Production of Λ, Λ , and K s 0 has been measured for a wide range of event multiplicity in S+Pb reactions at 200 GeV/c per nucleon. The production of Λ is shown to increase with multiplicity faster than expected from a superposition of p+p collisions. The effect is seen for low multiplicity (below 100 negative particles).
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The study of the K + total cross sections on a wide range of nuclei has revealed important modifications of the free-space K + -nucleon interaction when the nucleon is embedded in a nucleus. Data indicating such an effect were first obtained in a comparison of the total cross sections on carbon and deuterium. In this letter we report new measurements on 6 Li, silicon, and calcium, and demonstrate that the previously reported modifications occur quite generally.
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The depolarization parameter D 0 n 0 n in the charge-exchange reaction p p ↑→ n n ↑ has been measured for the first time at the CERN Low Energy Antiproton Ring (LEAR) at 875 MeV/ c antiproton beam momentum, in the forward hemisphere. The measured values of D 0 n 0 n are always smaller than ±0.3, indicating that the two-spin amplitudes dominate the scattering matrix as suggested by the meson exchange potential models.
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We report on the production characteristics and total cross section for 9 beauty hadron pairs produced by a 600 GeV/ c π − beam, the first such information in this energy region. The events were detected in the hybrid emulsion spectrometer of Fermilab Experiment E653. The measured pair cross section for all χ F , assuming linear A dependence, is 33±11 (stat.)±6(syst.) nb/nucleon. Fits of the inclusive single-hadron production distribution to the forms d σ d χ F ∝ (1−|χ F −χ 0 |) n and d σ d p T 2 ∝ exp (−bp t 2 ) give n=5.0 −2.1−1.7 +2.7+1.7 , χ 0 =0.06 −0.07−0.03 +0.06+0.02 , and b=0.13 −0.04−0.02 +0.05+0.02 ( GeV /c −2 . .The pairs tend to be produced back-to-back.
Cross section over all x assuming A**1 nuclear dependence.
Fit to data of form dsig/dx ^ (1-ABS(X-X0))**N yields X0 = 0.06 +0.06,-0.07(DSYS=+0.02,-0.03) and N = 5.0 +2.7,-2.1(DSYS=+-1.7).
Fit to data of form dsig/dPT**2 ^ exp(-B*PT**2) yields B = 0.13 +0.05,-0.04(DSYS=+-0.02).
The differential cross section for the reaction H2(γ,p)n has been measured at several center-of-mass angles ranging from 50° to 143° for photon energies between 0.8 and 1.8 GeV. The experiment was performed at the SLAC-NPAS facility with the use of the 1.6 GeV/c spectrometer to detect the high energy protons produced by a bremsstrahlung beam directed at a liquid deuterium target. Contributions from concurrent disintegration by the residual electron beam were determined by measuring the proton yield without the Cu photon radiator. At angles not very far from 90°, the energy dependence of the cross sections is consistent with predictions of scaling using counting rules for constituent quarks. At least one theoretical calculation based on a meson-baryon picture of the reaction is able to reproduce the magnitude and energy dependence of the 90° cross section. The angular distribution exhibits a large enhancement at backward angles at the higher energies.
THE QUOTED ERRORS ARE STATISTICAL ONLY.
Absolute π±d differential cross sections and charge asymmetries have been measured at incident pion energies of 30 and 50 MeV, using an active target of scintillator plastic to detect recoil deuterons in coincidence with scattered pions. In addition, a small set of data at 65 MeV was collected for comparision with the results of an earlier experiment performed by this group. Measurements at 50 MeV from the earlier experiment are compared with the results of the present experiment.
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In the CERN NA32 experiment a high-resolution silicon vertex detector and a purely topological approach were used to collect 557 events consistent with associated charm production, both decay vertices being observed. The pseudorapidity gap distribution appears to be nearly independent of the nature of the charmed hadrons. This distribution is reasonably consistent with the next-to-leading order QCD calculations. However the azimuthal-angle distribution is significantly broader than the above predictions.
FOR ONLY 20 EVENTS IN WICH BOTH DECAYS ARE FULLY RECONSTRUCTED ( 26 D0 , 8 D+ , 5 D/S+ , 1 LAMBDA/C+ CHARMED PARTICLES ).
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Data of the ηπ − system were obtained in the reaction π − p → ηπ − p at 6.3 GeV/ c beam momentum. About 17 k events of ηπ − were collected in the mass range 0.8 ⩽ M ηπ - ⩽ 1.8 GeV/ c 2 and in the range of the momentum transfer squared 0.075 ⩽ | t ′| ⩽ 0.60 (GeV/ c ) 2 . A large forward-backward asymmetry was observed around 1.3 GeV/ c 2 in the Gottfried-Jackson frame of the ηπ − system. A partial wave analysis of the data was performed. A peak of the D + wave attributed to a 2 (1320) is clearly seen. An enhancement is observed around 1.3 GeV/ c 2 in the P + wave.
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We present the first measurement of the left-right cross section asymmetry (ALR) for Z boson production by e+e− collisions. The measurement was performed at a center-of-mass energy of 91.55 GeV with the SLD detector at the SLAC Linear Collider which utilized a longitudinally polarized electron beam. The average beam polarization was (22.4±0.6)%. Using a sample of 10 224 Z decays, we measure ALR to be 0.100±0.044(stat)±0.004(syst), which determines the effective weak mixing angle to be sin2θWeff=0.2378 ±0.0056(stat)±0.0005(syst).
R and L refer to Right and Left handed beam polarization.
Effective weak mixing angle.
We have measured antiproton production cross sections as functions of centrality in collisions of 14.6 GeV/c per nucleon Si28 ions with targets of Al, Cu, and Pb. For all targets, the antiproton yields increase linearly with the number of projectile nucleons that have interacted, and show little target dependence. We discuss the implications of this result on the production and absorption of antiprotons within the nuclear medium.
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