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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
4 of 26J. Glatzer: Search for Chargino-Neutralino Production using Leptons23.11.2008
Decay of Chargino and Neutralino
Signature: 3 leptons and missing ET
5 of 26J. Glatzer: Search for Chargino-Neutralino Production using Leptons23.11.2008
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
6 of 26J. Glatzer: Search for Chargino-Neutralino Production using Leptons23.11.2008
The CDF DetectorTracker Hadronic Calorimeter Muon SystemElectromagnetic Calorimeter
Isolated tracks as a proxy for tau leptons.
Table of Contents
1. Introduction2. Analysis3. Results 4. mSUGRA Interpretation
8 of 26J. Glatzer: Search for Chargino-Neutralino Production using Leptons23.11.2008
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
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Standard Model Background
10 of 26J. Glatzer: Search for Chargino-Neutralino Production using Leptons23.11.2008
Control Regions
Missing ET (GeV)
11 of 26J. Glatzer: Search for Chargino-Neutralino Production using Leptons23.11.2008
Signal Optimization• Require missing ET
• Remove Z,J/ψ, contribution by cut on dilepton invariant mass
• Require low hadronic activity
Table of Contents
1. Introduction2. Analysis3. Results 4. mSUGRA Interpretation
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Final Predictions
Signal predictions for benchmark point.
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Final Predictions and Results
Signal predictions for benchmark point.
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Final Predictions and Results
Signal predictions for benchmark point.
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Display of an Eventin the three tight leptons channel
Jet59 GeV
Table of Contents
1. Introduction2. Analysis3. Results 4. mSUGRA Interpretation
18 of 26J. Glatzer: Search for Chargino-Neutralino Production using Leptons23.11.2008
Observed Limit on σ∗BR
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mSUGRA Exclusion Region
LEP direct limit
Decay dominantlyvia on-shell sleptons
Decay dominantlyvia off-shell W/Z
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mSUGRA Exclusion Region
LEP direct limit
Decay dominantlyvia on-shell sleptons
Decay dominantlyvia off-shell W/Z
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A limit on the chargino mass for m0=60 GeV/c²
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A limit on the chargino mass for m0=60 GeV/c²
We exclude chargino masses below ~145 GeV/c²
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mSUGRA Exclusion Region
LEP direct limit
Decay dominantlyvia on-shell sleptons
Decay dominantlyvia off-shell W/Z
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A limit on the chargino mass for m0=100 GeV/c²
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A limit on the chargino mass for m0=100 GeV/c²
We exclude chargino masses below ~127 GeV/c²
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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
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Display of an Eventin the two tight one track channel
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Candidate Events
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Results: 3 tight
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mSUGRA Exclusion Region
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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
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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
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Standard Model Background
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Reducing Backgrounds• Require missing ET
• Remove Z,J/ψ, contribution by cut on dilepton invariant mass
• Require low hadronic activity
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Control RegionsDilepton Trilepton
Missing ET (GeV)Missing ET (GeV)
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Methods for the Estimation of Backgrounds
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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
40 of 40J. Glatzer: Search for Chargino-Neutralino Production using Leptons23.11.2008
Systematics
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mSUGRA Branching Ratio
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