Tag Archives: LHC

A Higgs boson is produced in the ATLAS detector

The boring boson?

Last week scientists working on the Large Hadron Collider in Geneva updated their colleagues on the newly-discovered Higgs boson. They revealed what they now know about the particle – and so far, it is behaving exactly as they expected. While this might seem like good news, for some people it is the opposite, because a well-behaved Higgs might rule out some intriguing new physics theories.

A Higgs boson is produced in the ATLAS detector

A Higgs boson is produced in the ATLAS detector

The Higgs – the particle which explains why others have mass – is incredibly unstable and only exists for a fraction of a second before decaying into other, more common particles. Any information about it comes second-hand from these other particles, and working out the properties is rather like putting together clues in a Sherlock Holmes tale, only with more mathematics.

Finding the Higgs in July was a wonderful coup for the LHC, but there now follows years of painstaking work to determine its precise properties. If the Higgs behaves even a smidgen differently from predictions, then it might point scientists in the direction of a new theory.

One particularly popular idea has the rather grand name of “supersymmetry”, which as we wrote on this blog last week, is looking less likely to be true.

There are lots of problems with current theories about the Universe – they don’t explain dark matter, and particle physics is completely incompatible with Einstein’s theories of gravity. Supersymmetry solves some of these issues in a whizz of complicated mathematics, but requires the existence of a whole family of new particles. If they exist, the Higgs’ properties should reveal them.

The results announced on Wednseday in Japan don’t lend the under-fire supersymmetry any more support. They suggest that so far, the Higgs behaves just as our current theory predicts it should. Specifically, when it decays, it turns into different types of particles at the rates we expect.

To some in the community, the Higgs’ conformity is rather disappointing.  But not all of the analysis was ready for the Japan conference and there is still uncertainty around the results that were announced, and supersymmetry still could work.

Even though the LHC has already analysed more data in two years than its predecessor managed in twenty, the measurements are not yet particularly precise, and the Higgs may still harbour surprises. The LHC still has not detected a Higgs decaying into quarks (the smallest unit of matter), for example – we just know that since we haven’t seen it yet, it can’t happen often. In other words: watch this space.

Visitors to the Science Museum will have a chance to get up close and personal with the LHC at a new exhibition opening in November 2013.

View of the LHCb cavern

Supersymmetry in a spin

Dr. Harry Cliff, a Physicist working on the LHCb experiment and the first Science Museum Fellow of Modern Science, writes about a new discovery at CERN for our blog. A new Science Museum exhibition about the Large Hadron Collider will open in November 2013, showcasing particle detectors and the stories of scientific discoveries.

There were high hopes that the world’s most powerful particle collider would find evidence for the theory of supersymmetry, which postulates that every member of the known bestiary of sub-atomic particles has a related but much more massive “super-partner”. The theory is considered more elegant than the current Standard Model of particles and forces and is particularly appealing as some of these supersymmetric particles, or “sparticles”, could account for the “dark matter” that sculpts the structure of the visible universe.

But the experiment I work on at the Large Hadron Collider (LHC) has spotted of one of the rarest particle decays ever seen in nature, a result that poses a serious challenge to supporters of “new physics” theories like supersymmetry.

View of the LHCb cavern

View of the LHCb cavern. Image credit: CERN

Results presented at the Hadron Collider Physics conference in Kyoto early this morning show the first convincing evidence for a particle called a Bs meson decaying into two muons. The decay was seen by my colleagues at the LHC beauty (LHCb) experiment, a gigantic particle detector on the 27km LHC ring at CERN, near Geneva.

This process is predicted to be very rare in the Standard Model, but if ideas like supersymmetry are correct then it could be much more common. However, the decay seems to be just as rare as the Standard Model predicted.

As we sat sharing a coffee at the Cavendish lab in Cambridge, Dr Marc-Olivier Bettler, a member of the international team who produced the result, told me it puts “strong constraints” on supersymmetry.

Rarer than winning the lottery
The LHC has been smashing protons into each other at close to the speed of light almost non-stop since November 2009. Each collision creates a shower of new particles, and occasionally a Bs meson is produced. The LHCb detector was built to study exotic these exotic particles.

Dr Bettler and his colleagues churned through hundreds of trillions of collisions produced by the LHC in search of the decay. The huge amount of data recorded by the LHCb experiment was processed using a world-wide network of computer processors known as the Grid. In the end they turned up just a handful of likely candidates.

Their results show that the chance of a Bs meson converting to two muons is about one in 300 million. That’s thirty times less likely than winning the jackpot on the lottery with a single ticket.

New physics hiding
Finding evidence of the decay is a triumph for LHCb, but will be a big disappointment for theorists who have spent many years working on supersymmetry. Prof. Val Gibson, leader of the LHCb group at the University of Cambridge said “this key result is putting our supersymmetry theory colleagues in a spin”. The result also makes it much less likely that the other main LHC experiments, ATLAS and CMS, will discover signs of supersymmetric particles any time soon. “If new physics is present then it is hiding very well behind the Standard Model” said Dr Bettler.

Even though it may be less thrilling than discovering new particles or forces of nature, these extremely precise measurements are crucial to improving our understanding of the Universe. “This result is important because it tells us what new physics isn’t.” Dr Bettler certainly didn’t find the outcome disappointing, describing his reaction at seeing the results for the first time two weeks ago as “wow! I was very excited. It has been a very exciting two weeks, that’s for sure.”

Visitors to the Science Museum will have a chance to get up close and personal with the LHC at a new exhibition opening in November 2013. The exhibition will showcase real pieces of the LHC, including an intricate particle detector from the heart of the LHCb experiment.

The ENCODE display at the Science Museum

Heroes of Science

“If science is to inspire, engage and thrive, it needs its heroes more than ever.” This was the key message from Dr. Roger Highfield, our Director of External Affairs, and this year’s recipient of the Wilkins-Bernal-Medawar Medal, at his Royal Society lecture ‘Heroes of Science’ earlier this week.

Modern science is now so often a global collaborative effort, with thousands of researchers joining forces on gigantic scientific undertakings such as the Large Hadron Collider, ENCODE and the Polymath Project. As research teams have become the norm in scientific discovery, many are asking is modern science is too big for heroes?

The ENCODE display at the Science Museum

Roger disagrees, arguing in his lecture (and in this Daily Telegraph article) that “it would be a disaster if we provided an uninspiring vision of scientific advance as a relentless march of an army of ants.” The likes of Isaac Newton or Marie Curie, who won two Nobel prizes before dying due to prolonged radiation exposure, provide inspirational stories of scientific discovery, and these stories continue to this day through figures such as Peter Higgs, Craig Venter and Sir Tim Berners-Lee.

These scientists would never claim to have worked alone, but this is often how they are portrayed. In the crowded realm of ideas, heroes are often the most viral transmitters of the values of science. Our fascination with heroes could perhaps be explained by recent brain scan studies by Francesca Happé and colleagues in London, which show the existence of a hard-wired fondness for narratives in us all.

EEG hat

An EEG hat, used to measure brain activity

Roger ended his lecture with a final thought on the use of metaphors to convey complex ideas, noting that by the same token, heroic characters who appreciate scientific discovery are needed to express a vivid sense of the way science works.

The Wilkins-Bernal-Medawar lecture is given annually on a subject relating to the history, philosophy or social function of science. The accompanying Medal is named in memory of three Fellows of the Royal Society, John Desmond Bernal, Peter Medawar, and John Wilkins, the first Secretary of the Society. Previous recipients of the Medal include Melvyn Bragg, who lectured on the history of the Royal Society, and Professor David Edgerton, who discussed twentieth century science and history.

LHCb VELO Modules

LHC Exhibition: From Liverpool to the LHC, via easyJet

In autumn 2013 an exhibition about the LHC will open in the Science Museum, and we’re currently scouting out objects and stories for the show. This post is the first in a series about the exhibition. Myself and Harry Cliff from the LHC exhibition team ventured to Liverpool to take a closer look at the detector that sits at the heart of the LHCb experiment.

LHCb VELO Modules

The Oliver Lodge building, home to the Universityof Liverpool particle physics department, is a typically plain post-war block. But inside, technicians and researchers constructed one of the most beautiful parts of the Large Hadron Collider (LHC): the LHCb Vertex Locator or “VELO”.

The VELO is a precision engineered piece of equipment, and we had to put on teletubby-style outfits to enter the clean room where the modules were painstakingly put together. A peek through a microscope at a spare module revealed the intricate detail in each board; hundreds of perfectly aligned connections, delicate strips of silicon and tiny computer chips.

But once assembled, the modules are surprisingly hardy. Some were taken to the LHC in Geneva in hand baggage on an easyJet flight; brave researchers drove the rest through the Channel tunnel in a hire car. Once they arrived, this incredibly intricate device was carefully put in position. It sits just millimetres from awesome power of the LHC’s proton beams, enduring high levels of radiation for years on end without missing a beat.

Most of media flurry about the LHC has concentrated on the hunt for the Higgs boson. LHCb has a different mission. As Dr Tara Shears explained, our universe is made of normal matter, not its mirror image, antimatter, and at LHCb scientists are attempting to find out where the antimatter has gone.

The LHC collides protons at near light speed. The energy of the crash creates new particles that spray out in all directions. Our host at Liverpool, Dr Girish Patel, explained that the VELO comprises 42 modules, which are lined up in pairs to form circular detectors – the proton beams travel through the hole in the centre of each pair. The pairs are lined up along the beam to record the trajectory of the new particles.

The VELO allows scientists to work out precisely where particles were created, to within a hundredth of a millimetre. It is surrounded by much larger detectors that identify what types of particle were made in each collision. LHCb is looking for a type of particle known as a bottom quark. It doesn’t detect the bottom particles directly, because they decay into other particles before they reach VELO. LHCb tracks these other particles, looking for the fingerprint of the bottom quark among the mass of data.

Thanks to everyone at Liverpool for a fascinating day, particularly Girish, Tara and Themis. For more info on the VELO, take a look at the LHCb website.

Image courtesy of CERN