Rapidity dependence of multiplicity distributions in proton-nucleus collisions at 360 GeV/c

Multiplicity distributions in various rapidity intervals for charged particles produced in collisions of 360 GeV/c protons with aluminium (Al) and gold (Au) targets are presented. The data were analysed separately for the forward and backward hemispheres. Each distribution is well described by a negative binomial distribution. The experimental distributions are compared with the predictions of the multichain model calculated by the Monte Carlo program MCMHA in which the intranuclear cascade process is included, and also with the Lund Monte Carlo FRITIOF. The results of MCMHA reproduce quite well the multiplicity distributions for various rapidity intervals.     

Negative binomials and multiplicity distributions in 250 GeV/cK + and π+ interactions on Al and Au nuclei

The negative binomial distribution (NBD) is fitted to all charged and to negative particle multiplicity distributions in restricted rapidity intervals, both in the forward and backward c.m. hemispheres of positive meson interactions on Al and Au nuclei. For negative particle multiplicity distributions, the NBD parameters are also determined as a function ofn _g, the number of grey tracks, corresponding to varying number of intranuclear collisions. The data are interpreted in terms of the clan picture of Giovannini and Van Hove and compared to the MCMHA and Fritiof models. Both models reproduce quite well the global multiplicity distributions, but not when sub-samples are considered with fixed number of grey tracks. Regularities are better visible on the parton than on the particle level.     

Charged-particle multiplicity distributions in different rapidity windows in 800 GeV proton-nucleus interactions

Multiplicity distributions of charged particles produced in interactions of 800 GeV protons with emulsion nuclei in various rapidity windows are presented. The data is also analyzed separately for the forward and the backward hemispheres, for rapidity windows of different widths. It is found that the Negative Binomial Distribution (NBD) describes well the multiplicity distribution of secondary particles in various rapidity windows and also in both the hemispheres. We have compared the NBD parameters, in both the hemispheres, at 200 GeV and 360 GeV, with those at 800 GeV. The behaviour of NBD parameters in rapidity windows of different widths and for different targets has also been studied. Received: 30 August 2001 / Accepted: 28 January 2002     

Negative binomial distributions and clan model in proton-nucleus interactions

Experimental results on multiplicity distributions in different pseudorapidity intervals of charged shower particles produced in proton-AgBr and proton-CNO collisions at 800 GeV are presented. The different distributions are described well by the negative binomial form. We successfully interpret our results in terms of the clan model. The values of the rapidity gap probability in terms of average number of clans in different pseudorapidity intervals are also determined.     

Experimental properties of gluon and quark jets from a point source

Gluon jets are identified in hadronic Z decays as all the particles in a hemisphere opposite to a hemisphere containing two tagged quark jets. Gluon jets defined in this manner are equivalent to gluon jets produced from a color singlet point source and thus correspond to the definition employed for most theoretical calculations. In a separate stage of the analysis, we select quark jets in a manner to correspond to calculations, as the particles in hemispheres of flavor tagged light quark (uds) events. We present the distributions of rapidity, scaled energy, the logarithm of the momentum, and transverse momentum with respect to the jet axes, for charged particles in these gluon and quark jets. We also examine the charged particle multiplicity distributions of the jets in restricted intervals of rapidity. For soft particles at large , we observe the charged particle multiplicity ratio of gluon to quark jets to be , in agreement with the prediction that this ratio should approximately equal the ratio of QCD color factors, . The intervals used to define soft particles and large for this result, GeV/ and GeV/, are motivated by the predictions of the Herwig Monte Carlo multihadronic event generator. Additionally, our gluon jet data allow a sensitive test of the phenomenon of non-leading QCD terms known as color reconnection. We test the model of color reconnection implemented in the Ariadne Monte Carlo multihadronic event generator and find it to be disfavored by our data. Received: 24 February 1999 / Published online: 8 September 1999     

Hadron production ine +e− annihilation and μ-p collisions under the assumption of longitudinal phase space dominance

Rapidity and multiplicity distributions are calculated for the hadrons produced ine ⁺e^? annihilation and deep inelastic muon-proton collisions for c.m. energies of 10 to 40 GeV. The hypothesis of longitudinal phase space dominance leads to a probability distribution which is identical to that of a grand canonical ensemble of non-interacting particles. We successfully describe experimental rapidity distributions, domains of Feynman-x scaling and scaling violations and the rapidity dependence of the mean transverse momentum. Multiplicity distributions are derived to be close to negative binomial distributions even for finite rapidity intervals. The plateau in the rapidity distribution is the origin for the negative binomial distribution in multiplicity. The mean number of hadrons of each species and the mean overall transverse momentum are the main input parameters in our calculation and are taken from experiment.     

Independent <Emphasis Type="Italic">π</Emphasis><Superscript>−</Superscript>-meson production in <Emphasis Type="Italic">pp</Emphasis> interactions

It is shown that experimental data on the multiparticle production of negatively charged pions in proton-proton interactions at \(\sqrt s \leqslant 30 GeV\) do not involve significant indications of the existence of anycorrela tions between negatively charged pions, apart from those that are associated with momentum conservation and with interference. The multiplicity distributions in rapidity intervals, forward-backward correlations, and two-particle rapidity and transverse-momentum correlations do not contradict the independent production of negatively charged pions. No constraints on the multiplicity distributions of product particles follow from their independent production.     

Negative binomial multiplicity distributions for proton-nucleus collisions from a string model

Multiplicity distributions of charged particles produced in collisions of ultrarelativistic protons with nuclei are studied in a string model. Recently measured multiplicity distributions in proton-nucleus reactions display a negative binomial shape. The string model VENUS reproduces the data well. We trace back within the model the origin of the negative binomial form of the multiplicity distributions. We find that the final multiplicity distribution can be expressed as a continuous superposition of Poisson distributions with different mean multiplicities ∫dNW(N)P(N, n). The Poisson distribution represents the string fragmentation, whereas the weight factorW(N) reflects the string mass distribution. This quantity has contributions due to both the nuclear structure and the parton structure of nucleons. We show thatW(N) is very well approximated by a gamma-distribution . This leads to a negative binomial distribution \(\mathcal{N}(k,\bar N;n)\) with the same parameters as for . It is shown that the fluctuations in the multiplicity are dominated by the string fragmentation fluctuations for small rapidity intervals and by string mass and number fluctuations for large rapidity windows.     

Charged particle multiplicity distributions for fixed number of jets inZ0 hadronic decays

The multiplicity distributions of charged particles in full phase space and in restricted rapidity intervals for events with a fixed number of jets measured by the DELPHI detector are presented. The data are well reproduced by the Lund Parton Shower model and can also be well described by fitted negative binomial distributions. The properties of these distributions in terms of the clan model are discussed. In symmetric 3-jet events the candidate gluon jet is found not to be significantly different in average multiplicity than the mean of the other two jets, thus supporting previous results of the HRS and OPAL experiments. Similar results hold for events generated according to the LUND PS and to the HERWIG models, when the jets are defined by the JADE jet finding algorithm. The method seems to be insensitive for measuring the color charge ratio between gluons and quarks.     

Charged particle multiplicity distributions in restricted rapidity intervals inZ0 hadronic decays

The multiplicity distributions of charged particles in restricted rapidity intervals inZ ⁰ hadronic decays measured by the DELPHI detector are presented. The data reveal a shoulder structure, best visible for intervals of intermediate size, i.e. for rapidity limits around ±1.5. The whole set of distributions including the shoulder structure is reproduced by the Lund Parton Shower model. The structure is found to be due to important contributions from 3-and 4-jet events with a hard gluon jet. A different model, based on the concept of independently produced groups of particles, clans, fluctuating both in number per event and particle content per clan, has also been used to analyse the present data. The results show that for each interval of rapidity the average number of clans per event is approximately the same as at lower energies.This paper is dedicated to the memory of Léon Van Hove     

Fluctuations of multiplicities in rapidity windows in sulphur-sulphur collisions at 200A GeV

Multiplicity distributions and their second moments fornegatively charged particles produced in³²S-S central and minimum bias interactions at 200A GeV are studied in various rapidity intervals. Fritiof and Venus models mostly describe the dependence of second moments on rapidity intervals in minimum bias interactions, but not in central collisions. For central collisions the behaviour of second moments might indicate enhanced multiplicity fluctuations.     

Phase space dependence of the multiplicity distribution in π+ andpp collisions at 250 GeV/c

The charged particle multiplicity distribution has been studied for non-single-diffractive π⁺ p andpp collisions at \(\sqrt s = 22\) GeV, for full phase space as well as for intervals in rapidity, azimuthal angle and transverse momentum. In general, the multiplicity distribution is well described by a negative binomial. From comparison of the distribution for negative or positive particles to that of all charged particles, cascading is favoured as an interpretation over stimulated emission. Interesting consequences follow from a comparison of our results to those at collider energies and toe ⁺ e ^? data at comparable energy. Furthermore, evidence is given that the multiplicity distribution is not exactly of negative binomial type in every (connected or disconnected) phase space region.     

Structures and angular distributions of slow and relativistic charged particles produced in 7Li-emulsion interactions at 3 GeV/c per projectile nucleon

Experimental results on the multiplicity distributions of various particles produced in the interactions of ⁷Li with emulsion nuclei at a momentum of 3 GeV/c per projectile nucleon are reported. A comparison with data on collisions induced by other nuclei at a nearly identical momentum per nucleon is presented in order to reveal the dependence on the projectile mass. The internal structure of ⁷Li is explored by studying the projectile fragment. The mean multiplicity of shower particles, 〈n _s〉, induced by ⁷Li is found to be less than that in the case of ⁶Li projectiles. The angular distributions of target fragments and relativistic charged secondaries are investigated. No shock-wave phenomena are observed. Forward-to-backward ratios are calculated for each case. The probability distributions for relativistic secondaries produced per unit rapidity are studied in detail, along with the rapidity densities and their dependence on the projectile and the target mass. A comparison of the angular spectra of shower particles produced in central and peripheral collisions supports the limiting-fragmentation hypothesis. The collisions in question seem to become more central with increasing shower-particle multiplicity.     

A combined model for pseudorapidity distributions in p-p collisions at center-of-mass energies from 23.6 to 7000 GeV

In p-p collisions, the charged particles produced consist of two leading particles and those frozen out from the hot and dense matter created in the collisions. The two leading particles are in the projectile and target fragmentation regions, respectively, which, in this paper, are conventionally supposed to have Gaussian rapidity distributions. The hot and dense matter is assumed to expand according to unified hydrodynamics, a hydrodynamic model which unifies the features of the Landau and Hwa-Bjorken models, and freeze out into charged particles from a space-like hypersurface with a fixed proper time of τFO. The rapidity distribution of these charged particles can be derived analytically. The combined contribution from both leading particles and unified hydrodynamics is then compared against experimental data from a now available center-of-mass energy region from 23.6 to 7000 GeV. The model predictions are consistent with experimental measurements.     

Hadron Multiplicity Distributions and the Related Parameters in e+e－ Annihilation at Z0 Energy Region

The adaptability of charged hadron multiplicity distributions fitted with negative binomial and its related parameters,forward-backward multiplicity correlation,parameters of clan model,semi-inclusive rapidity distribution and the seagull plots describing the characteristics of transverse momenta of jets are discussed. In particular,the above mentioned parameters in restricted rapidity intervals are analysed and comparde with theoretical results of some phenomenological models of multiparticle production. Most of the results are obtained from 50000 Z⁰ events of ALEPH Collaboration at LEP.     

Correlations associated with particles produced at small angles in pp collisions at the CERN ISR

Data on correlations between momentum analysed protons, pions or K mesons, and charged particles produced in pp collisions at the CERN ISR are presented. The charged particles were detected in a ～4π scintillation counter hodoscope. The pseudo-rapidity distributions are well described by production within the limits of cylindrical phase space, with negative kaons and antiprotons yielding narrower distributions than protons, pions and positive kaons. The azimuthal distributions show symmetry around the t-channel axis in the rest frame of the recoiling mass M_x in pp → aX (a = detected proton, pion, positive kaon).     

Multiplicity and pseudorapidity distributions of charged particles from32S induced heavy ion interactions at 200A GeV

Multiplicity and pseudorapidity distributions have been measured for³²S+Al, Cu, Ag and Au at 200A GeV. The widths of the pseudorapidity distributions increase from central to peripheral collisions. The main contribution is assumed to come from the increasing fraction of charged particles stemming from the fragmentation of the target for peripheral collisions as compared to central collisions. On the average 170–180 charged particles per unit of pseudorapidity are attained for the most central³²S+Au events at the maximum of the distribution. The target dependence of the yield of charged particles for central collisions is investigated. In the target rapidity region the yield is directly proportional to the target mass. The transverse energy per charged particle has been studied as a function of centrality and pseudorapidity. The experimental results are compared to the results from the Monte-Carlo model VENUS 3.11 which includes rescattering among secondaries. A comparison between different centrality triggers is made.     

几率分布指数律与间歇现象

本文举例指出,落入快度区间的概率本身具有某种分布,并不一定能导致阶乘矩随区间长度变化的指数律,因此,不是导致Intermittency行为的充分条件.