Shrinking the Proton - Laser Spectroscopy for Nuclear Physics and fundamental Constants
16.03.2017
| Date | 16.03.2017 |
|---|---|
| Time | 16:00 |
| Place |
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| Speaker | R. Pohl |
| Area of expertise | Physics |
| Host | Dep. Physik |
| Contact | Spira |
| Abstract | 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 at PSI 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. |