Synopsis

Searching for Millicharged Particles

Physics 7, s146
Tiny dielectric spheres in an optical trap are used to search for hypothetical particles with a small fractional charge.
D. Moore/Stanford University

Some extensions of the standard model of particle physics predict the existence of particles with positive and negative charges far less than 1e. Searches for these so-called millicharged particles in terrestrial matter (as opposed to astrophysical environments) have so far only been sensitive to charges as small as 0.1e. Now, researchers in Giorgio Gratta’s group at Stanford University, California, have extended this search to charges with values as low as 5×10-5e by looking for their possible effect on tiny, suspended dielectric spheres in an oscillating electric field. The researchers reported that if the hypothetical particles exist, they have an abundance of no more than 2.5×10-14 per nucleon in the material tested.

In a series of repeated experiments, Gratta and his colleagues suspended a silica sphere, about 5 micrometers in diameter, in an optical trap. After carefully removing any integer charges on each sphere with ultraviolet light, they applied an ocillating voltage across the optical trap and used lasers to detect tiny deviations in the microsphere’s position that could result from electrostatic forces on the millicharged particles. The main limit to the charge sensitivity is any asphericity, or other inhomogeneity, in the silica spheres. The setup, which is sensitive to forces of less than an attonewton, could also be used to search for deviations from Newtonian gravity on length scales comparable to the size of the microspheres.

This research is published in Physical Review Letters.

–Katherine Kornei

Correction (18 December 2014): An earlier version incorrectly attributed the figure to Giorgio Gratta.


Subject Areas

Particles and Fields

Related Articles

Sterile Neutrino Down but Not Completely Out
Particles and Fields

Sterile Neutrino Down but Not Completely Out

Neutrino experiments place the most stringent limits to date on a hypothetical fourth neutrino, but the possibility that such a particle exists remains open. Read More »

Powdering Up for Neutrinos
Particles and Fields

Powdering Up for Neutrinos

The search for neutrinos from past supernovae is getting an upgrade as Japan’s Super-Kamiokande experiment begins adding gadolinium powder to its giant water-based detector. Read More »

Electron Accelerator Recycles Energy for a Brighter Beam
Particles and Fields

Electron Accelerator Recycles Energy for a Brighter Beam

A test electron accelerator reuses the energy of the particles in order to achieve a brighter beam without drawing more power from the grid. Read More »

More Articles