TY - JOUR
T1 - Instrumentation for laser-induced annihilation spectroscopy of metastable antiprotonic helium atoms
AU - Torii, H. A.
AU - Hayano, R. S.
AU - Maas, F. E.
AU - Morita, N.
AU - Kumakura, M.
AU - Yamazaki, T.
AU - Masuda, H.
AU - Sugai, I.
AU - Ketzer, B.
AU - Hartmann, F. J.
AU - Daniel, H.
AU - Von Egidy, T.
AU - Müller, W.
AU - Schmid, W.
AU - Horváth, D.
AU - Eades, J.
AU - Widmann, E.
N1 - Funding Information:
We are deeply indebted to the LEAR and PS staff at CERN for their tireless dedicationt o providing us with the precious antiprotonb eam, and to T. Morimoto for invaluable help in designing the experimentals etup. The simulation program for the energy loss and the trajectorieso f antiprotonsw as provided by M. Iwasaki. The presentw ork is supportedb y the Grants-in-Aid (JSPS) for Specially Pro-motedR esearcha nd for InternationalS cientific Researcho f the JapaneseM inistry of Education, Science and Culture, the Japan Society for the Promotion of Science (JSPS), the German Bundesministeriumf tir Forschung und Technolo-gie and the HungarianN ational Science Foundation.F .E.M. and H.A.T acknowledges upporto f INOUE foundationa nd JSPS. respectively.
PY - 1997/9/1
Y1 - 1997/9/1
N2 - We have established a technique for laser resonance spectroscopy of metastable antiprotonic helium atoms (pHe+) by successfully observing laser-induced annihilation. In this paper, we describe the full instrumentation of the experiment in detail, namely, the particle detectors, the laser system, the cryostat and the helium gas target, the data acquisition and analysis method. For an effective laser triggering selective to 3% metastable antiprotons, a highly efficient detection system for antiproton annihilation was required, with a suppressed inefficiency of less than a percent. Guided by simulations, we designed a system of seven lead-scintillator sandwich counters to detect the charged pions and π0-decay gamma rays from antiproton annihilation, and achieved 99.7 ± 0.1% efficiency for the detection of annihilation. We employed two identical sets of excimer-pumped dye laser systems with 2-5 mJ output energy per pulse, which were triggered by every metastable antiproton formed in a helium gas target of 0.3-1.0 bar at 4.5-10 K. The resonant deexcitation of the metastable states was detected as a spike-like forced annihilation in the time spectrum, thus revealing the level structure of this exotic atom. This powerful technique enabled us to study also the lifetimes and populations of specific metastable states, by changing the timing and the wavelengths of the laser pulses.
AB - We have established a technique for laser resonance spectroscopy of metastable antiprotonic helium atoms (pHe+) by successfully observing laser-induced annihilation. In this paper, we describe the full instrumentation of the experiment in detail, namely, the particle detectors, the laser system, the cryostat and the helium gas target, the data acquisition and analysis method. For an effective laser triggering selective to 3% metastable antiprotons, a highly efficient detection system for antiproton annihilation was required, with a suppressed inefficiency of less than a percent. Guided by simulations, we designed a system of seven lead-scintillator sandwich counters to detect the charged pions and π0-decay gamma rays from antiproton annihilation, and achieved 99.7 ± 0.1% efficiency for the detection of annihilation. We employed two identical sets of excimer-pumped dye laser systems with 2-5 mJ output energy per pulse, which were triggered by every metastable antiproton formed in a helium gas target of 0.3-1.0 bar at 4.5-10 K. The resonant deexcitation of the metastable states was detected as a spike-like forced annihilation in the time spectrum, thus revealing the level structure of this exotic atom. This powerful technique enabled us to study also the lifetimes and populations of specific metastable states, by changing the timing and the wavelengths of the laser pulses.
KW - Antiprotonic helium atom
KW - Delayed annihilation time spectrum
KW - Laser spectroscopy
KW - Laser-induced resonant annihilation
KW - Metastable state
KW - Shower counter
UR - https://www.scopus.com/pages/publications/0031236683
U2 - 10.1016/S0168-9002(97)00741-9
DO - 10.1016/S0168-9002(97)00741-9
M3 - Article
AN - SCOPUS:0031236683
SN - 0168-9002
VL - 396
SP - 257
EP - 271
JO - Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
JF - Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
IS - 1-2
ER -