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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The inclusive reaction pp → Λ + X ++ at 19 GeV/ c beam momentum has been analyzed in terms of the triple-Regge formalism. A good description of the structure function is achieved for events with | t | < 4 (GeV/ c ) 2 . The effective trajectory obtained from fits to the M 2 / s distribution in different t bins is α R ( t ) = −(0.38 ± 0.11) + (1.15 ± 0.07) t , which holds up to a | t | value of 4 (GeV/ c ) 2 . This is consistent with the K trajectory rather than the K ∗ trajectory which has been reported from other experiments.
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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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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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We report on an experiment in which the SLAC 40-in. hybrid facility was exposed to an 8.8-GeV/c antiproton beam. Using external detectors we have identified a large fraction of nonannihilation events and thus obtained a clean sample of annihilation data. Using proton interactions taken in the same detector at the same energy we have made a detailed study of (p¯p−pp) differences and explored their relationship to p¯p annihilations.
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Significant differences are observed between forward-produced Δ ++ (1232) and Λ 0 's in pp interactions and their corresponding anti-particles in p p interactions, as expected from quark counting and single q q annihilation. A possible relationship between these results and the p p -pp total cross section difference is discussed.
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Measurements of charged pion and kaon production in central Pb+Pb collisions at 40, 80 and 158 AGeV are presented. These are compared with data at lower and higher energies as well as with results from p+p interactions. The mean pion multiplicity per wounded nucleon increases approximately linearly with s_NN^1/4 with a change of slope starting in the region 15-40 AGeV. The change from pion suppression with respect to p+p interactions, as observed at low collision energies, to pion enhancement at high energies occurs at about 40 AGeV. A non-monotonic energy dependence of the ratio of K^+ to pi^+ yields is observed, with a maximum close to 40 AGeV and an indication of a nearly constant value at higher energies.The measured dependences may be related to an increase of the entropy production and a decrease of the strangeness to entropy ratio in central Pb+Pb collisions in the low SPS energy range, which is consistent with the hypothesis that a transient state of deconfined matter is created above these energies. Other interpretations of the data are also discussed.
The centrality of the collisions expressed as a percentage of the inelastic cross section (7.15nb), and the mean numbers of wounded nuclei.
The inverse slope parameter of the fitted transverse mass spectra.
The rapidity density averaged over the rapidity interval -0.6 to 0.6.
Inclusive measurements of Λ 0 , Λ 0 , Ξ − , Σ(1385) ± ) production in the forward direction at the CERN intersecting storage rings are presented. A signal for simulataneous Λ 0 Λ 0 production is also observed with total x > 0.6, 2.3 < M Λ Λ < 2.5 GeV and with a cross section of (1.7 ± 0.2) μb.
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Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
Inclusive K0K¯0, Λ0, and Λ¯0 cross sections have been determined using a 292-event/mb exposure of the hydrogen-filled 15-foot bubble chamber at Fermilab. From the invariant-mass distributions of V0π± pairs we find that σ(K*±(890))=4.4±1.4 mb, σ(Σ*±(1385))=0.54±0.40 mb, and σ(Σ¯*±(1385))=0.45±0.34 mb. It is estimated that 0.32 ± 0.11 of K0K¯0's, 0.21 ± 0.16 of Λ's, and 0.96 ± 0.75 of Λ¯'s originate from decays of K*(890) and Σ*(1385), respectively.
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