K. Böckmann

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.

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.

How well does an LPS analysis separate production mechanisms in π+p interactions at 8 and 16 GeV/c?

Abstract A longitudinal phase space (LPS) analysis has been performed on the reaction π+p→π+π+π−p at 8 and 16 GeV/c. Special attention has been given to the question of the separation of the various reaction mechanisms. The conclusions are: (i) Dissociation of the pion can be clearly isolated, both at 8 and 16 GeV/c. Baryon dissociation is fairly well separated at 16 GeV/c, but at 8 GeV/c it is strongly contaminated by the reactions δ++ϱ0 and even more by δ++f; (ii) The cross section for diffraction dissociation dominated regions of LPS is constant or even slightly increasing between 8 and 16 GeV/c.

Tests of s-and t-channel helicity conservation in pπ+ π−, K−π+π− and π±π+π− production in 16 GeV/c π±p and 10 GeV/c K−p interactions

Abstract Necessary conditions for s-and t-channel helicity conservation are tested for pπ+π−, K−π+π− and π±π+π− states produced in 16 GeV/c π±p and 10 GeV/c K−p interactions by means of a method which is independent of specific spin-parity assignments to these states. It is found that the production of pπ+π− states is generally consistent with t-channel helicity conservation for masses up to 2.4 GeV, but that for π±π+π− and K−π+π− some inconsistency with t-channel helicity conservation is found, primarily in the A1± and Q− mass regions. s-channel helicity conservation is excluded for all states.

Interference between (P, f0…) and (ϱ0, B0,…) exchanges in pion diffraction dissociation at 16 GeV/c

Abstract It is found in the reactions π±p→(π±π+π−)p, believed to be dominated by diffraction dissociation, that the d σ d t′ distributions show a “cross-over” effect at t′ ≈ 0.15, similar to the effect observed in elastic scattering. This gives evidence for the interference of (ϱ0, B0,…)-exchanges with ( P , f 0 , …) -exchanges in pion diffraction dissociation reactions. No such evidence is found for baryon dissociation, π±p→π±(pπ+π−), at the same energy.

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.

Charge Properties of the Hadronic System in Neutrino

Abstract Charge properties of the hadronic systems from νp and ν p scattering in BEBC are studied in the framework of the quark-parto model (QPM). The average charges 〈Q jet 〈 ν and 〈Q jet 〈 ν of a quark jet and a d-qua jet, respectively, are determined according to two different methods. The difference 〈Q jet 〈 ν − 〈Q jet 〈 ν is in agreement with e QPM value of 1. Scaling of charge and energy flow in the angular variable λ is demonstrated. The ratios ΔQ ν /ΔQ ν of charge flows in νp a ν p scattering are in accord with the QPM in both hemispheres.

p

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.

and Anti-neutrino

Abstract Three- and four-body final states with strange particles are studied in π + p and π − p interactions at 16 GeV/ c . We present cross sections and investigate their energy dependence. Production mechanism, resonance production and quantum number transfer are discussed. Strong Y ∗ (1385) production is found in the reaction π + p → Λ K + π + , while the corresponding π − p reaction is dominated by production of K ∗ (890). In the NK K π channels, the K and K are produced mainly at the same vertex, i.e. non-strangeness exchange ΔS = 0 is dominant (about 75% of the cases), whereas in the Λ K ππ channels, the Λ and K are more frequently produced at opposite vertices, i.e. | ΔS | = 1 exchange is important (about 60% of the cases). Results on the polarization of the lambdas produced in the π + p reactions are given.

p

Abstract A prism plot analysis of the reaction π−p→pπ+π−π− at 16 GeV/c has been made and the results are compared with those obtained in a similar analysis of the reaction π+p→ pπ+π+π− at the same energy. The three dominating reaction mechanisms (pion dissociation, reggeon exchange, proton diffraction dissociation) appear to be well separated, while considerable residual overlaps are present inside these classes. The prism plot method is discussed as a means for detecting hidden structures and some evidence is presented for a broad three-pion enhancement around 2 GeV decaying primarily into ϱ0π−.