[Jlab-seminars] Today's Physics Seminar: Jan C. Bernauer; Two-photon Exchange in Proton Elastic Scattering

[Stephanie Tysor]

*Physics Seminar*

*Jan C. Bernauer*

*Massachusetts Institute of Technology*

**

/Two-photon Exchange in Proton Elastic Scattering/


Abstract:


/Recent interest in the proton electromagnetic form factors is partly 
motivated by the discrepancy found in the determination of the 
electric-to-magnetic form factor ratio using different techniques. 
Results from scattering experiments using the Rosenbluth technique 
indicate that the form factor ratio is constant as a function of $Q^2$ 
while experiments employing polarization show a clear, roughly linear, 
decline of the ratio. A possible explanation is the typically 
unaccounted for contribution of hard two-photon exchange to the 
scattering process. Theoretical calculations show large variations, many 
indicating an effect of the right sign and magnitude. Direct 
verification was sought by experiments at VEPP-3, Jefferson Lab and by 
the OLYMPUS collaboration at DESY. In the talk, I will discuss the
OLYMPUS experiment and results and summarize our current understanding 
of TPE and the proton form factors in the context of the three experiments./

//

*Friday, January 13, 2017*

*11:00 am*

*CEBAF Auditorium*

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