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.
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The considerable polarization of hyperons produced at high xF has been known for a long time and has been interpreted with various theoretical models in terms of the constituents' spin. Recently, the analyzing power in inclusive Λ0 hyperon production has also been measured using the 200GeV/c Fermilab polarized proton beam. The covered kinematic range is 0.2≤xF≤1.0 and 0.1≤pT≤1.5GeV/c. The data indicate a negative asymmetry at large xF and moderate pT. These results can further test the current ideas on the underlying mechanisms for hyperon polarization.
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Data on stable hadron production in p + p and p + n interactions at 200 GeV/ c are reviewed. Methods to construct missing data in the p + p, p + n, and n + n interactions are derived from charge symmetry and charge, baryon and strangeness conservation, and used to yield nucleon-nucleon interaction results. These may be useful for evaluating nucleus-nucleus collision measurements in terms of enhancements and suppressions. Parameterizations of p t 2 and rapidity distributions are presented to provide yields in acceptance cuts for comparisons to nucleus-nucleus data. As an example the derived nucleon-nucleon multiplicities are reduced to the acceptances of the NA-35 CERN S + S experiment.
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The production of neutral strange particles (K0, Λ) inp Ar,pXe and\(\bar p\)Xe collisions at 200 GeV is investigated in the NA5 experiment using a streamer chamber at the CERN SPS. Results are presented on inclusive cross sections, average multiplicities, and on rapidity and transverse momentum distributions of neutral strange particles.
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Using a quark-diquark fragmentation model, in which either the Field-Feynman or the Lund model is coupled with a quark-diquark distribution function, we study transverse momentum distributions,pT, for the inclusive reactionspp→hadron +anything at 360 GeV/c. We find that a primordial mean transverse momentum 〈kT〉≃0.4 GeV/c can well reproduce thepT2 distributions of charged hadrons, π0,Ks0, Λ0,K* and Σ* and the Feynmanx−pT correlations. We confirm that a diquark in a proton plays an important rôle in reproducing thex−pT correlation of Λ0.
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We report Λ 0 -hyperon polarization measurements at the CERN intersecting storage rings from √ s of 31 to 62 GeV. P Λ 0 changes insignificantly, +(0.8±1.7)%, over this range of √ s . However, P Λ 0 is observed to grow with Feynman- x F and with transverse momentum. At an average p t of 1.1 GeV/ c , P Λ 0 depends linearly on x F and approaches −40% at x F =0.8.
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We have measured the polarization of Λ's in inclusive pp and K−p reactions and of Λ¯'s in p¯p interactions at a beam momentum of 176 GeV/c. Data were taken in the beam-fragmentation region with hyperon transverse momenta from 0.2 to 1.5 GeV/c. The P¯ produced Λ¯'s have the same magnitude and sign of polarization as the p-produced Λ's, whereas the Λ's from K−p interactions are more highly polarized and in the opposite direction.
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In an experiment at the CERN intersecting storage rings with √ s = 31 GeV, we have measured αP , the product of asymmetry parameter and polarization, for Λ 0 's and Λ 0 's produced in p p and pp interactions, respectively. The ratio, (αP) Λ /(αP Λ = −1.04±0.29 , is consistent with the value −1, and constitutes the first test of CP invariance in Λ decay.
The ratio CONST/CONST is obtained under assumption of POL(LAMBDA) = POL(LAMBDABAR).