Physics Letters B 792 (2019) 193–198 Contents lists available at ScienceDirect Physics Letters B www.elsevier.com/locate/physletb PandaX-II constraints on spin-dependent WIMP-nucleon effective interactions Jingkai Xia a, Abdusalam Abdukerim b, Wei Chen a, Xun Chen a, Yunhua Chen c, Xiangyi Cui a, Deqing Fang d, Changbo Fu a, Karl Giboni a, Franco Giuliani a, Linhui Gu a, Xuyuan Guo c, Zhifan Guo e, Ke Han a, Changda He a, Shengming He c, Di Huang a, Xingtao Huang f, Zhou Huang a, Peng Ji g, Xiangdong Ji a,h,1, Yonglin Ju e, Shaoli Li a, Heng Lin a, Huaxuan Liu e, Jianglai Liu a,h, Yugang Ma d, Yajun Mao i, Kaixiang Ni a, Jinhua Ning c, Xiangxiang Ren a, Fang Shi a, Andi Tan j, Anqing Wang f, Cheng Wang e, Hongwei Wang d, Meng Wang f, Qiuhong Wang d, Siguang Wang i, Xiuli Wang e, Xuming Wang a, Zhou Wang e, Mengmeng Wu g, Shiyong Wu c, Mengjiao Xiao j,k, Pengwei Xie h, Binbin Yan f, Jijun Yang a, Yong Yang a, Chunxu Yu g, Jumin Yuan f, Jianfeng Yue c, Dan Zhang j, Hongguang Zhang a, Tao Zhang a, Li Zhao a, Qibin Zheng l, ∗ ∗∗ Jifang Zhou c, Ning Zhou a, , Xiaopeng Zhou i, Wick C. Haxton m,n, a School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai Key Laboratory for Particle Physics and Cosmology, Shanghai 200240, China b School of Physics and Technology, Xinjiang University, Ürümqi 830046, China c Yalong River Hydropower Development Company, Ltd., 288 Shuanglin Road, Chengdu 610051, China d Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China e School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China f School of Physics and Key Laboratory of Particle Physics and Particle Irradiation (MOE), Shandong University, Jinan 250100, China g School of Physics, Nankai University, Tianjin 300071, China h Tsung-Dao Lee Institute, Shanghai 200240, China i School of Physics, Peking University, Beijing 100871, China j Department of Physics, University of Maryland, College Park, MD 20742, USA k Center of High Energy Physics, Peking University, Beijing 100871, China l School of Medical Instrument and Food Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China m Department of Physics, University of California, Berkeley, CA 94720, USA n Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA a r t i c l e i n f o a b s t r a c t Article history: We present PandaX-II constraints on candidate WIMP-nucleon effective interactions involving the nucleon Received 22 February 2019 or WIMP spin, including, in addition to standard axial spin-dependent (SD) scattering, various couplings Accepted 25 February 2019 among vector and axial currents, magnetic and electric dipole moments, and tensor interactions. The Available online 13 March 2019 data set corresponding to a total exposure of 54-ton-days is reanalyzed to determine constraints as a Editor: M. Trodden function of the WIMP mass and isospin coupling. We obtain WIMP-nucleon cross section bounds of × −41 2 × −42 2 Keywords: 1.6 10 cm and 9.0 10 cm (90% c.l.) for neutron-only SD and tensor coupling, respectively, ∼ 2 2 PandaX-II experiment for a mass MWIMP 40 GeV/c . The SD limits are the best currently available for MWIMP > 40 GeV/c . WIMP dark matter We show that PandaX-II has reached a sensitivity sufficient to probe a variety of other candidate spin- Spin-dependent effective interactions dependent interactions at the weak scale. © 2019 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3. * Corresponding author at: School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, 200240, China. ** Corresponding author at: Department of Physics, University of California, Berkeley, CA 94720, USA. E-mail addresses: [email protected] (X. Ji), [email protected] (N. Zhou), [email protected] (W.C. Haxton). 1 Spokesperson of PandaX Collaboration. https://doi.org/10.1016/j.physletb.2019.02.043 0370-2693/© 2019 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3. 194 J. Xia et al. / Physics Letters B 792 (2019) 193–198 Astrophysical and cosmological observations indicate that a We specialize to the scattering of a spin-1/2 WIMPs off a nat- large amount of non-luminous dark matter (DM) exists in our uni- ural xenon target, exploring four dimension-four and three higher verse, constituting ∼ 27% of the closure density. However, the exact dimension effective interactions, selected from Table 1 of Ref. [15]. nature of DM remains a mystery. One intriguing DM candidate, The operator dimension is defined as 4 + number of powers of mM a weakly-interacting massive particle (WIMP), arises naturally in in the denominator, where mM is a scale that governs the strength many extensions of the standard model [1,2]. Many WIMP searches of the WIMP and nucleon moments being coupled. The dimension- have been performed, including direct detection of their scattering four operators are the V-A interactions off target nuclei, indirect detection of their decay or annihilation, L5 ≡ ¯ μ ¯ → O and their production in collider experiments. In the analysis of di- int χγ χ NγμN 1 m rect detection experiments, frequently it is assumed that the scat- L7 ≡ ¯ μ ¯ 5 →− O + N O int χγ χ Nγμγ N 2 7 2 9 tering arises from the light-quark-level (u, s, d) effective interaction mχ 13 5 G L ≡ χγ¯ μγ χ N¯ γ N → 2O + 2O L ∼ √F ¯ VV ¯ μ + ¯ AA¯ μ int μ 8 9 χγμχ cq qγ q χγμγ5χ cq qγ γ5q (1) 2 L15 ≡ ¯ μ 5 ¯ 5 →− O q int χγ γ χ Nγμγ N 4 4 (2) which can be reduced to a nucleon-level operator useful in an- with mN the nucleon mass and O1 = 1χ 1N , O4 = Sχ · S N , O7 = alyzing the nuclear response to WIMP scattering [3]. Limits on ⊥ ⊥ q S N · v , O8 = S · v , and O9 = i(S × S N ) · the nonrelativistic χ χ mN the vector spin-independent (SI) and axial spin-dependent (SD) 5 SI,SD operators of [14,15]. While L generates the standard SI inter- WIMP-proton and WIMP-neutron cross sections σp,n can then be int action, the other interactions involve an axial coupling and thus derived. The recent stringent direct detection null results obtained depend on spin. successively by LUX [4,5], PandaX [6,7] and XENON [8–10]have SI,SD One can equally well start with a basis of light-quark effec- significantly tighten the bounds on σp,n [11]. tive operators, reducing these via chiral EFT to their nonrelativistic The interaction of Eq. (1)was motivated by supersymmetric DM nucleon equivalents [20,21]. The spin-dependent nucleon-level op- candidates, like the neutralino, that can naturally account for the erators arising from the axial part of Eq. (1)(the standard SD DM relic density. The motivation to focus exclusively on such can- interaction) and from the light-quark tensor interaction will be didates has weakened due in particular to collider constraints [12]. considered here. An alternative approach, effective field theory (EFT) [13–15], has gained favor because it allows one to do an analysis [16–19]free The dimension-five operators coupling the WIMP magnetic or of theory assumptions. One selects an EFT scale – e.g., the light- electric dipole moments with the nucleon’s vector current, and the quark or a nucleon scale – and constructs a complete basis of dimension-six operator coupling WIMP and nucleon magnetic mo- effective operators to a given order, taking into account all gen- ments, are examples of other potential sources of spin-dependent eral symmetries limiting that basis. The underlying UV theory of scattering, DM will reduce at that scale to some definite combination of the q L9 ≡ ¯ μν ν ¯ basis operators, regardless of its nature. Experimentalists can ex- int χ iσ χ NγμN mM plore the sensitivities of their detectors to the basis operators, to 2 2 make sure they are probing all possibilities. The EFT approach has q 2mN 2mN q →− O1 + O5 − ( O4 − O6) shown 1) relative experimental sensitivities depend on the oper- 2m m m m 2 χ M M M mN ator choice, and 2) direct detection is potentially more powerful 17 μν qν 5 ¯ 2mN than might appear from SI/SD analyses, as six (not two) indepen- L ≡ iχ¯ iσ γ χ NγμN → O11 int m m dent constraints on DM can be obtained, in principle [15]. M M α 2 2 The PandaX-II detector, located in the China Jinping Under- 10 μν qν ¯ q q mN L ≡ χ¯ iσ χ Niσμα N → 4( O4 − O6) (3) ground Laboratory (CJPL), is a dual-phase xenon time-projection int m m 2 2 M M mM mM chamber with 580 kg of liquid xenon in the sensitive target vol- q ⊥ q q ume. When the incoming WIMP scatters off a xenon nucleus, both Here O5 = iS · ( × v ), O6 = (S · )(S N · ), and O11 = χ mN χ mN mN the prompt scintillation photons (S1) in the liquid and the delayed · q iSχ m . The dependence on q implies nuclear form factors proportional scintillation photons (S2) in the gas are collected N that peak at larger momentum transfers, influencing experimen- by 55 top and 55 bottom Hamamatsu R11410-20 3-inch photo- tal strategies for optimally constraining such interactions.