T. Besliu

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.

Observation of t-channel helicity conservation in diffractive reactions producing A1 and Q-mesons

Abstract It is shown that helicity is conserved in the t-channel for A 1 and Q-meson production by pions of 8 and 16 GeV/ c and kaons of 10 GeV/ c , respectively. This is in contrast to evidence for s-channel helicity conservation reported for elastic scattering and rho photoproduction. This difference in behaviour of diffractive processes may be due to the fact that there is a change in spin in the former reactions but not in the latter, or, alternatively, to different mechanisms operating in the two cases.

Study of lambda production in 10 GeV/c K−p interactions

Lambda production is studied in K−p interactions at 10.1 GeV/c, where the dominant reaction is K−p → Λ + pions. General characteristics such as the distributions of the double differential cross section in the lab system, of the variable x = pL∗pmax∗, of p⊥2 and of the missing mass to the lambda are presented. Total cross sections for Λ production and for the various channels are given. Differential cross sections dσdt, dσdt′ and dσdu′ are presented. Forward and backward peaks are observed in the dσdt′ and dσdu′ distributions, respectively. It is found that the exponential slope of these distributions decreases with increasing missing mass to the lambda and, for dσdt′, also for increasing multiplicity in the final state. The polarization of the lambdas is studied as a function of multiplicity, pL∗, (Λπ±) effective mass, t′ and u′. The forward lambdas show

Dominance of isospin zero exchange in π±p → π(Nπ) at 16 GeV/c and production by it of a low mass (Nπ) enhancement

An isospin analysis has been made of the production of (Nπ) states in the reactions π±p → π(Nπ) at 16 GeV/c. The three independent amplitudes and their three interference terms have been determined as functions of the (Nπ) mass. It is found that at 16 GeV/c isospin-zero exchange is the dominant process, and isospin-one occurs much less frequently, mostly producing the I = 32 Δ (1236) isobar. Interference effects do not seem very important. The I = 12 (Nπ) mass spectrum due to isospin-zero exchange presents a broad enhancement from 1.1 to 1.8 GeV, with a broad maximum between 1250 and 1500 MeV. The N* isobars found by phase shift analyses at 1470, 1520, 1690, etc. MeV cannot account for the whole enhancement observed and in particular for its low-mass part. These results are consistent with the interpretation that diffractive phenomena are important at low Nπ masses and may cause mass enahancements not revealed byphase-shift analyses.

(pπ+π−) mass enhancements in the interactions of 8 Gev/c π+, 16 GeV/c π+, 16 GeV/c π−and 10 GeV/c K− with hydrogen

Abstract Two enhancements are observed in the (pπ+π−) mass spectrum at about 1460 MeV and about 1710 MeV in the reactions π−p→(pπ+π−)at 16 GeV/c, π+p→ (pπ+π−) π+at 8 and 16 GeV/c and K−p → (pπ+π−)K−at 10 GeV/c, with production cross sections of approximately 30 μb. Mass and width values closely agree for all these reactions. Fits to the combined distributions give M0 = 1462 ± 10 MeV and M0 = 1711 ± 10 MeV, with widths of 60 ± 20 MeV, respectively. Neither enhancement is seen in charge exchange reactions. Their production cross section is almost constant, varying with the incident momentum as σ = pLab−0.2. The differential cross section is exponential at small t-values, dσ/dt ∞ e−Qt, with Q about 15 GeV−2and about 6 GeV−2 for the first and the second enhancement, respectively. Both enhancements are interpreted as produced by a diffraction process. Evidence for the decay mode Δ++(1236)π for the 1460 MeV enhancement is presented, and the possible existence of both Δ++(1236)π and N ∗0 (1460)π decay modes for the 1710 MeV enhancement is discussed. These results are compared with previous bubble chamber data and with the results of both phase-shift analyses of formation experiments and missing mass spectra of counter experiments. It is suggested that the diffraction enhancements at 1460 and 1710 MeV found in these production experiments may be different from the isobars found by phase shift analyses of formation experiments. It is pointed out that the effects observed in the (pππ) final state are only one of the contributions deriving from the different final states globally observed in the MM spectra of electronic experiments.

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.

Limiting properties in inclusive π+p reactions at 8 and 16 GeV/c with exotic and non-exotic particle combinations

Abstract The distributions in the Feynman variable x for the pions produced in the inclusive reactions (1) π+p → π− + anything and (2) π+p → π+ + anything are compared at 8 and 16 GeV/c. The distributions are similar in first approximation, but second order differences are observed. In particular, at x ≈ 0 the distributionsfor π+ overlap at the two energies for π− they are different, and at x ≈ −2 they are similar for π− but not for π+. Comparison of the lonigtudinal momentum spectra in the lab. (target) system gives results consistent with limiting fragmentation for reaction (1), but not for reaction (2). Since the combination (abc) is (π+pπ+), exotic, for reaction (1) and (π+pπ−), non exotic, for reaction (2), these results are consistent with the suggestion of Chan et al. that when (ab c ) is exotic, limiting fragmentation may set in already at moderate (accelerator) energies.

Slopes and breaks of transverse-momentum-squared distributions in 16 GeV/c π−p interactions

Abstract Distributions of transverse momentum squared of pions and protons produced in π−p collisions at 16 GeV/c are studied both for final states of different charged multiplicities and for the inclusive reaction. It is shown that all inclusive distributions have a characteristic concave shape that can be described by the sum of a steeper and a flatter exponential component, with crossing point at about pT2 = 0.2 (GeV/c)2. The study of the semi-inclusive reactions indicates that this two-component behaviour originates in low-multiplicity channels (nc ⩽ 6). The steep component of π+ and π− spectra for channels of low charged multiplicities are studied in detail by comparing the observed sharp dependence of the slope upon the effective mass of the nucleon-pion system, with the corresponding results obtained for Monte-Carlo events. It is found that energy/momentum conservations, together with limitation of transverse momenta, give a quantitative description of these results. However, to justify the relative amount of steep and flat components in the inclusive spectra, the dynamics of resonance production are to be considered.

ω− production in K−p interactions

Abstract We report on 20 events of ω− production observed in K−p interactions at 10 GeV/c. A summary of the present world sample is given and new average values of the mass and lifetime of the ω− are calculated. Production and decay characteristics are discussed.

Evidence that the L-meson has decay modes other than K∗ (1420)π

Abstract It has been suggested that the (K ππ ) enhancement observed near 1780 MeV, the L-meson, can be explained as a threshold enhancement in the K ∗ (1420)π system. Here quantitative evidence is presented from 10 GeV/ c K − p interactions to show that this is not so and that the L-enhancement must have decay modes other than K ∗ (1420)π.