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Brockmann, Robert ; Harris, John W. ; Sandoval, Andres ; Stock, Reinhard ; Ströbele, Herbert ; Odyniec, Grazyna Janina ; Pugh, Howel G. ; Schroeder, Lee S. ; Renfordt, Rainer Arno Ernst ; Schall, Dietmar ; Bangert, Dieter ; Rauch, Wolfgang ; Wolf, Kevin L.
Pion and proton production are measured to investigate thermal equilibrium in central collisions of 40Ar+KCl at 1.8 GeV/nucleon. The bulk of the pion yield is isotropic in the c.m. system, with an apparent temperature of 58±3 MeV, much lower than the 118±2 MeV of the protons. It is shown that the low pion "temperature" can be explained by the decay kinematics of delta resonances in thermal equilibrium. A (5±1)% component in the pion spectrum is, however, found to have a temperature of 110±10 MeV. The effect on the spectra of possible contributions from collective radial flow is discussed.
Renfordt, Rainer Arno Ernst ; Schall, Dietmar ; Bock, Rudolf ; Brockmann, Robert ; Harris, John W. ; Sandoval, Andres ; Stock, Reinhard ; Ströbele, Herbert ; Bangert, Dietmar ; Rauch, Wolfgang ; Odyniec, Grazyna Janina ; Pugh, Howel G. ; Schroeder, Lee S.
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.
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 ; 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.
Harris, John W. ; Sandoval, Andres ; Stock, Reinhard ; Ströbele, Herbert ; Renfordt, Rainer Arno Ernst ; Geaga, Jorge V. ; Pugh, Howel G. ; Schroeder, S ; Wolf, Kevin L. ; Dacal, Ángel
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 Bc
Sandoval, Andres ; Stock, Reinhard ; Stelzer, Herbert ; Renfordt, Rainer Arno Ernst ; Harris, John W. ; Brannigan, James P. ; Geaga, Jorge V. ; Rosenberg, L. J. ; Schroeder, Lee S. ; Wolf, Kevin L.
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 <n pi -> 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.Dp