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Doojin Kim Searching for New Physics Leaving No Stone Unturned University of Utah, August 9 th , 2019 In collaboration with B. Dutta, L. Shu, J.-C. Park, S. Shin and L. Strigari [arXiv: 1906.10745 , PRL submitted] B. Dutta, L. Shu, J.-C. Park,

  1. Doojin Kim Searching for New Physics – Leaving No Stone Unturned University of Utah, August 9 th , 2019 In collaboration with B. Dutta, L. Shu, J.-C. Park, S. Shin and L. Strigari [arXiv: 1906.10745 , PRL submitted] B. Dutta, L. Shu, J.-C. Park, S. Shin and L. Strigari, in progress

  2. Current Status of Dark Matter Searches  No observation of DM signatures via non-gravitational interactions while many searches/interpretations designed/performed under nonrelativistic WIMP/WIMP-like scenarios  merely excluding more parameter space in dark matter models [US Cosmic Visions, Battaglieri et al ( 2017 )] Searching for new physics – Leaving no stone unturned Doojin Kim, University of Arizona 1

  3. The Dark Matter Landscape 𝑛 proton 𝑁 Planck 100 𝑁 ⨀ 10 −22 eV 10 9 eV 10 28 eV 10 68 eV 1 keV 1 GeV 1 TeV 1 MeV WIMPs  Probing dark sectors – “Leaving no stone unturned” : (Light) dark matter + new mediators  Less constrained by current searches (reason for the range choice discussed later) Searching for new physics – Leaving no stone unturned Doojin Kim, University of Arizona 2

  4. Light Dark-Sector Particle Models/Searches: Mediator  Various light mediator scenarios have been proposed.  Dark matter scenarios based on hidden sectors: e.g., models of asymmetric dark matter, Sommerfeld enhancements motivated by SIMP, etc (see the review [Essig et al ( 2013 )])  𝑕 − 2 of electron: 2.4𝜏 discrepancy [Davoudiasl, Marciano ( 2018 )]  Neutrino sector physics: new neutrino interactions to satisfy the MiniBooNE excess [Bertuzzo, Jana, Machado, Funchal ( 2018 )]  Solutions of Yukawa coupling hierarchy problem [Dutta, Ghosh, Kumar ( 2019 )]  See also US cosmic vision [Battaglieri et al ( 2017 )]  Light mediator searches at existing/future experiments, e.g., NA 64 , Belle I/II, Babar, SHiP, FASER, MATHSULA, SeaQuest Searching for new physics – Leaving no stone unturned Doojin Kim, University of Arizona 3

  5. Light Dark-Sector Particle Models/Searches: Dark Matter  Various light dark matter-involving pheno has been studied.  Boosted dark matter scenarios [Agashe, Cui, Necib, Thaler ( 2014 ); Berger, Cui, Zhao ( 2014 ); Kong, Mohlabeng, Park ( 2014 ); DK , Park, Shin ( 2016 )]  Fast-moving DM via induced nucleon decays [Huang, Zhao ( 2013 )]  MeV-range DM indirect detection at gamma-ray telescopes [Boddy, Kumar ( 2015 )]  Energetic cosmic-ray-induced (semi-)relativistic dark matter scenarios [Yin ( 2018 ); Bringmann, Pospelov ( 2018 ); Ema, Sala, Sato ( 2018 ); Dent, Dutta, Newstead, Shoemaker ( 2019 )]  Ultra high energy cosmic ray phenomena [Bhattacharya, Gandhi, Gupta ( 2014 ); Heutier, DK , Park, Shin ( 2019 )]  Cosmogenic light dark matter searches at existing/future experiments, e.g., SK/HK, COSINE- 100 , ProtoDUNE, DUNE  Beam-produced light dark matter searches at existing/future experiments, e.g., BDX, MicroBooNE, SeaQuest, LDMX, T 2 HKK, DUNE, SHiP, and proposals [Bjorken, Essig, Schuster, Toro ( 2009 ); Batell, Pospelov, Ritz ( 2009 ); deNiverville, Pospelov, Ritz ( 2011 ); Izaguirre, Krnjaic, Schuster, Toro ( 2014 ); Berlin, Gori, Schuster, Toro ( 2018 ), and many more] Searching for new physics – Leaving no stone unturned Doojin Kim, University of Arizona 4

  6. Goals  How to isolat late e (lig ight ht) ) dark rk matter er sign gnal al events from the SM (neutrino) backgrounds with timing ming spect ctra ra at neutrino experiments, taking COH OHERENT ERENT as a benchmark experiment  Application to the measurement data that COHERENT has released  How to inter nterpre pret t the e result sult assuming a (mild) excess and no excess Searching for new physics – Leaving no stone unturned Doojin Kim, University of Arizona 5

  7. COHERENT Experiment: Primer  Main mission: first direct measurement of Coherent Elastic Neutrino-Nucleus Scattering (CE ν NS). • Prompt ν’s: 𝜌 → 𝜈 + 𝜉 𝜈 • Delayed ν’s: 𝜈 → 𝑓 + 𝜉 𝜈 + 𝜉 𝑓  ~1 GeV proton beam on Mercury target (pulse duration: 380 ns FWHM 60 Hz) 5 × 10 20 protons-on-target (POT) delivered  per day Searching for new physics – Leaving no stone unturned Doojin Kim, University of Arizona 6

  8. Dark Matter Scenarios in COHERENT Hg target Detector 𝜓 𝑜 Proton beam 𝜓 𝜓 𝐵′ 𝜓 Stopped 𝜌 − 𝑂 𝑂 𝑞 in Hg target 𝜌 − + 𝑞 → 𝑜 + 𝐵′ 𝐵 ′ → 𝜓 + 𝜓 𝜓 + 𝑂 → 𝜓 + 𝑂 [deNivervill, Pospelov, Ritz ( 2015 )] 𝑕 𝐸 𝜓 𝜓 𝑟 𝜓 𝐵′ 𝐵′ 𝐵′ 𝑟 𝑕 𝐸 𝑅 𝑟 𝑓𝜗 1 𝜓 𝑟 𝑟 𝑟 𝑟 𝑅 𝑟 𝑓𝜗 1 Cf.) Another (subdominant) process: charge exchange, 𝜌 −/+ + 𝑞/𝑜 → 𝜌 0 + 𝑜/𝑞 , 𝜌 0 → 𝛿 + 𝐵′ [ JSNS 2 TDR] Probe dark photon decay into dark matter utilizing timing measurements! Searching for new physics – Leaving no stone unturned Doojin Kim, University of Arizona 7

  9. Timing Spectrum of Dark-Matter Events 𝐵 ′ decay vertex 𝜄′ 𝑤 𝐵′ (𝑢 − 𝑢 𝐺 ) 𝑤 𝜓 𝑢′ Detector 𝜄 Hg target 𝑦 0 𝐵′ production at 𝑢 𝐺 Dark matter flux at the detector : Model of 𝜌 − production timing (  POT)  from the decay law  Probability that DM travels towards the detector Cf.) Search strategy with timing information at the LHC [Liu, Liu, Wang ( 2018 )] Searching for new physics – Leaving no stone unturned Doojin Kim, University of Arizona 8

  10. Parameter Space: Dark Photon 𝑟 and 𝑛 𝐵′ )  Various possibilities for dark photon 𝐵′ (depending on 𝜗 1 𝑟 ) • Short-lived (large 𝜗 1 vs. Long-lived • Relativistic vs. Non-relativistic ( 𝑛 𝐵′ ~138 MeV) For τ <a few ns, we get maximum number of events Searching for new physics – Leaving no stone unturned Doojin Kim, University of Arizona 9

  11. Parameter Space: Dark Matter  Dark matter scatters off nucleus:  In general, the scattering process could be mediated by a 𝑕 𝐸 𝜓 𝜓 different particle (e.g., Baryon number gauged dark gauge 𝐵′ boson [deNiverville, Pospelov, Ritz ( 2015 )] ) 𝑟 𝑟 𝑟 𝑟 → 𝑅 𝐶 𝑓𝜗 2 𝑅 𝑟 𝑓𝜗 1 𝐸 → 𝑓𝜗 2 𝑟 , 𝑕 𝐸 = 𝑓𝜗 1 𝐸 : 𝐵′ → 𝑊′ , 𝑛 𝐵′ → 𝑁′ , 𝑅 𝑟 𝑓𝜗 1  Dark photon 𝐵′ production to dark matter scattering can be described by two variables. 𝑟 𝜗 2 𝑟 𝜗 2 𝐸 𝜗 ≡ 𝜗 1 BR 𝐵′→𝜓𝜓 and 𝑁′ Searching for new physics – Leaving no stone unturned Doojin Kim, University of Arizona 10

  12. Proposed Search Strategy  A combination of energy and timing cuts ① 𝐹 𝑠 > 14 keV • Prompt neutrino: completely removed • Delayed neutrino (and DM signal): still remains ② 𝑈 < 1.5 𝜈 s completely almost • Delayed neutrino: almost removed • DM signal: still remains completely almost Searching for new physics – Leaving no stone unturned Doojin Kim, University of Arizona 11

  13. Application to Existing CsI Data  Data released by COHERENT: CsI 14.5 kg × 308 days = 4,466 kg  day [Akimov et al, 1804.09459 ]  Analysis scheme (also following [Dutta, Liao, Sinha, Strigari ( 2019 )] for background estimate) • 𝑟 2 𝑡 2 Fix the size of neutron distribution to 𝑆 𝑜 = 4.7 fm Helm 𝑟 2 = 3𝑘 1 (𝑟𝑆 0 ) 𝐺 exp(− 2 ) 𝑂 𝑟𝑆 0 • 2 = 𝑆 0 2 + 5𝑡 2 14 keV < 𝐹 𝑠 < 28 keV , 𝑈 < 1.5 𝜈 s 𝑆 𝑜 97 : t otal events − 49 : classified as the steady-state (SS) background − 19 : identified as delayed neutrino events (SM) − 0 : identified as prompt neutrino events (SM) − 3 : beam-related neutron (BRN) backgrounds 26 : “Excess” Significance ( 𝑆 𝑜 = 4.7 fm): 𝟑. 𝟓 𝝉 Excess Significance = 2SS+BRN+SM [COHERENT, 1708.01294 ] Significance ( 𝑆 𝑜 = 5.5 fm): 𝟒. 𝟏 𝝉 Searching for new physics – Leaving no stone unturned Doojin Kim, University of Arizona 12

  14. Cut Optimization Significance Contours • 14 keV < 𝐹 𝑠 < 28 keV • 𝑈 < 1.5 𝜈 s Optimized set of cuts are independent of 𝑆 𝑜  Caveats: systematics on the SS background not considered, excess explained by other unidentified background Searching for new physics – Leaving no stone unturned Doojin Kim, University of Arizona 13

  15. Mild Excess? – Dark Matter Interpretation  Fit to the excess after the cuts needs to fit the full data set (before the cuts). • Baseline model point for the figure in the left: 𝜐 = 1 ns, 𝑛 𝐵′ = 75 MeV, 𝑛 𝜓 = 5 MeV • Nevertheless, the figure holds for  𝜐 ≤ 4 ns, 𝑛 𝐵′ < 138 MeV  𝜐 ≤ 30 ns, 𝑛 𝐵′ ≅ 138 MeV (non- relativistic dark photon case)  Any 𝑛 𝜓 < 𝑛 𝐵′ /2 𝑟 𝜗 2 𝑟 𝜗 2 𝐸 The mass of the DM-nucleus 𝜗 = 𝜗 1 BR 𝐵′→𝜓𝜓 interaction mediator Searching for new physics – Leaving no stone unturned Doojin Kim, University of Arizona 14

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