Issam Qattan, Northwestern U. and ANL Physics
Precision Rosenbluth Measurements and Their Constraints on Two-photon Exchange Effects
Physics Division Seminar - 15 Nov 2004

The electromagnetic structure of the proton is parameterized in terms of the electric and magnetic form factors. The ratio of the electric to magnetic form factors of the proton has been extracted using a new, high precision, Rosenbluth technique with uncertainties comparable to or better than the Jefferson Lab's recoil polarization measurements. The results of these measurements confirm the discrepancy between the results obtained by the conventional Rosenbluth and by polarization transfer measurements which can not be attributed to experimental error. Theoretical estimates indicate that this discrepancy might be due to two-photon exchange (TPE) effects. In addition to confirming the discrepancy, these improved Rosenbluth extractions can be used to study TPE effects. They provide improved limits on deviation from linearity of the reduced cross section. In addition, precise Rosenbluth data permits the quantitative assessment of any calculations that purport to reconcile the results from the two techniques. The impact of these results on our knowledge of the proton form factors will be discussed.

ANL Physics Division Seminar Schedule