Direct observation limits on antimatter gravitation

Fischler, M.; Lykken, J.; Roberts, T.

doi:10.2172/935492

Cited by 15 publications

(18 citation statements)

References 23 publications

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“…For instance, one such argument comes from the absence of anomalies in Eötvös experiments conducted with differing atoms4; the differing number of virtual particle–antiparticle pairs in such atoms might have caused gravitational anomalies to occur. However, all of these arguments are indirect and are not universally accepted11121314; they rely on assumptions about the gravitational interactions of virtual antimatter, on postulates such as CPT invariance, or on other theoretical premises. Although these arguments may well be correct, in a world in which physicists have only recently discovered that we cannot account for most of the matter and energy in the universe, it would be presumptuous to categorically assert that the gravitational mass of antimatter necessarily equals its inertial mass.…”

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confidence: 99%

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Description and first application of a new technique to measure the gravitational mass of antihydrogen

Ashkezari²,

et al. 2013

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Physicists have long wondered whether the gravitational interactions between matter and antimatter might be different from those between matter and itself. Although there are many indirect indications that no such differences exist and that the weak equivalence principle holds, there have been no direct, free-fall style, experimental tests of gravity on antimatter. Here we describe a novel direct test methodology; we search for a propensity for antihydrogen atoms to fall downward when released from the ALPHA antihydrogen trap. In the absence of systematic errors, we can reject ratios of the gravitational to inertial mass of antihydrogen >75 at a statistical significance level of 5%; worst-case systematic errors increase the minimum rejection ratio to 110. A similar search places somewhat tighter bounds on a negative gravitational mass, that is, on antigravity. This methodology, coupled with ongoing experimental improvements, should allow us to bound the ratio within the more interesting near equivalence regime.

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confidence: 99%

“…There have not yet been any direct14, free-fall or gravitational balance, tests of the gravitational interactions of observable matter and antimatter. Direct gravitational experiments with non-neutral antimatter, for example, isolated positrons or antiprotons, are exceedingly difficult because the electrical forces overwhelm the gravitational forces17.…”

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confidence: 99%

Description and first application of a new technique to measure the gravitational mass of antihydrogen

Ashkezari²,

et al. 2013

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“…Fortunately, the exponential 2 The only published direct test so far [4] has yielded the limit −65 <ḡ/g < 110. 3 For example, some authors [39][40][41][42] have suggested that antimatter be identified with the r < 0 solutions of GR's Kerr-Newman equation; in this caseḡ = −g would be the expected GR result. 4 This also suggests a solution to what has been called "the worst prediction in physics": that the gravitational zero-point energy of the universe seems to exceed the size of the cosmological constant by a factor ∼ 10 120 [43].…”

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confidence: 99%

Studying Antimatter Gravity with Muonium

Antognini

Kaplan

Kirch

et al. 2018

Atoms

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The gravitational acceleration of antimatter,ḡ, has yet to be directly measured; an unexpected outcome of its measurement could change our understanding of gravity, the universe, and the possibility of a fifth force. Three avenues are apparent for such a measurement: antihydrogen, positronium, and muonium, the last requiring a precision atom interferometer and novel muonium beam under development. The interferometer and its few-picometer alignment and calibration systems appear feasible. With 100 nm grating pitch, measurements ofḡ to 10%, 1%, or better can be envisioned. These could constitute the first gravitational measurements of leptonic matter, of 2 nd -generation matter, and possibly, of antimatter.And we note that arguments based on absolute gravitational potentials have been critiqued by Nieto and Goldman [2].Atoms 2018, xx, x 2 of 14 on quite general grounds [2]. 2 Such a measurement can be viewed as a test of general relativity or as a search for a fifth force and is of interest from both perspectives.Although the equivalence principle experiments indicate that nuclear binding energy gravitates in the same way as ordinary mass, absent validated models of gravity at a subnuclear scale, it is unclear how the gravitational interactions of virtual matter should be treated. Use of a pure-leptonic atom, such as positronium or muonium, evades these complexities. Moreover, no measurement has yet been made of the gravitational force on second-or third-generation matter or antimatter (although, with some assumptions, stringent limits can be obtained from neutral-meson oscillations, especially for K 0 -K 0 [14]). Since direct gravitational measurements on other higher-generation particles, such as hyperons, τ leptons, and c or b hadrons, appear impractical due to their short lifetimes, muonium may be the only access we have. Recent work [15][16][17] examining a possible standard-model extension emphasizes the importance of second-generation gravitational measurements. Current interest in "fifth force" models [18,19] (stimulated by evident anomalies in the leptonic decays of B mesons) also supports more detailed investigations of muonium.General relativity (GR) is generally taken to predict identical behaviors of antimatter and matter in a gravitational field. With the observation of gravitational waves [20], most of the predictions of GR are now experimentally confirmed. Nevertheless, GR is fundamentally incompatible with quantum mechanics, and the search for a quantum theory of gravity continues [21]. To date, the experimental evidence on which to base such a theory comes from observations of matter-matter and matter-light interactions. In a quantum field theory, matter-matter and matter-antimatter forces can differ -for example, suppressed scalar and vector terms might cancel in matter-matter interactions, but add in matter-antimatter ones [2], leading to small equivalence principle violations. Matter-antimatter measurements could thus play a key role.While most physicists expect that the equivalence principle a...

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“…Indeed, there has not yet been any direct experimental observations 4 of the effect of gravity, for example, the gravitational acceleration in the field of the Earth, on antimatter [24,25]. This is perhaps surprising, given that charged antiparticles have been available since the 1930s.…”

Section: Gravitational Interaction Between Matter and Antimattermentioning

confidence: 99%

Detection of Trapped Antihydrogen

Hydomako

2013

Springer Theses

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The ALPHA experiment is an international effort to produce, trap, and perform precision spectroscopic measurements on antihydrogen (the bound state of a positron and an antiproton). Based at the Antiproton Decelerator (AD) facility at CERN, the ALPHA experiment has recently magnetically confined antihydrogen atoms for the first time. A crucial element in the observation of trapped antihydrogen is ALPHA's silicon vertexing detector. This detector contains sixty silicon modules arranged in three concentric layers, and is able to determine the three-dimensional location of the annihilation of an antihydrogen atom by reconstructing the trajectories of the produced annihilation products.This dissertation focuses mainly on the methods used to reconstruct the annihilation location. Specifically, the software algorithms used to identify and extrapolate charged particle tracks are presented along with the routines used to estimate the annihilation location from the convergence of the identified tracks. It is shown that these methods can determine the annihilation location with a spatial resolution between about 0.6 to 0.8 cm (depending on the coordinate being measured). Furthermore, a robust analysis to identify and reduce cosmic ray background events is described. The cosmic ray background can obscure the trapped antihydrogen signal, and its suppression leads to a significant increase in the annihilation detection sensitivity. The background suppression analysis involves examining the reconstructed detector event based on several selection criteria, including: the number of charged particle tracks, the radial vertex position, and a fit of a straight line to the event hit positions. By carefully optimizing these criteria, (99.54 ± 0.02)% of cosmic ray events are rejected, while (64.4 ± 0.1)% of antihydrogen annihilation events are retained. Finally, the experimental results demonstrating the first-ever magnetic confinement of antihydrogen atoms are presented. These results rely heavily on the silicon i detector, and as such, the role of the annihilation vertex reconstruction is emphasized.

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Direct observation limits on antimatter gravitation

Cited by 15 publications

References 23 publications

Description and first application of a new technique to measure the gravitational mass of antihydrogen

Description and first application of a new technique to measure the gravitational mass of antihydrogen

Studying Antimatter Gravity with Muonium

Detection of Trapped Antihydrogen

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