Neutral charm production in 400 GeV proton-emulsion interactions

A search has been carried out for neutral charm production in 5,108 proton-emulsion interactions at 400 GeV/c. Nine charm candidates have been observed in our fiducial volume which extends from 100 μm-1,000 μm in the forward cone. One of these is a 4-prong and the others are 2-prong events with opening angle>10 mrad and momenta of both decay tracks>150 MeV/c. Search for associated charm decays was made in an extended fiducial volume around the primary stars of these nine candidates. This yielded two neutral 2-prong events, one associated with the 4-prong and the other with a 2-prong candidate. All unassociated candidates are consistent with being backgrounds due toK _s , Λ decays, neutral interactions and γ conversions whereas the background to associated events is negligible. Based on the two associated decays the inclusive cross section forD ^{0, ?0} production is determined as 27±20 μb/nucleon. Detailed measurements on the 4-prong candidate lead to the identification of one decay track as an electron and another as a kaon. This is interpreted as a semi-leptonic, Cabbibo favouredD ⁰/D ^?0 decay.     

Two particle rapidity correlation in proton-emulsion nucleus interactions at 400 GeV

We present a study of two-particle correlations in proton-emulsion nucleus reactions at 400 GeV. In particular the correlations at different nuclear excitations and different rapidity regions are treated. Positive correlations, depending on nuclear excitation, are observed in the rapidity region η<1.5.     

Jet production from nuclei at 400 GeV/c

Results are presented from a calorimeter study on the production of jets in large-E_T proton-nucleus collisions at 400 GeV/c. Jet-like large-p_T events from eight nuclear targets are seen with a special jet trigger. As previously observed, the cross section for such events increases slightly faster than the atomic number, much like in the production of large-p_T single hadrons. Data on energy flows and multiplicities suggest that a heavy nucleus does not significantly widen the angular distribution of the beam remmants. In the central region the particle flow in hard nuclear collisions is similar to that in soft nuclear collisions.     

Prompt neutrino production in 400 GeV proton-copper interactions

A new beam-dump experiment has been performed at the CERN Super Proton Synchrotron using the CHARM neutrino detector. The instrumentation and the statistics have been significantly improved with respect to earlier experiments. For a neutrino energy above 20 GeV the asymmetry of the prompt muon-neutrino and electron-neutrino fluxes \([(v_\mu + \bar v_\mu ) - (v_e + \bar v_e )]/[(v_\mu + \bar v_\mu ) + (v_e + \bar v_e )]\) is found to be 0.20±0.10 (stat.)±0.05 (syst.), and the asymmetry of prompt antineutrino and neutrino fluxes for muonneutrinos \((v_\mu - \bar v_\mu )/(v_\mu + \bar v_\mu )\) is 0.02±0.16 (stat.)±0.02 (syst.) in agreement with our previous results. For the cross-section times branching ratio for charm production and semileptonic decay we obtain a value of \(\sigma \times BR\left[ {D(\bar D) \to v_e (\bar v_e ) X} \right] = 1.9 \pm 0.2 \pm 0.2\mu b\) per nucleon. We find no evidence forv _τ orv _x interactions. The \((v_\tau + \bar v_\tau )\) flux is less than 21% of the total prompt neutrino flux. We derive an improved limit on the branching ratio \(\pi ^0 \to v\bar v\) of 6.5×10^?6, and as a verification of the universality of the neutral weak coupling we find \(g_{v_e \bar v_e } /g_{v_\mu \bar v_\mu } = 1.05_{ - 0.18}^{ + 0.15} \) .     

Hadron production inpBe interactions at 14.6 GeV/c

Invariant cross sections for the production of ^±,K ^±,p, andd inpBe interactions at 14.6 GeV/c are well reproduced by calculations carried out in the framework of the Rossendorf collision model.Communicated by: F. Lenz     

Nuclear effects in multiparticle production in 800 GeV and 400 GeV proton-nucleus interactions

We study nuclear effects in multiparticle production in proton-emulsion nuclei interactions at 800 GeV and 400 GeV. The observed pseudorapidity distributions are compared with the predictions of a simple quark model. The predicted dependence of the ratio of the normalised multiplicity distribution of the produced shower particles in hadron-nucleus (hA) to hadron-hadron (hh) interactions on the mean number of inelastic collisions in the central region is in good agreement with the experimental data.     

Hyperon production in\bar pp interactions at 22.4 GeV/c

In the present paper we investigate the production of charged hyperons and antihy-perons in p interactions at 22.4 GeV/c recorded in the 2m hydrogen bubble chamber Ludmila. After correction for losses due to the kinematics of hyperon decays and for scanning efficiency we have obtained 610 events with charged hyperons or antihyperons. A total cross section of 1.3 _–0.05 ^+0.4 mb for ^±/ has been obtained, and various associated charged particle multiplicity distributions are presented.We would like to express our gratitude to the Ludmila collaboration for the experimental material and continuous interest in this work. Especially we would express our sincere thanks to Professor I. M. Gramenitskii for his critical comments and fruitful discussions.     

Two-particle production inK + p interactions at 32 GeV/c

Results are presented on two-particle inclusive production inK ⁺ p interactions at 32 GeV/c. We study thex _1,2=x ₁+x ₂ dependence of invariant structure functions of (ππ)-pairs and compare them to single particle inclusive distributions in the fragmentation regions. Distributions of particles observed at Feynmanx ₂ in association with various “trigger” particles or systems atx ₁ in the same hemisphere are dicussed in terms of the reduced variable \(\tilde x_2 = x_2 /(1 - |x_1 |)\) . We further present absolute production rates and production ratios of π⁺'s and π^?'s associated with π^±,K _s ⁰ , Λ, \(\bar \Lambda \) ,K ^*+ (890), (K _s ⁰ π⁺), and (π⁺ π^?)-triggers, and compare them with qualitative predictions of the quark recombination model. Forwardbackward correlations between (K _s ⁰ π^±), (K _s ⁰ ,p), (Λ, π^?), \((\bar \Lambda \pi ^ \pm )\) , and (p, π^?) pairs are also discussed.     

Electron production by 4.0 GeV/cπ+p interactions

We have investigated electron production in 4.0 GeV/cπ⁺pinteractions. Limits to direct electron pair production are measured and an example of ?⁰ or ω⁰ decay to e⁺e^? is observed. The ratio of the number of singly produced electrons to the total number of charged pions is less than 6 × 10^-5 (at the 95% confidence level).     

Search for charm production in neutron interactions near 250 GeV/c

We have searched for narrow two-body enhancements produced in the forward direction in n-Be interactions near 250 GeV/c. We find no significant signal in any channel and report upper limits for charm production times branching rate to be 200–1000 nb/nucleon for masses in the range 1.7 ? m ? 3.5 GeV/c².     

Inclusive resonance production in 7.3 GeV/c\bar pp interactions

We present results on inclusive baryon and meson resonance production in \(\bar pp\) interactions at 7.3 GeV/c. Total inclusive and semi-inclusive cross sections are given for Δ(1232),∑ ^*(1385), ?⁰,f andK ^*±(892) production. For the meson resonances separation into annihilation and non-annihilation components has been made, the annihilation component being dominant at this energy. We find that the energy dependence of inclusive cross sections for ?⁰ production inpp interactions and \(\bar pp\) non-annihilations shows a type of scaling behaviour previously reported for ?, ψ, ψ′ and ? production inpp interactions.Δ ⁺⁺, ?⁰ andK ^*± production are studied in terms of Feynmanx,y ^* andp _T ² . For the vector mesons we compare they ^* andx dependences with the predictions of simple quark models.     

Charged pion production in 32GeV/c K + p interactions

Final data on topological cross sections are presented. Inclusive single particle distributions for the reactionsK ⁺ p→ π^± X at 32 GeV/c are discussed and compared with data at lower energies. Early scaling in the fragmentation regions is confirmed, while cross sections in th central region continue to rise with energy even faster than inpp interactions. Thex-andp _T -dependence of the π⁺/π^? ratio inK ⁺ p interactions is discussed and a comparison of reactionsK ⁺ p→ π^± X andK ^? p→ π^± X at 32 GeV/c is made in the context of constituent models. We also present transverse momentum distributions, show prominent seagull effects and study how they are influenced by resonance production.     

400GeV/c pp碰撞自仿射多重分形分析

利用分形来研究高能碰撞多粒子产生机制是新兴的交叉科学,而获取多粒子产生的多重分形谱对了解高能碰撞机制很重要.本文将改进的连续阶数阶乘矩方法应用于40 0GeV/cpp碰撞多重产生的自仿射分析中,首次得到了自仿射多重分形谱.     

ψψ production and limits on beauty meson production from 400 GeV/c protons

From a study of multimuon events obtained in a high luminosity proton-platinum experiment at 400 GeV/c, we find 5 ± 4ψψ events, which correspond to a production cross section σ(ψψ = 27 ± 10 pb. The observed production is compared to the ψψ events previously found in the same apparatus from incoming π^?; a comparison with QCD predictions is performed, giving a good agreement with expectations from gluon-gluon fusion. Finally, using like-sign dimuon, trimuon and quadrimuon events, we give model-dependent upper limits on beauty meson production: 2 nb/nucleon for central models, 20 nb/nucleon for diffractive production.     

Antiproton-neutron interactions at 100 GeV/c

From an exposure of the 30-inch deuterium filled bubble chamber to a 100 GeV/c antiproton-enriched beam at FNAL, we have calculated the topological cross sections for antiproton-neutron interactions with three or more charged particles in the final state. A comparison of our data with pn data at the same momentum allows us to estimate the annihilation contribution to each multiplicity, and hence calculate the average value, and width, of the annihilation multiplicity distribution. Our results are consistent with those from $\text{p}\text{p}$ data at 100 GeV/c, but depart from the trend of lower-energy $\text{p}\text{p}$ data.