The Asymmetry of Antimatter in the Proton

Abstract

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 for example its spin. The two up and the single down quarks that comprise the proton in the simplest picture account only for a few percent 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 where 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, since their masses are quite similar and small compared to the mass of the proton. In the present manuscript, we show evidence from muon pair production measurements that these distributions are significantly different, with more abundant down antimatter quarks than up antimatter quarks over a wide range of momentum. These results revive interest in several proposed mechanisms as the origin of this antimatter asymmetry in the proton that had been disfavored by the previous results and point to the future measurements that can distinguish between these mechanisms.

10 pages, 5 figures, 5 tables; Matches published version

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Cited by in corpus (37)

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• Lepton-Charge and Forward-Backward Asymmetries in Drell-Yan Processes for Precision Electroweak Measurements and New Physics Searches
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• Hadronic structure on the light-front V. Diquarks, Nucleons and multiquark Fock components
• Pineline: Industrialization of High-Energy Theory Predictions
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• Strangeness content of the pion in the U(3) Nambu-Jona-Lasinio model
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• Generalized parton distributions of sea quarks in the proton from nonlocal chiral effective theory
• Transverse Momentum and Transverse Momentum Distributions in the MIT Bag Model
• Hadron Structure using Continuum Schwinger Function Methods
• BASE-STEP: A transportable antiproton reservoir for fundamental interaction studies
• Extraction of the neutron F2 structure function from inclusive proton and deuteron deep-inelastic scattering data
• Pions in Proton Structure and Everywhere Else
• Connected and Disconnected Sea Partons from CT18 Parametrization of PDFs
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• Investigations on the flavor-dependent axial charges of the octet baryons
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• Effect of color reconnection on multiplicity dependent charged particle production in Pythia-generated $pp$ collisions at the LHC energies
• Flavor asymmetry from the non-perturbative nucleon sea
• Planck Formula for the Gluon Parton Distribution in the Proton
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• Probing nucleon spin structure in deep-inelastic scattering, proton-proton collisions and Drell-Yan processes
• The quark orbital angular momentum of ground state octet baryons
• Non-perturbative flavor asymmetry in the nucleon and deuteron: The light-front Hamiltonian effective field theory approach
• Bayesian Monte Carlo extraction of sea asymmetry with SeaQuest and STAR data
• Determination of the parton distribution functions of the proton using diverse ATLAS data from $pp$ collisions at $\sqrt{s}=7$, 8 and 13 TeV
• Constraints on the $U(1{)}_{B-L}$ model from global QCD analysis