High Energy / Nuclear Theory / RIKEN seminars

[CFNS seminar] Proton Radius puzzle and new results from Jefferson Lab Proton Radius (PRad) experiment

by Prof. Nilanga Liyanage (University of Virginia )

US/Eastern
Room 2-38 (Physics, Building 510 A)

Room 2-38

Physics, Building 510 A

Physics Department, Building 510 A
Description

The proton charge radius (r_p) is one of the important bench-mark  quantities in physics. Precise knowledge of its value is critically important for the understanding of the underlying quark-gluon structure of the nucleon as well as in  atomic physics, − especially in the spectroscopy of atomic hydrogen. The recent result from Lamb shift measurements from the muonic hydrogen: r_p =  0.8409(4) fm, with its unprecedented less than 0.1% precision, is currently up to eight standard deviations smaller than the average value from all previous experiments. This result  triggered  the well-known “proton radius puzzle'' in nuclear and atomic physics. So far, all theoretical efforts and more precise simulations have failed to explain this discrepancy on the value of this  fundamental quantity. This  situation urgently  requires  new high precision measurements to understand the source of the discrepancy.  The  Jefferson Lab Proton Radius (PRad) experiment collected data in 2016 for a high precision determination of the proton charge radius through the electron-proton elastic scattering process using a novel non-magnetic-spectrometer method.  Scattered electrons were detected in a high  resolution, large acceptance electromagnetic calorimeter, as well as  in a pair of large area Gas Electron Multiplier (GEM) detectors which provided precision coordinate determination. A  windowless hydrogen gas flow target was used to ensure that there was no target window background. Systematic uncertainty  in the ep cross section measurement was  controlled by  normalizing it to the simultaneously measured well known  Moller cross section. The final result from  PRad experiment has been accepted for publication in  Nature.  The  result will  be presented in this talk.

Organised by

Abha Rajan

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