Examining the time dependence of DAMA’s modulation amplitude

Abstract If dark matter is composed of weakly interacting particles, Earth’s orbital motion may induce a small annual variation in the rate at which these particles interact in a terrestrial detector. The DAMA collaboration has identified at a $$9.3\sigma $$ 9.3σ confidence level such an annual modu...

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Main Authors: Chris Kelso, Christopher Savage, Pearl Sandick, Katherine Freese, Paolo Gondolo
Format: Article
Language:English
Published: SpringerOpen 2018-03-01
Series:European Physical Journal C: Particles and Fields
Online Access:http://link.springer.com/article/10.1140/epjc/s10052-018-5685-4
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author Chris Kelso
Christopher Savage
Pearl Sandick
Katherine Freese
Paolo Gondolo
author_facet Chris Kelso
Christopher Savage
Pearl Sandick
Katherine Freese
Paolo Gondolo
author_sort Chris Kelso
collection DOAJ
description Abstract If dark matter is composed of weakly interacting particles, Earth’s orbital motion may induce a small annual variation in the rate at which these particles interact in a terrestrial detector. The DAMA collaboration has identified at a $$9.3\sigma $$ 9.3σ confidence level such an annual modulation in their event rate over two detector iterations, DAMA/NaI and DAMA/LIBRA, each with $$\sim 7$$ ∼7 years of observations. This data is well fit by a constant modulation amplitude for the two iterations of the experiment. We statistically examine the time dependence of the modulation amplitudes, which “by eye” appear to be decreasing with time in certain energy ranges. We perform a chi-squared goodness of fit test of the average modulation amplitudes measured by the two detector iterations which rejects the hypothesis of a consistent modulation amplitude at greater than 80, 96, and 99.6% for the 2–4, 2–5 and 2–6 keVee energy ranges, respectively. We also find that among the 14 annual cycles there are three $$\gtrsim 3\sigma $$ ≳3σ departures from the average in our estimated data in the 5–6 keVee energy range. In addition, we examined several phenomenological models for the time dependence of the modulation amplitude. Using a maximum likelihood test, we find that descriptions of the modulation amplitude as decreasing with time are preferred over a constant modulation amplitude at anywhere between $$1\sigma $$ 1σ and $$3\sigma $$ 3σ , depending on the phenomenological model for the time dependence and the signal energy range considered. A time dependent modulation amplitude is not expected for a dark matter signal, at least for dark matter halo morphologies consistent with the DAMA signal. New data from DAMA/LIBRA–phase2 will certainly aid in determining whether any apparent time dependence is a real effect or a statistical fluctuation.
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spelling doaj.art-ab5f1e3e38024a17b6b75a51e2fcec112022-12-22T03:50:26ZengSpringerOpenEuropean Physical Journal C: Particles and Fields1434-60441434-60522018-03-017831910.1140/epjc/s10052-018-5685-4Examining the time dependence of DAMA’s modulation amplitudeChris Kelso0Christopher Savage1Pearl Sandick2Katherine Freese3Paolo Gondolo4Department of Physics, University of North FloridaLeinweber Center for Theoretical Physics, Department of Physics, University of MichiganDepartment of Physics and Astronomy, University of UtahLeinweber Center for Theoretical Physics, Department of Physics, University of MichiganDepartment of Physics and Astronomy, University of UtahAbstract If dark matter is composed of weakly interacting particles, Earth’s orbital motion may induce a small annual variation in the rate at which these particles interact in a terrestrial detector. The DAMA collaboration has identified at a $$9.3\sigma $$ 9.3σ confidence level such an annual modulation in their event rate over two detector iterations, DAMA/NaI and DAMA/LIBRA, each with $$\sim 7$$ ∼7 years of observations. This data is well fit by a constant modulation amplitude for the two iterations of the experiment. We statistically examine the time dependence of the modulation amplitudes, which “by eye” appear to be decreasing with time in certain energy ranges. We perform a chi-squared goodness of fit test of the average modulation amplitudes measured by the two detector iterations which rejects the hypothesis of a consistent modulation amplitude at greater than 80, 96, and 99.6% for the 2–4, 2–5 and 2–6 keVee energy ranges, respectively. We also find that among the 14 annual cycles there are three $$\gtrsim 3\sigma $$ ≳3σ departures from the average in our estimated data in the 5–6 keVee energy range. In addition, we examined several phenomenological models for the time dependence of the modulation amplitude. Using a maximum likelihood test, we find that descriptions of the modulation amplitude as decreasing with time are preferred over a constant modulation amplitude at anywhere between $$1\sigma $$ 1σ and $$3\sigma $$ 3σ , depending on the phenomenological model for the time dependence and the signal energy range considered. A time dependent modulation amplitude is not expected for a dark matter signal, at least for dark matter halo morphologies consistent with the DAMA signal. New data from DAMA/LIBRA–phase2 will certainly aid in determining whether any apparent time dependence is a real effect or a statistical fluctuation.http://link.springer.com/article/10.1140/epjc/s10052-018-5685-4
spellingShingle Chris Kelso
Christopher Savage
Pearl Sandick
Katherine Freese
Paolo Gondolo
Examining the time dependence of DAMA’s modulation amplitude
European Physical Journal C: Particles and Fields
title Examining the time dependence of DAMA’s modulation amplitude
title_full Examining the time dependence of DAMA’s modulation amplitude
title_fullStr Examining the time dependence of DAMA’s modulation amplitude
title_full_unstemmed Examining the time dependence of DAMA’s modulation amplitude
title_short Examining the time dependence of DAMA’s modulation amplitude
title_sort examining the time dependence of dama s modulation amplitude
url http://link.springer.com/article/10.1140/epjc/s10052-018-5685-4
work_keys_str_mv AT chriskelso examiningthetimedependenceofdamasmodulationamplitude
AT christophersavage examiningthetimedependenceofdamasmodulationamplitude
AT pearlsandick examiningthetimedependenceofdamasmodulationamplitude
AT katherinefreese examiningthetimedependenceofdamasmodulationamplitude
AT paologondolo examiningthetimedependenceofdamasmodulationamplitude