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
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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
Thursday, 23 March, 17
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!
Thursday, 23 March, 17
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!
Thursday, 23 March, 17
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
Thursday, 23 March, 17
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!
Thursday, 23 March, 17
6
Vicinity of Weak Scale: A Prime Target
TeV
GeV
MeV
SM Matter Dark Matter?
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
Thursday, 23 March, 17
Generic mass scale for matter with O(1) coupling to origin of EWSB
7
Vicinity of Weak Scale: A Prime Target
TeV
GeV
MeV
SM Matter Dark Matter?
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!
Thursday, 23 March, 17
8
Vicinity of Weak Scale: A Prime Target
TeV
GeV
MeV
SM Matter Dark Matter?
me ⇠ small #⇥MW
MW
Mproton
⇠ Mlarge
e�#
(derived from weak scale)
(accidentally close to weak scale)
Where do we expect hidden-sector matter?
Generic mass scale for matter with O(1) coupling to origin of EWSB
small #⇥MW
(e.g. dark sector scalar mixing with SM higgs)
Thursday, 23 March, 17
⇠ MW ⇥ e�#
9
Vicinity of Weak Scale: A Prime Target
TeV
GeV
MeV
SM Matter Dark Matter?
me ⇠ small #⇥MW
MW
Mproton
⇠ Mlarge
e�#
(derived from weak scale)
(accidentally close to weak scale)
small #⇥MW
Generic mass scale for matter with O(1) coupling to origin of EWSB
Where do we expect hidden-sector matter?
(e.g. “hidden valley” scenario: ~conformal to weak scale, then confining)
Thursday, 23 March, 17
10
Vicinity of Weak Scale: A Prime Target
TeV
GeV
MeV
SM Matter Dark Matter?
me ⇠ small #⇥MW
MW
Mproton
⇠ Mlarge
e�#
(derived from weak scale)
(accidentally close to weak scale)
Generic mass scale for matter with O(1) coupling to origin of EWSB
Look here for hidden-sector matter!
⇠ MW ⇥ e�#
small #⇥MW
Thursday, 23 March, 17
11
Vicinity of Weak Scale: A Prime Target
TeV
GeV
MeV
SM Matter Dark Matter?
me ⇠ small #⇥MW
MW
Mproton
⇠ Mlarge
e�#
(derived from weak scale)
(accidentally close to weak scale)
10
Generic mass scale for matter with O(1) coupling to origin of EWSB
⇠ 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!
Thursday, 23 March, 17
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…
Thursday, 23 March, 17
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
Thursday, 23 March, 17
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′
Thursday, 23 March, 17
15
WIMP & Thermal LDM Programs: Phenomenology Similarities
Phenomenology of WIMP scenarios carries over to MeV-GeV WIMP-like scenarios:
Dark Matter CurrentParticle Type
Different Low-Energy Phenomenology!
Thursday, 23 March, 17
15
WIMP & Thermal LDM Programs: Phenomenology Similarities
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
Thursday, 23 March, 17
16
Key Thermal Targets Span Large Range.
WIMP & Thermal LDM Programs: Direct Detection Similarities
Z-tree
W-loop
GeV-10 TeV Thermal WIMPs
Thursday, 23 March, 17
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
Thursday, 23 March, 17
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
Thursday, 23 March, 17
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
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
Accelerators probe coupling strength vs. mass, not direct detection cross section vs. mass
current accelerator constraints
Milestone lines move up as assumptions are varied
Thursday, 23 March, 17
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
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
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
Thursday, 23 March, 17
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 ✏
Thursday, 23 March, 17
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
Thursday, 23 March, 17
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
Thursday, 23 March, 17
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?
Thursday, 23 March, 17
24
Accelerator Complementarity
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
Thursday, 23 March, 17
25
Accelerator Complementarity
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:
Thursday, 23 March, 17
26
Accelerator Complementarity
!!
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�
Missing Mass/Energy/Momentum
m� < mA0 < 2m�Case I:
Thursday, 23 March, 17
27
Accelerator Complementarity
A�E1 E1 x
E1 (1� x)
Fixed-Target
Colliders
Visible A’ searches give and ✏mA0
Missing Mass/Energy/Momentum
m� < mA0 < 2m�Case I:
Thursday, 23 March, 17
28
Accelerator Complementarity
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
m� < mA0 < 2m�Case I:
Thursday, 23 March, 17
29
Accelerator Complementarity
Missing Mass/Energy/Momentum
!!
A�E1 E1 x
E1 (1� x)
Fixed-Target
CollidersCase II: 2m� < mA0
⇥ ⇠ �21
E2CM
� ⇠ ✏21
m2A0
Rate gives ✏
Rate gives ✏
mA0
Thursday, 23 March, 17
30
Accelerator Complementarity
!!
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
Missing Mass/Energy/Momentum
Thursday, 23 March, 17
31
Accelerator Complementarity
Beam Dump Technique
� ⇠ ✏21
m2A0
� ⇠ ✏2
� ⇠ ↵D✏2
m2A0
N ⇠ ↵D✏4
m2A0
N ⇠ ↵D✏4
m4A0
or
Case II: 2m� < mA0
Thursday, 23 March, 17
32
Accelerator Complementarity
Given info about provides sensitivity to
mA0 ✏↵D
Case II: 2m� < mA0
Beam Dump Technique
Thursday, 23 March, 17
33
Accelerator Complementarity
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�
Case II: 2m� < mA0
Thursday, 23 March, 17
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
Thursday, 23 March, 17
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