A new measurement of the structure functions P_LL - P_TT/ ε and P_LT in virtual Compton scattering at Q² = 0.33 (GeV/c)²

The cross-section of the ep -> e'p'gamma reaction has been measured at Q(2) = 0.33 (GeV/c)(2). The experiment was performed using the electron beam of the MAMI accelerator and the standard detector setup of the A1 Collaboration. The cross-section is analyzed using the low-energy theorem for virtual Compton scattering, yielding a new determination of the two structure functions P-LL-P-TT/epsilon and P-LT which are linear combinations of the generalized polarizabilities of the proton. We find somewhat larger values than in the previous investigation at the same Q(2). This difference, however, is purely due to our more refined analysis of the data. The results tend to confirm the non-trivial Q(2)-evolution of the generalized polarizabilities and call for more measurements in the low-Q(2) region (<= 1 (GeV/c)(2)).