Going after the Dark at Colliders David Berge (CERN)

Going after the Dark at CollidersDavid Berge (CERN)


- Setting the stage- LEP neutralino constraints- LHC neutralino searches- LHC contact limits


Galaxy cluster Abell 2744

Particle :cCDM or WDMAxions, gravitinos, or WIMPs



c

c

SM

SM

c

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c

SM

SM

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Particle Dark Matter Searches based on:

Indirect Direct Colliders



c

c

SM

SM

c

SM

c

SM

SM

SM

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The endpoint of particle Dark Matter searches is a (likely combined) measurement of particle properties which allow connecting back to gravitational measurements!



c

c

SM

SM

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SM

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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)


As early as 1983 Supersymmetrie’s neutralino identified as WIMP candidate (Goldberg / Ellis et al)

LEP neutralino constraints


/g

Use GZ = Ginv + Ghadrons + Gleptons:

Measure:

K. Nakamura et al. (Particle Data Group), Journal of Physics G37, 075021 (2010)

http://pdg.lbl.gov/2011/html/authors_2011.html



/g


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





/g


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


SM

SM

c

c




The Large Hadron Collider


The Large Hadron Collider2011 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


The Large Hadron Collider2012 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


ATLAS

CMS

Two General Purpose Experiments: ATLAS & CMS

p

p Underlying event

X = jets, W, Z, top, Higgs, SUSY, …

Q 2 = MX


LHC Searches for WIMPs

Task: measure transverse energy



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


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




p p

X

jet

jet

jets/lepton

ETmiss

... + χ01


miss





if signal

SM

SM

c

c

SM

SM

c

c




p p

X

jet

jet

jets/lepton

ETmiss

... + χ01


miss





if signal

masssquark, gluino

LSP / Neutralino

Dm ≈ missing ET!

Amount of missing ET depends on mass difference!

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!

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

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/

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-12-005

http://cdsweb.cern.ch/search?ln=en&cc=CMS&p=&f=&action_search=Search&c=CMS+Physics+Analysis+Summaries&c=&sf=&so=d&rm=&rg=100&sc=1&of=hb

LHC Impact on constrained Supersymmetry Models


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


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?


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?



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?



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)


2: Generic WIMP Searches at Colliders


Assume:• X exists and can be pair produced• Only X in reach at LHC









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




arXiv:1109.4398David Berge (CERN) / 14 Mar 2012

g

g

Spin dependent Nucleon-WIMP scattering cross section

arXiv:1109.4398





LHC limits on annihilation cross section


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



Fermi / HESS limits


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


Limits on suppression scale L

• Take vector operator as example

• Convert cross section limits into limit on L for particular mc

arXiv:1109.4398


Limits on suppression scale L


Compare to values of L consistent with thermal relic density

L ( G

eV )

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

easi

ng c

oupl

ing

to q

uark

s

Incr

easi

ng re

lic d

ensi

ty

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


Going after the Dark at Colliders David Berge (CERN)

Documents

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