Rencontres de Moriond EW 2012: Theorists disprove one claim against DAMA/LIBRA

Josef Pradler, a theorist from the Perimeter Institute in Canada presented today at the Moriond conference new calculations that could disprove the main criticism of the DAMA oscillation data: the phenomenon cannot be produced by cosmic muons.


For more than 13 annual cycles, the DAMA experiment has been accumulating data in the Gran Sasso laboratory, looking for signs of dark matter. The ~250 kg NaI detector has revealed a 8-sigma modulated signal that stands unchallenged. Lately, though, several people have questioned the results, suggesting that the observed modulation could be due to cosmic muons.

Josef Pradler and his colleagues Spencer Chang (University of Oregon) and Itay Yavin (McMaster University and Perimeter Institute) just published a new analysis that shows in fact that the DAMA/LIBRA data is inconsistent with the cosmic muon hypothesis with 99% CL.

They compared the amplitude, phase, spectral power and correlation of cosmic muon data taken with the LVD (Large Volume Detector) experiment, an apparatus that measured the cosmic ray muon flux and that sits next to DAMA in the Gran Sasso laboratory. Especially using a correlation analysis that does not make any assumptions on a functional form of the signals, they could disprove the claim the observed signal came from muons. The analysis also confirmed that muons are out of phase with DAMA by approximately one month.

The modulations in the muon flux depend on air density that fluctuates seasonally with temperature with a fairly complex variability. The theorists therefore emphasise that it would be important for the DAMA collaboration to release the full time-series of their data to allow for an adequate and full correlation analysis.

Josef Pradler will be giving a Theory seminar at CERN next Friday, 16 March.

by Pauline Gagnon