G. Baroni

Electromagnetic dissociation of 200 GeV/nucleon 16O and 32s ions in nuclear emulsions

Abstract This work represents the results of an experimental investigation of the electromagnetic dissociation of 200 GeV/nucleon 16 O and 32 S ions in nuclear emulsions. Exclusive channels involving charged fragments have been studied as a function of the energy released, and, assuming a Weizsacker-Williams spectrum of virtual photons, there is a good agreement with results for the (γ, p) processes obtained with real photons. However, the rates found for other processes are larger, in particular for the (γ, α) on both nuclei. The values of the total integrated absorption cross sections are generally larger than those obtained from real photon experiments but the extent of the discrepancy depends strongly upon which photon results are used in the comparison.

THE DOUBLE ASSOCIATED PRODUCTION OF CHARMED PARTICLES BY THE INTERACTION OF 350 GEV/C PI-MESONS WITH EMULSION NUCLEI

Abstract Evidence is reported for the simultaneous production of four charmed particles in interactions induced by 350 GeV/ c π − mesons in stacks of nuclear emulsions. The events were found during a search for beauty particles among a sample of about 200 interactions with candidates for charmed particles. The events selected required the presence of at least one muon with a high component of momentum transverse to the beam direction.

A Hybrid Experiment to Search for Beauty Particles

We give here a detailed description of experiment WA75, which was performed at CERN to search for beauty particles. Events containing at least one muon with a high momentum transverse to the beam direction were selected; then the primary interactions and decay vertices, located in stacks of nuclear research emulsions, were examined and analysed. The various parts of the apparatus are described and the off-line analysis and search in emulsion are discussed. An estimate is made of the sensitivity of the experiment to beauty- and charmed-particle production.

Interactions of 60 and 200 A GeV 16O Ions in Nuclear Emulsion

A survey of the interactions of 16O nuclei of energies 60 and 200 A GeV in nuclear emulsions is presented. Correlations between projectile fragments and target evaporation are studied. The electromagnetic dissociation of 16O, mainly ascribed to absorption in the giant-resonance region, is found to contribute to a sizeable fraction of the cross-section, and increases with increasing energy.

Some properties of charmed particles produced in π−-nucleus interactions

Abstract The azimuthal correlation distribution of 102 charmed-particle pairs observed in the hybrid emulsion experiment WA75 is compared with theoretical predictions. The various pairs - (D − D 0 ), (D − D + ), (D 0 D 0 ) and (D + D 0 )-all s how, within statistical error, the same azimuthal correlation distribution, demonstrating its independence from the specific nature of the production channel. Among the decays of 150 charged charmed particles and 138 neutral ones seen, higher multiplicities are favoured for hadronic as opposed to semileptonic decays. The data are consistent with the muonic decays of charged D mesons proceeding through the channels (μ ± , v, K 0 ) and [μ ± , v, K ∗0 (892)] , the fraction through K 0 being 0.76±0.06.

Interactions of 200 GeV/nucleon 16O and 32S ions in nuclear emulsions

Abstract This paper presents and contrasts features of the inelastic nuclear reactions of 200 GeV/nucleon 16O and 32S ions with emulsion nuclei. Both the multiplicities of shower particles and the extent of target fragmentation have been studied for varying degress of disruption of the projectile nuclei. The results may be interpreted within a simple geometrical model. In particular the rapidity distributions of those events which exhibit complete projectile break-up without any overt sign of low-energy target fragmentation have been determined. The interaction of secondary projectile fragments of charge two or more issuing from oxygen interactions were also studied and the mean free paths in emulsion of the primary 16O and 32S ions and all such fragments have been compared to those predicted by a simple Glauber model.

The electromagnetic and hadronic diffractive dissociation of 16O ions

Abstract Events which satisfy the kinematics of p( 16 O,CHep), with low excitation energy in the (CHe) system and a low-energy recoil proton, have been identified in the interactions of 200 GeV/nucleon 16 O ions with nuclear emulsion. An eikonal DWIA estimate of the target A -dependence of strong-interaction diffractive dissociation suggests that, on the basis of these hydrogen data, most of the (CHe) final states, previously ascribed to electromagnetic dissociation on heavy nuclei, might rather be hadronic in character. This contamination is very much less important in the dominant (NH) channel.

200 GeV Proton Interactions in Nuclear Emulsion

The mean‐free‐path for inelastic interactions of 200 GeV protons in nuclear emulsion has been measured using the techniques of along‐the‐track scanning and area scanning. The results obtained are, respectively, λinelu2009=u200935.3u2009±u20091.0u2009cm and λinelu2009=u200933.1u2009±u20091.5u2009cm. The average charged multiplicities have been found to be 〈ns〉u2009=u20098.2u2009±u20090.2 for ‘white’ stars and 〈ns〉u2009=u200912.9u2009±u20090.15 for all events. A plot of ns versus Nh (where Nh is the number of black and grey tracks) shows a linear relation over the region 0u2009≤u2009Nhu2009≤u200925. The Castagnoli method applied to ‘white’ stars overestimates the C.M. energy by ∼ 40%, however, for stars with Nhu2009≥u20091, there is good agreement.

Interactions of 200xA GeV 16O and 32S studied by emulsion and CR39 in hybrid experiments

Abstract Ultrarelativistic ion collisions were studied by solid state particle track detectors. Physics results obtained by nuclear emulsions, stand-alone or with electronic counters, are reviewed, concerning both peripheral and central interactions. A new hybrid experiment, making use of nuclear emulsions and of CR39, is described. Data were taken last August. Preliminary technical results are presented, obtained by automatic track measurements on projectile fragments collected in previously exposed CR39 sheets.

Automatic devices' resolution in nuclear emulsion observation

Abstract Some results on the precision obtainable using automatic devices in nuclear emulsion measurements and simplified methods for their application in standard work are presented.