Isoscalar quadrupole strength in 40Ca from the (p,p′α 0) reaction at Ep = 100 MeV

Abstract

The 40Ca(p,p′ α) reaction has been studied at an incident proton energy E p = 99.5 MeV for proton laboratory scattering angles Θ p lab = 17°, 23° and 27°. Emission of α particles coincident with the scattered proton has been measured for an angular range Θ α ⋍ 0° − 180° relative to the recoil axis. A multipole decomposition for the α 0-decay channel to the 36Ar ground state has been performed from the angular-correlation functions. The energy distribution of the dominating E2 strength deduced in the excitation energy range E x = 11–21 MeV agrees reasonably well with the results from electron and α-induced α 0-decay investigations. The exhaustion of the E2 energy-weighted sum rule in this channel up to an energy of 17 MeV is 16.1(4.0)%, in accord with the study of the (α, α′ α 0) reaction. However, this value is twice what is found in the (e,e′ α 0) experiment in the same energy region. Thus, the puzzling discrepancy in the E2 strengths derived from electromagnetic and hadronic probes remains unsolved.