Tag Archives: Harry Cliff

Join our #smCollider Twitter Tour

Update: The Collider Twitter tour can now be seen below.

With just two weeks before our Collider exhibition closes, curator Harry Cliff will be inviting you to step inside the world’s greatest experiment as he takes you on an exclusive twitter tour of the exhibition on Thursday 17 April at 4.30pm (BST).

Curator Dr Harry Cliff in the Collider exhibition.

Curator Dr Harry Cliff in the Collider exhibition. Credit: Science Museum

Harry (who also works on the LHCb experiment at CERN) will live tweet his tour of the exhibition, sharing key objects used at CERN and explaining some of the science behind particle physics.

You can join the tour by following @sciencemuseum on Twitter at 4.30pm (BST) and by using #smCollider to ask any questions.

If you miss the tour (or don’t use Twitter) don’t worry, as we’ll be sharing the tour here on the blog. For more on particle physics and the fascinating work of CERN and our Collider exhibition read the Collider blog or watch our behind the scenes videos.

 

Collider runs at the Science Museum until 5 May 2014 (tickets can be booked here). The exhibition will then open at the Museum of Science and Industry in Manchester from May 23 – September 28 2014 (tickets available soon here).

The last particle?

Could the Higgs be the end of particle physics? We’re still a long way from answering one of the biggest questions of all, says Dr Harry Cliff, Head of Content on our Collider exhibition.

The 2013 Nobel Prize in Physics has been awarded to François Englert and Peter Higgs for their work that explains why subatomic particles have mass. They predicted the existence of the Higgs boson, a fundamental particle, which was confirmed last year by experiments conducted at CERN’s Large Hadron Collider.

But today’s celebrations mask a growing anxiety among physicists. The discovery of the Higgs boson is an undoubted triumph, but many note that it hasn’t brought us any closer to answering some of the most troubling problems in fundamental science.

A senior physicist went so far as to tell me that he was “totally unexcited by the discovery of the Higgs boson”. Though not the typical reaction, this discovery threatens to close a chapter of 20th century physics without a hint of how to start writing the next page.

Until July last year, when physicists at the Large Hadron Collider (LHC) announced its discovery, the Higgs boson remained the last missing piece of the Standard Model of particle physics, a theory that describes all the particles that make up the world we live in with stunning accuracy. The Standard Model has passed every experimental test thrown at it with flying colours, and yet has some rather embarrassing holes.

According to astronomical measurements, the matter described by the Standard Model that makes up the stars, planets and ultimately us, only accounts for a tiny fraction of the universe. We appear to be a thin layer of froth, floating on top of an invisible ocean of dark matter and dark energy, about which we know almost nothing.

Worse still, according to the Standard Model, we shouldn’t exist at all. The theory predicts that, after the Big Bang, equal quantities of matter and antimatter should have obliterated each other, leaving an empty universe.

Both of these are good scientific reasons to doubt that the Standard Model is the end of the story when it comes to the laws of physics. But there is another, aesthetic principle that has led many physicists to doubt its completeness – the principle of “naturalness”.

The Standard Model is regarded as a highly “unnatural” theory. Aside from having a large number of different particles and forces, many of which seem surplus to requirement, it is also very precariously balanced. If you change any of the 20+ numbers that have to be put into the theory even a little, you rapidly find yourself living in a universe without atoms. This spooky fine-tuning worries many physicists, leaving the universe looking as though it has been set up in just the right way for life to exist.

The Higgs’s boson provides us with one of the worst cases of unnatural fine-tuning. A surprising discovery of the 20th century was the realisation that empty space is far from empty. The vacuum is, in fact, a broiling soup of invisible “virtual” particles, constantly popping in and out of existence.

The conventional wisdom states that as the Higgs boson passes through the vacuum it interacts with this soup of virtual particles and this interaction drives its mass to an absolutely enormous value – potentially up to a hundred million billion times larger than the one measured at the LHC.

Theorists have attempted to tame the unruly Higgs mass by proposing extensions of the Standard Model. The most popular of which is “supersymmetry”, which introduces a heavier super-particle or “sparticle” for every particle in the Standard Model. These sparticles cancel out the effect of the virtual particles in the vacuum, reducing the Higgs mass to a reasonable value and eliminating the need for any unpleasant fine-tuning.

Supersymmetry has other features that have made it popular with physicists. Perhaps its best selling point is that one of these sparticles provides a neat explanation for the mysterious dark matter that makes up about a quarter of the universe.

Although discovering the Higgs boson may have been put forward as the main reason for building the 27km Large Hadron Collider (LHC), what most physicists have really been waiting for is a sign of something new. As Higgs himself said shortly after the discovery last year, “[The Higgs boson] is not the most interesting thing that the LHC is looking for”.

So far however, the LHC has turned up nothing.

If supersymmetry is really responsible for keeping the Higgs boson’s mass low, then sparticles should show up at energies not much higher than where the LHC found the Higgs. The fact that nothing has been found has already ruled out many popular forms of supersymmetry.

This has led some theorists to abandon naturalness altogether. One relatively new idea known as “split-supersymmetry” accepts fine-tuning in the Higgs mass, but keeps the other nice features of supersymmetry, like a dark matter particle.

This may sound like a technical difference, but the implications for the nature of our universe are profound. The argument is that we live in a fine-tuned universe because it happens to be one among an effectively infinite number of different universes, each with different laws of physics. The constants of nature are what they are because if they were different atoms could not form, and hence we wouldn’t be around to wonder about them.

This anthropic argument is in part motivated by developments in string theory, a potential “theory of everything”, for which there are a vast number (roughly 10500) different possible universes with different laws of physics. (This huge number of universes is often used as a criticism of string theory, sometimes derided as a “theory of everything else” as no one has so far found a solution that corresponds to the universe we live in.) However, if split-supersymmetry is right, the lack of new physics at the LHC could be indirect evidence for the existence of the very multiverse anticipated by string theory.

All of this could be rather bad news for the LHC. If the battle for naturalness is lost, then there is no reason why new particles must appear in the next few years. Some physicists are campaigning for an even larger collider, four times longer and seven times more powerful than the LHC.

This monster collider could be used to settle the question once and for all, but it’s hard to imagine that such a machine will get the go ahead, especially if the LHC fails to find anything beyond the Higgs.

We are at a critical juncture in particle physics. Perhaps after it restarts the LHC in 2015, it will uncover new particles, naturalness will survive and particle physicists will stay in business. There are reasons to be optimistic. After all, we know that there must be something new that explains dark matter, and there remains a good chance that the LHC will find it.

But perhaps, just perhaps, the LHC will find nothing. The Higgs boson could be particle physics’ swansong, the last particle of the accelerator age. Though a worrying possibility for experimentalists, such a result could lead to a profound shift in our understanding of the universe, and our place in it.

Discover more about the Higgs boson and the world’s largest science experiment in our new exhibition, Collider, opening on 13th November 2013.

This article first appeared on The Conversation.

Standard Model Stands Firm

Dr. Harry Cliff, a Physicist working on the LHCb experiment and the first Science Museum Fellow of Modern Science, writes about a recent discovery at CERN. A new Collider exhibition opens in November 2013, taking a behind-the-scenes look at the famous particle physics laboratory. 

On Friday afternoon, at the EPS conference in Stockholm, two colleagues of mine from CERN stood up to announce that the search for one of the rarest processes in fundamental physics is over. The result is a stunning success for the Standard Model, our current best theory of particles and forces, and yet another blow for those hoping for signs of new physics from CERN’s Large Hadron Collider (LHC).

The Compact Muon Spectrometer, an experiment at CERN. Image credit: CERN.

The Compact Muon Spectrometer, an experiment at CERN. Image credit: CERN.

The LHCb and CMS experiments at the LHC have made the first definitive observation of a particle called a Bs meson decaying into two muons, confirming a tentative sighting at LHCb (my experiment) last autumn. The discovery has far-reaching implications for the search for new particles and forces of nature.

Beyond the Standard Model

There are a lot of reasons to suspect that the current Standard Model isn’t the end of the story when it comes to the building blocks of our Universe. Despite agreeing with almost every experimental measurement to date, it has several gaping holes. It completely leaves out the force of gravity and has no explanation for the enigmatic dark matter and dark energy that are thought to make up 95% of the Universe. The theory also requires a large amount of “fine-tuning” to match experimental observations, leaving it looking suspiciously like the laws of physics have been tinkered with in a very unnatural way to produce the Universe we live in.

In the last few decades a number of theories have been put forward that attempt to solve some of the Standard Model’s problems. One particularly popular idea is supersymmetry (SUSY for short), which proposes a slew of new fundamental particles, each one a mirror image of the particles of the Standard Model.

The Large Hadron Collider beauty (LHCb) experiment at CERN. Image credit: CERN.

The Large Hadron Collider beauty (LHCb) experiment at CERN. Image credit: CERN.

SUSY has many attractive features: it provides a neat explanation for dark matter and unifies the strengths of the three forces of the Standard Model (this suggests that they could all be aspects of one unified force, which should definitely be referred to as The Force, if it turns out to exist someday). It would also keep my colleagues in work for decades to come, thanks to a whole new load of super-particles (or sparticles) to discover and study.

However, physicists were first attracted to it because the theory is aesthetically pleasing. Unlike the Standard Model, SUSY doesn’t require any awkward fine-tuning to produce laws of physics that match our experience. This is not a very scientific argument, more a desire amongst physicists for theories to be elegant, but historically it has often been the case that the most beautiful theory turns out to be right one.

On the hunt

The decay observed at LHCb and CMS is predicted to be extremely rare in the Standard Model, with a Bs meson only decaying into two muons about 3 times in every billion. However, if ideas like SUSY are correct than the chances of the decay can be significantly boosted.

Finding particle decays this rare makes hunting for a needle in a haystack seem like a doddle. Hundreds of millions of collisions take place every second at the LHC, each one producing hundreds of new particles that leave electrical signals in the giant detectors. Physicists from LHCb and CMS trawled through two years worth of data, searching untold trillions of collisions for signs of two muons coming from a Bs meson. The pressure to be the first to find evidence of this rare process was intense, as Dr. Marc-Olivier Bettler, a colleague of mine from Cambridge and member of the LHCb team told me.

“It is a very strange type of race. To avoid bias, we don’t allow ourselves to look at the data until the last minute. So it’s a bit like running blindfolded – you can’t see the landscape around you or your competitors, even though you know that they’re there, so you have no idea if you are doing well or not! You only find out after you cross the finish line.”

However, ultimately the race ended in a draw. Neither LHCb nor CMS alone had enough data to announce a formal discovery, each turning up just a handful of likely candidates. But when their results are formally combined next week it is expected that the number of observed decays will pass the all-important “five sigma” level, above which a discovery can be declared.

Standard Model Stands Firm

In a blow for supporters of SUSY, LHCb and CMS observed the decay occurring at exactly the rate predicted by the Standard Model – approximately 3 times in a billion. This is yet another triumph for the Standard Model and kills off a number of the most popular SUSY theories.

Professor Val Gibson, leader of the Cambridge particle physics group and member of the LHCb experiment explained that, Measurements of this very rare decay significantly squeeze the places new physics can hide. We are now looking forward to the LHC returning at even higher energy and to an upgrade of the experiment so that we can investigate why new physics is so shy.”

This result is certainly not the end of the road for ideas like supersymmetry, which has many different versions. However, combined with the recent discovery of the Higgs boson (whose mass is larger than predicted by many SUSY theories) this new result may only leave us with versions of SUSY that are somewhat inelegant, meaning that the original motivation – a natural description of nature – is lost.

This new result from CERN is yet another demonstration of the fantastic (and somewhat annoying) accuracy of the Standard Model. Incredible precision is now being achieved by experiments at the LHC, allowing physicists to uncover ever-rarer particles and phenomena. If ideas like supersymmetry are to survive the onslaught of high precision tests made by the LHC experiments, we may have to accept that we live in a spookily fine-tuned Universe.

LHC. Camera. Action! (part 1)

Dr. Harry Cliff, a Physicist working on the LHCb experiment and the first Science Museum Fellow of Modern Science, writes about his work on Collider, a new Science Museum exhibition opening in November 2013.

In the past year, I’ve become a regular passenger on the evening flight from Gatwick to Geneva, home of CERN and the mighty Large Hadron Collider.  I think I could recite Easyjet’s pre-recorded safety announcement pretty much word-for-word if pushed. But this was a rather special trip, as I was visiting CERN perhaps for the last time on museum business.

I was accompanied by a team with a dazzling array of skills. Creative mastermind Pippa Nissen had marshalled exhibition designersgraphic designers, a sound artist, an animator, a camera technician and a radio producer. Not to mention our video designer, Finn Ross, fresh from his win at the Olivier Awards, and the inevitable after-party hangover. And me, a quantum superposition of particle physicist, curator and travel rep.

Our mission was to capture the essence of CERN so that it can be (almost literally) recreated in the Science Museum’s upcoming exhibition, Collider. All this material was to be gathered in just three days, using only cameras, microphones and the minds of our design team.

Day 1, Wednesday

One does not simply walk into CERN. Its gates are guarded by unfailingly helpful, though rather formidable, security personnel and to gain access you must produce a CERN ID card or a visitor pass.

CERN security gate.

CERN security gate. Image credit: Science Museum

We had rather brilliantly chosen the 1st of May as our day to arrive, a national holiday in Switzerland, meaning the reception where we would normally collect our passes was closed. I had arranged for them to be left with the security guard at the main gate, but conveying this to him proved a challenge in my halting GCSE French. Finally, with a bit of gesticulating and some help from our more linguistically capable graphic designer, we located the passes and stepped across the threshold into the world’s largest physics laboratory.

CERN is the size of a medium-sized town, spread across several sites, the largest of which straddles the border between the Swiss suburb of Meyrin and the French village of St-Genis-Pouilly. The lab grew up organically from its beginnings in the 1950s and is a peculiar hodgepodge of office buildings, warehouses and laboratories. CERN’s rather shabby above ground stands in stark contrast to the shining machines that inhabit its subterranean spaces. As far as is possible, the money goes underground, spent on CERN’s reason for being: exploring the unknown regions of the quantum world.

Our job on day one, however, was to explore CERN’s above ground world. The first few hours were spent photographing the exteriors of buildings to act as backdrops in the exhibition. There was a particular warehouse door, in varying shades of rust and faded blue, that really caught the team’s attention. It will take me a while to forget the image of the design team gathered around it while Finn took high-res shots with his £20k camera. That’s designers for you I suppose.

The long beige corridors of CERN's Building 2. Image credit: Science Museum

The long beige corridors of CERN’s Building 2. Image credit: Science Museum

Then we ventured into the star of the show, the enigmatic Building 2, a 1970s block that houses a large number of institute offices. Along its long beige corridors you find offices of universities from all over the world, including the room where Tim Berners-Lee invented the World Wide Web and my own home-away-from-home, the Cambridge LHCb office. We spent a happy afternoon photographing the office doors, each with their own personal details that do more than any museum text panel could in getting across just how international a place CERN is. We owe a particular debt of thanks to a PhD student from Bristol, in on a holiday to work on her thesis, who obligingly allowed us barge into her office to take photographs.

Meanwhile our sound designer was busily recording the soundscape of CERN from the clanging of doors and the echo of footsteps on lino to the hum of electrical equipment. Once we had recorded enough material to rebuild Building 2 in its entirety should any calamity befall it, we made a brisk trip around nearby parts of the lab, taking in the main auditorium where the discovery of the Higgs boson was announced to the world, and a series of labs and warehouses including the LEIR accelerator ring, the machine responsible producing beams of lead ions for our muse, the Large Hadron Collider.

But after all that, we had only scratched the surface of the sprawling laboratory. The next day it would be time to go underground…