doojin kim - indico.fnal.gov · doojin kim, cern-2 dune bsm group meeting summary: production of...

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

𝜒1

𝑒/𝑁 𝑒/𝑁

𝜙

𝜒1

𝛾1

ProtoDUNE

𝜒1

𝜒1

𝜒0

𝜒0

Galactic Center𝜒1

𝑒/𝑁 𝑒/𝑁

𝜙

(in)visible

𝜒2 𝜒1

𝛾1

ProtoDUNE

(𝑎) Elastic scattering (eBDM) (cf. eBDM at DUNE [Necib, Moon, Wongjirad, Conrad (2016); Alhazmi, Kong, Mohlabeng, Park (2016)] )

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

• 𝜒0: heavier DM• 𝜒1: lighter DM• 𝛾1: boost factor of 𝜒1• 𝜒2: massive unstable dark-sector state• 𝜙: mediator/portal particle

𝑚0 = 𝐸1 = ~30 MeV −~10 GeV with ℱ𝜒1 = ~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)


Summary: Production of BDM & Benchmark Model

Vector portal (e.g., dark gauge boson scenario) [Holdom (1986)]

Fermionic DM

𝜒2: a heavier (unstable) dark-sector state

Flavor-conserving neutral current elastic scattering

Flavor-changing neutral current inelastic scattering

ℒint ∋ −𝜖

2𝐹𝜇𝜈𝑋

𝜇𝜈 + 𝑔11 𝜒1𝛾𝜇𝜒1𝑋𝜇 + 𝑔12 𝜒2𝛾

𝜇𝜒1𝑋𝜇 + h. c. +(others)

SM

Dar

k

𝛾 𝑋

𝜖

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)]

𝑋

𝜒2

𝜒1

𝑔12

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.

-3-

Challenge: Cosmic-origin BGs and eBDM Signal

Quite a few low-energy particles

Vertical muons above 10 MeV: ~𝟏𝟎𝟏𝟎 /𝐦𝟐/yr

Cosmogenic neutrons (very rare)

Atmospheric neutrinos (very rare): ~𝟒𝟎 single-track-involving e-like events/yr/kt

Signal of interest

𝑒−

𝑒−

𝑒−

irreducible

An impractically small mistake rate is demanded!


“Earth Shielding”

Earth

Cosmic muonsBoosted 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

of upward-muons induced by

muon neutrinos created by

DM annihilation [NOvA

Collaboration in progress])


Muon Flux inside the Earth

[Particle Data Group (2015)]

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

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

𝑁𝜇 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 𝜃 > 𝜃𝑐𝑟.

Flattened by neutrino-genic muons

2𝜃𝑐𝑟

𝜃𝑐𝑟

𝑅⨁

𝜃𝑐𝑟 ≈7 km

2𝑅⨁≈ 0.03∘


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

~40

2neutrino-induced e-like,

single-track events/yr/kt

𝝂 𝝌𝟏

ℱ𝜒1~3 × (101 − 106)

2cm−2yr−1

Effectively, half year


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)]

𝜃𝐶

What value of 𝜃𝐶 is the best/most optimal choice?


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.


Model-independent Sensitivity

Number of signal events 𝑁sig is

𝑁sig = 𝜎𝜖 ∙ ℱ ∙ 𝑡exp ⋅ 𝑁𝑒

𝜎𝜖: scattering cross section between 𝜒1 and (target) electron

ℱ: flux of incoming (boosted) 𝜒1

𝑡exp: exposure time

𝑁𝑒: total # of target electronsControllable! (once a detector is determined)

Realistic experimental effects such as cuts, energy threshold, etc are absorbed into 𝜎𝜖 .


More Familiar Form

More familiar parameterization possible with the below modification!

𝜎𝜖 vs. 𝑚0 (just like 𝜎 vs. 𝑚DM in conventional WIMP searches)

90% C.L.


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 𝜃𝐶

values differ detector-by-

detector & run time).


Dark Photon Parameter Space: Invisible X Decay

Case study 1: mass spectra

for which dark photon decays

into DM pairs, i.e., 𝑚𝑋 >

2𝑚1

1-year data collection from

the entire sky and 𝑔11 = 1

are assumed.

Elastic and inelastic

scattering channels are

complementary to each

other. Elastic scattering

Inelastic scattering

Babar


Dark Photon Parameter Space: Visible X decay

BabarNA48/2

Case study 2: mass spectra

for which dark photon decays

into lepton pairs, i.e., 𝑚𝑋 <

2𝑚1

1-year data collection from

the entire sky and 𝑔11 = 1

are assumed.

Elastic scattering channel

allows us to explore (slightly)

wider parameter space (for

the chosen benchmark

point).

Elastic scattering

Inelastic scattering


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 2𝑚1 > 𝑚𝑋 (i.e., the case of visibly-decaying X) and 𝑔11 = 1 are assumed.

Shown are the results with 1-year (effectively ½ -year) exposure.

SK

all

-sk

y 90%

C.L

. fro

m

atm

-𝜈m

easu

rem

ents

SK

all

-sk

y 90%

C.L

. fro

m

atm

-𝜈m

easu

rem

ents

SK 30∘–cone 90% C.L. from a BDM search


Expected Experimental Reach

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

Full ProtoDUNE and 2𝑚1 > 𝑚𝑋 (i.e., the case of visibly-decaying X) and 𝑔11 = 1 are assumed.

Shown are the results with 1-year and 2-year exposures.

SK

all

-sk

y 90%

C.L

. fro

m

atm

-𝜈m

easu

rem

ents

SK

all

-sk

y 90%

C.L

. fro

m

atm

-𝜈m

easu

rem

ents

SK 30∘–cone 90% C.L. from a BDM search


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.

𝑣𝐷𝑀Scattering

Non-relativistic(𝑣𝐷𝑀 ≪ 𝑐)

Relativistic(𝑣𝐷𝑀~𝑐)

elastic Direct detection Boosted DM (eBDM)

inelastic inelastic DM (iDM) inelastic BDM (𝑖BDM)


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 𝑉Detector for iBDM vs. 𝑉Detector for eBDM.


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


Two-component Boosted DM Scenario

𝜒0

𝜒0

𝜒1

𝜒1

SM

SM

A possible relativistic source: BDM scenario (cosmic frontier), stability of the two DM species ensured by separate symmetries, e.g., 𝑍2 ⊗𝑍2

′ , 𝑈 1 ⊗ 𝑈 1 ′, etc.

𝑌0 𝑌1

Freeze-out first

Dominant relic

“Assisted” freeze-out mechanism[Belanger, Park (2011)]

Freeze-out later

𝑌1Negligible, non-relativistic relic


“Relativistic” Dark Matter Search

𝜒0

𝜒0

𝜒1

𝜒1

𝜒1

(Galactic Center at CURRENT universe) (Laboratory)

becomes boosted, hence relativistic!(𝛾1 = 𝑚0/𝑚1)

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

Heavier relic 𝜒0: hard to detect it due to tiny/negligible coupling to SM

Lighter relic 𝜒1: hard to detect it due to small amount

𝜒0

𝜒0

𝜒1

𝜒1

SM

SM


eBDM Search at Super-K

[Super-K Collaboration, (2017)]

Single-ring-like objects only

High threshold energy


Model-independent Reach

Number of signal events 𝑁sig is

𝑁sig = 𝜎𝜖 ∙ ℱ ∙ 𝐴 ∙ 𝑡exp ⋅ 𝑁𝑒

𝜎𝜖: scattering cross section between 𝜒1 and (target) electron

ℱ: flux of incoming (boosted) 𝜒1

𝐴: acceptance

𝑡exp: exposure time

𝑁𝑒: total # of target electronsControllable! (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 𝜎𝜖 .

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