Dark Photon

Hidden Secluded Dark Sectors and Heavy Photons Mathew Graham SLAC Summer Institute July 30, 2012

Where does an extra force fit?

http://www.particleadventure.org/inter_summary.html

How could additional forces have escaped detection? • very high mass force carrier • small coupling to SM particles

2012 SLAC Summer Institute

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Mathew Graham

Where does an extra force fit? Dark Forces

http://www.particleadventure.org/inter_summary.html

How could additional forces have escaped detection? • very high mass force carrier • small coupling to SM particles •0 (direct) coupling to SM! 2012 SLAC Summer Institute

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Mathew Graham

Portals to a hidden sector Standard Model

“portal”

Dark Sector ??????

SU(3)×SU(2)×U(1)

vector Higgs neutrino axion 2012 SLAC Summer Institute

1 Y Fµ F 2 2

h |h|

µ

dark photon 2

| |

(hL)

1 µ ˜ aFµ F fa 4

dark scalar sterile neutrino ALPSs Mathew Graham

Kinetic mixing from the vector portal an old idea: if there is an additional U(1) symmetry in nature, there will be mixing between the photon and the new gauge boson Holdom, Phys. Lett B166, 1986

LU (1) =

1 2 Vµ 4

2

Vµ F

µ

+ |Dµ ⇥|

2

V (⇥)

Kinetic Mixing term

•extremely general conclusion...even arises from broken symmetries •gives coupling of normal charged matter to the new “dark photon” q=εe 2012 SLAC Summer Institute

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Mathew Graham

30 decades of heavy photons ...there is a lot of physics here!

Jaeckel and Ringwald, hep-ph/1002.0329 2012 SLAC Summer Institute

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Mathew Graham

Terminology break •

The literature is infested with different terms for (basically) the same things... • • •

dark sector=hidden sector=secluded sector dark photon=hidden photon=heavy photon=A′=U-boson ε2=κ2=α′/α

I will try to stick to dark sector, A′, and ε!


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Mathew Graham

1 Y Fµ F 2

What coupling?

µ

•Coupling is generated from non-perturbative loops •One-loop if the heavy particle is charged under both U(1)s

egD 16 2

...depends on coupling in dark sector

•Two-loop if one of the U(1)s is embedded into a higher symmetry...

X+ X−


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Mathew Graham

Ok, what about the mass? •Could be massless ⇒ millicharges! •Non-perturbative ⇒ chaos! •Same origin as weak scale ⇒ O(MZ)

Depending on model, mass scales like: M(A´)/M(W)~ε1-ε1/2 leading to M(A´)~MeV-GeV 2012 SLAC Summer Institute

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N. Weiner, JLAB PAC37 Talk

α´=αε Mathew Graham

A hint from above? excess in e+/e− ratio ...but not in p/p ratio

•FERMI sees it too!

Unknown source of high energy positrons... Is this astrophysics or particle physics? 2012 SLAC Summer Institute

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Mathew Graham

Dark matter annihilation and the dark sector

•new “dark force” with gauge boson ~ GeV while the dark matter

particle (charged under the new force) ~ TeV •decays to lepton pairs (e+e−, µ+µ−) but pp decays are kinematically forbidden


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Mathew Graham

Some existing constraints ge-2

gµ-2

e+e−→µ+µ−γ

lifetime limited coupling limited


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Mathew Graham

Dark photons and the g-2 anomaly If the g-2 anomaly is due to a heavy photon

10-2

0.01 ae

10-3

0.1 am

1 UH3SL

10-2 10-3

E774

10-4

10-4 E141

10-5

10-5

e

E137

10-6

10-6

10-7

10-7

10-8

10-8

10-9

SN

0.01

0.1 mA' HGeVL


1

10-9

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Mathew Graham

A´ decay products

...up to ~500 MeV, decay to leptons dominates 2012 SLAC Summer Institute

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Mathew Graham

A´ Lifetime 10-2 10 2

100 MeV mA

lower ε, lower mass → longer lifetime

0.1

ae

2

10-7

10-5 10

10 m

-6

10-7

10-8

10-8

10-9

10-9

0.01

0.1 mA' HGeVL

1

[Rouven Essig]

Much of parameter space will have displaced vertex 2012 SLAC Summer Institute

-3

10-4

1 cm

-6

10-2 10

1 µm

10-5 10

1 UH3SL

am

10-4 e

c

10

4

-3

0.01

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Mathew Graham

Collider vs. Fixed Target Wherever there is a photon there is a dark photon... Collider Fixed Target

mon th 2012 SLAC Summer Institute

...much higher backgrounds 16

Mathew Graham

Backgrounds at fixed target Two main backgrounds

Bethe-Heitler

Radiative

production rates of A’ and radiative are related:

Black: BH Red: Rad. BH→Ee++Ee−Radiative, but kinematics much different... Even after energy cut, BH background ~5x radiative

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Mathew Graham

...a little more subtle... Problem: cover the low coupling (ε>10−5 for 200>mA´>20MeV •running 3 months each at Ebeam=2.2 and 6.6 GeV

Δm/m~1% +

e ~10µ

pe

+

+ pe


e

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Mathew Graham

solid-2σ dashed-5σ

-4

10

HPS Expected Reach 0.01

0.1 am

ae

1 BaBar

-5

10

-6

a'êa

-6

10

E774

-7

10

Bump-hunt only

-8

-7

10

-8

10

10 E141

-9

10

-10

10

α′/α=ε2

10

-5

10 10

-4

Bump-hunt + Vertex


10

-10

Red: 450nA @ 6.6GeV target: 0.25% 3 months of beam at each energy

10

E137

0.01

-9

Blue: 200nA @ 2.2GeV target: 0.125%

0.1 mA' HGeVL

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Mathew Graham

It’s getting crowded... 10-2

0.01

0.1

1

am

ae

10-2

BaBar

Mainz

10-3

10-3

APEX Test

HPS

DarkLight

e

E774

APEX

10-4

10-4 E141

HPS

10-5

10-5

E137

0.01

0.1 mA' HGeVL


Many experiments in the works to look for Dark Forces:

1

22

Mainz and APEX (JLab) ~ forward spectrometers HPS (JLab) ~ compact Sibased vertex-tracker DarkLight (JLab FEL) ~ high acceptance, H2 gas target HIPS(DESY)~ beam dump (not shown)

Mathew Graham

Other direct dark force searches • Searches at e e colliders: BaBar & Belle(II), KLOE, BES + −

• • •

•

Lower luminosity + lower backgrounds Higher mass reach (up to ~10GeV) “exotic” dark force states: dark higgs, dark mesons

Searches at hadrons colliders:

• • •

ATLAS/CMS & CDF/D0

possible unique production path ⇒ cascades from SUSY particles “lepton-jets” signatures along with typical di-lepton mass peak potentially covers vast area of coupling-mass space, but with model assumptions

⇒ many public results already with more on the way...very active area of study! 2012 SLAC Summer Institute

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Mathew Graham

What now? My conclusions • • • •

The search for new gauge bosons has a long history over a huge range of mass scales Something like a dark photon is very well theoretically motivated and if we live in a GU universe it probably exists

•

What coupling? What mass? Who knows? I have my favorite region!

•

by the way, this doesn’t override SUSY...dark sector models and SUSY get along fine!

Dark matter naturally fits in this dark sector It’s very cool to think that there might be very complicated, very different physics going on all around us which we can’t examine but through this weak, tenuous connection


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Mathew Graham

What now next? •

Ok, say we are seeing DM annihilating (maybe via dark photons) in the PAMELA & FERMI data...what else should we see

• •

•

•

f(e+/e−) should cut off at ~ DM mass high energy photons from inverse Compton scattering & final state radiation ⇒ constraints from Fermi are discouraging imprints on the CMB ⇒ PLANK will be crucial...2013?

Possibly large impact on direct DM experiments

• • •

iDM ⇒ lower recoil energy DAMA/CoGeNT/CRESST anomalies? Xenon100, CDMS are putting big dent in iDM parameter space

“DM could have shown it’s face in many places, and didn’t...but has wiggle-room left.” - Rouven Essig Apart from these anomalies, the upcoming direct heavy-photon searches will block out a very interesting part of parameter space...maybe the dark sector will show it’s head before dark matter 2012 SLAC Summer Institute

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Mathew Graham