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Prof Chamkaur Ghag
Professor of Physics
Dept of Physics & Astronomy
Faculty of Maths & Physical Sciences
- Joined UCL
- 1st Jul 2012
Research summary
Precise cosmological measurements coupled with astronomical evidence tell us we live in a universe made up of contributions of 68% from ‘Dark Energy’, responsible for the accelerating expansion of the Universe, 5% baryonic ‘normal’ matter, and the remaining 27% from a ‘Dark Matter’ component. However, the nature of the dark elements remain unknown. My research focus is the experimental search for Dark Matter. Thermal relics left over from the Big Bang make compelling candidates for Dark Matter, with Weakly Interacting Massive Particles (WIMPs) a favoured solution, present today as the glue holding galaxies together. If these WIMPs were to collide with an atom in a detector, the energy of the recoiling nucleus could be recorded to detect the collision. However, the energy would be tiny. Moreover, this is expected to be an extremely rare process. Experimental searches must then operate detectors with very low energy thresholds, and very low background from regular radioactivity that might mask the faint Dark Matter signal. This means constructing some of the most sensitive and radioactively clean detectors in the world, and operating them deep underground to shield them from cosmic radiation.
I work on the leading experiments currently operating, and conduct R&D for the detectors of the future. I am a member of the LUX experiment (UK P.I.), using xenon in a two-phase time projection chamber, a technique pioneered by ZEPLIN and XENON experimental programmes that I worked in previously. Today, LUX is the world's most sensitive Dark Matter detector, located deep underground at the Sanford Underground Research Facility (SURF), S. Dakota, USA.
I am also a founding member and current international Spokesperson of LZ, a second generation experiment based on the same xenon technology, that became the world-leader in the field in 2022 and is now exploring unexplored parameter space towards a first discovery. I led several areas in these experiments, including pulse identification and event classification, data analysis techniques for signal-like event selection and background rejection, Monte Carlo simulations to calculate background expectations, and radio-assays for radio-pure construction - crucial in ensuring experimental sensitivity to Dark Matter signals.
My development of low-radioactivity techniques to meet the challenges in building and operating such cutting-edge detectors includes establishing trace radio-contaminant measurement facilities employing high purity germanium detectors at the Boulby Underground Laboratory, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) at UCL, and a radon emanation assay facility at the Rutherford Appleton Laboratory (RAL). Each of these facilities delivers world-class sensitivity and are being continuously improved to enable current and future rare event searches. These facilities also afford valuable opportunities for knowledge exchange and development with commercial and industrial partners towards realisation of socioeconomic impact.
Teaching summary
I am presently the organiser and lecturer for the 2nd year undergraduate ‘Environmental Physics’ (PHAS 0027) course, teaching topics that include the atmosphere, fluid dynamics, radiation, winds, climate modelling, global warming and energy. Given the reality of climate change this is an important course where many students are exposed for the first time to the details of the environment and the physical mechanisms behind atmospheric phenomena. I have taught the course since 2015, and have witnessed many of the students seek to deepen their learning through research, as well as engaging in environmental activities within both scientific and social spheres.
Since 2013, I have also organised and taught the 1st year undergraduate ‘Effective Communications’ (PHAS 0017) lectures, teaching students science communication, outreach and public engagement skills. In recent years students from this course have independently applied for and won grants and awards to develop teaching tools and deliver outreach events to the general public.
As part of my own commitment to public engagement and delivering effective science communication, I have taken part in many tens of outreach events since joining UCL. These range from workshops and science fairs, to media appearances through radio, newspaper and magazine features, as well as interviews and appearances in major television programmes, including 'Sky at Night' and the BBC's 'Light & Dark' series.
Finally, I supervise PhD students conducting Dark Matter research within my team (3 since 2012), act as secondary supervisor for other PhD students within the High Energy Group (a further 3 since 2012), and each year supervise several 4th year undergraduate MSci students that undertake Dark Matter research for their final year project (PHAS M201).
Education
- Institute of Education
- Other Postgraduate qualification (including professional), Postgraduate Certificate in Learning and Teaching in Higher Education | 2014
- University of Edinburgh
- Doctorate, Doctor of Philosophy | 2007
- University of London
- Other higher degree, Master of Natural Science | 2003
Biography
I graduated from Queen Mary University of London with an MSci in Physics in 2003 before moving to the University of Edinburgh to begin a PhD. My research focussed on direct Dark Matter searches and developing low background instruments capable of recording extremely rare and faint signals from particle interactions. In particular, I worked on directional Time Projection Chambers (TPC) with gaseous targets and the construction and exploitation of the DRIFT-II Dark Matter experiment at Boulby Mine.
Following the completion of my PhD in 2006 I remained in Edinburgh but moved to the ZEPLIN programme, building TPCs with dual-phase xenon targets. The ZEPLIN programme pioneered this technology, with ZEPLIN-II the first to search for Dark Matter. In 2011, after completion of the ZEPLIN-III experiment where I had led areas of analyses, Monte Carlo simulations, and delivery of the veto system for which I was awarded the Institute of Physics Astroparticle Physics Group's Early Career Researcher Award, I moved to UCLA. There I joined the XENON100 experiment based at Gran Sasso, Italy, working on calibrations, analyses and simulations. XENON100, also a xenon TPC, became the world’s most sensitive experiment, setting the most stringent constraints on Dark Matter interactions. I continued research in low radioactivity techniques and technologies there, developing novel ultra-low background photosensors, performing R&D for the XENON1T experiment, and argon-based TPCs for the DarkSide experiment, also based at Gran Sasso.
In 2012 I joined the High Energy Physics group at UCL to initiate direct Dark Matter research and noble gas TPC R&D. I joined the xenon TPC based LUX Dark Matter experiment, operated at SURF, S. Dakota, and led one of the primary analysis Working Groups to identify and characterise potential Dark Matter signals. LUX overtook XENON100 as the world-leading experiment in 2013 and has remained at the forefront of Dark Matter searches since, with a series of results of unprecedented sensitivity. I am the UK’s Principal Investigator for LUX.
I am one of the founding members and presently international Spokesperson of the LUX-ZEPLIN (LZ) Experiment that brings together the LUX and ZEPLIN programmes to deliver the most ambitious direct Dark Matter experiment yet. Following 10 years of construction, LZ released first results in 2022 from a short engineering run to demonstrate operation as designed whilst also establishing LZ as the most sensitive experiment in the search for galactic dark matter. LZ now enters completely unexplored parameter space in search of a first detection of dark matter. I led the crucial Backgrounds and Screening Work Package that ensures the experiment meets its low-background construction requirements, and delivers the high-precision Background Model against which any potential signal will be evaluated. Low-background construction is achieved through the world-class infrastructure I have developed in the UK.
I am also a member of the XLZD Consortium, serving on its Steering Group, to construct a global Xenon-based experiment that would definitively test the most promising dark matter models and prove exciting new physics inaccessible anywhere else.
I previously held roles including Chair of the Dark Matter UK (DMUK) Consortium; Chair of the STFC’s Particle Astrophysics Advisory Panel (PAAP); STFC Boulby Science Advisory Group and SNOLab Experiment Advisory Committee member.
