- th / 9 51 20 35 v 1 2 5 D ec 1 99 5 Isoscalar Roper Excitation in p ( α , α ′ ) Reactions in the 10 − 15 GeV Region

Recent experiments at Saturne at 4 GeV showed that the (α, α ′) reaction on the proton shows two distinctive peaks, which were associated to ∆ projectile excitation and Roper target excitation. A subsequent theoretical analysis has shown that this picture is qualitatively correct but there are important interference effects between the two mechanisms. Futhermore, at this energy the ratio of strengths for the Roper and ∆ peak is about 1/4. In the present paper we show that by going to the 10 − 15 GeV region the interference effects become negligible, the signal for the Roper excitation is increased by more than an order of magnitude and the ratio of cross sections at the peaks for Roper and ∆ excitation becomes of the order of unity, thus making this range of energies ideal for studies of isoscalar Roper excitation.