Trilepton search for
Chargino-Neutralino Production at CDF Inclusive
low-pT dimuon+lepton analysis with 1 fb-1
Gold, V. Rekovic, J. Strologas
University of New Mexico
Abstract: We present a search for chargino-neutralino production at 976 pb-1, using
low-pT dimuon triggers. We investigate the trilepton signature mu+mu+l,
where l can be an electron or a muon. In this analysis
we extend the search to transverse momenta as low as 5 GeV, for all leptons.
This inclusive low-pT channel
increases our reach and presents new challenges, due to the presence of heavy-flavor
background at low transverse momenta, a background that is estimated using data. We investigate 19 dilepton and trilepton
control regions, and we note good agreement between observation and
Standard Model (SM) predictions. At the same time, we remained statistically unbiased at the
signal region, by not looking at the data there, until the very end of the analysis. Upon examining the data yield in the signal region,
we observed one very interesting trimuon event, while we expected 0.4 +/- 0.1 SM events. An upper limit on the production of chargino-neutralino will be set.
strategy: Study the SM backgrounds and CDF data in well
defined control regions. Remain statistically unbiased at the signal
The D0 point (SIG2)
m0= 74, m1/2=168, A0=0, tanβ=3, μ > 0
σ*BR = 1.023 * 0.5 pb (Prospino)
Low pT dimuon triggers (two muons with pT>4 GeV).
selection: Require central (|eta|<1) muons passing the standard muon
ID cuts and having transverse energy of at least 5 GeV. In
addition, we require minimum dimuon mass of 10.5 GeV (exclusion of Y),
3-d deltaPhi less that 178,
and DeltaR between the muons more than 0.4.
selection: Require a third central (|eta|<1) muon passing the standard muon
ID cuts , or a central electron passing the standard electron
ID cuts. A minimum pT of 5 GeV for the third lepton and
additionally ET>5 GeV, if it is an electron are required. The
third lepton is also DeltaR>0.4 away from the two leading muons.
Cone size of 0.4, minimum level-5-corrected energy of 20 GeV, emf<0.9
Signal Region: Require three leptons, MET>15 GeV, dimuon mass greater than 15 GeV,
with the exclusion of the Z mass region (76 to 106 GeV), and no more than one jet.
backgrounds: Drell-Yan (DY), diboson (WW,WZ,ZZ), boson+parton (W+q, W+c, W+b) and
top-antitop backgrounds are estimated with Monte Carlo.
Fakes (jets faking electrons and tracks faking muons) are estimated with the application
of a fake rate on jets and tracks in real data.
Flavor Background estimation: A HF-rich data sample was created
by reversing the impact parameter cut for at least one of the two
leading muons. We fit the DY+HF dimuon mass to the data (DY is
absolutely normalized using the luminosity) for opposite-sign and same-sign
muons separately. The results of the fits are used to weight the
HF-rich data sample and treat it as HF, with a dimuon upper mass
cut at 35 GeV. The method gives good agreement in yields and shape of the HF in our control regions,
as can be seen here.
Regions investigated: They are parts of the mass vs. met phase space,
for low and high jet multiplicities, defined here.
Regions yields: yields
for all control and signal regions for dimuons and trileptons. The overview of the control and signal
regions can be found here.