An Inclusive Dilepton Analysis (AIDA)

An Inclusive Dilepton Analysis (AIDA)

em data

Authors Duke University	Sebastian Carron (carron@fnal.gov)
	D. Benjamin (dbenjamin@fnal.gov)
	Mircea Coca (cmircea@fnal.gov)
	M. Kruse (mkruse@phy.duke.edu)

Introduction
We present a method and the results from a global fit to the high-Pt dilepton sample. This method has greater statistical power over previous methods, and is potentially interesting for new physics searches (to be explored in the near future). One advantage of this analysis is that no events are lost from event cuts after the requirement of 2 high-P_t leptons (with a caveat for the ee and mumu channels where a missing energy cut is applied to reduce Drell Yan background), and the good separation of the main processes that constitute this sample in a met-N_jet phase space allows one to fit for each standard model (SM) contribution. There are relatively few standard model processes with a final state containing a highly energetic electron and muon, and for the main such processes, other characteristics of the events are very different. Most notably, top quark pair production and W boson pair production with decays in the dilepton channel, ttbar--> W^+b W^- bbar -->e mu nu nubar b bbar and W^+W^- -->e mu nu nubar, and the di-tau decays of Z^0 bosons, Z^0 --> tau^+ tau^- --> e mu nu nu nubar nubar, can all produce final states with high-Pt leptons, but are very distinct from each other when one considers the number of jets, N_{j}, and the missing transverse energy, met, expected in the event. Both t tbar and W^+W^- typically have large met from the final state neutrinos, however, due to the 2 final state b-quarks t tbar has greater jet activity than WW. Conversely, z tau tau events have small met (due to the neutrinos being of lower energy than in t tbar and WW, and typically being back-to-back), and not much jet activity. For both WW and Z tau tau jet activity can sometimes arise from initial state gluon radiation.

Introduction

We present a method and the results from a global fit to the high-Pt dilepton sample. This method has greater statistical power over previous methods, and is potentially interesting for new physics searches (to be explored in the near future).

One advantage of this analysis is that no events are lost from event cuts after the requirement of 2 high-P_t leptons (with a caveat for the ee and mumu channels where a missing energy cut is applied to reduce Drell Yan background), and the good separation of the main processes that constitute this sample in a met-N_jet phase space allows one to fit for each standard model (SM) contribution.

There are relatively few standard model processes with a final state containing a highly energetic electron and muon, and for the main such processes, other characteristics of the events are very different. Most notably, top quark pair production and W boson pair production with decays in the dilepton channel, ttbar--> W^+b W^- bbar -->e mu nu nubar b bbar and W^+W^- -->e mu nu nubar, and the di-tau decays of Z^0 bosons, Z^0 --> tau^+ tau^- --> e mu nu nu nubar nubar, can all produce final states with high-Pt leptons, but are very distinct from each other when one considers the number of jets, N_{j}, and the missing transverse energy, met, expected in the event. Both t tbar and W^+W^- typically have large met from the final state neutrinos, however, due to the 2 final state b-quarks t tbar has greater jet activity than WW. Conversely, z tau tau events have small met (due to the neutrinos being of lower energy than in t tbar and WW, and typically being back-to-back), and not much jet activity. For both WW and Z tau tau jet activity can sometimes arise from initial state gluon radiation.

Public Note
CDF 8146: pdf CDF 8146: ps

Grand Summary Table
(left-click to bring up the EPS version of the image) (right-click to save the GIF version of the image) Expected number of SM signal and background events in ee, em and mm, in 360/pb of CDF II data. Also the observed number of data events is shown.

Systematics Uncertainties
Uncertainties On Signal Acceptance: (left-click to bring up the EPS version of the image) (right-click to save the GIF version of the image)
Uncertainties On Background Acceptance: (left-click to bring up the EPS version of the image) (right-click to save the GIF version of the image)
Shape Uncertainties: (left-click to bring up the EPS version of the image) (right-click to save the GIF version of the image)

Results with 360/pb
Summary of the results

Cross Section	emu	ee+emu+mm
ttbar Cross Section	9.3_-2.6^+3.1 (fit)_-0.2^+0.7 (shape) pb	8.4_-2.1^+2.5(fit)_-0.3^+0.7(shape) pb
WW Cross Section	12.3_-4.4^+5.3(fit)_-0.1^+0.5(shape) pb	16.1^+5.0_-4.3(fit)_-0.2^+0.8(shape) pb
Z tautau Cross Section	292.7_-45.1^+48.9(fit) ± _-2.9^+5.9(shape) pb	-

The fit error refers to the error returned by the maximum likelihood fit; it incorporates the statistical component, the systematic error on acceptance and a 6% error on luminosity. The shape error refers to the effect on the fit due to the template shapes uncertainties.

Kinematic Distributions

(left-click to bring up the EPS version of the image) (right-click to save the GIF version of the image) (right-click to see the GIF version of the image)

Number of Jets ee	Number of Jets em	Number of Jets mm
Missing Energy ee	Missing Energy em	Missing Energy mm
Missing Energy ee 0jets	Missing Energy em 0jets	Missing Energy mm 0jets
Missing Energy ee 1jets	Missing Energy em 1jets	Missing Energy mm 1jets
Missing Energy ee 2jets	Missing Energy em 2jets	Missing Energy mm 2jets
Invariant Mass ee	Invariant Mass em	Invariant Mass mm
Lepton Pt - electrons	Lepton Pt - mouns

Further Details
More information for this analysis can be found at the documentation/Q&A page (restricted to CDF), or by contacting any one of the good people listed at the top of this page.

Mircea Coca

Last modified: Fri Apr 21 12:49:56 CDT 2006