Tag Archives: Particle physics

COSMO 2013 at Cambridge University

Today was the first day of the COSMO 2013 conference at Cambridge. Walking up the path to the hallowed Department of Applied Mathematics and  Theoretical Physics (DAMTP), I was gripped by my usual fear that I might meet with a frosty reception at the door; “No experimentalists, please!”


The hallowed halls of DAMTP

But it’s not that sort of conference. COSMO 2013 is a very nice mix of cosmology and particle physics, theory and experiment. You can see the conference poster and programme here.

This morning started with two contrasting plenary talks on particle physics; an experimental talk by Lars Sonneschein, and a more general talk ‘From the Higgs boson to Cosmology’ by well-known CERN theoretician John Ellis.

In his talk ‘Recent Results from the LHC’, Professor Sonnenschein gave a brief overview of recent results at the LHC, from current production rates of top anti-top quarks to the famous discovery of the Higgs boson. Much of this probably wasn’t that new to the audience given the number of Higgs talks last year, but it was good to see up-to-date information on the decay modes and coupling constants for the Higgs.The main point was that with more and more accurate measurements, there is still no evidence yet of any physics beyond the Standard Model, whether one was searching for dark matter, microscopic black holes or indeed supersymmetry (SUSY). On the other hand, there were grounds for good cheer for the experimentalists given the projections Lars gave for increased luminosity at the LHC in the next few years.

John Ellis’s talk took a very different tack. He starting by explaining why a light Higgs mass and weak couplings is a good result for supersymmetry (SUSY can stabilize a light Higgs), giving theorists yet another reason to take the theory seriously, despite the ecent narrowing of windows of possibility at the LHC (at least for minimal models). Professor Ellis then made a connection with cosmology, remarking that basic Wess-Zumino SUSY models can be shown to fit very well with many generic models of inflation;in particular, adding supersymmetry to the mix can give models that fit very comfortably within the recent PLANCK results (some fall well within the dark blue region in the famous Planck figure below). A colleague of a certain age commented to me afterwards  that he isn’t quite reconciled  with the way inflation has become the dominant paradigm in today’s cosmology; for my part, I can never get used to today’s discussions of  supersymmetry in both cosmology and particle physics, having grown up thinking of it as an obscure theory practised only by my father and a few colleagues around the world! Science truly evolves…


Prof Ellis wearing his Standard Model t-shirt


Generic SUSY versions of inflation can give models that fall within the most probable region (dark blue)

At question time afterwards, I commented that I was struck by the contrast between the two talks, i.e. the strong motivation for SUSY from theory but the lack of results so far at the LHC, and asked Professor Ellis whether he thought the first evidence for SUSY might indeed come from the cosmic microwave background rather than particle accelerators (I made a mess of the question, nervous for once!). He responded by pointing out that it took 40 years to find the Higgs in particle accelerators, thus we should not be too impatient.  This answer makes a lot of sense to me, I’m a bit dismayed at the way SUSY scepticism has quickly become almost as popular a sport as string theory scepticism. After all, theory is often decades ahead of experiment, particularly in particle physics…

There were two other plenary lectures after coffee, an overview of Dark Matter by Malcolm Fairbairn and a talk on neutrino masses by Silvia Pascoli. They were both excellent talks but there is so much going on I just can’t keep up! Also, Stephen Hawking is sitting three tables away, also working away at a computer – I’m going to tidy myself off to the afternoon sessions before someone mistakes me for a journalist and chases me out of the canteen!

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Filed under CERN, Cosmology (general)

The God particle at Trinity College

On Monday evening, I gave a public lecture on the Higgs boson at Trinity College Dublin. The talk was organised by Astronomy Ireland and I think it was quite a success; 200 tickets were sold and quite a few people had to be turned away.

In the Joly lecture theatre at Trinity College Dublin

How to explain the basics of particle physics to a public audience? As always, I presented the material as a short history of discovery: from the atom to the nucleus,  from protons and neutrons to Gell-mann’s quarks. I also included some theory on the fundamental interactions, right up to the Standard Model,  electro-weak unification and the role of the Higgs field in electro-weak symmetry breaking. Not for the first time, I came away with the impression that the Standard Model isn’t as intimidating for the uninitiated as you might expect. As for physics beyond the Standard Model, the audience seemed to take the hypothesis of grand unification in their stride, and the connection between particle experiments and the early universe struck a chord, as always.

The results  It was a pleasure to present the fantastic results of the ATLAS and CMS teams, first announced at CERN last July. Giving such talks is a lot easier now that the data are publicly available in two beautiful papers on the ArXiv here and here. I gave an overview of the main findings in the context of previous experiments at CERN and at the Tevatron,  and I think the audience got a feel for the historic importance of the result. Certainly, there were plenty of questions afterwards, which continued in the pub afterwards.

The famous bumps ( excess decay events) seen by both ATLAS and CMS at around 125 GeV in the di-photon decay channel

Combined signal (all decay channels) for both ATLAS and CMS

So what about that title? Yes, I did agree to the title ‘The God particle at last’? I am aware that most physicists have a major problem with the moniker; it is sensationalist, inaccurate and incurs a completely gratuitous connection with religion. (Some religious folk consider it blasphemous,  while others misunderstand the term as evidence for their beliefs).

A poster for the talk; naughty

All of this is true, yet I must admit I’ve got to like the nickname; it is catchy and just mysterious enough to cause one to think. I imagine a tired lawyer catching sight of the poster as she walks home after work;  ‘God particle’ might cause a moment of reflection, where ‘Higgs boson’ will not. At least the former expression contains the word ‘particle’, giving the reader some chance to guess the subject. Of course the ‘God’ part is hubris, but is hubris so bad if it gets people thinking about science? Also, I disagree with commentators who insist that the Higgs is ‘no more important than any other particle’. Since all massive particles are thought to interact with the Higgs field, finding the particle associated with that quantum field is of great importance.

So is it found?  CERN Director General Rolf Heuer stated in Dublin, “As far as the layman is concerned with have it. As far as the physicist is concerned, we have to characterize it”. Such characterization has been going on since July. Without question, a new particle of integer spin (boson) and mass 125 +- 0.5 GeV has been discovered. So far, the branching ratios (the ratio of various decay channels to lighter particles) match the prediction of a Standard Model Higgs boson very well. So it looks and smells like a Higgs, and we are all getting used to the idea of the Higgs field as reality rather than hypothesis. (That said, there is still the possibility of spin 1 or 2 for the new particle, but this is not very likely).

All in all, a very enjoyable evening. The slides and poster I used for the talk are available here.  No doubt, some Trinity professors may have been none too pleased to see ‘God particle’ posters in the Hamilton building. Me, I’ve decided I can live with the name if that’s what it takes to get the public excited about particle physics…


Some bloke called Zephyr is upset and accuses me of misleading the public (comments). His point is that I refer to the Higgs as a particle, instead of a quantum field. There is a valid point here; what were once thought of as elementary ‘particles’ of matter are now considered to be manifestations of quantum fields. However, in the business of communicating physics to the public, each physicist must find their own balance between what is accurate and what is comprehensible. My own experience is that people grasp the idea of the Standard Model reasonably well if it’s told as a story of particle discovery (phenomenology). A small amount on quantum theory is ok, but too much soon leaves ‘em bewildered. For this reason, I much prefer books like Particle physics: A Very Brief Introduction by Frank Close to books like Higgs: The Invention and Discovery of a Particle  (Jim Baggot)


Filed under CERN, Particle physics, Public lectures, Uncategorized

O’Raifeartaigh Conference in Munich

I’m in Munich this weekend, at a physics conference in honour of my late father. The 2012 O’Raifeartaigh Conference is taking place in Munich’s Ludwig Maximilians Universität (LMU) and there are speakers here from Harvard, MIT, Stanford, the University of Tokyo, the Niels Bohr Institute (DK), the Eugene Wigner Institute (HN) and the Dublin Institute for Advanced Studies.

It sounds rather grand, but such memorial conferences are a good way for researchers who work in related fields to meet and present their latest work to each other. Many of the speakers worked with Dad at one stage or another and I think he would be very pleased to be remembered in this way. There are also some really sharp young scholars here and he would have liked that too. It’s the third memorial conference in Lochlainn’s memory, see here for the programme and other details.

Munich itself is fantastic – the university is right in the middle of the city and the neighbourhood is full of bookshops, coffee-houses, museums and beer gardens. The teaching term is not yet finished in Germany so there are students everywhere (don’t tell Minister Quinn!). In fact, I have never seen so many bicycles and bookshops in one place. The conference talks are in the University’s Arnold –Sommerfeld Centre for Theoretical Physics and the building has a Museum for Modern Art on one side and a music conservatoire or Musik Hochshule down the block. I could get used to this.

LMU University Munich (Main Entrance)

Lochlainn’s work concerned the use of mathematical symmetry methods to describe the physics of the elementary particles. Throughout his career at the Dublin Institute for Advanced Studies, he was considered a leading expert in the field. He is probably best known for his contributions to a radical theory known as ‘supersymmetry’, a theory that is currently being tested at the Large Hadron Collider at CERN. You can read more on his career by clicking on the tab Lochlainn on the top of the page.

There are some great talks here although some are are far beyond the comprehension of yours truly (an experimentalist). As always, I’m impressed by the style of presentation in theoretical physics; there are no polite powerpoint lectures here, but chalk-and-blackboard sessions with searching questions from the audience every few minutes. ‘‘Does that function even have a ground state?’, a speaker was asked within the first two minutes of his talk. ‘‘Well, it doesn’t in anti-deSitter space, but I hope to convince you that it does in deSitter space”, was the response. Answers to the frequent questions are tackled at the board until everyone in the room is satisfied. No-one gets away with anything here, from the youngest postdoc to the most eminent physicist. I think it’s a style of presentation that helps both lecturer and audience and I wish the humanities would adopt it – my pet hate is listening politely to a philosopher or historian for an hour before one gets to question a statement made in the first three minutes.

I gave a short talk myself on Friday. This was a ‘life-in-science’ presentation where I used pictures of people and places that influenced Lochlainn during his career: from his early work on general relativity with JL Synge  at the Dublin Institute for Advances Studies to his work on quantum field theory with Walter Heitler at the University of Zurich, from his use of group theory to prove his famous no-go theorem at Syracuse University in New York State to his work on the history of gauge theory at L’Institut des Hautes Etudes in Paris. I was worried I might have got some things wrong (e.g. “No, that work was completely incidental!’’), but thankfully it didn’t happen. In fact, I think the audience enjoyed the presentation as many of them had known the people and places mentioned at firsthand. You can find the photos and slides I used here.


The conference is over today so Mum and I took an open bus tour of Munich. I find this a great way to get to know any city and it didn’t disappoint. Munich may not be as large as Berlin or Hamburg, but it is the capital of Bavaria and is an extremely impressive city. I’m amazed by the huge number of parks, wide boulevards and splendid buildings – clearly, it was did not suffer as much as so many other German cities from bombing in the war. This is one of the great privileges of being an academic – you get to see the most interesting places, all in the line of work.

The ‘heroes’ monument on Leopoldstrasse

And finally

On the way back to the hotel, I was intrigued to see a huge banner draped over the main university entrance; the legend’ STRINGS 2012′ is leaving the whole city in no doubt that a major conference on string theory is about to take place here! Such a civilised country..


Filed under Particle physics, Third level, Travel

Hawking, Walton and O’Raifeartaigh

I was surprised and delighted by the photograph below, prominently displayed in this week’s Irish Times magazine. In the accompanying article, journalist Arminta Wallace makes the point that the central figure in the photo is recognizable anywhere in the world, and challenges the reader to name the two Irish scientists flanking him (they are identified later in the piece).

This photo appeared in Saturday’s Irish Times under the caption Science Superstars

The scientist on Hawking’s right is the Irish physicist Ernest Walton, famous for splitting the atomic nucleus in 1932. The Cockroft-Walton experiment was the first successful accelerator experiment (and the first demonstration of E = mc2) and led to a well-deserved Nobel prize. As the prototype of all ‘atom-smashing’ experiments, Walton’s work is extremely relevant to this week’s discovery of the Higgs boson at the Large Hadron Collider (LHC).

The scientist on the left is my late father, Lochlainn O’Raifeartaigh. A senior professor in the School of Theoretical Physics at the Dublin Institute of Advanced Studies (DIAS), Lochlainn was a well known theorist in the field of elementary particle physics. The photo was taken at a conference at DIAS in 1983. I think it’s quite nice – it is not at all staged and one has the impression that the three physicists are enjoying a rare meeting. One sad aspect of the photo is that, even twenty years ago, there is already a marked deterioration in Hawking’s condition. That said, he has outlived the other scientists in the picture…

What would the trio have discussed? What do a leading particle theorist, a cosmologist and a Nobel experimentalist talk about over coffee? My guess is the newly-minted theory of cosmic inflation might have come up. Inflation is a theory that concerns the behaviour of the entire universe in the first fraction of a second, but it borrows heavily from ideas in particle physics. Hence it represents a convergence of cosmology ( the study of the universe at large) with particle physics (the study of the world of the extremely small). Given that the theory had only recently been posited, it’s highly likely that it was discussed by the trio with some excitement. (Of course Walton was an experimentalist but he had a lifelong interest in theory; it is often forgotten that he had a first class degree in mathematics as well as physics and he attended many conferences at the Institute over the years).

Ms Wallace draws a nice connection between the photo and the upcoming Dublin City of Science Festival. There is also a connection with science’s latest triumph, the discovery of a Higgs-like particle. First, Walton’s pioneering accelerator work laid the foundations for today’s experiments at the LHC (see above). Second,  Lochlainn made several important contributions to a theory now known as ‘supersymmetry’.  Supersymmetry is currently being put to the test at the LHC, as experimenters search for the ‘supersymmetric’ particles predicted by the theory. Thus the work of both Irish physicists remains relevant today.

You can read the Irish Times article here and more on Lochlainn’s work here. By coincidence, Lochlainn’s work will be celebrated at an international conference on theoretical physics in Munich next week.


Filed under CERN, Particle physics, Science and society

Discovery of the Higgs vs the discovery of the atom

Most people on the planet will hear sometime today that scientists at CERN, the particle physics laboratory in Switzerland, have announced the discovery of a new particle, almost certainly the Higgs boson. ‘Discovery’ is shorthand for 99% confidence level, so this is a great result, coming from two independent experiments at CERN. But what does it all mean?

Below is a script I used for interviews on tv (RTE 1 Six One News) and radio (RE 1 Drivetime); you can see the tv interview here

Q: How important is the discovery, what does it compare with?

It’s not unexpected, but it’s very important. I think it is quite similar to the discovery of the first experimental evidence for atoms by Jean Perrin in 1908 (following a suggestion by the young Einstein). Scientists had long suspected that matter is composed of tiny entities known of atoms but they had never been observed directly. Perrin demonstrated their existence by showing that the random motion of tiny grains of gum in water could be explained in terms of the collisions of the particles with the atoms of the liquid.

Q:What exactly is a Higgs boson, is it like an atom?

We now know that the atom consists of a minute nucleus, with tiny, sub-atomic particles called electrons orbiting the nucleus. The nucleus itself contains other sub-atomic particles of matter called proton and neutrons, themselves made up of even smaller entities called quarks. The full list of the elementary particles of matter is described by the ‘Standard Model of Particle Physics’, the modern theory of the structure of the atom and the forces that hold it together. The Higgs particle doesn’t live inside the nucleus, it is a ‘messenger particle’ predicted by the Standard Model; while all other particles predicted by the model have been detected in experiments in particle accelerators, the Higgs has remained outstanding until now.

Q: And that’s why it’s so important?

Not only that. The Higgs is also of central importance in our understanding of the atom. According to the Standard Model, particles acquire mass as a result of their interaction with the Higgs – or to be specific, their interaction with a certain type of quantum field named the Higgs field (after theoretician Peter Higgs of Edinburgh University). The Higgs particle is simply the ‘messenger particle’ associated with this field.

Q: Why is it sometimes called the God particle?

Most physicists dislike the name, but it is somewhat apt since the field associated with the Higgs particle is thought to endow all other particles with mass. Another reason is that the particle has become something of a Holy Grail in particle physics because it has proved remarkably hard to find over five decades. The discovery of the Higgs boson is an important confirmation that our view of the fundamental structure of matter is on the right track.

Q: How was the particle observed?

At the LHC, two beams of protons are slammed into each other at extremely high energy. Exotic particles are created out of the energy of collision, just as predicted by Einstein (E = mc2). These unstable bits of matter quickly decay into other particles, including Higgs bosons. The Higgs particles themselves then decay into lighter particles in a number of different ways or ‘decay channels’. These particles are detected at the giant particle detectors attached to the beam at CERN – two independent detectors  (ATLAS and CMS) have detected two different decay channels of the Higgs, hence the excitement.

Q: How definite are the results?

Each group is quoting a sigma level of 5, corresponding to 99% certainty. This certainty reflects that a new particle has been found with mass 125 GeV, consistent with a Higgs. However, further work is required to determine whether the particle has other properties consistent with a Higgs.

Q: What comes after the Higgs?

The Higgs particle closes one chapter, but opens another.This is because the Standard Model is known to be incomplete. The properties of the new particle should give great insights into new physics beyond the Standard Model. For example, evidence of more than one type of Higgs particle would be a strong hint of the existence of a whole new family of particles known as supersymmetric particles. The detection of these particles is an important test for unified field theories, theories that suggest that the four fundamental forces of nature once comprised a single force in the infant universe. Indeed, the next round of experiments should give us many important insights into the very early universe because the high-energy conditions resemble those that existed when our universe was very young.

Q: Does the Higgs have a technological application?

No. However, the technologies developed in particle experiments find important application in society. A good example is the use of accelerators in modern medicine. Another is the world-wide web, a software platform first developed at CERN in order to allow scientists to share collision data. The latest innovation is the GRID, the networking of thousands of computers worldwide in order to facilitate the analysis of huge amounts of data emerging from the LHC. Today’s result is a great triumph for the GRID, it is quite amazing that the data was analyzed so fast.

Q: To wrap up; an exciting discovery?

Huge. Expected, but huge. Compares with the discovery of the atom, or putting a man on the moon. The morale of the story is that scientists are like the Mounties – they always get there in the end.

There is a good summary of today’s result in the Guardian here


Filed under CERN, Particle physics, Science and society

How about Higgs particle instead of Higgs boson?

Like so many of us physicists, Micheal has a problem with the name ‘God particle’. Scientists have a healthy dislike of hubris (not to mention the needless antagonizing of religious-minded folk) and I am inclined to agree with a ‘do-er’, e.g. a researcher from CMS. Happy Higgs day Micheal, you and yours have done us proud!

Yet as someone who spends a lot of time attempting to engage the public’ s interest in science, I think there are several points worth examining here:

1. The name ‘Higgs boson’ isn’t great either, at least when dealing with the public. It is a classic case of over-specialization, as one immediately has to explain what a ‘boson’ is. Surely ‘Higgs particle’ would be better, as the audience immediately gets a pointer to the area of science under discussion, namely the world of the elementary particles (and whoever heard of the electron fermion?)

2. There is also the problem of priority; as every physicist knows, Professor Higgs was not the only theorist involved in the development of what is now known as the Higgs field (and he predicted the field, not the particle, as he often points out). Many theorists played a part in developing the theory, something that will create something of a Nobel headache – the name won’t help!

3, I still think the moniker ‘God particle’ has some good features; at least it contains the word ‘particle’,  and it is reasonably apt given that (i) the particle is an outstanding piece of the Standard Model (ii) it has an associated field that plays a crucial role in the acquisition of mass and (iii) it has proved remarkably hard to pin down. To put it another way, I suspect the moniker has been helpful in getting across the importance of the particle; without the nickname, I suspect it would have been harder to sustain the media’s attention in the search (how many members of the public were aware of the long search for the top quark?)

4. Could it that the hubris, which we physicists find so annoying, is exactly what it takes to get the public interested? Perhaps science journalists know more than we give them credit for.

Finally, there is the problem of religion/theology. Granted, there are some amongst the devout who take grave offence. Actually, I have never heard a serious theologian criticize or applaud the moniker – they understand the concept of a nickname. Those who can’t see past this may not be worth appeasing.

One obvious comparison here is the nickname ‘big bang’. However, cosmologists hate this moniker for a different reason;it is technically misleading because the theory says nothing about a bang (the name was originally coined by Hoyle as reductio ad absurdum). Yet the expression has been enormously useful at getting across a crude version of the theory. I would much prefer the expression ‘ evolving universe’, but I wonder would the theory have captured the imagination of the public to the same extent. Truth is, I suppose we’ll never know…in the meantime, I think I’ll compromise with ‘Higgs particle’ if I’m interviewed tomorrow!


In the comments section, Sean raises an important point I should have mentioned. A second disadvantage of the term ‘God particle’ is that it encourages those who are inclined to see their particular God in everything. At a time when science is under attack from ultra-conservative religious all over the world (note in particular the attacks on evolution, big bang cosmology and climate science in the US), it is a huge mistake to encourage this sort of sloppy writing. I agree absolutely so, again, I think ‘Higgs particle’ is a reasonable compromise


Filed under CERN, Particle physics

Book review: Neutrino

This week I’m reading ‘Neutrino’ by Frank Close, published by Oxford University Press in 2010.  It’s a real treat; a short, succinct account of the history of neutrino physics, from Pauli’s ‘difficult hypothesis’ of a particle that might never be detectable to Fermi’s theory of beta decay, from the successful detection of neutrinos by Cowan and Reines to the famous conflict of theory and experiment in the case of solar neutrinos.

The story is brought up to date with a superb overview of modern advances such as the detection of supernova neutrinos, the discovery of neutrino oscillation, the resolution of the puzzle of the missing solar neutrinos and the great promise of neutrino astronomy.

Neutrino (Frank Close , OUP)

I must say I think books like this do an enormous service to physics. Like John Gribbin and Paul Davies, Close is an expert in his field who presents his material as a simple, chronological story that is extremely readable. Neutrino physics is also a worthy topic as it is one of the few areas of major progress in particle physics in recent years. It’s often forgotten that the discovery of neutrino oscillation caused the first re-writing of the Standard Model for decades.

I particularly enjoyed the historical sections on Pauli and Fermi as the relative contributions of the two are often confused. I also enjoyed the description of the astonishing work of Bruno Pontecorvo and the early experiments of Ray Davis. As for John Bachall, I came away from the book feeling that he was very badly treated by the physics community; even when his calculations of solar neutrino flux were finally vindicated (having endured suspicion for many years) he was denied a Nobel prize, hard to understand why.

The book was published before this year’s ‘faster-than-light’ neutrino controversy. I’m glad for this as I always felt that story was a bit of a distraction. That said, I wish I had read Close’s book before the many talks I gave on neutrinos this year!


There is a very important international conference on neutrinos happening this week in Kyoto, Japan, see here for details of Neutrino 2012.


Filed under Particle physics, Science and society