Abstract:  We present a search for chargino-neutralino production at 312 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 no events, while we expected 0.1 SM events. An upper limit on the production of chargino-neutralino will be set.

CDF public note 8273

Analysis strategy:  Study the SM backgrounds and CDF data in well defined control regions.  Remain statistically unbiased at the signal region, defined as high MET, with the exclusion of the Z mass region (76 to 106 GeV), with or without upper jet-multiplicity cut.

SUSY signals:  Two points are investigated: 

The Anadi Point (SIG1)
m0=100, m1/2=180, A0=0, tanβ=5, μ > 0
σ*BR = 0.642 * 0.22 pb (Prospino)

The D0 point (SIG2)
m0=  74, m1/2=168, A0=0, tanβ=3, μ > 0
σ*BR = 1.023 * 0.5 pb (Prospino)

Luminosity: 312 pb-1.

Triggers: Low pT dimuon triggers.

Dimuon selection:  Require CMUP or CMX 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.

Trilepton selection: Require a third CMUP or a CMX muon passing the standard muon ID cuts , or a CEM 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.

Jet counting: Cone size of 0.4, minimum level-5-corrected energy of 20 GeV, emf<0.9

Heavy Flavor Background estimation:  Create a HF-rich data sample by reversing the impact parameter cut for at least one of the two leading muons.  Fit the DY+HF dimuon mass to the data (DY is absolutely normalized using the luminosity) for opposite-sign and same-sign muons separately.  Use the results of the fits 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.

Control Regions investigated: They are parts of the mass vs. met phase space, for low and high jet multiplicities, defined here.

Control Regions yields: yields and Observed/Expected (data statistics included)

Systematics study: systematics (breakdown of systematics for background/signal dileptons/trileptons and all control regions !)

Control Regions Plots:

CON_Z
CON_UNM
CON_E
CON_F
CON_G
CON_H
CON_I
CON_J
SIG_A
SIG_A2