going after the dark at colliders david berge (cern)
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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. Particle c: CDM or WDM Axions , gravitinos , or WIMPs. - PowerPoint PPT PresentationTRANSCRIPT
Going after the Dark at CollidersDavid Berge (CERN)
Going after the Dark at CollidersDavid Berge (CERN)
- Setting the stage- LEP neutralino constraints- LHC neutralino searches- LHC contact limits
Going after the Dark at CollidersDavid Berge (CERN)
Galaxy cluster Abell 2744
Particle c:CDM or WDMAxions, gravitinos, or WIMPs
Going after the Dark at CollidersDavid Berge (CERN)
Galaxy cluster Abell 2744
c
c
SM
SM
c
SM
c
SM
SM
SM
c
c
Particle Dark Matter Searches based on:
Indirect Direct Colliders
Going after the Dark at CollidersDavid Berge (CERN)
Galaxy cluster Abell 2744
c
c
SM
SM
c
SM
c
SM
SM
SM
c
c
Particle Dark Matter Searches based on:
Indirect Direct Colliders
The endpoint of particle Dark Matter searches is a (likely combined) measurement of particle properties which allow connecting back to gravitational measurements!
Going after the Dark at CollidersDavid Berge (CERN)
Galaxy cluster Abell 2744
c
c
SM
SM
c
SM
c
SM
SM
SM
c
c
Particle Dark Matter Searches based on:
Indirect Direct Colliders
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!
Beyond the Standard Model of Particle Physics
David Berge (CERN) / 14 Mar 2012
Supersymmetry
Standard Model Extra Dimensions Large, warped, or universal extra
dimensions (…) Dark Matter Hierarchy problem: lower Planck mass Unification of forces
Strong elw. symmetry breaking Modern variants of Technicolor Dark Matter Hierarchy problem Some of the predictions: composite
Higgs, new heavy vector bosons, 4th generation of quarks
Expect spectrum of (not too) heavy superpartners, light neutral Higgs
Dark Matter Higgs mass stable / hierarchy problem Unification of gauge couplings Unification of forces
WIMPs from Supersymmetry
• 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
As early as 1983 Supersymmetrie’s neutralino identified as WIMP candidate (Goldberg / Ellis et al)
LEP neutralino constraints
LEP neutralino constraints
/g
Use GZ = Ginv + Ghadrons + Gleptons:
Measure:
K. Nakamura et al. (Particle Data Group), Journal of Physics G37, 075021 (2010)
LEP neutralino constraints
/g
Use GZ = Ginv + Ghadrons + Gleptons:
Measure: Ginv compatible at 2s with 3 light neutrino species, Nn = 2.984 ± 0.008, not much room for:
c
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
/g
Use GZ = Ginv + Ghadrons + Gleptons:
Measure: Ginv compatible at 2s with 3 light neutrino species, Nn = 2.984 ± 0.008, not much room for:
c
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)
SM
SM
c
c
David Berge (CERN) / 14 Mar 2012
The Large Hadron Collider
David Berge (CERN) / 14 Mar 2012
The Large Hadron Collider
2011 performance Design performanceColliding 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 performanceColliding 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
ATLAS
CMS
Two General Purpose Experiments: ATLAS & CMS
p
p Underlying event
X = jets, W, Z, top, Higgs, SUSY, …
Q 2 = MX
David Berge (CERN) / 14 Mar 2012
LHC Searches for WIMPs
Task: measure transverse energy
David Berge (CERN) / 14 Mar 2012
David Berge (CERN) / 14 Mar 2012
Z ® mm event in ATLAS with 20 reconstructed vertices
Difficulty: event pile-up
Z+jets: mix of fake and true missing ET
Top quark pairs: genuine missing ET from real n’s
1: “Standard” Dark Matter Searches at Colliders
David Berge (CERN) / 14 Mar 2012
One possibility: search for large missing ET in (supersymmetric) cascade decays
p p
X
jet
jet
jets/lepton
ETmiss
... + χ01
experimental signature:jets + (leptons) + ET
miss
[2 LSPs escape scape detection]
Number of invisiblesMass scale of invisiblesSpin
Measure spectra, kinematic endpoints, model fits, etc
It’s all about controlling the backgrounds.
if signal
1: “Standard” Dark Matter Searches at Colliders
David Berge (CERN) / 14 Mar 2012
One possibility: search for large missing ET in (supersymmetric) cascade decays
p p
X
jet
jet
jets/lepton
ETmiss
... + χ01
experimental signature:jets + (leptons) + ET
miss
[2 LSPs escape scape detection]
Number of invisiblesMass scale of invisiblesSpin
Measure spectra, kinematic endpoints, model fits, etc
It’s all about controlling the backgrounds.
if signal
SM
SM
c
c
SM
SM
c
c
1: “Standard” Dark Matter Searches at Colliders
David Berge (CERN) / 14 Mar 2012
One possibility: search for large missing ET in (supersymmetric) cascade decays
p p
X
jet
jet
jets/lepton
ETmiss
... + χ01
experimental signature:jets + (leptons) + ET
miss
[2 LSPs escape scape detection]
Number of invisiblesMass scale of invisiblesSpin
Measure spectra, kinematic endpoints, model fits, etc
It’s all about controlling the backgrounds.
if signal
masssquark, gluino
LSP / Neutralino
Dm ≈ missing ET!
Amount of missing ET depends on mass difference!
ATLAS Supersymmetry Search in Hadronic Final States
David Berge (CERN) / 14 Mar 2012
“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!
Limits on CMSSM SUSY models.ATLAS (similarly CMS) excludes under certain model assumptions squarks and gluinos below 850 to 1400 GeV!
ATLAS-CONF-2012-037
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
David Berge (CERN) / 14 Mar 2012
CMSSM under a lot of pressure, but other models (with more parameters) remain viable
arXiv:1112.4192
Fit including LHC2011, WMAP, g-2, excluding XENON100
Baer et al 2012, arXiv:1202.4038
CMSSM scans, points after current LHC SUSY & Higgs results
LHC Impact on constrained Supersymmetry Models
David Berge (CERN) / 14 Mar 2012
CMSSM under a lot of pressure, but other models (with more parameters) remain viable
arXiv:1112.4192
Fit including LHC2011, WMAP, g-2, excluding XENON100
Baer et al 2012, arXiv:1202.4038
CMSSM scans, points after current LHC SUSY & Higgs results
LEP2
Few-parameter SUSY models like CMSSM increasingly unlikely!
So what?
David Berge (CERN) / 14 Mar 2012
How could strong SUSY production exist but be hidden?
Recall: we need to cancel the Higgs virtual corrections. Most important is top loop
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
ATLAS-CONF-2012-003
Both ATLAS & CMS focus now heavily on stop/sbottom searches!
So what?
David Berge (CERN) / 14 Mar 2012
How could strong SUSY production exist but be hidden?
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?
ATLAS-CONF-2012-037
masssquark, gluino
Dm ≈ missing ET!
LSP
Multi-jet search, this time considering models with gluinos and neutralinos.
So what?
David Berge (CERN) / 14 Mar 2012
How could strong SUSY production exist but be hidden?
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?
ATLAS-CONF-2012-037
masssquark, gluino
Dm ≈ missing ET!
LSP
Maybe squarks and gluinos are all too heavy and only neutralinos (WIMPs) are produced?
monojets!
Multi-jet search, this time considering models with gluinos and neutralinos.
ATLAS mono-jet event display
Jet
Missing energy
- Setting the stage- LEP neutralino constraints- LHC neutralino searches- LHC contact limits
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
David Berge (CERN) / 14 Mar 2012
Assume:• X exists and can be pair produced• Only X in reach at LHC
2: Generic WIMP Searches at Colliders
David Berge (CERN) / 14 Mar 2012
Assume:• X exists and can be pair produced• Only X in reach at LHC
2: Generic WIMP Searches at Colliders
David Berge (CERN) / 14 Mar 2012
Assume:• X exists and can be pair produced• Only X in reach at LHC
2: Generic WIMP Searches at Colliders
David Berge (CERN) / 14 Mar 2012
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
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 direct-detection experiments
• LHC limits don’t suffer from astrophysical uncertainties
arXiv:1109.4398David 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 direct-detection experiments
• LHC limits don’t suffer from astrophysical uncertainties
arXiv:1109.4398David Berge (CERN) / 14 Mar 2012
g
g
Spin dependent Nucleon-WIMP scattering cross section
arXiv:1109.4398
• LHC measurement translates into one line per operator
• Low-mass LHC reach complementary to direct-detection experiments
• LHC limits don’t suffer from astrophysical uncertainties
David Berge (CERN) / 14 Mar 2012
LHC limits on annihilation cross section
David Berge (CERN) / 14 Mar 2012
arXiv:1109.4398
• 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
- 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…
Summary
David Berge (CERN) / 14 Mar 2012
David Berge (CERN) / 14 Mar 2012
Fermi / HESS limits
David Berge (CERN) / 14 Mar 2012
WIMP annihilation into quark-antiquark pairs
HESS Galactic Center Analysis,PRL 106, 161301 (2011)
Fermi stacked Galactic satellites,PRL 107, 241302 (2011)
Expected signal missing ET distributions
Expect harder MET spectrum even for mc= 0 GeV!
MET ( GeV )
Truth-level, private plot
Alpgen Znn+jetsPythia Znn+jets
• Take vector operator as example
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
David Berge (CERN) / 14 Mar 2012
Compare to values of L consistent with thermal relic density
L (
GeV
)
Goodman et al,arXiv:1008.1783
LHC predictions(14 TeV, 100 fb-1)
Tevatron
Thermal relic density
ATLAS 1 fb-1 measurement (arXiv:1109.4398)
Incr
easin
g co
uplin
g to
qua
rks
Incr
easin
g re
lic d
ensit
y
This range excluded under the given assumptions
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