Kazuma Nakazawa

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.

Experimental Study of Double-Λ Hypernuclei with Nuclear Emulsion

briefly. Latest numerical values of energies are given for Λ-Λ interaction and binding of two Λ hyperons in several nuclei. A double-Λ hypernucleus of 6 ΛΛHe (“Lambpha” / NAGARA event) strongly suggested an weak attractive Λ-Λ interaction with ΔBΛΛ = 0.67±0.16 MeV, and the lower mass limit of the H-dibaryon to be 2223.7 MeV/c (90% C.L.). A probable candidate of 10 ΛΛBe ∗ nucleus was observed with its excitation energy of 2.8 ± 0.4 MeV.

A Hybrid Experiment to Search for Beauty Particles

We give here a detailed description of experiment WA75, which was performed at CERN to search for beauty particles. Events containing at least one muon with a high momentum transverse to the beam direction were selected; then the primary interactions and decay vertices, located in stacks of nuclear research emulsions, were examined and analysed. The various parts of the apparatus are described and the off-line analysis and search in emulsion are discussed. An estimate is made of the sensitivity of the experiment to beauty- and charmed-particle production.

Unusually penetrating particle detected by balloon-borne emulsion chamber

SummaryOne example of an unusual particle track has been recorded in an emulsion chamber exposed to cosmic rays on a ballon at the atmospheric depth 11.7 g/cm2. The particle arrived at the chamber withZ/β=40±2 and β≳0.8. What is extraordinary with this particle is its arrival zenith angle, 87.4°, which amounts to a traversed atmospheric thickness ∼200 g/cm2. The anomalous nature of the present track “ET” (exotic track) is demonstrated through the difficulties in reconciling it with the explanation that it is due to an ordinary ultra-heavy cosmic-ray nucleus.

Some properties of charmed particles produced in π−-nucleus interactions

Abstract 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.

Strangeness -2 studies at KEK

Abstract Studies of double-strangeness ( S = −2) systems at KEK are summarized. At KEK, beam exposures have been completed in three experiments, namely PS-E176, E224, and E248. The first two experiments provide interesting information on the Ξ- N interaction, which will be discussed. In E248, counter alignment calibrations are in progress. A fourth experiment, PS-E373, is waiting for its first period of beam exposure in February 1998 and should provide at least ten times better statistics on S = −2 systems than did E176 and E224.

Possibility of screen-type X-ray film for observation of heavy cosmic-ray primaries

Abstract This article discusses the possibility of screen-type X-ray film for the observation of heavy cosmic-ray primaries. We investigate in detail the optical characteristics of the intensifying screen Gd 2 O 2 S:Tb, and perform a simulation calculation for three-dimensional diffusion of scintillation light emitted from numerous δ-rays (knockon electrons produced by a heavy primary) in the screen. On the basis of these theoretical speculations, we report the experimental results obtained recently by a balloon-borne emulsion chamber with full use of the screen type X-ray film, focusing to the charge resolution of heavy primaries and their flux with energy larger than the rigidity cutoff at Sanriku latitude, E c ∼ 4 GeV/n. All results show that the emulsion chamber with multilayered screen-type X-ray film is quite valid and powerful for the observation of heavy cosmic-ray primaries.

The production of charmed particles in high-energy 16O-emulsion central interactions

Abstract 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.

Development of a GEM-TPC for H-dibaryon search experiment at J-PARC

We have developed a GEM-TPC for H-dibaryon search at J-PARC E42, which reconstructs charged particles from the H-dibaryon decay in (K−,K+) reaction. Since 106 cps/cm2 K− beams are injected to the TPC, GEMs and a gating grid are adopted to suppress positive ion feedback. The TPC is also designed to have good position resolutions corresponding to the ΛΛ invariant mass resolution of a few MeV/c2. The design of the E42 TPC, and performance evaluations of a prototype TPC are described.

Charged-particle multiplicity and transverse energy measured in32S central interactions at 200 GeV per nucleon

SummaryInteractions 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.