Annual modulations from secular variations: not relaxing DAMA?.

In a recent paper [arXiv:2002.00459], Buttazzo et al. show how the annually modulated rate of the DAMA experiments can be possibly interpreted as an artefact due to the interplay between a time-dependant background and the method to account for it. In this work, we compare this hypothesis against the sinusoidal dark matter signal as proposed by the DAMA collaboration. We produce in a Bayesian approach a quantitative comparison of how much the experimental observations are in support of each hypothesis. Our conclusions are that the odds against the hypothesis of a time varying background being responsible for the annual modulation are decreased by a Bayes factor larger than $10^8$ after considering the public available data of the DAMA/NaI and DAMA/LIBRA experiments. However, we agree with Buttazzo et al. that a possible time-dependant contribution of the background should be included in the fitted model. In addition, we argue that any data-taking cycle, even with a time interval different from one year, is informative and should be included in the residuals analysis by subtracting the non-zero averaged signal rate.