Search

Inclusive cross sections and longitudinal momentum distributions are presented for γ rays produced in K−p and K+p interactions at 32 GeV/c in the 4.5 m Mirabelle hydrogen bubble chamber at the Serpukhov accelerator. The average longitudinal and transverse momentum of neutral pions and the average π0 multiplicity 〈n π0〉 are estimated. It is found that 〈n π0〉 is an increasing function of the number of charged prongs.

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.

Lambda production is studied in K − p interactions at 32 GeV/ c . The total Λ cross section is 2.31±0.03 mb . Using the measured Λγ combinations we find that (31±4)% of all Λ's are produced via the Σ 0 → Λγ decay. About 60% of the Λ's are associated with either a N N or K K pair; about 40% of the Λ's are produced through the hypercharge annihiltion reaction K − p→ Λ + π 'a. The two-peak structure of the invariant x distribution can be related to fragmentation processes. The Λ is found to be unpolarized in the target fragmentation region, whereas a transverse polarization is observed for forward produced Λ's. As a function of p ⊥, a polarization effect is measured at medium p ⊥.

Longitudinal invariant structure functions E d σ d x for a number oflow p t hadronic fragments produced in K +- interactions at 32 GeV/ c are presented. Data were obtained in the Mirabelle bubble chamber. The fragmentation modes investigated are K ± → K 0 , K 0 , K ∗0,+ (890), K ∗0,− (890), ϕ, ϱ 0 , π +- , Λ, ḡL, and p → p inel , Δ ++ (1236), Λ, ḡL, π ± , K 0 , ϱ 0 . These various fragmentation spectra clearly fall into a definite hierarchy, the invariant cross sections being more suppressed at large | x | the bigger the difference between initial and final state hadron quantum numbers. Invariant cross sections in the fragmentation regions are adequately fitted by a power law Edσ / dx ∝ (1 − | x |) n as suggested by dimensional or Regge counting The values of n are in general consistent with values obtained at FNAL and ISR energies for comparable data. They are in good overall agreement with the quark counting rules as recently reformulated, and the deviations observed suggest corrections due to strange (s) and light (u, d) quark mass differences. The power laws governing the kaon valence quark structure functions behave at large x as s K V ( x ) x →+1 ∼ (1 − x ) 0.5 and ū K V (x) x→+1 ∼ (1 − x) 1.5 .

Charged hadron multiplicity distributions in $$\bar v_\mu n$$ and $$\bar v_\mu p$$ interactions in the energy range $$5< E_{\bar v}< 150GeV$$ GeV are presented. They are obtained from about $$6000\bar v_\mu $$ charged current events produced in BEBC filled with deuterium. Multiplicity moments are studied as a function of the invariant mass of the hadronic systemW. Results on multiplicity distributions in the forward and backward directions in the hadronic c.m.s. are presented and discussed within the framework of the quark parton model. Values for the average charge of the forward jet are also determined and compared with other experimental data.

Final data on topological cross sections are presented. Inclusive single particle distributions for the reactionsK + p→ π± X at 32 GeV/c are discussed and compared with data at lower energies. Early scaling in the fragmentation regions is confirmed, while cross sections in th central region continue to rise with energy even faster than inpp interactions. Thex-andp T -dependence of the π+/π− ratio inK + p interactions is discussed and a comparison of reactionsK + p→ π± X andK − p→ π± X at 32 GeV/c is made in the context of constituent models. We also present transverse momentum distributions, show prominent seagull effects and study how they are influenced by resonance production.

From the analysis of 5630 v υ and of 1372 v π charged current interactions, obtained in the BEBC bubble chamber filled with deuterium and exposed to the CERN wide band antineutrino beam, the ratios of cross section on neutron and photon targets have been measured and found to be R  σ ν)/σ v p = 0.51 ± 0.01 (±0.03) , and R  σ( ν n )/σ( v p ) = 22.2 ± 0.12 (±0.25) The dependence of these ratios on the x scaling variable shows, in a direct way, that the momentum distribution of the majority quark, up(x) = dn(x), is broader than that of the minority quark, un(x) = dp(x).

The inclusive cross section and the average multiplicity are evaluated for most of the charged (π±, p, K±) and neutral (γ, π0, K0, K0, Λ, Λ, n) particles produced in 32 GeV/c K−p interactions; corresponding results are obtained for each charged topology separately. New results are given for the total charged multiplicity cross sections. The average longitudinal momentum of neutrals is found to be roughly equal to that of charged particles. The π+ and π− multiplicity distributions are reconstructed and compared to the π0 and to the total charged multiplicity distributions.

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 .

Inclusive cross sections and one-particle inclusive spectra are given for neutral K, Λ and Λ produced in K − p and K + p interactions at 32 GeV/ c in the 4.5 m Mirabelle hydrogen bubble chamber at the Serpukhov accelerator. Cross sections for associated production are also given, and the energy dependences of the cross sections and of the x distributions in the central and in the fragmentation regions are discussed.

Antilambda production is studied inK−p interactions at 32 GeV/c. Both total and differential cross sections are presented. The inclusive\(\bar \Lambda \) production cross section amounts to 109±7 μb. A remarkable energy dependence is observed, σ(\(\bar \Lambda \)) increasing by a factor of four between 14.3 and 32 GeV/c. Thep⊥2 distribution exhibits an exponential fall-off with a slope of 3.3±0.2 (GeV/c)−2. Most of the\(\bar \Lambda \)'s are emitted in the forward hemisphere. The invariantx distribution increases between 14.3 and 32 GeV/c. Data are presented for\(\bar \Lambda \) production inK-p→Λ\(\bar \Lambda \)+XK-p→\(\bar \Lambda \)Kn+X, andK-p→\(\bar \Lambda \)p+X.

Data on Λ and\(\bar \Lambda \) polarization inK±p interactions at 32 GeV/c are presented. A comparison is made between the results of these two experiments as well as with the data at lower energies. The contribution of the different production mechanisms to the Λ(\(\bar \Lambda \)) polarization are discussed.

Results are presented on the inclusive π± production in K−p interactions at 32.1 GeV/c. The invariant longitudinal distributions have been calculated both for π+ and π− in the backward c.m. hemisphere and extrapolated in the forward hemisphere under some physical assumptions. The inclusive cross sections for π+ and π− amount to 32.9 ± 1.5 mb and 35.0 ± 0.7 mb respectively. The energy dependence of the inclusive pion production has been analyzed in the framework of Mueller-Regge phenomenology both in the proton fragmentation and in the central region.