DUNE BSM Group Meeting, April 10 th , 2018 In collaboration with KC - - PowerPoint PPT Presentation

Doojin Kim DUNE BSM Group Meeting, April 10th, 2018

In collaboration with KC Kong, Jong-Chul Park and Seodong Shin

Doojin Kim, CERN DUNE BSM Group Meeting

• 1-

Summary: Generic BDM Signatures

𝜓1 𝑓/𝑂 𝑓/𝑂 𝜚 𝜓1 𝛿1

ProtoDUNE

𝜓1 𝜓1 𝜓0 𝜓0

Galactic Center

𝜓1 𝑓/𝑂 𝑓/𝑂 𝜚 (in)visible 𝜓2 𝜓1 𝛿1

ProtoDUNE (𝑏) Elastic scattering (eBDM) (cf. eBDM at DUNE [Necib, Moon,

Wongjirad, Conrad (2016); Alhazmi, Kong, Mohlabeng, Park (2016)] )

(𝑐) Inelastic scattering (iBDM) (cf. iBDM at DUNE [DK, Park, Shin (2016)] )

• 𝜓0: heavier DM
• 𝜓1: lighter DM
• 𝛿1: boost factor of 𝜓1
• 𝜓2: massive unstable dark-sector state
• 𝜚: mediator/portal particle

𝑛0 = 𝐹1 = ~30 MeV −~10 GeV with ℱ

𝜓1 = ~10−1 − 10−6 cm−2s−1

Studied in arXiv:1803.03264 in collaboration with Chatterjee et al. Today’s focus (in collaboration with Kong, Park and Shin)

Doojin Kim, CERN DUNE BSM Group Meeting

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Summary: Production of BDM & Benchmark Model

 Vector portal (e.g., dark gauge boson scenario) [Holdom (1986)]  Fermionic DM  𝜓2: a heavier (unstable) dark-sector state  Flavor-conserving neutral current  elastic scattering  Flavor-changing neutral current  inelastic scattering

ℒint ∋ − 𝜗 2 𝐺

𝜈𝜉𝑌𝜈𝜉 + 𝑕11

𝜓1𝛿𝜈𝜓1𝑌𝜈 + 𝑕12 𝜓2𝛿𝜈𝜓1𝑌𝜈 + h. c. +(others)



SM Dark 𝛿 𝑌 𝜗  Not restricted to this model: various models conceiving BDM signatures  BDM source: galactic center, solar capture, dwarf galaxies, assisted freeze-out, semi-annihilation, fast- moving DM etc. [Agashe et al. (2014); Berger et al. (2015); Kong et al. (2015); Alhazmi et al. (2017); Super-K (2017);

Belanger et al. (2011); D’Eramo et al. (2010); Huang et al. (2013)]

 Portal: vector portal, scalar portal, etc.  DM spin: fermionic DM, scalar DM, etc.  iBDM-inducing operator: two chiral fermions, two real scalars, dipole moment interactions, etc. [Tucker-

Smith, Weiner (2001); Giudice, DK, Park, Shin (2017)]

𝑌 𝜓2 𝜓1 𝑕12



 Production of boosted DM: two-component boosted DM scenario [Agashe, Cui, Necib, Thaler (2014)]

Doojin Kim, CERN DUNE BSM Group Meeting Fiducial vol. Active vol. Insulator Exoskeleton Total vol.

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Challenge: Cosmic-origin BGs and eBDM Signal

Quite a few low-energy particles Vertical muons above 10 MeV: ~𝟐𝟏𝟐𝟏 /𝐧𝟑/yr Cosmogenic neutrons (very rare) Atmospheric neutrinos (very rare): ~𝟓𝟏 single- track-involving e- like events/yr/kt Signal of interest

𝑓− 𝑓− 𝑓− irreducible An impractically small mistake rate is demanded!

Doojin Kim, CERN DUNE BSM Group Meeting

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“Earth Shielding”

Earth Cosmic muons Boosted DM  Background and signal events are coming from everywhere.  Half of them travel through the earth.  Backgrounds can’t penetrate the earth while signals can!  Accept only events traveling through the earth (i.e., coming out of the bottom surface) at the price of half statistics; direction inferred from recoil track  Essentially no cosmic-origin BGs except atmospheric neutrino background (cf. observation

• f upward-muons induced by

muon neutrinos created by DM annihilation [NOvA

Collaboration in progress])

Doojin Kim, CERN DUNE BSM Group Meeting

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Muon Flux inside the Earth

[Particle Data Group (2015)]

 𝑂

𝜈 at sea level is ~100 m−2s−1sr−1 = 3 ×

109 m−2yr−1sr−1. [Particle Data Group (2015)]  𝑂

𝜈 at 20 km.w.e. ≈ 7 km below sea level is

~10−9 m−2s−1sr−1, i.e., suppressed by a factor of ~1011.  (Potential) muon- induced BG is negligible for muons incident at 𝜄 > 𝜄𝑑𝑠.

Flattened by neutrino-genic muons

2𝜄𝑑𝑠 𝜄𝑑𝑠 𝑆⨁

𝜄𝑑𝑠 ≈ 7 km 2𝑆⨁ ≈ 0.03∘

Doojin Kim, CERN DUNE BSM Group Meeting

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Situation with 1-yr Data Collection from “All” Sky

~

40 2 neutrino-induced e-like,

single-track events/yr/kt

𝝃 𝝍𝟐

ℱ

𝜓1~ 3 × (101 − 106)

2 cm−2yr−1 Effectively, half year

Doojin Kim, CERN DUNE BSM Group Meeting

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Improving Signal Sensitivities

 The neutrino flux is uniformly distributed, whereas the boosted DM flux is mostly coming from the Galactic Center!  An angle cut improves! [Necib, Moon, Wongjirad, Conrad (2016); Super-K

(2017)]

𝜄𝐷

 What value of 𝜄𝐷 is the best/most optimal choice?

Doojin Kim, CERN DUNE BSM Group Meeting

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Angular Cut to Maximize the Signal Sensitivity

 Various significance calculation methods are considered since # of expected BG events are small.  Comparison of different signal events for a fixed number of BG events  A larger angle cut is better if # of signal is bigger.  Comparison of different exposure times for a fixed model point  A larger angle cut is better if more data is collected.

Doojin Kim, CERN DUNE BSM Group Meeting

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Model-independent Sensitivity

 Number of signal events 𝑂sig is

𝑂sig = 𝜏𝜗 ∙ ℱ ∙ 𝑢exp ⋅ 𝑂𝑓

• 𝜏𝜗: scattering cross section between 𝜓1 and (target) electron
• ℱ: flux of incoming (boosted) 𝜓1
• 𝑢exp: exposure time
• 𝑂𝑓: total # of target electrons

Controllable! (once a detector is determined) Realistic experimental effects such as cuts, energy threshold, etc are absorbed into 𝜏𝜗.

Doojin Kim, CERN DUNE BSM Group Meeting

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More Familiar Form

 More familiar parameterization possible with the below modification! 𝜏𝜗 vs. 𝑛0 (just like 𝜏 vs. 𝑛DM in conventional WIMP searches)

90% C.L.

Doojin Kim, CERN DUNE BSM Group Meeting

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Model-independent Sensitivity

 1-year exposure, i.e., effectively half-year data collection (= 1.6 × 107 sec), is assumed.  The limits from all-sky data are DM halo model- independent (up to total flux).  Angular cuts improve the experimental sensitivities at the cost of DM halo model- dependence (optimal 𝜄𝐷 values differ detector-by- detector & run time).

Doojin Kim, CERN DUNE BSM Group Meeting

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Dark Photon Parameter Space: Invisible X Decay

 Case study 1: mass spectra for which dark photon decays into DM pairs, i.e., 𝑛𝑌 > 2𝑛1  1-year data collection from the entire sky and 𝑕11 = 1 are assumed.  Elastic and inelastic scattering channels are complementary to each

• ther.

Elastic scattering

Inelastic scattering

Babar

Doojin Kim, CERN DUNE BSM Group Meeting

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Dark Photon Parameter Space: Visible X decay

Babar NA48/2

 Case study 2: mass spectra for which dark photon decays into lepton pairs, i.e., 𝑛𝑌 < 2𝑛1  1-year data collection from the entire sky and 𝑕11 = 1 are assumed.  Elastic scattering channel allows us to explore (slightly) wider parameter space (for the chosen benchmark point).

Elastic scattering

Inelastic scattering

Doojin Kim, CERN DUNE BSM Group Meeting

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Expected Number of Signal Events

ProtoDUNE can cover the parameter space uncovered by SK! (especially the region where the relevant recoil energy is lower than 100 MeV.)  Full ProtoDUNE and 2𝑛1 > 𝑛𝑌 (i.e., the case of visibly-decaying X) and 𝑕11 = 1 are assumed.  Shown are the results with 1-year (effectively ½-year) exposure.

SK all-sky 90% C.L. from atm-𝜉 measurements SK all-sky 90% C.L. from atm-𝜉 measurements SK 30∘–cone 90% C.L. from a BDM search

Doojin Kim, CERN DUNE BSM Group Meeting

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Expected Experimental Reach

The analysis with an angle cut allows to probe more parameter space, as expected.

 Full ProtoDUNE and 2𝑛1 > 𝑛𝑌 (i.e., the case of visibly-decaying X) and 𝑕11 = 1 are assumed.  Shown are the results with 1-year and 2-year exposures.

SK all-sky 90% C.L. from atm-𝜉 measurements SK all-sky 90% C.L. from atm-𝜉 measurements SK 30∘–cone 90% C.L. from a BDM search

Doojin Kim, CERN DUNE BSM Group Meeting

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Conclusions

 Overwhelming cosmic-ray background can be controlled with the “Earth Shielding”.  ProtoDUNE possesses excellent sensitivities to a wide range of (light) boosted DM, hence allows a deeper understanding in non-minimal dark sector physics.  ProtoDUNE can provide an alternative avenue to probe dark photon parameter space and information complementary to that from iBDM searches.  Physics at ProtoDUNE can offer a more realistic BSM physics guideline for DUNE. 𝑤𝐸𝑁 Scattering Non-relativistic (𝑤𝐸𝑁 ≪ 𝑑) Relativistic (𝑤𝐸𝑁~𝑑) elastic Direct detection Boosted DM (eBDM) inelastic inelastic DM (iDM) inelastic BDM (𝑗BDM)

Doojin Kim, CERN DUNE BSM Group Meeting

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iBDM and eBDM Prospects at DUNE

 Comparison between ProtoDUNE 1-year vs. DUNE 10 kt + 10 kt, DUNE 20 kt + 20 kt 1-year with all-sky data for iBDM (left panel) and eBDM (right panel) signatures  The limit for iBDM (eBDM) becomes lower by ~2 (~1) orders of magnitude at DUNE due to background-free analysis (large neutrino-induced background).  Improvement by 𝑊

Detector for iBDM vs. 𝑊 Detector for eBDM.

Doojin Kim, CERN DUNE BSM Group Meeting

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Probing Dark Photon Parameter Space

 Comparison between ProtoDUNE 1-year vs. DUNE 10 kt + 10 kt 1-year with all-sky data for invisible X decay (left panel) and visible X decay (right panel)  iBDM achieves a wider coverage due to (almost) background-free analysis.  Searches for eBDM from point-like sources (e.g., Sun) are highly motivated as they also allow (almost) zero-background searches.

Back-up

Doojin Kim, CERN DUNE BSM Group Meeting

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Two-component Boosted DM Scenario

𝜓0 𝜓0 𝜓1 𝜓1 SM SM

 A possible relativistic source: BDM scenario (cosmic frontier), stability of the two DM species ensured by separate symmetries, e.g., 𝑎2 ⊗ 𝑎2

′, 𝑉 1 ⊗ 𝑉 1 ′, etc.

𝑍 𝑍

1

Freeze-out first Dominant relic

“Assisted” freeze-out mechanism

[Belanger, Park (2011)]

Freeze-out later

𝑍

1

Negligible, non-relativistic relic

Doojin Kim, CERN DUNE BSM Group Meeting

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“Relativistic” Dark Matter Search

𝜓0 𝜓0 𝜓1 𝜓1 𝜓1

(Galactic Center at CURRENT universe) (Laboratory) becomes boosted, hence relativistic! (𝛿1 = 𝑛0/𝑛1)

[Agashe, Cui, Necib, Thaler (2014)]

 Heavier relic 𝜓0: hard to detect it due to tiny/negligible coupling to SM  Lighter relic 𝜓1: hard to detect it due to small amount 𝜓0 𝜓0 𝜓1 𝜓1 SM SM

Doojin Kim, CERN DUNE BSM Group Meeting

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eBDM Search at Super-K

[Super-K Collaboration, (2017)]

Single-ring-like objects only High threshold energy

Doojin Kim, CERN DUNE BSM Group Meeting

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Model-independent Reach

 Number of signal events 𝑂sig is

𝑂sig = 𝜏𝜗 ∙ ℱ ∙ 𝐵 ∙ 𝑢exp ⋅ 𝑂𝑓

• 𝜏𝜗: scattering cross section between 𝜓1 and (target) electron
• ℱ: flux of incoming (boosted) 𝜓1
• 𝐵: acceptance
• 𝑢exp: exposure time
• 𝑂𝑓: total # of target electrons

Controllable! (once a detector is determined) Here determined by distance between the primary (ER) and the secondary vertices, other factors such as cuts, energy threshold, etc are absorbed into 𝜏𝜗.