Tag Archives: Physics

Test Beams

The last ten days or so I’ve spent at CERN testing new designs of pixel detectors for the ATLAS experiment. Since it was the IOP’s #iamaphysicist event on the same day we were setting up, I tweeted out the following picture.

To measure our pixel detectors, we need a beam of particles from a particle accelerator. Fortunately at CERN, we have many to chose from! Just see the diagram of all of the accelerators required to get the protons to the LHC. Our experiment uses the SPS, or Super Proton Synchrotron, the last accelerator in the chain of accelerators which feed the LHC with protons. The protons enter the SPS at 25 GeV and are accelerated up to 450 GeV (note the LHC accelerates to 7500 GeV, or 7.5 TeV, per beam). We then use a target to change the type of particle from a proton to a pion.

The LHC is the last ring (dark grey line) in a complex chain of particle accelerators. The smaller machines are used in a chain to help boost the particles to their final energies and provide beams to a whole set of smaller experiments, which also aim to uncover the mysteries of the Universe.

Continue reading Test Beams

An average day

I have a new flatmate now who has a keen interest in science. The other day when I came home he asked (in French) “What did you do today?”. It’s a simple question. Although it doesn’t always have a short answer as I also knew that he also wanted to understand, what do I do on a day-to-day basis as a scientist? This question is the inspiration of today’s post, which is a diary of my day.


Last night I was invited to the wine and cheese social event at a workshop taking place at my lab, which was a great chance to see a friend and former Manchester colleague who was attending the workshop, and also to meet new people in ATLAS who were outside of my analysis group (ATLAS is ~4000 people, so it’s not unusual that I haven’t met them all!). The conversation developed into some very interesting debates and I ended up staying later than I had planned. Hence this morning’s early start was a difficult one. I have an hour’s commute to get into work so on the way I grabbed a pain au chocolate at the train station (as I didn’t have time to eat breakfast at home) and spent the time on the train proof-reading the thesis of a PhD student I work with.


The first meeting of the day started at 8.30am. This was exceptional and was arranged to fit with the schedule of someone in Australia. For them the meeting was at 6.30pm, so it was just about reasonable for both sides. I am one of two contact people for a part of our analysis, which means I keep up-to-date with what everyone is doing and report back to the conveners of our analysis to make sure everything is on track. This is my first leadership position in ATLAS analysis and I learn a lot about how to do the job well every day. It’s useful to have these meetings to get advice and support from my superiors.

The second meeting, starting at 9am, continued on the same topic, but involved everyone from the analysis. We had presentations from studies that had taken place over the last week and discussed the results. It’s a long meeting, as there are many steps of the analysis to go over in detail. Continue reading An average day

Séminaire Poincaré

Last Saturday was the Séminaire Poincaré at l’Institut Henri Poincaré in Paris. There was a whole day of talks on ‘Le Boson H’ which translates to ‘the H[iggs] boson’, although for reasons that may soon become apparent, it was only referred to as the H boson in the talks. Unfortunately because of a flight that evening, I could only make the morning session, but the timing wasn’t too bad as the first talk was the one that I really wanted to see. That morning was one where I truly appreciated living in Paris. I woke up at a reasonable time for a Saturday morning and took a short bus to the institute, which is close to the Pantheon and just south of the Notre Dame cathedral.

Seminaire Poincare poster
Seminaire Poincare poster

The lecture theatre was smaller than I expected, but completely packed when I arrived and it was difficult to find a seat. Not surprising since the first talk was given by Professor François Englert, the Belgian theoretical physicist who shared the Nobel prize for physics in 2013 for: “… the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider”.

Prof. Englert answering questions after his Seminairé Poincaré talk.
Prof. Englert answering questions after his Seminairé Poincaré talk.

The talk was in French, but with the use of the slides and a knowledge of the subject I was able to follow along happily. When the seminar stopped for lunch, I went down to the front to talk to Prof. Englert. I asked if he would sign my copy of the seminar papers, which he was more than happy to do.

Signed copy of the Séminaire Poincaré papers by Prof. Englert.
Signed copy of the Séminaire Poincaré papers by Prof. Englert.

I explained to Prof. Englert that I was a particle physicist working on the ATLAS experiment at CERN. He asked if we’d met before and I told him that although we’d not met directly, we had been present in the same room, when the announcement of the new boson discovered at CERN was made in 2012. He apologised to me for not recognising me, to which I replied that it was a busy and exciting day, plus I was all the way at the back of an extremely packed auditorium, while he had been reserved a space at the front. It was a very nice chat and an honour to meet him. Afterwards I asked if we could have a photograph together.

Photo with Prof. Englert
Photo with Prof. Englert.

Edit: If you look closely at the photo you might be able to see that Prof. Englert was wearing a particle physics tie and, the ultimate physics fashion accessory, a Nobel prize gold pin.

Hunting the Higgs

Cropped version of the Higgs Hunting Conference Poster.
Cropped version of the Higgs Hunting Conference Poster. 

This week I’ve been at the Higgs Hunting workshop in Orsay near Paris, France. This also happens to be my home institute, so there was no travel involved. The conference is three days long and brings together theorists and experimentalists from around the world to discuss current Higgs results, and also to explore what we can expect (or even hope) to find in the future.

The Higgs boson was discovered at CERN in 2012 after a very long search (it was proposed in 1964!) and is the particle produced when the Higgs field interacts with itself. The Higgs field is the process that gives mass to fundamental particles. Most of the studies at CMS and ATLAS of this new boson are moving from discovery (simply finding if there is a particle there) to precision measurements (understanding how it interacts with other particles and measuring various properties). So far what we’ve found out about the Higgs is exactly what we expect from our theory: the Standard Model of Particle Physics. This is very boring for particle physicists as we love to find out that our theories are wrong! It is very important to make these studies to have a more complete picture of how our universe works, plus there are questions, such as what is dark matter, that could be explained by studying the Higgs in greater detail.

The first day of the workshop concluded with Sir Tom Kibble giving a talk on the ‘Prehistory of the Higgs’. Sir Tom is one of six theorists who, in three independent papers in the 1960’s, came up with the theory for the mechanism that gives mass to particles.

The final day of the workshop took place at the Institut des Cordeliers in central Paris with a beautiful courtyard leading to the auditorium (see below). The morning session focused on constraints on the Higgs boson, with the afternoon dedicated to discussions on future colliders.

Courtyard from the final day of the Higgs Hunting Conference
Courtyard from the final day of the Higgs Hunting Conference

It was a really interesting conference and, since I’m based at LAL, I’m already looking forward to going next year!

Graduation Day!

It’s been roughly nine months since I successfully defended my PhD thesis, and since then I’ve moved on to a new job, so I didn’t expect graduation day to be a big deal. I would put on the colourful robes, walk onto the stage to shake someone’s hand and collect my certificate – job done – but the day turned out to be a wonderful celebration of four great years of physics research with Manchester!

The year I started my PhD in the Particle Physics group in Manchester was a bumper year for graduate students. If I remember correctly, including the accelerator students, there were 13 of us starting at the same time. Adding in the students from the year below who have managed to complete things a little earlier and it meant that Wednesday was also a bumper day for graduations. At Manchester, there are ceremonies throughout two weeks which are generally split into subjects (especially if the subjects are large enough to fill the hall), so our graduation ceremony was only for the physics department. During this part of the ceremony I was reminded of how much outreach work was still required in my subject area; the students graduating at the ceremony were predominantly male and white. But, at least the post-grads are not a bad bunch!

PhD graduates in Physics, University of Manchester, 2014. Photo credit E.H.Maclean.
PhD graduates in Physics, University of Manchester, 2014. Photo credit E.H.Maclean.

The whole week was a time for celebration for my family as only the day before my older sister graduated from the University of Warwick with a PhD in Plant Sciences! Having the same first initial, we’d spent all of our lives getting confused by post addressed to Miss C. Nellist, but with us both becoming Dr Nellist, nothing changes – at least we’re in different fields!

Higgs Boson and Beyond

In my last post, I wrote about the second year anniversary of the Higgs boson discovery, so it was very timely that the weekend directly afterwards I spent at the Royal Society‘s Summer Science Exhibition, talking to the public about the Higgs boson and where it could lead.

The Higgs Boson and Beyond logo.
The Higgs Boson and Beyond logo.

The exhibit was a partnership of many UK universities and they all sent researchers to take shifts on the stall during the event. I went on behalf of the University of Manchester. Here is a lovely video about the Higgs discovery, which was made for the exhibit:

High-energy physics aims to understand how nature works at a fundamental level described by elementary particles. Our current theory, the Standard Model of Particle Physics, is remarkably successful. Find out what the Higgs boson can tell us about new physics beyond the Standard Model.

Since I was working the weekend shifts, the exhibit was very busy both days and I was able to chat with many different people, from very young children to senior citizens, all wanting to know: “what is the Higgs boson?”. There were a lot of activities for them to take part in, such as working out the mass of the Higgs on a tablet computer, to manipulating a beam of electrons in magnetic field and also a competition to find rare Higgs events (and win prizes!). We also had an actual piece of the ATLAS detector (left over from when it was built) and knitted particles to help explain the theory of supersymmetry (or SUSY for short).

It was also fantastic that so many female scientists were available to work on the exhibit – just being visible, especially when there were so many young children visiting the stall, makes a huge difference!

Speaking of children, they (and many adults) were very keen on our Nobel Prizes!

Unfortunately the Royal Society Summer Science event is over for this year, but I highly recommend that you take a look at the booklet (via the website) that was produced for the exhibit. It’s very beautiful and it elegantly explains the whole process of creating a Higgs boson and how we study it, including some very difficult concepts!

Also, if you’d like the Higgs Boson and Beyond stall for a future science festival event, get in contact with them either on Twitter, or through their website: http://the-higgs-boson-and-beyond.org . Alternatively, you can leave a comment below and I will pass the message on.

Happy Higgs Day!

Today is the Higgs boson’s second birthday! It was on this day, the fourth of July, in 2012 that the Higgs was unveiled to the world with the now immortal words of CERN Director General, Rolf Heuer, “I think we have it”.

Before the announcement was made, the atmosphere at CERN was like a rock concert. I, along with many PhD and summer students, spent the previous night waiting outside the auditorium where the talks from two of the LHC experiments, CMS and ATLAS, were to take place. This was to guarantee ourselves a seat to watch history being made.

Waiting in the queue for a seat in the CERN auditorium where the discovery of a Higgs-like boson was about to be announced.
Waiting in the queue for a seat in the CERN auditorium where the discovery of a Higgs-like boson was about to be announced.

It’s a shame that the room wasn’t larger as I know that many people were disappointed not to get a seat, especially if they had worked on the result, but I also think it’s fantastic that so many young people were able to be a part of it, as they will be the ones making the discoveries of the future. It was simultaneously streamed to other auditoriums in CERN, the ICHEP conference in Australia and online for the public to watch.

Joe Incandela from the CMS experiment went first to explain their results. He was followed by ATLAS spokesperson, Fabiola Gianotti. Despite the importance of the results, many people on the internet didn’t like Fabiola’s choice of colours or font for her presentation and “comic sans” even started trending on twitter! It has now become a running joke at CERN, and there was even a video this April that CERN would be switching to the font.

The presentations concluded with a a standing ovation!

Standing ovation for the announcement of a boson consistent with the Higgs! July 2012.
Standing ovation for the announcement by both CMS and ATLAS of a boson consistent with the Higgs! CERN, July 2012.

After the announcement, the audience poured out to join the crowds of people outside. My group headed the short distance to R1, CERN’s premiere restaurant. We sat outside and toasted the discovery with champagne and Pimms provided by Steve Bieniek from Heathrow airport. After a while excitement turned to exhaustion and I lay my head on my arms to nap.  I woke when a reporter from the Times came over: “I could tell you were British” he told us, “as I could see the bottle of Pimms from the other side of the courtyard”. He asked us questions about the announcement and what we thought it meant. It seemed that I was coherent enough, even though I had just woken up, to make it into the article! Although, unfortunately the article is behind a paywall.

The next day the Higgs result was everywhere. It even made it onto the front page of the New York Times! The photograph included about four pixels of my head and I asked my American friends if someone could get a copy for me. It was brilliant how excited the world was about our discovery!

On the day, I had seen Professor Higgs, along with the other major theorists, from a distance. A little over a year later I was able to meet him in person. In 2013, Prof. Higgs was given an honorary degree at the University of Manchester only days after the Nobel prize for physics had been announced. I had just submitted my thesis and so was more than happy to spend the day preparing for his arrival by building a LEGO version of the ATLAS detector.

The team who rebuilt the ATLAS LEGO model at the University of Manchester.
The team who rebuilt the ATLAS LEGO model at the University of Manchester.

Prof. Higgs was modest and fascinating to listen to as he told us the history of the theory. I was very fortunate to be able to get my copy of the New York Times front page article of the boson discovery signed by him!

Professor Higgs just after he had signed my NYT newspaper of the discovery of the Higgs boson at CERN. Photo credit: S.Marsden. (Also, note I'm not a giant, just  on the stairs)
Professor Higgs just after he had signed my NYT newspaper of the discovery of the Higgs boson at CERN. Photo credit: S. Marsden. (Also, note I’m not a giant, just on the stairs)
Signed copy of the front page of the New York Times from the day after the Higgs boson announcement, July 2012.
Signed copy of the front page of the New York Times from the day after the Higgs boson announcement, July 2012. If you look closely (and know where I was sitting) I can just be seen in the back of the auditorium!


If you’re celebrating Higgs-dependance day (as it was dubbed two years ago), you can re-live the excitement of the announcement by watching the recording on the CERN Document Server (CDS): http://cds.cern.ch/record/1459565

If you want to hear more about the Higgs boson (& beyond!), and are near London this week, the Royal Society has a Summer Science Exhibition including a Higgs boson stall. Since Tuesday, scientists from universities all over the UK have been talking to the public about the Higgs boson, it’s discovery two years ago and what we still want to learn. You can follow the Twitter account for the exhibit @HiggsBosonRS14 to see photos and find out more information. If you visit on Saturday or Sunday afternoon, I’ll be on the stall, so please come over and say hello!

Where were you when the Higgs boson discovery was announced? Did you watch online? Let me know in the comments below.