhancement to arise chiefly in the transition from the canonical to the grand canonical version of that model. I. e. enhancement results from the fading away of canonical suppression. The model also captures the striking strangeness maximum observed in the vicinity of sqrt s approx 8 GeV. A puzzle remains in the understanding of apparent grand canonical order at the lower SPS, and at AGS energies.