Recent results in the search for fractional charge at Stanford

Phillips, James D.; Fairbank, W. M.; Navarro, J. E. García

doi:10.1016/0168-9002(88)91113-8

Nuclear Instruments and Methods in Physics Research Section A:

1988

DOI: 10.1016/0168-9002(88)91113-8

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Recent results in the search for fractional charge at Stanford

James D. Phillips¹,

W. M. Fairbank²,

J. E. García Navarro³

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Cited by 6 publications

(33 citation statements)

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“…PACS numbers: 95. 35.+d, 42.50.Wk Millicharged particles, i.e., particles with charge |q| = ǫe for ǫ ≪ 1, have been proposed in extensions to the Standard Model that include new, weakly coupled gauge sectors (e.g. [1]).…”

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confidence: 99%

“…[1]). It is possible that millicharged particles are a component of the universe's dark matter [2,3]. If millicharged particles exist, they could have been produced in the early universe [4] and may have formed stable bound states that can be searched for in terrestrial matter today [5,6].…”

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confidence: 99%

“…Constraints on millicharged particles exist from astrophysical and cosmological observations [7,8] as well as laboratory measurements [9][10][11][12][13]. However, such limits are typically sensitive to the mass of the particles and do not provide significant constraints for particles with mass m χ 1 GeV [7]. In contrast, searches for millicharged particles bound in bulk matter are typically insensitive to the the mass of the new particle and can probe masses ≫ 1 GeV, but suffer from significant uncertainty on the relic abundance in terrestrial materials.…”

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confidence: 99%

“…In contrast, searches for millicharged particles bound in bulk matter are typically insensitive to the the mass of the new particle and can probe masses ≫ 1 GeV, but suffer from significant uncertainty on the relic abundance in terrestrial materials. The terrestrial abundance depends on the binding and ionization rate of the particles in the early universe, as well as subsequent enrichment or depletion processes [6].…”

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confidence: 99%

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Search for Millicharged Particles Using Optically Levitated Microspheres

2014

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We report results from a search for stable particles with charge ≳10^{-5}e in bulk matter using levitated dielectric microspheres in high vacuum. No evidence for such particles was found in a total sample of 1.4 ng, providing an upper limit on the abundance per nucleon of 2.5×10^{-14} at the 95% confidence level for the material tested. These results provide the first direct search for single particles with charge ≲0.1e bound in macroscopic quantities of matter and demonstrate the ability to perform sensitive force measurements using optically levitated microspheres in vacuum.

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Search for Millicharged Particles Using Optically Levitated Microspheres

2014

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“…By comparison, drop type experiments detect the presence of fractional charge modulo one unit of fractional charge. PACS numbers: 14.80.Dq, 29.40.Wk, 78.30.Hv Although pointlike fractionally charged constituents within hadronic particles have been clearly demonstrated experimentally, searches for free fractional charge in natural materials have not yielded any substantiated positive results [1,2]. The commonly accepted theoretical view is that at least one class of fractional-charge particles (FCP) is absolutely confined in integer-charge bound states.…”

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Search for fractional-charge impurities in silicon using infrared photoionization and field ionization

et al. 1993

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A search for unconfined fractional charges in Si based on fractional-charge impurity energy-level predictions of Derkits [Phys. Rev. Lett. 45, 1374 (1980)] is described. An upper limit (95% C.L.) of 2.3xlO~~2 0 fractional charges per atom is obtained using a combination of an infrared photoionization and a field ionization technique. This optoelectronic approach has the advantage of giving an estimate for the concentration of fractional charges, being repeatable and without mechanical techniques. By comparison, drop type experiments detect the presence of fractional charge modulo one unit of fractional charge. PACS numbers: 14.80.Dq, 29.40.Wk, 78.30.Hv Although pointlike fractionally charged constituents within hadronic particles have been clearly demonstrated experimentally, searches for free fractional charge in natural materials have not yielded any substantiated positive results [1,2]. The commonly accepted theoretical view is that at least one class of fractional-charge particles (FCP) is absolutely confined in integer-charge bound states. This view has made it appear doubtful that searches for fractional charge will be successful. On the other hand, newly developed theories must be tested and some past searches may have suffered from the elimination of FCP's from samples prior to or during experiments.This new FCP detection method is based on Chaudhuri, Coon, and Derkits' prediction [3] of the existence of localized states in semiconductors associated with electrons or holes weakly bound to fractional-charge impurities (FCI's), and the integer-charge experimental results [4]. In principle, the spectrum of states of electrons or holes weakly bound to FCLs could provide an experimental signature for fractional charge which is nearly as detailed as the H2 spectrum. Fractional-charge elements [5], if they exist, would consist of quarks or quarks bound to nuclei [6] surrounded by electrons and would not be neutral.In analogy with the well-known shallow "donor" impurities in semiconductors in which an electron is weakly bound to a positive ion D=D + +e~ the existence of shallow fractional-charge donors has been predicted [3], Z)~1 /3 =Z) +2/3 -r-^-,Z)-2/3 =Z) +1/3 + ^-. For a hydrogenic system, the binding energy is (m*/ m 0 )[Z//c-] 2 x 13.6(eV). Phosphorus in Si:P is similar to a proton bound to a Si atom giving rise to shallow levels, which can be observed by infrared (IR) spectroscopy [7]. The Z 2 scaling of hydrogenic energy levels has been found to hold true in the effective mass approximation [8], suggesting that impurity levels also scale as the square of the ionic charge, including fractional ionic charge. For Z < 1 valley-orbit splitting and central cell correction are less important relative to the effective mass approximation as they scale as Z 4 [3]. Shallow levels for integer ions have been observed [4] via a \s(A\)to 2p ~ transition peak [in the photoresponse at 32 pm (38.7 meV)] using this technique. This corresponds to the experimentally observed transition energy (39.2 meV) [7] and the effec...

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Analysis and simulation of the operation of a Kelvin probe

Reasenberg¹,

Donahue

Phillips

2013

Class. Quantum Grav.

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Experiments that measure extremely small gravitational forces are often hampered by the presence of non-gravitational forces that can neither be calculated nor separately measured. Among these spurious forces is electrostatic attraction between a test mass and its surroundings due to the presence of spatially varying surface potential known as the "patch effect." In order to make surfaces with small surface potential variation, it is necessary to be able to measure it. A Kelvin probe (KP) measures contact potential difference (CPD), using the time-varying capacitance between the sample and a vibrating tip that is biased with a backing potential. Assuming that the tip remains constant, this measures the sample's surface potential variation. We examine the operation of the KP from the perspective of parameter estimation in the presence of noise. We show that, when the CPD is estimated from measurements at two separate backing potentials, the standard deviation of the optimal estimate depends on the total observing time. Further, the observing time may be unevenly divided between the two backing potentials, provided the values of those potentials are correspondingly set. We simulate a two-stage KP data analysis, including a sub-optimal estimator with advantages for real-time operation. Based on the real-time version, we present a novel approach to stabilizing the average distance of the tip from the sample. We also present the results of a series of covariance analyses that validate and bound the applicability of the suboptimal estimator, make a comparison with the results of an optimal estimator and guide the user. We discuss the application of the KP to the LISA and to a test of the weak equivalence principle.

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Recent results in the search for fractional charge at Stanford

Cited by 6 publications

References 9 publications

Search for Millicharged Particles Using Optically Levitated Microspheres

Search for Millicharged Particles Using Optically Levitated Microspheres

Search for fractional-charge impurities in silicon using infrared photoionization and field ionization

Analysis and simulation of the operation of a Kelvin probe

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