D.H. Davis

Charged Σ hyperon production by K− meson interactions at rest

Abstract Bubble chamber pictures have been scanned for the interactions of stopping K− mesons in hydrogen. New determinations of the ratios γ= K − p →Σ − π + K − p →Σ + π − , R c = K − → charged particles K − p → all final states for K− meson interactions at rest, are presented, as well as the branching ratio B= Σ + → n π + Σ + → n + +, p π 0 . The values found for Rc, 0.664±0.011, and for B, 0.488±0.008, are in agreement with previous results. On the other hand, two values, resulting from different methods of analysis, have been found for γ, namely 2.38±0.04 and 2.35±0.07. They agree with one of the two previous precise measurements but are inconsistent with the other.

Direct observation of the decay of beauty particles into charm particles

Abstract The associated production of a pair of beauty particles B− and B 0 by a 350 GeV π− interaction has been observed in an emulsion target inserted in an array of silicon microstrip detectors. Both beauty particles decay into charm particles, both of which are also observed to decay in the emulsion. Two negative muons were identified and their momenta measured in a large muon spectrometer. One muon has a pT of 1.9 GeV/c and is associated with a beauty particle decay. The other, with a pT of 0.45 GeV/c is associated with a charm particle decay. The flight times of the two beauty particles are respectively (0.8 ± 0.1) × 10−13 s and (5+2−1) × 10−13 s. Alternative interpretations of this event have negligible probability.

Determination of the branching fractions for K − -meson absorptions at rest in carbon nuclei

SummaryThe branching ratios for the primary interactions of K−-mesons at rest with carbon nuclei have been determined by means of a heavy-liquid bubble chamber filled with a mixture of hydrocarbons. The results are compared with those obtained in other absorbing media, and the question of the existence of a halo of neutrons at the surface of heavy nuclei is discussed in the light of these new results.RiassuntoSi sono determinati i rapporti di diramazione per le reazioni primarie dei mesoni K− in quiete con nuclei di carbonio per mezzo di una camera a bolle a liquido pesante riempita con una miscela di idrocarburi. Si confrontano i risultati con quelli ottenuti in altri mezzi assorbenti, e si discute la questione dellesistenza di un alone di neutroni alla superficie dei nuclei pesanti alla luce di questi nuovi risultati.РезюмеОпределяются отношения ветвей для первичных взаимодействий K−-мезонов в покое с ядрами углерода, используя тяжеложудкостную пузырьковую камеру, наполненную смесью углеводородов. Полученные результаты сравниваются с результатами, полученными в других пиглошаюших средах. В свете этих новых результатов обсуждается вопрос сушествования гало нейтронов на поверхности тяжелых ядер.The branching ratios for the primary interactions of K--mesons at rest with carbon nuclei have been determined by means of a heavy-liquid bubble chamber filled with a mixture of hydrocarbons. The results are compared with those obtained in other absorbing media, and the question of the existence of a halo of neutrons at the surface of heavy nuclei is discussed in the light of these new results.

Observation of a likely example of the decay of a charmed particle produced in a high energy neutrino interaction

Abstract In a study of neutrino interactions occurring in nuclear emulsion, an event has been found that is most readily interpreted as the decay of a charmed particle with lifetime a few times 10 −13 s.

Proton decay of excited hypernuclei

Abstract A re-analysis of emulsion data on K−12C → π−p11ΛB shows 12 Λ C ∗ states, strongly excited, which decay by proton emission, one having width Γ ⪅ 100 keV, the others Γ ∼ 500 keV. They are compared with the (K−, π−) in-flight reaction data for 12C and interpreted as the (0±,2+,2+) states of the configurations p 3 2 ) N −1 ( p j ) Λ . The most straightforward approach assigns the narrowest level to 0+ but this leaves one difficulty, so that the proper interpretation is not yet settled. There is moreover no similar narrow level observed in K −16 0 → π −16 Λ 0 ∗ → π − p 15 Λ 0 .

A compilation of binding energy values of light hypernuclei

Abstract The results of a compilation of the binding energy values of light hypernuclei ( A ⩽ 16) obtained by the European K − Collaboration and the EFINS-North-western Collaboration are presented. The events were analysed by the same computer programme and uniform stringent selection criteria were applied.

Electromagnetic dissociation of 200 GeV/nucleon 16O and 32s ions in nuclear emulsions

Abstract This work represents the results of an experimental investigation of the electromagnetic dissociation of 200 GeV/nucleon 16 O and 32 S ions in nuclear emulsions. Exclusive channels involving charged fragments have been studied as a function of the energy released, and, assuming a Weizsacker-Williams spectrum of virtual photons, there is a good agreement with results for the (γ, p) processes obtained with real photons. However, the rates found for other processes are larger, in particular for the (γ, α) on both nuclei. The values of the total integrated absorption cross sections are generally larger than those obtained from real photon experiments but the extent of the discrepancy depends strongly upon which photon results are used in the comparison.

A Search for Charmed Particles Originating from the Interactions of 300-GeV/c Protons in Emulsion Nuclei.

Abstract The associated production of charmed particles by the interactions of 300 GeV/ c protons with complex nuclei has been sought using nuclear emulsions. The failure to observe any candidates for this process among some 60,000 interactions investigated implies, provided charmed particles lifetimes are in the range 10 −12 to 10 −14 s, a cross section for their associated production by the interactions of 300 GeV/ c protons with nucleons of less than 1.5 microbarns at a 90% confidence level.

Is there a bound Σ4He

Abstract Recent KEK data on the inclusive (K−, π−) reaction for K− mesons stopping in a helium target have been interpreted as evidence for an unstable bound state Σ4He. We examine here data, largely background-free, on exclusive (K−, π−) reactions for K− stops in helium bubble chambers, using an impulse-approximation model including final-state interactions for the hyperons. These data indicate strong attraction, but no unstable bound state, for the systems ( 3 H , 3 He )Σ .

THE DOUBLE ASSOCIATED PRODUCTION OF CHARMED PARTICLES BY THE INTERACTION OF 350 GEV/C PI-MESONS WITH EMULSION NUCLEI

Abstract Evidence is reported for the simultaneous production of four charmed particles in interactions induced by 350 GeV/ c π − mesons in stacks of nuclear emulsions. The events were found during a search for beauty particles among a sample of about 200 interactions with candidates for charmed particles. The events selected required the presence of at least one muon with a high component of momentum transverse to the beam direction.