H. Kirk

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.

Inclusive single-particle distributions in π±p reactions at 8 and 16 GeV/c

Abstract Invariant single-particle cross sections for pion and proton production in π ± p interactions at 8 and 16 GeV/ c are presented in terms of integrated distributions as functions of x , reduced rapidity ζ and p ⊥ 2 , and also in terms of double differential cross sections E d 2 σ /(d x d p ⊥ 2 ) and d ζ d p ⊥ 2 ). A comparison of π ± and π − induced reactions is made and the energy dependence is discussed. It is shown that the single-particle structure function cannot be factorized in its dependece on transverse and longitudinal momentum. For the beam-unlike pion, there is an indication for factorizability in terms of rapidity and transverse momentum in a small central region.

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.

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.

Determination of the fire-ball dimensions from second-order interference between two pions

Abstract Positive correlations are observed for pion pairs of equal charge and similar momentum vectors, produced in the reactions π p→p+5 π and π p→p + 7 π at 4 to 25 GeV/ c . The results are consistent with being due to the second-order interference effects expected for pairs of identical bosons and lead to the determination of the average dimension of the “fire-ball’ from which the pions are emitted (〈 R 〉 = 1.0 ± −0.2 +0.4 fm). Attempts are made to study the fire-ball shape by selecting pions pair emitted in various polar and azimuthal directions.

Study of momentum distributions of particles produced in K−p interactions at 10 and 16 GeV/c

The momentum distributions of particles produced in K−p interactions at 10 and 16 GeV/c are studied. In particular the average transverse momentum is presented as a function of the reduced longitudinal momentum for six different secondary particles, namely: π+, π−, K−, K0, p and Λ. The average transverse momentum increases with increasing mass of the particle produced and tends to increase with increasing energy.

Simplicity of “transverse energy” spectra of hadrons

Abstract Using data from a 16 GeV/c π+p bubble chamber experiment, we have studied the production of pions and meson resonances in the central region. Transverse spectra have been analysed in terms of the transverse energy variable Et=√pt2+M2. We find that the Et spectra of “stable” particles, of resonances like ϱ, ω and f, and of corresponding non-resonant two- and three-pion systems all follow one simple exponential in Et over several orders of magnitude in cross section. All spectra are consistent with one common slope parameter of approximately (120 MeV)−1.

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.

Pomeron dominance in a triple-Regge representation of inclusive Δ++ production in K−p and π−p reactions

Data are presented on the reactions K−p → Δ++ + anything at 10 and 16 GeV/c and π−p → Δ++ + anything at 16 GeV/c. In the K−p reaction, scaling is observed between 10 and 16 GeV/c in the variable M2/s. The scaling occurs at relatively low values of M in marked contrast to the reaction π+p → Δ++ + anything. This result can be explained by duality arguments on a triple Regge picture, since the exchanged reggeon-incident particle scattering is exotic. Comparison of the π−p reaction, which is similarly exotic, with the K−p reaction at the same energy gives further evidence for factorization in pomeron-dominated inclusive reactions.

Transverse spectra in π±p and K−p interactions between 8 and 16 GeV/c

Abstract Using data from several bubble chamber experiments, we have studied the inclusive reactions π ± p → π − + X, K − p → K 0 + X and K−p → Λ + X at incident momenta ranging from 8 to 16 GeV/c. Single particle spectra are given as functions of the transverse energy E ⊥ = (p ⊥ 2 + m 2 ) 1 2 for selected intervals of the longitudinal rapidity y. Using these two variables we find a simple, mass independent, representation of all particle spectra. Within a large range of y, non-Lorentz-invariant E⊥ distributions are nearly exponential and, over several orders of magnitude in cross section, can be fitted well with the single-parameter function (eE⊥/T −1)−1. The slope parameter T is shown to depend on y but, in the central region, it appears to be independent of the particle mass and gives indications of approaching a limiting value of approximately 120 MeV. Implications of these results with regard to thermodynamic models are briefly discussed.