1. Going after the Dark at Colliders David Berge (CERN)

2. Going after the Dark at Colliders David Berge (CERN)
Setting the stage
LEP neutralino constraints
LHC neutralino searches
LHC contact limits

3. Going after the Dark at Colliders David Berge (CERN)
Particle c:
CDM or WDM
Axions, gravitinos, or WIMPs
Galaxy cluster Abell 2744
So there are typically a number of assumptions made:
WIMPs exist and are in the GeV to TeV mass range
A single new particle makes up the whole of Dark Matter
Beyond gravitational interactions there are interactions of the new particle with the SM

4. Going after the Dark at Colliders David Berge (CERN)
Galaxy cluster Abell 2744
Searches in the following really WIMP searches
No SM particle could make up Dark Matter
Additional motivation for building high-energy particle colliders
Particle Dark Matter Searches based on: c SM c c SM c c SM SM SM SM c
Indirect
Direct
Colliders

5. 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
Searches in the following really WIMP searches
No SM particle could make up Dark Matter
Additional motivation for building high-energy particle colliders
Particle Dark Matter Searches based on: c SM c c SM c c SM SM SM SM c
Indirect
Direct
Colliders

6. 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
Searches in the following really WIMP searches
No SM particle could make up Dark Matter
Additional motivation for building high-energy particle colliders
Particle Dark Matter Searches based on: c SM c c SM c c SM SM SM SM c
Indirect
Direct
Colliders

7. Beyond the Standard Model of Particle Physics
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
SUSY must be broken, important to remember that in order to solve fine-tuning of Higgs mass, need superpartners at a few hundred GeV
----- Meeting Notes (2/14/12 09:46) -----
Supersymmetry is an extension which adds super partners to every SM particles, where the superpartners differ by half a unit in spin from their partners. Furthermore, sparticles need to be heavier (since we didn't find them yet).
ED's solve hierarchy problem by having gravity extend in extra dimensions, where it's as strong as the weak force, hence the Planck mass in all dimensions is smaller.
Finally, strong elw sym 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

8. WIMPs from Supersymmetry
As early as 1983 Supersymmetrie’s neutralino identified as WIMP candidate (Goldberg / Ellis et al)
Minimal Supersymmetric Standard Model (MSSM): 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)
Speaking of WIMPs in a supersymmetric picture, as early as 1983 people realised that Supersymmetrie offers WIMP candidates
David Berge (CERN) / 14 Mar 2012

9. LEP neutralino constraints
Pandora’s cluster

10. LEP neutralino constraints
Measure: /g
Use GZ = Ginv + Ghadrons + Gleptons:
Pandora’s cluster
K. Nakamura et al. (Particle Data Group), Journal of Physics G37, (2010)

11. LEP neutralino constraints
Measure:
Ginv compatible at 2s with 3 light neutrino species, Nn = ± 0.008, not much room for: c /g c
Use GZ = Ginv + Ghadrons + Gleptons:
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: ,2009)
Imposing CMSSM constraints, however, mc > 46 GeV holds
Pandora’s cluster
K. Nakamura et al. (Particle Data Group), Journal of Physics G37, (2010)

12. LEP neutralino constraints
Measure:
Ginv compatible at 2s with 3 light neutrino species, Nn = ± 0.008, not much room for: c SM c /g SM c c
Use GZ = Ginv + Ghadrons + Gleptons:
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: ,2009)
Imposing CMSSM constraints, however, mc > 46 GeV holds
Pandora’s cluster
K. Nakamura et al. (Particle Data Group), Journal of Physics G37, (2010)

13. The Large Hadron Collider
David Berge (CERN) / 14 Mar 2012

14. 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

15. 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

16. Two General Purpose Experiments: ATLAS & CMS
David Berge (CERN) / 14 Mar 2012

17. LHC Searches for WIMPs p Q 2 = MX X = jets, W, Z, top, Higgs, SUSY, …
Underlying event
X = jets, W, Z, top, Higgs, SUSY, …
Q 2 = MX
David Berge (CERN) / 14 Mar 2012

18. Task: measure transverse energy
David Berge (CERN) / 14 Mar 2012

19. Difficulty: event pile-up
Z+jets: mix of fake and true missing ET
----- Meeting Notes (2/14/12 10:17) -----
High lumi comes at a price: pile-up
additional energy shot constantly and at random into the detector
Here a picture that proves we are doing well
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

20. 1: “Standard” Dark Matter Searches at Colliders
One possibility: search for large missing ET in (supersymmetric) cascade decays
jet
It’s all about controlling the backgrounds.
jet
jets/lepton X
ETmiss p p
Measure spectra, kinematic endpoints, model fits, etc
To good generality we can expect:
High-pT jets from squark & gluino decays
Leptons from gaugino & slepton decays
Missing energy from LSPs
Task for experimentalists: model backgrounds, understand performance
If discovery, try to infer properties of potential Dark Matter candidates to check validity of Dark Matter hypo
if signal
... + χ01
experimental signature: jets + (leptons) + ETmiss
[2 LSPs escape scape detection]
Number of invisibles
Mass scale of invisibles
Spin
David Berge (CERN) / 14 Mar 2012

21. 1: “Standard” Dark Matter Searches at Colliders
One possibility: search for large missing ET in (supersymmetric) cascade decays SM c
jet SM c
It’s all about controlling the backgrounds.
jet
jets/lepton X
ETmiss p p
Measure spectra, kinematic endpoints, model fits, etc
To good generality we can expect:
High-pT jets from squark & gluino decays
Leptons from gaugino & slepton decays
Missing energy from LSPs
Task for experimentalists: model backgrounds, understand performance
If discovery, try to infer properties of potential Dark Matter candidates to check validity of Dark Matter hypo
if signal
... + χ01
experimental signature: jets + (leptons) + ETmiss
[2 LSPs escape scape detection]
Number of invisibles
Mass scale of invisibles
Spin
David Berge (CERN) / 14 Mar 2012

22. 1: “Standard” Dark Matter Searches at Colliders
One possibility: search for large missing ET in (supersymmetric) cascade decays
squark, gluino SM c
mass
jet SM c
Dm ≈ missing ET!
It’s all about controlling the backgrounds.
jet
jets/lepton X
LSP / Neutralino
ETmiss p p
Measure spectra, kinematic endpoints, model fits, etc
Amount of missing ET depends on mass difference!
To good generality we can expect:
High-pT jets from squark & gluino decays
Leptons from gaugino & slepton decays
Missing energy from LSPs
Task for experimentalists: model backgrounds, understand performance
If discovery, try to infer properties of potential Dark Matter candidates to check validity of Dark Matter hypo
if signal
... + χ01
experimental signature: jets + (leptons) + ETmiss
[2 LSPs escape scape detection]
Number of invisibles
Mass scale of invisibles
Spin
David Berge (CERN) / 14 Mar 2012

23. ATLAS Supersymmetry Search in Hadronic Final States
“At least 7 high-energy jets plus missing transverse energy”
ATLAS-CONF
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!
David Berge (CERN) / 14 Mar 2012

24. 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
CMS-PAS-SUS
David Berge (CERN) / 14 Mar 2012

25. 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
Baer et al 2012, arXiv:
arXiv:
David Berge (CERN) / 14 Mar 2012

26. 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:
arXiv:
Few-parameter SUSY models like CMSSM increasingly unlikely!
David Berge (CERN) / 14 Mar 2012

27. So what? How could strong SUSY production exist but be hidden?
ATLAS-CONF
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
Both ATLAS & CMS focus now heavily on stop/sbottom searches!
David Berge (CERN) / 14 Mar 2012

28. So what? squark, gluino mass Dm ≈ missing ET! LSP
ATLAS-CONF
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?
squark, gluino
mass
Dm ≈ missing ET!
Multi-jet search, this time considering models with gluinos and neutralinos.
LSP
David Berge (CERN) / 14 Mar 2012

29. So what? squark, gluino mass Dm ≈ missing ET! LSP
ATLAS-CONF
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?
Maybe squarks and gluinos are all too heavy and only neutralinos (WIMPs) are produced?
squark, gluino
mass
Dm ≈ missing ET!
Multi-jet search, this time considering models with gluinos and neutralinos.
LSP
monojets!
David Berge (CERN) / 14 Mar 2012

30. LEP neutralino constraints LHC neutralino searches LHC contact limits
Setting the stage
LEP neutralino constraints
LHC neutralino searches
LHC contact limits
Jet
Missing energy
Pandora’s cluster
ATLAS mono-jet event display

31. 2: Generic WIMP Searches at Colliders
Consider WIMP pair production at colliders, idea goes back to:
Birkedal et al (hep-ph/ )
Beltran et al: Maverick Dark Matter (hep-ph/ )
Latest papers based on LHC results:
Fox et al, arxiv: and arXiv: (FNAL crew)
Rajamaran et al, arxiv: (UCI crew)
New CMS result in Sarah’s talk after me
Assume WIMPs produced in pairs, expect missing transverse energy plus jet(s)
----- Meeting Notes (2/14/12 10:33) -----
Let's be model independent, and just search for WIMPs in reach by LHC
David Berge (CERN) / 14 Mar 2012

32. 2: Generic WIMP Searches at Colliders
Assume:
X exists and can be pair produced
Only X in reach at LHC
Don’t assume any model
Just assume that WIMPs exist and can be pair produced at LHC
Then treat pair creation as a contact operator and do an effective field theory Ansatz, just like Fermi it for the 4-fermion contact interaction before the W boson could be resolved.
One has to pick out only the subset of events with a hard radiation jet recoiling against the WIMPs, otherwise the trigger and usual event selections would not select these events
The contact operator for example for a vector interaction looks like this, there are other operators to be considered (scalar, axial-vector, pseudo-scalar) which can result in different rates for chichi bar
The suppression scale, in case of a non-detection, would be used to set bounds on, from the cross section limit. Interestingly, these limits on lambda can be translated into bla
Positive signals in this final state are probably not the first sign we see (other analyses should see excess earlier), moreover we will have to try to derive from jet pt shapes or MET spectrum information about the underlying physics, which isn’t easy. As I said, we may already have other hints from LHC analyses by then, which would need to be combined to try and learn something about the Dark Matter properties.
Check dilepton edges!
David Berge (CERN) / 14 Mar 2012

33. 2: Generic WIMP Searches at Colliders
Assume:
X exists and can be pair produced
Only X in reach at LHC
Don’t assume any model
Just assume that WIMPs exist and can be pair produced at LHC
Then treat pair creation as a contact operator and do an effective field theory Ansatz, just like Fermi it for the 4-fermion contact interaction before the W boson could be resolved.
One has to pick out only the subset of events with a hard radiation jet recoiling against the WIMPs, otherwise the trigger and usual event selections would not select these events
The contact operator for example for a vector interaction looks like this, there are other operators to be considered (scalar, axial-vector, pseudo-scalar) which can result in different rates for chichi bar
The suppression scale, in case of a non-detection, would be used to set bounds on, from the cross section limit. Interestingly, these limits on lambda can be translated into bla
Positive signals in this final state are probably not the first sign we see (other analyses should see excess earlier), moreover we will have to try to derive from jet pt shapes or MET spectrum information about the underlying physics, which isn’t easy. As I said, we may already have other hints from LHC analyses by then, which would need to be combined to try and learn something about the Dark Matter properties.
Check dilepton edges!
----- Meeting Notes (2/14/12 10:33) -----
Squark t channel exchange in SUSY
David Berge (CERN) / 14 Mar 2012

34. 2: Generic WIMP Searches at Colliders
Assume:
X exists and can be pair produced
Only X in reach at LHC
Don’t assume any model
Just assume that WIMPs exist and can be pair produced at LHC
Then treat pair creation as a contact operator and do an effective field theory Ansatz, just like Fermi it for the 4-fermion contact interaction before the W boson could be resolved.
One has to pick out only the subset of events with a hard radiation jet recoiling against the WIMPs, otherwise the trigger and usual event selections would not select these events
The contact operator for example for a vector interaction looks like this, there are other operators to be considered (scalar, axial-vector, pseudo-scalar) which can result in different rates for chichi bar
The suppression scale, in case of a non-detection, would be used to set bounds on, from the cross section limit. Interestingly, these limits on lambda can be translated into bla
Positive signals in this final state are probably not the first sign we see (other analyses should see excess earlier), moreover we will have to try to derive from jet pt shapes or MET spectrum information about the underlying physics, which isn’t easy. As I said, we may already have other hints from LHC analyses by then, which would need to be combined to try and learn something about the Dark Matter properties.
Check dilepton edges!
----- Meeting Notes (2/14/12 10:33) -----
Zprime, new heavy vector bosons exist in many models
David Berge (CERN) / 14 Mar 2012

35. 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
Don’t assume any model
Just assume that WIMPs exist and can be pair produced at LHC
Then treat pair creation as a contact operator and do an effective field theory Ansatz, just like Fermi it for the 4-fermion contact interaction before the W boson could be resolved.
One has to pick out only the subset of events with a hard radiation jet recoiling against the WIMPs, otherwise the trigger and usual event selections would not select these events
The contact operator for example for a vector interaction looks like this, there are other operators to be considered (scalar, axial-vector, pseudo-scalar) which can result in different rates for chichi bar
The suppression scale, in case of a non-detection, would be used to set bounds on, from the cross section limit. Interestingly, these limits on lambda can be translated into bla
Positive signals in this final state are probably not the first sign we see (other analyses should see excess earlier), moreover we will have to try to derive from jet pt shapes or MET spectrum information about the underlying physics, which isn’t easy. As I said, we may already have other hints from LHC analyses by then, which would need to be combined to try and learn something about the Dark Matter properties.
Check dilepton edges!
----- Meeting Notes (2/14/12 10:33) -----
Structure of interaction doesn't matter, we play Fermi's trick and assume everything in the bubble is heavy, in which case the interaction vertex can be seen as a contact interaction and parametrised depending on spin structure
Suppression scale Lambda, related to heavy messenger or mediator particles, sets the cross section
LHC limit on cutoff scale can be translated to direct or indirect detection plane!
Cutoff scale
David Berge (CERN) / 14 Mar 2012

36. 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:
David Berge (CERN) / 14 Mar 2012

37. 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 g g
arXiv:
David Berge (CERN) / 14 Mar 2012

38. Spin dependent 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:
David Berge (CERN) / 14 Mar 2012

39. 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:
David Berge (CERN) / 14 Mar 2012

40. LHC limits potentially very competitive
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…
Pandora’s cluster
David Berge (CERN) / 14 Mar 2012

41. David Berge (CERN) / 14 Mar 2012

42. Fermi / HESS limits Fermi stacked Galactic satellites,
PRL 107, (2011)
HESS Galactic Center Analysis,
PRL 106, (2011)
WIMP annihilation into quark-antiquark pairs
David Berge (CERN) / 14 Mar 2012

43. Expected signal missing ET distributions
Truth-level, private plot
Take vector operator as example
Alpgen Znn+jets
Pythia Znn+jets
----- Meeting Notes (2/14/12 10:33) -----
Once again, search for high MET excess events
MET ( GeV )
Expect harder MET spectrum even for mc= 0 GeV!
David Berge (CERN) / 14 Mar 2012

44. Limits on suppression scale L
Take vector operator as example
Convert cross section limits into limit on L for particular mc
----- Meeting Notes (2/14/12 10:33) -----
ATLAS EPS cross section limit translated into limit on Lambda
arXiv:
David Berge (CERN) / 14 Mar 2012

45. Limits on suppression scale L
Compare to values of L consistent with thermal relic density
LHC predictions
(14 TeV, 100 fb-1)
Thermal relic density
ATLAS 1 fb-1 measurement (arXiv: )
Increasing coupling to quarks
Increasing relic density
L ( GeV )
Tevatron
----- Meeting Notes (2/14/12 10:33) -----
ATLAS EPS cross section limit translated into limit on Lambda
Goodman et al,
arXiv:
This range excluded under the given assumptions
David Berge (CERN) / 14 Mar 2012

46. 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
33 minutes
David Berge (CERN) / 14 Mar 2012