electron positron production of dark sector particles

@ f l i p . t a n e d o AWLC 2020
electron–positron production
of dark sector particles
Flip Tanedo
October 20, 2020
at a future linear collider
Americas Workshop
On Linear Colliders 2020

@ f l i p . t a n e d o AWLC 2020 22
2
Ask not what a linear collider can do
for your favorite dark sectors…
• Clean machine: ~10x the tracking of the LHC, excellent vertexing

• No multiple collisions/pileup; no need to trigger

• Control of initial state polarization
ILC TDR v2: 1306.6352

@ f l i p . t a n e d o AWLC 2020 22
3
for your favorite dark sectors,
Ask what you can do for dark sectors
with a linear collider.
What studies can be done now to help us maximize a linear collider
as a “lamp post” for searching for dark sectors.

@ f l i p . t a n e d o AWLC 2020 22
Dark Sectors at a Linear Collider
Adapting James Carville (1992)
1. Change vs. more of the same
2. It’s the economy, stupid
3. Don’t forget healthcare
https://en.wikipedia.org/wiki/It's_the_economy,_stupid
4
what you would cover from a WIMP search
mediator
beam polarization
(new possibilities)

@ f l i p . t a n e d o AWLC 2020 22
Dark Sector
“It’s the mediator, stupid” (paraphrasing J. Carville)
Mediator mass 
Mediator spin 
Coupling to visible matter (strength and portal) 
Coupling to dark matter
5
Visible Matter
Mediator
Dark Matter
W H AT W E W A N T :
( F O R E A C H M E D I AT O R )
S M I N E R T S TAT E
e.g. for thermal freeze out
large range; ballpark: below DM mass, above ~10 MeV (e.g. BBN)
e.g. to avoid overclosure
e.g. could benchmark to 100 MeV mediator, 100 GeV dark matter
linear collider?

@ f l i p . t a n e d o AWLC 2020 22
Some favorite portals
(Near-)Renormalizable
Other options: sterile neutrino 
& other “t-channel” mediators
6
spin-1
spin-0
CP Even
CP Mixed
CP Even
CP Odd
kinetic mixing
kinetic mixing

+ mass mixing
Higgs portal
e.g. anomaly
e.g. dark photon
e.g. dark Higgs
e.g. axion-like particle
e.g. dark Z
S-CHANNEL
T-CHANNEL
see e.g. 2005.01515 (rev)
see e.g. 1203.2947
see e.g. 1512.04119
see e.g. 1808.10323
Do we have a systematic study of these
cases for a linear collider?

@ f l i p . t a n e d o AWLC 2020 22
Reminder of 2010
Missing energy/mono-X: EFT vs. Simplified Models
EFT/Contact: Maverick DM: 1002.4137, UCI: 1005.1286, 1008.1783; FNAL: 1005.3797, 1103.0240
7
Simplified Models: Busoni et al: 1307.2253, 1402.1275 (s), 1405.3101 (t); UCI: 1111.2359, An et al: 1202.2894,
Frandsen et al: 1204.3839, Buchmuller et al: 1308.6799, 2014 report: 1409.2893, 2015 report: 1506.03116, Albert
et al: 1607.06680, De Simone and Jacques review: 1603.08002, Kahlhoefer review: 1702.02430, [many others]
TAG
MISSING ET
TAG
MISSING ET
MEDIATOR
contact int. / “EFT” / “WIMP” simplified model / “UV model”

@ f l i p . t a n e d o AWLC 2020 22
Low-Hanging Fruit
Bump hunting?
e.g. Leptophilic mediators (gauged Lμ - Le)  
How well can we do with displaced vertices?
Contact interactions: see, e.g. hep-ph/0111017, 1211.2254, 1211.4008, 2001.03011
8
TAG
MISSING ET
MEDIATOR
AND PT
MEDIATOR
VISIBLE
VISIBLE
RADIATIVE RETURN
See Jenny List’s talk 
& e.g. 2001.03011
What limits mediator mass
determination for low masses?
Can we measure partial widths?

@ f l i p . t a n e d o AWLC 2020 22
Low-Hanging Fruit
Dark Sectors at Lepton Colliders
ILC TDR Vol. 2: 1306.6352
9
FOR PT
MEDIATOR
VISIBLE
VISIBLE
What limits mediator mass
determination for low masses?
Can we measure partial widths?
UV Motivated (e.g. GUT). What happens for 
lower masses and smaller couplings?
e.g. Leptophilic mediators (gauged Lμ - Le)  
How well can we do with displaced vertices?

@ f l i p . t a n e d o AWLC 2020 22
Reminder: Chirality & Mediator Spin
L and R refer to “am I an electroweak doublet or singlet?"
Each term corresponds to one of the four beam polarization configurations. 
Assuming: negligible electron mass limit, 100% polarization
10
spin-1
spin-0
does not mix EW doublet/singlet
mixes EW doublet/singlet
POSITRONS
ELECTRONS “SPIN-1 COUPLING” "PARITY”

@ f l i p . t a n e d o AWLC 2020 22
Polarization
For argument’s sake, assume chiral limit and 100% polarized beams
Homework: do the realistic case; may be a good Snowmass white paper
In addition to kinematics (cos θ dependence), one could turn on/oﬀ the
resonance by changing the polarization of the beam.

Measure the chiral couplings (dark photon vs. dark Z)?
Polarization in contact interaction approach: hep-ph/0111017, 1211.4008; Polarization for ILC physics: 1801.02840
11
SAME
CHIRALITY
OPPOSITE
CHIRALITY
SPIN-1 SPIN-0

@ f l i p . t a n e d o AWLC 2020 22
Do this for spin-1 mediators?
Map dark Z to chiral couplings
A generic spin-1 portal has
kinetic mixing and mass mixing.
The ratio of the two determines
the how vector-like or chiral the
fermion couplings are.
Potential of the ILC to Discover New Particles: 1702.05333
12
... - gZ
R/gZ
R
-330% -20% -10% 10% 20%
6
gZ
L /gZ
L
-20%
-10%
10%
20%
v
SM
uLight top partners [35]
u
Light top partners
Alternative 1 [75]
u
Light top partners Alternative 2 [75]
uLittle Higgs [76]
uRS with Custodial SU(2) [28]
uComposite Top [77]
u
5D Emergent [78]
u
4D Composite Higgs Models [79]
u
RS with Z-Z’ Mixing [27]
ILC Precision
Figure 4: Predictions of several Randall-Sundrum (RS) models and/or compositeness or
Little Higgs models on the deviations of the left- and right-handed couplings of the t quark
to the Z0
boson. The ellipse in the frame in the upper right corner indicates the precision
that can be expected for the ILC at
p
s = 500 GeV with L = 500 fb 1
of integrated
luminosity shared equally between the beam polarisations Pe , Pe+ = ±0.8, ⌥0.3 [80].
3.3 Electroweak Precision Measurements at the ILC
+ ¯
Is this useful/trivial?

@ f l i p . t a n e d o AWLC 2020 22
Another note about spin-1
“Heavy dark photons”
“Search for a heavy dark photon at
future e+e− colliders”
Is there really a gap in the LHC
search between Z pole and 150
GeV?

He, He, Huang, Li: 1712.09095
13
50 100 150 200 250 300 350
1e-4
5e-4
0 001
0 005
0 010
0 050
0 100
FCC-ee (350 GeV) 1.5/ab
C13 3 / b
1 0 .0 0 5
Cb
C13/1 300/ b
C13/1
3/ab
C
C ( 0 GeV) 5/ab
FCC-ee (1 0 GeV) 10/ab
LHC: Drell-Yan from 1412.0018; fig 8
μμƔ final state
Do lepton colliders fill this gap?
Large Z-mixing when dark photon
mass ~ mZ (hypercharge portal)

@ f l i p . t a n e d o AWLC 2020 22
Long Lived, Low Mass Particles
From Higgs decays. Are there dedicated studies?
Studies inspired by neutral naturalness e.g.
boosted objects from Higgs

Sensitive to m ~ 10 GeV, cτ ~ cm
UCSB: 1812.05588; Cheung & Wang: 1911.08721, Dark sector states from heavy SM, see e.g. 1710.07635
14
10-5 0.001 0.100 10
10-5 0.001 0.100 10
5.×10-5
1.×10-4
5.×10-4
0.001
0.005
0.010
95%
Br(h->XX)
Limit
mX = 7.5 GeV
0.005
0.010
)
Limit
mX = 25 GeV
LARGE MASS

ANALYSIS

(MIN CLUSTER DIST)
CEPC/FCCee
PROPER DECAY LENGTH [M]
LONG

LIFETIME

ANALYSIS
By the way: we are skipping dark sector states from decay of SM states
see, e.g. Zhen Liu’s talk for dark sector from Higgs decay (e.g. dark Higgs)
Recast? Dedicated studies for
associated production of long-lived
mediators?

@ f l i p . t a n e d o AWLC 2020 22
Dark Sector Spectroscopy at the ILC
Beyond mono-photon (mono-dilepton)
Andersen, Rauch, Spannowsky 1308.4588 15
0 1 2 3
10 3
10 2
10 1
SM background
8 GeV S
120 GeV X
8 GeV S
5 GeV X
8 GeV V
5 GeV X
8 GeV V
120 GeV X
SPIN
MASS SCALES
& polarization helps!
Example: scalar vs. vector with heavy/light dark matter

@ f l i p . t a n e d o AWLC 2020 22
Dark Sector Spectroscopy at the ILC
Beyond mono-photon
Andersen, Rauch, Spannowsky 1308.4588 16
SPIN
MASS SCALES
& polarization helps!
powers depend on spin of
t-channel exchange particle
Trick: multi-Regge kinematics
Are there generalizations of this approach? 
Systematic study for a scan of models? 
What about parity? (A’ vs Z’, ALP vs. hD)
t1
t2
t3

@ f l i p . t a n e d o AWLC 2020 22
e+
e
Z
, Z
a
Figure 1: Tree-level Feynm
radiated o↵ an initial-state elec
hence neglected here. ALPs can
in association with a , a Z or
association with a , a Z or a H
d (e+
e ! a)
d⌦
= 2⇡↵↵2
d (e+
e ! Za)
d⌦
= 2⇡↵↵2
e+
e
Z
, Z
a e
e+ , Z
a
e+
e
Z
h
a
Figure 1: Tree-level Feynman diagrams for the processes e+e ! Xa with X = , Z, h.
e+
e
Z
, Z
a e
e+ , Z
a
Figure 1: Tree-level Feynman diagrams for the processes e
radiated o↵ an initial-state electron are suppressed by m2
e/s r
hence neglected here. ALPs can be radiated of a photon or a Z
in association with a , a Z or a Higgs. The di↵erential cros
association with a , a Z or a Higgs boson are given by
✓ ◆
Axion Like Particles
ALPs at future colliders: 1808.10323
17
-
- - - - -
-
-
-
F
F
Figure 4: Left: Summary plot of constraints on the parameter space spanned by the ALP mass
and ALP-photon coupling. Right: Enlarged display of the constraints from collider searches: LEP
(light blue and blue), CDF (purple), LHC from associated production and Z decays (orange), LHC
associated production
photon fusion @ LHC
Photon fusion at 
lepton collider?

@ f l i p . t a n e d o AWLC 2020 22
Axion Like Particles at CLIC/FCC
18
- - - - -
-
-
- - - - -
-
-
CLIC380
CLIC1500
CLIC3000
FCC-ee
e+
e ! a e+
e ! Za
Figure 6: Projected sensitivity regions for searches for e+e ! a ! 3 (left) and e+e ! Za !
Zvis (right) at future e+e colliders for Br(a ! ) = 1. The constraints from Figure 4 are shown

@ f l i p . t a n e d o AWLC 2020 22
… similar reach to LHC (Drell Yan, Z decay)
19
- - - - -
-
-
-
1 10 100
10 3
10 2
LHC
LHC27
FCC-hh
Z ! a

@ f l i p . t a n e d o AWLC 2020 22
Dark-onia / Displaced Lepton Jets
Targeting dark matter self-interactions
1 5 10 50 100
10
50
100
500
1000
m [GeV]
m
z
d
[MeV]
N
o
b
o
u
n
d
s
t
a
t
e
1-3 cm2
/g
3-10 cm2
/g
= 0.2
m
Z
d
>
0
.
6
m
Figure 2. Left: Dark photon masses and kinetic mixing parameters that we use for the collider study (red
dots). We also show the existing bounds from the BaBar [59], LHCb [60] and beam dump experiments (gray
shaded), see, e.g., [61–63]. Future measurements from the LHCb [64] (blue dashed) and the proposed FASER
WIMPonium: 0901.2125, SIDM bound states: 1811.05999
20
A
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Bps
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¯
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Displaced Lepton
Jets (DLJs)
`+
`
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p
A
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¯
Bps
Zd
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Displaced Lepton
Jets (DLJs)
`+
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`+
`
g
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g
<latexit sha1_base64="jOndNTz7oOjPRDD+0pZ/+rey2rI=">AAAB6HicbVBNS8NAEJ3Ur1q/qh69LBbBU0lU0GPRi8cW7Ae0oWy2k3btZhN2N0IJ/QVePCji1Z/kzX/jts1BWx8MPN6bYWZekAiujet+O4W19Y3NreJ2aWd3b/+gfHjU0nGqGDZZLGLVCahGwSU2DTcCO4lCGgUC28H4bua3n1BpHssHM0nQj+hQ8pAzaqzUGPbLFbfqzkFWiZeTCuSo98tfvUHM0gilYYJq3fXcxPgZVYYzgdNSL9WYUDamQ+xaKmmE2s/mh07JmVUGJIyVLWnIXP09kdFI60kU2M6ImpFe9mbif143NeGNn3GZpAYlWywKU0FMTGZfkwFXyIyYWEKZ4vZWwkZUUWZsNiUbgrf88ippXVS9y6rbuKrUbvM4inACp3AOHlxDDe6hDk1ggPAMr/DmPDovzrvzsWgtOPnMMfyB8/kDzR+M7Q==</latexit>
ed lepton jet signatures from the SIDM bound state at the LHC. In the model we consider, a
r (A) couples the SIDM particle ( ) to gluons (g), a dark photon (Zd) mediates dark matter
nd leads to formation of the bound state (Bps). The boosted Zd decays to SM charged leptons
g portal.
k matter self-interactions in the halos. The resulting bound state can annihilate into
iators, which subsequently decay back to the SM particles, as illustrated in Fig. 1. If
SMALL SCALE STRUCTURE TARGETS
How would this look at a lepton collider? 
Clean machine: tracking and vertexing?

@ f l i p . t a n e d o AWLC 2020 22
More Exotic Cases: are linear colliders helpful?
Soft bombs, e.g. from hidden valleys
Portal to hidden valley-type model with large ’t Hooft coupling 
Spherically symmetric spray of soft particles.

Is Knapen et al. study amenable to a linear collider?
Fichet (et al): 1705.10331, 1710.00850, 1910.02972
Perelstein and San: 2009.09867 (muonic puzzles),
21
Quantum forces
Knapen et al. 1612.00850; FT et al. 2002.12335
Non-renormalizable interaction with a pair of
light mediators.

@ f l i p . t a n e d o AWLC 2020 22
22
for your favorite dark sectors,
Ask what you can do for dark sectors
with a linear collider.
https://www.symmetrymagazine.org/article/october-2005/snowmass-2005
(+16)

@ f l i p . t a n e d o AWLC 2020 22
References to get started
Perhaps useful for those arriving from the dark sector
• ILC TDR, Vol 2: Physics: 1306.6352

• ILC Study Questions for Snowmass: 2007.03650

• CLIC Potential for New Physics: 1812.02093
SLAC Dark Forces ’09: https://indico.cern.ch/event/67760/timetable/ ; see S. Thomas
23
• Dark Sectors 2016 Community Report: 1608.08632

• US Cosmic Visions: New Ideas in Dark Matter 2017 Report: 1707.04591

Dark sectors 101 for energy frontier folk

electron positron production of dark sector particles

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