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An account is given of the close collaboration of Dick Dalitz with the European K- Collaboration over many decades in many aspects of hypernuclear physics. In particular, emphasis is given to the topics of double hypernuclei and the discovery and resolution of p-wave Lambda strangeness exchange states., Invited talk at HYP06, Mainz, October 2006

An event emitting a Σ- -hyperon from a Ξ- -hyperon nuclear capture at rest has been observed in a hybrid-emulsion experiment. The event has been analyzed as the first observation of the weak decay of the S = - 2 system.

An account is given of the discovery of hypernuclei some fifty years ago together with a review of the early work on hypernuclear physics mainly performed using the photographic emulsion technique.

A hybrid-emulsion experiment has been carried out at KEK-PS to study S = −2 nuclei. With the analysis of about 35% of total emulsion, we have successfully found three events of sequential weak decay of a double-hypernucleus. The results of these E373 events are summarized together with those of past experiments. The first experimental study of the branching ratios of weak decay modes of double-hypernuclei has been performed.

An analysis of emulsion data on the K− meson capture reaction on oxygen, K−16O → π−pΛ15N reveals the formation of two intermediate states of the hypernucleus Λ16O∗ which subsequently decay by proton emission. The states are relatively broad, as expected for Q-values of a few MeV, and are attributed to the 0+ and 2+ levels of Λ16O from the configurations [(p12)N−1 (p12,32) Λ] with Λ-binding energies equal to 1.54±0.09 MeV and 3.10±0.08 MeV, respectively, where BΛ for Λ15N is 13.59 MeV. The 2+-0+ BΛ difference is almost independent of the present statistical error (±0.15 MeV) on BΛ(Λ15N). Provided the state more abundantly produced is assigned to the 2+ level, their relative positions and production rates agree well with the theoretical predictions. A comparison with results from counter experiments is made. The extraction of the Λ spin-orbit splitting from the 2+-0+ energy difference is discussed using calculations for several different ΛN potentials.

A brief review is given of hypernuclear physics from its inception in 1952 to the counter spectroscopy experiments in the early seventies. The early experiments were mainly performed using nuclear emulsions, although studies of the lightest hypernuclei were also made using helium bubble chambers, and elicited the properties of hypernuclear ground states.

Results are presented on the production cross-section of charmed particles obtained from the WA75 emulsion hybrid experiment. The events, selected by the presence of a muon with a high momentum transverse to the beam direction, were located and analysed in nuclear emulsions. A Monte Carlo simulation allowed the computation of acceptances due to both apparatus and selection, as well as scanning and finding efficiencies. The ccBAR hadroproduction cross-section has been determined over the entire X(F) region as sigma(ccBAR)=23.1+/-1.3(stat)+4.0/-3.3(syst) mu-b per nucleon assuming an A0.87 dependence.

Results are presented on the production characteristics of charmed particles obtained from the WA75 emulsion hybrid experiment. The events, selected by the presence of a muon with a high momentum transverse to the beam direction, were located and analysed in nuclear emulsions. Inclusive and correlation properties are systematically compared with the lowest-order QCD calculations for DDBAR hadroproduction. Results concerning the correlation properties indicate some contribution from next-to-leading order [O(alpha(s)3] subprocesses.

A search for non-statistical fluctuations was performed in 200 GeV per nucleon oxygen and sulphur ion-emulsion interactions selected by a high transverse energy trigger. No clear signal of dynamical correlations or of unusual fluctuations was found.

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 .

A double-hyperfragment event has been found in a hybrid-emulsion experiment. It is identified uniquely as the sequential decay of ${}_{\ensuremath{\Lambda}\ensuremath{\Lambda}}^{6}\mathrm{He}$ emitted from a ${\ensuremath{\Xi}}^{\ensuremath{-}}$ hyperon nuclear capture at rest. The mass of ${}_{\ensuremath{\Lambda}\ensuremath{\Lambda}}^{6}\mathrm{He}$ and the $\ensuremath{\Lambda}\ensuremath{-}\ensuremath{\Lambda}$ interaction energy $\ensuremath{\Delta}{B}_{\ensuremath{\Lambda}\ensuremath{\Lambda}}$ have been measured for the first time devoid of the ambiguities due to the possibilities of excited states. The value of $\ensuremath{\Delta}{B}_{\ensuremath{\Lambda}\ensuremath{\Lambda}}$ is $1.01\ifmmode\pm\else\textpm\fi{}{0.20}_{\ensuremath{-}0.11}^{+0.18}\phantom{\rule{0ex}{0ex}}\mathrm{MeV}$. This demonstrates that the $\ensuremath{\Lambda}\ensuremath{-}\ensuremath{\Lambda}$ interaction is weakly attractive.

Interactions induced by 200 GeV per nucleon32S ions on heavy targets were selected by the HELIOS calorimeters and studied in nuclear emulsions. Global observables, such as charged particle multiplicity and transverse energy, were determined event-by-event. Multiplicity and transverse energy were measured as a function of the pseudorapidity over the large acceptance of the present experiment (0.6≤η≤5.5). A comparison of the experimental data with those provided by the event generators FRITIOF and VENUS shows remarkable differences both in the target spectator region and in the participant region. An attempt is made to interpret these discrepancies in terms of plausible mechanisms, like baryon-pair production or rescattering.

An emulsion-counter hybrid set-up to detect charmed particle decays in samples of triggered 32 S-nucleus central interactions is described. A new tracking technique with two emulsion tapes was developed and used successfully.

Events which satisfy the kinematics of p( 16 O,CHep), with low excitation energy in the (CHe) system and a low-energy recoil proton, have been identified in the interactions of 200 GeV/nucleon 16 O ions with nuclear emulsion. An eikonal DWIA estimate of the target A -dependence of strong-interaction diffractive dissociation suggests that, on the basis of these hydrogen data, most of the (CHe) final states, previously ascribed to electromagnetic dissociation on heavy nuclei, might rather be hadronic in character. This contamination is very much less important in the dominant (NH) channel.

This paper presents and contrasts features of the inelastic nuclear reactions of 200 GeV/nucleon 16O and 32S ions with emulsion nuclei. Both the multiplicities of shower particles and the extent of target fragmentation have been studied for varying degress of disruption of the projectile nuclei. The results may be interpreted within a simple geometrical model. In particular the rapidity distributions of those events which exhibit complete projectile break-up without any overt sign of low-energy target fragmentation have been determined. The interaction of secondary projectile fragments of charge two or more issuing from oxygen interactions were also studied and the mean free paths in emulsion of the primary 16O and 32S ions and all such fragments have been compared to those predicted by a simple Glauber model.

This report addresses groundwater modeling performed to support the Environmental Impact Statement (EIS) that is being prepared by the Department of Energy (DOE). The EIS pertains to construction and operation of a new production reactor (NPR) that is under consideration for the Savannah River Site (SRS). Three primary issues are addressed by the modeling analysis: (1) groundwater availability, (2) changes in vertical hydraulic gradients as a result of groundwater pumpage, and (3) migration of potential contaminants from the NPR site. The modeling indicates that the maximum pumpage to be used, 1000 gpm, will induce only minor drawdown across SRS. Pumpage of this magnitude will have a limited effect on the upward gradient from the Cretaceous into the Tertiary near Upper Three Runs Creek. Potentiometric surface maps generated from modeled results indicate that horizontal flow in the water table is either towards Four Mile Creek to the north or to Pen Branch on the south. Particle tracking analysis indicates that the primary flow paths are vertical into the Lower Tertiary Zone, with very little lateral migration. Total travel times from the NPR site to the edge of the model (approximately 3 miles) is on the order of 50 years. The flowmore » direction of water in the Lower Tertiary Zone is relatively well defined due to the regional extent of the flow system. The Pen Branch Fault does not influence contaminant migration for this particular site because it is in the opposite direction of Lower Tertiary Zone groundwater flow. 20 refs., 27 figs., 2 tabs.« less

An emulsion study of 16O and 32S interactions at 200 GeV per nucleon selected by transverse energy

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.

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.

The azimuthal correlation distribution of 102 charmed-particle pairs observed in the hybrid emulsion experiment WA75 is compared with theoretical predictions. The various pairs - (D − D 0 ), (D − D + ), (D 0 D 0 ) and (D + D 0 )-all s how, within statistical error, the same azimuthal correlation distribution, demonstrating its independence from the specific nature of the production channel. Among the decays of 150 charged charmed particles and 138 neutral ones seen, higher multiplicities are favoured for hadronic as opposed to semileptonic decays. The data are consistent with the muonic decays of charged D mesons proceeding through the channels (μ ± , v, K 0 ) and [μ ± , v, K ∗0 (892)] , the fraction through K 0 being 0.76±0.06.

Charged-current neutrino interactions have been analysed in a sample of pictures from BEBC equipped with a TST. Using a method independent of both the neutrino flux and nuclear interaction corrections, the ratio R= σn/σp has been measured. The result is R=1.98±0.19 for the ratio of total cross sections. Bjorken x distributions for proton and neutron targets and for u and d quarks are compared. © 1981., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

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 .

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.

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.

A review and comparative study of the various optimisation methods applied to electrical power systems is made in this paper. The linear optimal control derived by solving the matrix Riccati equation requires feedback of all the state variables. It is shown that the suboptimal control using feedback of a selected number of variables derived by Liapunov method can be equally effective. Under certain conditions optimal control derived from lineamised system equations can give improved system perfommance following large disturbances. However to achieve maximum improvement it is necessary to retain all the system nonlinearities in the optimisation procedure. A method of optimising a system for a nonlinear mode of operation retaining the advantages of closed loop control is described. Finally, the feasibility of practical implementation is investigated by incorporating the various optimal controls derived in a laboratory micromachine system.

A search for the purely leptonic neutral current process induced by antineutrinos: v μ + e − → v μ + e − , has been performed in the BEBC “TST” experiment. No contradiction has been observed with the Salam-Weinberg model.

In an experiment on K--proton interactions in a hydrogen bubble chamber, the cross sections and angular distributions have been studied for elastic and charge-exchange scattering, and charged sigma hyperon production in the momentum range 90-300 MeV/c. Good agreement is found with previous cross sections except for the charge-exchange channel where the new values are 60% larger. The production distributions of the charged sigma hyperons and the polarisation of the Sigma + hyperon clearly indicate that P waves are present down to about 150 MeV/c, much lower than previously reported.

Previous studies of predictors of narcotic abuse have been retrospective and based on samples of long-term addicts obtained from legal or medical channels. There are several methodological problems in this approach. The present study is an attempt to test certain alleged predictors of narcotic use in a cohort of 898 Vietnam veterans. The design overcomes several of the methodological weaknesses of previous studies. Eight variables which have been reported as predictors of drug use or addiction in the drug literature were inquired about during a personal interview which included the premilitary life of each subject. The antecedent variables were socioeconomic background, inner city residence, psychiatric illness, broken home, race, employment history, education and antisocial history. Using information obtained from interviews and military records, we then tested the predictive value of each of these antecedents by comparing narcotic used and addiction in Vietman and use after Vietnam in men differing with respect to each antecedent. Results indicate that some of the variables were very poor, and others very good predictors of the various levels of narcotic involvement. The predictive value and overall importance of each of the variables we tested are discussed.

A renewed analysis of six, most probably 12 ΛC , events observed in emulsion is presented. The binding energy, B Λ , of this hypernucleus is estimated to be (10.80 ± 0.18) MeV. The ΔB Λ values for mirror hypernucleus pairs, ΔB Λ being the B Λ value of the hypernucleus with the smaller atomic number less that of the one with larger Z , seem to become more positive with increase in mass number.

For e + energy > 0.3 GeV and 10 GeV ƒ = (v μ + Ne → μ − e + )/(v μ + Ne → μ − ) = (0.41 ± 0.15)% ; (ii) 1.2 ± 0.5 neutral strange particles are produced per μ − e + event; (iii) the lifetime of possible positron-parent particles is −10 s (90% C.L.); (iv) the cross section for direct e + production via the neutral current is + , decaying into e + … is −3 times that for μ − production, implying M (L + ) > 10 GeV.

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.

The production of charmed particles has been detected in 200 GeV per nucleon 16 O-emulsion central interactions. Their production cross section in elementary nucleon-nucleon processes has been estimated to be charm = [14.1±9.3(stat.) −8.4 +5.6 (syst.)] μ b.

The existence of the H particle, the dihyperon predicted by Jaffe, would bring into question the existence of double hypernuclei. We review the two double hypernucleus events published in the literature. We include an independent report, hitherto unpublished, which was made on the ΛΛ 10 Be event in 1963 and clarifies the salient features of the event; this report reaffirms its published interpretation. We have made a simple calculation of the energy spectrum for Ξ - hyperons produced with K - beams in past emulsion experiments, with a result which accounts adequately for the paucity of reported double hypernucleus events. We outline a hybrid emulsion experiment that would locate Ξ - hyperon interactions efficiently and could thereby greatly improve our knowledge of double hypernuclei.

The associated production of a pair of beauty particles B- and B0 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, 0, SCOPUS: ar.j, info:eu-repo/semantics/published

The results of a search for the presence of sharp resonances in systems of four nucleons produced as a result of various π ± mesonic decay modes of the hypernuclei ∧ 4 H and ∧ 4 He are presented.

The results of a search for final-state interactions between the decay products of some light hypernuclei are presented. The following π− mesonic decays have been considered: Λ 3 H → π − + 1 H , Λ 4 H → π − + 1 H + 3 H , Λ 4 He → π − + 1 H + 3 He , Λ 5 He → π − + 1 H + 4 He , Λ 7 Li → π − + 3 He + 4 He , Λ 7 Li → π − + 1 H + 2 H + 4 He , Λ 7 Li → π − + 1 H + 6 Li , Λ 8 Li → π − + 4 He + 4 He , Λ 9 Li → π − + 4 He + 4 He + n , Λ 9 Be → π − + 1 H + 4 He + 4 He and Λ 12 B → π − + 4 He + 4 He + 4 He .

The results of mass measurements on the fast baryons emitted in the capture at rest of 7600 K--mesons are described. The analysis has been restricted to those interactions from which neither charged π-mesons, nor slowΣ-hyperons (kinetic energy ⩽ 60 MeV), nor hyperfragments are emitted. As already reported in a prelious work (see ref. (1)), a substantial number of deuterons and tritons is present among the fast baryons: the proportion of deuterons of kinetic energy exceeding 84 MeV is (11.1±2.5)%, that of tritons is (2.3±1.0)%. Fast deuterons and tritons of ranges greater than 1 cm are emitted from at least (1±0.2)% of K--mesons interactions at rest in nuclear emulsion. Among the fast baryons a number ofΣ-hyperons decaying in flight has been observed and measured: no (Σ-n) hypernucleus has been detected.

A study of fast baryons emitted from 12 150 K− meson interactions at rest in emulsion has been made in order to determine the nature and extent of K− meson-multinucleon capture processes. Fast Σ hyperons are produced in at least 9 per cent of all interactions while direct fast Λ0 hyperon production is indicated by the presence of 3 protons with energies exceeding 200 MeV. An upper limit of 30% is obtained for multinucleon processes (not producing π mesons) from consideration of π meson emission. The energy spectra for fast Σ hyperons and fast protons are given and mass determinations on a sample of so-called fast protons have revealed about 10% of deuterons and tritons. The suggestion in K− European Collaboration Part II of an apparent infrequency of the reaction K−+n+n→Σ−+n has been confirmed and anα-particle model of K− meson multinucleon interaction has been put forward to explain both this and the emission of deuterons and tritons.

A study has been made of those disintegrations produced in photographic emulsion by the nuclear capture at rest ofK--mesons, from which fast charged∑-hyperons are emitted. In a sample of 63 events, six were analyzed unambiguously as being due to absorption in carbon, nitrogen or oxygen without the emission of any neutrons. An additional eight were found to be consistent with capture by a light nucleus with the emission of one neutron only in each case. The fraction of disintegrations due toK--meson capture in light nuclei from which a fast charged∑-hyperon is emitted has been estimated.

Results are presented on the\(B_\Lambda \) values of hypernuclei in the mass rangeA=3 toA=12 obtained from a sample of 595 uniquely identified π−-mesonic decays. The problems of what constitute adequate selection criteria for the unique identification of an event are discussed. The disagreement between the\(B_\Lambda \) values obtained from different decay modes of\({}^4B_\Lambda \) indicates a possible error in the range-energy relationship.

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.

The decay of charmed particles produced by high-energy neutrinos has been studied by an experiment using simultaneously emulsion, bubble chamber and counter techniques. Eight charmed particle candidates, 5 positively charged and 3 neutral, have been found in the emulsion, where their production and decay have been directly observed. One of these events is identified as a Λ c + baryon of mass 2.26±0.02 GeV/ c 2 which undergoes the decay Λ c + →pK − π + after a proper time of (7.3±0.1) · 10 −13 s. A statistical analysis of the other observed decays leads to the mean-life values τ + =(2.5 −1.1 +2.2 ) · 10 −13 s, τ 0 =(0.53 −0.25 +0.57 ) · 10 −13 s, for the sample of charged particles enriched by a similar event found in a previous experiment, and for the sample of 3 neutral particles, respectively. The former value is only slightly affected by including in the sample the Λ c + event or excluding that of the previous experiment.

An attempt at the direct observation of the cascade decay of beauty particles, produced by π- of 350 GeV/c leading to 3 muons or 4 muons in the final state, has been made in an emulsion/counter hybrid experiment at CERN. Under the assumption that the lifetime of beauty particles is of the order of 10-13s the non-observation of any candidates provides an upper limit for beauty production of ∼90 nb at the 90% confidence level., 0, SCOPUS: ar.j, info:eu-repo/semantics/published