PoS(ICHEP2020)643 2 c / 99.99% https://pos.sissa.it/ > 6 GeV < 휒 푚 ∗ 푎, [email protected] 98% C.L., respectively. These results correspond to the best sensitivities at > Speaker ∗ among WIMP AM measurements. Institute of Physics, Academia Sinica, Taipei E-mail: We present results on light weakly interactingmodulation massive (AM) particle analysis (WIMP) on searches data [1] from withthe a annual CDEX-1B 1-kg experiment mass at p-type the point-contact China germaniumregions Jinping detector implied Underground of by Laboratory. the DAMA/LIBRA The and CoGeNT 90% AM-based C.L. analysis allowed are excluded at and Copyright owned by the author(s) under the terms of the Creative Commons 푎 © Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). 40th International Conference on High EnergyJuly physics 28 - - ICHEP2020 August 6, 2020 Prague, Czech Republic (virtual meeting) Hau-Bin Li (on behalf of CDEX Collaboration) New Limits on WIMP Dark MatterAnalysis from of Annual the Modulation CDEX Experiment atUnderground the Laboratory China Jinping PoS(ICHEP2020)643 -N) 휒 1.4 keVee. PCGe) [15] − 푝 -N can provide 휒 -N rates have distinctive 휒 from AM-based analysis of 휎 ) is a favored candidate of dark 휒 and 2.2 휎 Hau-Bin Li (on behalf of CDEX Collaboration) 2 -type point contact germanium detectors ( 푝 PCGe target of mass 1 kg (fiducial mass of 939 g, after 푝 0.12 mm surface layer) was shielded with 20 cm of copper, 20 cm of ± ) polyethylene room with wall thickness of 1 m. The target was enclosed 푊 -N candidate events with time is demonstrated in1 Fig. with the bulk event count 4 m( 휒 × . ) 2 퐿 c / . 8 m( 휒 × 4.2 yr), with the total exposure of 1107.5 kg-day. ) 푚 8 GeV ∼ 퐻 The Weakly Interacting Massive Particle (WIMP, denoted as Positive results were concluded at significance of 12.9 The CDEX-1B experiment is the second phase of the CDEX experiment and has previously The 4.2 yr of CDEX-1B data are separated into 35 subdatasets in different time bins, each with Stability of The only requirement for AM analysis is to have stable background with time. The modeling The CDEX experiments, located in the China Jinping Underground Laboratory (CJPL) with = 휒 -N recoil spectral analysis [16]. The 휒 푚 New Limits on WIMPJinping Dark Underground Matter Laboratory from Annual Modulation Analysis of the CDEX Experiment at the China matter (DM). The direct laboratory searches of WIMPs can be probed by WIMP-nucleus ( elastic scattering. Within the astrophysical dark matter halo model, the given the upper limits for spin-independent (SI) and spin-dependent (SD) cross sections by the annual modulation (AM) feature withEarth’s maximum motion intensity relative at to to June the andsmoking-gun galaxy signatures a dark for period WIMPs matter of independent distribution. 1 of AM background yr modeling. analysis due of to the for dark matter direct detection. Thewith low germanium analysis can threshold complement of the aboutallowed 200 liquid parameter eVee space xenon implies of results. AM DAMA/LIBRA and studies CoGeNT It andlower provides extends the an reach alternative of probe AM test to to the lower corrections due to a 0.88 polyethylene and 20 cm of lead,6 m( from inside to outside. The whole setup was assembled inside a about 1 month of live time. WIMPbasic candidate cuts events in and the bulk the of the bulkdone detector by or are likelihood selected surface fitting via of (B/S) some the events(PDFs) bulk discrimination. and or has surface no rise-time The cut distribution B/S efficiency probability associated correction density [16]. functions procedure is rates after B/S correction at three energy ranges which are mostof relevant their to the origins sensitivities andspectral at spectral analysis, is shapes, not whichcontribution involved. plus are an exponentially sources time-dependent We background of adopted contributionfrom from cosmogenic a uncertainties the isotopes. L-shell scenario The in x-rays expected time of dependence the duecontributions the to time-integrated the was cosmogenic time-independent origin background observed. background It dominated the background in energy ranges of 1.0 by an NaI(Tl) anti-Compton detectorsubsequently from without September NaI(Tl) 27, (replaced 2014December by 2, to 2018 passive August (Run-2). 2, copper The 201716, gaps shielding) from 2016 (Run-1), from December to and 27, August June 2014 02, 4, toThe 2016 March two runs 2017 8, were have 2015 751.3 due till and and to 428.1 from live calibrationdays days, March ( respectively, with and together neutron span gamma-ray a total sources, of respectively. 1527 calendar about 2400 m of rock overburden, utilizes DAMA/LIBRA [2,3] and CoGeNT [4]were experiments, challenged respectively. by However, integrated these rate interpretations 10], experiments with ionization liquid germanium xenon [5–7], [11]XMASS-1 cryogenic detectors [12] bolometer and [8– and XENON100 [13, were14] probed experiments as and well. excluded by AM analysis from PoS(ICHEP2020)643 (1) 0.8 keVee, < , 1800 1800 1800 2 )) ) 휙 − 푗 1600 1600 1600 푦푟 푡 푇 ( Time (days) 휋 2 ( Run 2 corresponding to the respective bin 1400 1400 1400 푐표푠 푖 푖 푗푘 퐴 푛 Zn, with intensities fixed by the measured 2 푖 푗푘 − of individual energy bins are treated inde- Δ 65 1200 1200 1200 푖푘 푖 퐵 퐴 Run 1 Hau-Bin Li (on behalf of CDEX Collaboration) − 3 Ga and 1000 1000 1000 푖 푗푘 analysis was performed simultaneously, with 푃 68 2 휒 − Ge, 800 800 800 푖 푗푘 68 푛 (fixed at 1 year) are, respectively, the modulation phase and is the time-varying background contributions of the L-shell ( 푦푟 is the background level, in which we adopted a time-independent 푖 푗푘 푇 푁 Time 푃 푖푘 600 600 600 ∑︁ ∈ are the combined statistical and systematic errors dominated by the 푗 퐵 2 푖 푗푘 Run 2 ∈ ∑︁ Δ 푘 400 400 400 = 10.8 keV, 2 푖 1.8 keVee, respectively, according to the requirements of statistical accuracy 휒 − energy bin, a minimum > 5.8 keVee were analyzed, below the region of internal K-shell X-rays. The 0.65 - 0.85 keV 0.45 - 0.65 keV 0.25 - 0.45 keV 0.25 - 0.45 − 200 200 200 th 푖

1 1 1 -N rates were treated as a component of the constant background in AM analysis. 2 3 2 2 3

1.5 2.5 1.5 0.5 2.5 1.5 2.5 휒 Counts day Counts kg

-1 -1 =(energy, time, run). The B/S corrected bulk event counts versus time at three energy ranges, where the shaded area (fixed at 152.5 days) and 휙 푖, 푗, 푘 1.6 keVee and The data are first studied with a model-independent analysis without invoking astrophysical Data at 0.25 For each of − K-shell X-rays at 8.5 models and parameters. The modulation amplitude background scenario, and B/S correction [16]. There are in total 40 energy bins, with 35 time bins divided into 2 runs. with X-rays from long-lived isotopes such as where period. The corrected counts of bulk events are denoted by selected energy-bin-sizes are 50 eVee, 100 eVee and 200 eVee for measured energy at Figure 1: denotes the period of gammabin source size calibration. is adopted A in bin the size analysis. of 200 eVee is used in thisThe plot, time-independent while different background levels ofwere every uncorrelated energy between bin Run-1 wereunmodulated and taken Run-2 as due free to parameters the and different shielding configurations. The 0.8 in B/S correction. New Limits on WIMPJinping Dark Underground Matter Laboratory from Annual Modulation Analysis of the CDEX Experiment at the China PoS(ICHEP2020)643 ), 휒 푚 1319 / are de- 20 between are then . 푆퐼 2 휒 휎 푆퐼 휎 are shown in 1330 = value = 0.14. 2 푝 1280 휒 ( / 2 47 . cm km/s, an Earth’s velocity 41 , and the uncertainty of K/L − 1280 푆퐼 10 . The difference in = 544 휎 f )× distribution at . = o 2 . 5 43 1320 . 휒 d / 1 } km/s and local dark matter density / 푒푠푐 ) 2 푖 ± 휐 27 . Energy (keVee) are correlated with a known function of 휒 푦푟 37 푖 푇 . Í 퐴 0 )/ . The distributions show consistency with null 1330 푖 = 휙 (− 퐴 4 = f Hau-Bin Li (on behalf of CDEX Collaboration) − . = f 푡 o 4 . ( . o 푆퐼 d 휋 . . / 휎 2 d 휒 (Na-recoil) [2,3, 18 ] and CoGeNT [4] experiments, 2 ( / is 푚 휒 휒 2 98% C.L., respectively. The DAMA/LIBRA high- 2 휒 > 푚 c 푐표푠 at 90% C.L. The upper limits at 90% C.L. on 3 / 2 15 + cm CoGeNT 90% CDMS-II DAMA/LIBRA 90% (phase-1, Na-recoil) DAMA/LIBRA 90% CDEX-1B GeV 41 − at different 232 is consistent with null results, showing no evidence of modulation =7.9 of Eq. (1), The Unified Approach [21] is then used to place the upper 푖 10 ={ 휒 푆퐼 2 99.99% and 2 푖 퐴 × 퐸 휎 푚 휒 > 휐 99 . Í 1 km/s, a galactic escape velocity of < . Quenching factor of Ge is derived by the TRIM software package [20] with ) 3 푆퐼 1 220 휎 cm 2 = c and bin-size, while the function is related to the applied astrophysics models. Data are 0 /( Best-fit solutions of modulation amplitude 휐 퐸 , 1 1 GeV 0 3 2 4

푆퐼 −

The best-fit solution at For the model-dependent analysis, the individual The B/S discrimination contributes less than 8% deviation of 휎 kg (keV Count ) day

, -1 -1 -1 휒 푚 Figure 2: of 0.3 valuated by minimizing bounds of positive definite pendently, from which the best-fit results a 10% systematic error adopted for the analysis. Best-fit values of unconstrained results, i.e., no significantfor modulation all signatures. energy For ranges. illustrationDAMA/LIBRA (Na-recoil) purpose, [18] Derived and we best-fit adopted modulation modulationsuperimposed. 200 signals amplitudes eVee of A from bin-size CDMS-II bin distributed size 90% of results C.L. 200 [19] eVee are allowed is used region in of this plot, CoGeNT while different [4, bin17], size is adopted in the analysis. New Limits on WIMPJinping Dark Underground Matter Laboratory from Annual Modulation Analysis of the CDEX Experiment at the China 2.Fig. The distribution of behavior. The null hypothesis test gavenull a hypothesis and independent-amplitude analysis is within then analyzed under the standardspeed spherical of isothermal galactic halo model, with a most probable related to dark matter of or equivalently, rived and shown in3. Fig. The resultsanalysis refute of the 90% DAMA/LIBRA-phase C.L. 1 allowed regions low- inferredproviding from an AM-based exclusion at region (I-recoil) is not probed in this analysis. PoS(ICHEP2020)643 Phys. Phys. , , Eur. Phys. J. C , ) (2010) 39. 2 67 20 (GeV/c χ m , blue: 90% C.L.) [2,3, 18] and CoGeNT Eur. Phys. J. C 휎

, CDEX-1B time-integrated CDEX-1B & 90% (2019) 221301. σ Hau-Bin Li (on behalf of CDEX Collaboration) 5 123 10 (2013) 012002. 9

88 CDEX-1B Modulation (this work) (this Modulation CDEX-1B 8 7 Phys. Rev. Lett. , 6 Phys. Rev. D , 5 CoGeNT: A search for low-mass dark matter using p-type point contact Final model independent result of DAMA/LIBRA-phase1 New results from DAMA/LIBRA Results from a search for dark matter in the complete LUX exposure Search for light weakly-interacting-massive-particle dark matter by annual Dark matter search results from a one ton-year exposure of XENON1T (2018) 111302. XMASS 2018 (2017) 021303. CoGeNT 90% DAMA/LIBRA phase-1, Na-recoil: 5 4 121 118 Limits at 90% C.L. from CDEX-1B AM-analysis (red) on spin-independent WIMP-nucleon cross

(2013) 2648. 41 40

− −

SI 10 10 73 germanium detectors Rev. Lett. modulation analysis with a point-contact germaniumUnderground detector Laboratory at the China Jinping Rev. Lett.

(cm ) σ 2 [3] R. Bernabei et al., [5] E. Aprile et al., [4] C.E. Aalseth et al., [6] D.S. Akerib et al., [2] R. Bernabei et al., [1] L.T. Yang et al., References (green: 90% C.L.) [4].(black Constraints dotted from line) the as CDEX-1B comparison. time-integrated spectral analysis [16] are displayed Figure 3: section. Also shownallowed are regions other of AM-based DAMA/LIBRA results: (Na-recoil, 90% pale C.L. blue: upper 5 limits of XMASS-1 (dark-gray) [12], New Limits on WIMPJinping Dark Underground Matter Laboratory from Annual Modulation Analysis of the CDEX Experiment at the China ratios is also incorporated in the systematic uncertainty budget. PoS(ICHEP2020)643 , J. , Phys. , Phys. , (2018) (2016) IEEE , 42 116 , (2004) 1027. Chin. Phys. C , Phys. Rev. Lett. 219 , Hau-Bin Li (on behalf of CDEX Collaboration) 6 (2016) 092003. 93 . Unified approach to the classical statistical analysis of (1998) 3873. Nucl. Instr. Meth. Phys. Res. B , (2009) 010. (2016) 25. 57 (2017) 101101. 04 Phys. Rev. D 76 , (2018) 102006. 118 (2014) 241302. (1989) 926. . Search for an annual modulation in three years of CoGeNT dark matter Results on light dark matter particles with a low-threshold CRESST-II 97 SRIM-2003 New results from the search for low-mass weakly interacting massive 36 Search for low-mass weakly interacting massive particles with SuperCDMS Search for annual modulation in low-energy CDMS-II data Compatibility of DAMA/LIBRA dark matter detection with other searches Limits on light WIMPs with a 1 kg-scale germanium detector at 160 evee Low capacitance large volume shaped-field germanium detector 112 Search for event rate modulation in XENON100 electronic recoil data Search for electronic recoil event rate modulation with 4 years of XENON100 Search of low-mass WIMPs with a p-type point contact germanium detector in arXiv:1401.3295 Phys. Rev. D (2015) 091302. (2017) 181302. Direct dark matter search by annual modulation with 2.7 years of XMASS-I Dark matter results from 54-ton-day exposure of PandaX-II experiment , , 115 119 Eur. Phys. J. C , Phys. Rev. D Phys. Rev. Lett. , , physics threshold at the China Jinping Underground Laboratory Trans. Nucl. Sci. small signals data data 071301. detector the CDEX-1 experiment Rev. Lett. 023002. detector data Cosmol. Astropart. Phys. arXiv:1203.1309 particles with the CDMS low ionization threshold experiment Phys. Rev. Lett. Rev. Lett. [9] R. Agnese et al., [8] R. Agnese et al., [7] X. Cui et al., [16] L.T. Yang et al., [13] E. Aprile et al., [15] P.N. Luke et al., [21] G.J. Feldman and R.D. Cousins, [10] G. Angloher et al., [11] W. Zhao et al., [12] K. Abe et al., [14] E. Aprile et al., [17] C.E. Aalseth et al., [18] C. Savage et al., [19] Z. Ahmed et al., [20] J.F. Ziegler et al., New Limits on WIMPJinping Dark Underground Matter Laboratory from Annual Modulation Analysis of the CDEX Experiment at the China