CDF Logo W±Z0 Anomalous Triple Gauge Couplings in 1.9 fb-1 of ppbar Collisions at √s=1.96 TeV CDF Logo



The goal of this study is to form limits for anomalous triple gauge couplings on the WWZ vertex. This analysis is an extension of the update of WZ cross section measurement using 1.9 fb^-1 of integrated luminosity. The W±Z0 final state used will be 3 e,&mu leptons and missing tranverse energy (MET) from the unobserved neutrino in lepton decay of the W± boson. At tree level, the W±Z0 final state has the s-channel (left) and t-channel (right) contributions shown in these diagrams:

The s-channel diagram provides sensitivity to the WWZ vertex coupling. The W±Z0 final state is unique among the triple gauge coupling (TGC) final states, providing access to this coupling separately from the WW&gamma coupling. The analysis of triple gauge couplings in WZ production is based on analysing the Z pT distribution in the observed 25 events in 1.9fb-1 in the cross section times branching fraction measurement of WZ->lllnu described in CDF8539 and PRL 98, 161801. We consider the anomalous triple gauge couplings lambda, delta g, delta kappa as defined in PRL D60,113006 and Nucl. Phys. B282, 253 and implemented in MCFM. In the Standard Model all three of these couplings are zero. Additionally the values delta kappa = delta g = -1 turns off the WWZ vertex leaving only the t-channel production and a cross section that violates unitarity. To avoid this unitarity violation the WWZ vertex is modified by a form factor that implements a cut-off by multiplying the coupling with 1/(1+shat/Lambda^2)^2. We calculate the limits for two values of Lambda = 1.5TeV and 2.0TeV.

Summary of Results

Previously Published W±Z0 Search Analysis

Analysis Methods

The Z-pT distribution measured for the observed 25 events is fitted for each of the paramaters: lambda, delta g, delta kappa. This is done individually as well as two dimensional pairs. The Z-pT distribution is used since it is sensitive to these couplings and it can be measured experimentally.

In order to avoid CDF full simulation for every possible coupling it was shown that the efficiency at a given Z-pT is the same for any given coupling. This was investigated using leading order MCFM interfaced to Pythia followed by full realistic Monte Carlo detector simulation using cdfSim and standard reconstruction. The resulting efficiency curve is then applied to MCFM next to leading order matrix element simulations of a given coupling combination to arrive at an expected observed Z-pT distribution for each combination of coupling values.

A -2log(Likelihood) is then formed for a binned distribution in data to come from an expected Z pT distribution given any coupling value. Shown below are the various -2log(likelihood) distributions for the 3 couplings (lambda, delta g, delta kappa). The red curve represents the systematically varied -2log(likelihood) while the black curve is without systematics.

-2log(likelihood) distribution for lambda with /\=1.5TeV eps

-2log(likelihood) distribution for delta g with /\=1.5TeV eps

-2log(likelihood) distribution for delta kappa with /\=1.5TeV eps

-2log(likelihood) distribution for lambda with /\=2.0TeV eps

-2log(likelihood) distribution for delta g with /\=2.0TeV eps

-2log(likelihood) distribution for delta kappa with /\=2.0TeV eps

Table of Results for 1-dimensional Limits:
/\=1.5 lambda delta g delta kappa
With Systematics: -0.14 < lambda < 0.15
delta g = delta kappa = 0
-0.14 < delta g < 0.25
lambda = delta kappa = 0
-0.81 < delta kappa < 1.29
delta g = lambda = 0
/\=2.0 lambda delta g delta kappa
With Systematics: -0.13 < lambda < 0.14
delta g = delta kappa = 0
-0.13 < delta g < 0.23
lambda = delta kappa = 0
-0.76 < delta kappa < 1.18
delta g = lambda = 0
Expected Limit: -0.15 < lambda < 0.16
delta g = delta kappa = 0
-0.18 < delta g < 0.28
lambda = delta kappa = 0
-0.68 < delta kappa < 1.00
delta g = lambda = 0

Shown below are the systematically varied and nominal contours (inner curve is statistical only while outer curve is statistical+systematic). Both are at 95% confidence level.

delta g vs lambda 2-dimensional contour /\=2.0TeV central value=(0.07,0.01) eps

delta g vs delta kappa 2-dimensional contour /\=2.0TeV central value=(-0.04,0.05) eps

delta kappa vs lambda 2-dimensional contour /\=2.0TeV central value=(0.15,-0.01) eps

Rami Vanguri