Production of direct single electrons in proton-nucleus collisions at 13 GeV/c

Direct production of single electrons in proton-nucleus collisions at 13 GeV/c has been measured. A rising $\text{e}\text{π}$ ratio with decreasing p_T above the 10^?4 level is observed for low p_T single electrons. The source of the rising $\text{e}\text{π}$ ratio at low $\text{e}\text{π}$ ratio at low p_T is discussed in connection with the low mass dielectron continuum below the ? mass region.     

Measurement of D0, D+, Ds+ and D*+ production in fixed target 920?GeV proton–nucleus collisions

The inclusive production cross sections of the charmed mesons D⁰,D⁺,D_s ⁺ and D^*+ have been measured in interactions of 920 GeV protons on C, Ti, and W targets with the HERA-B detector at the HERA storage ring. Differential cross sections as a function of transverse momentum and Feynman’s x variable are given for the central rapidity region and for transverse momenta up to p_T=3.5 GeV/c. The atomic mass number dependence and the leading to non-leading particle production asymmetries are presented as well. PACS 13.85.Ni; 24.85.+p; 13.20.Fc     

J/ψ and ψ′ production and their normal nuclear absorption in proton-nucleus collisions at 400?GeV

We report a new measurement of J/ψ, ψ^′ and Drell–Yan cross-sections, in the kinematical domain -0.425<y_cm<0.575 and -0.5<cosθ_CS<0.5, performed at the CERN-SPS using 400 GeV/c incident protons on Be, Al, Cu, Ag, W and Pb targets. The dependence of the charmonia production cross-sections on the size of the target nucleus allows to quantify the so-called normal nuclear absorption. In the framework of the Glauber model, this new measurement is combined with results previously obtained with the same apparatus, under different experimental conditions, and leads to a precise determination of the J/ψ and ψ^′ absorption cross-sections in the surrounding nuclear matter.     

Λ and K0 production in p↑p interactions at 6 GeV/c

Results on K⁰ and Λ production in p↑p interactions at 6 GeV are presented. The data are from an exposure of the Argonne 12 ft bubble chamber to a 60% transversely polarized proton beam. Results include data on Λ and K⁰ inclusive production, and on the reactions p↑p → pΛK⁺(pΣ⁰K⁺). The beam asymmetry parameter for $\text{p}\text{↑}\text{p}\text{→}\text{K}{}^0\text{(}\text{K}{}^0\text{) +}\text{X}$ is determined to be (?0.52 ± 0.12).     

Backward elastic scattering and ϱ− production in π−p collisions at 10 GeV/c

The reactions π^?p → p π^? and π^?p → p?^? (?^? → π^?π⁰) at 10 GeV/c with the proton in the forward direction in the c.m.s. are discussed on the basis of 953 elastic scattering events and 2240 events of the reaction π^?p → pπ^?π⁰. The total backward cross sections are 0.52±0.10 and 1.52±0.28 μb, respectively. In both cases the production mechanism is compatible with the dominance of the baryonic Δ_δ Regge trajectory exchange. The ?^? decay angular distributions are studied in the u-channel helicity frame and the spin density matrix elements are presented as functions of u.     

ΛO production in π−p interactions at 20 GeV/c

Lambda production in 20 GeV/c π^? interactions in hydrogen is studied. The distributions of the Λ^O and pion c.m. production angle, transverse momentum and c.m. longitudinal momentum as functions of the charge multiplicity are discussed. The effective-mass distributions are also studied and it is found that Y^1±(1385) production occurs in 18% of the interactions.     

Backward production of ϱ0 and f0 mesons in π+n interactions at 6 GeV/c

Backward production of ?⁰ and f⁰ mesons in π⁺n interactions at 6 GeV/c is presented. Total and differential cross sections are reported along with spin density matrix elements.     

Incoherent production of pη+η− systems in proton-nucleus collisions at 18.6 GeV

Experimental data on incoherent nuclear production and their theoretical interpretation are reported. We obtain pπ⁺π^?-nucleon total cross sections which are smaller than those obtained from optical model fits in coherent production.     

Hadron production at transverse momenta from 0.5 up to 2.2 GeV/c in proton-proton collisions at 70 GeV

The cross sections for π^±, K^±, p, and $\text{p}$ production in pp collisions have been measured at transverse momenta from 0.48 up to 2.21 GeV/c at 70 GeV. The data are compared with results obtained at lower and higher proton energies and also with the quantum chromodynamics parton model (QPM) calculations. Common behaviour of the cross sections of the form $\text{g(p}{}_{\mathrm{\perp }}\text{)?(x}{}_{\mathrm{\perp }}\text{)}$ in the energy range above 200 GeV does not take place at lower energies. Qualitatively QPM fits the data and the best agreement is for π⁺/π^? and K⁺/π⁺ ratios.     

Inclusive production of Σ±(1385) in pp interactions at 12 and 24 GeV/c

The inclusive production of Σ^±(1385) is studied in pp interactions at 12 and 24 GeV/c. In this energy range, the inclusive cross sections for Σ⁺(1385) and Σ^?(1385) rise from 0.20 ± 0.03 mb to 0.28 ± 0.03 mb and from 0.07 ± 0.02 mb to 0.12 ± 0.02 mb. The decays of Σ^±(1385) account for ～20% of all observed Λ hyperons. The p_T² distributions are compatible with an exponential decrease and the slopes are in agreement with a common value of B ～ 3 (GeV/c)^?2. The longitudinal spectra are significantly different: Σ^?(1385) is mainly produced in the central region, whereas proton fragmentation contributes strongly to Σ⁺(1385) production.     

An inclusive study of π-, K0 and a production from pn reactions at 11.6 GeV/c

Cross sections, multiplicities and particle inclusive spectra are presented for π^-, K⁰ and Λ produced in pn reactions at 11.6 GeV/c beam momentum. The results are compared with the data from pp interactions in the same energy range. Correlations between two π^- are also discussed. The main results are: the π^-, K⁰ and Λ all behave similarly as a function of transverse momentum squared; π^- in the forward c.m. hemisphere have spectra in x and y consistent with that of pp interactions, whereas the spectra of π^- in the backward hemisphere fall off more slowly with ∥x∥ and ∥y∥ than those in the forward hemisphere, suggesting n-fragmentation effects. The K⁰ and Λ have x and y distribution roughly similar to those in pp interactions. The K⁰ and Λ are consistent with a modified form of KNO scaling.     

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.     

Electroproduction of π0 mesons in the resonance region at q2=1.0 (GeV/c)2

Data are presented for the reaction ep → epπ⁰ at a nominal momentum transfer squared of 1.0 (GeV/c)². The data were obtained using an extracted electron beam from NINA and two magnetic spectrometers for coincidence detection of the electron and proton. Differential cross sections have been measured for isobar masses in the range 1.19–1.73 GeV/c².     

D0—⦶D0 mixing: Standard versus non-standard scenarios

D⁰—?D⁰ mixing is estimated in several extensions of the minimal SU(2)_LxU(1) model. In some of these models the theoretical upper bound on this mixing (which is known to be strongly suppressed in the standard model) turns out to be rather large - sometimes even close to the present experimental upper bound.     

Evidence for ψψ production in π− interactions at 150 and 280 GeV/c

From the analysis of multimuon events produced by π^? interactions at 150 and 280 GeV/c in the NA3 spectrometer, we present evidence for the production of two J/ψ mesons in the same interaction (13 events seen, for an expected background of about 0.2 events). Some possible production mechanisms are described and an estimation of the cross section is given.     

Λ production in K−p interactions at 32 GeV/c

Lambda production is studied in K^?p interactions at 32 GeV/c. The total Λ cross section is 2.31±0.03 mb. Using the measured Λγ combinations we find that (31±4)% of all Λ's are produced via the Σ⁰→Λγ decay. About 60% of the Λ's are associated with either a $\text{N}\text{N}\text{or K}\text{K}$ pair; about 40% of the Λ's are produced through the hypercharge annihiltion reaction K^?p→Λ+π'a. The two-peak structure of the invariant x distribution can be related to fragmentation processes. The Λ is found to be unpolarized in the target fragmentation region, whereas a transverse polarization is observed for forward produced Λ's. As a function of p⊥, a polarization effect is measured at medium p⊥.     

Coherent A2− production of nuclei observed in the K−KS0 decay channel at 17.2 GeV/c

We have studied A₂^? production by π^? on a nuclear target in the K^?K_S⁰ decay channel, where the A₂^? is observed above a small background at 17.2 GeV/c incident momentum. Direct confirmation of coherent A₂ (J^P = 2⁺) production has been found.     

Inclusive production in K+d reactions at 4.6 GeV/c

The investigations presented here are based on the data from a K⁺d experiment at 4.6 GeV/c performed with the 2 m bubble chamber at CERN. The topological K⁺d cross sections are determined. The integrated (semi-) inclusive single-particle cross sections for the production of π^?, K⁰ and Λ as well as (semi-)inclusive x- and p_T² distributions are measured and discussed.     

A comparative study of the dissociation of protons into low-mass pπ+π− systems in coherent and incoherent proton-nucleus collisions at 18.6 GeV/c

A decay angular moments analysis has been performed on 8500 pπ⁺π^? events produced by the interaction of high-energy protons with nuclear targets. The analysis was carried out separately for the low-t, coherent events and high-t, incoherent events. The moments of the two samples show significant differences and possible reasons for such differences are discussed.     

Multiparticle production in pTa interactions at 8 GeV/c

pTa interactions have been studied. The total inelastic cross section, multiplicities, net charge distributions and inclusive momentum and rapidity spectra for produced particles are reported. The correlations between fast and slow particles are presented and the reaction mechanisms for multiparticle production in pTa interactions are discussed.