Multiplicity distribution at 104 GeV and the two-component models

We present the multiplicity distribution in pp collisions at 10⁴ GeV and compare with it the predictions of the two-component models. It is concluded that the data seem to rule out all those models which predict a dip in the multiplicity distribution at this energy. The data indicate that within the framework of two-component models the average multiplicity of the “diffractive’ component must also grow with energy so as to avoid the appearance of a bimodal multiplicity distribution at 10⁴ GeV.     

Universal multiplicity formula

Thermodynamic reasoning is used to derive a universal multiplicity formula for particle production in high energy collisions. Among the results are the equality of πp, pp and γp multiplicity, the prediction of a slow decrease in deep inelastic multiplicity when Q² increases, and the prediction of an s${}^{\mathrm{<mtext>3</mtext><mtext>8</mtext>}}$ dependence of hadronic multiplicity in e⁺ ? e^? annihilation.     

Multiplicity structure of inclusive diffraction in À+ p andK + p interactions at 250 GeV/c

Results on the multiplicity structure of diffractively excited meson and proton systems in À⁺/K⁺ p interactions at 250 GeV/c are presented for diffractive masses up to about 9 GeV. The energy dependence of the average charge multiplicity and the shape of the multiplicity distribution in terms of KNO-scaling and negative binomial distribution are investigated. The diffractive systems are compared toe ⁺ e ^–,lh and non-diffractivehh final states as suggested by modern approaches of the Pomeron-hadron collision. Systematic differences are found between diffractive meson and proton systems but also between diffraction and the reactions compared to.     

Comparison of K−p Topological Cross Sections at 32 and 33.8 GeV/c with Lower Energy Data

The K⁻p experiments at 32.1 GeV/c and 33.8 GeV/c in the Mirabelle bubble chamber are reviewed and the resulting topological cross sections are compared to lower energy data with beam momenta between 4.2 and 16 GeV/c. Some quantities characterizing the multiplicity distributions are compiled for these data and their energy dependence is compared to results from pp experiments. Studying the scaling behavior of the K⁻p multiplicity distributions, “quasi scaling” is observed for data with p_Lab ≧ 8.25 GeV/c.     

Angular momentum dependence of the giant dipole resonance width in excited nuclei of mass

Gamma ray spectra in the energy range of 4–25 MeV were measured in the reaction ²⁸Si + ¹²⁴Sn at E(²⁸Si) 150 MeV in coincidence with low energy γ-multiplicities. The spectra were analysed using a simulated Monte Carlo CASCADE code. The centroid energy and width of the giant dipole resonance were extracted for various multiplicity windows. The average angular momentum and temperature of the final states populated after the giant dipole photon emission range from 25 and 1.5 MeV to 56 and 1.3 MeV, respectively. The extracted widths are almost constant for the lower multiplicity windows and show an increase of 1.4 MeV at the highest window. The nuclei are expected to be near the liquid drop regime and the experimental results are not inconsistent with the liquid drop behaviour.     

Soft and hard processes in QCD

QCD equations for the generating functions are applied to separate soft and hard jets in e⁺e^? processes of multiparticle production. The dependence of average multiplicities and higher moments of multiplicity distributions of particles created in “newly born” soft subjets on the share of energy devoted to them is calculated in fixed coupling gluodynamics. This dependence is the same as for the total multiplicity up to a constant factor if soft jets are defined as those carrying out a fixed share of initial energy at all energies. The constant factor depends on this share in a nontrivial way. Other definitions are also proposed. The relation between these quantities for soft and hard processes is discussed.     

Classical-equations-of-motion calculations of multiplicities for high-energy collisions of 20Ne+20Ne

Nucleon multiplicity distributions have been obtained as a function of impact parameter b for ²⁰Ne + ²⁰Ne at a laboratory energy of 800 MeV/nucleon with classical-equations-of-motion calculations. The average multiplicity decreases-quite rapidly with b, but there is a quite wide spread of multiplicities for a given b. This indicates, at least for equal-mass, light nuclei, that the multiplicity can only determine the impact parameter with rather poor resolution.     

Multiplicity of charged particles in electron-induced showers developing in oriented silicon and tungsten crystals

A more than twofold increase in the average multiplicity of charged particles in electromagnetic showers initiated by electrons with an energy of 26 GeV in tungsten crystals 2.7, 5.8, and 8.4 mm thick, oriented along the 〈111〉 axis, in comparison with misoriented crystals is shown. For a silicon crystal 20 mm thick, oriented along the 〈110〉 axis, at an electron energy of 28 GeV, the average multiplicity of charged particles increases by a factor of ～1.6. The widths of the orientation dependences of the average multiplicity of charged particles in electron-induced showers in silicon and tungsten crystals are proportional to the crystal thickness and depend on the electron energy as E ^?1/2.     

Multiplicities in electroproduction and e+e− annihilation

It is shown how more sophisticated versions of the parton model can replace the naive expectation of final state hadrons being produced in ep or e⁺e^? collisions in two jets of finite multiplicity, well-separated in rapidity, with a picture that permits the rapidity gap to be filled in and allows the multiplicity to rise with energy, even up to the limit imposed by energy conservation. Large multiplicity is shown to imply a rather slow approach to scaling and a significant tail in the transverse momentum distribution.     

Multiplicity distributions in e+e− annihilations at petra energies

Measurements of the charged multiplicities for hadron production in e⁺e^? annihilation in the center of mass energy range 9–32 GeV have been made. The average charged multiplicity has an energy dependence much stronger than ln s and similar to that reported for pp collisions. Quantitative differences are observed in the magnitude of both the average multiplicity 〈n_ch〉 and the dispersion D_ch for e⁺e^? and pp interactions at the same center of mass energy. 〈n_ch〉 and the ratio 〈n_ch/D_ch in e⁺e^? annihilations are significantly larger than in pp collisions and are found to be in overall agreement with QCD predictions. KNO scaling is seen to be satisfied.     

Charged multiplicities in K−p interactions at 100 GeV/c

The charged multiplicity distribution is presented for K^?p interactions produced in the hydrogen bubble chamber, BEBC, using an r.f. separated, tagged K^? beam of 110 GeV/c momentum. A comparison with K⁺p, πp and pp data at lower energies shows that the main features of the multiplicity distributions depend on energy and charge of the incident particles, but not on their strangeness. At high energies, only the energy is important.     

Indication of an onset of hard-like effects in K+p, π+p and pp collisions at 250 GeV/c: EHS/NA22 Collaboration Aachen-Antwerp/Brussel-Berlin (Zeuthen)-Helsinki-Cracow-Moscow-Nijmegen-Rio de Janeiro- Serpukhov-Warsaw-Yerevan

Similarly as in lepton-hadron scattering, but less pronounced than in e⁺e⁻ annihilation at comparable energies, we observe a rise of the “sea-gull” wings with CMS energy. The large average transverse momenta around Feynman |x_F|=0.4 are mainly due to high multiplicity events, for which also a tail develops in the multiplicity distribution. Neither of these effects can be reproduced by currently used low-p_T fragmentation models.     

Rapidity correlations in π+ p,K + p andpp interactions at 250 GeV/c

Two- and three-particle rapidity correlations are analyzed inK ⁺ p and π⁺ p-interactions at 250 GeV/c. The main contribution to the two- and three-particle correlation functions comes from mixing of events of different multiplicity. The (short range) two-particle correlation remaining after exclusion of mixing is significantly larger for (+?) than for the equal charge combinations, and is positive for a wider range in rapidity difference. FRITIOF and a 2-string DPM are excluded by our data. A quark-gluon (multi-)string model can describe our inclusive correlation function, but needs to be tuned on the short range part. The multiplicity mixing part increases much faster with increasing energy than the short range part. In the central region, our correlation is similar to that observed ine ⁺ e ^? and μp collisions at similar energy.     

First results from the hybrid emulsion experiment on16O-nucleus collisions at 200 GeV/N

First data from the HELIOS hybrid experiment are presented. The set-up and experimental procedure are described, and a study of medium multiplicity events and of high transverse energy, high multiplicity events is reported. A study of unbiased samples of¹⁶O-emulsion interactions, showing in particular the importance of electromagnetic dissociation of the projectile, is presented.     

Investigation of the 208Pb(18O, f) fission reaction: Mass-energy distributions of fission fragments and their correlation with the gamma-ray multiplicity

The mass-energy distributions of fragments originating from the fission of the compound nucleus ²²⁶Th and their correlations with the multiplicity of gamma rays emitted from these fragments are measured and analyzed in ¹⁸O + ²⁰⁸Pb interaction induced by projectile oxygen ions of energy in the range E _lab = 78–198.5 MeV. Manifestations of an asymmetric fission mode, which is damped exponentially with increasing E _lab, are demonstrated. Theoretical calculations of fission valleys reveal that only two independent valleys, symmetric and asymmetric, exist in the vicinity of the scission point. The dependence of the multiplicity of gamma rays emitted from both fission fragments on their mass, M_γ(M), has a complicated structure and is highly sensitive to shell effects in both primary and final fragments. A two-component analysis of the dependence M_γ(M) shows that the asymmetric mode survives in fission only at low partial-wave orbital angular momenta of compound nuclei. It is found that, for all E _lab, the gamma-ray multiplicity M_γ as a function of the total kinetic energy (TKE) of fragments, M_γ(TKE), decreases linearly with increasing TKE. An analysis of the energy balance in the fission process at the laboratory energy of E _lab = 78 MeV revealed the region of cold fission of fragments whose total kinetic energy is TKE ～Q _max.     

Heavy flavour multiplicities at very high energies

We calculate the total multiplicity of heavy flavours in e⁺e^? annihilation at very high energies in the framework of QCD. The problem is dominated by the soft limit of the perturbative expansion and we develop suitable techniques to resum to all orders the leading double logarithmic terms. The results indicate at very high energy a growth of multiplicity faster than any power of log. We find an interesting asymptotic factorization of energy dependence and flavour mass dependence of multiplicities.     

Hadron multiplicities

We review results on hadron multiplicities in high-energy particle collisions. Both theory and experiment are discussed. The general procedures used to describe particle multiplicity in quantum chromodynamics (QCD) are summarized. The QCD equations for the generating functions of the multiplicity distributions are presented both for fixed and running coupling strengths. The mean multiplicities of gluon and quark jets, their ratio, higher moments, and the slopes of multiplicities as a function of energy scale, are among the main global features of multiplicity for which QCD results exist. Recent data from high energy e⁺e⁻ experiments, including results for separated quark and gluon jets, allow rather direct tests of these results. The theoretical predictions are generally quite successful when confronted with data. Jet and subjet multiplicities are described. Multiplicity in limited regions of phase space is discussed in the context of intermittency and fractality. The problem of singularities in the generating functions is formulated. Some special features of average multiplicities in heavy quark jets are described.     

Quark model and π+p-pp multiplicity difference

Hadron interactions at high energy are sensitive to the space-time structure of the parton model. Based on this structure we propose a model of particle production in which collective collisions among the constituents can take place. We show that the π⁺p-pp multiplicity difference and the asymmetry in π⁺p collisions should decrease with rising energy.     

Semi-inclusive π− cross sections in pp interactions up to 300 GeV/c

Semi-inclusive π^? cross sections in 200 and 300 GeV/c pp interactions are presented and compared with lower energy data. In the target fragmentation region the data are compared to the hypothesis of semi-inclusive KNO scaling. The energy and charge multiplicity dependences of the semi-inclusive cross sections in the central region are studied and a simple parametrization of the semi-inclusive density function is described.     

Yrast feeding and multiplicity of gamma transitions in the reaction 124Sn(28Si, 5n) 147Gd at 139, 146 and 152 MeV

The population of high-spin yrast and near yrast states of ¹³⁴⁷Gd and the associated multiplicity of feeding transitions have been studied in the ¹²⁴Sn (²⁸Si, 5n) reaction at 139, 146 and 152 MeV. The yrast feeding is found to be independent of the initial angular momentum distribution and very weak for states of spin greater than 30 ħ. The average multiplicity of γ-transitions is found to increase with increasing beam energy. The experimental results are interpreted in terms of collective excitations within rotational bands that channel the γ- decay towards the known oblate single-particle yrast states below ~30 ħ.