Synopsis: Dark Matter or Neutrons?

The previously observed signal from a direct-dark-matter-detection search may instead be due to neutrons generated from solar neutrinos and atmospheric muons.

Dark matter, inferred to exist on the basis of the dynamics of galaxies, has never been conclusively detected in a direct way. The DAMA/LIBRA experiment in Italy is one of several ongoing searches for dark-matter particles interacting with ordinary matter. The collaboration has recently reported a modulation in their data with a period of one year, consistent with a dark-matter-related signal. However, new calculations published in Physical Review Letters suggest that such a signal may instead be caused by neutrons created by solar neutrinos and atmospheric muons.

DAMA/LIBRA focuses on measuring annual modulations in dark-matter flux caused by the combined motion of the Earth around the Sun and of the Solar System within the Galaxy. Researchers have observed a temporal variation in their data that exhibits a peak in late May, as expected if signals were due to dark-matter particles originating from the Milky Way’s dark-matter halo. But DAMA/LIBRA’s interpretation of dark matter requires a particle-interaction cross section and mass that are ruled out by other dark-matter experiments. This fact prompted Jonathan Davis at Durham University (UK) to propose an alternative explanation for the DAMA/LIBRA signal. Davis’s calculations show that the combined effect of both solar neutrinos and atmospheric muons could be responsible for the signal; the neutrinos and muons impinge on the lead shielding of DAMA/LIBRA and the surrounding rock and liberate neutrons, which then interact with heavy nuclei to produce recoil events that mimic those arising from dark-matter interactions.

The flux of atmospheric muons has been shown to vary with a period of approximately the Solar activity cycle (i.e., about 11 years). Additional DAMA/LIBRA data over a longer time baseline are necessary to look for a sign (or lack thereof) of such a periodic mode. – Katherine Kornei


Features

More Features »

Announcements

More Announcements »

Subject Areas

Particles and FieldsAstrophysics

Previous Synopsis

Materials Science

Self-Replicating Cracks

Read More »

Next Synopsis

Related Articles

Synopsis: Space Measurements of Secondary Cosmic Rays
Astrophysics

Synopsis: Space Measurements of Secondary Cosmic Rays

New data from the International Space Station shed light on how secondary cosmic rays propagate through space. Read More »

Focus: Detecting Gravitational Waves by Watching Stars
Astrophysics

Focus: Detecting Gravitational Waves by Watching Stars

A passing gravitational wave produces shifts in the apparent positions of the stars, and these motions should be detectable with the Gaia space telescope. Read More »

Viewpoint: Reining in Alternative Gravity
Astrophysics

Viewpoint: Reining in Alternative Gravity

Theorists have tightly constrained alternative theories of gravity using the recent joint detection of gravitational waves and light from a neutron star merger. Read More »

More Articles