GeV-Scale Collider and Fixed-Target Experiments to Search for

Dark Gauge Forces

Philip Schuster (SLAC)TeVPA 2009, July 13

with Rouven Essig, and Natalia Toro (0903.3941)

with James D. Bjorken, Rouven Essig, and Natalia Toro (0906.0580)

• Theory of New Vector Bosons (and hints from dark matter)

• e+e- Collider Searches (Babar and Belle)

• Fixed-Target Experiments (e.g. @ JLab)

A program of GeV scale collider and fixed-target experiments that can search for MeV-

GeV gauge forces

see: 0903.3941

see: 0906.0580

Known interactions:

New Forces?

If ordinary matter is charged under a new force, we would have seen it (for masses ~TeV or less)

What about forces we are not charged under?

SU(3) SU(2)× ×U(1)(Strong) (Electro-weak)

?×

Photon Mixing with New Vector BosonNew vector bosons couple to the Standard Model by

mixing with the photon

GUT or Planck scale quantum correctionsε ! egD

16π2∼ 10−4 − 10−3

γ A′

[Holdom ʻ86]

A′A′m2

A′ ∼ εM2W(mass inherited from “electro-weak” scale)

[Cheung, Ruderman, Wang, Yavin; Katz and Sundrum; Morrissey, Poland, Zurek]

δL = εFY FA′

Ordinary Matter is Milli-Charged

(equivalent)

Photon mixing with A’ is equivalent to electrically charged matter acquiring a milli-charge under the A’

A′

γ∗

e

e− e+

×e× ε

A′

e− e+

What about the rest of the matter in the Universe?

ε

Suppose Dark Matter is Charged Under a GeV-Scale Gauge Force

• Annihilation enhanced at low velocities

• Annihilation into light, not heavy states

• Excited states split by O(MeV)

• Scattering off matter:

• rate similar to neutral current

• scattering into excited state, enhanced modulation

Several Striking Consequences:

Annihilation into Leptons

[A. Strumia, Planck ’09] [Meade, Papucci, Strumia, Volansky 0905.0480]

} Standard ModelParticles

(m<mA’/2)

DM

DM

A′

A′

[Arkani-Hamed, Finkbeiner, Slatyer, Weiner;Cholis, Finkbeiner, Goodenough, Weiner;Pospelov & Ritz]

A’ Mediation of Inelastic DM-Nuclei Scattering

arXiv:0804.2741, Bernabei et. al.

Large modulation amplitude, characteristics of recoil spectrum, and null results of other

experiments explained by inelastic collisions

Dark matter mass splitting: ~100 keV

[Tucker-Smith and Weiner; Arkani-Hamed, Finkbeiner, Slatyer, Weiner]

The Origin of a 100 keV Dark Sector Splitting

New particles at the GeV-scale are required

(radiative splittings) (custodial symmetry breaking )

δMDM ∼ αDδMgauge ∼ α2DMgauge ∼ 100 keV

Non-Abelian Confined Sector:[Alves, Behbahani, PS, Wacker]Dark matter is a dark heavy flavor meson

[Arkani-Hamed, Finkbeiner, Slatyer, Weiner]Non-Abelian Higgsed Sector:Dark matter is a charged multiplet

δMDM ∼Λ2

Dark

MDM∼ 100 keV→ ΛDark ∼ GeV

(hyperfine splittings)

New Gauge ForcesDAMA/LIBRA is suggestive of a small MeV mass scale

and new gauge force

PAMELA/ATIC/FERMI is suggestive of a MeV-GeV mass scale and new gauge force

[Arkani-Hamed, Finkbeiner, Slatyer, Weiner;Cholis, Finkbeiner, Goodenough, Weiner;Pospelov & Ritz]

[Tucker-Smith and Weiner; Arkani-Hamed, Finkbeiner, Slatyer, Weiner; Alves, Behbahani, PS, Wacker]

This might be true!

How do we find out?

Radiative returnOff-Shell A′

Dark Sector Collider Production

σ ∝ ε2/s High-luminosityGeV-scale colliders

Normalizing Production Rates from DAMA/LIBRA

∝eε gD

eε

gD

q2 = s = (10.58 GeV)2 q2 = µ2v2 ! m2A′

Can estimate production cross-section from DAMA/LIBRA scattering cross-section

DAMA-Normalized Production Rates

1.00.5 2.00.2 5.00.1 10.010!4

0.1

100

105

108

A' Mass !GeV"

Cross!Section!fb"

ΓA' Pair Cross Section !Form!Factor iDM"MDM#1000 GeV, C

$#0.01

ΑD#10!4

ΑD#Α

ΑD#1

Σ!off!shell"!reference"

Z decay sensitivity

!g!2"Μ constraint~100 eventsin BaBar data

Higgsed/Confined Dark Sector Signatures

!+

!+!−

!−

WD

WD

hD

W ′D

!+

!−

e+e−

(a) (b)

!+!−

WD

WD

hD

W ′D

e+e−

γ

A′

!+

!−

!+

!−

!+

!−

e+e−

!+ !−

qD

φD

φD η′D

!"#$%&'()*#&+*,'#-.+"!#*/01")0*/

φD

φD

q̄D

!+!−

φD

!+ !−

!+ !−

!+!−

√s " ΛD

23-!/"4-&)")'&0/-(*4405")'!-6')&

√s ! ΛD

#*78+49-&:+'#0("4-';'/)

mA′ ! ΛD

<**&)'!-:#*!7()&-#'(*04-*==-:+*)*/

γ

η′D φD

!+!−Higgsed: Confined:

Wide variety of multi-lepton final states

[also see: Batell, Pospelov, Ritz]

Detection Prospects

• For either higgsed or confined dark sectors, easy to get much higher lepton multiplicities in final state than SM backgrounds (eff: many photons without paying α for each)

• Possible to have displaced vertices (good discriminator) or completely invisible final state (ɣ+nothing search)

• Optimistically, reconstruct dark-sector spectrum from decay products

• Searches underway in BaBar and KLOE

• Theory of New Vector Bosons (and hints from dark matter)

• e+e- Collider Searches (Babar and Belle)

• Fixed-Target Experiments (e.g. @ JLab)

A program of GeV scale collider and fixed-target experiments that can search for MeV-

GeV gauge forces

see: 0903.3941

see: 0906.0580

µ+

µ−Nucleus

A′E1 E1 x

E1 (1− x)

Collider vs. Fixed-Target

O(few) ab−1 per decade O(few) ab−1 per day

σ ∼ α2ε2

E2σ ∼ α3Z2ε2

m2∼ O(10 fb) ∼ O(10 pb)

∼(mA

E

)3/2

(wide)

(narrow)

e−

Kinematics very different from massless photon bremsstrahlung

Energy = E

Unique Fixed-Target Kinematics

e−

∼(mA

E

)1/2

l+

l−∼ mA

EA′

Heavier product (here A’) takes most of beam energy

EA ∼ E −mA

Ee ∼ mA

dσ

dx∝ α3

π

1m2

e · x+m2A(1− x)/xε2

...or other decays

x =EA

E

0.01 0.1 110!910!810!710!610!510!410!3

0.010.01 0.1 1

10!910!810!710!610!510!410!3

0.01

mA'!GeV

Ε

MegaWatt x Yearlower limit for

seeing >10 events

(g − 2)e (g − 2)µ Υ(3S)→ (µ+µ−)γBABAR

cτ ≈ 1 cm

cτ ≈ 80 µm

Fixed-Target Territory

prompt decays

cm-m decays

m-10’s km

[see also: Reece and Wang; Batell, Pospelov, Ritz]

tracking, calorimetry, ...

decay volume(50 cm - 100 m)

shield(10 cm - 100 m)

e beam

thick target

Beam Dump Experiments

SLAC E137: 1020 e- (30 C) at 20 GeV, 200m shield

SLAC E141: 1016 e- at 9 GeV, 12 cm W target

FNAL E774: 1010 e- at 275 GeV, 20 cm W target

10!2 10!1 110!910!810!710!610!510!410!310!2

10!2 10!1 1

10!910!810!710!610!510!410!310!2

mA' !GeV"

Ε E137E141

E774 aΜae $!3S"

SN

Past Beam Dump LimitsDi-lepton

decay channel

0.01 0.1 110!8

10!7

10!6

10!5

10!4

10!3

0.010.01 0.1 1

10!8

10!7

10!6

10!5

10!4

10!3

0.01

mA'!GeV

Εtrackingstations

ecal/trigger

~30 cm decayvolume

10 cmtarget

10 cmshield

“D-term” line – also explains DAMA/LIBRA

New Beam Dump Reach

Good Beams:FEL at JLabSLACELSA, Mainzer Mikrotron (MAMI), Max-lab

Di-leptondecay channel

γcτ ! cm

Discovery Approaches:

Vertex

Bump hunt

Low-background

Clean signal,Limited by instrumental bkg

Fight backgroundwith high intensity,resolution

}Same device,

differentanalyses

(x severalgeometries)

Beam dump

γcτ ∼ cm

γcτ ∼ m

To maximize search reach:

Approaches for New Experiments

• Very good forward coverage (signal production is peaked forward)

• Small and fast (want to operate with intense beams)

• 1% or better mass resolution (kinematic discrimination)

• Silicon good for precision tracking (use vertex discrimination)

Beam's eye:

A B

C

.

!cm

trackingstations

ecal/trigger

A

B

C

10 cm

2 cm0.1 X0 W

Two-arm spectrometer

Small with variable geometry

A Fixed-Target Search Program

0.01 0.1 110!8

10!7

10!6

10!5

10!4

10!3

0.010.01 0.1 1

10!8

10!7

10!6

10!5

10!4

10!3

0.01

mA'!GeV

Ε

1st generation reach of experiments: see 0906.0580

Existing facilities (JLab) and detection methods

Di-leptondecay channel

Future Prospects

Clear physics program to look for new gauge forceat existing labs (JLab, SLAC...etc)

Various decay modes can be searched for (including “invisible”) and suggest closely related approaches

Tremendous discovery potential!

Numerous alternative approaches not discussed (muon beams, neutrino detectors...etc)

Backup

GeV-Scale CollidersFigure of Merit is: Lint/s

430 fb−1

(10.6 GeV)2725 fb−1

(10.6 GeV)2

BELLE BaBar

100,000170,000

≈ 1 fb−1

(4 GeV)2

1,000

CLEO-C

No. of events for αD = α, ε = 10−2 (approx):

50,000

KLOE

2.5 fb−1

(1 GeV)2?? fb−1

(4 GeV)2

BES III

Missing from numerical comparison: – accessible mass range– kinematic acceptance & visibility of events

Broad range of searches needed