Search

A study of the inclusive and semi-inclusive Λ and Λ production in K+p interactions at 32 GeV/c is presented. The inclusive cross sections for Λ and Λ amount to 0.78 ± 0.05 and 0.42 ± 0.04 mb thus showing a remarkable growth between 16 and 32 GeV/c with a factor of 1.7 for Λ and 2.8 for Λ . Target and beam fragmentation processes are found to be dominant for Λ and Λ production respectively with the following lower limits for the corresponding cross sections: σ(p → K + ʌ) > 0.5 mb and σ(K + → p ʌ ) > 0.3 mb . Although the early scaling conditions are fulfilled for the Λ production in the target fragmentation region, and Λ production in the beam fragmentation region, scaling is not observed between 16 and 32 GeV/c in the x and pT2 Feynman variables. The Λ production is found to be very similar in the K+p inclusive reaction at 32 GeV/c and in the semi-inclusive reaction K − p → Λ K K X at the same energy. The Λ Λ pair production cross section increases significantly in K+p interactions from 16 to 32 GeV/c where it reaches the value σ Λ Λ = 47 ± 11 μ b . The cross sections for Λ or Λ produced in association with an identified proton are also given and discussed.

Results are presented onK + p andK − p elastic scattering at 32.1 GeV/c in the |t| interval 0.06–1.4 GeV2. The samples contain approximately 15,000 events each and are obtained in the MIRABELLE bubble chamber at the Serpukhov accelerator. The |t| distributions are parametrized by quadratic exponential formsdσ/dt=A exp (bt+ct 2). The total elastic cross sections, obtained by integrating the fitted distributions, are (2.39±0.07) mb and (2.57±0.10) mb inK + p andK − p interactions, respectively. A cross-over between theK + p andK − p differential cross sections is found at |t c |=0.17±0.02 GeV2. The hypothesis of geometric scaling becomes valid somewhere between 32 and 70 GeV/c forK + p interactions, and is trivially verified forK − p scattering. Finally, an impact parameter analysis of the difference betweenK − p andK + p elastic amplitudes is presented.

Production of Σ ∗− and Ξ ∗− antibaryon resonances in K+ fragmentation processes is observed by studying inclusive λ π + and λ K + invariant mass distributions in 32 GeV/c K+p interactions. A possible Ξ ∗− state is reported with a mass of 2137±4 MeV and width ≲20 MeV. Signals are observed at λ K + masses of 2240, 2380 and 2540 MeV, which correspond to previously observed Ξ ∗− states. Evidence is presented for a low-mass λ p enhancement around 2145 MeV.

Four- and six-body final states in K + p interactions at 32 GeV/ c are studied in terms of principal-axis variables. Evidence is found for considerable alignment of the final-state particles towards a preferred plane in momentum space. The experimental results are compared with an uncorrelated production model which, apart from the alignment effects, reproduces satisfactorily the main characteristics of the principal-axis variables. The slope of the “generalized scattering angle” distribution is found to provide information on the r.m.s. initial-state impact parameter of the reaction.

The inclusive production of resonances is systematically studied in K + p interactions at 32 GeV/ c . Total production cross sections are given for three baryon resonances, five vector and three 2 + tensor mesons. We also compare the central and fragmentation components of the total production cross sections with quark model predictions.

The inclusive production of Ξ+ and Ξ− hyperons is investigated in K+ p interactions at 32 GeV/c. The production cross sections, 36.4±9 μb for the Ξ+ and 6.5±3 μb for the Ξ−, are rising strongly with energy similarly to Λ and Λ production in K+ p interactions. The Ξ+ are produced preferentially in the forward direction in the c.m.s., while the Ξ− are produced dominantly backwards. The average transverse momenta 〈pT〉Ξ+=0.73±0.09 GeV/c and 〈pT〉Ξ−=0.58±0.09 GeV/c.

We present evidence for a new narrow state decaying into oπ + with a mass of 2145 ± 10 MeV/ c 2 and an experimental width of 25 MeV/ c 2 , produced in K + p interactions at 32 GeV/ c . The production cross section σ · BR (→ oπ + ) is equal to 11 ± 3 μb .

We present results on a number of non-diffractive two-body channels contributing to reactions K+p→K0π+p and K+p→K+π−π+p. The data come from an exposure of the Mirabelle bubble chamber to an r.f. separated K+ beam of 32 GeV/c at the Serpukhov accelerator. Total cross sections are given for the final states K ∗+ (890) p , K ∗+ (1420) p , K 0 Δ ++ (1232), K ∗+ (890) p , Δ ++ (1232), K ∗0 (1420) Δ ++ (1232), K ∗0 (1780) Δ ++ (1232) and K ∗0 (890) Δ ++ (1950) . The differential cross sections are given for all channels with sufficient statistics. The energy dependence of the total and differential cross sections is studied.

We present an analysis of the reaction K + p → K 0 + anything at incident momenta of 5, 8.2 and 16 GeV/ c in terms of the Bjorken variables gw and x . Assuming dominance of ϱ exchange, we derive the structure function F 2 ( x , y ) which is found similar to the one obtained in deep inelastic electroproduction.