Oxford Standard Model Physics Group

Understanding the Standard Model (SM) at the LHC is vital, as there are SM backgrounds to all potential discovery channels. The Oxford group have led SM measurements of various combinations of W and Z bosons and hadronic jets, which have improved the modelling of many SM processes and reduced the uncertainties on the parton distribution functions. The measurements also allow the extraction of important electroweak parameters, such as the W boson mass. The W boson mass played a key role in predicting a low-mass Higgs boson, which was discovered in the predicted mass window. With the Higgs boson mass now given as input, new processes (such as those predicted by supersymmetry) can be constrained or indirectly observed with a higher precision measurement of the W boson mass.

Forces in the SM are due to the exchange of gauge bosons. The gauge group structure determines the form of the interaction, predicting interactions among the gauge bosons themselves. Using the electroweak gauge bosons it is possible to study these self-interactions to high precision by measuring processes where multiple bosons are produced, or where a single boson is produced by boson-boson fusion (commonly referred to as vector-boson fusion). These are key processes for Higgs boson measurements, and the high statistics W and Z samples are used by the Oxford group to study them in detail.

Precision SM measurements can be used as a way of performing model-independent searches for new physics in a way that is complementary to the searches for specific models such as SUSY. Very good precision can be achieved using measurements of ratios of cross sections in which many systematic errors cancel. We have studied "Rjets", the cross section ratio for W+jets to Z+jets. We are currently measuring the ratio of cross sections (Z \rightarrow \nu \nu + jets)/(Z \rightarrow l^+l^- + jets). This should give a direct determination of the invisible width of the Z as well as being useful for constraining models of exotic physics.

Event display for a Z\rightarrow \mu^+\mu^- event from ATLAS at 13 TeV

Projects for Students W boson mass measurement
W/Z/photon self-coupling measurements through diboson production and vector-boson fusion
Measurements of W & W+jets & Z & Z+jets
Precision ratio measurements to probe the SM such as the invisible width of the Z
Related Performance Studies Missing transverse energy; electron identification; jet energy scale; trigger development.

Current Students

Student Topic
Francesco Giuli Low-mass Drell-Yan and PDF constraints

Past Students and Theses

Student Thesis Link Year
James Henderson Vector-boson fusion production of W bosons 2015
Craig Sawyer R-Jets (ratio of W + jets to Z + jets) 2015
Ellie Davies W mass measurement 2014
Nick Ryder A direct measurement of the invisible width of the Z with the ATLAS detector 2014
Robert King A First Measurement of Electroweak Production of a W Boson in Association with Two Jets with the ATLAS Detector 2013
Adrian Lewis Inclusive W-Boson cross-section 2014
James Buchanan A measurement of the ratio of the W + 1 jet and Z + 1 jet cross sections using the ATLAS detector at the LHC 2012
Samuel Whitehead A Measurement of the W Boson Charge Asymmetry with the ATLAS Detector 2012
Caterina Doglioni Measurement of the inclusive jet cross section with the ATLAS detector at the Large Hadron Collider 2011
Maria Fiascaris W Boson Production in Association with Hadronic Jets at ATLAS 2010
Kristin Lohwasser The W Charge Asymmetry: Measurement of the Proton Structure with the ATLAS detector 2010
Ellie Dobson A feasibility study into the measurement of W and Z cross sections with the ATLAS detector 2009
Guillaume Kirsch Study of the sensitivity of jet parameter distributions to the strong coupling constant αs in Z0→e+e− events at ATLAS 2009
Florian Heinemann Robust Track Based Alignment of the ATLAS Silicon Detectors and Assessing Parton Distribution Uncertainties in Drell-Yan Processes 2007
Alessandro Tricoli Constraining the proton structure at ATLAS 2006

A. Cooper-Sarkar, C. Hays, C. Issever, J. Tseng, T. Weidberg