[Halld-physics] Mass radius of the proton

[Mark-Macrae Dalton]

Dear Colleagues,

There will be a talk tomorrow on the mass radius of the proton extracted from GlueX data.

Best,
Mark




Date: Thursday, Mar. 4 at 4:00 PM EST
Venue: https://bluejeans.com/240467456/5520<https://urldefense.proofpoint.com/v2/url?u=https-3A__bluejeans.com_240467456_5520&d=DwMFaQ&c=CJqEzB1piLOyyvZjb8YUQw&r=XZ-uzdYsDwJAJMSlBfjvRw&m=JnZJO6XcT3lbja3TEX531hl92lzWSBpc1OplAdsK0Ac&s=q5fkfwVKbBKtuFzw2dTA0VK2XvT3T5MDygr2-kk6EBM&e=>
Meeting ID: 240 467 456
Participant Passcode: 5520
Webpage: https://www.stonybrook.edu/cfns/activities/seminars.php<https://urldefense.proofpoint.com/v2/url?u=https-3A__www.stonybrook.edu_cfns_activities_seminars.php&d=DwMFaQ&c=CJqEzB1piLOyyvZjb8YUQw&r=XZ-uzdYsDwJAJMSlBfjvRw&m=JnZJO6XcT3lbja3TEX531hl92lzWSBpc1OplAdsK0Ac&s=yft-NG8cwvv87aDKEQeE5tguPdIgzZzXzXxSAmOg2-U&e=>
Presented by: Prof. Dmitri Kharzeev, SBU and BNL

Title: Mass radius of the proton

Abstract:

The mass radius is a fundamental property of the proton that so far has not been determined from experiment. Basing on my recent paper arXiv:2102:00110, I will show that the mass radius of the proton can be rigorously defined through the formfactor of the trace of the energy-momentum tensor (EMT) of QCD in the weak gravitational field approximation, as appropriate for this problem. I will then demonstrate that the scale anomaly of QCD enables the extraction of the formfactor of the trace of the EMT from the data on threshold photoproduction of J/ψ and Υ quarkonia, and use the recent GlueX Collaboration data to extract the r.m.s. mass radius of the proton R_m = 0.55 ± 0.03 fm. The extracted mass radius is significantly smaller than the r.m.s. charge radius of the proton R_C = 0.8409 ± 0.0004 fm. I will discuss the possible origin of this difference, and outline future measurements at JLab, RHIC and EIC that should enable a more precise determination.

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