̽��ֱ�� of Cambridge - Large Hadron Collider

New result from LHCb experiment challenges leading theory in physics

sc604 — Tue, 23 Mar 2021 09:42:57 +0000

Results from the LHCb Collaboration at CERN suggests particles are not behaving the way they should according to the guiding theory of particle physics – suggesting gaps in our understanding of the Universe.

Physicists from the Universities of Cambridge, Bristol, and Imperial College London led the analysis of the data to produce this result, with funding from the Science and Technology Facilities Council. ̽��ֱ��result - which has not yet been peer-reviewed - was announced today at the Moriond Electroweak Physics conference and published as a preprint.

Beyond the Standard Model

Scientists across the world will be paying close attention to this announcement as it hints at the existence of new particles not explained by the Standard Model.

̽��ֱ��Standard Model is the current best theory of particle physics, describing all the known fundamental particles that make up our Universe and the forces that they interact with. However, the Standard Model cannot explain some of the deepest mysteries in modern physics, including what dark matter is made of and the imbalance of matter and antimatter in the Universe.

Dr Mitesh Patel of Imperial College London, and one of the leading physicists behind the measurement, said: “We were actually shaking when we first looked at the results, we were that excited. Our hearts did beat a bit faster.

“It’s too early to say if this genuinely is a deviation from the Standard Model but the potential implications are such that these results are the most exciting thing I’ve done in 20 years in the field. It has been a long journey to get here.”

Building blocks of nature

Today’s results were produced by the LHCb experiment, one of four huge particle detectors at CERN’s Large Hadron Collider (LHC).

̽��ֱ��LHC is the world’s largest and most powerful particle collider – it accelerates subatomic particles to almost the speed of light, before smashing them into each other.

These collisions produces a burst of new particles, which physicists then record and study in order to better understand the basic building blocks of nature.

̽��ֱ��LHCb experiment is designed to study particles called ‘beauty quarks’, an exotic type of fundamental particle not usually found in nature but produced in huge numbers at the LHC.

Once the beauty quarks are produced in the collision, they should then decay in a certain way, but the LHCb team now has evidence to suggest these quarks decay in a way not explained by the Standard Model.

Questioning the laws of physics

̽��ֱ��updated measurement could question the laws of nature that treat electrons and their heavier cousins, muons, identically, except for small differences due to their different masses.

According to the Standard Model, muons and electrons interact with all forces in the same way, so beauty quarks created at LHCb should decay into muons just as often as they do to electrons.

But these new measurements suggest this is not happening.

One way these decays could be happening at different rates is if never-before-seen particles were involved in the decay and tipped the scales in favour of electrons.

Dr Paula Alvarez Cartelle from Cambridge’s Cavendish Laboratory, was one of the leaders of the team that found the result, said: “This new result offers tantalising hints of the presence of a new fundamental particle or force that interacts differently with these different types of particles.

“ ̽��ֱ��more data we have, the stronger this result has become. This measurement is the most significant in a series of LHCb results from the past decade that all seem to line up – and could all point towards a common explanation.

“ ̽��ֱ��results have not changed, but their uncertainties have shrunk, increasing our ability to see possible differences with the Standard Model.”

Not a foregone conclusion

In particle physics, the gold standard for discovery is five standard deviations – which means there is a 1 in 3.5 million chance of the result being a fluke. This result is three deviations – meaning there is still a 1 in 1000 chance that the measurement is a statistical coincidence.

It is therefore too soon to make any firm conclusions. However, while they are still cautious, the team members are nevertheless excited by this apparent deviation and its potentially far-reaching implications.

̽��ֱ��LHCb scientists say there has been a breadcrumb trail of clues leading up to this result – with a number of other, less significant results over the past seven years also challenging the Standard Model in a similar way, though with less certainty.

If this result is what scientists think it is – and hope it is – there may be a whole new area of physics to be explored.

Dr Konstantinos Petridis of the ̽��ֱ�� of Bristol, who also played a lead role in the measurement, said: “ ̽��ֱ��discovery of a new force in nature is the holy grail of particle physics. Our current understanding of the constituents of the Universe falls remarkably short – we do not know what 95% of the Universe is made of or why there is such a large imbalance between matter and anti-matter.

“ ̽��ֱ��discovery of a new fundamental force or particle, as hinted at by the evidence of differences in these measurements could provide the breakthrough required to start to answer these fundamental questions.”

Dr Harry Cliff, LHCb Outreach Co-Convener, from Cambridge’s Cavendish Laboratory, said: “This result is sure to set physicists’ hearts beating a little faster today. We’re in for a terrifically exciting few years as we try to figure out whether we’ve finally caught a glimpse of something altogether new.”

It is now for the LHCb collaboration to further verify their results by collating and analysing more data, to see if the evidence for some new phenomena remains.

Additional information – about the result

̽��ֱ��results compare the decay rates of Beauty mesons into final states with electrons with those into muons.

̽��ֱ��LHCb experiment is one of the four large experiments at the Large Hadron Collider (LHC) at CERN in Geneva, and is designed to study decays of particles containing a beauty quark

This is the quark with the highest mass forming bound states. ̽��ֱ��resulting precision measurements of matter-antimatter differences and rare decays of particles containing a beauty quark allow sensitive tests of the Standard Model of particle physics.

Rather than flying out in all directions, beauty quarks that are created in the collisions of the proton beams at LHC stay close to the beam pipe.

̽��ֱ��UK team studied a large number of beauty or b quarks decaying into a strange-quark and two oppositely charged leptons. By measuring how often the b-quark decays into a final state containing a pair of muons or a pair of electrons, they found evidence that the laws of physics might be different, depending on whether the final state contains electrons or muons.

Since the b-quark is heavy compared to the masses of the electron and muon it is expected that the b-quark decays with the same probability into a final state with electrons and muons. ̽��ֱ��ratio between the two decay probabilities is hence predicted to be one.

However analysis of the UK team found evidence that the decay probability is less than one.

UK particle physicists have today announced ‘intriguing’ results that potentially cannot be explained by the current laws of nature.

This new result offers tantalising hints of the presence of a new fundamental particle or force that interacts differently with these different types of particles.

Paula Alvarez Cartelle

CERN

LHCb experiment

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Opinion: Large Hadron Collider sees tantalising hints of a new particle that could revolutionise physics

Anonymous — Thu, 17 Dec 2015 11:38:32 +0000

At the start of December a rumour swirled around the internet and physics lab coffee rooms that researchers at the Large Hadron Collider had spotted a new particle. After a three-year drought that followed the discovery of the Higgs boson, could this be the first sign of new physics that particle physicists have all been desperately hoping for?

Researchers working on the LHC experiments remained tight-lipped until December 14 when physicists packed out CERN’s main auditorium to hear presentations from the scientists working on CMS and ATLAS experiments, the two gargantuan particle detectors that discovered the Higgs boson in 2012. Even watching the online webcast, the excitement was palpable.

Everybody was wondering if we would witness the beginning of a new age of discovery. ̽��ֱ��answer is … maybe.

Baffling bump

̽��ֱ��CMS results were revealed first. At first the story was familiar, an impressive range of measurements that again and again showed no signs of new particles. But in the last few minutes of the presentation a subtle but intriguing bump on a graph was revealed that hinted at a new heavy particle decaying into two photons (particles of light). ̽��ֱ��bump appeared at a mass of around 760GeV (the unit of mass and energy used in particle physics – the Higgs boson has a mass of about 125 GeV) but was far too weak a signal to be conclusive on its own. ̽��ֱ��question was, would ATLAS see a similar bump in the same place?

̽��ֱ��ATLAS presentation mirrored the one from CMS, another list of non-discoveries. But, saving the best for last, a bump was unveiled towards the end, close to where CMS saw theirs at 750GeV – but bigger. It was still too weak to reach the statistical threshold to be considered solid evidence, but the fact that both experiments saw evidence in the same place is exciting.

̽��ֱ��discovery of the Higgs back in 2012 completed the Standard Model, our current best theory of particle physics, but left many unsolved mysteries. These include the nature of “dark matter”, an invisible substance that makes up around 85% of the matter in the universe, the weakness of gravity and the way that the laws of physics appear fine-tuned to allow life to exist, to name but a few.

Could supersymmetry one day crack the mystery of all the dark matter lurking in galaxy clusters? NASA/wikimedia

A number of theories have been proposed to solve these problems. ̽��ֱ��most popular is an idea called supersymmetry, which proposes that there is a heavier super-partner for every particle in the Standard Model. This theory provides an explanation for the fine-tuning of the laws of physics and one of the super-partners could also account for dark matter.

Supersymmetry predicts the existence of new particles that should be in reach of the LHC. But despite high hopes the first run of the machine from 2009-2013 revealed a barren subatomic wilderness, populated only by a solitary Higgs boson. Many of the theoretical physicists working on supersymmetry have found the recent results from the LHC rather depressing. Some had begun to worry that answers to the outstanding questions in physics might lie forever beyond our reach.

This summer the 27km LHC restarted operation after a two-year upgrade that almost doubled its collision energy. Physicists are eagerly waiting to see what these collisions reveal, as higher energy makes it possible to create heavy particles that were out of reach during the first run. So this hint of a new particle is very welcome indeed.

A cousin of Higgs?

Andy Parker, head of Cambridge’s Cavendish Laboratory and senior member of the ATLAS experiment, told me: “If the bump is real, and it decays into two photons as seen, then it must be a boson, most likely another Higgs boson. Extra Higgs are predicted by many models, including supersymmetry”.

Perhaps even more exciting, it could be a type of graviton, a hypothesised particle associated with the force of gravity. Crucially, gravitons exist in theories with additional dimensions of space to the three (height, width and depth) we experience.

For now, physicists will remain sceptical – more data is needed to rule this intriguing hint in or out. Parker described the results as “preliminary and inconclusive” but added, “should it turn out to be the first sign of physics beyond the standard model, with hindsight, this will be seen as historic science.”

Whether this new particle turns out to be real or not, one thing that everyone agrees on is that 2016 is going to be an exciting year for particle physics.

Harry Cliff, Particle physicist and Science Museum fellow, ̽��ֱ�� of Cambridge

This article was originally published on ̽��ֱ��Conversation. Read the original article.

̽��ֱ��opinions expressed in this article are those of the individual author(s) and do not represent the views of the ̽��ֱ�� of Cambridge.

Harry Cliff (Cavendish Laboratory) discusses the potential discovery of a new particle at the Large Hadron Collider and its implications for particle physics.

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̽��ֱ��Large Hadron Collider/ATLAS at CERN

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Large Hadron Collider restarts after two years

sc604 — Tue, 07 Apr 2015 14:26:52 +0000

Early on Easter Sunday, the Large Hadron Collider’s second run got underway, when proton beams began rotating in the 27-kilometre ring for the first time in two years. Over the coming weeks, the beams will be accelerated to speeds close to the speed of light, running at the unprecedented energy of 13 Terra-electron-volts (TeV), well above the 8 TeV level of the last run, which discovered the long-sought Higgs boson in 2012.

̽��ֱ��new run will subject the Standard Model of particle physics to its toughest tests yet, and may help identify some of the fundamental forces of nature that the Standard Model does not include. With 13 TeV proton-proton collisions expected before summer, the LHC experiments will soon be exploring uncharted territory in particle physics.

Cambridge researchers at CERN are playing a major part in preparing the ATLAS detector – the largest of LHC’s seven particle detectors – for action with new upgraded systems ready to go to work as soon as the beam start to collide. All the preparations are in place to being to analyse the data and early results could be expected before the end of the year if all goes well.

“ ̽��ֱ��current Standard Model explains the known particles and forces, and the discovery of the Higgs completed that picture,” said Professor Andy Parker, Head of the Cavendish Laboratory at the ̽��ֱ�� of Cambridge, and one of the founders of ATLAS. “But the Standard Model does not explain dark matter, which is believed to make up most of the Universe, nor Dark Energy, a mysterious force driving the galaxies ever further apart.”

̽��ֱ��answers to these problems in cosmology might lie in the realm of sub-atomic physics studied at CERN. For example, the LHC might be able to produce dark matter particles, which would be glimpsed in the debris of collisions detected by the ATLAS and CMS experiments.

“Even more exciting is the possibility that the Universe could have more than three space dimensions, and that other spaces are hidden all around us,” said Parker. “This could also be revealed at CERN by the production and decay of microscopic quantum black holes, a particular interest of the Cambridge researchers at CERN. Detailed studies of the Higgs boson are also going to test our understanding of the Standard Model, with any unexpected effects leading us towards new physics. ̽��ֱ��upgrade of the LHC will allow scientists to search for new discoveries which have so far been out of reach.”

̽��ֱ��upgrade was a Herculean task. Some 10,000 electrical interconnections between the LHC’s superconducting dipole magnets were consolidated. Magnet protection systems were added, while cryogenic, vacuum and electronics were improved and strengthened. Additionally, the beams will be set up in such a way that they will produce more collisions by bunching protons closer together; with the time separating bunches being reduced from 50 nanoseconds to 25 nanoseconds.

After the discovery of the Higgs boson in 2012 by the ATLAS and CMS experiments, physicists will be putting the Standard Model of particle physics to its most stringent test yet, searching for new physics beyond this well-established theory describing particles and their interactions.

With superconducting magnets cooled to the extreme temperature of -271°C, the LHC is capable of simultaneously circulating particles in opposite directions, in tubes under ultrahigh vacuum, at a speed close to that of light. Gigantic particle detectors, located at four interaction points along the ring, record collisions generated when the beams collide.

In routine operation, protons cover some 11,245 laps of the LHC per second, producing up to 1 billion collisions per second. ̽��ֱ��CERN computing centre stores over 30 petabytes of data from the LHC experiments every year, the equivalent of 1.2 million Blu-ray discs.

After two years of intense maintenance and consolidation, and several months of preparation for restart, the Large Hadron Collider, the most powerful particle accelerator in the world, is back in operation after a major upgrade.

̽��ֱ��upgrade of the LHC will allow scientists to search for new discoveries which have so far been out of reach

Andy Parker

CERN

3D dipole integration panoramic poster

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Firing up the proton smasher

fpjl2 — Mon, 16 Feb 2015 12:33:08 +0000

While it slept, we were allowed into the tunnels.

̽��ֱ��Large Hadron Collider (LHC) had shut down for two years to upgrade following the discovery of the Higgs boson. In the main ring, 175 m underground, chunks had been cut out of the snaking tubes for essential maintenance. These tubes fire protons in opposite directions, whipping them ever faster until they almost reach the speed of light. Along the 27 km run are four ‘experiments’: vast machines envelop the points at which tubes intersect and particles collide to capture the results. ̽��ֱ��largest of these, ATLAS, is the size of a six-storey building.

Each collision, known as an ‘event’, produces a splurge of elementary particles such as quarks, gluons and – as we now know – Higgs bosons. On average, events occur 40 million times a second in the LHC.

̽��ֱ��precision required for these events is exquisite. Our guide tells us to imagine two people standing six miles apart and each simultaneously firing a gun so that the bullets meet exactly head-on. Except instead of bullets, imagine needles. Inside the tunnels, engineers zip past on bicycles – the best way to get around underground unless you’re a proton. Next to every lift shaft is a bike rack.

In the next few months, the LHC will be switched back on. ̽��ֱ��2012 triumph of demonstrating the Higgs boson affirmed the Standard Model: the elegant solution to the building blocks of the Universe. Now, with an anticipated almost doubling of energy for the LHC’s second run, physicists are aiming to “go beyond” the Standard Model.

One of the central goals is to prove or disprove the theory of supersymmetry: the “prime candidate” theory for unlocking the mystery of the dark matter in our Universe.

“Observable matter only makes up 5% of the Universe; the rest is what we call dark matter. We know it’s there because we can see galaxies rotating at velocities which require surrounding matter for such gravitational pull – but, unlike the part of the galaxies that we can see, we cannot detect it optically,” said Professor Val Gibson, Head of the Cambridge High Energy Physics (HEP) group.

Supersymmetry theory essentially predicts that every particle in the Standard Model has a matching particle waiting to be found. These partner particles (or ‘sparticles’) could be candidates for dark matter, but we haven’t yet seen them – perhaps because they are heavier and take more energy to generate, a problem LHC Run II could overcome.

“Supersymmetry theory predicts there is a sister particle of the electron called a ‘selectron’, which would have integer ‘spin’: its intrinsic angular momentum. For the quark, there would be a supersymmetric ‘squark’, and so on for every elementary particle we know,” said Gibson. If supersymmetry is correct, there would also be a further four Higgs bosons for us to discover.

“Proton collisions in the LHC might produce a heavy supersymmetric particle which decays into its lightest form, a light neutral particle, but different from those we know about in the Standard Model,” said Gibson.

“We have been looking for supersymmetry particles throughout the first run of the LHC, and the increase in power for Run II means we can look at higher energies, higher mass, and gradually blot out more areas of the map in which supersymmetrical particles could be hiding.”

Will supersymmetry be proved by the end of next year, or will the data show it’s a red herring? For HEP research associate Dr Jordi Garra Ticó, what is really fundamental is experimental evidence. “I just want to see what nature has prepared for us, whether that’s consistent with some current theory or whether it’s something else that no one has ever thought about yet, outside of current knowledge.”

̽��ֱ��two experiments that Cambridge researchers work on are the mighty ATLAS and the more subtle LHCb – known as LHC ‘Beauty’ – which is Gibson and Garra Ticó’s focus. Beauty complements the power of ATLAS, allowing scientists to ‘creep up’ on new physics by capturing rare particle decays that happen every 100 million events.

Garra Ticó spent six months in Cambridge before taking up residence at CERN, where he works on LHCb. LHCb’s 10 million events a second create 35 kbyte of data each, a figure that is expected to go up to 60 kbyte during Run II – too much to ever imagine storing. “There is no guidebook,” he explained. “These machines are prototypes of themselves.”

ATLAS, the biggest experiment, feels like the lair of a colossal hibernating robot. Engineers perch in the crevices of the giant machine, tinkering away like tiny cleaner birds removing parasites. And sealed in the heart of this monster is layer upon layer of the most intricate electronics ever devised.

Dr Dave Robinson arrived in CERN as a PhD student in 1985, and joined the Cambridge HEP group in 1993. He went back to CERN in 2004 – expecting a stint of “one to two years” – and has remained. He is now Project Leader for the most critical detector system within ATLAS, the Inner Detector, which includes the ‘semi-conductor tracker’ (SCT), partially built
in Cambridge.

Each collision event inside ATLAS leaves an impression on the layers of silicon that make up the SCT like an onion skin – enabling scientists to reconstruct the trajectory of particles in the events. “ ̽��ֱ��sensitivity of the tracker is vital for making precise measurements of the thousands of particles generated by the head-on collisions between protons, including decay products from particles like b-quarks which only exist for picoseconds after the collision,” said Robinson.

He is currently working with Gibson and colleagues at the Cavendish Laboratory on the next generation of radiation-proof silicon technology in preparation for the LHC shutdown of 2020, the next time they will be able to get at the SCT, which is otherwise permanently locked in the core of ATLAS. ̽��ֱ��technology will have an impact on areas like satellite telecommunications, where cheaper, radiation-hardened electronics could have a huge effect.

This, for Gibson, is the way science works: solving technical problems to reveal nature’s hidden secrets, and then seeing the wider applications. She recalls being in CERN when she was a postdoc in the 1980s at the same time as Tim Berners-Lee, who was working on computer-sharing software to solve the anticipated data deluge from LHC-precursor UA1. He ended up calling it the World Wide Web.

Inset image – top: representation of the Higgs Boson particle; Credit: CERN.

Inset image – bottom: Professor Val Gibson.

̽��ֱ��Large Hadron Collider is being brought back to life, ready for Run II of the “world’s greatest physics experiment”. Cambridge physicists are among the army who keep it alive.

I just want to see what nature has prepared for us, whether that’s consistent with some current theory or whether it’s something else that no one has ever thought about yet, outside of current knowledge

Jordi Garra Ticó

CERN

Large Hadron Collider

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How to explore the whole universe: watch COSMO 2013 live

sj387 — Wed, 04 Sep 2013 10:48:58 +0000

̽��ֱ��past year has been an extraordinary one for particle physicists and cosmologists, with the Planck satellite revealing the Universe’s earliest light, and the tentative discovery of the Higgs-Boson at the Large Hadron Collider (LHC).

Data collected from LHC experiments and the Planck mission - and their implications for the Universe - will be discussed by some of the giants of cosmology and particle physics during this week’s COSMO conference, all of which is being streamed live on YouTube.

Alongside the five-day long scientific conference - with days variously focused on Particle Physics, Cosmic Microwave Background, Large-Scale Structure, Primordial Cosmology and Cosmic Acceleration - there will also be a public symposium tonight, which, with speakers such as Stephen Hawking, Brian Cox and Andrew Liddle, will be a highlight of the COSMO YouTube broadcast.

Andrew Liddle, Professor of Theoretical Astrophysics at the ̽��ֱ�� of Edinburgh, will open the symposium with a talk on cosmology and the Planck satellite, currently being used to map the relic radiation expelled by the Big Bang. COSMOS 2013 is one of the first opportunities for researchers to gather and discuss the recent discoveries, with other lectures on the Planck data from George Efstathiou (Institute of Astronomy) and Ben Wandelt among others.

̽��ֱ��Planck satellite has given us a highly detailed image of the Universe a mere 380,000 years after the Big Bang; and will be used by researchers to learn about the origins of the Universe, its probable fate, and, ultimately, about existence itself.

̽��ֱ��night’s second speaker, Professor Brian Cox, has been credited with helping to demystify physics for the public. ̽��ֱ��former musician is now a particle physicist, Royal Society research fellow and professor at the ̽��ֱ�� of Manchester; he also works on the ATLAS experiment at the CERN super collider. Though a full time lecturer at Manchester, he is a prolific broadcaster and host of many science programmes such as the recent BBC series Wonders of Life.

̽��ֱ��symposium will finish with a talk from Stephen Hawking, the world-famous theoretical physicist, cosmologist and author. Hawking, author of the best-selling A Brief History of Time, gained his Ph.D. at Trinity Hall, Cambridge, was the Lucasian Professor of Mathematics at the ̽��ֱ�� for 30 years and is a Fellow at Gonville and Caius College. He is also the Director of Research at ̽��ֱ��Stephen Hawking Centre for Theoretical Cosmology at the ̽��ֱ��.

Among Hawking’s many achievements is the proposal that black holes are not entirely black, but instead emit a type of thermal radiation now known as “Hawking radiation”. His talk, entitled Fire in the Equations, is likely to prove a spell-binding conclusion to the public evening of COSMO 2013.

COSMO 2013 is sponsored by Intel who are providing the live feed for the public event. Richard Curran, Intel Director Enterprise Server and Software Enabling Group EMEA, said “At Intel we have a long and successful history of working with Professor Hawking. We are proud to be supporting the team in its analysis of the data collected from the Planck satellite and wait with great anticipation to the insights the research can offer us about the universe and its origin. We are excited to open this research up to the public and we hope it encourages more people to take an interest in physics and the amazing work being done”.

Watch speakers such as Stephen Hawking and Brian Cox this evening as the public symposium of the 17th International Conference on Particle Physics and Cosmology, known as COSMO 2013, is broadcast live on YouTube.

Arun Venkataswamy

Orion Nebula / M42

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Large Hadron ‘insider’

fpjl2 — Fri, 14 Jun 2013 10:33:57 +0000

In October 2000, I arrived in Geneva from Stansted airport ready to start a two year research job at the European centre for particle physics (CERN) with my heart in my throat. This was before all of the recent excitement about the Large Hadron Collider, but for a particle physicist, CERN is the ultimate temple of physics and for me, it was my lifetime ambition to work there. I had recently daringly, and many said stupidly, turned down a life-time lectureship at another university so that I might have a chance of working at CERN (the offer came with an inflexible initial start date).

CERN really is an amazing place. There are some 10,000 physicists and engineers working on the site, which straddles the Franco-Swiss border, just outside Geneva, underneath the Jura Mountains. Everyone is working for ̽��ֱ��Cause - our common goal is to find out what the stuff that makes up our universe is like, and how it behaves.

When I arrived, the Large Hadron Collider had not been built and the previous one was toward the end of its operation. While I was there, there was a potential hint of a higgs signal in the data. All of a sudden, CERN was completely abuzz. Everyone was trying to find out the latest rumours. There were four independent experiments back then, all competing with each other. ̽��ֱ��idea behind this was that they can check each other's results, and keep each other unbiased. But because of this competition, the experiments were rushing to make a big discovery before the others, but they also wanted to keep their data secret so as not to give the others a clue.

I am a theoretical physicist: I do the mathematics and interpret experimental data, rather than actually run the experiments. My theoretical colleagues had spies on the experiments, which they were trying to push for information to find out the latest on the Higgs boson. Then they would tell their friends, and all sorts of wild rumours would start to fly about. Mostly this wasn't done for any personal advantage, it was just that we were fascinated, and really wanted to know what was going on at the cutting edge as early as possible. Once every month or two, the experiments would hold seminars and do official releases of data. Sometimes we already knew what they were going to say but sometimes it was a surprise.

In the end, it turned out that the hint of a signal that we were all getting so excited about was just a random fluctuation of the data. We couldn't really know this for sure though until we had seen the LHC data, and that didn't arrive for another eight years or so.

At the time though, since there was the hint of a higgs boson signal in the data, and since the collider only had a year or so left before shutdown to make way for the LHC, the accelerator engineers started to ramp up the energy as much as possible. This was a risky strategy, because parts started to break down, being under a lot of strain (I imagine the accelerator engineers, like Scottie from Star Trek, shouting "she cannae take any more captain!") My friend worked on one of the experiments, and many times he was paged from the pub and had to taxi up to the experiment to try and get it working once it had all broken down.

Since the beam was still on, the experiment was losing valuable data that all of the other experiments were taking, and could lose out on a discovery as a result. One time, his boss had to be called in at 1am from a birthday party to coordinate everyone. ̽��ֱ��first thing to do was pour coffee down him to try to sober him up.

People often think that the biggest man made experiment on earth will be ultra high-tech and efficiently squeaky clean. In some ways this is true, but there was also a sort of Heath-Robinson aspect too. For instance, the accelerator is a complicated beast with thousands of different magnets and sub-pieces, all with complex and nervy feedback across them. As a result, driving it is something of a black art: apparently you get the "feel" of how it is behaving that day and some of the operators were particularly good at this knack. During 1998, the best operators by far were the French accelerator engineers: they just had the most experience, and an uncanny sense of how it would behave in the following five minutes. That year, the football world cup was in France, and we were praying that France would be knocked out early because the rate of good beam was really low: all the good French operators were taking days off to watch their team's matches.

It was hard getting research jobs in the subject back then: the competition was ultra-tough, and I was far from sure I would be able to get the next job. Whenever I thought about leaving the subject, I think how sad I would be to read about a big discovery (like the recent Higgs boson discovery) and to know that I could have been involved, at least in some small way. I really feel that I am super lucky to be still researching in the field. I work from the ̽��ֱ�� of Cambridge, but visit CERN several times a year for research. If you ever go to Geneva, I thoroughly recommend you to get on the CERN website several weeks beforehand, and book yourself in to a guided tour. I guarantee it will be an incredible scientific journey.

Inset image: Ben Allanach working it out during his time at CERN

In a recent talk for TEDx, theoretical physicist Professor Ben Allanach explored the research he undertook during the two years he spent working on the Large Hadron Collider at CERN in Switzerland. Here, he takes us back to his time as one of the scientists working on the biggest scientific experiment in human history.

We were praying that France would be knocked out of the World Cup because the rate of good beam was really low

Ben Allanach

̽��ֱ��micro frontier: Benjamin Allanach at TEDxDanubia 2013

Sir Cam

̽��ֱ��Large Hadron Collider projected onto the Old Schools, the ̽��ֱ��'s administrative centre, during the 800th Anniversary celebration year

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Supersymmetry squeezed as LHC spots ultra rare particle decay

ns480 — Tue, 13 Nov 2012 10:30:22 +0000

̽��ֱ��result is very damaging to new theories like the extremely popular Supersymmetry.

Current knowledge about the most fundamental matter particles (quarks and leptons, such as an electron) and the forces between them is embedded in the so-called Standard Model. ̽��ֱ��particle masses are a consequence of their interactions with the Higgs field. Exciting the Higgs field in particle collisions at the LHC recently resulted in the discovery of the Higgs boson.

However, the Standard Model is not the ultimate theory; it does not include gravity nor explain 95% of the Universe, which is in the form of Dark Matter and Dark Energy.

Supersymmetry is called in to fill some of the gaps of the Standard Model. Since it predicts new phenomena, the theory of Supersymmetry can be thoroughly tested at the LHC. A very good place to search is through the decay of a B_s particle (composed of a beauty quark and a strange anti-quark) into two muons (very heavy electrons). It is expected to be a very rare event but can be greatly enhanced be the presence of new physics.

This decay has been observed for the first time by a team at the LHC beauty (LHCb) experiment, a gigantic particle detector at one of the collision points on the 27 km LHC collider.

̽��ֱ��LHC, the world’s most powerful particle accelerator ever built, has been accelerating protons to almost the speed of light and bringing them to collision since November 2009. Each collision produces a shower of particles, among which a B_s particle is occasionally present. ̽��ֱ��B_s particle is not stable and decays an instant (within a million millionth of a second) after its production. During its short lifetime, it travels far enough (approximately a centimetre) to be observed by the LHCb detector. It can decay in a variety of other particles and in an extremely rare occurrence, about one in 300 million chance, into two muons.

̽��ֱ��team of physicists has analysed the tremendous amount of collisions recorded by LHCb, searching for this decay. In the end, they have spotted a handful of likely candidates. Observing this ultra-rare decay is a triumph for LHCb.

Professor Val Gibson, leader of the Cambridge LHCb team, says “An observation of this very rare decay is a key result that is putting our Supersymmetry theory colleagues in a spin. Results of this quality rely on the dedication and enthusiasm of research post-docs who analyse the data as it pours from the experiment”

̽��ֱ��observation is bang on the Standard Model prediction, but comes as very bad news for supporters of Supersymmetry. Indeed, new physics failed to show up where it had the best opportunity. “If new physics exists, then it is hiding very well behind the Standard Model” commented Cambridge physicist Dr Marc-Olivier Bettler, a member of the analysis team.

Nevertheless, Supersymmetry also benefits from this measurement, as Dr Bettler explains “This result is important because it tells us what new physics is not.”

Cambridge scientists at the Large Hadron Collider (LHC) at CERN, near Geneva, have spotted one of the rarest particle decays ever seen in nature.

An observation of this very rare decay is a key result that is putting our Supersymmetry theory colleagues in a spin. Results of this quality rely on the dedication and enthusiasm of research post-docs who analyse the data as it pours from the experiment

Professor Val Gibson

CERN

Primary interaction

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