Quantum Diaries

In less than 24 hours the 2013 Nobel Prize for Physics will be announced and there seems to be one word on everyone’s lips… Higgs. The scientific community appears to hope en masse that Peter Higgs and Francois Englert collect a Nobel for their prediction of the Brout-Englert-Higgs mechanism, the mechanism by which elementary particles such as quarks and electrons acquire mass. There is however competition. Here are some of the other front-runners:

Iron-based superconductors – Hideo Hosono

Superconducting materials have zero electrical resistance when cooled below a critical temperature – a very useful property as it allows for the highly efficient transfer of electrical signals. Today’s most efficient superconductors incorporate a layer of superconducting copper oxide which must be cooled to very low temperatures to operate. For example, in the Large Hadron Collider (LHC) the operating temperature of the superconducting electromagnets, which are used to steer the beam of particles around the accelerator, is retained at around -271°C. The highest temperature at which today’s superconductors can operate is around -140°C, which is still fairly chilly.

A magnet levitating above a high-temperature superconductor, cooled with liquid nitrogen. (Image by Mai-Linh Doan.)

The possibility of an iron-based superconductor, which could in theory have a much higher critical temperature, had previously been dismissed as it was assumed that the large magnetic moment of iron prevented the emergence of pairs of electrons known as ‘Cooper pairs’, which are required for superconductivity in conventional superconductors. However, in 2008 Hideo Hoson of the Tokyo Institute of Technology accidentally stumbled across the first iron-based layered superconductor. Iron-based devices may hold the key to the holy grail of superconductivity – room temperature superconductors – which would certainly make running the LHC at bit cheaper!

Discovery of extrasolar planets – Geoffrey Marcy, Michel Mayor and Didier Queloz 

In 1995 Michael Mayor and Didier Queloz of the University of Geneva announced the discovery of a massive exoplanet in orbit around the star 51 Pegasi, and they used a sneaky technique know as the radial velocity method to find it. The gravitational field of the orbiting planet causes 51 Pegasi to ‘wobble’ in its own small orbit. Using the Doppler effect, Mayor and Queloz were able to measure the variations in the radial velocity of 51 Pegasi, that is the speed at which the star was moving towards and away from Earth in its orbit, to infer the existence of a massive exoplanet. Clever!

Geoffrey Marcy of the University of California has discovered more exoplanets than anybody else, including 70 out of the first 100 identified. Indeed he was the first to verify the existence of Mayor and Queloz’s exoplanet around 51 Pegasi. He has also discovered the first transiting planet around another star, the first extrasolar planet beyond 5 AU, the first Neptune-sized exoplanets, and the first multiple planet system around a star similar to the Sun. He is the quintessential planet-hunter.

An artist’s impression of an exoplanet.

And the winner is…

So tomorrow’s announcement is not a foregone conclusion. Profs Englert and Higgs, and any others hoping to be awarded a Higgs-related Nobel prize, have some stiff competition. Exoplanets have provided some of the buzziest science headlines in recent years, while iron-based superconductors could have hugely significant practical applications, including in particle physics.

However, one senses that it is perhaps the right time for science’s ultimate accolade to be awarded for the prediction and/or observation of the Higgs, which has undoubtedly been one of the most significant discoveries in science in the past century. And with Profs Englert and Higgs in their 80s and Nobels not awarded posthumously (which is why Robert Brout, who collaborated with Englert and died in 2011, cannot be awarded the prize), one suspects that the Nobel committee is somewhat feeling the pressure.

Stay tuned to Quantum Diaries tomorrow where we’ll be blogging live to keep you informed of the latest developments in the run-up to and following the prize announcements. I will also be doing a bit of tweeting @JimmyDocco. And there is already an excellent blog post up in anticipation of the big announcement here.

They say a picture says a thousand words – so here is my story of a summer at CERN in 12,000 words.

Welcome to CERN baby! – this year’s crop of summer students gather in front of the Globe for a group photo (first to spot me gets a postcard!)

The sun was shining and the weather sweet – the summer held much promise. And with CERN located in the midst of agricultural estates, there were a few nice strolls to be enjoyed too.

We got acquainted with the stars of CERN – a cross section of the Large Hadron Collider (LHC). Notice the two beam pipes through which particles circulate around the 27 km circular accelerator in different directions.

And its giants – the gargantuan particle detector, CMS. This 12,500 tonne beasty is located 80 metres underground at a point where the beams of the LHC cross and particles collide.

The weekends afforded a fine opportunity to soak up some Swiss culture – here a group of Swiss horn players in Gruyère.

Or to take a quiet Saturday morning stroll around CERN, where you never know what you’ll find – I stubbled across this old decommissioned detector.

Now there was of course some work to be done – my experiment coupling a laser into optical fibres and through a birefringent crystal.

And while most of us came to learn about the laws of Physics, some sought to defy them – Filip levitating.

But we did learn about the stranger goings-on at CERN – Michael “Antimatter” Doser himself explains the workings of the Antimatter Decelerator, which is used in the production of antimatter.

There was plenty of time for a few nights at the movies – a reveller caught in the spotlight at the outdoor film at Perle du Lac, Geneva.

And a few more down the pub – Cian and Donal of the Emigrants jamming in Charly O’Neills.

All in all, it was a rather memorable summer at…

I have spent much of the past three months in a dark room as my research at CERN has involved using lasers to develop a new type of beam position monitor (BPM) for the Large Hadron Collider (LHC). From a technological perspective, this is seriously cool.

What is a beam position monitor?

To thread a beam of particles through a narrow accelerator beam pipe and around various obstacles you need to control and steer the beam using magnets. This is important for two key reasons: firstly, you want your beam to accurately hit its intended target; and, secondly, if you loose beam aperture in high energy accelerators, stray particles will damage your machine – and you don’t want to damage a $10 billion machine such as the LHC.

You can only control what you can measure and so BPMs are of fundamental importance in the operation of particle accelerators.

The current generation of BPMs are mostly electromagnetic in their operation. They use metal strips, known as striplines,  which line the inside of the beam pipe, to measure beam position. A beam of charged particles has an electric field which causes the striplines to become charged – so the striplines essentially act as electrodes. The closer the beam gets to a particular stripline, the larger the charge build-up on that stripline. So by measuring the voltage which builds up across the striplines, one can calculate the position of the beam.

Grand – so we’re sorted for BPMs then? Not quite…

Intra-bunch head-tail instabilities

Yikes, what are those?

Beams are made up of many discrete bunches of particles. Those bunches have beginnings and ends, known as heads and tails. Sometimes the heads and tails vibrate, resonate or even swap position. Such so-called ‘head-tail instabilities’ lead to beam instability and hence accelerator operators need to monitor such phenomena very carefully.

Plots of intra-bunch head-tail instabilities in the PS in 1974 as recorded on an oscilloscope (courtesy of J. Gareyte, “Head-Tail Type Instabilities in the PS and Booster”, CERN, 1974).

The plots above show such intra-bunch head-tail instabilities observed in CERN’s Proton Synchrotron (PS) in 1974. Note that the time period over which each plot is recorded is 200 nanoseconds (ns), meaning the bunches were approximately 120 ns in length. The problem is that today bunches are hundreds to thousands times shorter than that – so accelerator operators require BPMs of much wider bandwidth to monitor these kind of instabilities.

A new type of BPM…?

I’ve been working on a new type of BPM which uses birefringent crystals to monitor beam position and that, in theory, should have wide enough bandwidth to observe intra-bunch head-tail instabilities in the LHC. To understand how it works we need to understand birefringence…

When light enters a birefringent crystal it is polarised in two different planes – lets say horizontal and vertical. Now each of those planes has a different refractive index due to the structure of the crystal. So the light in the horizontal plane travels at a different speed to the light in vertical plane. This causes light to rotate or twist as it travels through the crystal. The refractive indexes in the crystal change in the presence of an electric field, and this is known as Pockels effect.

An electro-optical (EO) BPM

We can use the birefringent nature of the crystals, combined with the Pockels effect, to monitor the position of a particle beam. As we know, the beam is made up of charged particles and therefore has an electric field. So if you put a birefringent crystal next to the beam, and the beam then changes position, the refractive index of the crystal changes. If we can measure this change of refractive index then we can calculate the position of the beam.

To do this you fire a laser  through the crystal and use a light sensor to detect the intensity of the laser after it exits the crystal. By cleverly placing and orientating a polariser before the crystal (to linearly polarise the light entering the crystal) and then another polariser (known as an analyser) after the crystal, you can block all the light leaving the crystal – so the detector reads zero. This is analogous to rotating a pair of 3D glasses as shown below.

Two pairs of 3D glasses with linearly polarised lenses. When the planes of polarisation are parallel, linearly polarised light emerges from the lenses.

The same 3D glasses but now with the planes of polarisation perpendicular to each other. The first lens polarises light in the horizontal plane and the second polarises light in the vertical plane.  The result – light is extinguished.

So when the beam is in its optimal position, you ideally wish to be getting a zero reading on your light detector.

Then, when the beam strays from the optimal position, the refractive index of the birefringent crystal changes, causing the light passing through the crystal to rotate to a different degree.  The analyser (which is calibrated to extinguish light emerging from the crystal when the beam is in its optimal position) no longer blocks all of the laser – so you get a reading on your light detector which you can use to calculate the beam position. Easy-peasy!

The advantages of the EO BPM

Birefringent crystals are really sensitive to changes in electric field. So if we can measure changes to the refractive index we can very accurately calculate the position of the beam. Moreover, the laser in the BPM will be coupled into optical fibres and so the signal will not suffer the same levels of attenuation as those carried through the electrical cables of electromagnetic BPMs. We can therefore monitor the position of the beam at much higher bandwidths, as required.

Due to the efficiency of optical fibres in transmitting signals, the crystal may be placed hundreds of meters underground in the accelerator tunnel, while more complicated equipment (including the light detector) can be placed on the surface – where operators may calibrate and control the BPM – without any significant loss of signal bandwidth. The crystals are also tiny so may fit where other BPMs can’t reach.

My experimental set-up in the lab – the laser is coupled into the optical fibre using mirrors. It then travels through the optical fibre, is polarised by the system of paddles in the foreground, before emerging from the fibre. The laser beam then passes through the analyser before hitting the light detector.

When will it be in operation?

The EO BPM is still under R&D but we hope to have a prototype ready to test in the Super Proton Synchrotron at the end of Long Shutdown 1 (LS1) in mid-2014. So, the EO BPM is in the pipeline, or at least it will be soon…

The EO BPM is the brainchild of Ralph Steinhagen.

My pal got chatting to a drunk fella in a bar a few weeks before he started a new job at CERN. When he mentioned the identity of his future employer, the drunk fella guffawed with a “well you’re not going to find a girlfriend there!”.

Now, either this intoxicated chap was implying that my pal is inherently unattractive to particle physicists (which seems unlikely as he’s a very handsome man) or he was insinuating that there aren’t too many women working at CERN. I think it was more likely the latter and to that my response would be – not so!

I’m not sure of the exact figures but from a cursory glance around the lecture theatre there seems to be a roughly equal number of women and men on the CERN Student Summer Programme this year. Moreover, a significant proportion of our lecturers are female, with Daniela Bortoletto, Tara Shears and Magdalena Kowalska proving to be fantastic communicators as well as scientists.

Women are prominent at CERN. For example, the observation of the Higgs, one of the most important discoveries in modern science, was partly announced by Fabiola Gianotti as spokesperson of the ATLAS detector.

Fabiola Gianotti appears in Time magazine.

Now, that’s not to ignore the reality that the ratio of sexes at CERN more generally is still tipped in favour of males but, nevertheless, particle physics isn’t solely a man’s world. A CERN website specifically states that:

“CERN hopes to… send a clear message to all young women interested in particle physics and high technology that they are welcome in the field as physicists, engineers and computer scientists… Particle physics is a field where women play an active role at the forefront of experimental research.”

CERN even has an official and very active Women’s Club to provide an additional support network for females working at CERN. 

So, if you are female and hoping to break into particle physics, the opportunities, support structures and role models are there for you to get your foot in the door and progress to the pinnacle of your field.  So no excuses – get the application in…

Epilogue

Contrary to the predictions of an inebriated man in an Oxford drinking establishment, my pal is now dating a very lovely female particle physicist. So ha!

The Summer Student Webfest 2013 was held at CERN during the first weekend of August. The objective of the weekend was for student web enthusiasts to work together in teams to design web-based applications that will encourage the public to learn more about science, and in particular CERN, the LHC and particle physics.

The Webfest is modelled on events called hackfests which bring together computer aficionados for intense periods of web-based creativity that energize many open source communities.

The opening session saw fifteen brave souls pitch their ideas to an auditorium full of eager students. The ideas included games, volunteer computing projects, educational tools and open source platforms. Twelve of the pitches found sufficient support to proceed and the competition commenced.

To be successful each project required a range of skills including coding expertise, graphical design, writing skills and physics knowledge. It was only those teams that could combine their skills and work together effectively that would succeed in creating engaging applications.

Webfest participants with John Ellis (front row with red t-shirt).

Many of the students worked almost solidly through the weekend, only taking breaks to top up their mugs of coffee or to attend some of the workshops which were interspersed throughout the event. The workshops provided introductions to various online tools including the citizen science site crowdcrafting.org.

Sunday afternoon arrived as all twelve teams rushed to prepare slides for their presentations at the judging session.  On the judging panel was John Ellis, an eminent CERN-based particle physicist – so nerves were jangling.

After the unveiling of twelve innovative entries, the creators of ‘Mother-hunting’, a game in which a fundamental particle explores CERN to try to trace its family history, were crowned winners. Along the way the particle meets famous physicists – including John Ellis – who give it clues to its origin and the ‘mother-particles’ from which it decayed.

Another successful entry was the Antimatter crowdcrafting.org application which invites members of the public to analyse real experimental data to help CERN scientists work out how antimatter interacts with gravity.  (See here for further details on this application or here to measure antimatter.)

The Webfest is a testament to what can be achieved with enthusiasm, creativity, teamwork and caffeine. The teams produced twelve sophisticated scientific applications which have undoubtedly enriched the online scientific environment.

The Crowdcrafting.org antimatter application team.

This post focuses on the social aspects of life on the CERN Student Summer Programme. Gathering hundreds of 20-somethings from around the globe and plonking them in Switzerland is inevitably going to lead to some shenanigans – right?

CERN has approximately 10,000 people on site each day and a plethora of clubs and societies to cater for their wide ranging interests – from amateur radio to Zumba.  The students are also proactive in setting up their own clubs and sharing their special interests. We’ve had student-led salsa, acroyoga, Balfolk dancing, French and Spanish lessons running throughout the programme.  I’ve even taught a bit of Capoeira.

At the epicentre of a CERN summer student’s social life are the parties in the Pump Room – a large multi-function room on the Meyrin site. The loud techno music, strobe-lighting, cheap booze and lads dancing topless on a table to YMCA makes the parties feel like the illegitimate lovechild of a German rave and American frat party.  The students love’em though.

Physicists in their spare time.

If you’re into live music then there’s lots to keep you entertained. The Montreax Jazz Festival runs through most of July and attracts some big acts. There are also loads of smaller festivals close by which students come back from looking bleary-eyed on a Monday morning. The Fete du Geneve turns Geneva into party central and concludes with a firework display of epic proportions while the Lake Parade in July is Geneva’s answer to the Rio carnival – although my mate Bruno from Rio wasn’t so impressed.

If the great outdoors is more your thing then Geneva is well situated. The Jura mountain range (from which we get the word ‘Jurassic’) are within cycling distance. I’ve had a few great days hiking in the Jura. If you’re feeling slightly more adventurous then you can hop on a bus to the French Alps to tackle some high peaks including Mont Blanc. There’s also white water rafting, bungee jumping and downhill mountain biking nearby for the adrenalin junkies.

Jura a bunch of eejits – summies frollicking in the hills.

Lots of the students, particularly the non-Europeans, take advantage of Geneva’s central location to see some of Europe with Paris, Nice and Zurich being popular destinations. Closer to home the Swiss towns of Lausanne and Gruyere are popular destinations for a dose of Swiss culture and fondue.

One of my favourite activities has undoubtedly been chilling out at Lake Geneva. You can have a swim, drink a beer and (beautiful) people watch. Then stay put at Perle du Lac to catch a free outdoor film – I saw ‘Shaun of the Dead’ which was accompanied by an obligatory zombie invasion.

However, the undeniable best entertainment to be found in Geneva is in Charly O’Neils Irish Bar on a Thursday night where my mate Cian’s traditional Irish band -The Emigrants – busts out the jigs and reels. Slainte!

The mighty Emigrants.

This article was also published on CERN’s website on 8.8.13.

3D model of particle tracks.

Does antimatter fall up or down?

The AEgIS experiment at CERN needs your help to analyse experimental results to figure out how antimatter is affected by gravity. Just join the dots to reconstruct particle tracks and your contribution could be included in an upcoming scientific publication.

The aim of AEgIS is to measure the effect of the Earth’s gravitational acceleration on antihydrogen. Seeing a different behavior for antimatter than for matter would be a huge surprise, and would indicate that gravity is much more complicated than our present understanding indicates.

In the AEgIS experiment, antihydrogen atoms are made to fly horizontally, dropping by a tiny amount, before colliding with matter. On collision the antihydrogen and matter annihilate, producing a burst of mostly pions and some other particles. These particles then travel through an emulsion containing silver bromide developed by the University of Bern in Switzerland that makes their tracks visible. Tracing these tracks to their point of origin tells the AEgIS team exactly where each annihilation occurred, which in turn allows them to calculate how far each particle travels, and how far the particle’s path drops. From the distance the particles fly and fall the AEGIS team hope to calculate the effect of gravity on antimatter.

AEgIS needs your help to map the paths that particles take through the emulsion. As part of the CERN Summer Webfest some of this year’s summer students have created a web application to map particle tracks. All you have to do is join the dots!

“In principle, tracking could be digitized, but computers can miss tracks that are related, but far apart,” says AEgIS spokesperson Michael Doser, who, inspired by astronomy websites such as Astrowatch and Galaxy Zoo, decided to crowdsource the analysis. “I’m using human pattern recognition – we’re pretty good at seeing things that belong together.”

First test data from AEgIS have been uploaded to the web application directly and have never been analysed before. So you can make a genuine contribution to CERN’s research. The data you provide will be openly available and help physicists at CERN with their analysis of the experiment. The results will be visualized on this page as a 3D Model.

The experiment requires about 1000 antihydrogen annihilations for a statistically significant observation, says Doser, but he hopes to have anywhere from 10,000 to 100,000 particle tracks analysed to check AEgIS’s algorithms for even tiny biases.

“Algorithms are not curious,” says Doser. “If we had something unexpected, a computer may not see it. But humans are open to new ways of looking at things. And besides, it’s fun!”

Epilepsy warning: The particle tracks contain rapidly flashing screens. If you are epileptic, perhaps best to skip this bit.

Analyse AEgIS data now!

It’s just another average day on the CERN student summer programme. I attend lectures, have lunch with the crew and cycle across to Prévessin in glorious sunlight. I sweatily open the door to my office and to my surprise am confronted by four grinning Aussies – “G’day mate”.

You’ve already met my summie office mate Josh. Roger is Josh’s professor from Melbourne University. Mark is a director from the Australian Synchrotron outside Melbourne. And Tom was a summer student last year and will be here to work for a few weeks.

Tom – takes laboratory safety seriously.

The Aussies have descended as they collaborate with CERN on developing beam position monitoring systems for both the Large Hadron Collider (LHC) and the Australian Synchrotron.

The banter flows freely and I am invited along to dinner.

Now there are many fine eating establishments in Geneva but I was pleasantly surprised to arrive at a grill next to CERN where the waiters bring out raw meat on a plate to barbecue yourself at the table. I should have known…

Interestingly Roger and Mark have travelled to CERN with Chris Henschke, a Melbournian artist who was previously in residence at the Australian Synchrotron. During his visit he meets up with CERN’s resident artist Bill Fontana. Bill does some fascinating work on the sounds of the LHC and is yet to reveal his centrepiece sculpture – “Acoustic Time Travel”.

It’s a great evening. There are some Australian teachers across undertaking training at CERN so, along with the artists, physcists, some CERN big cheeses and an Irish fella, it makes for a colourful night.

The evening ends with an invite to visit the lads in Melbourne. Um – yes please!

It’s the 4th of July 2013 – Happy Higgsdependence Day! It is exactly one year since the observation of a ‘Higgs-like particle’ was announced at CERN in the auditorium in which I now sit.

I remember stealthily watching the live stream of the announcement at my office desk last year. If you had suggested to me then that one year later I would be working at CERN I would have told you (in a broad Northern Irish accent) to ‘catch yourself on’.

Peter meet François – Professors Higgs and Englert, who collaborated during the 1960s, meet for the first time on 4 July 2012. Notice the back of the room is filled with last years summer students who camped overnight for seats for the Higgs announcement.

This of course means that the summer lecture series has started in earnest with a gentle introduction to the ‘Particle World’ from Dr Tara Shears. I understand the content of the lecture so am feeling confident, comfortable and optimistic.

Until lecture series Day 2 when Dr James Wells hits us with his lectures on the Standard Model – our best model for explaining the interaction of fundamental particles.

James is an eminent theorist and is clearly at the top of his game. He poetically weaves an intricate mathematical web to explain the subtleties of the Standard Model using an area of mathematics known as Group Theory. I nod along knowingly with the other students but am feeling a bit bamboozled by all the tensors, boosts and Lagrangians.

Next up is the über cool Prof. Cranmer and his jazzy neon shoe laces to teach us all about statistics. (See my last post “Die – electronics, Die” on the importance of statistics at CERN.)

“And that’s the difference between a quark and a fork” – me telling Dr Wells all about the Standard Model.

My favourite lectures however are on physics beyond the Standard Model. The no-nonsense Italian Dr Gian Giudice gives the clearest descriptions of the Higgs, Supersymmetry and dark energy that I have come across, while quirky Professor Gia Dvali reassuringly concludes that black holes are different from elephants. Phew.

After each morning’s three lectures there is a half hour discussion session where the students interrogate the lecturers. While some students nip off for an early lunch I find these sessions often provide the best insight into the day’s topics.

So, set yourself a mad old goal for this time next year – it just might happen…

(You can view the lecture programme and speaker’s slides for this and previous year’s CERN Summer Student Lectures at http://summer-timetable.web.cern.ch/summer-timetable/.)

My first project as a CERN summer student was to assemble an electronic die. After a few hours of soldering and burnt fingers I produce this:

My creation

How does it work?

When you tap the die on a table a piezo sensor glued to the base ‘feels’ the impact and sends a small current through the printed circuit board and into a chip.

The chip converts the analog signal into a decimal value (for example a 1.24167 volt signal is converted to the number 1.24167) and reads the least significant decimal place to generate a random number. The LEDs then light up to show a number 1 to 6.

What’s the point?

Over the course of a week, and much to the annoyance of my office mates, I tap the die on my desk 1500 times, compile a data set of the numbers thrown and go about analysing whether the die is fair or biased.

What’s this got to do with CERN then? 

Well statistical analysis is key to what CERN does and the discovery of the Higgs is a pertinent example.

In the Large Hadron Collider a Higgs boson is produced by approximately 1 in every 10 million particle collisions. The boson then decays in a fraction of a microsecond while the other collisions produce an array of other particles.

To make the hunt even more tricky, scientists didn’t know the exact energy level at which the Higgs would be found so they had to collide particles at a variety of energy levels.

A graph showing the energy at which the Higgs was found.

So searching for the Higgs was like looking for a tiny needle in a massive haystack full of other needles where your needle exists for a minute fraction of a second and you don’t really know what it looks like.

Scientists therefore had to statistically analyse trillions of collisions to be sure that the small bump at 125GeV in the graph above was the signature of the Higgs and not just an unlikely random fluctuation.

Before announcing the discovery of a ‘Higgs-like particle’ in July 2012 scientists were 99.9999% sure they’d found their boson i.e. there was only a one in a million chance this was not the Higgs.

What’s that got to do with the die?

In figuring out whether the die was fair I produced a relatively large data sample then used statistical techniques to conclude with 95% confidence that any bias displayed wasn’t just a random fluke. So in a way the exercise was analogous to the search for the Higgs but on a much smaller scale.

Discover anything interesting?

After some intense number crunching, detailed analysis and complex modelling I concluded (drum roll please) – bet on the number 2.

It turned out my supervisor sabotaged my die. So the key lesson learned was – don’t dice with physicists.