Deeply bound pionic atoms

Deeply bound pionic atom state was discovered at GSI, Darmstadt in 1996 using (d, 3He) reaction on heavy element (Pb, Sn). The precisely-determined π-nucleus potential lead to a unique determination of a reduction of the quark condensation in a nuclear medium by ~35% [1]. In order to further improve an experimental precision and hence to better constrain the theoretical scenario of the dynamical generation of hadron masses from spontaneously broken chiral symmetry, a new series of experiments is proposed to make use of high intensity deuteron beam which became recently available at the new RI Beam Facility and the fragment separator (BigRIPS) at RIKEN, Japan. In the short pilot experiment in 2010, primarily meant to develop the required special  momentum-matching beam optics, we succeeded to collect an equivalent statistics as the preceding GSI experiment and observed deeply-bound 1s, 2s, 2p peaks of 121Sn for the very first time. We also succeeded to observe an angular dependence of the production of the deeply- bound states in the (d, 3He) reaction for the first time thanks to the large angular acceptance of the BigRIPS. The successful pilot experiment lead naturally the project to go on for a further systematic study. An isotonic scan on N=68 line as well as an isotopic scan on Z=50 line (Sn) are intended, that will reduce the biggest uncertainty in the analysis of the preceding experiment, the uncertainty of the neutron density distributions of the core nucleus. In 2013 we presented the result of 2010 run at an international conference [2], as well as we worked on a preparation for the main beamtime anticipated in the May 2014.

[1] K. Suzuki et al., Precision Spectroscopy of Pionic 1s state of Sn Nuclei and Evidence for Partial Restoration of Chiral Symmetry in the Nuclear Medium, Phys. Rev. Lett. 92 (2004) 072302.
[2] Hadron 2013, XV International Conference on Hadron Spectroscopy, Nara, Japan.