Past Seminars Seminários Já Decorridos 2010

Laser Spectroscopy of the Lamb-Shift in Muonic Hydrogen – Determination of the Proton Radius

By: Joaquim dos Santos
From: Univ. Coimbra
At: Instituto de Investigação Interdisciplinar, Anfiteatro
[2010-11-25] 11:30

The measurement of the Lamb-shift in muonic hydrogen was achieved successfully, at last. We have measured the energy splitting in μp with an experimental accuracy of 15 ppm, twice better than our proposed goal. Using today’s QED calculations for the fine-, hyperfine, QED and finite size contributions we obtain a root-mean square proton charge radius of rp= 0.84184 (67) fm. This value is ten times more precise, but 5 standard deviations smaller, than the value of 2006 CODATA. The cause of this discrepancy is not known and the scientific community is at present concentrating efforts to solve “the proton radius puzzle”, finding out the reasons for such difference.

The importance of this discovery justified its publication in “Nature”, being even chosen for the cover of the respective volume. The experiment was developed throughout one decade in the “Hollywood movie” type, “everything goes wrong until the very last five minutes before the END” and it is an example that, by pushing the limits of technology, one may reach results well beyond the initially established goals.