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The first attempt to measure both the longitudinal and transverse spin-isospin responses was carried out at the High-Resolution Spectrometer (HRS) at the Los Alamos Meson Physics Facility (LAMPF) using a 500 MeV polarized proton beam on and targets at q = 1.75 . The results are reported in [Car84]. The outgoing protons were momentum analyzed in the HRS and the polarization observables measured with the use of a focal plane polarimeter. See [McC84] for details on this technique.

Figure: Ratio of IVSL to IVST response functions for at q = 1.75 and = 500 MeV. The dashed line shows the Alberico et al. calculations [AEM82] at full nuclear density; the dotted line, at half nuclear density. [Car84]

The results of the HRS experiment are shown in figure gif. The ratio () is consistent with unity for this experiment and does not show the enhancement expected from calculations. For reference the predicted response ratios are shown on figure gif for calculations at full- and half- nuclear density. The prediction for half nuclear density was considered because at 500 MeV nucleon-nucleus scattering tends to be peaked at the surface of the nucleus where the nuclear density is decreasing. However, even with the density correction the data obviously does not confirm the predictions of Alberico et al. [AEM82]. This was the first indication from quasifree nucleon scattering that the nuclear pion field did not show the enhancement expected. However, the results should be considered with some skepticism since the probe is not the perfect probe of spin-isospin densities. The interaction has a large isoscalar component which is not easily separable from the isovector part of the interaction.

Michael A. Lisa
Tue Apr 1 08:52:10 EST 1997