corner
corner
APS » Journals » Phys. Rev. A » Volume 70 » Issue 1
< Previous Article | Next Article >

Phys. Rev. A 70, 012504 (2004) [16 pages]

Populations and lifetimes in the v=n−ℓ−1=2 and 3 metastable cascades of p̅ He+ measured by pulsed and continuous antiproton beams

Download: PDF (285 kB) Buy this article Export: BibTeX or EndNote (RIS)

M. Hori, J. Eades, E. Widmann*, and T. Yamazaki†
CERN, CH-1211 Geneva 23, Switzerland

R. S. Hayano, T. Ishikawa, and H. A. Torii‡
Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

T. von Egidy, F. J. Hartmann, B. Ketzer, C. Maierl, and R. Pohl§
Physik-Department, Technische Universität München, D-85747 Garching, Germany

M. Kumakura** and N. Morita
Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan

D. Horváth
KFKI Research Institute for Particle and Nuclear Physics, H-1525 Budapest, Hungary

I. Sugai
High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan

Received 11 October 2003; published 26 July 2004

The time evolution of the state populations in the v≡n−ℓ−1=2 and 3 metastable cascades of antiprotonic helium (p̅ 4He+) atoms were studied using laser spectroscopy. The antiprotonic states (n,ℓ)=(39,35), (40,36), and (41,37) in the v=3 cascade were estimated to initially contain, respectively, (0.28±0.04)%, (0.06±0.02)%, and (0.02±0.01)% of the antiprotons stopped in the helium target, while the corresponding values for states (37,34), (38,35), and (39,36) in the v=2 cascade were (0.21±0.04)%, (0.49±0.07)%, and (0.19±0.07)%. The shortening of the state lifetimes due to collisions between p̅ He+ and helium atoms was studied. As the atomic density of the target was increased from ρ=2×1020 to 2×1021 cm−3, the lifetime of state (37,34) decreased by an order of magnitude, whereas the higher states (38,35) and (39,35) were relatively unaffected. Between densities ρ=6×1020 and 2×1022 cm−3, a short-lived component with a time constant τ∼0.2 μs appeared at early times in the delayed annihilation time spectrum of p̅ He+, while the total fraction of long-lived antiprotons decreased from 3.0 to 2.5%. These effects were caused by the lifetime-shortening of specific p̅ He+ states such as (37,34).

© 2004 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevA.70.012504
DOI:
10.1103/PhysRevA.70.012504
PACS:
36.10.Gv, 32.70.Cs, 34.90.+q

*Present address: Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.

†Present address: RI Beam Science Laboratory, RIKEN, Wako, Saitama 351-0198, Japan.

‡Present address: Institute of Physics, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan.

§Present address: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.

**Present address: Department of Physics, Faculty of Science, Kyoto University, Kyoto 606-8502, Japan.

 
< Previous Article | Next Article >