Continuum polarization transfer in 500 MeV proton scattering and pionic collectivity in nuclei

Abstract

A complete set of polarization transfer observables was measured for inclusive 500 MeV proton scattering fram H, Ca(nat. ), and Pb(nat. ) at 8"& --18. 5' (q=1.75 fm '). The excitation energy ranged over the entire quasielastic peak from 20 to 100 MeV. Longitudinal and transverse spin-flip probabilities were extracted from the data. These have simple model-dependent connections to the spin-longitudinal and transverse response functians for the heavy targets. Detailed analysis of the data reveals no evidence for collective enhancement in the spin-longitudinal response function. The relation of this analysis to the interpretation of the European Muon Collaboration effect in terms of excess pions is discussed in detail.

Pion excess, nuclear correlations, and the interpretation of(p→,n→)spin transfer experiments

“…The predictions of RPA models of this collectivity [6,11] give enhanced values of this ratio at moderate excitation energies of the order of the quasifree peak. The experimental values of this ratio [7,8,9,10] do not show this collective enhancement. This lack of enhancement of the R L /R T ratio has been used as evidence for the absence of a pion excess.…”

“…This is best done by spin-transfer experiments, which separate the longitudinal and transverse response functions. A series of such experiments was carried out at LAMPF with polarized protons of about 500 MeV, first for ( p, p ′ ) scattering [7], and later for ( p, n) reactions [8,9,10]. These last are of most direct interest for us, since the nuclear response is purely isovector, allowing isolation of the pionic (longitudinal) mode.…”

Revealing nuclear pions using electron scattering

“…Such models [4] explain the shift in the valence distribution and provide also an enhanced nuclear anti-quark distribution, observable in Drell-Yan experiments [7]. However, no such enhancement was observed [8], and no substantial pionic enhancement was found in (p,n) reactions [9]. These failures to observe the influence of nuclear pions were termed a severe crisis for nuclear theory [10].…”

Polarization transfer measurements forC12(p→,nDozono1, Wakasa2, Ihara3 et al. 2009Phys. Rev. C5000View full textAdd to dashboardCite

“…scattering [15,16,17,18,19] and ( p, n) reactions [20,21,22,23,24] on various targets at intermediate energies. However, these experimental data did not show the theoretically expected enhancements.…”