ww/wz production in electron-neutrino plus dijet final state at cdf aps april meeting
DESCRIPTION
WW/WZ production in electron-neutrino plus dijet final state at CDF APS April Meeting 14-17 April 2007 Jacksonville, FL Anna Sfyrla (CDF Collaboration) University of Geneva, Switzerland. WW/WZ Production. - PowerPoint PPT PresentationTRANSCRIPT
WWeνjj@CDF14 April 2007 APS April Meeting
WW/WZ production in electron-neutrino plus dijet
final state at CDF
APSAPSApril MeetingApril Meeting
14-17 April 2007Jacksonville, FL
Anna Sfyrla(CDF Collaboration)
University of Geneva, Switzerland
WWeνjj@CDF14 April 2007 APS April Meeting
WW/WZ Production
2
WW Production WZ Production
WW/WZ observed so far only in the fully leptonic decay channel, in hadron colliders
Aim of this analysis the observation in the semi-leptonic channel!
• X-Section Measurement• comparison with SM theoretical predictions
•Triple gauge couplings (WWZ/γ)• favorable channel for the triple gauge couplings due to the big branching ratio with respect to the leptonic channel
• Significant background for other interesting processes• ex. H WW
• Channel topologically similar to WH lνbb• techniques developed in this analysis are also applicable there
WWeνjj@CDF14 April 2007 APS April Meeting
The CDF DetectorA general purpose detector at TeV, FNALDesigned with the classic layered structure
Central EM Calorimeter
Central Outer Tracker(Drift Chambers)
Central Inner Tracker(Silicon)
Forward Calorimeter
Muon Chambe
rs
Central Hadronic
Calorimeter
Main objects in this analysis
ElectronsReconstructed
in the Central EM Calorimeter
using tracking information
NeutrinosMissing transverse
energy
JetsReconstructed
in the calorimeter
3
WWeνjj@CDF14 April 2007 APS April Meeting
Event Selection & Backgrounds
σWW*BR = 12.4 pb *0.146
= 1.81 pb
σWZ *BR = 3.96 pb *0.07 =
0.28 pb
σW(e)jj = 320.4 pb
Signal/Background initially very
poor
Signal Definition
Exactly 1 Central ElectronMissing Transverse Energy > 25 GeV
2 or more Jets (PT>15GeV)
Similar Event Topology(Backgrounds)
W eν + jetsW τν + jetsZ ee + jets
QCDt-tbar
4
W/Z
W
eν
jet
jet
WWeνjj@CDF14 April 2007 APS April Meeting
Neural Netwo
rkVAR 6
VAR 4VAR 2
VAR 1
NN OUT0 1
Analysis methodology – 1.
Maximum Significance Gain
[Significance = S/(S+B)]
Dijet Inv. MassDijet Inv. Mass
Dijet Inv. MassDijet Inv. Mass
AFTER NN CUT
INITIALLYVery Poor
S/B
VAR 3VAR 5
5
WWeνjj@CDF14 April 2007 APS April Meeting
Dijet Inv. MassDijet Inv. Mass Dijet Inv. MassDijet Inv. Mass
Signal shape fixed using MCBackground parameterization motivated by MC
Both plugged into a likelihood fitterBackground parameters and signal fraction given by
likelihood fit to data
Dijet Inv. MassDijet Inv. Mass
Overall parameterization
fs*ψ(x) + (1-fs)*φ(x)
-2logQ-2logQ
CLs methodA L Read 2002 J. Phys. G:
Nucl. Part. Phys. 28 2693-2704
used to give the sensitivity of the
analysis and the significance of the measurement
6
Analysis methodology – 2.
S+BHypothesis
B-OnlyHypothesis
WWeνjj@CDF14 April 2007 APS April Meeting7
Dijet invariant mass before NN training
Overall S/(S+B)=3.Signal region S/(S+B)=3.5
Signal
Region
(MC)
Signal Region
WWeνjj@CDF14 April 2007 APS April Meeting8
NN training
JETNEJETNETT
NNNN
Point of Maximum
Significance Gain
Signal BGR
NN Inputangles or angle-related
variables
NN Outputas less correlated to thedijet invariant mass as
possible
WWeνjj@CDF14 April 2007 APS April Meeting9
Gain of
~20%
in
significance!
!
Overall S/(S+B)=3.4Signal region S/(S+B)=4.2
Signal Region
Dijet invariant mass after NN training
Expected significance ~4σ
WWeνjj@CDF14 April 2007 APS April Meeting
Likelihood fit to data
10
P-value: ~0.0065
2.7σ significance
WWeνjj@CDF14 April 2007 APS April Meeting
Measured Numbers
Having used 1.29 fb-1 of data
Measured Number of WW/WZ Events
(mjj[40,160]GeV)266 ± 173 (stat) ± 40 (sys)
Cross section (mjj[40,160]GeV)
σBR = (1.45 ± 0.95 (stat) ± 0.29 (sys)) pbTheoretical
σBR = 2.1 ± 0.2 pb
[BR : (Weν,W/Zjj) ]
95%CL upper limitσBR(Weν,W/Zjj) < 3.4 pb
11
Signal Fraction
Jet Energy Scale
10%
Jet Resolution 10%
Background Shape
3%
Acceptance
Jet Energy Scale
3%
ISR 2%
FSR 10%
W leptonic 3%
Cross section
Total Signal Fraction
15%
Total Acceptance
11%
Luminosity 6%
Total Cross Section
20%
Systematics Summary
WWeνjj@CDF14 April 2007 APS April Meeting
Summary
A search for WW/WZ in the semi-leptonic decay channel
has been presented, using 1.29 fb-1 of the CDF data
So far in the analysis
Central electrons have been used in the lepton selection&
the event selection is optimized with the use of a Neural Network
A 2.7A 2.7σσ significance measurement has been significance measurement has been performedperformed
The measurement is statistically limited at this The measurement is statistically limited at this stagestage
Next Steps in the analysis
There is a lot of potential for improvement!There is a lot of potential for improvement!
Adding muons and forward electrons in the event selection and adding more data,
the event yield can be more than doubled,introducing a large factor in the significance!
Search for Anomalous Gauge Couplings will followSearch for Anomalous Gauge Couplings will follow12
WWeνjj@CDF14 April 2007 APS April Meeting
Backup
WWeνjj@CDF14 April 2007 APS April Meeting
DATA-MC agreement - NN output
Point of Maximum
Significance Gain
14