G. Labrosse

Study of the Kππ system produced in K−p → KππN reactions at 14.3 GeV/c

We have studied the Kππ system in the 14.3 GeV/c reactions K−p → K−π+π−p, K−p → K0π−π0 and K−p → K0π+π−n. The data have been obtained from a 500 000 picture exposure of the CERN 2m HBC. The first two final states are dominated by Q-production in the Kππ system; there is also an L-signal at M (Kππ) ∼ 1.75 GeV. The reaction cross sections are compared to K−p data at other energies. We discuss the Kππ mass dependence of the diffractive production slope. Evidence is presented for a Q−p versus Q+p differential cross section cross-over around |t| = 0.17 GeV2. A t-channel isospin analysis for the KN → K∗(890)πN channels in the Q-region shows that the I = 1 exchange amplitude is ⋍ 10% of the dominant I = 0 exchange amplitude. The Kππ decay distributions indicate a predominant JP = 1+ state in the Q-region, and an important JP = 2− contribution in the L-region. We find neither s-channel nor t-channel helicity conservation at the meson vertex in the Q- or L-regions. The Kπ angular correlation moments within the Kππ diffractive system are characteristic of Kπ elastic scattering, suggesting a π-exchange Deck-type production mechanism. There is evidence for a Kf0 and κπ contribution (where κ is the JP(Kπ) = 0+ state) to the diffractive Kππ system. A fit to the K−π+π− and K0π−π0 Dalitz-plot distributions for the Q-re gion indicates that the ratio of Kϱ to K∗π decay amplitudes decreases with increasing Kππ mass.

Inclusive production of charged and neutral sigma hyperons in K−p interactions at 14.3 GeV/c

Abstract Inclusive production of Σ + , Σ − and Σ 0 hyperons in K − p interactions at 14.3 GeV/ c has been studied and compared to Λ production. Cross sections are presented as a function of longitudinal and transverse momenta and compared to the pp → Σ + + anything data.

K−π− elastic scattering cross section measured in 14.3 GeV/c K−p interactions

Results are presented on a measurement of the I = 3/2 Kπ elastic scattering cross section by applying the Chew-Low extrapolation method in the reaction K−p → K−π−Δ++at14.3GeV/c. The magnitude of σ(K−π− → K−π−) is found to be about 3 mb at threshold and slowly falling with energy to about 1.5 mb at 2.8 GeV. The off-mass-shell moments of the differential elastic cross section are given. The absolute value of δ30 is found to be increasing slowly from 0° to 20° between threshold and 1.2 GeV.

The reactions K−p → K∗o(890)N and K−p → K∗o (1420)N at 14.3 GeV/c

Abstract Preliminary results are presented on K ∗ (890) and K ∗ (1420) production in three-body final states of 14.3 GeV/ c K − p interactions. For K ∗ō (890) production, the total and differential cross-sections and the density matrix elements are determined. The K ∗− reaction is found to be dominated by natural parity exchange and the charge exchange reaction by unnatural parity exchange. The total cross sections are given for K ∗ō (1420) production.

A triple Regge analysis of the reactions K−p → Λ and K−p → K0 + X at 14.3 GeV/c

Abstract New data from the reactions K − p → Λ + X and K − p → K 0 + K at 14 GeV /c are presented. From an analysis of the distributions of M X 2 within the framework of a triple Regge formalism we obtain the effective Regge trajectories corresponding to ϱ, K or K ∗ and nucleon exchange.

Inclusive γ production in K− p interactions at 14.3 GeV/c

Abstract Results are presented on γ production in K− p interactions at 14.3 GeV/c. The analysis is based on 2 541 fitted e+e− pairs in a hydrogen bubble chamber. The inclusive cross section for γ production is found to be (54.5 ± 1.8) mb. The average number of γs per inelastic event is 2.93 ± 0.12; it exhibits no strong dependence on charged multiplicity. From the PL and PT2 invariant distributions of the γ, a simple function describing the π° invariant distribution is determined.

Factorisation in the inclusive reactions π±p → + X and K−p → Λ + X

Abstract A test is made of the factorisation scheme proposed by Miettinen for the inclusive reaction π±p → Λ + X at 18.5 GeV/c and K−p→ Λ + X at 14.3 GeV/c. The test is applied to the lambda differential cross section and polarisation via a sum rule derived within the concepts of duality and exchange degeneracy, and SU3. The original scheme is found not to agree with the experimental data. A possible explanation of the disagreement is discussed.

Momentum transfer distributions of some diffractive enhancements in K−p interactions at 14.3 GeV/c

We discuss the structure of the momentum transfer distributions for the diffractive dissociation processes p → nπ+, p → Δ++π− and K− → K890∗0π−. In the near-threshold mass region a clear break of slope is found around t′KK ∼ 0.25 GeV2 for the two baryonic channels, whereas no comparable structure is seen for the mesonic system. The K → K∗π differential cross section exhibits a nearly exponential behaviour up to t′pp ∼ 0.6 GeV2, falling over three orders of magnitude. The slope variations and breaks are strongly correlated both to the mass region considered and to the decay angle of the fragmentation system.

Determination of the K−π− inelastic cross sections for c.m. energy up to 2.8 GeV

The reaction K−p→Δ++ + anything was studied at 14.3 GeV/c and is production mechanism was found to be consistent with one pion exchange at low momentum transfer. K−π− inelastic and total cross sections have been determined by a Chew-Low extrapolation method in the c.m. energy range from threshold to 2.8 GeV. Cross sections for various K−π− final states are presented.

Energy dependence of the reactions K±p → K∗±(890)p and K±p → K∗±(1420)p

Abstract New high energy results for the reactions K − p → K ∗− (890) p and K − p → K ∗− (1420) p confirm a definite flattering in the energy dependence of the cross sections; such a flattering is not observed in the corresponding K+ channels. The contributions of natural parity exchange at small t accounts for this effect and suggests a possible explanation in terms of pomeron (P) trajectory exchange, giving rise to ωP interference.