Probing the Dark Sector by Electromagnetic Interactions · Probing the Dark Sector by Electromagnetic Interactions T. Beranek1, A. Denig1, M. Vanderhaeghen1 1Institut für Kernphysik,

Johannes Gutenberg-Universität MainzInstitut für Kernphysik

Probing the Dark Sector byElectromagnetic Interactions

T. Beranek1, A. Denig1, M. Vanderhaeghen1

1Institut für Kernphysik, Johannes Gutenberg-Universität Mainz, Deutschland

EMG Annual Retreat,Bingen, 27.09. - 29.09.2010

Tobias Beranek Probing the Dark Sector by Electromagnetic Interactions

http://www.uni-mainz.de


http://www.kph.uni-mainz.de

mailto:[email protected]


Energy Density of the Universe

No Big Bang

1 20 1 2 3

expands forever

−1

0

1

2

3

2

3

closed

Supernovae

CMB

Clusters

SNe: Knop et al. (2003)CMB: Spergel et al. (2003)Clusters: Allen et al. (2002)

ΩΛ

ΩM

open

flat

recollapses eventually

The stuff our world is made of...

Total energy density is critical: Ωtot w 1

Data from CMB, SN1A, baryon genesisand structure formation

Baryonic matter contributes only < 5%

23% contributed by Dark Matter (DM)

ΩΛ w 72%, ΩDM w 23%, ΩB w 4.6%,

Ωγ w 0.005%, 0.1% . Ων . 1.5%

Dark Matter from two points of viewDM is needed in the cosmological Standard Model (ΛCDM) to explain Ωtot

DM appears in particle physics automatically

F. D. Steffen, Eur. Phys. J. C 59 (2009) 557 [arXiv:0811.3347 [hep-ph]].W. M. Yao et al. [Particle Data Group], J. Phys. G 33 (2006) 1.







The WIMP Hypothesis

Motivation of WIMPSΛCDM does not require DM to have any interactions with SM except gravity

Weakly Interacting Massive Particles are possible dark matter candidates

Motivation results from particle physics attempts to solve weak scalequestions like the gauge hierachy problem using e.g. SUSY

The WIMP MiracleWIMPs are not introdced to explain DM, but...

they have a mass ∼ 100 GeV − ∼ 10 TeV consistend with DM properties

they naturally lead to a relic density which is consistend with that of darkmatter

⇒ Particle physics leads to a DM candidate

J. L. Feng, arXiv:1003.0904 [astro-ph.CO].







Implications from Indirect Dark Matter Detection

χ

χ

SM

SM PAMELASharp upturn in positron fraction from10− 100 GeV;in contraction to expectation frominteractions of high-energy cosmic rayswith ISM

Possible explanation DM→ e+e−, butunnaturally large cross section andsuppressed p production required⇒ Contradiction to WIMP DM

DM charged under new gaugesymmetry automatically has correctthermal relic abundance like WIMP DMand can explain observations⇒ new massive gauge boson A′ atmass scale 50 MeV to 1 GeV!

O. Adriani et al. [PAMELA Collaboration], Nature 458 (2009) 607 [arXiv:0810.4995 [astro-ph]]N. Arkani-Hamed, D. P. Finkbeiner, T. R. Slatyer and N. Weiner, Phys. Rev. D 79 (2009) 015014







Motivation for New Physics at the GeV ScaleThe GeV-scale of the A′ mass can be motivated from

SUSYLow-energy SUSY allows to determine the A′ mass from same physicsgenerating W± and Z 0 massesElectroweak symmetry breaking generates a mass term for the A′, thus

mA′ ∼ MeV − GeV

ObservationsCalculations for DM annihilationswith O(GeV) A′ andSommerfeld enhancementreconcile PAMELA data

p production kinematicallysuppressed

0.01

0.1

1

10 100

φ e+ /

(φe+

+ φ

e- )

Energy (GeV)

e+e- Channel

mχ = 850 GeV, BF = 450

mχ = 300 GeV, BF = 64

mχ = 100 GeV, BF = 8.1

Background

PAMELA Data

I. Cholis, G. Dobler, D. P. Finkbeiner, L. Goodenough and N. Weiner, Phys. Rev. D 80 (2009) 123518R. Essig, J. Kaplan, P. Schuster and N. Toro, arXiv:1004.0691 [hep-ph].







Motivation for New Physics at the GeV Scale

l

l′

χ

χ

γ A′

Standard Model ExtensionsInteraction with SM particles:L = g′ A′µψγµψ

Kinetic mixing between two U(1)gauge symmetry force carriers, e.gγ and A′, i.e. Lmix = ε

2 FµνY F ′µν withnaturally ε . 10−1 − 10−9 is a possibleSM extension

Consequence: A′ opens window to ahidden sector, that can be studied withfixed target experiment at moderateenergies (Bjorken et al.) and probe e.g.supersymmetry at relatively lowenergies

B. Holdom, Phys. Lett. B 166 (1986) 196.J. D. Bjorken, R. Essig, P. Schuster and N. Toro, Phys. Rev. D 80, 075018 (2009)







Motivation for New Physics at the GeV Scale

l

l′A′ǫ

Standard Model ExtensionsInteraction with SM particles:L = ε e A′µψγµψ

Kinetic mixing between two U(1)gauge symmetry force carriers, e.gγ and A′, i.e. Lmix = ε

2 FµνY F ′µν withnaturally ε . 10−1 − 10−9 is a possibleSM extension

Consequence: A′ opens window to ahidden sector, that can be studied withfixed target experiment at moderateenergies (Bjorken et al.) and probe e.g.supersymmetry at relatively lowenergies

B. Holdom, Phys. Lett. B 166 (1986) 196.J. D. Bjorken, R. Essig, P. Schuster and N. Toro, Phys. Rev. D 80, 075018 (2009)







A New Dark Gauge Boson

ConstraintsConstraints on coupling and massconfigurations result from

electron and muon anomalousmagnetic moment(ae and aµ)

BABAR search forΥ(3S)→ γµ+µ−

beam-dump experiments at SLACand Fermilab(E137, E141, E774)SN cooling

10-2 10-1 110-9

10-8

10-7

10-6

10-5

10-4

10-3

10-210-2 10-1 1

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

mA' HGeVLΕ E137

E141

E774aΜ

ae UH3SL

SN

(Bjorken et al., Phys.Rev.D 80)







A New Dark Gauge Bosonχ

χ

A′

A′

l+

l−

l+

l−

Production at Accelerators(a) + (b): Production at e+e− colliders:⇒ powerful tool at larger masses andε, but limited by luminosity andbackground(c): Production from fixed nucleontarget:⇒ much larger luminosities can beachieved, existing experiments provideadequate setups for search

e−

e+

X

X

A′∗

(a)

e−

e+

γ

A′(b)

e− e−

γ∗

A′

N N(c)







Production Cross Section: Computation

e−(k) e−(k ′)

p(p) p(p′)

q′

e−(l−)

e+(l+)

A′, γ

(a) timelike gauge boson

e−(k) e−(k ′)

p(p) p(p′)

q = k − k ′

e−(l−)

e+(l+)γ

(b) spacelike gauge boson

Constraints

Bethe-Heitler process(e−p → e−pγ) is mostimportant background

A′ signal is supressed by atleast a factor of ε2

no possibility to annihilatebackground⇒ investigate decay of thetimelike gauge boson toe+e− pair

10-8

10-6

10-4

10-2

100

102

104

106

108

-150 -100 -50 0 50 100 150

dσ/(

dEe’

dΩ

e’L d

Ωp’

cm)

[nb/

GeV

]

θpcm [deg]

A’ signal vs Bethe-Heitler, Ee = 855 MeV, Ee’ = 748 MeV, θe’L = 15.1°, Φ = 0°

Bethe-HeitlerA’ signal, mA’ = 50 MeV, ε = 0.001







Production Cross Section: Cross-Checks

Parameters in Labe− beam: Ee = 855 MeV,Ee′ = 748 MeV, θe′ = 15.1

p target: |~p′| = 274 MeV,θp′ = −61.1, Φ = 0

e+e− pair: Ee+ = 56.7 MeV,θe+ = 90

Results

Production cross sectionstrongly depends on mA′ ,scales with ε4

Comparison ofbackground and signalleads to checkableparameter space region

best kinematic has to befound

10-4

10-3

10-2

10-1

100

101

102

103

104

105

0 10 20 30 40 50 60 70

d7 σ/(d

Q2 d

x B d

t dΦ

dq’

2 dΩ

e+e- )

[nb/

GeV

6 ]

We+e- [MeV]

Background process: e+e- pair production via A’/γ*

both BH contributionstimelike outgoing γspacelike outgoing γA’ signal, mA’ = 25 MeVA’ signal, mA’ = 50 MeV







A′ search at MAMI

e−beam

e−(Spec .A)

e+(Spec .B)e ′

200 250 300 0

1000

2000

3000

4000

5000

Eve

nts

/ 0.5

MeV

mA’ [MeV/c2]950 960 970 980 990 1000

0

1000

2000

3000

4000

5000

6000

7000

Cou

nts/

0.00

15

x [10−3]

Courtesy of H. Merkel (A1 collaboration) x =Ee+ +Ee−

E0







Exclusion limit for ε:

Approximation for Heavy NucleiBjorken et al. use Weizsäcker-Williams approximation to compute a minimal εthat can be checked in particular experiments

In WW approximation: Recoil on heavy nucleus is small⇒ leptonic currentincluding A′ production and hadronic current can be separated:

dσ ∼ |M′|2˛θp′=0, φp′=0

·Z

dΩp′ fN“

(p − p′)2”

Computation of the signal to background ratio

d7σA′+BH

d7σBH

J. D. Bjorken, R. Essig, P. Schuster and N. Toro, Phys. Rev. D 80, 075018 (2009) [arXiv:0906.0580 [hep-ph]].







Exclusion limit for ε: PRELIMINARY

1

1.005

1.01

1.015

1.02

1.025

0 0.5 1 1.5 2 2.5 3 3.5 4

d7 σ A’+

BH

/d7 σ B

H

ε/(10-3)

ε dependence for mA’ = me+e- = 259.52 MeV, Ee = 855 MeV

A = 181

Lepton pair:˛~l+˛

= 470 MeV, θ+ = 15.2,˛~l−˛

= 338 MeV, θ− = 22.8







Conclusions & Outlook

Summary & Conclusions

Strong evidence for physics beyond the standard model is given

Dark Matter motivates the theory of a further gauge boson whichmixes with electromagnetic sector

Exclusion of parameter regions possible by fixed targetexperiments at accelerators like MAMI

Bethe-Heitler background much stronger than signal in real A′

production⇒ Detection of decay products may improve the signal tobackground ratio

Precise study of signal and background is performed

First estimate for MAMI at 1% accuracy:ε . 2.5 · 10−3 for mA′ = 259.52 MeV

This work is supported by the research center"Elementare Kräfte und Mathematische Grundlagen"






Documents

Probing the Dark Sector by Electromagnetic Interactions · Probing the Dark Sector by Electromagnetic Interactions T. Beranek1, A. Denig1, M. Vanderhaeghen1 1Institut für Kernphysik,