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Unified Search for Associated Production of Chargino-Neutralino using Leptons
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We present a search for the associated production of chargino and neutralino supersymmetric
particles using data collected by the CDF II experiment at the Tevatron. We analyze events
with three charged leptons and momentum imbalance, in five exclusive channels. We observe no
excess over standard model expectation. We present upper limits on the production cross section
in the mSUGRA model.
Blessed Plots and Tables
(Click on images for Full Size)
Jump to Final Tables, Result Plots, Final Selections,
Event Displays, Dilepton control regions, Trilepton control regions
Definitions of Exclusive Channels
Table shows the definitions of the exclusive channels.
`Tight' refers to a restrictive selection of lepton to keep high purity,
`Loose' is with some requirements relaxed to keep high acceptance.
Final Tables
Table shows the final expected signal and background events along
with the observed candidate events in the five channels. Signal point considered here is mSUGRA point
with following parameters -- m0=60, m½=190, tan(beta)=3, A0=0, sign(mu)>0
Table shows the list of systematic uncertainties in percentage
broken down by channels. The systematic uncertainties are
ID : Lepton identification Trig : Trigger efficiency
JES : Jet energy scale X-sec : Process cross-section, NLO corrections to X-sec
PDF : Parton distribution functions ISR/FSR: Initial/Final State Radiation
Conv: Photon conversion removal
ITR(nom) : Isolated Track Rate with nominal parametrization
ITR(alt) : Isolated Track Rate with alternate parametrization
Fake: Misidentification of hadrons as leptons.
Table shows some properties of the candidate events broken down by channels.
FINAL RESULT PLOTS for mSUGRA
Branching Ratio (Chargino/Neutralino to 3 Leptons)
EPS The plot shows the branching ratio of chargino-neutralino to 3 leptons.
In the region with m(Neutralino)<m(sleptonR), the neutralino(chargino) decay via a virtual Z(W)
or virtual sleptons. In the region with m(Neutralino)>m(sleptonR), the neutralino/chargino can
in addition also decay through intermediate slepton states, which enhances the trilepton branching
ratio. In the region with m(sneutrino)<m(Neutralino), the decay of the neutralino to sneutrino+neutrino
reduces the trilepton branching ratio.
Exclusion Region in mSUGRA
EPS The plot shows the excluded region in mSUGRA m0-m½ space for tan(β)=3, A0=0, μ>0
The exclusion plot has two regions :
1) m(stau1)>m(Neutralino) - The 3-body decays of neutralino/chargino are dominant here.
2) m(stau1)<m(Neutralino) - The 2-body decays of neutralino/chargino through intermediate
slepton states are dominant here.
To the immediate left of the line indicating m(stau1)=m(Neutralino), the mass difference between
the neutralino and the sleptons is small. The neutralino decay to slepton + lepton leads to a
lepton with low pT, below the thresholds of this analysis. Hence this leads to a drop in signal
acceptance and we are unable to exclude this region.
EPS Same plot as above in color.
EPS The plot shows the excluded region in mSUGRA m0-m½ space for tan(β)=3, A0=0, μ>0
overlaid on the theory cross section times branching ratio (σ∗BR).
Observed Limits in mSUGRA
EPS The plot shows the observed experimental 95% CL limits in mSUGRA m0-m½ space
for tan(β)=3, A0=0, μ>0. The different regions are as described for the branching ratio plot above.
EPS Same plot as above without the different regions indicated.
Observed σ∗BR Limits in mSUGRA
EPS Plot shows the final limit for the
mSUGRA model with parameters indicated on the plot (with m0=60 GeV/c²).
m½ is varied to get the chargino mass along X-axis.
The red curve shows the theory cross section (PROSPINO 2.0). The dashed and solid
black lines show the expected and observed limits respectively. We exclude charginos
with Mass < 145.4 GeV/c².
The uncertainty on the theory cross section is folded into the limit calculation for expected
and observed limits. Additional information about the limit.
EPS Plot shows the final limit for the
mSUGRA model with parameters indicated on the plot (with m0=100 GeV/c²).
m½ is varied to get the chargino mass along X-axis.
The red curve shows the theory cross section (PROSPINO 2.0). The dashed and solid
black lines show the expected and observed limits respectively.
The line indicating m(stau1)=m(Neutralino) is shown. As we move to the right of
this line, the small mass difference between Neutralino and sleptons leads
to a soft lepton, and thus reduced acceptance. Hence the limits worsen. When
the soft lepton is above thresholds for our analysis the limits improve
once again.
We exclude charginos with Mass < 127.0 GeV/c².
FINAL SELECTIONS
We show distributions of final selection variables after all other selections except the one being plotted
are made. We also indicate the value of the cut we make by an arrow on the plot.
Selection: 3tight
Plot shows the missing energy, we keep events with missing transverse energy > 20 GeV.
Plot shows the number of jets (jet ET>15 GeV), we reject events with more than one jet.
Plot shows the highest invariant mass of opposite-charge lepton pairs.
We reject events if 76<Mass<106 GeV/c²
Selection: 2tight,1Track
Plot shows the missing energy, we keep events with missing transverse energy > 20 GeV.
Plot shows the number of jets (jet ET>15 GeV), we reject events with more than one jet.
Plot shows the highest invariant mass of opposite-charge lepton pairs.
We reject events if 76<Mass<106 GeV/c²
Plot shows the azimuthal separation between opposite-sign lepton pairs.
We keep events with DeltaPhi < 2.8 radians.
Selection: 1tight,1loose,1Track
Plot shows the missing energy, we keep events with missing transverse energy > 20 GeV.
Plot shows the azimuthal separation between opposite-sign lepton pairs.
We keep events with DeltaPhi < 2.8 radians.
EVENT DISPLAYS
Event 1 : Three tight electrons: ET = 24, 17, 5.8 GeV - COT, Lego, CAL3D
Event 2 : Two tight muons, One Track: PT = 34, 6.2, 9.2 GeV - COT, Lego, CAL3D
Page 2 for control regions plots.
Sourabh Dube
Last modified: Wed Jun 4 14:11:15 CDT 2008
