Professor Mark Thomson

Professor of Experimental Particle Physics
Professorial Fellow of Emmanuel College
Co-spokesperson of the DUNE collaboration

Group: High Energy Physics

Address:
Room 951 Rutherford Building,
Cavendish Laboratory,
JJ Thomson Avenue,
Cambridge CB3 0HE.
Tel: +44 (0)1223 765122
Email: thomson "at" hep.phy.cam.ac.uk


Modern Particle Physics

Modern Particle Physics is a widely-used up-to-date textbook aimed at final year undergraduate students and first year graduate students. It covers all topics ain contemporary particle physics and is accessible to students with a grounding in quantum mechanics and special relativity.

Modern Particle Physics is published by Cambridge University Press. Further details can be found on the CUP web pages.



Biographical Information

2015-2018              Co-spokesperson of the DUNE collaboration
2008-              Professor of Experimental Particle Physics at the Cavendish Laboratory and Professorial Fellow of Emmanuel College, Cambridge
2004-2008 Reader in Experimental Particle Physics at the Cavendish Laboratory and Fellow of Emmanuel College, Cambridge
2000-2004 University Lecturer in Physics at the Cavendish Laboratory and Fellow of Emmanuel College, Cambridge
1996-2000 Staff Research Physicist, CERN, Geneva, Switzerland
1994-1996 CERN Fellow, CERN, Geneva, Switzerland
1992-1994 Research Fellow in the High Energy Physics group, University College London, London.
1988-1991 D.Phil. in Experimental Particle Astrophysics in the Department of Nuclear Physics, Oxford
1985-1988 BA Physics at the University of Oxford

Research Summary

My main research interests are neutrino physics, the physics of the electroweak interactions, and the design of detectors at a future colliders. I am co-spokesperson of the DUNE collaboration, which consists of over 1000 scientiests and engineers from over 170 institutions in 31 nations across the globe. The Cambridge neutrino group splits its acivities between MicroBooNE and DUNE and is using advanced particle flow calorimetry techniques to interpret the images from large liquid argon TPC neutrino detector.


DUNE

Overview
DUNE will be the largest particle physics project ever undertaken in the US. It involves firing an intense neutrino beam from Fermilab, near Chicago, to the DUNE far detector in the Sanford Underground Research Facility (SURF) in South Dakota; a distance of 1300 km. The DUNE far detector is conceived as four vast liquid argon time projection chambers (LAr-TPCs), each consisting of an active volume of 10,000 tons of liquid argon. The LAr-TPC technology provides 3D images of the particles produced in neutrino interactions. The experiment aims to discover CP violation in neutrino oscillations, which could explain the observed excess of matter over antimatter in the Universe. It also enables a powerful search for proton decay, which is predicted in Grand Unified theories, and is sensitive to neutrinos from core collapse super-novae. DUNE is a major international collaboration of over 1000 scientists and engineers from aroudn the globe. The installation of the first far detector is module is planned for 2022.

The UK in DUNE
Professor Thomson is the leader of the DUNE-UK project and secured STFC grants amounting to almost £7M support 16 UK institutions through the "development" and "pre-construction" phases (2015-2019). He was the scientific lead in the £65M UK investment in the DUNE construction project that was announced by the UK Science Minister in September 2017. The UK is playing a leading role in DUNE and will contribute to the construction of: the detector readout wire planes; the detector data acquisition system; SRF and cryo-modules for the PIP-II accelerator; and the LBNF neutrino target.

Cambridge and DUNE
Cambridge has been a member of the predecesor LBNE collaboration since the very early days of the experiment concept. In 2014, the collaboration was reformulated into the Long Baseline Neutrino Facility (LBNF) and the Deep Underground Neutrino Experiment (DUNE), with increased international involvement. We are currently working on the reconstruction of the neutrino interactions in the LBNF LAr TPC. The Cambridge DUNE group uses state-of-the-art PandoraPFA reconstruction tools, initially developed for particle flow reconstruction at a future linear collider. The reconstruction of LBNF events is particularly challenging due to the higher energy neutrino beam spectrum that results on complex final states.


The MicroBooNE Experiment

Cambridge joined MicroBooNE in 2013. The MicroBooNE detector is a large 170 ton Liquid Argon (LAr) Time Projection Chamber (TPC) located along the Booster Neutrino Beam (BNB) line The experiment will measure low energy neutrino cross sections and investigate the low energy excess events observed by the MiniBooNE experiment. The detector serves as the necessary next step in a phased program towards the construction of massive kiloton scale LArTPC detectors for the LBNE experiment. The experiment has been operational since August 2017. The Cambridge MicroBooNE group is working on state-of-the art reconstruction software for extracting physics observables from the "photograph-like" images of neutrino interactions in the LAr TPC. This work represents the first end-to-end fully-automated reconstruction of LAr-TPC images and is a central to the anaysis of MicroBooNE data.


Particle Flow Calorimetry

Professor Thomson pioneered the technique of high-granularity Particle Flow Calorimetr, which is a new technique for large-scale particle detectors at future colliders such as the ILC and CLIC. He was the first to demonstrate definitavely that this technique can provide improvements of more than a factor of two in jet energy resolution compared to conventional calorimetry. This development lies at the heart of the design of the detectors for the ILC and CLIC.

This work also formed the basis for the more recent developments in LAr-TPC reocnstruction. This was possible due to the transformation of the intial particle flow software into a fully-fledged pattern recognition framework, the Pandora SDK. As a result the Pandora-based reconstruction techniques are at the forefront of both the development of detectors future electron-positron colliders and the LAr-TPC neutrino programme.


The MINOS Experiment

The MINOS experiment is a second-generation Long Baseline (LBL) neutrino oscillation experiment. A beam of muon neutrinos is produced from protons extracted from the Main Injector at Fermilab (just outside Chicago). These are then detected 735 km away in the main 5400 ton MINOS Far Detector half a mile underground in the Soudan mine. In addition a much smaller (1000 ton) Near Detector, is located 290 m from the decay pipe. If neutrinos have mass then some of the muon neutrinos will oscillate to become tau neutrinos during the journey to the Soudan mine. Neutrino oscillations are investigated by studying and comparing the rates and energy spectra of Charged Current interactions in the MINOS near and far detectors. Beam data taking commenced in March 2005 and ended in 2015. Professor Thomson and the Cambridge MINOS group played a major role in the MINOS research activities including:

  • development of pattern recognition and reconstruction software;
  • the analysis of atmospheric neutrino data;
  • the development and application of a powerful approach to the search for sub-dominant muon to electron neutrino oscillations. The results, along with those from T2K, provided the first evidence for a non-zero value of theta_13;
  • the analysis of charged-current events for muon neutrino disappearance.



The ILC and CLIC

The ILC and CLIC are two possible options for future colliders after the LHC. Both are electron-positron colliders and focus on precision measurements rather than direct probes of the high-energy scale at hadron collider such as the LHC. The International Linear Collider (ILC) would be a lower energy machine, most likely operating in the range 250 - 500 GeV. The Compact Linear Collider (CLIC) is a higher-energy option (350 GeV - 3 TeV). The ILC is currently under discussion for Japan. CLIC provides a possible future option for CERN.

Professor Thomson played a central role in the design and optimisation of the detectors for the ILC and CLIC, focussing on the ILD detector concept for high-granularity particle flow calorimetry. The development of the pandoraPFA software provided, for the first time, a concrete demonstration of the power of particle flow calorimetry in a high-energy electron-positron collider.

Professor Thomson also worked on the physics case for the ILC and, in particular CLIC, focusing on precision measurements of the Higgs Boson couplings to other particles. In a relativelt recent publication he demonstrated that the fully-hadronic Z Boson decays in ZH events could be used to make a model-independent measurement of the cross section. This is signifcant because it argues against the need to operate a Linear Collider at a centre-of-mass energy of 250 GeV in order to measure the invisible width.


The ATLAS Experiment at the LHC

The ATLAS experiment at the Large Hadron Collider (LHC) at CERN is one of the two large experiments at the forefront of the energy frontier of particle physics. One of the main challenges is separating the interesting interactions from the less interesting interactions. Because of the very high event rates the first stage on trigger on on interesting events has to be done in real time in the 25ns between bunch crossings. From 2012-2015 Professor Thomson managed the project to upgrade the first level hardware calorimeter trigger, where the UK is developing a new system for the Phase-1 luminosity upgrade of the LHC.


The OPAL Experiment at LEP

The OPAL experiment ran from 1989-2000. It was designed to test the Standard Model of the electroweak interaction with unprecedented precision.

Professor Thomson's main research activities with the OPAL experiment at CERN, centred on the precision experimental measurements of the properties of the W± and Z bosons responsible for mediating the neutral and charged current weak interactions. He performed a number of important measurments at both LEP 1 (e+e- -> Z0) and LEP 2 (e+e- -> W+W-). Including:the first experimental limits on possible anomalous quartic gauge boson couplings by studying hard photon radiation in WW events; measurments of the WW cross-section and, in particular, the OPAL measurements of the e+e- -> W+W- -> qqlvl cross-section; devoloped of algorithms to identify e+e- -> W+W- -> qqlvl events with high efficiency; leading the OPAL measurements of the W boson mass at and above threshold; measurements of the tau polarization at LEP 1 using the method of Maximum Entropy for the reconstruction of ECAL clusters in the OPAL detector; measurements of the tau-pair production cross section as inputs to the global electroweak fits; and measurements of the luminosity at LEP 1, which was another essential component to the electroweak fits