Friday, 28 June 2013

O Rila?

View from conference room
Around this time last year, I blogged about my attendance at a workshop in the Rila Mountains in Bulgaria.  I came back again this year.  The view from the conference room window has not changed a lot, as can be seen in the photograph compared to the one from last year.

Probably for the first time ever at a conference I was the first speaker.  My status has reached such a lofty status (and the original first speaker cancelled).  I think my talk went pretty well.  With more preparation time, I  might have generated more movies, which always look nice, and are quite possible since my talk was on a time-dependent method of calculations, but I'd prepared well enough to talk competently and hopefully give a coherent account of the problem, and the solution.  I aim to write a separate post about the work some day.

Coming to theory workshops in Eastern Europe leaves one prey to talks assuming a level of mathematics incommensurate with my own personal reality, though I tried to fit in, mentioning a large number of so-called special functions.  It turned out I was not the only one to mention Whittaker functions, though I think only I said the name "Hankel" and pretty sure only I mentioned the Fadeeva function.  

The rest of the talks were generally pretty interesting, and came in a number of styles.  These days, with overhead projectors no longer provided at conferences, the possibility to give a talk with crowded hand-drawn acetates full of complicated equations is more limited than it used to be.  Fortunately, an enterprising Bulgarian managed to produce a series of "slides" in the form of photographs of dense hand-written notes.  I think the audience was generally quite amused with this.  I did have difficulty with some of the more abstract talks, and I could swear that one of the speakers said "to make it more difficult to understand, we can introduce the intrinsic group".  Probably I mis-heard, but it was already difficult enough for me.

Still, I have come away with a list of things to do, inspired by the talks.  In particular, AK Jain of Roorkee presented a remarkable description of isospin distribution in fission fragments.  It is remarkable because of its simplicity, the apparent agreement with experiment and that no-one had thought of it before.  I look forward to seeing the work published, and have plans to make some complementary calculations.

On the first day of the conference, I had one delegate ask to have her picture taken with me, because of the usual reason.  They should have got me to play Mycroft in the BBC Sherlock Holmes adaptation, really.

Tuesday, 18 June 2013

Early one morning in the Rila Mountains

Normally, as I prepare to go to a conference,  I get a talk ready, and maybe prepare an article for the conference proceedings.  Or at least, I think about preparing those two things and make sure I know that I have the means to actually write the talk on the journey there.

Next week I'll be at the Rila Mountain workshop, in Bulgaria.  It's a long-standing annual meeting organised by the theoretical nuclear physics group in Sofia, and takes place in a somewhat isolated spot in the Rila mountains of Bulgaria.  I went last year for the first time, and discovered that as well as the scientific preparation, I was obligated to provide some kind of entertainment, as the sole British representative at the meeting.  The idea is that at the conference dinner, one person from each country represented must do something, such as recite a poem, or sing a song - or even tell a joke - that is somehow related to the place they are from.  I was caught a bit unawares by this last time.  I found out either on the day of the dinner, or the evening before.  Still, it was enough time to pick out a poem by Robert Burns, though not my favourite one, which had the benefit that I would be reading something incomprehensible to the non-native speakers of Scots, just like they would be with their poems and songs.  It seemed to go down okay.

This year, I am better prepared.  In a homage to Radio 4's defunct UK theme, I have learnt to play Early One Morning on the ukulele, and will attempt to sing along to my playing.  With luck, no-one will take a movie of it and post it online.

Monday, 17 June 2013

Interview with me

A few weeks ago, I conducted an online interview about science communication.  It's online now, and reading it back doesn't make me cringe, so if you fancy reading it, take a look here.

The picture they used (because I sent it to the interviewer), on the other hand, does make me cringe a bit.  It's my official university publicity shot.  It's an okay picture, but the more I see it, the more I think it makes me look as though I am straining slightly, or can smell something bad.  

Thursday, 13 June 2013

Lectureship at Surrey


As happens once in a blue moon, we currently have a permanent position open for application at the moment for an experimental nuclear physicist.  

I won't go over the details of the job specification, since it can be found here.  Suffice to say that if you are an experimental nuclear physicist, you will have a good idea already of what the job will involve. 

If you successfully apply, you will meet some of the people in the picture, which was taken a little while ago now.  I'm in the picture, fourth from the left.  On my right (i.e. third from the left in the picture) is Paddy Regan, whose elevation to a joint Surrey-NPL position means that the new position is available.  

Wednesday, 12 June 2013

50 years of the Cabibbo mechanism

Fifty years ago this week, the journal Physical Review Letters published an article by Nicola Cabibbo entitled "Unitary Symmetry and Leptonic Decays".  It gave a working and quantitative theoretical description of how particles which interact by the strong interaction (one of the fundamental forces of nature) can decay according to the weak interaction (another of them).  It was already known that there were some patterns and rules that seemed to be obeyed, but Cabibbo gave a beautifully simple  explanation that also made successful predictions, and that went on to be extended and incorporated into what is now called The Standard Model of Particle Physics.

50 years ago, the number of observed particles in particle physics experiments was becoming so large that they no longer felt like the basic building blocks of nature.  Just like the complexity of chemistry had been simplified to the building blocks of elements, and the many elements had been explained by the properties of three constituents (protons, neutrons and electrons), so did the increasing number of observed particles suggest that they too must possess an underlying structure.   The patterns and regularity reinforced this idea.

These patterns included the fact the particles, most of which are unstable, seemed to decay in a rather uniform way, with understandable lifetimes.  Only, some of them did not, and these were called strange particles.  However, it appeared that at least the strange particles behaved rather similarly to other strange particles.

A breakthrough came when Murray Gell-Mann and Yuval Ne'eman independently spotted that if one ignored strangeness and electrical charge then the particles could be grouped into sets which more or less looked the same.  For example, a group of so-called mesons, consisting of mostly of things which now bear the name pions and kaons, could be considered as different manifestations of one kind of more fundamental particle, exhibiting different properties only because of their charge and strangeness (whatever that was).  Pretty soon, the quark model was proposed, and all known particles at the time were described in terms of only three underlying quarks, or their mirror-image antiquarks.  These three are known as the up (u), down (d) and strange (s) quarks.  We now say that particles have strangeness because they have a strange quark or antiquark, but the strangeness categorisation existed before the quark hypothesis.

Cabibbo's paper deals with the observed fact that decays in which the weak interaction is in play works in two different ways according to whether on not the strangeness changes during the decay.  In doing this he was able to suppose the very clear and unifying idea that the weak interaction behaves in a very universal way, both for particles that do not interact strongly (leptons, such as electrons and neutrinos) and those that do.  He said that, if there is a universal weak interaction strength G, then

strangeness conserving decays have weak coupling Gcosθc
strangeness changing decays have weak coupling Gsinθc

where θc is another universal parameter called the Cabibbo Angle (don't worry too much about the designation angle.  Partly you can think of it as just the obvious way to parameterise the process by a single number).  Leptons have a weak coupling G with no Cabibbo factor. 

Cabibbo's paper doesn't mention constituent quarks at all, as the paper slightly predates the concept, and today we would rather describe the Cabibbo mechanism via the direct coupling between the weak interaction bosons and the quarks, often drawing Feynman diagrams as I have done to illustrate this post.  We still use the Cabibbo angle, at least as a first approximation.  Cabibbo's key idea was further developed, when more quarks were discovered, into the CKM (Cabibbo-Kobayashi-Maskawa) matrix.  It describes the way the weak interaction interacts with mixed combinations of the strongly-interacting quarks, using generalisations of the Cabibbo angle.

It was not without some controversy when Kobayasi and Maskawa were awarded a share of the Nobel Prize in Physics in 2008, while Cabibbo was not.

As we remember the 50th anniversary of Cabibbo's paper, it is curious to note that Google's PageRank algorithm rates the importance of his paper #1 of all papers published in APS journals - above any Nobel Prize winner.

As a wistful final word, I note that Cabibbo's paper runs to just two pages.  That used to be common in Physical Review Letters.  Now practically every paper I see pushes the 4-page limit.  Or exceeds it.

----- citation appears below ----

Cabibbo, N. (1963). Unitary Symmetry and Leptonic Decays Physical Review Letters, 10 (12), 531-533 DOI: 10.1103/PhysRevLett.10.531

Friday, 7 June 2013


It was always bound to end like this, but it is still sad to have to say goodbye.  I can't even remember how long it lasted - but longer than I could reasonably have expected.  Today I left my hotel in Florence, packing my suitcase in the bedroom but forgetting about the stuff in the bathroom.  So - goodbye to my faithful wash bag, and all its contents.  Without fail you have helped me to wash, shave,  and smell nice.  I'm sorry that I left you in Florence.

Wednesday, 5 June 2013

INPC update: Encumbered by my appearance,

Sherlock HolmesNuclear Physicist

It's day three at INPC, which means that there has been a day and a half of talks since I last posted, along with the poster session and an excursion.  Before commenting on any of that, though, I should mention a funny thing that happened to me.

At the end of the poster session last night, I was milling around waiting to meet up with people to go off to dinner.  Someone came up to me and told me that they had a confession to make - that she had posted a photo of me to Facebook (unbeknown to me), but a mutual friend tagged me in the comments. She felt she would have to come clean as a result, as I would be bound to see a notification about it.

The reason she took the photo was the same reason that, last Tuesday in the Science Museum, two Chinese tourists asked me to have a picture taken with them - because "I look like Sherlock Holmes".  It's quite amusing, really.  I can certainly see the resemblance in certain shots of me and of Benedict Cumberbatch that we look similar.  The surreptitious shot posted to Facebook is shown above, with a picture of young Mr Cumberbatch for comparison.  Perhaps I ought to make more of this.  Maybe I should watch an episode of his Sherlock Holmes and copy his mannerisms.  Perhaps I can even give my talk tomorrow in the style of a Holmesian investigation.  Or maybe I just need to befriend a Martin Freeman lookalike and start hanging around with him.  Anyway.  Much hilarity ensued as a result of the exchange, and I am now Facebook friends with the photo-taker.  In fact, it seems I had to be to see the picture;  I received no notification and she had no need to worry.

Well,  as for the conference itself.  Yesterday and today featured a selection of talks of various natures which stirred various things in me.  The one that always happens in conferences is that of a reinvigoration of interest in nuclear physics in general.  I find it quite easy to get a bit jaded in my research, and to let other aspects of university life feed the feeling of jadedness, but a few conference talks that make me think "I can answer that question" or "this is what I need to do next" usually give me a kick to both talk to other researchers to collaborate on problems, and to go away and do some calculations that might prove useful to the community.  You may correctly point out that I'm in fact writing a blog post instead.

Aside from the spur in research ideas, it's also nice to meet up with old friends.  I saw that one such for me, Sait Umar from Vanderbilt University, was supposed to be attending and was disappointed that I didn't see him on the first day.  Fortunately he did come, and I bumped into him and his wife in the poster session.  That meant I ended up not looking at as many posters as I might have, but I still managed to look round quite a few.  Being accepted for a poster at a conference, rather than a talk, is generally considered a bad outcome, but really, a 12 minute talk in a 9-way parallel session (as in my case) is not necessarily better than a poster in a 2h long poster session in which an approximately infinite supply of free prosecco is provided.  I wandered around the posters chatting to quite a few people, and generally enjoyed learning about the broad range of things that are going on in nuclear physics.  I particularly enjoyed talking to a postdoc in Brussels working on the nuclear input to neutron star properties.  After we talked, realising that we have a lot research-wise in common, we discussed being in touch.  I said that I'd be able to remember her by thinking of Les Miserables - her surname is Fantina.  She laughed uneasily.  I am reading the book at the moment, on the suggestion of Matt Kelly, and am enjoying it very much.  I rather think - being 100 pages in - that I have not learnt yet what happens to Fantine.

That takes me to the end of yesterday.  A post for today may follow, but I should see if I can find anyone to have dinner with, being that I'm back at my hotel with no plans to meet up with conference attendees.  I suspect general wandering around will fix this. Ciao!

Monday, 3 June 2013

INPC Day One - bouncing neutrons

It's the end of the first day of INPC2013 here in Florence.  I must say that it has gone a lot more smoothly than many physics conferences, and I rather suspect that this is because it's being run professionally rather than by the scientific organisers themselves.  If only they had managed to organise for there not to be a thunderstorm at lunchtime when we were supposed to be off in town fending for ourselves in some nearby trattoria.

So I attended all the plenary sessions this morning and then wended my way through a selection of the parallel sessions in the afternoon.  I went for a combination of things that are very much up my alley (I hope I'm not mixing metaphors here) and some session which were a bit more alien to me.  

One talk I went to in the "new-to-me" session was about an experiment called qBounce.  It involves bouncing a neutron off of a reflecting mirror, ever bound to fall back down and bounce again due to gravity.  It's a pretty amazing combination of a gravitational potential and a tricky-to handle neutral elementary particle used to make a quantum bound state.  I was a bit sceptical at first, and was the only person to ask questions at the end.  It's still surprising to me that the experimental details all work out, and I have to accept to some extent that they do, and that other experimentalists have peer-reviewed their work competently.  For the more technically-minded readers, there seems to be an open access paper available here from an Elsevier proceedings journal that I haven't heard of.

I'm glad I went to that session, though I'm not entirely sure where it fits in a nuclear physics conference.  Neutrons sometimes get knocked out of nuclei, I guess.  Mind you, a few of the plenary talks seemed to be more about mesons than nuclei, so what do I know?  Well, I know that I took the attached picture from the window of the conference centre in the afternoon.  The remnants of the lunchtime storm are still there to see in the clouds.

As one does at conferences, I went out to dinner in the evening.  As I do when travelling I managed, when eating bread dipped in oil, to spill some oil around the groin on my trousers.  At home it wouldn't matter as I'd have plenty of changes of clothes available.  Now I have to face walking round with conspicuous stains on my trousers.  Oh well.  It's a physics conference.  

Saturday, 1 June 2013


Who would have thought that it would be June already?  Anyone with a basic grasp of the calendar and the passage of time, I suppose, though it seems to have taken me by surprise.   I've just had a week off during the half-term holiday of my daughter Flora, culminating in a train journey to Gatwick Airport where she met her mum, to go back to stay with her, and where I checked in for a flight to Florence to attend a conference.  In reverse to the usual way of things, I have already written the conference proceeding paper, so that I could upload it to the arXiv and help the case for my recently-finished PhD student in securing a fellowship, but have not yet written the talk.  I should probably be doing that now as I sit at the airport, rather than writing this... but there's plenty of time before I talk on Thursday.  It's only a 10 minute talk, and I've done all the preparation for the paper, so all will be well.

Fortunately, on the way to the train station in Guildford we had enough time to stop at the play park.  Flora was keen to have a go on the swings, and here she is in the picture, having what I hope is a good time.