Experimental study of proton-emulsion nuclei interactions at high energy

Proton-emulsion nuclei interactions at 200 and 400 GeV have been studied. The results on the energy dependence of <n _s(n _s-1)> and <n _s>/D, multiplicity scaling, multiplicity density scaling in the central region, integral angular distribution, rapidity dispersion and maximum rapidity gap are presented and compared with those of proton-nucleon interactions at the corresponding energies.     

Comment on isospin mixing in nuclei

The central collisions of 70 GeV/c protons with Ag, Br and Pb nuclei have been studied, with the help of BR-2 photoemulsion and emulsion of the same constitution loaded with Pb nuclei. It is shown that the average multiplicity of produced particles (s-particles) increases slowly with increasing the atomic weight of the target nucleus. The ratio of the average multiplicity for these particles to the average charged particle multiplicity for protonproton interactions equals 3.2 forp-Ag, Br and 3.5 forp-Pb. The average multiplicities of particles from nuclear disintegration with energies for protons from 26 up to 400 MeV (g-particles) are 14.2±0.8 forp-Ag, Br and 23.0±1.0 forp-Pb corresponding to the emission of about half of all nucleons from the nucleus at the first rapid stage of interaction. The difference of thes-particle pseudorapidity distributions forp-Ag, Br, Pb andp-p interactions at pseudorapidities larger than 4.2 can be explained by successive interactions of the incident proton with nucleus nucleons.     

Multiplicity of charged particles in 800 GeV p-p interactions

Results are reported concerning the charged-particle multiplicity distribution obtained in an exposure of the high-resolution hydrogen bubble chamber LEBC to a beam of 800 GeV protons at the Fermilab MPS. This is the first time that such data have been available at this energy. The distribution of the number n_ch of charged particles produced in inelastic interactions obeys KNO-scaling. The average multiplicity is 〈n_ch〉 = 10.26±0.15. For n_ch⩾8 the data can be well fitted to a negative binomial. The difference between the overall experimental multiplicity distribution and that resulting from the latter fit is in agreement with the contribution expected from diffractive processes.     

A phenomenological investigation of the shower particle pseudorapidity fluctuations in hadron-nucleus collisions

From the experimental matrix $\text{?(N}{}_{\mathrm{<mtext>g</mtext>}}\text{; n}{}_{\mathrm{<mtext>s</mtext>}}\text{, Δη}{}_{\mathrm{i}}\text{)}$ (the number of events with a given number N_g of particles with velocity 0.3c<v<0.7c, and n_s, the number of shower particles (v > 0.7c) in a pseudo-rapidity interval Δη_i) obtained from the Heidelberg-Igel hadron-nucleus experiment at CERN, we extract the shower particle multiplicity distributions as a function of ν, the number of nucleons that interacted with the projectile. We use a theoretically justified statistical correlation between ν and N_g (recoil protons) and the assumption that the correlation between n_s and N_g is given merely through ν. The data used are for incoming energies 50 and 150 GeV with a proton or pion as the projectile and Cu or Pb as the target. We find that the shower particle multiplicity distributions are of a Poissonian character in each η bin and for each value of ν. The average multiplicities $\text{〈n}{}_{\mathrm{<mtext>s</mtext>}}\text{〉(ν)}\text{Δη}{}_{\mathrm{i}}$ are approximately the same for the two targets and for the different projectile, possibly with a small excess for the pion projectile.The results are compared to a rather general theoretical model of the soft interaction type. The predictions from this model for the shower particle pseudorapidity distributions are very close to the derived values.     

Intranuclear cascading at ultrahigh energy in heavy-ion interactions

Intranuclear cascading mechanism one of the important non-linear effects in high energy nucleusnucleus collisions is investigated. The data on multiplicity (n _s ) and pseudorapidity (η) distributions of shower particles produced by³²S and¹⁶O at 200A GeV,¹⁶O at 60A GeV,²⁸Si at 14.5A GeV and He at ≈140A GeV are presented and compared with the string model VENUS, which takes into account the cascade interactions of secondary particles. The effect of the intranuclear collisions on the distributions of <η> versus <n _s > is discussed for all the beams.     

Topological cross sections in hadron-nucleon and hadron-nucleus collisions at very high energies

We apply our microscopic model for the topological cross section σ_n to produce n charged particles in hadron-proton interactions to hadron-nucleus scattering. The model is based on a stochastic branching process for hadronization. We calculate multiplicity distributions of hadron-nucleus collisions for 50 GeV ? E_L ? 400 GeV based on a multiple collision model. The production of “grey” $\text{(0.3 <}\text{ν}\text{c}\text{< 0.7)}$ particles is considered together with the shower $\text{(}\text{ν}\text{c}\text{> 0.7)}$ particles in order to test the model for higher number of collisions. The joint probability distribution of numbers of shower and grey particles F(n_s, n_g) is calculated. Finally, we critically compare the results to experimental data.     

Energy dependence of multiplicity in proton-nucleus collisions and models of multiparticle production

This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR _em = 〈n _s〉/〈n _ch〉, where 〈n _ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R _em = 1·71 implies an effectiveA-dependence ofR _A =A ^0.18,i.e., a very weak dependence. Predictions ofR _em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production.     

A study of fast neutron production in p20Ne and pp interactions at 300 GeV/c

Data on the multiplicity, momentum and angular spectra of fastp _n1 GeV/c) neutrons produced in inelastic interactions of protons with neon nuclei and protons at 300 GeV/c are presented. The experimental results obtained for p²⁰Ne interactions are compared with predictions of the additive quark model in which the intranuclear cascading of slow particles is taken into account.We thank V. G. Grishin and R. J. Loveless for valuable discussions.     

Projectile stopping in nucleus-nucleus and hadron-nucleus collisions at 4.2 and 10 GeV/c per nucleon

The collisions ofp,²H,⁴He and C with carbon and tantalum nuclei at 4.2 GeV/c per nucleon as well as the collisionsp-C andp-Ta at 10 GeV/c from 2-m propane bubble chamber have been studied. New results on nuclear stopping have been obtained from the examination of proton rapidity distributions and average rapidity of leading protons for collisions of various degree of centrality: our study points out that a proton projectile is fully stopped in the centralp-Ta collisions at 4.2 GeV/c but only partly stopped at 10 Gev/c. The proton multiplicity in the centralp-Ta collisions at 10 GeV/c can be described by the binomial distribution,P(n), which expresses the probability that the projectile meetsn protons among the nucleons being along the diameter of a target nucleus.     

Kaon production in\bar pp interactions at c.m. energies from 200 to 900 GeV

A detailed analysis ofK _s ⁰ production in \(\bar pp\) |<2.5 the average transverse momentum is found to be 0.53±0.07 GeV/c at 200 GeV and 0.62±0.08 GeV/c at 900 GeV, which is an increase with respect to data at c.m. energies below 60 GeV. TheK _s ⁰ production cross sections in inelastic collisions are 29±4 mb at 200 GeV and 63±6 mb at 900 GeV, showing an increase compared to lower energy data. The central kaon density is found to increase as a logarithmic function of energy. At 900 GeV, where statistics are sufficient to allow one to draw conclusions, the average transverse momentum is higher in events with large charged multiplicity than in events with low multiplicity.     

Nuclear effects in 800 GeV proton interactions

We discuss here the nuclear effects in multiparticle production processes in 800 GeV proton-emulsion nuclei interactions. The multiplicity of medium energy particles (N _g ) was used as a measure of the average number of projectile collisions (<v(N _g )>). To study nuclear effects, we determined <v(N _g )> and ratio of normalized rapidity density of all produced charged particles in hadron-nucleus to hadron-hadron interaction,R(N _η ). It was found that the average multiplicity of shower particles increases with <v(N _g )>. From theR(N _η ) distribution, we find; a strong maxima in the target fragmentation region, a plateau in the central region and depletion of particle density in the projectile fragmentation region.     

Fast helium production in interactions of 3.7 A GeV <Superscript>24</Superscript>Mg with emulsion nuclei

We have studied the properties of the relativistic helium fragments emitted from the projectile in the interactions of ²⁴Mg ions accelerated at an energy of 3.7 A GeV with emulsion nuclei. The total, partial nuclear cross-sections and production rates of helium fragmentation channels in relativistic nucleus-nucleus collisions and their dependence on the mass and energy of the incident projectile nucleus are investigated. The yields of multiple helium projectile fragments disrupted from the interactions of ²⁴Mg projectile nuclei with hydrogen H, light CNO and heavy AgBr groups of target emulsion nuclei are discussed and they indicate that the breakup mechanism of the projectile seems to be independent of the target mass. Limiting fragmentation behavior of fast-moving helium fragments is observed in both the projectile and target nuclei. The multiplicity distributions of helium projectile fragments emitted in the interactions of ²⁴Mg projectile nuclei with the different target nuclei of the emulsion are well described by the KNO scaling presentation. The mean multiplicities of the different charged secondary particles, normally defined shower, grey and black ( n_s, n_g and n_b) emitted in the interactions of 3.7 A GeV ²⁴Mg with the different groups of emulsion nuclei at different ranges of projectile fragments are decreasing when the number of He fragments stripped from projectile increases. These values of n_i ( i = s, g, b and h particles) in the events where the emission of fast helium fragments were accompanied by heavy fragments having Z 3 seem to be constant as the He multiplicity increases, and exhibit a behavior independent of the He multiplicity.     

Large transverse momentum particle production in αα and pp collisions at the CERN ISR

The production of charged hadrons with high p_T in αα collisions at √s=126 GeV and pp collisions at √s=31 and 63 GeV is compared, and the structure of the events associated with the high-pT particles is studied. The probability of finding associated particles close to the trigger particle increases strongly between √s=31 and 63 GeV for pp collisions. For p_T>2.5GeV/c the αα/pp cross section ratio at the same energy per nucleon is measured to be 18.7 ± 2.0, to be compared with A² = 16, and a higher associated multiplicity is observed for αα.     

Investigation of quasielastic muon-neutrino scattering on nuclei at <Emphasis Type="Italic">E</Emphasis><Subscript>v</Subscript> < 1 GeV

Quasielastic muon-neutrino scattering on nuclei of propane-Freon mixture at energies in the range E _v < 1 GeV is studied. The multiplicity, momentum, and emission-angle distributions of final protons are measured along with the dependence of the mean values for these distributions on the neutrino energy in the range 0.2 < E _v < 1 GeV.     

Multiple production in pion-nucleus interactions in the additive quark model

An analysis of multiplicity distributions of secondary particles produced in pion-nucleus interactions in the framework of the additive quark model (AQM) is presented. The experimental results on average multiplicities, multiplicity distributions, dispersion and normalized multiplicity etc., at various energies, are satisfactorily reproduced by the predictions of AQM except for the 〈n_s〉, n_g correlation.     

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 semi-statistical model of high-energy collisions

The emission of particles directly created in high-energy collisions is considered to be only partly governed by statistical laws as in Fermi's model. The motion of the created particles is to some degree related to the former motion of the incoming colliding particles. In first approximation this intermediate state is built up of two extremes: two Lorentz systems are introduced from which the particles are emitted isotropically and according to statistical laws. In the centre-of-momentum system (CMS) of the collision these two systems move in the directions of the incoming particles after collision. This approximation corresponds to the two-fireball model which we regard as a representative of a mathematical method of dealing with correlations. In further approximation phase space distributions are replaced by the thermodynamic Fermi or Bose distributions for relativistic particles. Both experimental data such as the nearly constant mean transverse momentum¯p _t and phase space calculations with constant interaction volume show that the temperaturekT reaches an upper limit asymptotically at high energies; the asymptotic region begins at about 30 GeV. The comparison with experimental particle spectra from accelerators in the 10–30GeV region shows good agreement if one uses a smooth dependence ofkT on the collision energyE ₀ and, for each independent set of measurements, an individual choice of \(\bar \gamma _f \) , the mean Lorentz factor of the “fireballs” in the CMS, and of ¯n, the mean number of created particles. The p_t-distribution of pions and the dependence of¯p _t on the particle mass can also be successfully described. At very high energies the model gives production ratios of the various kinds of particles which lie within the range of the experimental determinations. The dependence of \(\bar \gamma _f \) onE ₀ is concluded to be of the form \(\bar \gamma _f \propto E_0^{1/2} /\bar n(E_0 ) \approx 0.5E_0^{1/4} \) , i.e. CMS anisotropy is related to multiplicity.     

Target mass dependence of charged particle multiplicity inp-nucleus interactions

The shower particle multiplicity (〈n _s 〉) in thep-nucleus interactions for different targets, in the incident energy range of ～6–500 GeV has been studied. The variation of multiplicity parameters with target mass (A) or with number of interactions that the incident hadron suffers inside the nucleus (v _A ) and with the changed particle multiplicity inp-p interactions (〈n _ch〉) has been examined in the light of the various models of multiparticle production. The present analysis favours the hydrodynamical model though some other models can not be conclusively ruled out.     

Multiplicity of charged particles π− interactions on nuclei at 40 GeV/c

Multiparticle production in π^?-nucleus interactions at 40 GeV/c (Fifth Joint CERN-Serpukhov Experiment) has been studied using a spark-chamber technique at the Serpukhov accelerator. The mean multiplicities, the pseudorapidity distributions and the dispersion of the multiplicity distributions of charged particles produced on C, Al, Cu and Pb targets are presented. The data have been analysed, both subtracting and including secondary protons with p < 1 GeV/c. In the region of pseudorapidity η > 3.4 the average multiplicity is nearly independent of the size ($\text{ν}$) of the target nucleus, while it increases for η < 3.4. In the forward direction (η > 4) the mean multiplicity on nuclei is smaller than the mean multiplicity on hydrogen. The dependence upon $\text{ν}$ in the target fragmentation region is stronger when the emitted protons are included in the pseudorapidity distributions of the secondary particles. The dispersion of the multiplicity distributions for the different nuclear targets versus the mean multiplicity shows the same slope as found by the world statistics on hydrogen and by other experiments on nuclei at different energies. The results are compared with the predictions of the coherent tube model and with the soft hadron-nucleus collision model.