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Going after the Dark at Colliders
David Berge (CERN)
Going after the Dark at Colliders
David Berge (CERN)
-
Setting the stage
LEP neutralino constraints
LHC neutralino searches
LHC contact limits
Going after the Dark at Colliders
David Berge (CERN)
Particle c:
CDM or WDM
Axions, gravitinos,
or WIMPs
Galaxy cluster Abell 2744
Going after the Dark at Colliders
David Berge (CERN)
Galaxy cluster Abell 2744
Particle Dark Matter Searches based on:
c
SM
c
c
SM
SM
Indirect
Direct
c
SM
c
SM
SM
c
Colliders
Going after the Dark at Colliders
David Berge (CERN)
The endpoint of particle Dark Matter
searches is a (likely combined)
measurement of particle properties
which allow connecting back to
gravitational measurements!
Galaxy cluster Abell 2744
Particle Dark Matter Searches based on:
c
SM
c
c
SM
SM
Indirect
Direct
c
SM
c
SM
SM
c
Colliders
Going after the Dark at Colliders
David Berge (CERN)
Since up to now there are no
undisputed positive measurements
(definitely true for colliders),
interpreting exclusion limits in terms
of c involve assumptions about the
red bubble!
Galaxy cluster Abell 2744
Particle Dark Matter Searches based on:
c
SM
c
c
SM
SM
Indirect
Direct
c
SM
c
SM
SM
c
Colliders
Beyond the Standard Model of Particle Physics
Standard Model
Extra Dimensions




Large, warped, or universal extra
dimensions (…)
Dark Matter
Hierarchy problem: lower Planck mass
Unification of forces
Strong elw. symmetry breaking

Supersymmetry





Expect spectrum of (not too) heavy
superpartners, light neutral Higgs
Dark Matter
Higgs mass stable / hierarchy problem
Unification of gauge couplings
Unification of forces
David Berge (CERN) / 14 Mar 2012



Modern variants of Technicolor
Dark Matter
Hierarchy problem
Some of the predictions: composite
Higgs, new heavy vector bosons, 4th
generation of quarks
WIMPs from Supersymmetry
As early as 1983 Supersymmetrie’s neutralino identified as WIMP candidate (Goldberg / Ellis et al)
• Minimal Supersymmetric Standard Model (MSSM): 105+1+18
parameters
• Simplified MSSM sub-spaces with less parameters used as
benchmarks
– E.g. CMSSM/mSUGRA (5 parameters), NUHM1/2 (5 parameters), pMSSM (19
parameters)…
• Neutralinos WIMP candidates: many Supersymmetry versions
predict these to be stable, neutral, massive and the lightest
particles (Lightest Supersymmetric Particle / LSP)
David Berge (CERN) / 14 Mar 2012
LEP neutralino constraints
LEP neutralino constraints
Measure:
/g
Use GZ = Ginv + Ghadrons + Gleptons:
K. Nakamura et al. (Particle Data Group),
Journal of Physics G37, 075021 (2010)
LEP neutralino constraints
Measure:
Ginv compatible at 2s with 3 light neutrino
species, Nn = 2.984 ± 0.008, not much room for:
c
/g
Use GZ = Ginv + Ghadrons + Gleptons:
c
- If neutralinos couple to Z boson, LEP’s Ginv
implies mc > 46 GeV
- Not generically true in MSSM, 0 GeV mc well
possible
• See e.g. Dreiner et al (Eur.Phys.J.C62:547-572,2009)
- Imposing CMSSM constraints, however, mc >
46 GeV holds
K. Nakamura et al. (Particle Data Group),
Journal of Physics G37, 075021 (2010)
LEP neutralino constraints
Measure:
Ginv compatible at 2s with 3 light neutrino
species, Nn = 2.984 ± 0.008, not much room for:
c
/g
Use GZ = Ginv + Ghadrons + Gleptons:
c
SM
c
SM
c
- If neutralinos couple to Z boson, LEP’s Ginv
implies mc > 46 GeV
- Not generically true in MSSM, 0 GeV mc well
possible
• See e.g. Dreiner et al (Eur.Phys.J.C62:547-572,2009)
- Imposing CMSSM constraints, however, mc >
46 GeV holds
K. Nakamura et al. (Particle Data Group),
Journal of Physics G37, 075021 (2010)
The Large Hadron Collider
David Berge (CERN) / 14 Mar 2012
The Large Hadron Collider
2011 performance
Design performance
Colliding bunches
1331
2808
Energy
3.5 TeV x 3.5 TeV
7 TeV x 7 TeV
Bunch spacing
50 ns
25 ns
Luminosity
3.6 x 1033 cm-2 s-1
1034 cm-2 s-1
Pile-up interactions
~20
~25
David Berge (CERN) / 14 Mar 2012
The Large Hadron Collider
2012 performance
Design performance
Colliding bunches
1331
2808
Energy
4 TeV x 4 TeV
7 TeV x 7 TeV
Bunch spacing
50 ns
25 ns
Luminosity
6.8 x 1033 cm-2 s-1
1034 cm-2 s-1
Pile-up interactions
~35
~25
David Berge (CERN) / 14 Mar 2012
Two General Purpose Experiments: ATLAS & CMS
ATLAS
CMS
David Berge (CERN) / 14 Mar 2012
LHC Searches for WIMPs
p
x1 × pp
x2 × pp
p
David Berge (CERN) / 14 Mar 2012
Q 2 = MX
X=
Underlying event
jets, W, Z, top, Higgs,
SUSY, …
Task: measure transverse energy
David Berge (CERN) / 14 Mar 2012
Difficulty: event pile-up
Z+jets: mix of fake and
true missing ET
Top quark pairs: genuine
missing ET from real n’s
Z  mm event in ATLAS with 20 reconstructed vertices
David Berge (CERN) / 14 Mar 2012
1: “Standard” Dark Matter Searches at Colliders
One possibility: search for large missing ET in (supersymmetric) cascade decays
jet
jet
It’s all about controlling the
backgrounds.
jets/lepton
X
p
ETmiss
p
if signal
Measure spectra,
kinematic endpoints,
model fits, etc
... + χ01
experimental signature:
jets + (leptons) + ETmiss
[2 LSPs escape scape detection]
David Berge (CERN) / 14 Mar 2012
Number of invisibles
Mass scale of invisibles
Spin
1: “Standard” Dark Matter Searches at Colliders
One possibility: search for large missing ET in (supersymmetric) cascade decays
c
SM
c
SM
jet
jet
It’s all about controlling the
backgrounds.
jets/lepton
X
p
ETmiss
p
if signal
Measure spectra,
kinematic endpoints,
model fits, etc
... + χ01
experimental signature:
jets + (leptons) + ETmiss
[2 LSPs escape scape detection]
David Berge (CERN) / 14 Mar 2012
Number of invisibles
Mass scale of invisibles
Spin
1: “Standard” Dark Matter Searches at Colliders
One possibility: search for large missing ET in (supersymmetric) cascade decays
SM
SM
c
mass
c
squark, gluino
jet
Dm ≈ missing EIt’s
T! all about controlling the
jet
backgrounds.
jets/lepton
X
p
miss
LSP / ENeutralino
T
Measure spectra,
p
kinematic
endpoints,
Amount of missing ET depends on mass
difference!
if signal
model fits, etc
... + χ01
experimental signature:
jets + (leptons) + ETmiss
[2 LSPs escape scape detection]
David Berge (CERN) / 14 Mar 2012
Number of invisibles
Mass scale of invisibles
Spin
ATLAS Supersymmetry Search in Hadronic Final States
“At least 7 high-energy jets plus missing transverse energy”
Missing transverse energy divided by sqrt
of Hadronic transverse energy
(“significance of missing ET”).
Nothing beyond expected backgrounds,
set limits!
David Berge (CERN) / 14 Mar 2012
ATLAS-CONF-2012-037
Limits on CMSSM SUSY models.
ATLAS (similarly CMS) excludes under certain
model assumptions squarks and gluinos below
850 to 1400 GeV!
CMS Supersymmetry Search in Hadronic Final States
• CMS ‘razor’ analysis
• Searches for pair
production of heavy
new particles,
decaying to LSP and
jet(s)
• Exclusion of squarks
and gluinos below
1.3 TeV for equal
masses
David Berge (CERN) / 14 Mar 2012
CMS-PAS-SUS-12-005
LHC Impact on constrained Supersymmetry Models
CMSSM under a lot of pressure, but other models (with more parameters) remain viable
CMSSM scans, points after current
LHC SUSY & Higgs results
Baer et al 2012, arXiv:1202.4038
David Berge (CERN) / 14 Mar 2012
Fit including LHC2011, WMAP, g-2,
excluding XENON100
arXiv:1112.4192
LHC Impact on constrained Supersymmetry Models
CMSSM under a lot of pressure, but other models (with more parameters) remain viable
CMSSM scans, points after current
LHC SUSY & Higgs results
Fit including LHC2011, WMAP, g-2,
excluding XENON100
LEP2
Baer et al 2012, arXiv:1202.4038
Few-parameter SUSY models like CMSSM increasingly unlikely!
David Berge (CERN) / 14 Mar 2012
arXiv:1112.4192
So what?
How could strong SUSY production exist but be hidden?
ATLAS-CONF-2012-003
Recall: we need to cancel the Higgs virtual
corrections. Most important is top loop
H
t
H
t
t
H
H
Contrary to the SM, 3rd generation squarks
can be lighter than 1st and 2nd generations
 Maybe all squarks except stop and sbottom
are heavy?
Gluinos produce sbottoms which decay to
bottom and neutralino. The bottom quarks can
be “tagged” in the detector
Both ATLAS & CMS focus now heavily on stop/sbottom searches!
David Berge (CERN) / 14 Mar 2012
So what?
How could strong SUSY production exist but be hidden?
ATLAS-CONF-2012-037
Maybe the neutralinos are almost as
heavy as the squarks and gluinos so that
not enough missing ET is produced in the
decays to select SUSY events?
squark, gluino
mass
Dm ≈
missing ET!
LSP
David Berge (CERN) / 14 Mar 2012
Multi-jet search, this time considering
models with gluinos and neutralinos.
So what?
How could strong SUSY production exist but be hidden?
ATLAS-CONF-2012-037
Maybe the neutralinos are almost as
heavy as the squarks and gluinos so that
not enough missing ET is produced in the
decays to select SUSY events?
Maybe squarks and gluinos are all
too heavy and only neutralinos
(WIMPs) are produced?
squark, gluino
mass
Dm ≈
missing ET!
monojets!
LSP
David Berge (CERN) / 14 Mar 2012
Multi-jet search, this time considering
models with gluinos and neutralinos.
-
Setting the stage
LEP neutralino constraints
LHC neutralino searches
LHC contact limits
Jet
Missing
energy
ATLAS mono-jet event display
2: Generic WIMP Searches at Colliders
• Consider WIMP pair production at colliders, idea goes back to:
– Birkedal et al (hep-ph/0403004)
– Beltran et al: Maverick Dark Matter (hep-ph/1002.4137)
• Latest papers based on LHC results:
– Fox et al, arxiv:1109.4398 and arXiv:1202.1662 (FNAL crew)
– Rajamaran et al, arxiv:1108.1196 (UCI crew)
• New CMS result in Sarah’s talk after me
• Assume WIMPs produced in pairs, expect missing transverse energy plus jet(s)
David Berge (CERN) / 14 Mar 2012
2: Generic WIMP Searches at Colliders
Assume:
• X exists and can be pair produced
• Only X in reach at LHC
David Berge (CERN) / 14 Mar 2012
2: Generic WIMP Searches at Colliders
Assume:
• X exists and can be pair produced
• Only X in reach at LHC
David Berge (CERN) / 14 Mar 2012
2: Generic WIMP Searches at Colliders
Assume:
• X exists and can be pair produced
• Only X in reach at LHC
David Berge (CERN) / 14 Mar 2012
2: Generic WIMP Searches at Colliders
Assume:
• X exists and can be pair produced
• Only X in reach at LHC
• Effective field theory approach
• X—SM coupling set by mc and L
Cutoff scale
David Berge (CERN) / 14 Mar 2012
LHC limit on cutoff scale can
be translated to direct or
indirect detection plane!
Spin independent Nucleon-WIMP scattering cross section
•
•
•
LHC measurement
translates into one line per
operator
Low-mass LHC reach
complementary to directdetection experiments
LHC limits don’t suffer from
astrophysical uncertainties
arXiv:1109.4398
David Berge (CERN) / 14 Mar 2012
Spin independent Nucleon-WIMP scattering cross section
•
•
•
LHC measurement
translates into one line per
operator
Low-mass LHC reach
complementary to directdetection experiments
LHC limits don’t suffer from
astrophysical uncertainties
g
g
arXiv:1109.4398
David Berge (CERN) / 14 Mar 2012
Spin dependent Nucleon-WIMP scattering cross section
•
•
•
LHC measurement
translates into one line per
operator
Low-mass LHC reach
complementary to directdetection experiments
LHC limits don’t suffer from
astrophysical uncertainties
arXiv:1109.4398
David Berge (CERN) / 14 Mar 2012
LHC limits on annihilation cross section
• DM annihilation at freeze-out
temperatures
• Assume DM couples to quarks
only (else bounds weaker)
• Assume effective field theory
approach is viable
• Masses < 15 and 70 GeV ruled
out for vector and axial-vector
operators
arXiv:1109.4398
David Berge (CERN) / 14 Mar 2012
Summary
- Particle Dark Matter searches at colliders
integral part of LHC physics
- Models / assumptions needed to port
collider exclusions to Dark Matter limits
- LHC limits potentially very competitive
- Hopefully soon we’ll have positive
measurements to debate about…
David Berge (CERN) / 14 Mar 2012
David Berge (CERN) / 14 Mar 2012
Fermi / HESS limits
Fermi stacked Galactic satellites,
PRL 107, 241302 (2011)
HESS Galactic Center Analysis,
PRL 106, 161301 (2011)
WIMP annihilation into
quark-antiquark pairs
David Berge (CERN) / 14 Mar 2012
Expected signal missing ET distributions
• Take vector
operator as
example
Truth-level, private plot
Alpgen Znn+jets
Pythia Znn+jets
MET ( GeV )
Expect harder MET spectrum even for mc= 0 GeV!
David Berge (CERN) / 14 Mar 2012
Limits on suppression scale L
• Take vector
operator as
example
• Convert cross
section limits
into limit on
L for
particular mc
arXiv:1109.4398
David Berge (CERN) / 14 Mar 2012
Limits on suppression scale L
Compare to values of L consistent with thermal relic density
L ( GeV )
Increasing relic density
Increasing coupling to quarks
LHC predictions
(14 TeV, 100 fb-1)
ATLAS 1 fb-1 measurement
(arXiv:1109.4398)
Tevatron
Goodman et al,
arXiv:1008.1783
This range excluded under
the given assumptions
David Berge (CERN) / 14 Mar 2012
Limits in “direct-detection plane”
Now convert the high-energy limit on L into limits on sc-Nucleon
Caveats:
• Uncertainty of hadronic matrix elements
• Spin-independent vs spin-dependent interactions depending
on operator
• Simple transfer of LHC limits potentially problematic if
• mediators are light
• interactions are non-flavour-universal
David Berge (CERN) / 14 Mar 2012

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