Light Thermal Dark Matter & Accelerator Complementarity · Outline 2 • Thermal Dark Matter is important beyond WIMPs •sub-GeV (i.e. Standard Model scales!) is the next obvious

U.S. Cosmic Visions: New Ideas In Dark Matter March 23, 2017

Light Thermal Dark Matter & Accelerator Complementarity

Philip Schuster (SLAC)

Thursday, 23 March, 17

Outline

2

• Thermal Dark Matter is important beyond WIMPs

• sub-GeV (i.e. Standard Model scales!) is the next obvious place to seriously explore thermal DM

• The key role of accelerator experiments in any light dark matter program

• Comments on testing or discovering LDM


TeV

Thermal DMAxions

SterileNeutrinos

Hidden sector

WIMP

Asymmetric

Gravitino

µeV keV MeV GeV

Targeted Exploration

• Wide range of possibilities – even the ones highlighted by P5 span ~20 orders of magnitude in DM mass!


TeV

Thermal DMAxions

SterileNeutrinos

Hidden sector

WIMP

Asymmetric

Gravitino

µeV keV MeV GeV

Targeted Exploration

Thermal Dark Matter of particular importance

• Wide range of possibilities – even the ones highlighted by P5 span ~20 orders of magnitude in DM mass!


Thermal Dark Matter: A Prime Target

Simple: Interactions between dark and familiar matter maintain thermal equilibrium as Universe cools, until critical density below which dark matter annihilation “freezes out”

Predictive: Strength of dark matter interaction with familiar matter determines the residual abundance –so observed DM abundance predicts strength of DM interactions

Straightforward: Many well-motivated models have the ingredients to realize thermal dark matter(including, but not limited to, WIMPS)

Data Driven! Evidence from CMB and BBN for hot & dense thermal phase of Universe. We don’t have to speculate (much) about thermal origin possibility.

4


5

Vicinity of Weak Scale: A Prime Target

TeV

GeV

MeV

SM Matter Dark Matter?

me ⇠ small #⇥MW

Mproton

⇠ Mlarge

e�#

Look for new stable matternear familiar stable matter!


6


TeV

GeV

MeV


me ⇠ small #⇥MW

MW

Mproton

⇠ Mlarge

e�#

For decades: look here!

Look for new stable matternear familiar stable matter!

Generic mass scale for matter with O(1) coupling to origin of EWSB



7


TeV

GeV

MeV


me ⇠ small #⇥MW

MW

Mproton

⇠ Mlarge

e�#

(derived from weak scale)

(accidentally close to weak scale)...but where do we expect hidden sector matter – with only small couplings to SM matter (generated radiatively)?

For decades: look here!


8


TeV

GeV

MeV


me ⇠ small #⇥MW

MW

Mproton

⇠ Mlarge

e�#


(accidentally close to weak scale)

Where do we expect hidden-sector matter?


small #⇥MW

(e.g. dark sector scalar mixing with SM higgs)


⇠ MW ⇥ e�#

9


TeV

GeV

MeV


me ⇠ small #⇥MW

MW

Mproton

⇠ Mlarge

e�#



small #⇥MW


Where do we expect hidden-sector matter?

(e.g. “hidden valley” scenario: ~conformal to weak scale, then confining)


10


TeV

GeV

MeV


me ⇠ small #⇥MW

MW

Mproton

⇠ Mlarge

e�#




Look here for hidden-sector matter!

⇠ MW ⇥ e�#

small #⇥MW


11


TeV

GeV

MeV


me ⇠ small #⇥MW

MW

Mproton

⇠ Mlarge

e�#



10


⇠ MW ⇥ e�#

small #⇥MW

Expect hidden sector matter in the vicinity of – but naturally below – weak scale

The broad vicinity of the weak scale is perhaps the best motivated place to discover dark matter:

• An important scale!

• Familiar stable matter resides here!

• Thermal DM works well here!


12

Scientific Goal

Test Thermal Dark Matter in the MeV-TeV Range

Need experiments that can explore the MeV-GeV “WIMP”-like scenarios, analogous to the Direct Detection, LEP, and LHC efforts to test WIMPs in the GeV-TeV range.

What are the ingredients of a high-impact program that can address the sub-GeV mass range?

Look to the 30-yr WIMP effort for lessons. Many similarities and a few critical differences…


13

WIMP & Thermal LDM Programs: Improved Starting Information

Cosmology and astrophysics is far more advanced: narrows the set of thermal scenarios

Standard Model is far better explored and understood: narrows the set of interactions

…weakly coupled MeV-GeV vector mediator interactions preferred

…p-wave and co-annihilation scenarios preferred


14

Characterize the “dark” current - SM current interactions mediated by a vector

WIMP & Thermal LDM Programs: Phenomenology Similarities

Xe�

e+

γ

✏+ other modes

Aʹ′ �̄

�

JµDM Jµ

SMXγ

✏

Aʹ′


15


Phenomenology of WIMP scenarios carries over to MeV-GeV WIMP-like scenarios:

Dark Matter CurrentParticle Type

Different Low-Energy Phenomenology!


15


Phenomenology of WIMP scenarios carries over to MeV-GeV WIMP-like scenarios:

Dark Matter CurrentParticle Type

Different Low-Energy Phenomenology!

Just like sneutrino or Dirac neutrino WIMP candidate

Just like neutralino WIMP candidates


16

Key Thermal Targets Span Large Range.

WIMP & Thermal LDM Programs: Direct Detection Similarities

Z-tree

W-loop

GeV-10 TeV Thermal WIMPs


16

Key Thermal Targets Span Large Range.

WIMP & Thermal LDM Programs: Direct Detection Similarities

Z-tree

W-loop

GeV-10 TeV Thermal WIMPs

Similar to WIMPs: thermal LDM motivates large range of direct detection cross-section

HPseudoLDirac FermionInelastic Scalar

Majorana Fermion

Elastic Scalar

1 10 102 10310-55.

10-53.

10-51.

10-49.

10-47.

10-45.

10-43.

10-41.

10-39.

10-37.

10-35.

mDMHMeVL

seHcm

2 L

current constraints

MeV-GeV Thermal LDM

A’-tree

A’-loop


17

WIMP & Thermal LDM Programs: Radically Different Story for Accelerators

TeV-scale electro-weak states were not easily accessible to accelerators when WIMP effort started!

Decades of development of mid- to high-energy accelerator infrastructure and impressively powerful particle detector technology has now taken place...

In fact, a tremendous amount of sub-GeV parameter space has already been explored by accelerator experiments!

Whereas sub-GeV weakly coupled particles readily accessible to accelerators as the LDM effort begins


18

•Accelerators probe DM interactions at the same momentum scales governing freeze-out: much sharper coupling vs. mass milestones

•Plot sensitivity with unfavorable assumptions for unknown model parameters

Accelerators: Thermal LDM Readily Accessible

Elastic an

d Inelastic

Scalar Rel

ic Bound

Majorana

Fermion R

elic Bound

Pseudo-D

irac Fermi

on Relic B

ound

10 102 10310-1410-1310-1210-1110-1010-910-810-710-610-510-4

A' Mass HMeVL

e2

A'Æ DM pair ConstraintsmA '=3 mDM , aD=0.5


Majorana Fermion

Elastic Scalar

1 10 102 10310-55.

10-53.

10-51.

10-49.

10-47.

10-45.

10-43.

10-41.

10-39.

10-37.

10-35.

mDMHMeVL

seHcm

2 L

Accelerators probe coupling strength vs. mass, not direct detection cross section vs. mass

current accelerator constraints

Milestone lines move up as assumptions are varied


19

•Accelerators probe DM interactions at the same momentum scales governing freeze-out: much sharper coupling vs. mass milestones

•Plot sensitivity with unfavorable assumptions for unknown model parameters


Majorana Fermion

Elastic Scalar

1 10 102 10310-55.

10-53.

10-51.

10-49.

10-47.

10-45.

10-43.

10-41.

10-39.

10-37.

10-35.

mDMHMeVL

seHcm

2 L

Can instead use variable that determines freeze-out abundance vs dark matter mass

Pseudo-D

irac Fermi

on Relic T

arget

Majorana

RelicTarg

et

Elastic &

Inelastic S

calarRelic

Targets

BaBar

LHC

LEP

NA64

Belle IIE137

MiniBooNE

LSND

Pseudo-D

irac Fermi

on Relic T

arget

Majorana

RelicTarg

et

Elastic &

Inelastic S

calarRelic

Targets

1 10 102 10310-1610-1510-1410-1310-1210-1110-1010-910-810-710-610-510-4

mc @MeVD

y=e2aDHm cêm A

'L4

Thermal Relic Targets & Current Constraints

Milestone are fixed, but accelerator experiments move down the plot as assumptions are varied

Accelerators: Thermal LDM Readily Accessible


20

Accelerator Experiments already exploring LDM

Remaining 1-3 orders of magnitude represent some of the best motivated parameter space. Accelerator efforts poised for discovery or decisive result. An amazing opportunity!

1 10 102 10310-4

10-3

10-2

10-1

1

10

aEM

0.5

4 p

mDM HMeVL

aD

Pseudo-Dirac Thermal DM

mA '=3 mDM

BaBar

NA64LSND

Belle-I

I

1 TeV Landau pole

1 10 102 10310-4

10-3

10-2

10-1

1

10

aEM

0.5

4 p

mDM HMeVLaD

Majorana Thermal DM

mA '=3 mDM

BaBar

NA64MiniBoone

LSND

Belle-I

I

E137

1 TeV Landau pole

Assuming thermal abundance to fix ✏


21

Much of both scalar DM scenarios has been probed, but it’s critical to close the remaining territory!

1 10 102 10310-4

10-3

10-2

10-1

1

10

aEM

0.5

4 p

mDM HMeVL

aD

Scalar Inelastic Thermal DM

mA '=3 mDM

BaBar

NA64

MiniBoone

LSNDBell

e-II

E137

1 TeV Landau pole

1 10 102 10310-4

10-3

10-2

10-1

1

10

aEM

0.5

4 p

mDM HMeVLaD

Scalar Elastic Thermal DM

mA '=3 mDM

BaBar

NA64

MiniBoone

LSND

Belle-I

I

E137

1 TeV Landau pole

CR

ESST

-II

SuperCDMSSNOLAB

Assuming thermal abundance to fix ✏

Accelerator Experiments already exploring LDM


22

Thermal LDM: Mediator Physics Plays a Central Role

Accelerator experiments leading the way exploring the possible mediator physics! This is a crucial part of the physics!

Elastic andInelasticScalar Relic Bound

Majorana FermionRelicBound

Pseudo-Dirac FermionRelicBound

1 10 102 10310-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

A' Mass HMeVL

e2

mA '=1.3 mDM , aD=0.5

Territory above the red lines motivated by thermal DM!

current constraints


23

Accelerator Complementarity

Accelerator experiments are in the best position to test all GeV-scale (and below) thermal DM scenarios.

WG3: Can this be done quickly and at reasonable cost?

WG3/4: How far do new experiments need to push for a null result to be robust (i.e. of lasting value)?

WG3/4: What are the important contributions from existing and already planned experiments?


24


For this purpose, a clear case can be made that multiple techniques are required:

Conversely, can a convincing discovery be made? After all, some of the best motivated parameter space is still unexplored!

Accelerator Missing Mass/Energy/Momentum

Accelerator Beam Dump Technique

Direct Detection Technique


25


Missing Mass/Energy/Momentum

!!

A�E1 E1 x

E1 (1� x)

Fixed-Target

Colliders

� ⇠ ↵D✏21

E2CM

� ⇠ ↵D✏21

m2�

Rate gives coupling information

m� < mA0 < 2m�Case I:


26


!!

A�E1 E1 x

E1 (1� x)

Fixed-Target

Colliders

10 MeV

100 MeV

200 MeV

500 MeV

1000 MeV

1500 MeV

InclusiveSingle e-Background

�

0 100 200 300 400 500

10-3

10-2

10-1

1

Electron |PT | [MeV]

EventFraction/5MeV

Electron |PT | Distributions, 50 MeV < Ee < 1.2 GeV, pZ > 0

Kinematics gives m�

Kinematics gives m�




27


A�E1 E1 x

E1 (1� x)

Fixed-Target

Colliders

Visible A’ searches give and ✏mA0




28


Can separately measure:

mA0 ✏ m� ↵D

From visible A’ exp. From missing mass/momentum exp.(and beam dumps)

Accelerator experiments can untangle the physics in detail

Still want Direct Detection to verify cosmological stability



29



!!

A�E1 E1 x

E1 (1� x)

Fixed-Target

CollidersCase II: 2m� < mA0

⇥ ⇠ �21

E2CM

� ⇠ ✏21

m2A0

Rate gives ✏

Rate gives ✏

mA0


30


!!

A�E1 E1 x

E1 (1� x)

Fixed-Target

Colliders

10 MeV

100 MeV

200 MeV

500 MeV

1000 MeV

1500 MeV

InclusiveSingle e-Background

�

0 100 200 300 400 500

10-3

10-2

10-1

1

Electron |PT | [MeV]

EventFraction/5MeV

Electron |PT | Distributions, 50 MeV < Ee < 1.2 GeV, pZ > 0

Kinematics gives mA0

Kinematics gives mA0

Case II: 2m� < mA0



31


Beam Dump Technique

� ⇠ ✏21

m2A0

� ⇠ ✏2

� ⇠ ↵D✏2

m2A0

N ⇠ ↵D✏4

m2A0

N ⇠ ↵D✏4

m4A0

or



32


Given info about provides sensitivity to

mA0 ✏↵D


Beam Dump Technique


33


Can separately measure:

mA0 ✏ ↵D

From missing mass/momentum exp. From beam-dump exp.

Accelerator experiments can almost untangle the physics in detail

Need Direct Detection to measure and verify cosmological stability

m�



34

Conclusions• Thermal dark matter is simple, predictive, and arguably the

least speculative possibility. If we do nothing else, we should test this idea!

• The broad vicinity of the weak scale is an excellent place to be looking –– the logical extension to the WIMP program.

• Accelerator experiments are in the best position to test (i.e. rule out or discover) light thermal DM –– all important scenarios are within 1-3 orders of magnitude of existing experiments’ cross-section reach.

• Accelerator experiments can also make a decisive discovery, and combined with direct detection experiments, can reveal the underlying dark sector physics


Documents

Light Thermal Dark Matter & Accelerator Complementarity · Outline 2 • Thermal Dark Matter is important beyond WIMPs •sub-GeV (i.e. Standard Model scales!) is the next obvious