P. Seyboth

Charged Particle Multiplicity Distributions in p p Collisions at ISR Energies

Abstract We present the first direct measurements of charged-particle multiplicity distributions for pp collisions at ISR energies. The measurements are performed by means of a streamer chamber detector with large solid-angle coverage and excellent multitrack efficiency. Particle densities are observed to rise in the central region as s increases. The multiplicity distributions in this region deviate from a Poisson Law, thus giving evidence for correlations. These correlations are of the same type as those obtained from clustering of the collision products. The mean charged multiplicity over the full rapidity range increases faster than log s . Our data do not support an early onset of KNO multiplicity scaling.

Energy dependence of pion and kaon production in central Pb¿Pb collisions

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.

Evidence for an Exotic S = -2, Q = -2 Baryon Resonance in Proton-Proton Collisions at the CERN SPS

Results of resonance searches in the Xi- pi-, Xi- pi+, antiXi+ pi- and antiXi+ pi+ invariant mass spectra in proton-proton collisions at sqrt{s}=17.2 GeV are presented. Evidence is shown for the existence of a narrow Xi- pi- baryon resonance with mass of 1.862+/-0.002 GeV/c^2 and width below the detector resolution of about 0.018 GeV/c^2. The significance is estimated to be 4.0 sigma. This state is a candidate for the hypothetical exotic Xi_(3/2)^-- baryon with S = -2, I = 3/2 and a quark content of (d s d s ubar). At the same mass a peak is observed in the Xi- pi+ spectrum which is a candidate for the Xi_(3/2)^0 member of this isospin quartet with a quark content of (d s u s dbar). The corresponding antibaryon spectra also show enhancements at the same invariant mass.

Multiplicity and transverse energy flux in 16O+Pb at 200 GeV per nucleon

Abstract First results from ultrarelativistic 16 O+Pb collisions at 200 GeV/nucleon are presented. The transverse energy E T in average central collisions is ≈ 75 GeV for the interval 2.2⩽ y ⩽3.8. A 16-fold convolution of the inelastic p+Au transverse energy spectrum, also measured at 200 GeV, reproduces the mean E T of 16 O+Pb. The amount of nuclear stopping power appears to be high.

Onset of deconnement in nucleus-nucleus collisions: Review for pedestrians and experts

Evidence for the energy threshold of creating the quark-gluon plasma in nucleusnucleus collisions, the so-called onset of deconnement, has been found by the energy scan program of the NA49 experiment at the CERN SPS. In this paper we review the experimental and theoretical status of this phenomenon. First, the basic, qualitative ideas are presented for non-experts. Next, the latest experimental results are compared to a statistical model within which the onset of deconnement and its signals had been predicted. Finally, alternative interpretations and open questions are discussed.

Angular correlations between the charged particles produced in pp collisions at ISR energies

Abstract We present an analysis of rapidity and azimuthal correlations between the charged products of pp collisions at ISR energies. The use of streamer chambers as detectors permits a study of the correlation mechanism at fixed multiplicities. The analysis is restricted to the central rapidity region to suppress diffractive production. A strong short-range correlation is observed, which can be described by independent emission of low-multiplicity clusters, suggestive of abundant resonance production.

Neutral strange particle production in sulphur-sulphur and proton-sulphur collisions at 200 GeV/nucleon

AbstractThe production of Λ,

A study of deep inelastic hadron-hadron collisions with a large acceptance calorimeter trigger

\bar \Lambda