M. Iwasaki

Spectroscopy of hypernuclei with stopped kaons — recent result of KEK experiment

Abstract Pion momentum spectra from K− absorption at rest on various nuclear targets were measured by means of a magnetic spectrometer with wide momentum range (100 ∼ 300 MeV/c). The ground state of Σ− hypernucleus, if well bound with a narrow width, is expected to be populated in 12C(stopped K−, π+) inclusive (untagged) spectrum, but such a peak was not observed. The spectrum is compared with the DWIA calculations by Morimatsu and Yazaki, indicating that the depth of the nuclear potential of Σ− is shallower than 12 MeV, and that its imaginary part is larger than 5 MeV if the potential depth is about 10 MeV. In the 12C(stopped K−, π−) spectrum, the ground state (( p 3 2 ) n −1 ( s 1 2 )Λ) and the excited states (( p3 2 ) n −1 ( p )Λ) of Λ12C were observed, and their formation probabilities were roughly in agreement with the results of DWIA calculations. In the π− spectra on 12C, 9Be, and 7Li targets a distinct peak was observed at 132.1±0.7 MeV/c. It is ascribed to π− from the mesic decay of Λ4H; Λ4H → 4He π−. The formation probability of Λ4H on C, Be, or Li target is much larger than those of the discrete states of Λ12C via the direct (stopped K−, π−) reaction.

Muon catalyzed fusion experiments on muonic deuterium atom deceleration in thin solid deuterium films

Abstract Muon catalyzed fusion was investigated in a series of thin solid deuterium films by detecting protons from dd fusion. Two different contributions to the total fusion yield resulting from dμ atoms emitted from a primary hydrogen layer and from incident muons directly stopped in the deuterium film itself were observed. The thickness dependence of the fusion yield suggested the importance of molecular effects in dμ elastic scattering in D 2 .

Hypernuclear spectroscopy using stopped K

Abstract Recent development of hypernuclear spectroscopy using stopped K − is described. Its characteristic features are emphasized, and preliminary experimental results as well as future plans at KEK are reported.

New aspects and new tools in hypernuclear studies: Experiments with a superconducting toroidal spectrometer

SummaryThe experimental program with a new superconducting toroidal spectrometer system which will be installed in a new low-momentum K-meson beam line at KEK is discussed based on the recent development of hypernuclear studies using stopped-K− reactions. Current topics, such as bound Σ hypernuclei, weak pionic decays of Λ hypernuclei and production of Λ hypernuclei via direct and indirect reactions, are described.RiassuntoSi discute il programma sperimentale con un nuovo sistema a spettrometro toroidale superconduttore che sarà installato in una nuova linea di fascio di mesoni K a basso impulso a KEK basandosi sugli sviluppi recenti degli studi sugli ipernuclei che utilizzano le reazioni con K− assorbito a riposo. Si descrivono gli argomenti correnti, come gli ipernuclei legati Σ, is decadimenti pionici deboli e la produzione di ipernuclei Λ mediante reazioni dirette e indirette.РеэюмеОбсуждается зкспериментальная программа на новой системе с сверхпроводяшим тороидальным спектрометром, которая установлена в новой линии на пучке K-меэонов с малым импульсом в KEK. Программа преднаэначена для исследования гиперядер, обраэованных в реакциях остановивщихся K−-меэонов. Обсуждаются свяэанные Σ-гиперядра, слабые пионные распады Λ-гиперядер и обраэование Λ-гиперядер в реэультате прямых и непрямых реакций.

Kaonic hydrogen X-ray experiment at KEK

Abstract For the further understanding of the K -N interaction in the low energy region, we are performing a measurement of K−p X rays at KEK which adopts a new technique to improve the signal-to-background ratio (S/N); specifying the final state of the K−p reaction and using a gaseous hydrogen target (4 atm at 100 K). With this technique three orders of magnitude better S/N and one order higher statistics are expected as compared to previous experiments.

Ultra-slow muon facility for surface HFI studies

A concept, a design, a construction and an account of commissioning experiments are given for the recently completed ultra-slow muon facility at the pulsed muon facility of UT-MSL/KEK. The intense (more than 103/s) slow μ+ beam with an extremely narrow phase-space volume (0.2 eV×(3 cm)2) to be produced in this facility will open a new muon science including surface physics and chemistry and fundamental atomic physics.

Antiproton trapping in various helium media: report of the HELIUMTRAP experiment at LEAR

Abstract HELIUMTRAP (PS205) investigates the recently discovered anomalously long-lived states of antiprotons in various helium media. An overview is given of experiments stopping antiprotons in several phases of helium performed at LEAR in the last two years.

A naturally occurring trap for antiprotons

The phenomenon of delayed annihilation of antiprotons in helium is the first instance of a naturally occurring trap for antimatter in ordinary matter. Recent studies of this effect at CERN are summarised, and plans are described for laser excitation experiments to test its interpretation in terms of metastable exotic helium atom formation.

Polarization of strangeness Arizona muon

The longitudinal polarization of “strangeness Arizona muon”, namely, the 236 MeV/cμ+ from the K+→μ+vμ decay, has been measured to search for right-handed weak current in the strangeness changing process. The polarization has been determined to be −0.967±0.047.