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The asymmetry of antimatter in the proton

Dove, J. and Kerns, B. and McClellan, R. E. and Miyasaka, S. and Morton, D. H. and Nagai, K. and Prasad, S. and Sanftl, F. and Scott, M. B. C. and Tadepalli, A. S. and Aidala, C. A. and Arrington, J. and Ayuso, C. and Barker, C. L. and Brown, C. N. and Chang, W. C. and Chen, A. and Christian, D. C. and Dannowitz, B. P. and Daugherity, M. and Diefenthaler, M. and El Fassi, L. and Geesaman, D. F. and Gilman, R. and Goto, Y. and Guo, L. and Guo, R. and Hague, T. J. and Holt, R. J. and Isenhower, D. and Kinney, E. R. and Kitts, N. and Klein, A. and Kleinjan, D. W. and Kudo, Y. and Leung, C. and Lin, P.-J. and Liu, K. and Liu, M. X. and Lorenzon, W. and Makins, N. C. R. and Mesquita de Medeiros, M. and McGaughey, P. L. and Miyachi, Y. and Mooney, I. and Nakahara, K. and Nakano, K. and Nara, S. and Peng, J.-C. and Puckett, A. J. and Ramson, B. J. and Reimer, P. E. and Rubin, J. G. and Sawada, S. and Sawada, T. and Shibata, T.-A. and Su, D. and Teo, M. and Tice, B. G. and Towell, R. S. and Uemura, S. and Watson, S. and Wang, S. G. and Wickes, A. B. and Wu, J. and Xi, Z. and Ye, Z. (2021) The asymmetry of antimatter in the proton. Nature, 590 (7847). pp. 561-565. ISSN 0028-0836.

[img] Image (JPEG) (Extended Data Fig. 1: Comparison of NuSea and SeaQuest data with NLO calculations) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 2: Extrapolation to zero intensity) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 3: Reconstructed invariant mass spectra) - Supplemental Material
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[img] Image (JPEG) (Extended Data Table 1: Ratios σ_D/(2σ_H) as a function of P_T) - Supplemental Material
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[img] Image (JPEG) (Extended Data Table 2: Ratios σ_D/(2σ_H) as a function of M) - Supplemental Material
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[img] Image (JPEG) (Extended Data Table 3: Spectrometer acceptance) - Supplemental Material
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The fundamental building blocks of the proton—quarks and gluons—have been known for decades. However, we still have an incomplete theoretical and experimental understanding of how these particles and their dynamics give rise to the quantum bound state of the proton and its physical properties, such as its spin. The two up quarks and the single down quark that comprise the proton in the simplest picture account only for a few per cent of the proton mass, the bulk of which is in the form of quark kinetic and potential energy and gluon energy from the strong force. An essential feature of this force, as described by quantum chromodynamics, is its ability to create matter–antimatter quark pairs inside the proton that exist only for a very short time. Their fleeting existence makes the antimatter quarks within protons difficult to study, but their existence is discernible in reactions in which a matter–antimatter quark pair annihilates. In this picture of quark–antiquark creation by the strong force, the probability distributions as a function of momentum for the presence of up and down antimatter quarks should be nearly identical, given that their masses are very similar and small compared to the mass of the proton. Here we provide evidence from muon pair production measurements that these distributions are considerably different, with more abundant down antimatter quarks than up antimatter quarks over a wide range of momenta. These results are expected to revive interest in several proposed mechanisms for the origin of this antimatter asymmetry in the proton that had been disfavoured by previous results, and point to future measurements that can distinguish between these mechanisms.

Item Type:Article
Related URLs:
URLURL TypeDescription ReadCube access
Daugherity, M.0000-0002-1781-9077
Diefenthaler, M.0000-0002-4717-4484
Goto, Y.0000-0002-2973-7458
Kinney, E. R.0000-0002-4176-5283
Leung, C.0000-0001-7907-3728
Liu, K.0000-0002-6676-8165
Reimer, P. E.0000-0002-0301-2176
Rubin, J. G.0000-0002-9408-297X
Sawada, S.0000-0002-7122-1690
Sawada, T.0000-0001-5726-7150
Su, D.0000-0002-8381-7846
Towell, R. S.0000-0003-3640-7008
Uemura, S.0000-0003-3458-4625
Wang, S. G.0000-0001-8474-9817
Ye, Z.0000-0002-1873-2344
Additional Information:© 2021 Nature Publishing Group. Received 02 June 2020; Accepted 15 December 2020; Published 24 February 2021. We thank G. T. Garvey for contributions to the early stages of this experiment. We also thank the Fermilab Accelerator Division and Particle Physics Division for their support of this experiment. This work was performed by the SeaQuest Collaboration, whose work was supported in part by the US Department of Energy under grants DE-AC02-06CH11357, DE-FG02-07ER41528, DE-SC0006963; the US National Science Foundation under grants PHY 0969239, PHY 1306126, PHY 1452636, PHY 1505458, PHY 1614456; the DP&A and ORED at Mississippi State University; the JSPS (Japan) KAKENHI through grant numbers 21244028, 25247037, 25800133; the Tokyo Tech Global COE Program, Japan; the Yamada Science Foundation of Japan; and the Ministry of Science and Technology (MOST), Taiwan. Fermilab is operated by Fermi Research Alliance, LLC, under contract number DE-AC02-07CH11359 with the US Department of Energy. Data availability: Raw data were generated at the Fermi National Accelerator Laboratory. Derived data supporting the findings of this study are available from the corresponding author upon request. Author Contributions: P.E.R. and D.F.G. are the co-spokespersons for the experiment. The entire SeaQuest Collaboration constructed the experiment and participated in the data collection and analysis. Substantial contributions to the cross-section ratio analysis were made by graduate students J.D., B.K., R.E.M., S.M., D.H.M., K. Nagai, S.P., F.S., M.B.C.S. and A.S.T. The development of the technique of extrapolation to zero intensity greatly benefited from the work of A.S.T. All authors reviewed the manuscript. The authors declare no competing interests. Peer review information: Nature thanks Gerald Miller, Gunar Schnell and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Funding AgencyGrant Number
Department of Energy (DOE)DE-AC02-06CH11357
Department of Energy (DOE)DE-FG02-07ER41528
Department of Energy (DOE)DE-SC0006963
Mississippi State UniversityUNSPECIFIED
Japan Society for the Promotion of Science (JSPS)21244028
Japan Society for the Promotion of Science (JSPS)25247037
Japan Society for the Promotion of Science (JSPS)25800133
Tokyo Tech Global COE ProgramUNSPECIFIED
Yamada Science FoundationUNSPECIFIED
Ministry of Science and Technology (Taipei)UNSPECIFIED
Department of Energy (DOE)DE-AC02-07CH11359
Subject Keywords:Experimental nuclear physics; Experimental particle physics
Issue or Number:7847
Record Number:CaltechAUTHORS:20210302-070239792
Persistent URL:
Official Citation:Dove, J., Kerns, B., McClellan, R.E. et al. The asymmetry of antimatter in the proton. Nature 590, 561–565 (2021).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108261
Deposited By: Tony Diaz
Deposited On:02 Mar 2021 19:00
Last Modified:02 Mar 2021 19:00

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