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Probing the Dark Sector by Electromagnetic Interactions · Probing the Dark Sector by...
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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
Johannes Gutenberg-Universität MainzInstitut für Kernphysik
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.
Tobias Beranek Probing the Dark Sector by Electromagnetic Interactions
Johannes Gutenberg-Universität MainzInstitut für Kernphysik
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].
Tobias Beranek Probing the Dark Sector by Electromagnetic Interactions
Johannes Gutenberg-Universität MainzInstitut für Kernphysik
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
Tobias Beranek Probing the Dark Sector by Electromagnetic Interactions
Johannes Gutenberg-Universität MainzInstitut für Kernphysik
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].
Tobias Beranek Probing the Dark Sector by Electromagnetic Interactions
Johannes Gutenberg-Universität MainzInstitut für Kernphysik
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)
Tobias Beranek Probing the Dark Sector by Electromagnetic Interactions
Johannes Gutenberg-Universität MainzInstitut für Kernphysik
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)
Tobias Beranek Probing the Dark Sector by Electromagnetic Interactions
Johannes Gutenberg-Universität MainzInstitut für Kernphysik
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)
Tobias Beranek Probing the Dark Sector by Electromagnetic Interactions
Johannes Gutenberg-Universität MainzInstitut für Kernphysik
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)
Tobias Beranek Probing the Dark Sector by Electromagnetic Interactions
Johannes Gutenberg-Universität MainzInstitut für Kernphysik
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
Tobias Beranek Probing the Dark Sector by Electromagnetic Interactions
Johannes Gutenberg-Universität MainzInstitut für Kernphysik
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
Tobias Beranek Probing the Dark Sector by Electromagnetic Interactions
Johannes Gutenberg-Universität MainzInstitut für Kernphysik
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
Tobias Beranek Probing the Dark Sector by Electromagnetic Interactions
Johannes Gutenberg-Universität MainzInstitut für Kernphysik
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]].
Tobias Beranek Probing the Dark Sector by Electromagnetic Interactions
Johannes Gutenberg-Universität MainzInstitut für Kernphysik
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
Tobias Beranek Probing the Dark Sector by Electromagnetic Interactions
Johannes Gutenberg-Universität MainzInstitut für Kernphysik
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"
Tobias Beranek Probing the Dark Sector by Electromagnetic Interactions