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Search for Supersymmetry Using the Trilepton Signature of Chargino-Neutralino Production

Julian Glatzeron behalf of the CDF collaboration

Table of Contents

1. Introduction2. Analysis3. Results 4. mSUGRA Interpretation

3 of 26J. Glatzer: Search for Chargino-Neutralino Production using Leptons23.11.2008

Chargino Neutralino Production

Decay of Chargino and Neutralino

Signature: 3 leptons and missing ET

Decay of Chargino and Neutralino

Signature: 3 leptons and missing ET

MET > 20 GeVpT

1 > 15…20 GeVpT

2 > 5…10 GeVpT

3 > 5…10 GeV

The CDF DetectorTracker Hadronic Calorimeter Muon SystemElectromagnetic Calorimeter

Isolated tracks as a proxy for tau leptons.

Table of Contents

The AnalysisUnbiased counting experiment

Control Regions: also Dileptons

Find three tight leptonsElse, two tight and one loose lepton

Else, one tight and two loose leptonsElse, two tight leptons and one isolated track

Else, one tight, one loose lepton and one isolated track

Standard Model Background

Control Regions

Missing ET (GeV)

Signal Optimization• Require missing ET

• Remove Z,J/ψ, contribution by cut on dilepton invariant mass

• Require low hadronic activity

Table of Contents

Final Predictions

Signal predictions for benchmark point.

Final Predictions and Results

Display of an Eventin the three tight leptons channel

Jet59 GeV

Table of Contents

Observed Limit on σ∗BR

mSUGRA Exclusion Region

LEP direct limit

Decay dominantlyvia on-shell sleptons

Decay dominantlyvia off-shell W/Z

LEP direct limit

A limit on the chargino mass for m0=60 GeV/c²

We exclude chargino masses below ~145 GeV/c²

LEP direct limit

We exclude chargino masses below ~127 GeV/c²

Summary• We looked for Chargino-

Neutralino production in a trilepton + missing ETsignature with 2.0 fb-1 of data

• Observations are consistent with the standard model

• We have set a direct exclusion in mSugra for chargino/neutralino

Accepted by PRLarXiv: 0808.2446

Thank you

Backup

Display of an Eventin the two tight one track channel

Candidate Events

Results: 3 tight

mSUGRA

5 free parameters:– m0: common scalar mass at

GUT scale– m½: common gaugino mass

at GUT scale– tan(β): Ratio of the Higgs

VEV– A0: common trilinear coupling

at GUT scale– sign(μ): μ is the Higgsino

mass parameter

minimal supergravity grand unification

Our benchmark point: m0 = 60 GeV/c², m½ = 190 GeV/c² , tan(β) = 3, A0 = 0, μ > 0

Five different channels

Find three tight leptons (15,5,5)Else, two tight and one loose lepton (15,5,10)

Else, one tight and two loose leptons (20,8,5/10)Else, two tight leptons and one isolated track (15,5,5)

Else, one tight, one loose lepton and one isolated track (20,8/10,5)

Decreasing purity

are defined as five different, mutually exclusiveexperiments.Why do we do this? Combining channels with different signal over background gives more significant results than one channel with average S/B.

Lepton pT

Standard Model Background

Reducing Backgrounds• Require missing ET

• Remove Z,J/ψ, contribution by cut on dilepton invariant mass

• Require low hadronic activity

Control RegionsDilepton Trilepton

Missing ET (GeV)Missing ET (GeV)

Methods for the Estimation of Backgrounds

Background Estimation:The Isolated Track RateGetting the isolated track rate:• Use data from pT lepton lepton

triggershigh • Select Z ee and Z μμ by

cut on invariant mass of dileptons|Mll -91.2|<15 GeV/c2

• Count the number of events with at least one extra isolated track as a fuction of number of „good“ tracks.

Application of the isolated track rate:

• Select event with 2 leptons and no third isolated track

• Apply isolated track rate as an event weight

The Fake RateA hadron is faking a lepton• Events with more than one fake

are negligible• In „Jet-Triggered“ events the

number of identified leptons per jet (electron) or isolated track (muon) as a function of the transverse energy of the denominator object is measured.

• The fake rate is applied as a weight to fakeable events in data.

• Measured and applied in data

Results

Systematics

mSUGRA Branching Ratio

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