An induced annual modulation signature in COSINE-100 data by DAMA/LIBRA’s analysis method

Abstract

The DAMA/LIBRA collaboration has reported the observation of an annual modulation in the event rate that has been attributed to dark matter interactions over the last two decades. However, even though tremendous efforts to detect similar dark matter interactions were pursued, no definitive evidence has been observed to corroborate the DAMA/LIBRA signal. Many studies assuming various dark matter models have attempted to reconcile DAMA/LIBRA’s modulation signals and null results from other experiments, however no clear conclusion can be drawn. Apart from the dark matter hypothesis, several studies have examined the possibility that the modulation is induced by variations in detector’s environment or their specific analysis methods. In particular, a recent study presents a possible cause of the annual modulation from an analysis method adopted by the DAMA/LIBRA experiment in which the observed annual modulation could be reproduced by a slowly varying time-dependent background. Here, we study the COSINE-100 data using an analysis method similar to the one adopted by the DAMA/LIBRA experiment and observe a significant annual modulation, however the modulation phase is almost opposite to that of the DAMA/LIBRA data. Assuming the same background composition for COSINE-100 and DAMA/LIBRA, simulated experiments for the DAMA/LIBRA without dark matter signals also provide significant annual modulation with an amplitude similar to DAMA/LIBRA with opposite phase. Even though this observation does not directly explain the DAMA/LIBRA results directly, this interesting phenomenon motivates more profound studies of the time-dependent DAMA/LIBRA background data.

Dark Matter: DAMA/LIBRA and its perspectives

“…[2][3][4][5][15][16][17]19,20]. As regards the odd idea that the low-energy rate in DAMA/LIBRA might increase with time due to spill out of noise [27] , we just recall two facts that rule out this possibility: 1) the stability with time of noise, reported in several papers [2][3][4][5][15][16][17]19,20]; 2) the estimate of the remaining noise tail after the noise rejection procedure ≪ 1% [6].…”

“…Despite this obvious fact, Refs. [26,27] claim that the DAMA annual modulation result might be mimicked by the adopted analysis procedure. Detailed analyses on this argument have already been reported in Ref.…”

“…[27] claims that an annual modulation in the COSINE-100 data can appear if they use an analysis method somehow similar to DAMA/LIBRA. However, as expected from the rate of COSINE-100 very-decreasing with time and from what mentioned above, the authors obtain a modulation with reverse phase [27]; this corresponds, when fixing the phase to t 0 = 152.5 day, to NEGATIVE modulation amplitudes, as expected by the elementary considerations reported before. This artificial effect has no way to mimic the observed DM signature with its peculiarity.…”

Mass production of ultra-pure NaI powder for COSINE-200

“…However, there have been long-standing questions about this claim because no other experimental searches have observed similar signals [17]. Besides, possible spurious effects have been widely investigated, but none provides a convincing explanation of the modulation signal observed by DAMA/LIBRA [18,19].…”

Long-term temporal stability of the DarkSide-50 dark matter detector

“…[6][7][8][9][10][11][12][13][14]. DAMA's observation represents a long-standing anomaly, while other experiments adopting technologies similar to DAMA's are making progress towards definitively testing the result [15][16][17].…”