T. Yoneyama

Precision spectroscopy of pionic 1s states of Sn nuclei and evidence for partial restoration of chiral symmetry in the nuclear medium

Deeply bound 1s states of pi(-) in (115,119,123)Sn 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)m(-1)(pi). The observed enhancement of |b(1)| over the free piN value (b(free)1/b1=0.78+/-0.05) indicates a reduction of the chiral order parameter, f*pi(rho)2/f2pi approximately 0.64, at the normal nuclear density, rho=rho(0).

A search for deeply bound kaonic nuclear states

Abstract We have measured proton and neutron energy spectra by means of time-of-flight (TOF) from 4He( K stopped − , p / n ) reactions (KEK PS E471 experiment). In the proton spectrum, a clear mono-energetic peak was observed under semi-inclusive condition, which was assigned to the formation of a strange tribaryon S0(3115) with isospin T = 1 . The mass and width of the state were deduced to be 3117.7 −2.0 +3.8 ( syst . ) ± 0.9 ( stat . ) MeV / c 2 and 21.6 MeV / c 2 , respectively, and its main decay mode was Σ N N . In the neutron spectrum, a mono-energetic peak was found as the result of a detailed analysis, which was assigned to the formation of another kind of strange tribaryon S+(3140). The mass and width of the state were deduced to be 3140.5 −0.8 +3.0 ( syst . ) ± 2.3 ( stat . ) MeV / c 2 and 21.6 MeV / c 2 , respectively, and its main decay mode was Σ ± N N . The isospin of the state is assigned to be 0. The results are compared with recent theoretical calculations.

Experimental indication of a reduced chiral order parameter from the 1s π− state in 205Pb

Abstract The isovector potential parameter ( b 1 ) of the s -wave pion–nucleus interaction was deduced to be b 1 =−0.116 +0.015 −0.017 m π −1 by using the binding energy and width of the recently observed deeply bound 1 s π − state in 205 Pb combined with the known 1 s states of light pionic atoms. An enhancement of b 1 over the free- πN value (|−0.090|) is indicated, which may infer that the chiral order parameter (squared pion decay constant, f π 2 ) is reduced by a factor of 0.78 +0.13 −0.09 in the nuclear medium of 205 Pb where the bound π − is located. The isoscalar part is accounted for as arising mainly from a double-scattering effect, without invoking a large density-quadratic term.

Observation of Pionic 1s States in Sn Nuclei and Its Implications on Chiral Symmetry Restoration

We observed deeply bound π - is states in 1 1 5 , 1 1 9 , 1 2 3 Sn for the first time in 1 1 6 , 1 2 0 , 1 2 4 Sn(d3,He) reactions at recoil free conditions to determine the 1s binding energies and the widths precisely. A preliminary result is used to deduce the isovector scattering amplitude as b 1 = 0.115 ′ 0.005 m - 1 π . The observed enhancement of b 1 over the free πN value infers 35% reduction of f 2 π at the normal nuclear density. ρ = 0.17 fm - 3 .

Deeply bound pionic 1s states in Sn isotopes

Abstract We successfully observed deeply bound pionic 1s states in Sn isotopes ( 115 Sn, 119 Sn, 123 Sn) using the Sn( d , 3 He) pion-transfer reaction under the recoil-free condition. The 1s binding energies and widths were determined to high precision. The present results indicate that the isovector part of the s-wave pion-nucleus interaction is significantly enhanced, giving a clear evidence for partial restoration of chiral symmetry in the nuclear medium.

Deeply bound 1s and 2p pionic states in 205Pb and effective pion mass in nuclear matter

Recently we have succeeded in observing the 1s and 2p bound pionic states in 205Pb nucleus as well separated peaks in the excitation spectrum of the 206Pb(d,3He) reaction. The observed spectrum agreed quite well with the theoretical prediction where the formation cross section was calculated for the deeply bound pionic states [1]. These states are accommodated in proximity to the nuclear surface as halo states in a potential provided by the attractive Coulomb and the repulsive core. The binding energies and the widths were precisely determined, and the values were used to deduce the unknown s-wave part of the π-nucleus interaction and to translate it to the effective pion mass in nuclear matter.