E. Andersen

Strangeness enhancement at mid-rapidity in Pb Pb collisions at 158-A-GeV/c

We study the influence of lexical subsumption on the semantic proximity of terms. By studying the semantic relation between lexically subsumed terms in an existing controlled vocabulary and those in a corpus, we formulate hypotheses on the underlying specific relations. These hypotheses enable us to propose an ordering of term variants found in the corpus, by probability of decreasing semantic proximity. Results from our experiment show that surface indices like the presence of proper names, compounds and the number of added words in a term variant are criteria for ordering the variants of the same term. The ranking obtained will enable us to form more semantically-cohesive clusters. Applications targeted are text mining, question-answering and science and technology watch.

LAMBDA , XI AND OMEGA PRODUCTION AT MID-RAPIDITY IN PB-PB AND P-PB COLLISIONS AT 158 A GEV/C

Λ, Ξ and Ω yields and transverse mass spectra measured at central rapidity in Pb-Pb and p-Pb collisions at 158 A GeV/c are presented. The yields in Pb-Pb interactions are given as a function of the collision centrality and compared with those obtained from p-Pb collisions. The dependence of hyperon yields on the centrality of the impact and on the strangeness content of the hyperon are discussed.

Strangeness production at mid-rapidity in S + Pb collisions at 200 GeV/c per nucleon

Abstract Experimental evidence is presented for a source of unusually high strangeness content located at mid-rapidity in 200 GeV/ c per nucleon collisions of 32 S projectiles with a Pb target. The enhancement is not seen in p+Pb reactions measured in the same apparatus at the same energy. This source becomes dominant for central collisions.

A study of cascade and strange baryon production in sulphur-sulphur interactions at 200 GeV/c per nucleon

Strange and multistrange baryon and antibaryon production has been studied in sulphur sulphur interactions at 200 GeV/c per nucleon at central rapidity using the CERN Omega Spectrometer. Particle production ratios and transverse mass spectra are presented for Λ, Ξ−, Λ and Ξ−.

Multiplicity dependence of strangeness production in S + Pb collisions at 200 GeV/c per nucleon

Abstract 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).

A (t, p) study of levels in 156Gd, 157Gd, 158Gd and 159Gd

Abstract Angular distributions of the 154, 155, 156, 157Gd(t, p) 156, 157, 158, 159Gd reactions have been measured using 17 MeV tritons from the McMaster University tandem Van de Graafi accelerator. The reaction products were analyzed with a magnetic spectrograph and detected with photographic emulsions. Excited members of the ground bands in both even and odd nuclei were populated in multistep processes with magnitudes and angular distributions satisfactorily described in CCBA calculations. Levels populated with L=0 transitions were identified from the angular distributions. The 0+ levels at 1050 keV in 156Gd and 1461 keV in 158Gd which were strongly populated in (p, t), were weakly populated in (t, p) in agreement with a recent α-cluster calculation. The summed L=0 strength was smaller in odd than in even nuclei. An increase in the L=0 strength to excited states towards N=98 was observed.

Production of Λ, Λ, and Ξ−, Ξ+ particles in S+Pb collisions at 200 GeV/c per nucleon☆

Abstract The yields of Λ, Λ , and Ξ−, Ξ + have been measured close to mid-rapidity in sulphur reactions on a Pb target at 200 GeV/c per nucleon beam momentum. Fully corrected production ratios of Λ Λ , Ξ + Ξ , Ξ − Λ and Ξ Λ are presented. The ratios have been analysed both in the context of a rapidly disintegrating quark-gluon plasma and a hadronic resonance gas. Our analysis shows that the hadron gas model is sufficient to explain the observed particle yields.

A TPC in the context of heavy-ion collisions

Abstract The design of a TPC for a high-multiplicity environment is described. The sense plane is composed of a matrix with 40 rows of short anode wires. The end-cap is completed with rod and wire electrodes to establish the amplification region and to minimize space charge effects. The digital readout of more than 6000 channels is performed by a combination of purpose-built comparators and FASTBUS TDCs. The performance of the chamber is briefly described, and some ideas to improve the hit efficiency and resolution in a new end-cap design are discussed.

DI-V

The first results on V0-V0 pairs, namely invariant masses and HBT correlations, obtained by the WA97 experiment in Pb-Pb collisions are presented. There is no evidence for any resonance signal.

^{0}

KS0, Λ, Ξ, Ω and negative particle h− yields and transverse mass spectra, measured at central rapidity in p-Pb and Pb-Pb collisions at 158 A GeV/c, are presented and discussed. Yields are studied as a function of the number of nucleons participating in the collision Npart, which have been estimated using the Glauber model. From p-Pb to Pb-Pb collisions the particle yields per participant increase substantially. Such an enhancement is more pronounced for multiply strange particles, and reaches an order of magnitude for Ω. For a number of participants Npart > 100, however, all yields per participant appear to be constant.