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.
Pseudorapidity distribution at 23.6 GeV.
Pseudorapidity distribution at 45.2 GeV.
Pseudorapidity distribution at 62.8 GeV.
The average charged multiplicity in proton-proton interactions has been studied at √ s = 62 GeV. A very good agreement with the average charged multiplicity measured in e + e − annihilation at different energies is obtained by redefining, in p-p, the correct energies available for particle production. This means that a p-p collision at √ s = 62 GeV does in fact correspond to a large range of effective hadronic energies available for particle production.
AVERAGE CHARGED MULTIPLICITY AS A FUNCTION OF HADRONIC ENERGY WHERE E(NAME=HAD) IS THE INCIDENT PROTON ENERGY (COLLIDING BEAM ENERGY) MINUS THE LEADING PROTON ENERGY.
By using three different c.m. energies in pp interactions,\(\sqrt s \), 44, 62 GeV, it is shown that the average charged-particle multiplicity <nch> sclaes with\(\sqrt s \) once the correct hadronic energy available for multiparticle production,Ehad, is used as basic parameter. The pp data, analysed in this way, are compared with e+e− data at equivalent energies. The agreement is very satisfactory.
WITH SQRT(S) OF 30 GEV.
WITH SQRT(S) OF 44 GEV.
WITH SQRT(S) OF 62 GEV.
Measurements of charged particle multiplicity distributions in the central rapidity region in p-p and p-α, and α-α collisions are reported. They are better fitted to the “wounded nucleon” than to the “gluon string” model. The average transverse momenta, for all three reactions, are identical (and almost independent of multiplicity) up to very high multiplicities.
THE FIRST PP DATA IS AT 44 GEV, THE SECOND AT 63 GEV.
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The multiplicities of charged secondaries in proton-proton collisions were determined using the split-field-magnet detector at the CERN Intersecting Storage Rings (ISR). Measurements are presented on multiplicity distributions both for inelastic and non-single-diffractive events at four different energies s=30.4, 44.5, 52.6, and 62.2 GeV. The results reported here represent the first high-statistics measurement of charged multiplicity distributions at ISR energies with a magnetic detector covering nearly the full solid angle.
INELASTIC EVENTS.
NON-SINGLE-DIFFRACTIVE EVENTS.
Moments of the multiplicity distributions for Inelastic events.
We present the general properties of jets produced bye+e− annihilation. Their production and fragmentation characteristics have been studied with charged particles for c.m. energies between 12 and 43 GeV. In this energy rangee+e− annihilation into hadrons is dominated by pair production of the five quarksu, d, s, c andb. In addition, hard gluon bremsstrahlung effects which are invisible at low energies become prominent at the high energies. The observed multiplicity distributions deviate from a Poisson distribution. The multiplicity distributions for the overall event as well as for each event hemisphere satisfy KNO scaling to within ∼20%. The distributions ofxp=2p/W are presented; scale breaking is observed at the level of 25%. The quantityxpdδ/dxp is compared with multigluon emission calculations which predict a Gaussian distribution in terms of ln(1/x). The observed energy dependence of the maximum of the distributions is in qualitative agreement with the calculations. Particle production is analysed with respect to the jet axis and longitudinal and transverse momentum spectra are presented. The angular distribution of the jet axis strongly supports the idea of predominant spin 1/2 quark pair production. The particle distributions with respect to the event plane show clearly the growing importance of planar events with increasing c.m. energies. They also exclude the presence of heavy quark production,e+e−→Q\(\bar Q\) for quark masses up to 5<mQ<20.3 GeV (|eQ|=2/3) and 7<mQ<19 GeV (|eQ|=1/3). The comparison of 1/σtotdδ/dpT measured at 14, 22 and 34 GeV suggests that hard gluon bremsstrahlung contributes mainly to transverse momenta larger than 0.5 GeV/c. The rapidity distribution forW≧22 GeV shows an enhancement away fromy=0 which corresponds to an increase in yield of 10–15% compared to the centre region (y=0). The enhancement probably results from heavy quark production and gluon bremsstrahlung. The particle flux around the jet axis shows with increasing c.m. energy a rapidly growing number of particles collimated around the jet axis, while at large angles to the jet axis almost noW dependence is observed. For fixed longitudinal momentump‖ approximate “fan invariance” is seen: The shape of the angular distribution around the jet axis is almost independent ofW. The collimation depends strongly onp‖. For smallp‖,p‖<0.2 GeV/c, isotropy is observed. With increasingp‖ the particles tend to be emitted closer and closer to the jet axis.
R VALUES BELOW 32.5 GEV ARE IDENTICAL TO THOSE GIVEN IN BRANDELIK ET AL., PL 113B, 499 (1982).
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CHARGED PARTICLE MULTIPLICITY DISTRIBUTIONS.
The inclusive production of π± andK± mesons and of protons and antiprotons ine+e− annihilations has been measured at 34 GeV and 44 G
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The production of strange baryons ine+e− annihilation has been studied at centre of mass energies of 34.8 GeV and 42.1 GeV, using the TASSO detector at DESY. Inclusive cross-sections have been obtained forΛ0 andΞ− production and an upper limit has been placed upon the production rate of Σ*±(1385). We measure theΛ0 multiplicity per event to be\(\begin{gathered}\hfill \\0.218_{ - 0.011}^{ + 0.011}\pm 0.021 \hfill \\ \end{gathered} \) and\(0.256_{ - 0.029}^{ + 0.030}\pm 0.025\) at\(\sqrt s=34.8\) and 42.1 GeV respectively. The Ξ− multiplicity per event is found to be\(0.014_{ - 0.003}^{ + 0.003}\pm 0.004\) at\(\sqrt s=34.8 GeV\). An investigation has been made of the extent to whichΛ0 are produced in pairs. TheΛ0 cross-section has been studied as a function of event sphericity.
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We report on an analysis of the multiplicity distributions of charged particles produced ine+e− annihilation into hadrons at c.m. energies between 14 and 46.8 GeV. The charged multiplicity distributions of the whole event and single hemisphere deviate significantly from the Poisson distribution but follow approximate KNO scaling. We have also studied the multiplicity distributions in various rapidity intervals and found that they can be well described by the negative binomial distribution only for small central intervals. We have also analysed forward-backward multiplicity correlations for different energies and selections of particle charge and shown that they can be understood in terms of the fragmentation properties of the different quark flavours and by the production and decay of resonances. These correlations are well reproduced by the Lund string model.
RATIO of MULT/DISPERSION for the whole event to that for the single hemisphere data.
Complete event multiplicities.
Single hemisphere multiplicities.
Results are presented on an investigation of photons produced in multihadronic final states frome+e− annihilation at 35 GeV and 44 GeV center of mass energies. Scalling violation between 14 and 44 GeV is observed in inclusive photon spectra. Comparing inclusive π0 spectra with charged pion spectra it is found that the average π0 multiplicity exceeds the charged pion multiplicity scaled by factor of 0.5 by (16±5)% and (21±7)% at 35 and 44 GeV respectively. The excess can be attributed to isospin violating decays of hadrons. The η multiplicity is found to be 〈nη〈=0.64±0.09±0.06 at 35 GeV. With a significance of three standard deviations a signal from quark bremsstrahlung is observed. The measured charge asymmetry in hadronic final states, due to the interference between initial and final state radiation, ofA=−0.141±0.041 is in accord with QED expectations. An interference effect in the azimuth angle distribution of charged jets around the photon direction is observed for the first time.
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