Hadron Medium Modifications

Proton recoil polarization in quasielastic electron scattering is a powerful tool to study properties of nucleons bound in the nuclear medium. The most precise results have been obtained at Jefferson Lab in the 4 He(e, e ′ p ) 3 H reaction at four momentumtransfers of Q 2 = 0.8 (GeV/ c ) 2 and at 1.3 (GeV/ c ) 2 . The ratio of polarization-transfer components, P ′ x / P ′ z , is significantly reduced compared to the ratio obtained in elastic 1 H(e, e ′ p ) scattering. This depletion is well described with models which include in-medium modifications of the proton form factor or, alternatively, by strong charge-exchange final-state interactions. A future experiment will measure the dependence of this effect on the momentum of the struck nucleon in both, the 4 He(e, e ′ p ) 3 H and 2 H(e, e ′ p ) n reactions.