Accelerator Prospects for Sub-GeV DM. June 07 2019, New Directions - - PowerPoint PPT Presentation

cluster of Excellence Quantum universe

Accelerator Prospects 
 for Sub-GeV DM.

June 07 2019, New Directions in the Search for LDM Particles, Fermilab Torben Ferber (torben.ferber@desy.de)

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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• Types of accelerator searches
• Types of DM signatures at accelerators
• Benchmark searches: Visible and Invisible Dark Photons
• Beyond simple models: iDM, DM bound states, Z’

Overview

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

• 3

New mediators

L = X

n=k+l4

cn Λn O(SM)

k

O(med)

l

= Lportals + O ✓ 1 Λ ◆ = − ✏ 2BµνA0

µν − H†H(AS + S2) − Y ij N ¯

LiHNj + O ✓ 1 Λ ◆

Vector Portal: Massive A’ mixes with SM γ via strength parameter ε Scalar Portal: Additional dark Higgs Neutrino Portal: Sterile neutrinos, heavy neutral leptons e.g. Axion Portal: Massive ALP couples to SM bosons

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Accelerator landscape

Collider

Specialized (e.g. g-2, EDM)

Beam dumps Fixed target

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Accelerator landscape

Collider

Specialized (e.g. g-2, EDM)

Beam dumps Fixed target

Electrons Protons
 Passive target Electrons 
 Active target e+e- (intensity frontier, e.g. Belle II) pp (energy frontier, LHC) future e+e- (energy frontier, e.g. ILC) Multi-purpose detectors
 (tracking, calorimeters, 
 particle identification, …)

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Accelerator landscape

Direct (new) mediator production Particle decays Precision measurements

DM DM SM SM DM DM

Resonances in meson decays, e.g. π0→A’γ (Dark Photon) B→K(*)a (ALP) B→Kχχ
 + clean, effjcient trigger, difgerent couplings

• kinematics limited by meson mass

Missing energy or resonance searches, e.g. A→Invisible (Dark Photon) a→γγ (ALP)

+ maximum mass reach, high rate

• high backgrounds, diffjcult trigger

Precision observables modified by DM, e.g. Difgerential cross section B→Kμμ

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Accelerator landscape

Direct (new) mediator production Particle decays Precision measurements

DM DM SM SM DM DM

Resonances in meson decays, e.g. π0→A’γ (Dark Photon) B→K(*)a (ALP) B→Kχχ
 + clean, effjcient trigger, difgerent couplings

• kinematics limited by meson mass

Missing energy or resonance searches, e.g. A→Invisible (Dark Photon) a→γγ (ALP)

+ maximum mass reach, high rate

• high backgrounds, diffjcult trigger

Precision observables modified by DM, e.g. Difgerential cross section B→Kμμ

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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New mediator production and decay Invisible


(subleading visible)

Visible

• fg-shell

long-lived

DM DM e, μ, … e, μ, … γ γ γ

2me mA’ = 2mDM DM mass mDM Mediator mass mA’

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Visible Dark Photon decays: e+e- collider

A’ electron positron photon leptons or hadrons*

*prompt or displaced

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Visible Dark Photon decays: e+e- collider (e.g. BaBar, Belle II)

• Bump hunts over smooth, large SM

backgrounds

• Sensitivity scales only very slowly with

integrated luminosity: ~ℒ 1/4

• Hadronic final states are more

challenging but possible

• ττ channels have not been exploited

yet (missing energy from neutrinos)

2 4 6 8 10 Entries / 0.1 GeV

5

10

6

10 2 4 6 8 10 Entries / 0.1 GeV

5

10

6

10

Data

• µ

+

µ γ →

• e

+

MC e R γ →

• e

+

MC e

(GeV)

2 µ

• 4m

2µ µ

m =

R

m 2 4 6 8 10 Data/MC 0.9 1

• Phys. Rev. Lett. 113, 201801 (2014)

BaBar

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Visible Dark Photon decays: Fixed target

A’ electron thin target electron electrons

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Visible Dark Photon decays: Fixed target (e.g. HPS@JLab)

• Thin O(0.1X0) W target
• Compact spectrometer
• PbWO4 ECal to withstand ultra high single

electron rate

• SM background from radiative electron pairs

(tridents: eZ → eee)

• “Dead zone” in spectrometer from passing

beam (extremely high rate)

• Short commissioning runs in 2015/16, physics

runs in 2018 (4.4 GeV) and 2019 (2.2 GeV)

!8

~ 1 m e t e r

Silicon Vertex Tracker ECal

e−

e−

e+

~1 meter

e−

e−

e+

A′

.

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Limits for visible Dark Photon decays

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Visible Dark Photon decays: Limits (and expectations until 2021)

US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report

beyond 2021:

• NA62, SHiP, SeaQuest, …
• Belle II 50ab-1
• LHCb e+e-

Displaced decays

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Invisible Dark Photon decays: e+e- collider

A’ light dark matter electron positron photon

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

Belle II (simulation)

• 16

Invisible Dark Photon decays: e+e- collider (e.g. BaBar, Belle II)

• Requirement:
• Single photon trigger (Eth ≈ 1GeV at a B-factory)
• Effjcient outer detector to veto ECAL gaps
• BaBar’s Achilles heel: projective calorimeter

crystals → large backgrounds

• SM background if one misses all but one γ:
• Low mass A’ (= high energy single γ): ee→γγ(γ)
• High mass A’ (= low energy single γ): ee→ ee(γ)

Eγ=s−M A'

2

2√ s

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Invisible Dark Photon decays: beam dumps (e.g. BDX@MESA)

electron A’ light dark matter electron light dark matter target electron

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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• Thick target O(20X0)
• Thick shielding O(100X0)
• ECAL O(10m) away from 


source plus cosmic veto

• One possibility: 


BDX at the Mainz Energy-Recovering Superconducting Accelerator (MESA). 135 MeV beam (below pion threshold), 1022 EOT, ~2020+

Model for A’ Bremsstrahlung

• radiative production of (massive) dark photon A’ coupling with ε
• α

ε α

• pprox. total A’ no. according to

‘

and ϵ

• integrated total A’ no.: 2 x 10

Χ A’

α

Model for A’ Bremsstrahlung

• radiative production of (massive) dark photon A’ coupling with ε
• α

ε α

Detector

θRMS ∼ m Ebea

Model for A’ Bremsstrahlung

• radiative production of (massive) dark photon A’ coupling with ε
• α

ε α

• pprox. total A’ no. according to

‘

and ϵ

• integrated total A’ no.: 2 x 10

Χ A’

α

Model for A’ Bremsstrahlung

• radiative production of (massive) dark photon A’ coupling with ε
• α

ε α

YP rod ∼ ✏2/m2

A

Model for A’ Bremsstrahlung

• radiative production of (massive) dark photon A’ coupling with ε
• α

ε α

• pprox. total A’ no. according to

‘

and ϵ

• integrated total A’ no.: 2 x 10

Χ A’

α

Model for A’ Bremsstrahlung

• radiative production of (massive) dark photon A’ coupling with ε
• α

ε α

YDet ∼ ✏2↵D/m2

A

Invisible Dark Photon decays: beam dumps (e.g. BDX@MESA (planned))

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

• 19

Invisible Dark Photon decays: Fixed targets (e.g. LDMX)

A’ electron thin target electron light dark matter

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

• 20

Invisible Dark Photon decays: Fixed targets (e.g. LDMX (planned))

• Thin O(0.1X0) W target
• Similar tracker than HPS before and after

target

• Fast, granular, radiation hard, deep

O(40X0) ECAL (e.g. CMS HGCAL)

• Deep HCAL to veto rare photonuclear

events and wide angle bremsstrahlung

• Electron beam O(10 GeV) at SLAC, JLab,
• r CERN (eSPS) under discussion

!43

tagging tracker recoil tracker target Silicon Sensors

~1 m

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Limits for invisible Dark Photon decays

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Invisible Dark Photon decays: Limits (and expectations until 2025)

Scalar Relic Target BaBar

MMAPS

Belle II LDMX

LSND

BDX

NA64 CRESST II

E137

X E N O N 1 / 1 MiniBooNE

SBN

SBNe SHiP

C O H E R E N T

1 10 102 103 10-16 10-15 10-14 10-13 10-12 10-11 10-10 10-9 10-8 10-7 10-6

m [MeV] y = 2D (m/mA')4

Scalar Elastic DM (Kinetic Mixing)

mA’ = 3mχ, αD = 0.5

BaBar

MMAPS

Belle II LDMX

LSND

BDX

NA64

E137

M i n i B

• N

E

C O H E R E N T

Pseudo-Dirac Relic Target

SBN

SHiP SBNe

1 10 102 103 10-16 10-15 10-14 10-13 10-12 10-11 10-10 10-9 10-8 10-7 10-6

m [MeV] y = 2D (m/mA')4

Pseudo-Dirac DM (Kinetic Mixing)

mA’ = 3mχ, αD = 0.5

US Cosmic Visions: New Ideas in Dark Matter 2017 : Community Report

BDX and LDMX have difgerent beam option with difgerent sensitivity. Plot for BDX@CEBAF(A), JLab and LDMX@DASEL, SLAC. not in the plots: BESIII (low energy e+e- near charm threshold) has (some) data with single photon triggers. Scalar DM Pseudo-Dirac DM

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Dark Photons at the LHC?

• Drell-Yan production pp→A’→μμ

(some mild model-dep. near Z peak)

• Dedicated LHCb analysis of 13TeV

data (incl. meson decays). A future analysis of A’→ee from D* is a potential game-changer

• h→Z*ZD (kinetic mixing) is

complementary but not very sensitive

• EW global fits
• Phys. Rev. Lett. 120, 061801 (2018)

2 −

10

1 −

10 1 10

12 −

10

11 −

10

10 −

10

9 −

10

8 −

10

7 −

10

6 −

10

5 −

10

4 −

10 m(A0) [ GeV ] ε2

LHCb

LHCb Previous Experiments 90% CL exclusion regions on [m(A0), ε2]

10 102 103 10-3 10-2 10-1 mZD [GeV] ϵ

EWPT BaBar

Red: DY (pp→ZD→ℓ+ℓ-)

CMS7, DY A T L A S 8 / C M S 8 , D Y CMS8, h→ZZD LHC8, 20/fb LHC14, 3000/fb 1 T e V , 3 / f b L H C 1 4 , 3 / f b 1 T e V , 3 / f b

• Phys. Rev. D 90, 075016
• J. High Energ. Phys. (2015) 2015: 157

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

• 24

Accelerator strategies, next steps

• Belle II and LDMX are at the intensity frontier: No clear path to improve sensitivity beyond

~2027 by just continue with searches for “simple” models

• Complex final states from specific models are more predictive and more powerful
• Avoid existing bounds to explain anomalies like g-2:
• Search for explicit couplings to muons or taus
• Avoid direct detection bounds:
• Search for inelastic DM
• Lifetime frontier: Long-lived particles
• …

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Example: Complex final state from SIDM at Belle II

ϒD A’ A’ A’ A’ A’ A’ A’ A’ γ

DM bound states

ηD

• 2 on-shell A’ decaying

into electrons

• 1 ofg-shell A’ decaying

into leptons/hadrons free parameters:
 m(A’), ε, m(χ), gD

• 3 on-shell A’ decaying

into leptons/hadrons

• 1 γ (→ on-shell A’)

states, 1S0 (JPC ¼ 0−þ) and ϒ , respectively and 3S1 (JPC ¼ 1−−),

• ely. The condition for

PRL 116, 151801 (2016)

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Example: Explicit coupling to muons at Belle II

Z’ does not couple to electrons free parameters:
 m(Z’), g(Z’) Lμ-Lτ (Z’)

Z’ γ* μ μ X X

Two muons + Missing energy

Belle II analysis with 2018 data ongoing.

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Example: Inelastic Dark Matter at Belle II

Inelastic DM (iDM)

e- e+ X2 A’ X1 X1 A’ γ γ

DM coupling via 
 Dark Photon A’ (kinetic mixing ε) on-shell Cascade decay with two χ1 (missing energy) A’ must ultimately decay back to SM particles (e, μ, hadrons, …) χ2 lifetime can be long A’ lifetime very short (for not too small ε) free parameters:
 m(A’), ε, m(χ1), Δ(m), gD

arXiv:1508.03050v2

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Summary

• Accelerator searches for LDM…
• …are usually mediator searches. LDM generally appears as missing energy.
• …do not rely on LDM history
• …do not rely on LDM being a scalar particle
• Belle II started data taking some weeks ago, first results this year. Together with LDMX

it will be able to cover simple relic targets for vector mediators

• The collider searches are moving into more model dependency in exchange for more

predictive final states (including long lived particles (LLPs))

Deutsches Elektronen Synchrotron www.desy.de Contact Torben Ferber email: torben.ferber@desy.de website: https:/ /www.desy.de/~ferber ORCID: 0000-0002-6849-0427

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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The e+e- collider flagship: Belle II

positrons e+ electrons e-

KL and muon detector (KLM):


Resistive Plate Counters (RPC) (outer barrel) Scintillator + WLSF + MPPC (endcaps, inner barrel)

Particle Identification (PID):


Time-Of-Propagation counter (TOP) (barrel) Aerogel Ring-Imaging Cherenkov Counter (ARICH) (FWD)

Electromagnetic calorimeter (ECL):


CsI(Tl) crystals
 waveform sampling (energy, time, pulse-shape)

Vertex detectors (VXD):


2 layer DEPFET pixel detectors (PXD)* 4 layer double-sided silicon strip detectors (SVD)

Central drift chamber (CDC):


He(50%):C2H6 (50%), small cells, 
 fast electronics

Magnet:


1.5 T superconducting

Trigger*:


Hardware: < 30 kHz Software: < 10 kHz

DEPFET: depleted p-channel field-effect transistor
 WLSF: wavelength-shifting fiber
 MPPC: multi-pixel photon counter

* Some modifications for early data taking

Accelerator Prospects for Sub-GeV DM (Torben Ferber)

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Invisible Dark Photon decays: Belle II

Background MC, 40 fb-1 
 after selection

ee→eeγ
 both electrons 


• ut of tracking acceptance

ee→2γ and 3γ 1γ in ECL 90° gap 1γ out of ECL acceptance ee→2γ 1γ in ECL BWD or FWD gap ee→3γ 1γ in ECL BWD gap 1γ out of ECL acceptance

Belle II MC

Eγ=s−M A'

2

2√ s