ISOSCALAR ROPER EXCITATION IN P(ALPHA,ALPHA') REACTIONS IN THE 10-15 GEV REGION

Recent experiments at Saturne at 4 GeV showed that the (alpha, alpha') reaction on the proton shows two distinctive peaks, which were associ ated to Delta projectile excitation and Roper target excitation. A sub sequent theoretical analysis has shown that this picture is qualitativ ely correct but there are important interference effects between the t wo mechanisms. Furthermore, at this energy the ratio of strengths for the Roper and Delta peak is about 1/4. In the present paper we argue t hat by going to the 10-15 GeV region the interference effects become n egligible, the signal for the Roper excitation is increased by more th an an order of magnitude and the ratio of cross sections at the peaks for Roper and Delta excitation becomes of the order of unity, thus mak ing this range of energies very appropriate for studies of isoscalar R oper excitation.