1Alan Barr PASCOS 09 PASCOS 2009 DESY 9 July 2009 …AT THE LHC DARK MATTER … Alan Barr University...

1Alan Barr PASCOS 09PASCOS 2009 DESY 9 July 2009

…AT THE LHC

DARK MATTER …

Alan BarrUniversity of Oxford

On behalf of the

ATLAS and CMScollaborations

2Alan Barr PASCOS 09

You may have noticed there is a new collider

starting operation


Motivation

stop

higgs higgs

+SUSY

Log10 (μ / GeV)

1/α

The value of prejudice rapidly decreasing


The machine …

26.659 km circumference9300 magnets Four experiments(two general purpose)

26.659 km circumference9300 magnets Four experiments(two general purpose)

ATLASCMS

• Proton-proton– controlled

environment– up to 14 TeV– 109 collisions/second– ~ decade operation

• Proton-proton– controlled

environment– up to 14 TeV– 109 collisions/second– ~ decade operation


Segment of 4π detector


Beam splash2008-09-10

Beam splash2008-09-10

CMS


Events…From Steve Meyers

More info: http://indico.cern.ch/conferenceDisplay.py?confId=62277 More info: http://indico.cern.ch/conferenceDisplay.py?confId=62277


Dark Matter … Z2 ?

• Events build from blobs with 2 “exotic legs”

• A pair of cascade decays results

• Complicated end result

• Events build from blobs with 2 “exotic legs”

• A pair of cascade decays results

• Complicated end result

Time

standard

2 exotics

Production part

Time

standard

heavyexotic lighter

exotic

Decay part Time

Complete “event”

= exotic= standard

Candidates include: {Supersymmetry, UED, Little Higgs}+ appropriate parity

Candidates include: {Supersymmetry, UED, Little Higgs}+ appropriate parity


• Assume R-parity• Look for:

– Jets from squark & gluino decays – Leptons from gaugino & slepton decays– Missing energy from (stable) LSPs

Example SUSY search

“Typical” SUSY spectrum

Missing energy + JetsMass (GeV)


Cross-sections etc

Lower backgrounds

Higher backgrounds

“Rediscover”

“Discover”

ZZ

WW

ProspinoProspino


Caveats

• Current public results mostly:– √S = 14 TeV– ∫L ≥ 1 fb-1

– no pile-up†

• Initial conditions will be different• Work in progress for smaller √S, ∫L

– 10 TeV– 10-100 pb-1

• Current public results mostly:– √S = 14 TeV– ∫L ≥ 1 fb-1

– no pile-up†

• Initial conditions will be different• Work in progress for smaller √S, ∫L

– 10 TeV– 10-100 pb-1

†some CMS physics TDR results include 5 pile-up events


Typical search: inclusive distributions

• Jet pT > {100, 50,50,50} GeV

• pT > 100 GeV

• pT > 0.2 meff

• ST > 0.2

• Δφ(pT,j) > 0.2j = {1,2,3}

• No e or μ

• meff > 800 GeV

• Jet pT > {100, 50,50,50} GeV

• pT > 100 GeV

• pT > 0.2 meff

• ST > 0.2

• Δφ(pT,j) > 0.2j = {1,2,3}

• No e or μ

• meff > 800 GeV

i

iTE

missTeffm p

i

iTE

missTeffm p

SignalSignal

BGBG

Example 4 jet + pT distributionExample 4 jet + pT distribution


Standard Model backgrounds

• Statistics limited– Also use:– W (μ) + jet– γ + jet

• Statistics limited– Also use:– W (μ) + jet– γ + jet

Measure in Z -> μ μ

Use in Z -> νν

R: Z -> ννB: Estimated R: Estimated

R: Z -> ννB: Estimated R: Estimated


W, t backgrounds

Search region

Control Region

Good match to “true” background

missT

lT

missT

lTT ppEEm 2

missT

lT

missT

lTT ppEEm 2

These are examples onlyLots of detail about Z, top, QCD, detectorBGs in further reading


Multiple channels for discovery

Different final states accessible

Different final states accessible

Below the lines = discoveredBelow the lines = discovered

1 fb-1, 14 TeV1 fb-1, 14 TeV

Systematics include BGdetermination


Measuring masses

• Large literature exists • Practical methods will be put to the test

• Large literature exists • Practical methods will be put to the test

SUS-08-001• l+l- : pT > 10 GeV, |η|<2.4• 3 jets |η|<3 ET>120,80,30 GeV• pT

miss > 200 GeV

• l+l- : pT > 10 GeV, |η|<2.4• 3 jets |η|<3 ET>120,80,30 GeV• pT

miss > 200 GeV

mll = ½ mllmax (1 – cos θ)


Dark matter relic density?

• “Predict” relic density of observed LSPs

• Caveats:– lifetimes beyond

detector?– optimistic case (light

sparticles)– many annihilation

modes need to be checked

• “Predict” relic density of observed LSPs

• Caveats:– lifetimes beyond

detector?– optimistic case (light

sparticles)– many annihilation

modes need to be checked

PoleselloTovey

Drees, Kim, Nojiri hep-ph/0007202Polesello, Tovey hep-ph/0403047 (cMSSM)Nojiri, Polesello, Tovey hep-ph/0512204 (MSSM)Moulin et al. arXiv:0712.3151 (Focus point)

Drees, Kim, Nojiri hep-ph/0007202Polesello, Tovey hep-ph/0403047 (cMSSM)Nojiri, Polesello, Tovey hep-ph/0512204 (MSSM)Moulin et al. arXiv:0712.3151 (Focus point)

01~

01~ f

f


ATLASCERN-OPEN-2008-020arXiv:0901.0512

To find out more…

New results will appear at:• https://twiki.cern.ch/twiki/bin/view/CMS/PhysicsResults• https://twiki.cern.ch/twiki/bin/view/Atlas/AtlasResults

Results for EPS and summer conferences in progress

New results will appear at:• https://twiki.cern.ch/twiki/bin/view/CMS/PhysicsResults• https://twiki.cern.ch/twiki/bin/view/Atlas/AtlasResults

Results for EPS and summer conferences in progress

CMSCERN-LHCC-2006-021J.Phys.G34:995-1579,2007


Conclusions


Extras


Importance of detailed detector understanding

• Simulation shows events with large fake missing energy

• Vital to remove these in missing energy tails

• Large effort in physics commissioning

• Simulation shows events with large fake missing energy

• Vital to remove these in missing energy tails

• Large effort in physics commissioning

Lesson from the TevatronEt(miss)


Spin measurements…Neutralino spin from angles in decay chains

l+~

θq q

_

l-~

Slepton spin from angles in Drell-Yan production

1Alan Barr PASCOS 09 PASCOS 2009 DESY 9 July 2009 …AT THE LHC DARK MATTER … Alan Barr University...

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