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Light Dark Matter and Neutrinos

I. Coordinator:

  • 王子敬Henry T. Wong(AS, exp.), 吳孟儒Meng-Ru Wu(AS, th.)


II. Core Members:

  • Core members
  • 王子敬Henry T. Wong(AS, exp.), 吳孟儒Meng-Ru Wu(AS, th.), 陳俊瑋Jiunn-Wei Chen(NTU, th.), 紀信昌Hsin-Chang Chi(NDHU, th.), 劉承邦Cheng-Pang Liu(NDHU, th.).
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  • Young Participants
  • Mukesh Kr Pandey(NTU, Postdoc, th.), Lakhwinder Singh(AS, Postdoc, exp.), Vivek Sharma (AS, Postdoc, exp), 吳峙磐Chih-Pan Wu(NTU, postdoc, th.), Mehmet Agartioglu (NDHU, Phd, exp.), 謝仲鈞 (NTU, undergrad, th.), 宋亞倫Allan Sung (NTU, undergrad, th.).
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  • [*] Note that our group has established strong collaboration (e.g., publish papers together that acknowledge NCTS’s support) with the following foreign researchers whom we would list as our adjunct members: 黃克寧Keh-Ning Huang(四川大學, th.), Muhammed Deniz and Saime Kerman(Dokuz Eylül University, Turkey, exp. & th.) , 林興德Shin-Ted Lin(四川大學, exp.), 岳騫 Qian Yue(北京清華大學, exp., Chief Scientist of the China Dark Matter Experiment).

 


I
II. Research Themes:

  • The main research theme of our group is to apply state-of-the-art many-body methods to understand detector responses in direct dark matter searches and neutrino detection – a subject that theory and experiment largely intersect. The goals are not only to provide reliable constraints to dark matter and neutrino physics with experimental data, but also to explore potential new channels to shed light on these areas. In addition, we plan to further explore potential signals and constraints from astrophysical observations. The topics we currently focus on include:
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  • Light dark matter
  •    Dark sectors consisting of light, weakly-coupled particles are attractive and emergent field in dark matter (DM) physics. Compared with weakly-interacting massive particles (WIMPs), these particles with masses ranging from eV to GeV scales are much less explored and searches of them have great discovery potential. (See arXiv:1311.0029 for a comprehensive community report.)
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  •    As these light particles are less likely to generate detectable nuclear recoils, the electronic recoils are primary signals. In the past, we have carried out high-quality many body calculations in atomic ionization processes of germanium [PLB 731, 159 (2014); PRD 90, 011031(R) (2014); PRD 91, 013005 (2015)] and xenon [PLB 774, 656 (2017)], and studied the generic interactions between dark matter and atom using hydrogen as an illustration [PRD 92, 096013 (2015)]. Therefore, it is an area we think our expertise and experience can be readily applied.
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  •    The first light dark matter species we have looked is keV-scale sterile neutrinos using data taken by the TEXONO germanium detector [PRD 93, 093012 (2016)]. This is followed by constraints on milli-charged WIMP dark matter [arXiv:1808.02719] and improved WIMP-electrons scattering cross-section calculations [forthcoming]. S everal projects are currently under progress. Our ultimate goal is to study a broad class of light dark matter candidates including sub-GeV weakly-interacting particles, dark photons, etc. with general interactions formulated through effective field theory.
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  •    On the astrophysics side, one of our new core member has recently started to work on deriving novel constraints from supernovae to dark photons, keV sterile neutrinos, etc. We plan to further seek for possibilities of developing new collaborations in having complementary astrophysical constraints by utilizing the low-energy experiments that is the core strength of the group.
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  • Low energy neutrinos
  •    While high energy and intensive beams of neutrinos are the main sources and focus of next generation neutrino oscillation experiments, low energy neutrinos and their detection still play important roles in many topics of fundamental importance in neutrino physics. In light of the future large-scale, low-threshold detectors that will open windows to detect them, we are particularly interested in the solar neutrinos, supernova neutrinos, the relic neutrinos, and the neutrino-nucleus interactions.
  •    The solar neutrinos from proton-proton fusion and 7Be decay take up 98% of the solar neutrino flux, however, they have not been measured precisely enough to the level to check the standard solar model predictions. The future multi-ton scale liquid xenon detectors provide a good opportunity. Our recent work [PLB 774, 656 (2017)] showed that many-body effect is important and it reduces the event count rate by about 25% than previously estimation. As solar neutrinos are the main messengers that carry the information of solar interior, this is an area that our work is very relevant to solar astrophysics.
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  •    Neutrinos of all flavors coming from core-collapse supernovae are unique messengers to explore physics at the very center of the dying stars. For a next Galactic one, although the existing and planned detectors will be able to record more than thousands of events and offer unprecedented statistics to test standard astrophysical scenario as well as beyond-the-Standard-Model physics, precise measurement of the muon and tau (anti)neutrinos spectrum at energy window below roughly 15 MeV still represents a big challenge. Any new channel combining both the theoretical and experimental efforts towards this direction will be highly relevant for this research direction and we plan to explore this possibility.
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  •    The relic neutrino background in our Universe, if measurable, can bring significant insights to cosmology, in complementary to the cosmic microwave background. It is definitely interesting to explore such possibilities with new- or future-generation detectors.
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  •    The neutrino-nucleus interactions are a broad and rich subject. At low-energy transfer in elastic scattering, the coherency [PRD 93, 113006 (2016)] enhances the scattering cross section and the sensitivity to non-standard (beyond the Standard Model) interactions. On the other hand, such scattering induced by the solar neutrinos forms the major irreducible background that WIMP searches will be limited or have to surpass. At intermediate energy when inelastic scattering channels are open, these events can serve as signals for neutrino detection or should be removed as backgrounds for dark matter searches – either role is important.
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  • Neutrinoless double beta decay
  •    As one of the golden channels to unravel the Dirac or Majorana nature of neutrinos and their mass hierarchy, neutrinoless double beta decay has been a forefront subject for decades. On the experimental side, the new generation large scale xenon and germanium detectors are capable of improving the current limits by orders of magnitude and reach the sensitivity needed to solve the mass hierarchy problem. It is for this reason that many large detectors proposed to be built for WIMP searches also have attention on their multi-purpose ability in neutrinoless double beta decay.
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  •    On the theory side, the most outstanding problem is the evaluation of nuclear matrix elements. Additionally, there are questions such as atomic many-body effects on the
    spectra of beta-decay electrons, two-electron capture process (the inverse of double beta decay) etc. We think our existing expertise can contribute.
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  • Our group started out as a small theorists’ team and now has evolved to a closely-working collaboration involving substantial contributions from experimentalists of the TEXONO Collaboration (led by H. Wong, one of our core members) and the CDEX Collaboration (S.-T. Lin and Q. Yue, two of our adjunct members) at the China Jinping Underground Laboratory. In the recent two years, we also had communications with people from the PandaX (e.g., Jianglai Liu) and LZ (e.g., Harry Nelson) Dark Matter Experiment. With NCTS’s support, we anticipate our collaboration network will have a steady and healthy growth both internationally and domestically.
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IV
Tentative plan of activities:
  • A. Weekly meetings of core members: Our members have been operating weekly collaboration meetings (1~2 hours) through audio/video conferencing on a regular basis for years and we expect to continue such meetings. 
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  • B. Semi-annual joint meetings with TEXONO/CDEX and adjunct members: We plan to have a one-day, mini-workshop-like meeting twice a year, one in Taipei and the other in Hualien, with experimental colleagues of the TEXONO and CDEX Collaborations and our adjunct members. The main purposes of these joint meetings are to update recent progress in both theory and experiment, and to make coherent efforts on both sides.
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  • C. Invitation of international visitors: To make our works known to international communities and to seek potential collaborations, we would like to invite 2-3 visitors per year. We certainly can coordinate the schedules of our visitors with other NCTS’s groups and activities (schools, meetings, etc.) to ensure they bring maximal benefits to NCTS.
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  • D. Participation of international workshops/conferences/schools: To allow our core members without other/sufficient travel funds to participate major international events, such as TAUP 2019 (Toyama, Japan, Sept. 9-13, 2019) and Neutrino 2020 (Chicago, USA, Jun. 21-27, 2020), or visit foreign collaborators.
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  • E. International meetings: We would like to organize two international meetings, one in 2018 and one in 2019. The format can be either a small-size workshop spearheaded by our group with participation of other NCTS programs, or jointly with other NCTS’s groups as a part of a large-size conference. 
     
 

 

VExpected achievements:

  • A. Academic performance
    • The scientific projects we plan to conduct in 2019-2020 include:
    • 1. Light dark matter scattering with germanium, xenon, and argon detectors
    • 2. Database of detector response functions for open access
    • 3. Pilot study of deriving novel constraint utilizing both the astrophysical sources and low-energy experiments.
    • 4. Low energy solar neutrino detection with multi-ton scale liquid xenon detectors
    • 5. Pilot study of low energy supernova muon/tau (anti)neutrino detection
    • 6. Feasibility study of relic neutrino detection
    • 7. Constraining neutrino non-standard interactions in coherent neutrino scattering
    • 8. Study of inelastic neutrino-nucleus scattering
    • 9. Pilot study of topics related to neutrinoless double beta decay
  •    Overall, we expect 6+ publications in 2019-2020 out of our group activities and acknowledging NCTS’s support.
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  • B. Nurturing
    • 1. Postdocs: 4 (M. Pandey, L. Singh, V. Sharma, C.-P. Wu)
    • 2. Ph.D. students: 1 (M. Agartioglu)
    • 3. Undergraduate student: 2 (謝仲鈞, 宋亞倫)
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  • C. International visibility
    • 1. International meetings: 2 (2019-2020)
    • 2. International visitors: 4+ (2019-2020)
    • 3. Oral/Poster presentations at major international conferences: 2+ (2019-2020)

 

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