Cambridge ATLAS Standard Model Group

Tree-level diboson production diagrams
Gluon-fusion diboson production diagrams

Richard Batley, Will Buttinger, John Chapman, Steven Kaneti, Pat Ward

Introduction

Observations of p-p collisions at the LHC will test the Standard Model at the highest energies yet achieved on Earth (14 TeV). Precision measurements of Standard Model processes will be vital at ATLAS, both to test the theory and to understand possible backgrounds to new physics.

Our Work

The Cambrige ATLAS standard model group is currently interested in diboson events.

The top three diagrams on the right are the Standard Model tree-level diboson production diagrams, where V, V1, V2 = (W, Z, γ).
The s-channel diagram contains the trilinear gauge boson vertex:

  • Only WWg and WWZ allowed in the SM
  • Measuring Anomalous Triple Gauge Couplings (TGC) probes new physics.

In order to investigate possible Anomalous Triple Gauge Couplings, we are investigating events in which two Z-bosons are produced. We will attempt to use these events to set limits on γZZ and ZZZ couplings, which are zero in the standard model.

The Next-to-Leading Order (NLO) cross-section for ZZ production at the LHC is calculated to be 15 pb. However, this does not include the contribution from the process of gluon-fusion, which can also produce two Z-bosons. Gluon-fusion is shown in the lower two diagrams on the right. Although there is no tree-level contribution for this process it makes a significant O(15%) contribution to the total ZZ production cross-section. In order to set limits on any Anomalous Triple Gauge Couplings these the effect of these diagrams must be taken into account in any predictions.

Further Information