W. Lohmann

Lambda polarization in inclusive K−p interactions at 10 and 16 GeV/c

A strong negative transverse polarization Pz is found for forward produced lambdas observed in 10 and 16 GeV/c K−p interactions. This indicates that exchanges of natural spin-parity are dominant in the production process. Using the polarization results, the dσdu′ distributions for natural and unnatural spin-parity exchanges are derived. For unnatural exchanges, a dip is observed at u′≅0.3 GeV2, which can be explained as a nonsense-wrong-signature zero of the Nβ trajectory. The value of Pz for forward producted lambdas is constant with energy. This is in agreement with the triple-Regge model prediction, as is the fact that Pz is constant as a function of M2s. The two non-transverse polarization components, Px and Py, have been measured and are found to be consistent with zero for all x values, unlike Pz.

Study of the reactions π+p → π0 Δ++(1236), ηΔ++(1236) and η′Δ++(1236) at 16 GeV/c

Abstract The reactions π+p giving π0Δ++(1236), η(549) Δ++(1236) and η′(958) Δ++(1236) are studied at 16 GeV/c. Cross sections, differential cross sections and Δ++(1236) spin density matrix elements are presented. The π0Δ++(1236) differential cross section d σ d t′ indicates a dip towards t′ = 0 and has a minimum at t′ ≅ 0.6 GeV2. The Δ++(1236) spin density matrix elements are consistent with the predictions of the Stodolsky-Sakurai model, except perhaps near the forward direction. For ηΔ++(1236), the differential cross section d σ d t′ turns over in the forward direction and presents no further structure. SU(3) sum rules are tested and found to be approximately satisfied. The data agree with factorization of ϱ exchange. The effective A2 trajectory is calculated and found to be consistent with that reported from the reaction π−p → ηn.

Two-body hypercharge-exchange reactions in K−p and π+p interactions at 10 and 16 GeV/c

Cross-section values or upper limits are presented for twenty-five two-body hypercharge-exchange reactions in K−p and π+p interactions at 10 and 16 GeV/c. The 16 GeV/c results are compared with some predictions of line-reversal plus exchange-degenerate Regge poles, of SU(3) and of the additive quark model. Agreement is found in all cases.

Study of the reaction π+p → ϱ0 Δ++(1236) at 16 GeV/c

Abstract The reaction π+p→ωΔ++(1236) is studied at 16 GeV/c. Cross section, differential cross section, single and joint spin-density matrix elements are given and the correlations between the e and Δ++(1236) decay angular distributions are investigated. Natural and unnatural spin-parity exchanges contribute to this reaction in roughly equal amounts. Natural exchanges lead predominantly to Δ++(1236) with helicity ± 3 2 , while unnatural exchanges lead predominantly to Δ++(1236) with helicity ± 1 2 and to e with helicity zero. Furthermore, unnatural exchanges are small at t′≅0.2 GeV2 compared to other t′ values, which may be due to the nonsense wrong-signature-zero of the B-meson exchange. Quark model relations are found to be satisfied by the data.

Study of proton dissociation into ΛK+ in 3-body final states at 10 and 16 GeV/c

Abstract Results are presented for p → (ΛK+) dissociation in the reactions K−p → ΛK+K− and and π±p → ΛK+π±at 10 and 16 GeV/c. The cross sections for the low-mass ΛK+ enhancement are compatible with the energy dependence σ ∝ plab−0.3. The t′ spectra or the (ΛK+) threshold enhancement are exponential in shape. Its decay angular distribution reveals neither s-channel nor t-channel helicity conservation. The relative probabilities of the processes p → p, p → ( N π) I= 1 2 and p → (Λ K + ) dissociation are in the ratios 100 : 10 : 0.2, independent of the nature of the incident particle.

Investigation of the low-mass πKK system in the reactions π±p→(π±K+K−)p at 16 GeV/c

The reactions π±p→(π±K+K−)p are studied, at 16 GeV/c, and in particular the low-mass π±K+K− system is compared with the diffractively produced 3π system in the reactions π±p→(π±π+π−)p at the same energy. Similarities are found in (a) the weak energy dependence of their cross sections, (b) the shape of the three-meson mass spectra, (c) the differential cross sections which have the same slope for the same value of the three-meson invariant mass, (d) the general characteristics of the partial-wave composition of the low-mass three-meson systems (as for the 3π case, the πKK system is produced in unnatural spin-parity states with JP=1+ dominant at low πKK mass, the state JP=0−, however, may be relatively more abundant in the πKK than in the 3π case) and (e) the exchange which is almost entirely of natural parity. We conclude that the reaction π±p→(π±K+K−p, for low values of the πKK mass, represents the diffractive dissociation process π→πKK, which is less probable than π→πππ by one order of magnitude.