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Phys. Rev. Lett. 92, 072302 (2004) [4 pages]

Precision Spectroscopy of Pionic 1s States of Sn Nuclei and Evidence for Partial Restoration of Chiral Symmetry in the Nuclear Medium

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K. Suzuki1, M. Fujita2, H. Geissel3, H. Gilg4, A. Gillitzer5, R. S. Hayano1, S. Hirenzaki2, K. Itahashi6, M. Iwasaki6, P. Kienle4,7, M. Matos3, G. Münzenberg3, T. Ohtsubo8, M. Sato9, M. Shindo1, T. Suzuki1, H. Weick3, M. Winkler3, T. Yamazaki10, and T. Yoneyama9
1Department of Physics, School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
2Department of Physics, Nara Women’s University, Kita-Uoya Nishimachi, Nara 630-8506, Japan
3Gesellschaft für Schwerionenforschung, D-64291 Darmstadt, Germany
4Physik-Department, Technische Universität München, D-85748 Garching, Germany
5Institut für Kernphysik, Forschungszentrum Jülich, D-52425 Jülich, Germany
6Muon Science Laboratory, RIKEN, 2-1 Hirosawa, Wako-shi, Saitama, 351-0198 Japan
7Institute for Medium Energy Physics of the Austrian Academy of Sciences, Boltzmanngasse 3, A-1090 Vienna, Austria
8Department of Physics, Niigata University, 2-8050, Igarashi, Niigata-shi, Niigata, 950-2181, Japan
9Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
10RI Beam Science Laboratory, RIKEN, 2-1 Hirosawa, Wako-shi, Saitama, 351-0198 Japan

Received 18 November 2002; revised 10 June 2003; published 19 February 2004

Deeply bound 1s states of π- in 115,119,123Sn were preferentially observed using the Sn(d,3He) pion-transfer reaction under the recoil-free condition. The 1s binding energies and widths were precisely determined and were used to deduce the isovector parameter of the s-wave pion-nucleus potential to be b1=-(0.115±0.007)mπ-1. The observed enhancement of |b1| over the free πN value (b1free/b1=0.78±0.05) indicates a reduction of the chiral order parameter, fπ*(ρ)2/fπ2≈0.64, at the normal nuclear density, ρ=ρ0.

© 2004 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.92.072302
DOI:
10.1103/PhysRevLett.92.072302
PACS:
13.75.Gx, 14.40.Aq, 25.45.Hi, 36.10.Gv
 
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