A small proton charge radius from an electron–proton scattering experiment. 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. Nature, 575(7781):147–150, 2019.
doi  abstract   bibtex   
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.
@article{xiong_small_2019,
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.},
author = {Xiong, W. and Gasparian, A. and Gao, H. and Dutta, D. and Khandaker, M. and Liyanage, N. and Pasyuk, E. and Peng, C. and Bai, X. and Ye, L. and Gnanvo, K. and Gu, C. and Levillain, M. and Yan, X. and Higinbotham, D. W. and Meziane, M. and Ye, Z. and Adhikari, K. and Aljawrneh, B. and Bhatt, H. and Bhetuwal, D. and Brock, J. and Burkert, V. and Carlin, C. and Deur, A. and Di, D. and Dunne, J. and Ekanayaka, P. and El-Fassi, L. and Emmich, B. and Gan, L. and Glamazdin, O. and Kabir, M. L. and Karki, A. and Keith, C. and Kowalski, S. and Lagerquist, V. and Larin, I. and Liu, T. and Liyanage, A. and Maxwell, J. and Meekins, D. and Nazeer, S. J. and Nelyubin, V. and Nguyen, H. and Pedroni, R. and Perdrisat, C. and Pierce, J. and Punjabi, V. and Shabestari, M. and Shahinyan, A. and Silwal, R. and Stepanyan, S. and Subedi, A. and Tarasov, V. V. and Ton, N. and Zhang, Y. and Zhao, Z. W.},
doi = {10.1038/s41586-019-1721-2},
issn = {14764687},
journal = {Nature},
number = {7781},
pages = {147--150},
pmid = {31695211},
title = {{A small proton charge radius from an electron–proton scattering experiment}},
volume = {575},
year = {2019}
}

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