WFU Physics Colloquium

TITLE: The Size of the Proton: How Big is It?

SPEAKER: Professor Ashot Gasparian ,

TIME: Wednesday January 16, 2013 at 4:00 PM

PLACE: Room 101 Olin Physical Laboratory

The proton is the primary building block of the visible Universe and, its charge radius (R_p) is one of the most fundamental quantities in physics. Precision knowledge of its value is critically important for the understanding of the underlying quark-gluon structure of the nucleon in the theory of strong interactions. The precise determination of R_p is also critical for atomic physics - especially in the spectroscopy of atomic hydrogen. In the past, three major methods have been used to measure R_p: (a) ep-elastic scattering experiments; (b) Lamb shift measurements from the electronic hydrogen atom; and (c) Lamb shift measurements from the muonic hydrogen atom. Very recently, a new result from the studies of muonic hydrogen was published that provides a factor of ten more precise value (R_p=0.84184 (67 fm)) than all previous experiments. With its unprecedented less than 0.1% precision, it is currently up to seven standard deviation smaller than the average value from all previous experiments, triggering the well-known "proton charge radius crisis". in nuclear and atomic physics. In this talk I will discuss the methods and the recent experiments for R_p, as well as, the recent proposal developed by our group, for a new independent experiment to address this "crisis" in physics.