gev-scale collider and fixed-target experiments to search
TRANSCRIPT
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)
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