WW e ν jj@CDF 14 April 2007 APS April Meeting WW/WZ production in electron-neutrino plus dijet...

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


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


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


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


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


AFTER NN CUT

INITIALLYVery Poor

S/B

VAR 3VAR 5

5


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


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


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


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


Likelihood fit to data

10

P-value: ~0.0065

2.7σ significance


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


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


Backup


DATA-MC agreement - NN output

Point of Maximum

Significance Gain

14

WW e ν jj@CDF 14 April 2007 APS April Meeting WW/WZ production in electron-neutrino plus dijet...

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