Susan Cartwright

Favourite Thing: Understand something new – either new to me or (better still) genuinely new.



Larbert High School, 1970-76; Glasgow University, 1976-80 (BSc) and 1980-83 (PhD).


Scottish Highers in Biology, Chemistry, English, French, Geography, Mathematics and Physics. BSc (1st class) in Astronomy and Natural Philosophy. PhD in particle physics.

Work History:

1983-86: postdoctoral researcher working for the Rutherford Appleton Laboratory (but based in DESY, Hamburg). 1987-88, postdoctoral researcher for MIT (based in SLAC, California). 1989 onwards, current post.

Current Job:

Senior Lecturer in Physics and Astrophysics, University of Sheffield


University of Sheffield

Me and my work

I am an experimental neutrino physicist – I’m trying to find out whether neutrinos, the least massive and least strongly interacting of all the known particles, might hold the key to understanding why our universe is made up of matter and not antimatter.

Neutrinos are probably the second most common particle in the whole universe, after photons, but they interact so weakly that they are incredibly difficult to detect.  There are three distinct types, associated with their three charged partner, the electron, the muon, and the tau, but one of the great discoveries of late 20th century particle physics was that neutrinos produced as one type sometimes later interact as a different type, a phenomenon known as neutrino oscillations.  The mathematics of this personality change include a factor which distinguishes between matter and antimatter, and it is possible that in the first fraction of a second after the Big Bang this distinction might have led to the situation we see today, where the Universe contains matter but almost no antimatter.  (This never happens in our particle accelerators like the LHC, where every particle created is matched by an antiparticle.)

I work on an experiment called T2K, in Japan.  We use an intense beam of protons to create a nearly pure beam of muon-type neutrinos.  These neutrinos travel 295 km across Japan, where a tiny fraction of them interact in our far detector, Super-Kamiokande, a massive water tank 40 m in diameter by 40 m high (imagine a dozen Olympic swimming pools stacked on top of each other…).  We are interested in the composition of the beam as sampled here: what fraction of our initial muon neutrinos have become tau neutrinos (answer – most of them), and what fraction have become electron neutrinos (not many – but, crucially, not zero)?  Now we are making the measurements again with an anti-neutrino beam, to see if there is a difference.

This experiment is an international collaboration, with colleagues from Japan, the UK, the USA, Canada and Europe – like most of my British colleagues, I work mostly on the near detector, ND280, which is situated only 280 m from where the beam starts and measures the neutrinos before they have had a chance to change type.  This is necessary because our beam is not quite 100% muon neutrinos: a few electron neutrinos are produced as well, so we have to check how many there are initially, and subtract this from the number we find at Super-K, in order to measure the probability that a neutrino that was originally muon-type interacts at Super-K as electron-type.

I’m also working on the proposed successor to T2K, called Hyper-Kamiokande.  While Super-K contains 50000 tons of water, Hyper-K is designed to be 20 times larger, containing A MILLION TONS.  Both Super-K and Hyper-K are located in mine workings under mountains, to shield us from background from cosmic rays, which would otherwise drown out our neutrino signal (we measure the muon or electron produced when a neutrino interacts – cosmic ray particles are already muons, and would look too much like interacting muon neutrinos in Super-K): we’re going to need a very large cavern for Hyper-K!

More about the T2K experiment can be found on our website,  I can be heard talking about neutrinos on Radio 4’s In Our Time with Melvyn Bragg in the In Our Time Archive (we’ve made the Science Top 10!).

Apart from being a neutrino physicist, I graduated with a degree in Physics and Astronomy (or, as they called it then, Astronomy and Natural Philosophy – if it was good enough for Newton, it was good enough for us) at the University of Glasgow, did my PhD at the DESY lab in Hamburg, again with Glasgow, and then worked for the Rutherford Appleton Laboratory and MIT before settling in Sheffield.  I teach neutrino physics, problem solving, introductory cosmology, the history of astronomy and particle astrophysics to undergraduate students, give talks to astronomical societies and schools, like walking and bird-watching, own a lineolated parakeet and a budgie, and am trying to learn Chinese calligraphy.

My Typical Day

My typical day includes lecturing, talking to students, participating in meetings, thinking about neutrinos, and trying to write code that does what I want it to do instead of what I told it to do.

I am a senior lecturer in a busy and expanding physics department, so quite a lot of my typical day is taken up by teaching-related activities like giving lectures, supervising project students, helping students who are having problems, and marking.  I am head of the Study Abroad programme, so sometimes I have an email from a Sheffield student who’s currently on placement in Australia, Canada or the USA, asking for advice about choosing courses.  I also try to spend some time each day talking to my PhD students, Callum and Patrick – though Callum is just about to graduate and disappear off to a research job in Switzerland.

As a member of Hyper-Kamiokande, I am currently working on the prospects for detecting neutrinos from supernovae – exploding massive stars.  In 1987, Super-Kamiokande’s much smaller predecessor, Kamiokande-II, detected a dizen neutrinos from a supernova in the Large Magellanic Cloud, 160000 light-years away.  Hyper-K is about 300 times bigger than Kamiokande-II, and a supernova in our Galaxy would be about 5 times closer than SN 1987A, so we could expect to see something like 100000 neutrinos if a supernova exploded near the centre of our Galaxy.  This would give us an unprecedented window into the actual stellar explosion – unlike the visible light, the neutrinos come from close to the exploding core of the star.  It might also tell us more about the neutrinos themselves.  Although we can’t predict when the next Galactic supernova will happen, it’s fair to say that one is overdue: the last two seen on Earth occurred only 32 years apart, in 1572 and 1604, so it seems a bit unfair that 400 years have passed without another one!  I am corresponding with supernova experts in Germany, who have produced a simulation that tells me how many neutrinos to expect from an exploding star of a given mass, and my colleague Matt and I are working out from that how many to expect in Hyper-K, allowing for their varying energies and for the fact that no experiment detects 100% of the interactions that occur (we miss the ones that have too low an energy, and may accidentally reject ones that happen to look like background).

This is not Hyper-K’s main focus – like T2K, it will be supplied with a beam of neutrinos from the J-PARC accelerator, 295 km away on Japan’s east coast – but because of its huge size it will be an excellent detector for neutrinos from other sources such as the Sun, cosmic rays hitting the Earth’s atmosphere and – yes – supernovae.  It’s only fair to remember that the first evidence for changing neutrino types came from solar and atmospheric neutrinos, not from neutrino beams.

What I'd do with the money

I think I’d hide the solar system in the university campus.

I have a primary school talk in which I use pieces of string to build up a scale model of the solar system in the classroom.  In order to get it to fit in the classroom, I have to shrink the Sun down to 2 mm across – then Neptune is about 6.4 m away.

I think it would be nice to do this on a larger scale across the Sheffield university campus.  I reckon, if I restricted myself to the central campus, I could have a model with a scale of 1 to 10 billion, with would make the Sun about 14 cm across (and the Earth a less than impressive 1.3 mm!).  I envisage getting plaques mounted on the walls of buildings, so that people could go looking for them without having to have access to the lecture theatres or anything.  It might cost more than £500, but if I won I’m sure I could extract a bit more money from the university to make up the difference.

My Interview

How would you describe yourself in 3 words?

Enthusiastic. Knowledgeable. Impatient.

Who is your favourite singer or band?

Loads of people you’ve never heard of, including Martin Simpson, Chris Smither, Steve Tilston.

What's your favourite food?

I don’t really have one – I’ll eat anything (unfortunately for my waistline).

What is the most fun thing you've done?

White-water rafting down the Colorado, when I was based in the US.

What did you want to be after you left school?

Either a particle physicist or an astrophysicist.

Were you ever in trouble at school?

Not really, though when we moved from Lancashire to Scotland when I was 8 I spent about 6 months unable to understand what my teachers were saying (and vice versa).

What was your favourite subject at school?


What's the best thing you've done as a scientist?

Helped to measure the Z width at LEP, and hence discovered that the number of neutrino types is 3. Also, trained a number of young physicists who are probably better than me.

What or who inspired you to become a scientist?

My father, who was an industrial chemist.

If you weren't a scientist, what would you be?

I don’t know. I wanted to do science for as long as I can remember – certainly since I was 7. Maybe a writer?

If you had 3 wishes for yourself what would they be? - be honest!

Be fitter: I eat too much and I don’t exercise enough. Have more ideas. Write a successful book.

Tell us a joke.

The Dean of the Faculty of Science calls the Head of the Department of Experimental Physics into his office. “Why are your people so expensive?” he demands. “Particle accelerators, electron microscopes, clean rooms, helium liquefiers – they’re costing us a fortune! Why can’t you be more like the Department of Theoretical Physics? They only ask for paper, pencils and wastepaper baskets. Or, come to think of it, the Department of Philosophy. They’re even cheaper: they don’t ask for the wastepaper baskets.”

Other stuff

Work photos:


The T2K Collaboration (I am in there somewhere, but lurking invisibly at the back).


J-PARC, where our neutrino beam is made.  Our near detector, ND280, lives in the tiny white buildings at the top, about 1/3 of the way along (between the two pylons).


ND280, the near detector, from above.  To put it on the same line as Super-K, ND280 lives at the bottom of a pit.


Super-Kamiokande, the far detector, being refilled after routine maintenance.  The inflatable dinghy gives some sense of scale!