At the Rencontres de Moriond conference today, theorist Josef Pradler of the Perimeter Institute in Ontario, Canada, presented calculations that could support evidence for dark matter in the galactic halo. The results from Pradler and his collaborators refute earlier claims that a signal observed at the Gran Sasso laboratory in Italy could have come from cosmic muons.
For 13 years the DAMA/LIBRA experiment at Gran Sasso had been scouring galaxies for signs of dark matter. Then in 2008 the 250-kilogram sodium-iodide detector revealed an 8-sigma signal, which DAMA claimed could be evidence for dark-matter particles in the galactic halo. Lately, critics have suggested these results could come from cosmic muons.
Now an analysis by Pradler and Itay Yavin of the Perimeter Institute and Spencer Chang of the University of Oregon shows the DAMA/LIBRA data is inconsistent with the cosmic-muon hypothesis. The team compared the amplitude, phase, spectral power and correlation of the DAMA result with cosmic-muon data taken with the Large Volume Detector experiment, a machine that sits right next to DAMA and measures the cosmic-ray-muon flux.
Using a correlation analysis that makes no assumptions about the functional form of the signals, they disproved the claim that the observed result came from muons. The analysis also confirmed that muons are out of phase with DAMA by approximately one month - modulations in the muon flux depend on air density, which changes seasonally in a complex interaction with temperature.
The theorists called for the DAMA collaboration to release more data to allow for a full and adequate correlation analysis.
Pradler is giving a theory seminar at CERN on 16 March.