Search for Milli-Charged Particles at SLAC

Abstract

Particles with electric charge q Qe 10 ,3 e and masses in the range 1 1000 MeV c 2 are not excluded by present experiments or by astrophysical or cosmological arguments. A beam dump experiment uniquely suited to the detection of such milli-charged" particles has been carried out at SLAC, utilizing the short-duration pulses of the SLC electron beam to establish a tight coincidence window for the signal. The detector, a large scintillation counter sensitive to very small energy depositions, provided much greater sensitivity than previous searches. Analysis of the data leads to the exclusion of a substantial portion of the charge-mass plane. In this report, a preliminary mass-dependent upper limit is presented for the charge of milli-charged particles, ranging from Q = 1 : 7 10 ,5 at milli-charged particle mass 0.1 MeV c 2 to Q = 9 : 5 10 ,4 at 100 MeV c 2 .

Lamb shift in muonic hydrogen—II. Analysis of the discrepancy of theory and experiment

“…Some of these experiments are sensitive only to stable millicharged particles, because they depend on obtaining a signal from particle detectors, as pointed out in Ref. [49]. Several bounds have been derived regarding the mass and charge of such particles, which have otherwise been quoted as a candidate for dark matter (see Refs.…”