Direct dark matter search by annual modulation in XMASS-I

K Abe,K Fushimi,J.S Lee,K Miuchi,Y Takeuchi,Y.D Kim,S Tasaka,M Yamashita,N.Y Kim,S Moriyama,H Sekiya,K Masuda,O Takachio,T Norita,R Kegasa,H Takiya,K Hiraide,J Liu,K.B Lee,Y Kishimoto,Y Itow,M Nakahata,Y Fukuda,M.K Lee,K Hosokawa,K Nishijima,K Martens,Naoki Oka ,Yoshihiro Suzuki ,Masaaki Kobayashi ,Hiroshi Ogawa ,Kunihiro Ichimura ,Ryuichi Fujita ,Yoon Hak Kim ,B D Xu ,Kazuyoshi Kobayashi ,B S Yang ,Yoshiaki Onishi ,Atsushi Takeda ,Shōgo Nakamura

doi:10.1016/j.physletb.2016.05.081

Abstract

A search for dark matter was conducted by looking for an annual modulation signal due to the Earth's rotation around the Sun using XMASS, a single phase liquid xenon detector. The data used for this analysis was 359.2 live days times 832 kg of exposure accumulated between November 2013 and March 2015. When we assume Weakly Interacting Massive Particle (WIMP) dark matter elastically scattering on the target nuclei, the exclusion upper limit of the WIMP-nucleon cross section 4.3$\times$10$^{-41}$cm$^2$ at 8 GeV/c$^2$ was obtained and we exclude almost all the DAMA/LIBRA allowed region in the 6 to 16 GeV/c$^2$ range at $\sim$10$^{-40}$cm$^2$. The result of a simple modulation analysis, without assuming any specific dark matter model but including electron/$\gamma$ events, showed a slight negative amplitude. The $p$-values obtained with two independent analyses are 0.014 and 0.068 for null hypothesis, respectively. we obtained 90\% C.L. upper bounds that can be used to test various models. This is the first extensive annual modulation search probing this region with an exposure comparable to DAMA/LIBRA.

Highlights

There is strong evidence that about 5 times more dark matter exists in the universe than ordinary matter
The DAMA/LIBRA experiment reported an observation of event rate annual modulation with a 9σ significance in 1.33 ton·year of data taken over 14 annual cycles with 100 to 250 kg of NaI(Tl) detectors
Their signal may be caused by light Weakly Interacting Massive Particle (WIMP), or other types of dark matter producing electrons or gamma rays

Summary

Introduction

There is strong evidence that about 5 times more dark matter exists in the universe than ordinary matter. The DAMA/LIBRA experiment reported an observation of event rate annual modulation with a 9σ significance in 1.33 ton·year of data taken over 14 annual cycles with 100 to 250 kg of NaI(Tl) detectors Their signal may be caused by light WIMPs, or other types of dark matter producing electrons or gamma rays. The signal is not observable to direct search experiments if they remove electron events In this situation, dark matter models, for instance, with interaction via dark matter-electron scattering become well motivated which produce keV energy deposition in the detector because they provide a explanation for the DAMA/LIBRA result while avoiding other direct detection constraints [14, 15, 16]. Note that XMASS tests this modulation hypothesis with almost half the energy threshold (∼ 1keV) than theirs in a different environment and underground site

The XMASS experiment

Data Analysis

Results and Discussion

Conclusions