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Bochum 1998 – wissenschaftliches Programm

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HK: Hadronen und Kerne

HK 5: Hadronic Probes I, Protons, Antiprotons, Pions

HK 5.3: Gruppenbericht

Montag, 16. März 1998, 15:00–15:30, C

Deeply bound pionic states and the effective π mass in lead* — •H. Gilg2, H. Geissel1, A. Gillitzer2, R.S. Hayano3, J. Homolka2, K. Itahashi3, N. Iwasa1, P. Kienle2, M. Knülle2, M. Münch2, G. Münzenberg1, K. Oyama3, W. Schott4, and T. Yamazaki51Gesellschaft für Schwerionenforschung, D-64291 Darmstadt, Germany — 2Physik-Department E12, Technische Universität München, D-85748 Garching, Germany — 3Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan — 4Physik-Department E18, Technische Universität München, D-85748 Garching, Germany — 5Institute of Particle and Nuclear Studies, High Energy Accelerator Research Organization, 3-2-1 Midori-cho, Tanashi, Tokyo 188, Japan

Recently the deeply bound pionic states (2p)π and (1s)π in 207Pb coupled to (p1/2, f5/2, p3/2)n−1 neutron hole states were discovered in an experiment performed at the GSI Fragment Separator [1]. Already in a first analysis the Q-value spectrum of the 208Pb(d,3He) reaction at Td=600MeV revealed a prominent peak at Q∼ −135.5MeV which could be attributed to the population of the (2p)π state. In the more strongly bound region a shoulder of this peak was seen at the predicted position of the (1s)π peak.

Meanwhile a more involved analysis of the data was performed, where various corrections, such as for the time dependence of the beam energy, the ion-optical aberrations of the FRS, and the long term shifts of the FRS magnetic fields, were taken into account. Due to the considerably improved instrumental resolution (δ Q ∼ 0.4MeV) the binding energy of the (1s)π state could be determined (Bπ(1s) = (7.1 ± 0.2)MeV) and more precise values for the binding energy and the width of the (2p)π state (Bπ(2p) = (5.31 ± 0.09)MeV, Γπ(2p) < 0.6MeV) were obtained. The (2p)π binding energy puts a constraint on the so far poorly known local (s-wave) part of the π-nucleus optical potential which was determined to be V0 = (19.3 ± 2.7) MeV [2] in the 207Pb nucleus.

[1] T. Yamazaki et al., Z. Phys. A355 (1996) 219

[2] T. Yamazaki et al., to be published in Phys. Lett B

*supported by BMBF (06TM365)

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