H. Saarikko

ϱ0 and f production in π+p interactions

Abstract Inclusive ϱ 0 and f(1270) production are analysed in π + p collisions at 8, 16 and 23 GeV/ c . The ϱ 0 cross section increases with energy such that the ϱ 0 /π − ratio remains constant. Emphasis is laid on cross sections as a function of the transverse momentum and of the Feynman x variable. The ϱ 0 s can be attributed to two sources: some ϱ 0 s are centrally produced, but there is a pronounced forward peak. The distribution of leptons coming from ϱ 0 decay is discussed.

Production of ρ0 and f in π−p interactions at 16 GeV/c and separation into fragmentation and central components

The production of ρ0(770) and f(1270) is studied in π−p interactions at 16 GeV/c. By comparison with inclusive K∗0 production in the reaction K−p → K∗0 + anything, and with inclusive ρ0 production in the reaction pp → ρ0 + anything, it is found that the data can be interpreted in terms of two production processes: the central production of resonances and the fragmentation of the beam particle. For the π−p reaction, the inclusive ρ0 beam fragmentation cross section is 3.1 ± 0.3 mb while that for central production is 1.6 ± 0.5 mb. The ρ0 central production cross section is consistent with increasing with energy as ln s behaviour. The ratio of ρ0 to π− inclusive cross sections (excluding the leading π−) is ∼0.2, independent of energy. The ρ0 to π− ratio increases as a function of pT to a constant value of ∼12 above 1 GeV/c. The ρ (charged and neutral) and f decays account for (25 ± 4)% and (1.4 ± 0.3)%, respectively, of all pions produced.

Vector and tensor meson production in K−p interactions at 32 GeV/c

Inclusive production of vector and tensor mesons is studied in a K−p experiment at 32 GeV/c in the MIRABELLE bubble chamber. The K∗0(890), ϱ0 and ω cross sections are comparable, about 4 mb each. The K∗0(1420 and cross sections are also comparable, about 1 mb each. The K∗o+(890), Φ, K∗o−(1420) and f cross sections beam fragmentation; ϱ production is almost forward-backward symmetric in the c.m.s. The pT production slopes of K∗o−(890) and ϱ are similar, the Φ slope is shallower. Vector and tensor mesons alone are responsible for ≅50% (≅60%) of final-state pions

A study of direct and indirect pion production in π+p interactions at 16 GeV/c

Abstract The sources of negative pions are analysed in π+p interactions at 16 GeV/c. It is shown that the kinematics of resonance decay is crucial in determining the pions′ longitudinal and transverse momentum spectra. The identifiable meson resonances, of which η, ω, ϱ0 and f are the dominant ones, account for about 50% of all π−s produced. The “direct” pions, i.e. those that are primary products of the π+p interactions, appear to constitute 10 to 30% of the total π− yield.

Inclusive production of K̄∗(890) and K̄∗(1420) in K̄−p interactions at 10 and 16 GeV/c

Abstract The inclusive production of K∗(890) and K∗(1420) is studied in K−p interactions at 10 and 16 GeV/c. At 10 GeV/c an enhancement in the ( K 0 π − ) mass distribution is found at 1.74 GeV, but no clear signal is seen at 16 GeV/c. The fraction of K 0 s coming from decay of the K ∗ (890) or K ∗ (1420) is large, being (50 ± 6)% and (45 ± 5)% at 10 and 16 GeV/c, respectively. The inclusive cross sections for K∗−(890) and K ∗0 (890) production are almost constant with energy from 8 to 32 GeV/c with values of 3.5 and 3.3 mb, respectively. The K ∗ (890) production cross section is studied as a function of transverse and longitudinal variables and found to derive mainly from fragmentation of the incident K− meson. The spectra of K 0 s resulting from the decay of K ∗ (890) are studied.

Inclusive K∗±(892) production in pp and π+p interactions

A study is presented of the inclusive production cross sections of K∗±(892) vector mesons in pp interactions at 12 and 24 GeV/c and in π+p interactions at 16 GeV/c. The K∗± inclusive cross section is ∼0.9 mb for both pp at 24 GeV/c and π+p interactions at 16 GeV/c. For pp interactions, σ(K∗+) and σ(K∗−) are seen to rise with energy, showing a threshold behaviour. In both pp and π+p interactions, σ(K∗+) largely exceeds σ(K∗−) at these energies and this excess is interpreted as K∗+ production by beam and target fragmentations. The decays of K∗±0 yield ∼30% of the K0 observed in the final states. The pT2 dependence of both K∗+ and K∗− cross sections is described by an exponential with slope of ∼3.3 (GeV/c)−2. The longitudinal momentum spectra for K∗+ in 16 GeV/c π+p and 24 GeV/c pp interactions are similar in shape in the target hemisphere. The K∗− spectra are similar over the whole kinematic region when viewed in the quark c.m.s. and point to a central production mechanism. Comparing K∗+ and ρ0 production, striking similarities are found.

Observation of scaling deviations in the energy distribution of secondary hadrons in inelastic neutrino-proton interactions

Abstract An analysis is presented of the z distributions of secondary hadrons produced in 5600 charged current events from a BEBC neutrino-hydrogen experiment. Evidence is presented for scaling deviations in the z distributions and a breakdown of factorization in the single particle inclusive cross sections. The results are consistent with the leading order QCD predictions on the q 2 dependence of nonsinglet moments of quark fragmentation functions, yielding a value of Λ ≈ 0.6 GeV.

Eta and omega meson production in medium energy π+-p and K−p interactions

The production of η(550) and ω(780) mesons is studied in π±p interactions at 16 GeV/c and K−p interactions at 10 and 16 GeV/c. Cross sections for exclusive channels are presented, and for the π+p data differential cross sections are given for quasi-inclusive production where the η or ω is required to be accompanied by charged particles only. Close similarities are observed between η, ω and also ϱ0(770) production in terms of longitudinal and transverse variables. By a rough estimate, the η, ω and ϱ0 inclusive yields are found to be in the ratio 0.32 : 0.85 : 1, respectively, for 16 GeV/c π+p collisions. For non-peripheral production we estimate this same ratio to be 0.34 : 0.9 : 1.

Production of charmed mesons in neutrino interactions in hydrogen

Abstract Production of charmed mesons has been observed in neutrino-hydrogen interactions in 285 000 photographs of BEBC exposed to the CERN wide-band neutrino beam. In ∼ 6000 charged current events, two events have been found each giving a three-constraint kinematical fit with production of only one strange particle, namely a K−, which is identified by its characteristic reaction K−p→Σ−π+. These events are thus examples of ΔS=−ΔQ reactions corresponding to charm production on a valence quark. For both events the effective mass of a (K− + pions) system is equal to the D0(1863) mass while the effective mass of this system plus a π+ is equal to the D∗+(2009) mass. The mass difference ΔM=M( D ∗+ )−M D 0 is 145.2 ± 0.6 MeV. The first event is interpreted as ν p →μ − pD ∗+ and the second as ν p →μ − pD ∗+ π + π − , both with D ∗+ → D 0 π + . The rate of inclusive D∗+ production has been estimated for all events by assuming that each negative track in turn is a K− and using the fact that the error on ΔM is small. It is found that the cross section σ(ν p →μ − D ∗+ + anything ) relative to σ(νp→μ− + anything), above the D∗ threshold, is (4.1 ± 2.4)%.

Approach to scaling in proton fragmentation studied in the reactions K+p → π±X and K−p → π±X

Abstract Data are presented on inclusive single particle distributions in the proton fragmentation region for the reactions K + p → π ± X at 8.2 and 16 GeV/ c and K − p → π ± X at 10 and 16 GeV/ c . The energy dependence is studied and compared with the dual Regge model predictions for approach to scaling. None of the existing models is in full agreement with the data. The model of Chan and his collaborators is consistent with our results under the additional assumption of equality of vector and meson coupling constants in the p π + vertex in the Mueller diagram.