[PRad] Fwd: [Jlab-seminars] Upcoming Physics Seminars: January 13, 2017 (Jan C. Bernauer), January 20, 2017 (Randolf Pohl)

Eugene Pasyuk pasyuk at jlab.org
Fri Jan 6 11:32:26 EST 2017

There will be a seminar next Friday. It is of interest to PRad group. 


From: "Stephanie Tysor" <stysor at jlab.org> 
To: jlab-seminars at jlab.org 
Cc: "Janet Prater" <prater at jlab.org>, "Kim Kindrew" <kindrew at jlab.org> 
Sent: Friday, January 6, 2017 11:04:24 AM 
Subject: [Jlab-seminars] Upcoming Physics Seminars: January 13, 2017 (Jan C. Bernauer), January 20, 2017 (Randolf Pohl) 

Physics Seminar 

Jan C. Bernauer 

Massachusetts Institute of Technology 

Two-photon Exchange in Proton Elastic Scattering 


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 


Physics Seminar 

Randolf Pohl 

Johannes Gutenberg-University, Mainz Germany 

Max-Planck Institute of Quantum Optics, Garching Germany 

Shrinking the Proton –Laser Spectroscopy for Nuclear Physics and Fundamental Constants 

For more than a decade, the rms charge radius of the proton was known to be 
0.88fm, with about 1% uncertainty [1]. Two methods, elastic electron scattering 
and precision laser spectroscopy of atomic hydrogen, yielded consistent values. 

In 2010, our result from laser spectroscopy of the exotic "muonic hydrogen" atom 
yielded a 4% smaller value, 0.84 fm, with an uncertainty of less than 0.1% 
[2,3]. In muonic hydrogen, a negative muon orbits a proton with a 200 times 
smaller Bohr orbit than in regular hydrogen, which increases the sensitivity of 
muonic hydrogen to the proton charge radius by 200^3 ~ 10 million! 
Since 2010, the discrepancy increased to more than 7 sigmas [4], making it one 
of the biggest discrepancies in the Standard Model. 

I will discuss the so-called "proton radius puzzle" [5], report on more 
measurements in muonic atoms [6], and the result of a new measurement in regular 
atomic hydrogen. 

[1] P.J. Mohr et al. (CODATA 2006), Rev. Mod. Phys. 80, 633 (2008 ) 
[2] Pohl et al. (CREMA coll.), Nature 466, 213 (2010 ) 
[3] Antognini et al.,(CREMA coll.), Science 339, 417 (2013 ) 
[4] Olive et al. (PDG 2014), Chin. Phys. C40, 090001 (2014 ) 
[5] Pohl et al., Annu. Rev. Nucl. Part. Sci 63, 175 (2013 ) 
[6] Pohl et al. (CREMA coll.), Science 353, 669 (2016 ) 

Friday, January 20, 2017 

11:00 am 

CEBAF Auditorium 

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