CERN Special Supplement Winter 2014/15

Summer 2014

CERN special supplement Winter 2014/15

CERN special

An interview CERN Where’s with walkabout SUSY? John Ellis

page 4 page 8 page 16 CERN special supplement Winter 2014/15 WELCOME CONTENTS

Welcome to Fascination’s Ever wondered what it’s like inside CERN? Walk the corridors of the world’s most famous research facility for the special CERN supplement first time with our roving STFC explorer on page 10. Particle physics is the study of the fundamental particles The search for dark matter is on. Find out why it’s important of the Universe. It seeks to understand the fundamental on page 14. forces of nature at a basic level, so we can learn more about Can you tell your ATLAS from your CMS? Now’s your chance the world we live in. Often this knowledge is the basis of to swat up and learn more about CERN’s awesome science dramatic changes in technology, from the discovery of facilities with our ‘CERN: decoded’ feature on page 20. electricity to the invention of the World Wide Web. STFC If leading physicist John Ellis, Professor of Theoretical funds particle physics projects at home and in locations all Physics at CERN, could design and build a new science over the world. We also fund the UK’s membership to CERN, facility with a limited budget, what would he build? Find out the world’s largest and most famous centre for scientific on page 4. research in the field. We hope you enjoy this special edition. Join the In this one-off extra edition, we celebrate some of the conversations on Twitter using #UKatCERN. Please let us exciting developments the UK is involved with at CERN - know if there’s another subject you’d like to see us dedicate from the discovery of the elusive Higgs boson through to the another special edition to. search for supersymmetry – and why they’re so important. Best wishes, Your Fascination editorial team ABOUT US Our scientific research seeks to understand the Universe from the largest astronomical scales to the tiniest constituents of matter. Providing access to and managing a range of world-class research facilities, STFC delivers fundamental insight and scientific breakthroughs in areas ranging from particle and nuclear physics to space, laser and materials science. Through our UK operations and our involvement in major international collaborations, we generate outcomes that shape societies, strengthen economies, build industries, create jobs and transform lives. 20 Don’t miss an issue

Fascination is STFC’s quarterly in-house magazine. We also produce ad-hoc themed editions like this one throughout the year. To receive an electronic version straight into your inbox, please visit: www.stfc.ac.uk/fascination and subscribe. 4 An interview with John Ellis 10 CERN walkabout CONTACT US We’d love to hear what you think. 12 CERN news Tell us what you’d like to see in the next edition, or if you have any news or features ideas you’d like us to cover. Email: [email protected] 14 Delving into the dark Write: Fascination editor, Office B89, STFC, Daresbury Laboratory, Sci-Tech Daresbury, Daresbury, Cheshire, WA4 4AD 16 Where’s SUSY? www.stfc.ac.uk New horizons beckon for the Higgs boson Cover: Copyright STFC/Ben Gilliland 18 14 20 CERN: decoded

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What is exciting you most about your field at immediately. The discoveries we’re making today may the moment? not have an impact on our lives until 50 years’ time – like Maxwell’s electromagnetic theory, which now underpins “Right now we’re in a transition from understanding just An interview with the technology used in TVs and radio. Another example is the visible stuff in the universe to going far beyond that. We the theory of relativity and quantum mechanics; together know how the visible stuff, like stars, planets, etc, are made they predicted anti-particles, and these are used in - but we don’t understand dark matter, and we think this medical diagnosis. Particle physics has a huge influence could be how galaxies were formed. We know the Universe By Charlotte Houghton on our understanding of the Universe. Physicists do not John Ellis used to be much smaller and denser and that it’s expanding, yet know all the rule book, but we are trying to read the but how did the matter in the universe get born out of the instruction manual. We’re trying to figure out what the John Ellis CBE is a British-born theoretical primordial soup? Another deep problem that interests me Universe does and what to do with it. It may take some physicist, who is working on some of the is that we haven’t been able to combine our understanding time to revolutionise human life but it will revolutionise our most exciting discoveries with the Large of gravity and the theory of matter. We’re currently chasing understanding of the Universe now.” Hadron Collider at CERN. Currently Clerk the answer now.” What do you think the Higgs discovery and legacy has Maxwell Professor of Theoretical Physics You mentioned primordial soup - what exactly is it? at King’s College London, John’s CERN done for the world of science and particle physics? “Primordial soup was the state of the universe when it was activities have covered everything from “I think the Higgs boson has finally convinced us that we’re a fraction of second old, with particles running around but Division Leader for Theory to studies on the right track in our understanding and our work. This no larger structures.” for future particle accelerators. As well allows us to go on and answer bigger questions like, what’s as his inspiring research, John has also What’s your favourite physics theory and why? dark matter? How to unify fundamental forces? It gives us received a number of awards including; “Supersymmetry. So far it’s a confidence to go further.” the Mayhew Prize, the Maxwell Medal hypothesis, but it’s a beautiful What do you think the and Prize and the Paul Dirac Medal and and elegant hypothesis that I find it interesting tax payer gets back from Prize. We caught up with him to find out could solve our current large- scale science facilities more about his work at CERN and his problems. I really hope that one to talk to philosophers like CERN? love of science. day we find it. It could explain and I hope they find “Well you get new dark matter and it could also technologies, for example, combine gravity with the theory it interesting to talk the World Wide Web was John Ellis, CERN, King’s College London. Credit: Wikipedia, CC BY 2.0 of matter. It could be a biggie!” invented at CERN to enable With your interest in future to me, but I wouldn’t scientists around the world Nice to talk to you, John. You’re a theoretical particle You’ve mentioned in the past that your primary school opportunities for particle to work together. You also physicist - could you explain the term ‘theoretical headteacher was an Antarctic explorer. How did this want to be one accelerators at CERN, you get a lot of technologies that particle physics’ in laymen’s terms? influence your curiosity about the world we live in? Did think a lot about out what’s come out of CERN that can be this ignite your interest in science? “Physicists try to understand how the Universe works, on the horizon. So what’s next used in medicine, for example, particle physicists try to understand what the Universe is “My primary school head teacher played a part in getting for CERN? diagnosing and treating cancer. There’s also lots of highly- made out of. Some particle physicists do experiments and me interested in science, but what really turned me “In a few months we will restart the LHC (Large Hadron trained young people here at CERN that have a lot of skills, the theorists try to understand what the experiments have onto science was reading those popular science books Collider), and then we’ll be able to do experiments with and a lot of them don’t decide to stay in research science. found. They also predict some of the questions that could in the library. My other family members had no scientific double the energy and produce more collisions, which will So those high-level skills go out into industry and are of be asked in the future.” background so it was the library that really got me mean the experiments will be more powerful. The first run direct benefit to the economy.” interested in science. I hope the kids of today have access How did your career in science begin? of experiments on the LHC had tremendous impact and If you could design and build a new facility at CERN to a local library to read books.” we’re hoping to get a similar reaction the second time “It was around age 12 that I really started to become (with a limitless budget), what would it be? How has theoretical particle physics changed during round.” interested in science. I used to read lots of books from the “I would like to build another larger, circular tunnel, three your career, in particular looking at the popularity of local public library. I found the children’s fiction books Will the LHC make another discovery on the same or four times larger than the current tunnel. Improvements physics? very boring, so I used to read the science books - which magnitude as the Higgs? If so, what will this mean, and in technology would mean we would be able to collide I found very interesting - and that got me hooked! I did “In the 1960s, particle physics theories didn’t have will it influence everyday life? particles at much higher energies, which could allow us to maths and science at school and wanted to study these the same scope they do today. Back in those days, the “I don’t know whether another discovery will have the see further back in time to what the Universe was like and subjects further. I went on to do a degree in mathematical theories were complicated and it was difficult to interpret same importance. It may well do, but we need to be how it works. The circular tunnel is the most powerful ‘tool’ physics and then did my PhD in theoretical particle the experiments. However, in the 1970s, the experiments realistic. The Higgs boson discovery, or even if we discover we can use to understand the Universe.” physics at Cambridge.” starting finding evidence of some of the exciting new dark matter, is not going to revolutionise people’s lives theories that helped us understand what the Universe is made of and how it works.”

4 Science and Technology Facilities Council - Fascination Science and Technology Facilities Council - Fascination 5 CERN special supplement Winter 2014/15

Do you enjoy communicating science to the general public and what is your most effective method of doing this? “Certainly, I really like engaging with the general public. Often the most interesting and challenging thing for me is trying to answer their questions. Often their questions make me look at things in a different way. I have to come up with new ways to explain things and it’s useful for our work.” You have a reputation for wearing science t-shirts. If you designed your own t-shirt, what would it say? “Ahhhh, errrm, well I think I would like ‘I <3 susy.’” There are many pictures of your office on the CERN website and you seem to have a permanent resident in there, how long has the skeleton been in there with you and why’s she there? “The skeleton has been there for 5-8 years. She belonged to a young scientist at CERN when we were working together a few years back, I inherited the skeleton when he left and I’ve been looking after her ever since. It’s a reminder John Ellis, © Sadık Güleç | Dreamstime.com of what happens to people who think badly of supersymmetry.” What advice would you give to someone who has ambitions to work at CERN? If you could find an answer to a fundamental physics You’ve sat on a lot of non-particle physics science question that is yet to be answered, what would it be? panels, including the STFC science board. What interests “Whatever a person does, they need to make sure you most in other sciences? it’s what they want to do and they enjoy doing it. “I’d like to know if dark matter and supersymmetry are If you want to get into science and you enjoy it, right or wrong. If I was only allowed one answer, I’d have to “I’m interested in astronomy and cosmology. There’s lots then go for it! You should look around at different say I’d like to understand how our theory of gravity can be of interplay between these disciplines and particle physics websites and, if people still read nowadays, combined with our theory in trying to understand read books. There’s lots of good ones about the of matter, which is known the Universe. When other Universe. It will help them to better understand as string theory.” areas of science come up what we’re trying to do. It will make them more Physicists do not yet with new ideas I always You have been invited to interested and excited about science and find it interesting, and I philosophical festivals in particle physics.” John’s office at CERN. Credit: CERN know all the rule book, think it’s important that we the past, do you find this all share these ideas with Thanks for talking to us, John. area of science interesting but we are trying to read each other. For example, and why? the instruction manual I went to a lecture on “Yes, I have been to a few cold atoms a couple of philosophical festivals. I weeks ago and I think More information Careers at CERN: like to think outside the there’s many things that they could teach us. All of science Would you like to follow in John’s footsteps? Do you want to box: I think this is very important in our line of work. I think is interdependent and we should all talk to each other and To find out more about CERN’s work, work at CERN, home to the world’s largest science experiment? it’s very important to look at the facts and to build theories help each other.” visit the website: on the facts. I find it interesting to talk to philosophers and http://home.web.cern.ch/ Find out about the latest vacancies and placements at CERN on I hope they find it interesting to talk to me, but I wouldn’t #UKatCERN their website: http://jobs.web.cern.ch. want to be one.”

6 Science and Technology Facilities Council - Fascination Science and Technology Facilities Council - Fascination 7 CERN special supplement Winter 2014/15

Don’t forget your toothbrush Before reaching the hive of activity where the food, coffee and wine(!) is sold, I pass through the main foyer; which is more like a shopping centre than a laboratory. As I wonder CERN walkabout past the huge butterfly staircase I can see a bank, travel agents and post office; and as I get closer to the restaurant, CERN, the European Organisation for Nuclear Research, home to the a kiosk selling Switzerland memorabilia. And if you can’t find what you need amongst the red and white flags, shot Higgs boson. We’ve all heard about this wondrous place, but what is glasses and playing cards, you’ll definitely find it in the it really like to be there? Join our communications officer, Charlotte vending machines. Yes, you read correctly, the vending machines contained everything from snacks and drinks to Houghton, as she walks the corridors of CERN for the first time. toothbrushes and cleaning products.

The hive Chatter, in several languages, hits me like a wall of ATLAS art mural. Credit: CERN excitement as I enter the packed-out restaurant. Everyone from press officers, scientists, engineers and Nobel Prize The obligatory winners to PhD students grab their food fix here, and science selfie the place is alive with activity. Not only do people have As we reach the industrial-sized lift we all get ready, their food in here, they also have their meetings, Skype with our hard hats, for the 100m decent to the scientific colleagues in other countries and ponder their work over a world below. As we exit and make our way down a cup of tea or coffee, too. No wonder they get through 30kg brightly lit corridor, I can’t resist taking a science selfie to of coffee beans every day! I notice a distinctly international, commemorate the occasion! family-friendly feel to the place. This is also where the children from the nursery come to eat, and through the window of an adjoining room I see tiny tables and chairs brightly decorated with cartoons. Getting ready After lunch, the anticipation grows as I begin to make my way to the meeting point for the best part of the day; the tour. As CERN gears up for the Large Hadron Collider (LHC) start-up there’s people everywhere - some pulling huge cables, some typing ferociously on their laptops and others whizzing round with tables, boxes and odd-looking scientific instruments. They’re all extremely busy, but never too busy to say a jolly “hello” (or “bonjour”, as the case may be). Everyone is working towards one goal: ensuring the LHC is The Globe of Science and Innovation, the landmark of CERN. Credit: STFC in working order. During the period the LHC has been shutdown, staff working here at CERN have managed to upgrade Sitting on the tram, watching the huge wooden globe The thin black line the power from particle energies of 8 trillion electron-volts (teraelectronvolts or TeV) to 14TeV, meaning, when it’s of science and innovation drawing closer, the feeling of After receiving my visitor pass and an essential map, I set switched back on, scientists are able to gather data from excitement and anticipation grows. As the trams pulls to a off to negotiate the meandering corridors into the depths of the highest-energy collisions ever attempted. This is all very halt in the small, sheltered station on the public road that CERN. On the floor, I notice a thick black line that runs along exciting for everybody here and around the world. cuts through the CERN site, I sit there in awe of the sheer each of the corridors with me. After following it for a while, size and brilliance of the surrounding infrastructure. You I realise it’s there to lead people to what I soon discovered As we make our way to the building where we will go down can’t miss the long line of flags, one for each of the 21 is the hub of CERN - the restaurant. It’s only later on that I to see ATLAS, one of the LHC detectors, a huge painted wall member states and the Canton of Geneva, showcasing realised why this is so useful – if ever you get lost at CERN with an LHC instrument stands before us. the international greatness behind the gates I am about to (and there are plenty of rabbit holes you can wander down), walk through. you always have a guide.

Charlotte’s science selfie

8 Science and Technology Facilities Council - Fascination Science and Technology Facilities Council - Fascination 9 ATLAS art mural. Credit CERN ATLAS

Lego model of ATLAS. Credit: STFC

Meeting ATLAS The language of science When we reach the end of the corridor, Wherever you go at CERN, there are we finally reach the giant room where the always masses of people and lots of detector is housed. It’s huge! I peered over chatter. Possibly every language known the safety bar to get a proper look at this to man is spoken in this place, and many piece of engineering brilliance, and spotted people seemed to speak a language the occasional miniature-looking human referred to as CERNglish. CERNglish was walking around the detector, making sure explained to me as a language that starts kit is all in working order. Realising they’re in English, and ends in whatever language actually the same size as you, you begin to has the most appropriate word. Listening comprehend how big the ATLAS detector to how everyone speaks this new language really is. It’s a million times bigger than the of science makes you feel welcome and at Lego version, anyway. home. It also made me really want to learn a second language! Old meets new An inspirational place Walking around CERN, you get the distinct Trying to find my way around the giant feeling of old meets new. Some of its laboratory, there were a few occasions corridors are dark, with lots of wood, where I lost myself and had to find my posters from years gone by and a distinct way back to the thick, black line on smell of machinery, which are a massive the floor again. I make my way back to contrast to some of the ground-breaking the restaurant and take my seat on the discoveries happening here. I found myself science-themed tables, a Higgs boson strolling down some of the most dark, table to be exact. Everything around this dingy corridors located deep within the place is designed to be inspirational for depths of CERN, and it’s here, amongst the people who work here: the buildings, all the old paraphernalia, that I saw the the kit, the machines. Even the Coca Cola birthplace of the World Wide Web. The bottles. As I get ready to wrap up my day, biggest and most influential invention of I stroll happy out of the main entrance, our generation, that changed our lives through the gift shop where I purchase a forever, was invented by Tim Berners-Lee, CERN pen, and onto the tram stop. I notice Tour the LHC for yourself a Brit, on this very corridor. Although it’s I’m leaving with happy feelings and a true In 2015, our touring LHC roadshow will be visiting locations up and down the country. a very ordinary looking corridor, I feel like sense of international collaboration. As • Go inside our replica LHC cavern I’m somewhere special. I reflect on the fact that STFC funds the • Find out more about neutrino observatories UK’s membership to this amazing place, I • Have a go on a cosmic ray detector understand for the first time how valuable • See the inner workings of the dipole this is. No one scientist or one nation owns • Find out all you need to know about CERN the work that goes on here - we’re all in Keep your eye on our website to find out where you can see it! it together!

10 Science and Technology Facilities Council - Fascination CERN special supplement Winter 2014/15 The latest UK news from CERN A window to another world A new scientific collaboration is getting underway, and one of its #UKatCERN first meetings was held at CERN. The experiment itself, the Long Baseline Neutrino Facility (LBNF), will be split across two sites in USA, but like CERN, it will be a thoroughly international affair, and Calibrating ALICE and LHCb the UK is already involved. LBNF is going to investigate whether neutrinos Sanford Laboratory in the former Homestake Mine in The LHC won’t start operating until Spring 2015, but two exhibit CP violation, the subtle difference between South Dakota. The beam will travel through rock up matter and antimatter that has led to us living in a to 30km below the surface. experiments have already captured their first data. Universe made of matter. Weak CP violation has been “Eventually the detector will comprise approximately observed in quarks, most notably using the LHCb 40 kilotonnes (40,000 tonnes) of liquid Argon cooled experiment – but the effect is not considered to be to -184°C,” says Stefan, “but it will be installed as sufficient to explain the asymmetry between matter modules, with the first of those installed and ready to and antimatter. detect the neutrino beam in 2021. If everything goes “We don’t know whether neutrinos also show to plan, we should have our first results two years CP violation,” says Stefan Soldner-Rembold later.” (Manchester), one of the UK members of the The fact that LBNF could be operational so quickly international board responsible for bringing the new is attributed to two separate project proposals, one collaboration together, “but neutrino physics is the in Europe and the other in the US, which had similar sector of particle physics where the most unexpected goals and methodologies. Bringing the R&D work for effects [such as oscillations] and first deviations both projects together, along with the engineering from the Standard Model have been found. They are and scientific expertise, has created an even stronger very strange particles - neutral and light - and lots collaboration for LBNF. More than 100 institutes Excitement in the LHCb control room of researchers believe that they offer a window into around the world are involved, including CERN and – Collaboration Spokesperson Guy physics beyond the Standard Model.” Wilkinson (Oxford) along with 10 groups from the UK. In particular, the UK is leading the shift leader, run coordinator and This ‘other worldliness’ leads Stefan and his development of technology for the Liquid Argon sub-detector experts, keeps a close international collaborators to believe that they will Time Projection Chambers (LArTPCs), novel detectors eye on the data acquisition computer screens. Credit: CERN/LHCb find CP violation in neutrinos. Their plan is to send designed to have exceptional neutrino detection a beam of neutrinos 1300km from Fermilab near efficiency and background capabilities. Chicago to a detector deep underground in the In December, as part of the preparations for restarting the allowed LHCb and ALICE to do some useful calibrations. LBNF will be launched officially in January 2015. LHC, accelerator operators tested the transfer lines between The precise timing of each beam dump allowed the the Super Proton Synchrotron (SPS) and LHC. The tests were experiments to tune their detectors and triggers to the used to check the control systems, beam instrumentation LHC clock. In LHCb, the data will also be used to check the and transfer line alignment. The team also performed alignment of the different sub-detectors with respect to the first optics measurements and examined the beam each other. This was the first time that the transfer lines had trajectory. seen beams in more than a year, and the first opportunity Subscribe to UK News from CERN to test the LHC’s operation system. The LHC operators Although a 21.6 tonne beam dump made of graphite, successfully commissioned the LHC’s injection and ejection aluminium and copper absorbed the accelerated particles UK News from CERN (UKNFC) is a fortnightly newsletter you’d like to become a CERN supplier, UKNFC brings magnets, all without beam in the machine itself – an and prevented the SPS protons from entering the LHC, for anyone with an interest in CERN. Whether you’re you the latest news and opportunities. important milestone in the preparations for the restart of secondary muons produced by the beam hitting the stopper interested in science and technology, the career the LHC in 2015. opportunities for students, teachers and researchers or Read UKNFC and subscribe at: www.stfc.ac.uk/2596

12 Science and Technology Facilities Council - Fascination Science and Technology Facilities Council - Fascination 13 CERN special supplement Winter 2014/15 Delving into the dark Here’s a surprising and perhaps shocking statistic: normal matter makes up just 5% of the Universe. Accounting for the other 95% is much more of a challenge and means wrestling with two major cosmic mysteries: ‘dark matter’ and ‘dark energy’. But shedding light on these curious phenomena is vital to answering some big questions about how the Universe works – and what the future may have in store for it.

The dark matter mystery strewn pretty evenly throughout the cosmos, it’s so hard It’s never been seen. We don’t know what it consists to detect because it’s only present at very low densities. of, although super-particles predicted by the theory of In our own Solar System, for instance, there may be just ‘supersymmetry’ are a possible candidate (see ‘Where’s a few tonnes in total between the Sun and the orbit of SUSY?’, p.16). As it doesn’t emit or reflect light, its most Neptune, the outermost planet. obvious feature is invisibility. Yet scientists generally Recently, some cosmologists have even suggested that agree that dark matter accounts for around a quarter of dark matter might be slowly turning into dark energy, the cosmos. potentially hastening the point when the Universe will So why such confidence? One clue to dark matter’s ‘die’ in the sense of becoming virtually empty of matter. existence emerged when astronomers tried to explain But as that probably wouldn’t happen for 100 billion why galaxies rotating at hundreds of thousands of miles years or so, the human race arguably has more pressing an hour don’t hurl their stars out into space. Clearly priorities to worry about. something holds galaxies together and it’s not just the gravity produced by visible matter. There’s simply not Science turns detective enough of it. The solution seems to be that a completely When considering dark matter and dark energy, then, different type of matter is also present – a type that can’t there are more questions than answers. A big step forward be seen. And indirect evidence for this dark matter has would be to pinpoint exactly what they are. Efforts to continued to stack up. Looking into deep space, we can detect dark matter arriving from space are especially see its influence almost everywhere – from ensuring advanced, although yet to identify a signal. Techniques that the edges of spiral galaxies rotate at virtually the generally fall into two categories: ‘indirect detection’ same speed as their centres, to explaining why light from where dark matter particles colliding with each other galaxies billions of light years away ‘bends’ as it travels would give themselves away by producing gamma rays, towards us. for example; and ‘direct detection’ where dark matter particles striking atomic nucleuses would make them The dark energy enigma recoil, similar to the way snooker balls recoil when they But things get even murkier when we turn to dark energy, hit one another. widely believed to make up a staggering 70% of the Located in Switzerland, the Large Hadron Collider (LHC) at Universe. The concept was put forward in response to a CERN (the European Organization for Nuclear Research) key 1990s discovery based on observations of exploding is taking a different approach. With its recent two-year stars in far-off galaxies. These observations showed that shutdown providing the perfect opportunity to boost its the expansion of the Universe is actually accelerating awesome capabilities, this unique particle accelerator rather than slowing down as might be expected. To will in future produce higher-energy proton collisions that account for this, it’s thought that an as yet undiscovered could actually generate dark matter here on Earth. It may type of energy permeates space and counteracts gravity, even be that the LHC could establish a kind of production which would otherwise slow cosmic expansion down. line where protons routinely turn into dark matter Credit: STFC/Ben Gilliland Where dark energy is concerned, however, we’re firmly in particles for further study – helping to dispel a little of the realm of the theoretical – and of complex theories, at the darkness that still surrounds our understanding of this that. What exactly is it? How precisely does it function? extraordinary Universe. We simply don’t know. It may be that, while dark energy is

14 Science and Technology Facilities Council - Fascination Science and Technology Facilities Council - Fascination 15 CERN special supplement Winter 2014/15 Where’s SUSY? Supersymmetry or ‘SUSY’ is one Exhibit ‘A’ Of course, CERN is a global powerhouse of particle physics But perhaps the ‘failure’ of the search for SUSY is simply and home to countless ‘expert witnesses’ with world- of the most ingenious theories a question of energy. Attention is now turning to the LHC. leading knowledge. So it’s perhaps instructive that some of Located at CERN (the European Organization for Nuclear its very best brains have made a small bet on the subject ever devised by particle physicists. Research) in Switzerland and housed in an underground of supersymmetry, with a bottle of cognac reputedly riding tunnel 17 miles in circumference, the most powerful on the outcome. The issue is whether at least one type Potentially, it could plug some particle accelerator ever built has been undergoing a major of super-particle will be discovered by noon on 16th June revamp since February 2013. When it comes back to life in 2016. The number saying ‘yes’ is more or less matched by troubling gaps and glitches in our 2015, it will generate substantially higher-energy proton the number saying ‘no’, with a number of abstentions and at understanding of the Universe. beams than it did before. This could be the long-awaited least one expert apparently sitting squarely on the fence and game-changer, with the proton collisions created by the plumping for ‘yes and no’! But there’s no hard evidence that new, improved LHC finally delivering proof of super- Within the particle physics community, then, the jury’s still particles’ existence – the experimental equivalent of very much out on SUSY. But what’s your verdict? supersymmetry actually exists Exhibit ‘A’. – and even the experts are split on the issue. So can SUSY really come to the rescue? We invite you to be the judge…

The facts of the matter The case for It’s a complicated topic, so let’s distil it down to the SUSY’s key attraction is that the existence of the essentials. Over the last century or so, our view of the super-particles it predicts could help eliminate many of subatomic world has advanced enormously. We know that those niggling discrepancies in our current view of the tiny elementary particles such as quarks and electrons are cosmos. Super-particles may help to account for dark the building blocks of matter. We know that photons and matter, for instance. Just as importantly, if proven, the other ‘gauge bosons’ do the vital job of transmitting forces theory would unify matter particles and force carriers, and that hold matter together. And since its much-publicised mathematically bind together some of the key forces that discovery at the Large Hadron Collider (LHC) back in 2012, shape nature. In short, everything would become much we can now add to the list the famous Higgs boson – a force neater, tidier and more comprehensible. Supersymmetry carrier that helps explain why matter has mass. clearly has the potential to provide a deeper, fuller understanding of the foundations of the Universe, enabling But the picture is far from complete. To take just one particle physics to take a huge step forward. example, the nature of the baffling ‘dark matter’ that’s believed to account for 25% of the Universe remains a The case against mystery (see ‘Delving into the dark’, p.14). Add SUSY to the The theory of supersymmetry has been around for nearly mix, however, and a lot of the headaches could disappear. half a century. So if SUSY’s real, why is there absolutely The basic idea is this: every type of subatomic particle that no firm evidence for it? To date, not one experiment has we currently know about has an undiscovered super-particle been able to prove that super-particles exist anywhere as its ‘twin’. These super-particles include the squark beyond the world of the imagination. If evidence continues which partners the quark, the selectron which partners the to remain elusive, it could soon be time to call off the electron, the Higgsino which partners the Higgs boson, and search and rethink the whole theory of supersymmetry – so on. However, these twins differ from their ‘conventional’ or perhaps look for different solutions altogether. Where partners in some key respects, such as their greater mass. science is concerned, being neat and tidy is unfortunately no guarantee of truth. Credit: STFC/Ben Gilliland

16 Science and Technology Facilities Council - Fascination Science and Technology Facilities Council - Fascination 17 New horizons beckon for the Higgs boson

The long-awaited discovery of the Higgs boson happened in 2012 – but what have we learned? And what happens next?

4 July 2012 was a day to go down in the history of – produced data used to prove the Higgs boson’s existence What are all the possible final states that it decays into? science. Before the eyes of the world, Rolf-Dieter Heuer, as it disintegrated into other bosons. Since then, ATLAS How exactly does it couple to other particles? Are there Director-General of the European Organization for and CMS have gathered evidence that the Higgs can decay more types of Higgs bosons to be discovered? Above Nuclear Research (CERN), announced the discovery of the into fermions too (fermions and bosons being the two key all, what are the full implications of the Higgs and its Higgs boson. It was the long-awaited confirmation that, classes of particles in quantum mechanics). properties for the Standard Model of particle physics after a search lasting nearly five decades – an inspiring and the theoretical explanation this model puts forward In fact, by the end of its first three-year running period, and relentless quest that stretched imaginations and regarding the interactions between subatomic particles? the LHC had produced an impressive 14,000 Higgs bosons tested convictions across the global particle physics for study. But the second run due to start in 2015, with its Unravelling the mysteries of the Higgs and penetrating community – the previously unseen particle first predicted higher-energy proton beams and higher rate of collisions, its opaque world won’t just help us understand why the in the 1960s had finally come to light. is expected to produce up to ten times more. Throw in Universe is as it is now. It’s like taking a time machine But discovery is never the end of a journey. In this case, a range of new equipment, more computing power and back to when the cosmos was in its infancy – just after it was just the prelude to intensive efforts to study the smarter algorithms to make sense of the data generated the Big Bang created everything in an explosion of precocious new kid on the subatomic block. We may have – and the result will be a substantial improvement in our unimaginable intensity, an event whose fall-out is still a basic understanding of the Higgs – the crucial particle ability to probe the particle’s properties. evident in a background ‘hiss’ of microwave radiation. that helps explain how infinitely small particles can still This can give us a glimpse of when the Higgs field first So what exactly is our current state of knowledge about a have finite mass. Now, though, the focus is on finding out appeared, and helped to shape the Universe we know particle that provides vital evidence for the existence of a much more about the only subatomic particle that can today. ‘Brout-Englert-Higgs field’ giving matter mass and enabling justifiably claim global ‘celebrity’ status. it to form into atoms? We know how much the particle Seen in these terms, the painstaking process of more The Higgs boson takes its name from Professor Peter weighs – 125.36 (plus or minus 0.41) gigaelectronvolts, detailed observation and more precise measurement – Higgs of Edinburgh University, one of six scientists who or around 130 times more than a proton. We have a good and the relentless drive towards further enlightenment predicted its existence half a century ago. But the star idea of how long it ‘lives’ before it decays away – around – is every bit as important as that remarkable discovery in the drama of its eventual discovery was CERN’s Large a tenth of a billion-trillionth (10-22) of a second – and announced back in July 2012. Hadron Collider (LHC), with UK researchers prominently we’ve started to explore those decay patterns. But more involved. Deep down in its 27 km tunnel spanning the precise measurements of its lifespan are needed, as well Franco-Swiss border, high-energy beams of protons as answers to a raft of questions. Exactly how many crashed together and two experiments – ATLAS and CMS collisions at the LHC does it take to produce a Higgs?

18 Science and Technology Facilities Council - Fascination Science and Technology Facilities Council - Fascination 19 CERN special supplement Winter 2014/15 CERN: decoded What’s the difference between ATLAS and ALICE? What does LHCb stand for? Find out as we explain CERN’s amazing facilities and what they do.

CMS ATLAS

What is CMS? How does it work? What is ATLAS? ATLAS is large, but very lightweight. In fact, if you put ATLAS in water, it would float. CMS (Compact Muon Solenoid) is one of the four main The CMS detector is built around a huge solenoid magnet. ATLAS is one of the four main experiments at the Large experiments at the Large Hadron Collider at CERN. This takes the form of a cylindrical coil of superconducting Hadron Collider at CERN. As mentioned in the CMS ATLAS records sets of measurements on the particles Compared with its sister experiment, ATLAS, CMS is the cable that generates a field of 4 tesla (about 100,000 description, the two are looking for the same thing created in collisions - their motion, energies, and their ‘little one’ which is why its name begins with the word times the magnetic field of the Earth). The field is confined (supersymmetry, extra dimensions and dark matter), but use characteristics. This is done by six different detecting ‘compact’. by a steel ‘yoke’ that forms the bulk of the detector’s different technical approaches. subsystems that identify particles and measure their 12,500-tonne weight. momentum and energy. CMS, like ATLAS, is a general purpose detector designed How does it work? to investigate a wide range of physics including Unlike the other LHC experiments, CMS was constructed ATLAS has the largest volume of any collider detector ever The main feature of ATLAS is its enormous magnet system; supersymmetry, extra dimensions and particles that could in 15 sections at ground level. Each section was lowered constructed. It was built in a cavern, 100m below ground eight 25m long superconducting magnet coils forming a make up dark matter. 100m into the underground cavern near Cessy in France near the village of Meyrin in Switzerland. cylinder around the beam pipe at the heart of the detector. and reassembled. The detector can be opened to allow The scientific goals for the two experiments are the The magnets bend the paths of charged particles to measure maintenance and upgrade. same, but they use different technical solutions. These their momentum. similar science goals, but different designs allow the two experiments to cross-check results and confirm exciting discoveries such as a Higgs boson.

About the detector About the detector Size 21m long, 15 m high and 15 Size 46 metres long, 25 metres m wide in diameter Weight 12500 tonnes Weight 7,000 tonnes Design Barrel plus endcaps Design Barrel plus endcaps About the people About the people Collaboration 3820 people including Collaboration More than 3000 physicists, physicists engineers, engineers, technicians and technicians, students and support staff support staff Number of institutes 174 Number of institutes 182 Number of countries 38 Number of countries 42 Number of UK institutes 16 Number of UK institutes 5

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ALICE LHCb

What is ALICE? How does it work? What is LHCb? How does it work? ALICE (A Large Ion Collider Experiment) is one of the four For one month each year, the LHC accelerates two beams of LHCb (Large Hadron Collider beauty) is one of the four main LHCb studies the decay of particles containing b and main experiments at the Large Hadron Collider at CERN. highly charged lead ions – lead atoms stripped of all 82 of experiments at the Large Hadron Collider at CERN LHCb was anti-b quarks, collectively known as ‘B mesons’. Physicists ALICE was built in a cavern 100m below ground near St their electrons. When they collide, the beams of ions create built in a cavern 100m below ground near Ferney-Voltaire in think that by comparing these decays, they may be able Genis-Pouilly in France. sub-atomic fireballs in the heart of the ALICE experiment. France. to gain useful clues as to why nature prefers matter over Measurements show that the resulting temperatures and antimatter. ALICE is a heavy-ion detector designed to investigate the One of the most fundamental questions is: ‘why is our densities are the highest ever created on Earth. A sugar properties of the strong force that keeps particles inside the Universe made of matter’? It is widely thought that initially Rather than flying out in all directions, B mesons formed by - lump sized piece of this primordial soup of quark-gluon atomic nucleus together, and how this energy generates equal amounts of matter and antimatter were created, and the colliding proton beams (and the particles they decay plasma would weigh 40 billion tonnes! mass. It is the force that we know least about. currently there is no evidence opposing this. Experimental into) stay close to the line of the beam pipe, and this is By measuring the lead ion collisions and comparing these measurements and theoretical calculations hint that almost reflected in the design of the LHCb detector. Quantum Chronodynamics (QCD) theory goes some way to results to proton-proton and proton-lead ion collisions, all matter and antimatter would have annihilated each other to explain how the Strong Force works but it leaves a lot Unlike ALICE, ATLAS and CMS which each surround the ALICE is already increasing our understanding of the leaving behind a residual amount of matter to form our of questions unanswered. For example, free quarks do not entire collision point with layers of sub-detectors, like an Strong Force. Universe. The mechanism that would have favoured matter exist in nature, but QCD predicts that they do at the kinds of onion, the LHCb detector stretches for 20 metres along the against antimatter is called CP violation. LHCb investigates temperatures and densities that were present at the start of beam pipe, with its sub-detectors stacked behind each other the subtle differences between matter and antimatter. the Universe. like books on a shelf. Although absent from the Universe today, particles known ALICE recreates conditions that existed only 0.00001 Each one of LHCb’s sub-detectors specializes in measuring a as ‘beauty (b) quarks’ were common in the aftermath of seconds after the Big Bang; temperatures 300,000 times different characteristic of the particles produced by colliding the Big Bang, and are generated in their billions by the hotter than the Sun and densities 50 times greater than in protons. Collectively, the detector’s components gather LHC, along with their antimatter counterparts, anti-beauty the core of a neutron star. information about the identity, trajectory, momentum quarks. That explains why the word ‘beauty’ crops up in and energy of each particle generated, and can single out LHCb’s name – it’s not just a pretty facility! individual particles from the billions that spray out from the collision point.

About the detector About the detector Size 26m long, 16m in diameter Size 21 m long, 10 m high, 13m Weight 10,000 tonnes wide Design Central barrel with a Weight 5600 tonnes single arm forward muon Design Forward spectrometer with spectrometer planar detectors About the people About the people Collaboration More than 1500 physicists, Collaboration 920 physicists, engineers, engineers technicians, technicians, students and students and support staff support staff Number of institutes 154 Number of institutes 65 Number of countries 37 Number of countries 17 Number of UK institutes 3 Number of UK institutes 11

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