V. Manzari

Ξ−, Ξ−, Λ andΛ production in sulphur-tungsten interactions at 200 GeV/c per nucleon

Abstract Multi-strange baryon and antibaryon production is expected to be a useful probe in the search for quark-gluon plasma formation. We present the transverse mass distributions of negative particles, Λ s , Λ s and Ξ − s produced in sulphur-tungsten interactions at 200 GeV/c per nucleon and give the corrected rations Λ /Λ, Ξ − /Λ and Ξ − / Λ . Our ratio Ξ − / Λ appears to be larger than that from pp interactions.

Observation of a narrow scalar meson at 1450 MeV in the reaction pp → pƒ(π+π−π+π−)ps at 450 GeV/c using the CERN Omega spectrometer

Abstract The reaction pp → pƒ(π + π − π + π − )p s has been studied at 450 GeV/c in an experiment designed to search for gluonic states. In addition to the well known ƒ 1 (1285) , the π+π−π+π− mass spectrum shows evidence for two states pre only observed by the WA76 experiment, the X(1450) and X(1900). An analysis of the X(1450) shows that it is a relatively narrow state (Γ = 56 ± 12 MeV) with I(JPC) = 0(0++) which decays to ϱ0π+π−. The X (1900) could either b single broad state (Γ = 370±70 MeV) with I(JPC) = 0(2++) or possibly separate states.

Production of multistrange baryons and antibaryons in sulphur-tungsten interactions at 200 GeV/c per nucleon

Abstract Production of Ξ − and Ξ − has been observed for the first time in heavy ion interactions by the WA85 Experiment. Multistrange baryon and antibaryon production is expected to be a useful probe in the search for quark-gluon plasma formation. We describe the procedure used to select these cascade candidates and show that Ξ − and Ξ − decays can be identified. The ratio of Ξ Ξ production, corrected for geometrical acceptances and reconstruction efficiencies, is 0.39 ± 0.07 for sulphur-tungsten interactions in the central rapidity interval 2.3 Y lab p T >1.1 GeV/ c .

A further study of the centrally produced π+π− and π+π−π+π− channels in pp interactions at 300 and 450 GeV/c

Abstract An analysis of the centrally produced π + π − and π + π − π + π − mass spectra from the WA76 and WA91 experiments is presented, which shows that in the π + π − π + π − channel there are two new states, the f 0 (1450) and f 2 (1900). There is another new state in the π + π − channel with M = 1497 ± 30 MeV and Γ = 199 ± 30 MeV, which is compatible with the f 0 (1520) observed by the Crystal Barrel experiment. Another interpretation is discussed, where the 1450 and 1497 GeV structures are explained as being due to an interference effect between the f 0 (1365) and f 0 (1520).

Xi-, anti-xi-, Lambda and anti-Lambda production in sulphur - tungsten interactions at 200-GeV/c per nucleon

Abstract Multi-strange baryon and antibaryon production is expected to be a useful probe in the search for quark-gluon plasma formation. We present the transverse mass distributions of negative particles, Λ s , Λ s and Ξ − s produced in sulphur-tungsten interactions at 200 GeV/c per nucleon and give the corrected rations Λ /Λ, Ξ − /Λ and Ξ − / Λ . Our ratio Ξ − / Λ appears to be larger than that from pp interactions.

A hybrid silicon pixel telescope tested in a heavy-ion experiment

Abstract Specific features of the OMEGA-ION pixel detector are the adjustable delay with external trigger capability and the detector leakage current compensation. A row of pixels can be used for testing the electrical performance of the amplifier and comparator circuits. Detailed results of these electrical tests are presented. A telescope made of three OMEGA-ION hybrid silicon pixel detectors has been successfully tested in the heavy-ion experiment WA94. Each plane consisted of a single detector with 1006 active pixels (500 μm×75 μm), each one being bump-bonded to the readout chip, and arranged in 16 columns and 63 rows respectively. With a sensitive area as small as 8000 × 4725 μm 2 several million events with at least one track originating from the sulphur-sulphur interaction have been recorded in a few hours. Results on target reconstruction, tracking accuracy and efficiency are presented.

Observation of Ω− and Ω− in sulphur-tungsten interactions at 200 GeV/c per nucleon

Abstract Multistrange baryon and antibaryon production is suggested to be a useful probe in the search for Quark-Gluon Plasma formation. We report the detection of an Ω − + Ω − signal in central S + W interactions at 200 A GeV/c and measure the ratio Ω − Ω − = 0.57±0.41 at central rapidity and p T >1.6 GeV/ c .

Performance of 0.5 × 106 sensitive elements pixel telescope in the WA97 heavy ion experiment at CERN

Abstract A silicon pixel telescope, consisting of seven planes for a total of about 0.5 M sensor elements with size of 75 μ m × 500 μ m, was successfully employed in the WA97 experiment at CERN. We describe here the overall performance of the detector; we also report some early results from Pbue5f8Pb and p-Pb runs, showing the powerful capability to measure particle momenta and the effective mass of hyperons with a good resolution.

Production of strange and multistrange hyperons and antihyperons in S-W interactions at 200 GeV/c per nucleon

Strange and multistrange baryon and antibaryon production is a useful probe into the dynamics of the hot hadronic matter created in central heavy ion interactions. Relative production yields and transverse mass spectra are presented for Λ, Λ, Ξ− and Ξ+ hyperons produced in central sulphur-tungsten interactions at 200 GeV/c per nucleon.

Confirmation of a soft photon signal in excess of Q.E.D. expectations in π−p interactions at 280 GeV/c

Abstract Photons produced in π − p interactions at 280 GeV/ c were detected by reconstructing the e + e − pairs produced via the materialisation of the photons in a 1 mm thick lead sheet placed in front of the MWPCs of the OMEGA spectrometer at CERN. A soft photon signal 7.8 ± 1.5 times the Q.E.D. inner bremsstrahlung prediction was observed confirming the results of a previous experiment.Photons produced in π − p interactions at 280 GeV/c were detected by reconstructing the e + e − pairs produced via the materialisation of the photons in a 1 mm thick lead sheet placed in front of the MWPCs of the OMEGA spectrometer at CERN. A soft photon signal 7.8 ± 1.5 times the Q.E.D. inner bremsstrahlung prediction was observed confirming the results of a previous experiment.