PHYSICAL REVIEW C VOLUME 47, NUMBER 6 JUNE 1993 Search for an g bound state in pion double charge exchange on 180 J. D. Johnson, ~ ) G. R. Burleson, ~ ) C. Edwards, ~ ) M. El-Ghossain, ~ ) M. A. Espy, &s) R. Garnett, ( ) A. Hussein, ( ) K. Johnson, ( ) C. F. Moore, ( ) C. L. Morris, ~ ) J. M. O'Donnell, ~3) M. Palarczyk, ~ ) M. Rawool-Sullivan, ~ H. Ward (1) D. Watson, ~") C. Whitley(1) and A. L. Williams~6) ~'l The University of Texas at Austin, Austin, Texas 78712 ~ lKing Fahd University of Petroleum and Minerals, Dhahran 81M1 Saudi Arabia ~ l Los Alamos National Laboratory, Los Alamos, New Mexico 875/5 ¹n Mexico State University, Ias Cruces, New Mexico 88008 ~ l University of Minnesota, Minneapolis, Minnesota 55/55 ~ l University of Pennsylvania, Philadelphia, Pennsylvania 1910$ University of York, York Y01 5DD, -United Kingdom (Received ll November 1992) The search for an g bound state in the double charge exchange (DCX) reaction to the double isobaric analog state (DIAS) O(sr+, n )' Ne(DIAS) has been carried out at LAMPF using the P channel and the LAS spectrometer. An excitation function for this reaction was measured for energies ranging from 350 to 440 MeV and for momentum transfers of 0, 105, and 210 MeV/c. The measured cross sections tend to agree with previous results for DCX on O. The measured excitation function shows some evidence for structure near the rI production threshold. PACS number(s): 25.80.Gn, 27. 20. +n Coupled-channel calculations by Bhalerao and Liu have shown that the q-X interaction is attractive for nuclei with A &12 [1]. Recent calculations by Haider and Liu [2] have predicted that a bound state between an rl and a nucleus may occur as an intermediate state in pion double charge exchange (DCX). Such an effect would compete with vr' and rl channels in the contin- uum. The existence of such a mesic nucleus would lead to a resonancelike structure in the DCX excitation function at fixed momentum transfer, due to the interference be- tween these channels. Calculations made for the reaction C(sr+, vr ) O(DIAS) predict that this structure should occur with a fluctuation ratio of (cr ~„— o~;„)/o~ „~g, 79'%%uo for DCX reactions at a momentum transfer of q = 210 MeV/c [2]. It should occur at the rl production threshold with a width on the order of 10 MeV and add to the smoothly varying continuum amplitude. It should be noted that because of the greater level density compared to C, the fluctuation ratio for 0 may be smaller. Chi- ang et al. predict that the width of the rl bound state for a nucleus like oxygen will be around 30 MeV or larger [3]. If the width is larger than the 10 MeV predicted for C then the fluctuation ratio will also be smaller. Haider and Liu [2] note that if the width is a factor of four greater than the 10 MeV expected, the fluctuation ratio should still be ~ 20%%uo at q = 210 MeV/c. For the reaction isO(~+, vr ) (DIAS) the rl threshold occurs when the rl is bound in the first nuclear orbital of rsF [2]. Taking into account the excitation energy to the isobaric analog state (T = 1) in sF, the resonance effect should be seen at 420 MeV. Lich et al. [4] have seen possible evidence of an rl bound state from studies of the reaction A(sr+, p)gA-1. How- ever, Chrien et al. [5], found no evidence of the creation of an rl bound state with width 9 MeV, but their up- per limit, for a Huctuation ratio 3 of the predicted size, is larger than that estimated by Haider and Liu. This paper reports an attempt to confirm this new type of nu- clear matter with an experiment at LAMPF devised to search for an rl-nucleus bound state in the DCX reaction O(x+, vr ) (DIAS). The excitation function for this re- action was measured for momentum transfers of q = 0, 105, and 210 MeV/c for energies ranging from T = 350 to 440 MeV. This experiment was carried out using the Large Ac- ceptance Spectrometer (LAS) in the Ps East channel at LAMPF, as configured for DCX measurements [6, 7]. The P channel was tuned for a dispersed beam with a hori- zontal dispersion of 2 cm/%, giving a beam spot of about 2. 5 cm (horizontal) x 3.5 cm (vertical) and an energy resolution of 0.15'%%uo, delivering approximately 1 — 2 x 107 pions/s to the LAS spectrometer. The LAS spectrometer consists of a C magnet, a quadrupole doublet, a 45' dipole magnet, two pairs of drift chambers, a Cherenkov detector, and two scintilla- tors. To minimize multiple scattering, helium bags were installed after the target chamber and through to the rear chamber. The C magnet was used to sweep away pro- tons and positive pions and gave a 10' horizontal bend to particles with momentum matched to the spectrom- eter. The LAS spectrometer has a momentum accep- tance of + 8'%%uo in dp/p, a horizontal angular acceptance of +3. 5', a vertical angular acceptance of +2.5, and it subtends a maximum solid angle of AA 12 msr. There was one pair of delay-line readout drift chambers located before and one pair after the dipole, which were used for 0556-2813/93/47(6)/2571(3)/$06. 00 47 2571 1993 The American Physical Society