Doojin Kim Searching for New Physics Leaving No Stone Unturned - - PowerPoint PPT Presentation

Doojin Kim

Searching for New Physics – Leaving No Stone Unturned University of Utah, August 9th, 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

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

Current Status of Dark Matter Searches

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 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)]

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

The Dark Matter Landscape

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10−22 eV 109 eV 1028 eV 1068 eV 𝑛proton 𝑁Planck 100 𝑁⨀ 1 keV 1 MeV 1 GeV 1 TeV

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)

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

Light Dark-Sector Particle Models/Searches: Mediator

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 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., NA64, Belle I/II, Babar, SHiP, FASER, MATHSULA, SeaQuest

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

Light Dark-Sector Particle Models/Searches: Dark Matter

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 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, T2HKK, 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]

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

Goals

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 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

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

COHERENT Experiment: Primer

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 Main mission: first direct measurement of Coherent Elastic Neutrino-Nucleus Scattering (CEνNS).

• Prompt ν’s: 𝜌 → 𝜈 + 𝜉𝜈
• Delayed ν’s: 𝜈 → 𝑓 + 𝜉𝜈 + 𝜉𝑓

 ~1 GeV proton beam on Mercury target (pulse duration: 380 ns FWHM 60 Hz)  5 × 1020 protons-on-target (POT) delivered per day

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

Dark Matter Scenarios in COHERENT

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𝐵′ 𝜓 𝜓 Proton beam Hg target Stopped 𝜌− 𝑞 in Hg target 𝑜 𝜓 𝜓 𝑂 𝑂 Detector 𝜌− + 𝑞 → 𝑜 + 𝐵′

[deNivervill, Pospelov, Ritz (2015)]

𝐵′ 𝑟 𝑟 𝑅𝑟𝑓𝜗1

𝑟

𝐵′ → 𝜓 + 𝜓 𝐵′ 𝜓 𝜓 𝑕𝐸 𝜓 + 𝑂 → 𝜓 + 𝑂 𝜓 𝜓 𝑟 𝑟 𝑅𝑟𝑓𝜗1

𝑟

𝑕𝐸 𝐵′ Cf.) Another (subdominant) process: charge exchange, 𝜌−/+ + 𝑞/𝑜 → 𝜌0 + 𝑜/𝑞, 𝜌0 → 𝛿 + 𝐵′ [JSNS2 TDR] Probe dark photon decay into dark matter utilizing timing measurements!

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

Timing Spectrum of Dark-Matter Events

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𝜄 𝜄′ 𝑦0 𝑤𝐵′(𝑢 − 𝑢𝐺) 𝑤𝜓𝑢′ Hg target Detector 𝐵′ decay vertex 𝐵′ production at 𝑢𝐺

Dark matter flux at the detector:

 from the decay law  Probability that DM travels towards the detector Model of 𝜌− production timing ( POT)

Cf.) Search strategy with timing information at the LHC [Liu, Liu, Wang (2018)]

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

Parameter Space: Dark Photon

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 Various possibilities for dark photon 𝐵′ (depending on 𝜗1

𝑟 and 𝑛𝐵′)

• Short-lived (large 𝜗1

𝑟)

• vs. Long-lived
• Relativistic
• vs. Non-relativistic (𝑛𝐵′~138 MeV)

For τ<a few ns, we get maximum number of events

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

Parameter Space: Dark Matter

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 Dark matter scatters off nucleus:

𝜓 𝜓 𝑟 𝑟 𝑅𝑟𝑓𝜗1

𝑟

𝑕𝐸 𝐵′

 In general, the scattering process could be mediated by a different particle (e.g., Baryon number gauged dark gauge boson [deNiverville, Pospelov, Ritz (2015)]) : 𝐵′ → 𝑊′, 𝑛𝐵′ → 𝑁′, 𝑅𝑟𝑓𝜗1

𝑟 → 𝑅𝐶𝑓𝜗2 𝑟, 𝑕𝐸 = 𝑓𝜗1 𝐸 → 𝑓𝜗2 𝐸

 Dark photon 𝐵′ production to dark matter scattering can be described by two variables.

𝜗 ≡ 𝜗1

𝑟𝜗2 𝑟𝜗2 𝐸

BR𝐵′→𝜓𝜓 and 𝑁′

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

Proposed Search Strategy

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 A combination of energy and timing cuts

① 𝐹𝑠 > 14 keV

• Prompt neutrino: completely removed
• Delayed neutrino (and DM signal): still remains

completely

② 𝑈 < 1.5 𝜈s

completely

• Delayed neutrino: almost removed
• DM signal: still remains

almost almost

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

Application to Existing CsI Data

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 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)

• Fix the size of neutron distribution to 𝑆𝑜 = 4.7 fm
• 14 keV < 𝐹𝑠 < 28 keV, 𝑈 < 1.5 𝜈s

𝐺

𝑂 Helm 𝑟2 = 3𝑘1(𝑟𝑆0) 𝑟𝑆0

exp(−

𝑟2𝑡2 2 )

𝑆𝑜

2 = 𝑆0 2 + 5𝑡2

97 : total 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 (𝑆𝑜 = 4.7 fm): 𝟑. 𝟓 𝝉 Significance (𝑆𝑜 = 5.5 fm): 𝟒. 𝟏 𝝉

Significance =

Excess 2SS+BRN+SM [COHERENT, 1708.01294]

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

Cut Optimization

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Significance Contours

• 14 keV < 𝐹𝑠 < 28 keV
• 𝑈 < 1.5 𝜈s

Optimized set of cuts are independent of 𝑆𝑜  Caveats: systematics on the SS background not considered, excess explained by other unidentified background

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

Mild Excess? – Dark Matter Interpretation

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 Fit to the excess after the cuts needs to fit the full data set (before the cuts).

𝜗 = 𝜗1

𝑟𝜗2 𝑟𝜗2 𝐸

BR𝐵′→𝜓𝜓

• Baseline model point for the figure in the left:
• Nevertheless, the figure holds for

 𝜐 ≤ 4 ns, 𝑛𝐵′ < 138 MeV  𝜐 ≤ 30 ns, 𝑛𝐵′ ≅ 138 MeV (non- relativistic dark photon case)  Any 𝑛𝜓 < 𝑛𝐵′/2 𝜐 = 1 ns, 𝑛𝐵′ = 75 MeV, 𝑛𝜓 = 5 MeV

The mass of the DM-nucleus interaction mediator

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

Preferred Parameter Values

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 Single mediator scenario (i.e., the case where the dark photon 𝐵′ mediates the scattering process of dark matter at the detector) 𝜗 = 𝜗1

𝑟𝜗2 𝑟𝜗2 𝐸

BR𝐵′→𝜓𝜓 → (𝜗𝑟)2𝜗2

𝐸

BR𝐵′→𝜓𝜓 → (𝜗𝑟)2/𝑓

𝜗𝑟 ≡ 𝜗1

𝑟 = 𝜗2 𝑟

𝜗2

𝐸 = 1/𝑓, BR = 1 for simplicity (𝑕𝐸 ≡ 𝑓𝜗2 𝐸)

 Multi-mediator scenario (i.e., the case where another mediator mediates the scattering process of dark matter at the detector)

 𝜗𝑟 above can be interpreted as (𝜗1

𝑟𝜗2 𝑟𝜗2 𝐸𝑓)1/2

 𝜗2

𝐸 is not the same as 𝜗1 𝐸 which controls 𝜐 of 𝐵′, so longer-lived dark photon could be

possible.

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

Mild Excess? – Alternative Interpretation: NSI

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 Example alternative new physics possibility, Non-Standard Interaction

• Benchmark case: non-zero coupling 𝑕𝑓, the

NSI in the 𝜉𝑓 neutral-current interaction (along with a new mediator).  No overlapping regions, especially the prompt timing bin (i.e., 𝑈 < 1.5 𝜈s) doesn’t show a good fit. NSI affects the

• verall normalization of neutrino flux!
• The situation becomes even worse with 𝑕𝜈 ≠

0, since it affects not only the delayed but the prompt spectrum.

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

No Excess? – Constraining Parameter Space

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 Assuming no excess is observed, we can constrain parameter space.

• 𝛽𝐸 ≡

(𝑓𝜗2

𝑟)2

4𝜌

= 0.5

• 𝑁′: the mass of the DM-nucleus interaction mediator
• Solid orange and green lines: single mediator

scenario, i.e., 𝜗𝑌 = 𝜗1

𝑟 = 𝜗2 𝑟

• Dashed orange and green lines: multi-mediator
• scenario. One of them is fixed to 10−2 (e.g., Baryon

number gauged dark gauge boson [deNiverville, Pospelov,

Ritz (2015)])

• For LDMX, 𝜗𝑓 in [LDMX, 1808.05219] identified as 𝜗𝑌.
• Sensitivity reach is already better than DUNE,

compared to the result in [De Romeri, Kelly, Machado

(2019)].

Doojin Kim, University of Arizona Searching for new physics – Leaving no stone unturned

Conclusions

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 Null signal observation at conventional dark matter detection experiments motivates us to look into mass scales other than that of WIMP.  Models with light mediators and dark matter are interesting and receiving rising attention.  Not only energy spectrum but also timing spectrum can be utilized in the search for light dark matter-induced signals: A combination of timing and energy cuts can eliminate SM neutrino backgrounds efficiently.  The current CsI data shows a 2.4 − 3𝜏 excess which can be explained by dark matter arising from dark photon decay.  The experimental sensitivities for dark matter parameter space is already better than the DUNE expectation, and comparable to the LDMX expectation.