Category Archives: Particle physics

The first antimatter

Reading the post below on the spectrum of anti-hydrogen, it strikes me that I haven’t explained the concept of antimatter very well. AM has always been one of my favourite manifestations of the strange world of quantum physics (hence the blog title), so let’s have a proper post on it…

The idea of antimatter first emerged in 1928. In that year, Paul Dirac derived, from first principles of quantum theory, a wave equation for the electron that included the effects of special relativity. It was a stunning achievement and marked the beginning of modern quantum field theory. However, the Dirac equation had one very strange property – there were dual solutions for the equation, implying that positive and negative energy levels existed for the particle.

What was the physical meaning of a whole extra set of energies of opposite sign for the electron ? It couldn’t be that a repulsive electromagnetic force also existed, as the atom would fly apart. Dirac eventually decided that the only sensible answer was that the equation also described the energy of a particle of opposite sign to the electron.

This was an outlandish prediction of a brand new version of quantum theory and few scientists were convinced. However, in 1932 the experimentalist Carl Anderson discovered the decay track of an intriguing new particle in studies of cosmic rays – a particle that was of the same mass as the electron, but of opposite charge (the anti-electron or positron). It was a spectacular success for Dirac’s equation and marked a watershed in quantum theory. Long years later, other anti-particles were discovered in accelerator experiments, from the anti-proton to the anti-neutrino.

The discovery of the positron (1932): the particle was deflected by a magnetic field in the opposite direction to the electron, but was too light to be a proton

In the 1980s, accelerator physicists managed to create entire anti-atoms of hydrogen, by allowing positrons to be trapped by anti-protons. However, such ‘hot’ anti-atoms are hard to study and the next challenge was to create ‘cold’ anti-atoms so their properties could be studied in detail; this was achieved in the late 1990s.

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A fundamental problem

From the first, it was realised that antimatter and matter would annihilate on contact (from relativity), and this raised a new fundamental question in physics: Why do we live in a universe made almost entirely of matter? Why didn’t matter and anti-matter annihilate immediately after the Big Bang? This puzzle hints at a deep asymmetry in the decay of matter and antimatter and is known as the puzzle of baryogenesis, more on this later..

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Spectrum of anti-hydrogen?

What does the spectrum of anti-hydrogen look like?

This question came up at our Maths/ Physics Seminar Series on Wednesday, during a presentation I gave on the forthcoming experiments at the LHC (slides here).  It’s a good question, I never thought to ask it before. Before I look it up, here is my guess at an answer – any comments welcome.

First a definition: as you know, antimatter is the name given to matter consisting of elementary particles in which the electric charge (or other quantum property) of each particle is the reverse of that in ordinary matter (see blog title). Just as a Hydrogen atom consists of an electron orbiting a proton, an anti-Hydrogen atom consists of a positron orbiting an anti-proton. However, although antiparticles are often found in cosmic rays or produced in accelerators,  anti-atoms are very rare: only a few atoms of anti-Hydrogen are made at accelerator facilities around the world.

My guess is that the sprectrum of anti-H looks exactly like that of Hydrogen. After all, the emission spectrum of Hydrogen is due to an excited electron jumping from the excited energy level down to a lower level(s): presumably the positron in anti-H has the same separation of energy levels, so I can’t see how there would be any difference in the light emitted.

Pictorial representation of H and anti-H

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However, there is a problem with this answer: how do we detect anti-atoms if their spectrum is the same as normal atoms? By deflection in a magnetic field, you say – this is how the positron was first discovered. But anti-atoms are neutral and in any case antimatter is not always matter of opposite charge, sometimes it is another quantum property that is swapped (consider the anti-neutrino). Indeed, how do we distinguish anti-neutrinos from neutrinos? I’m not sure, but I know we can.

Also, I think I  read somewhere that we have detected clusters of antimatter in some places in the universe. Again, how do we know it’s antimatter? These sort of unexpected questions are what makes giving a seminar worthwhile..

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Thoughts on CERN and NASA

I’ve been meaning to point out that you can view the slides used by the incoming Director General of CERN, Rolf Heuer, in his recent inaugural address to the CERN community here.

Rolf-Dieter Heuer

There are many interesting points, but one that comes across clearly is Heuer’s vision of CERN as a global centre for particle research. Of course, one could argue that it already is, but it’s clear from the presentation that the scope of the facility is expected to broaden even further. Fascinating that an inter-european project involving a handful of sparring nations has become so successful that it is now one of the world’s most successful centres for scientific research – and all the more reason for Ireland to join, as I have said many times in public and in the press.

It’s often said that CERN is the NASA of the particle world, but it’s actually more. Quite apart from the opportunity for scientists to work at a top-level facility, with top-level scientists, I think the international aspect of the project is important in itself – perhaps science can give humans a taste of how genuine co-operation of individual nations working in harmony can yield a result that is greater than the sum of its parts…

The world’s largest acclerator (LHC) at CERN under Geneva

Of course, CERN isn’t perfect and I think there are PR lessons to be learnt from the media coverage of the LHC startup:

(i) A spurious story of black hole creation was allowed to dominate the coverage

(ii) A serious technical setback ocurred in the full glare of maximum publicity (the consequence of a single faulty weld)

As a result of these, the general public saw the LHC first as a threat, and then as something that broke down at the first fence….hardly confidence inspiring.

In fact, I saw remarkably few articles in the press on the beauty of particle physics, or the ‘why’ of the experiment. One reason was that sporadic press contributors (like this one) couldn’t get articles accepted due to the sheer volume of articles on the topic by regular journalists (who knew little of the topic). Instead, the public were presented with repeated technical details that interested no-one.

Perhaps it is true that scientists do not convey the excitement of their work very well – but I wonder. I wouldn’t mind a shot at disproving this theory. I’m currently trying to persuade The Irish Times to run a regular column on cosmology and particle physics (The Puzzling Universe) and they seem interested ..we’ll see…

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Standard Model at Trinity College

I gave an introductory talk on the Standard Model and the forthcoming LHC experiments to some physics students in Trinity College last night. There wasn’t a huge turnout, but it was great being back in the Schroedinger Theatre – lovely wooden theatre, steep tiered seating, buckets of atmosphere. All mod cons of course but also a good big old fashioned blackboard for back-of-the-envelope calculations to accompany the slides (you can get the slides here).

It was a real trip down memory lane – as a postgrad, I used to give quantum mechanics tutorials in the same theatre to 2nd year theoretical physics. I used to spend hours preparing answers to Denis Weaire’s problem sheets, only to find the students hadn’t opened a book!

Anyway, I think the lecture went well (I heard it was completely incomprehensible  – Ed). The best thing about it was the poster – students really know how to put a poster together.

glendagilson1

I also found time to point out that Ireland is not a member of CERN, almost uniquely in western Europe (see September posts on this). This denies our best students and researchers the opportunity to work with world-class researchers at a world-class facility – an omission that has had a devasting effect on experimental particle physics in Ireland. The map below says it all really.

The 20 member states of CERN (blue) do not include Ireland. Many non-European States have associate membership (U.S., China, India and Japan), but this does not include Ireland either.

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LHC: Hawking v Higgs

As you may have heard, the LHC at CERN has had a technical setback (see here and here). It will take several months to fix, so it’s a good time to do a post on a matter I’ve been meaning to discuss…

An unexpected aspect of the media coverage of the LHC startup was a public disagreement between two world-famous physicists: cosmologist Stephen Hawking and particle physicist Peter Higgs (the latter first postulated the existence of the Higgs field and the famous Higgs boson).

Stephen Hawking and Peter Higgs: disagree on existence of the Higgs boson

Hawking has renewed his bet of 100$ that the Higgs boson will not be found at the LHC, making the point that it will make for more interesting physics if it isn’t. (The Higgs boson is the one particle of the Standard Model of particle physics that has not ben detected experimentally, and it is is crucial to the theory (see post below) – any evidence that it doesn’t exist at the energies expected would force a radical think of the Standard Model

Not for the first time, Peter Higgs has not responded kindly to Steven Hawking’s remarks, stating that he feels that the Hawking analysis is seriously flawed…this story got great coverage in the press, and you can read the view of physicists on it about it here and here.

I suspect there is more to this story than meets the eye: Peter Higgs is an extremely quiet, self-effacing scientist, long retired, who rarely comments on physics in public or seeks the limelight. His reaction to Hawking’s bet is not attention-seeking, but represents the view of the particle physics community (I have often heard similar views expressed by particle physicists I know). After all, one of the  major reasons for building the LHC in the first place is precisely the detection of the Higgs particle –  in other words, most particle physicists expect it to show up at the energies available.

It’s worth remembering that theoretical particle physics is a very special branch of physics. Concerned primarily with the worlds of quantum physics (because particles are so small) and that of special relativity (because small particles can travel at relativistic speed), it has traditionally been considered to be the most difficult, abtruse and mathematical area of all of physics. Cosmology, by contrast, was considered a fairly speculative science until the 1970s. It’s only in recent years that cosmology has started to attract great theoreticians such as Roger Penrose and Stephen Hawking. However, although Hawking is highly respected as a cosmologist (and as a great populariser of science), he frequently comments on fields far from his area of expertise  – notably on particle physics. It’s unfortunate, as he occasionally makes fairly outlandish statements that really irritate the particle physicists.

Thousands of particles explode from the collision point of two gold ions in the STAR detector of the Relativistic Heavy Ion Collider. Electrically charged particles are discernible by the curves they trace in the detector’s magnetic field.

That said, in the same statement it’s interesting that Hawking says that he thinks there is a good chance that supersymmetry (see post below) might be seen at the LHC – which is nice to hear. Generally, evidence for supersymmetry is expected to be more elusive than evidence for the Higgs – but if found, SUSY will open up a whole new vista in particle physics (while evidence for the Higgs will close a chapter). Hence, I for one suspect Hawking’s bet on the Higgs was taken with tongue firmly in cheek.

Update: there is a very nice (and rare) interview with Peter Higgs in last week’s issue of New Scientist. In the interview, Higgs hints that, as a new generation of mathematicians turned their attention to the Higgs field in the 1970s, he began to feel a little out of his mathematical depth. He turned to the emerging field of supersymmetry, but soon ran into the same problem. Intruiging that even the best minds could have problems with the maths of particle physics!

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LHC: unplugged

Tomorrow should be interesting as I’ve been asked to give an informal talk on the LHC to our physics staff and students. I’m looking forward to it as the only rule is no powerpoint, just whiteboard and marker, i.e. unplugged. I’ve been thinking about how to give such a talk for all levels, I’ll think I’ll break it up as

1 WHAT

Particle colliders, new LHC vs old LEP, energy achievable etc.

Reason for vacuum (UHV), reason for low tempT, physics of focusing etc

Description of detectors

2. WHY

Creation of exotic particles (E = mc2), study of fundamental particles

Study of fundamental interactions and  unified field theory

Cosmology: glimpse of early universe, info on matter/antimatter asymmetry, info on dark matter

3. A BRIEF HISTORY OF PARTICLE PHYSICS

The proton and the periodic table

The nuclear model of the atom

The particle zoo and the quark model

Six quarks and six leptons

The Standard Model: fermions and bosons, E-W theory, QCD, the Higgs boson

4. LHC EXPECTATIONS: STANDARD MODEL

Higgs boson, explanation for mass, explanation for matter/antimatter asymmetry

5. MORE THEORY: BEYOND the STANDARD MODEL

Grand Unified Theories

Theories of Everything

Supersymmetry: SUSY breaking, SUSY particles: which model of SUSY?

Neutralinos: candidates for dark matter?

6. LHC EXPECTATIONS: BEYOND the STANDARD MODEL

SUSY particles

Neutralinos

WIMPs

7. SUMMARY

HIGGS: could close chapter on Standard Model

SUSY: could open new chapter in particle physics

SUSY: could explain dark matter

OTHER: extra dimensions? mini-black holes? other surprises? evidence for strings?

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Useful pics I might use are:

II The Standard Model

III. Unified Field Theory

Might finish with this great pic and text from the search for Higgs at FERMILAB

In the Standard Model of particles and forces, the masses of the W boson, the top quark and the Higgs boson are connected. If one knows the mass of any two of the three particles, then the mass of the third particle can be calculated. This plot illustrates that relationship. It depicts the mass of the Higgs boson as a function of top quark and W-boson mass. Each diagonal line represents a single Higgs boson mass; examples chosen are MH = 114, 300 and 1000 GeV/c2. Based on theoretical constraints and direct experimental searches, scientists expect the mass of the Higgs boson to lie somewhere in the green-banded region. The new CDF measurement of the W-boson mass (see this press release) indicates that the W-boson mass is heavier than previously measured (worldwide average). Since the top quark mass did not change, a heavier W-boson mass indicates a lighter Higgs Boson. The blue ellipse shows the most likely values for the top quark and W-boson masses, based on all available experimental information, including the CDF result, at the 68 percent confidence level. The intersection of this ellipse with the green band indicates the most likely Higgs boson mass. This result can be compared to an older result (red ellipse), which did little to constrain the Higgs boson mass. Credit: Fermi Lab

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Update: Phew, that’s over. I now appreciate slides, powerpoint etc – definitely harder to keep the story linear on the blackboard. I went way overtime which is not like me. Still, it’s great to have an educated audience. Good questions afterwards – and nobody mentioned earth-eating Black Holes.

Now I’m off to the mountains of Mourne for a hill-walking weekend with GLENWALK, the well-known walking club with a  drinking problem…yipee

Update II: A few people have asked me for a hardcopy of the talk. I’ll try and knock something up and stick on the My Seminars page of the blog, but it’ll take some time as I used the whiteboard on the day. I’m giving a simpler talk on the same subject to schools on 12th october for Maths Week 2008, will definitely prepare a powerpoint presentation for that ..

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Ireland, CERN and the LHC

There was more coverage of the opening of the LHC in the Irish media over the weekend. My favourite was Ross O’ Carroll Kelly’s piece on the end of the world in The Irish Times on Saturday.

(Three rugger buggers are cowering behind the sofa: “Any last wishes before they hit the button?” – “Yes, I wish I’d studied physics at UCD instead of Orts”).

R.O.C.K. I wish I’d studied physics at UCD instead of Orts

I personally think this sort of coverage gets science into public consciousness far better than any number of earnest articles and letters. More seriously, there was also an excellent article titled ‘Science fact of fiction’ in the same paper on the reporting of ‘nonscience’ such as earth-eating black holes.

Best of all, The Irish Times devoted their Saturday editorial to the LHC, describing the importance of the experiment and bemoaning the lack of participation of Irish scientists due to the fact that Ireland is not a member of CERN. On the same page, they also published a letter of mine on the same subject – not as good as getting an article published, but it’s not every day one’s letter coincides with the theme of the editorial..

Hopefully, all this coverage will help re-ingnite the debate on Irish membership of CERN once more.. .below is my letter

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Madam, – The Irish Times has given exemplary coverage of recent events at Cern, The European Organisation for Nuclear Research, with comprehensive articles, cartoons and other pieces all helping to raise public awareness of this outstanding international scientific centre.

It is a proud moment for Europe, as the experiments at the new particle accelerator will be watched with intense interest by scientists the world over for information on the fundamental structure of matter, and on the evolution of the early universe.

However, as your Science Editor Dick Ahlstrom points out, the participation of Irish scientists in this historic research will be severely limited by the fact that the Republic, almost uniquely among western European nations, is not a member of Cern. This oversight has decimated Irish research in particle physics, despite a proud tradition in the field (Ireland’s only Nobel prize in science was awarded for the splitting of the atomic nucleus by Ernest Walton). More pragmatically, Irish high-tech companies are severely disadvantaged in bidding for the huge contracts available in engineering and information technology at Cern.

So much for our efforts to become a world leader in science and technology. – Yours, etc,

Dr CORMAC O’RAIFEARTAIGH,

Lecturer in Physics, Waterford Institute of Technology

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Update I: it looks like the editorial and my letter have sparked a debate on the topic, there are three letters on the subject in Tuesday’s Irish Times. One of them makes an interesting point:

Madam, – Both you and Dr Cormac O’Raifeartaigh (September 13th) have pointed out that Ireland, almost uniquely among European countries, is not a member of Cern. Surely the reason is simple: the presence of the dreaded word “nuclear” in the organisation’s title…

– Yours, etc,

DAVID SOWBY, Knocksinna Crescent, Dublin 18.

The point here is that Ireland is resolutely anti-nuclear (both power and weapons). Of course, it’s ironic if this is the problem – the name CERN is a misnomer, as it is the physics of elementary particles (not of the nucleus) that is studied at CERN. If you find David Sowby’s suggestion far-fetched consider another letter on the subject in the same paper:

Madam, – Unlike Dr Cormac O’Raifeartaigh (September 13th), I am not at all concerned that Ireland, “almost uniquely among western European nations”, did not pour millions of hard-earned taxpayers’ money into the Cern project.

Whenever I hear the words “nuclear research” other words, such as “Nagasaki” and “Chernobyl” spring to mind and I wish that Ernest Walton and his peers had not “split the atom”. I am sure that if “Irish high-tech companies” have the capability, they will not be “severely disadvantaged in bidding for huge contracts available in engineering and information technology” by our unwillingness to pour millions down the bottomless pit of Cern.

– Yours, etc,

W.J. MURPHY, Malahide, Co Dublin.

I rest my case – perhaps Irish scientists are paying a price for a famous misnomer!

Update II:

Two more letters on the subject in Wednesday’s Irish Times, both of them castigating W.J. Murphy above. Actually, I think they’re a little hard on him – how is Joe Public supposed to guess that the European Organization for Nuclear Research is not involved in nuclear power or weapons? In fairness, it’s a pretty miseading title…here is what one of them said

Madam, – W.J. Murphy (September 16th) says, in a parody of Goering’s remark about Kultur, “Whenever I hear the words ‘nuclear research’ other words, such as ‘Nagasaki’ and ‘Chernobyl’ spring to mind’.

This ridiculous statement demonstrates the widespread ignorance that exists about anything to do with nuclear matters. The words “nuclear research” in Cern’s title refer solely to man’s attempts to discover the basic nature of the matter of which everything in the universe is made. At Cern it has nothing to do with weapons or power.

The comment about Ernest Walton and his peers is merely petty and uneducated. – Yours, etc,

DAVID SOWBY, Knocksinna Crescent, Dublin 18.

True, but a bit harsh, in my opinion

Update III: More letters on the topic in Thursday’s Irish Times. The hapless W. J. Murphy responds to the criticism above by retracting and apologising for the ‘nuclear’ slur, but raises a more difficult issue:

Madam, – David Sowby and George Reynolds (September 17th) are understandably critical of my letter of the previous day, but this is based on a misunderstanding. That is probably my fault: in an attempt to be brief, I grossly over-simplified a complex argument. I would agree with both of their points.

I wonder if they would agree with my substantive point: that the immediate results of the Cern project would not justify the pouring of millions of hard-earned Irish taxpayers money into it and that Irish high-tech companies that have the capability to win contracts in engineering and information technology will not be disadvantaged by this?

I accept that the word “nuclear” means different things to different people. And I should not have referred to Ernest Walton, mea culpa. – Yours, etc,

W J MURPHY, Malahide, Co Dublin

This is the hard question of course: would this money be better spent elsewhere? My own view is that the annual fee (about 10 million) is smaller than some Science Foundation Ireland grants for domestic research – the difference is that CERN is truly world-class work. Just how much it costs to deprive our staff and students the opportunity to work at this level will probably never be known. (We do know for a fact that Irish high-tech companies are seriously disadvantaged in bidding for the most lucrative contracts due to our non-membership, Murphy is quite wrong on this).

Update IV: I have written a new letter to The Irish Times on the above points. They won’t print it, having closed the debate, thus leaving Murphy with the last (incorrect) word. Sigh. I suspect this is why most scientists choose not to get involved in public debate

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LHC: D-day at last

So the big news: the first proton beam got all the way around the LHC ring this morning without mishap. Cue much celebration in the CERN control room and around the particle physics community.

There is a live webcast available on the CERN website, although some people are having problems viewing it due to the huge interest. There are also some great updates by physicists at the scene describing the day’s events on blogs such such as US LHC Blog, RESONAANCES, Charm&C, Higgs

The redoubtable Lubos Motl has a great discussion on his blog The Reference Frame explaining why he expects supersymmetry to be seen at the LHC, it’s a very nice piece

For more live postings describing the day’s events, see the list on the international particle physics website interactions.org , it’s almost as good as being there.

P.S. No earth-eating black hole so far…surprise surprise.

Update: the Science Gallery at Trinity College Dublin are celebrating with an open day on the topic, with live feeds, talks and commentary by physicists all day…well worth popping in

Update: a second success… a proton beam successfully completed the loop in the opposite direction in the afternoon, this is way ahead of schedule.

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LHC: it’s not the end of the world

The world is not going to end tomorrow (September 10th) and the LHC startup does not constitute a danger to the public, contrary to claims by one or two scientists (non-physicists) that have been widely reported in the media (see here and here for example). Instead, tomorrow marks the beginning of an exciting new era in particle physics – the start of experiments at the world’s most powerful particle accelerator, the Large Hadron Collider at CERN.

Below is part of an article on the LHC that I wrote for an Irish newspaper (they may not use it, thanks to a large number of articles on the same topic by people who know little about the subject). The two main points I wanted to highlight were the safety of the experiment, and the fact that Ireland, almost uniquely among EU nations, is not a member of CERN – despite the fact that our only Nobel prize in science is in precisely this area.

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September 2008 marks an important month for European science. This month, measurements begin at the new “atom-smasher” at CERN, the European Organization for Nuclear Research. Long the jewel in the crown of European science, CERN truly becomes the NASA of the sub-atomic world with the opening of its Large Hadron Collider (LHC), the world’s newest and most powerful particle accelerator.

Situated in a vast 27 km-long tunnel deep beneath the Franco-Swiss border, the new machine at CERN is probably the largest scientific experiment on planet earth. The experiments at the facility will be watched with intense interest by scientists the world over for information on the fundamental structure of matter, and on the evolution of the early universe.

How does it work? Beams of the smallest particles of matter travelling almost at the speed of light will be smashed together in head-on collision. Out of the intense energy of collision, exotic short-lived elementary constituents of matter not seen since the Big Bang will be fleetingly created and tracked in giant particle detectors.

Such experiments offer not only a glimpse of the deep structure of matter, but also of the nature of the forces that hold it together. For example, evidence of the existence of the elusive Higgs boson or ‘God particle’ could offer support for the so-called Standard Model of particle physics, confirming that our view of the origin of mass is correct. Glimpses of exotic entities such as ‘supersymmetric’ particles could reveal deep connections between all the fundamental forces of nature. Other experiments might reveal the true nature of space and time.

Cosmologists hope that the experiments at CERN might offer insight into the formation of the early universe, as the giant collider will achieve energies not seen since the Big Bang. In particular, a glimpse of certain particles could shed light on the nature of Dark Matter, one of the great puzzles of the universe at large.

Is the LHC safe? This question has recently received much attention in the world’s media. In fact, the accelerator is simply a more powerful version of previous machines and constitutes no danger to the public. Rumours that it could create a giant earth-eating black hole arise from a misunderstanding of the physics of black holes (although there is an intriguing possibility that harmless mini-black holes could be created in the experiment).

The 27km tunnel at CERN: experiments will not destroy the earth

Such research into the realm of the sub-atomic might seem of dubious practical application in today’s world. However, the technical spin-offs of experiments at facilities such as CERN are legendary. In 1990, the world wide web was created by CERN physicist Tim Berners-Lee in order to provide a platform for scientists to share and analyse experimental data. Accelerator technology developed at CERN is now routinely used in important medical applications. Most recently, CERN scientists have pioneered the use of GRID computing, a new type of computing that involves the networking of thousands of computers, in order to facilitate the analysis of vast amounts of data that will be collected at the LHC.

CERN is regularly cited as an outstanding example of European collaboration. Created in the 1950s to counter the brain-drain of European scientists to the U.S., it now provides a world-class facility for the scientists of over 20 European nations, while a host of non-European nations such as China Japan, India, the U.S. and Russia all enjoy associate membership. In fact, there are more American particle physicists working at CERN today than in the U.S.

Europe has reason to be proud, but Ireland has not. The participation of Irish scientists in the historic experiments will be severely limited by the fact that the Republic, almost uniquely among EU nations, is not a member of CERN. This omission has decimated Irish research in experimental particle physics, one of the most fundamental fields of the sciences (with the honourable exception of one group at UCD). It has also rendered it almost impossible for Irish engineers and scientists to bid for the large international contracts in high-tech software and hardware projects, a fact that sits awkwardly with our efforts to become a world leader in science and technology.

Strangest of all, Ireland has a proud tradition in this field of science. In 1932, the Irish scientist Ernest Walton and his Cambridge colleague John Cockcroft built the world’s first particle accelerator and used it to split the atomic nucleus, an achievement for which they were awarded the Nobel prize. This work opened up the field of sub-atomic physics, and a version of their machine is used today as a preliminary accelerator in the new facility at CERN.
One wonders what Walton would have made of the Irish absence at CERN at this historic time…

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P.S. Just about every physicist with a blog is writing about the CERN experiments this week, there is a good list of blogs on the topic on the particle physics website interactions.org


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