title: An improved limit on the charge of antihydrogen from stochastic acceleration.
abstract: Antimatter continues to intrigue physicists because of its apparent absence in the observable Universe. Current theory requires that matter and antimatter appeared in equal quantities after the Big Bang, but the Standard Model of particle physics offers no quantitative explanation for the apparent disappearance of half the Universe. It has recently become possible to study trapped atoms of antihydrogen to search for possible, as yet unobserved, differences in the physical behaviour of matter and antimatter. Here we consider the charge neutrality of the antihydrogen atom. By applying stochastic acceleration to trapped antihydrogen atoms, we determine an experimental bound on the antihydrogen charge, Qe, of |Q| < 0.71 parts per billion (one standard deviation), in which e is the elementary charge. This bound is a factor of 20 less than that determined from the best previous measurement of the antihydrogen charge. The electrical charge of atoms and molecules of normal matter is known to be no greater than about 10(-21)e for a diverse range of species including H2, He and SF6. Charge-parity-time symmetry and quantum anomaly cancellation demand that the charge of antihydrogen be similarly small. Thus, our measurement constitutes an improved limit and a test of fundamental aspects of the Standard Model. If we assume charge superposition and use the best measured value of the antiproton charge, then we can place a new limit on the positron charge anomaly (the relative difference between the positron and elementary charge) of about one part per billion (one standard deviation), a 25-fold reduction compared to the current best measurement.
authors.affiliation: Department of Physics, University of Liverpool, Liverpool L697ZE, UK.
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authors.lastname: Ahmadi
authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300, USA.|Centre de Recherches en Physique des Plasmas (CRPP), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
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authors.affiliation: Centre for Cold Matter, Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2AZ, UK.|Physics Department, European Organisation for Nuclear Research (CERN), CH-1211 Geneva 23, Switzerland.
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authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300, USA.
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authors.affiliation: Department of Physics, Swansea University, Swansea SA2 8PP, UK.
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authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300, USA.
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authors.affiliation: Department of Physics, Swansea University, Swansea SA2 8PP, UK.
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authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300, USA.
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authors.affiliation: Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
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authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300, USA.
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authors.affiliation: TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3, Canada.
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authors.affiliation: TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3, Canada.
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authors.affiliation: Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
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authors.affiliation: Department of Physics, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada.
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authors.affiliation: Department of Physics, Swansea University, Swansea SA2 8PP, UK.
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authors.affiliation: Physics Department, European Organisation for Nuclear Research (CERN), CH-1211 Geneva 23, Switzerland.
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authors.affiliation: Department of Physics, Swansea University, Swansea SA2 8PP, UK.
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authors.affiliation: Department of Physics, Swansea University, Swansea SA2 8PP, UK.
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authors.affiliation: Department of Physics, Swansea University, Swansea SA2 8PP, UK.
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authors.affiliation: TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3, Canada.
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authors.affiliation: TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3, Canada.
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authors.affiliation: Department of Physics, University of Liverpool, Liverpool L697ZE, UK.
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authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300, USA.
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authors.affiliation: Department of Physics, University of Liverpool, Liverpool L697ZE, UK.
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authors.affiliation: Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark.
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