Details

Autor(en) / Beteiligte

• Xiong, W.
• Gasparian, A.
• Gao, H.
• Dutta, D.
• Khandaker, M.
• Liyanage, N.
• Pasyuk, E.
• Peng, C.
• Bai, X.
• Ye, L.
• Gnanvo, K.
• Gu, C.
• Levillain, M.
• Yan, X.
• Higinbotham, D. W.
• Meziane, M.
• Ye, Z.
• Adhikari, K.
• Aljawrneh, B.
• Bhatt, H.
• Bhetuwal, D.
• Brock, J.
• Burkert, V.
• Carlin, C.
• Deur, A.
• Di, D.
• Dunne, J.
• Ekanayaka, P.
• El-Fassi, L.
• Emmich, B.
• Gan, L.
• Glamazdin, O.
• Kabir, M. L.
• Karki, A.
• Keith, C.
• Kowalski, S.
• Lagerquist, V.
• Larin, I.
• Liu, T.
• Liyanage, A.
• Maxwell, J.
• Meekins, D.
• Nazeer, S. J.
• Nelyubin, V.
• Nguyen, H.
• Pedroni, R.
• Perdrisat, C.
• Pierce, J.
• Punjabi, V.
• Shabestari, M.
• Shahinyan, A.
• Silwal, R.
• Stepanyan, S.
• Subedi, A.
• Tarasov, V. V.
• Ton, N.
• Zhang, Y.
• Zhao, Z. W.

Titel

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

Ist Teil von

• Nature (London), 2019-11, Vol.575 (7781), p.147-150

Ort / Verlag

London: Nature Publishing Group UK

Erscheinungsjahr

2019

Beschreibungen/Notizen

• Elastic electron–proton scattering (e–p) and the spectroscopy of hydrogen atoms are the two methods traditionally used to determine the proton charge radius, r p . In 2010, a new method using muonic hydrogen atoms 1 found a substantial discrepancy compared with previous results 2 , 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 hydrogen 3 , 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, r p  = 0.831 ± 0.007 stat  ± 0.012 syst  femtometres, is smaller than the most recent high-precision e–p measurement 5 and 2.7 standard deviations smaller than the average of all e–p experimental results 6 . The smaller r p we have now measured supports the value found by two previous muonic hydrogen experiments 1 , 7 . In addition, our finding agrees with the revised value (announced in 2019) for the Rydberg constant 8 —one of the most accurately evaluated fundamental constants in physics. A magnetic-spectrometer-free method for electron–proton scattering data reveals a proton charge radius 2.7 standard deviations smaller than the currently accepted value from electron–proton scattering, yet consistent with other recent experiments.