A small proton charge radius from an electron–proton scattering experiment

W. Xiong, A. Gasparian (), H. Gao, D. Dutta (), M. Khandaker, N. Liyanage, E. Pasyuk, C. Peng, X. Bai, L. Ye, K. Gnanvo, C. Gu, M. Levillain, X. Yan, D. W. Higinbotham, M. Meziane, Z. Ye, K. Adhikari, B. Aljawrneh, H. Bhatt, D. Bhetuwal, J. Brock, V. Burkert, C. Carlin, A. Deur, D. Di, J. Dunne, P. Ekanayaka, L. El-Fassi, B. Emmich, L. Gan, O. Glamazdin, M. L. Kabir, A. Karki, C. Keith, S. Kowalski, V. Lagerquist, I. Larin, T. Liu, A. Liyanage, J. Maxwell, D. Meekins, S. J. Nazeer, V. Nelyubin, H. Nguyen, R. Pedroni, C. Perdrisat, J. Pierce, V. Punjabi, M. Shabestari, A. Shahinyan, R. Silwal, S. Stepanyan, A. Subedi, V. V. Tarasov, N. Ton, Y. Zhang and Z. W. Zhao
Additional contact information
W. Xiong: Duke University and Triangle Universities Nuclear Laboratory
A. Gasparian: North Carolina A&T State University
H. Gao: Duke University and Triangle Universities Nuclear Laboratory
D. Dutta: Mississippi State University
M. Khandaker: Idaho State University
N. Liyanage: University of Virginia
E. Pasyuk: Thomas Jefferson National Accelerator Facility
C. Peng: Duke University and Triangle Universities Nuclear Laboratory
X. Bai: University of Virginia
L. Ye: Mississippi State University
K. Gnanvo: University of Virginia
C. Gu: Duke University and Triangle Universities Nuclear Laboratory
M. Levillain: North Carolina A&T State University
X. Yan: Duke University and Triangle Universities Nuclear Laboratory
D. W. Higinbotham: Thomas Jefferson National Accelerator Facility
M. Meziane: Duke University and Triangle Universities Nuclear Laboratory
Z. Ye: Duke University and Triangle Universities Nuclear Laboratory
K. Adhikari: Mississippi State University
B. Aljawrneh: North Carolina A&T State University
H. Bhatt: Mississippi State University
D. Bhetuwal: Mississippi State University
J. Brock: Thomas Jefferson National Accelerator Facility
V. Burkert: Thomas Jefferson National Accelerator Facility
C. Carlin: Thomas Jefferson National Accelerator Facility
A. Deur: Thomas Jefferson National Accelerator Facility
D. Di: University of Virginia
J. Dunne: Mississippi State University
P. Ekanayaka: Mississippi State University
L. El-Fassi: Mississippi State University
B. Emmich: Mississippi State University
L. Gan: University of North Carolina
O. Glamazdin: Kharkov Institute of Physics and Technology
M. L. Kabir: Mississippi State University
A. Karki: Mississippi State University
C. Keith: Thomas Jefferson National Accelerator Facility
S. Kowalski: Massachusetts Institute of Technology
V. Lagerquist: Old Dominion University
I. Larin: Alikhanov Institute for Theoretical and Experimental Physics NRC “Kurchatov Institute”
T. Liu: Duke University and Triangle Universities Nuclear Laboratory
A. Liyanage: Hampton University
J. Maxwell: Thomas Jefferson National Accelerator Facility
D. Meekins: Thomas Jefferson National Accelerator Facility
S. J. Nazeer: Hampton University
V. Nelyubin: University of Virginia
H. Nguyen: University of Virginia
R. Pedroni: North Carolina A&T State University
C. Perdrisat: College of William and Mary
J. Pierce: Thomas Jefferson National Accelerator Facility
V. Punjabi: Norfolk State University
M. Shabestari: Mississippi State University
A. Shahinyan: Yerevan Physics Institute
R. Silwal: Massachusetts Institute of Technology
S. Stepanyan: Thomas Jefferson National Accelerator Facility
A. Subedi: Mississippi State University
V. V. Tarasov: Alikhanov Institute for Theoretical and Experimental Physics NRC “Kurchatov Institute”
N. Ton: University of Virginia
Y. Zhang: Duke University and Triangle Universities Nuclear Laboratory
Z. W. Zhao: Duke University and Triangle Universities Nuclear Laboratory

Nature, 2019, vol. 575, issue 7781, 147-150

Abstract: Abstract Elastic electron–proton scattering (e–p) and the spectroscopy of hydrogen atoms are the two methods traditionally used to determine the proton charge radius, rp. In 2010, a new method using muonic hydrogen atoms1 found a substantial discrepancy compared with previous results2, which became known as the ‘proton radius puzzle’. Despite experimental and theoretical efforts, the puzzle remains unresolved. In fact, there is a discrepancy between the two most recent spectroscopic measurements conducted on ordinary hydrogen3,4. Here we report on the proton charge radius experiment at Jefferson Laboratory (PRad), a high-precision e–p experiment that was established after the discrepancy was identified. We used a magnetic-spectrometer-free method along with a windowless hydrogen gas target, which overcame several limitations of previous e–p experiments and enabled measurements at very small forward-scattering angles. Our result, rp = 0.831 ± 0.007stat ± 0.012syst femtometres, is smaller than the most recent high-precision e–p measurement5 and 2.7 standard deviations smaller than the average of all e–p experimental results6. The smaller rp we have now measured supports the value found by two previous muonic hydrogen experiments1,7. In addition, our finding agrees with the revised value (announced in 2019) for the Rydberg constant8—one of the most accurately evaluated fundamental constants in physics.

Date: 2019
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DOI: 10.1038/s41586-019-1721-2

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