Shigeru Tasaka

EXPERIMENTAL DETAILS ON LIFETIME MEASUREMENTS OF NEUTRINO PRODUCED CHARMED PARTICLES IN A TAGGED EMULSION SPECTROMETER

Abstract A new type of hybrid appaatus, which consisted of an emulsion target and a magnet spectrometer, was successfully used in an experiment to measure lifetimes of charmed particles produced by the wide-band neutrino beam from 350 GeV protons at Fermilab. The emulsion target was essential to find short distance decay vertices andthe counter spectrometer was used both to localize the neutrino events in the emulsion and also to identify the particles from weak decays and those produced in the neutrino interactions. Newly introduced emulsion techniques such as the changeable sheet as a low background interface to couple the emulsion target with the counter spectrometer, and the single track followback method to locate interaction and decay vertices in the emulsion, were proved to be very powerful. Details of the experimental apparatus and of the method of analysis employed are described.

Charmed hadron production by neutrinos

Abstract Charmed hadron production has been studied using a hybrid emulsion spectrometer in the Fermilab wide-band neutrino beam. The relative rates of D0, D+, F+, and Λ+c production have been measured - the fraction of D mesons is 69 ± 8 10 % . Momentum, transverse momentum, Feynman X, and fragmentation (Z) distributions are presented. The mean Z for charmed hadrons is 0.59 ± 0.03 (±0.03). Charmed target fragments have been observed.

Cross sections for charm production by neutrinos

The production of charmed particles has been measured using a hybrid emulsion spectrometer in the Fermilab wide-band neutrino beam. The relative cross section for charged current charmed particle production is σ(v → μ−c)/σ(v → μ−) = 6.5 ±1.91.8%, and the energy dependence of the cross section is presented. One event with charm pair production was observed. A limit of σ(v → μcc)/σ(v → μc) < 6% (90% CL) is found for the ratio of charged current pair and single charm production.

Search for highly ionizing particles in e+e− annihilations at √s=50−60.8 GeV

Abstract New results are reported from a search for highly ionizing particles at the TRISTAN ring at KEK. Employing dielectric track detectors, this search is sensitive to Dirac monopoles with charge g = 68.5 e ≡ g D and g =2 g D . New upper limits are established on the production of monopoles with charge g D and mass up to 28.8 GeV/ c 2 , Cumulative results from 30.2 pb −1 data at √ s = 50−60.8 GeV are discussed.