Jong-Chul Park

4th TAU Meeting2020.06.09

with B. Dutta, D. Kim, S. Liao, S. Shin, L. Strigari & A. Thompson [PRL (2020) & 2006.XXXXX]

DM SM

SMDM

Interaction

Correct thermal relic abundance:

Ωℎ2~0.1 𝑝𝑏

𝜎𝑣with 𝜎𝑣 ~

𝛼𝑋2𝑚𝜒

2

𝑀4 (M: dark scale/mediator)

Weak coupling naturally weak scale mass:

~1 GeV – 10 TeV mass range favored

weak scale (new) physics

* Axion: another classic solution by CAPP.

annihilation

Freeze-out

Relic abundance

IceCube

CTA

Fermi-LAT

SK

XENON1T

AMS-02

DAMA

ATLAS

Planck

CMS

COSINE-100

OnlyWIMP? No!

10-22 eV keV MeV GeV TeV PeV 100𝑀⨀~1068 eV

MACHO /Primordial

BHsnon-particle

10-22 eV keV MeV GeV TeV PeV

Superheavy/ Composite

WIMPzillaQ-ball

Dark-quark nugget

non-thermal

WIMPwell-

motivatedextensively

studiedthermal

Lightparticle

DMcan be

thermal

SuperlightWDM

Sterile νmay be thermal

Ultralight Scalar field

(QCD) AxionHidden photon

non-thermal

100𝑀⨀~1068 eV

10-22 eV keV MeV GeV TeV PeV

Lightparticle

DM

For heavy mediator, 𝜎𝑣 ~𝛼𝑋2𝑚𝜒

2

𝑀4

For weak scale physics,

sub-GeV DM overproduction

New mediator < 𝑀𝑊 for freeze-out

or freeze-in, …

100𝑀⨀~1068 eV

New DM relic determination mechanisms:

Assisted Freeze-Out [arXiv:1112.4491]

Cannibal DM [arXiv:1602.04219, 1607.03108]

Co-Decaying [arXiv:1105.1652, 1607.03110]

Semi-Annihilation [arXiv:0811.0172, 1003.5912]

SIMP [arXiv:1402.5143]

… Various light DM/mediator scenarios:

MeV DM for GC 511 keV line observation [astro-ph/0309686]

Secluded MeV DM [arXiv:0711.3528, 0711.4866]

Sommerfeld enhancement for 𝑒+ excess [arXiv:0810.0713]

(𝑔 − 2)𝑒, 𝜇: ~2 − 3𝜎 discrepancy [arXiv:1806.10252]

New ν interactions for the MiniBooNE excess [arXiv:1807.09877]

Solutions of Yukawa coupling hierarchy prob. [arXiv:1905.02692]

…

10-22 eV keV MeV GeV TeV PeV

Lightparticle

DM

𝐸𝑘~𝑚𝑣2< 𝑶(keV) with 𝑣~10−3:

< 𝐸𝑟𝑡ℎ of typical DM direct detectors

for nuclear recoils

100𝑀⨀~1068 eV

Cosmogenic energetic DM searches: COSINE-

100, DUNE/ProtoDUNE, IceCube, SK/HK/KNO, …

GC, Sun, …

Large Vol. detector

New ideas for low 𝐸𝑟𝑡ℎ are required!

Ionization by e-recoils (semiconductor)

[arXiv:1108.5383, 1509.01598]

Ejection of e’s (graphene, C-nanotube)

[arXiv:1606.08849, 1706.02487, 1808.01892]

Evaporation of He by nuclear-recoils

[arXiv:1706.00117]

Gaphene-Josephson-junction (sub-keV~MeV)

D. Kim, JCP, KC Fong, GH Lee [arXiv:2002.07821]

…

Seodong’s Talk

[Passive]

Should we just

wait for

something

dropping from

the sky?Active

searches!

Active searchesPassive searches

Cloud chamber:

𝑒+, 𝜇±, …

Collider: controlled environment

Conventional colliders

Head-on collision of light

SM-sector (stable) particles

to produce heavier SM states

and study resulting pheno.

~5% visible sector

Direct detection: (hopefully) DM?

DM “Production” (e.g. fixed target exp.): controlled environment

Dark matter productions

Dump of SM-sector (stable)

particles onto a target

to produce dark-sector states

and study resulting pheno.

~25% dark sector

A new strategy to search for DM signals in ν experiments:

we can efficiently isolate DM signals from the SM ν BGs

using timing & energy spectra at (certain kinds of) neutrino experiments

with low-E & pulsed-beam, “CEνNS”.

Application: the measured CsI data of the COHERENT experiment

Result: mild (𝟐. 𝟒 − 𝟑𝝈) excess beyond known backgrounds!

The excess can be explained by light DM arising from dark gauge boson decay.

Various current/future Coherent Elastic ν-Nucleus Scattering (CEνNS) experiments

Beam-induced ν: CCM, COHERENT, (JSNS2), …

Reactor ν: CONNIE, CONUS, MINER, NEON, Nu-Cleus, ν GEN, RED-100, Ricochet,

TEXONO, …

(JSNS2)NEON

Low E, High luminosity, Pulsed beam

Hyun Su’s Talk

Main goal: direct measurement of coherent

elastic ν-nucleus scattering (CEνNS)

dominant interaction for 𝐸𝜈 ≲ 50 MeV

COHERENT @ Oak Ridge: 1 GeV p beam on Hg target,

600 ns wide pulses & 60 Hz, ~8.8 × 1015 POT/s

(JSNS2) @ J-PARC: 3 GeV p beam on Hg target, 2 × 100 ns

pulses separated by 440 ns & 25 Hz, ~2.1 × 1015 POT/s

CCM @ LANL: 0.8 GeV p beam on W target, 290 ns wide

pulses & 20 Hz, ~5.6 × 1014 POT/s

Gd-LS17 ton

2.6 MeV

COHERENT

JSNS2

𝝁 decay:delayed ν’s

𝝅 decay:prompt ν’s

COHERENT [1803.09183] & JSNS2 [1705.08629]

14.6 kg6.5 keV

24 kg20 keV

185 kg13 keV

10 kg5 keV

Low E, High luminosity, Pulsed beam

Prompt ν’s: 𝑇 < ~1 𝜇s & 𝐸𝜈 = 29.8 MeV

Delayed ν’s: mostly 𝑇 > ~1 𝜇s &

𝐸𝜈 = 0 − 53 MeV

𝜋 decay

𝜇 decay

COHERENT [arXiv:1803.09183 & 1804.09459]

𝝁 decay:delayed ν’s

𝝅 decay:prompt ν’s

𝐸𝜈 = 30 MeV & CsI: 𝐸𝑟,𝑁𝑚𝑎𝑥~15 keV

Low 𝐸𝑡ℎ required, e.g. DM direct detectors!

Meson decays (P1): 𝜋0(𝜂) → 𝛾 + 𝛾/𝑿

𝜋− absorption (capture) process (P2): 𝜋− + 𝑝 → 𝑛 + 𝛾/𝑿 (X: single-valued E)

Charge exchange processes (P3): 𝜋−(+) + 𝑝 𝑛 → 𝑛 𝑝 + 𝜋0 & 𝜋0 → 𝛾 + 𝛾/𝑿

𝑒±-induced cascade (P4): electromagnetic cascade showering & 𝛾 → 𝑿

𝑿

𝜒

𝜒

Proton beam

Target

𝜋0, stopped 𝜋±

𝑝/𝑛 in target

Detector

𝑿𝑓

ҧ𝑓

𝜿𝒇𝑿𝒙𝒇

𝑿𝑿

𝜒

𝜒𝜿𝑫𝑿

GEANT4 (p dump ~ γproduction) + our own code

Nucleus scattering (D1): (small 𝐸𝑟)

Electron scattering (D2): (large 𝐸𝑟)

𝑿

𝜒

𝜒

Proton beam

Target

𝜋0, stopped 𝜋±

𝑝/𝑛 in target

𝜒𝜒

𝑁/𝑒

Detector

𝑁/𝑒𝜒 𝜒

𝑓 𝑓𝜿𝒇𝑽𝒙𝒇

𝑽

𝜿𝑫𝑽

𝐴′

Key specification of benchmark experiments (Low E, High luminosity, Pulsed

beam) & detectors under consideration

The protons-on-target (POT) values are expected spills for 5000-hours operation per year

The mass of the LAr detector in parentheses in COHERENT is for a future upgrade.

COHERENT: 1 GeV p beam, 600 ns wide pulses & 60 Hz

JSNS2: 3 GeV p beam, 2 × 100 ns pulses separated by 440 ns & 25 Hz

CCM: 0.8 GeV p beam, 290 ns wide pulses & 20 Hz

Possible models relevant to the benchmark experiments

Respective coupling constants & gauge charges

Production & detection channels

Various possibilities for a dark 𝐴′

Relativistic (solid) vs. Non-relativistic

(dotted)

Short-lived vs. Long-lived

𝑚χ = 5 MeV

Relativistic: Prompt t-bins,

DM flux maximized for 𝜏 < a few × 10 ns

Non-relativistic: Only for 𝑚𝐴′ ≈ 138 MeV (≈

𝑚𝜋− +𝑚𝑝 −𝑚𝑛), Mostly Prompt t-bins (𝜏 ≲ 0.1𝜇𝑠)

DM flux maximized for 𝜏 < a few ns

𝑚χ: 5 MeV is assumed,

but OK for any values < 𝑚𝐴′/2

𝑝 + 𝑇 → 𝐴′ +⋯𝐴′ → 𝜒 ҧ𝜒

completely

considerablycompletely

considerably

𝐸𝑟 > 14 keV (𝐸𝑟𝑚𝑎𝑥 ≃ 2𝐸𝜈

2/𝑀𝑇 for CsI)

Prompt ν: completed removed

Delayed ν (& DM signal): still remains

𝑇 < 1.5 μs

Delayed ν: considerably removed

DM signal: still remains

for CsI at COHERENT

Expected unit-normalized t-distributions of DM

& ν scattering events

ν events: ν scattering cross sections convolved

and stacked & collectively unit-normalized.

With appropriate t-cuts, delayed ν can be

significantly removed while a large portion of

DM events are retained.

Before t-cut After t-cut

t-cuts: delayed ν significantly removed & DM events almost retained.

CsI

LAr

E-cuts: prompt ν (completely) removed & DM events considerably retained.

Before t-cut After t-cut

t-cuts: delayed ν significantly removed & DM events almost retained.

CCM LAr

JSNS2

Gd-LS

E-cuts: prompt ν (completely) removed & DM events considerably retained.

COHERENT & CCM: designed to be sensitive the nucleus recoil [low 𝐸𝑟~𝑂(10 keV)]

JSNS2: a good sensitivity to the electron recoil [high 𝐸𝑟~𝑂(10 MeV)]

COHERENT-CsI: an upper 𝐸𝑟-cut beyond which BG uncertainties are high.

CCM: 50 keV is not the optimized cut, only 𝐸𝑟 > 50 keV data will be available.

CCM: two working points (WP) – a tight cut (the experimental recommendation) & a loose

cut (the t-spectrum of the DM signal)

Data released by COHERENT: CsI detector 14.57 kg×308.1 days [arXiv:1804.09459]

Analysis scheme

Fix the average rms radius of the neutron distribution to 𝑅𝑛 = 4.7 fm

14 keV < 𝐸𝑟 < 28 keV & 𝑇 < 1.5 μs 𝐹𝑁Helm 𝑞2 =

3𝑗1(𝑞𝑅0)

𝑞𝑅0exp(−

𝑞2𝑠2

2)

𝑅𝑛2 = 3𝑅0

2/5 + 3𝑠2

97 : total events

− 49 : classified as steady-state (SS) backgrounds

− 19 : identified as delayed (SM) ν events (due to 𝐸𝑟 & 𝑇-cuts)

− 0 : identified as prompt (SM) ν events (due to 𝐸𝑟-cut)

26 : “Excess!!”

Significance (𝑅𝑛 = 4.7 fm): 𝟐. 𝟒 𝝈

Significance (𝑅𝑛 = 5.5 fm): 𝟑. 𝟎 𝝈Significance =

𝑁obs−𝑁SS−𝑁BRN−𝑁𝜈

2𝑁SS+𝑁BRN+𝑁𝜈[arXiv:1801.05546]

[arXiv:1801.05546]

− 3 : beam-related neutron (BRN) backgrounds

Fits to the data w/ the cuts vs. w/o cuts (=the full data)

1𝜎-credible regions

𝑚𝑉

𝑚𝜒= 3 & 𝛼𝐷 =

𝜅𝐷𝑉 2

4𝜋= 0.5

A best-fit 𝐸𝑟 spectrum after t-cut

(𝑚𝑉 = 138 MeV & 𝑌 = 6.7 × 10−11)

Best-fit values of Y for several choices of 𝑚𝑉

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

Projected sensitivity in the single-

mediator scenario: a dark photon

mediator

Data & information about BGs are

available for COHERENT, but not for

CCM &JSNS2

A different curvature of JSNS2: due to

𝑚𝑒 ≪ 𝑚𝑉, but 𝑚𝑁 ≫ 𝑚𝑉 for others

NA64, BaBar: missing 𝐸𝑇

𝑚𝑉

𝑚𝜒= 3 & 𝛼𝐷 =

𝜅𝐷𝑉 2

4𝜋= 0.5

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

Projected sensitivity in the double-

mediator scenario: a U(1)B gauge

boson + a dark photon mediator for

illustration

𝜅𝑓𝑋 = 𝑔𝐵 = 2 × 10−3 & 𝜅𝐷

𝑋 = 10−7,

𝜅𝑓𝑉 = 𝜖𝑒, 𝛼𝐷 = 𝜅𝐷

𝑉 2/4𝜋 = 0.5

A different curvature of JSNS2: due to

𝑚𝑒 ≪ 𝑚𝑉, but 𝑚𝑁 ≫ 𝑚𝑉 for others

NA64, BaBar: missing 𝐸𝑇

No firm signal observation at conventional DM searches light dark sector.

A new strategy to search for light DM signals: A combination of T & E-cuts can

efficiently eliminate SM ν BGs at neutrino-beam experiments, e.g., CEνNS.

Application: the measured CsI data of the COHERENT experiment

Result: 𝟐. 𝟒 − 𝟑𝝈 excess!

The excess can be explained by DM arising from dark gauge boson decays.

COHERENT, CCM, JSNS2: capable of probing wide ranges of unexplored

parameter space, getting closer to the thermal DM relic density line via the

“appearance” of produced DM.

Back-Up

GEANT4 10.5 (FTFP_BERT) simulation results

𝑁𝑖: the fractional number of particles of species i per POT

The 4th ~ 9th rows: further processes that produced charged pions undergo