Large Hadron Collider - early results

From the BBC today:

LHC finds 'interesting effects'

Image of a 7 TeV proton-proton collision in CMS producing more than 100 charged particles. Scientists have tracked particle paths in billions of collisions at the LHC

Scientists at the Large Hadron Collider say they are getting some fascinating early results as they get set to probe new areas of physics.

The giant machine on the Franco-Swiss border is studying the fundamental nature of matter by smashing together proton particles at near light-speed.

Its CMS detector is reported to have seen "new and interesting effects".

These effects concern the particular paths taken by the debris particles as they move away from the impacts.

These angular correlations emerged in the statistical study of hundreds of particle movements in billions of collisions.

"In some sense, it's like the particles talk to each other and they decide which way to go," explained CMS Spokesperson Guido Tonelli.

"There should be a dynamic mechanism there somehow giving them a preferred direction, which is not down to the trivial explanation of momentum and energy conservation. It is something which is so far not fully understood," he told BBC News.

Mr Tonelli said the effects were small and had prompted much debate; although he said they probably did not indicate any new physics.

"We claim only that we have seen something unusual and we want the scientific community to criticise us, to understand if we did things correctly or if we did something wrong," he added.

The results are said to be interesting because they mirror similar observations at the US Brookhaven National Laboratory, which has been employing a lower energy machine but using more massive atomic nuclei as the impactors.

Such investigations are part of the quest to understand the hot dense state in which matter is thought to have existed just fractions of a second after the Big Bang.

Researchers want to see evidence of this state, known as a quark-gluon plasma, so they can explain how it transitioned into the ordinary nuclear material that makes up the Universe today.

The LHC will begin to probe this domain itself in November when it starts colliding the nuclei of lead atoms.

The £6bn ($10bn) machine is operated by Cern (the European Organization for Nuclear Research), based near Geneva.

Opened in 2008, it already works at energies that exceed those of previous colliders and is still some way short of its maximum design performance.

Currently, much of what the collider is doing is proofing its own operation by re-measuring known physics.

This will give researchers a baseline from which to understand better the results thrown up by future, more ambitious experiments.

Original Post
The Hadron Collider is live and kicking. From the BBC today:

Large Hadron Collider (LHC) generates a 'mini-Big Bang'

One of the lead-ion collisions, as seen by the ALICE experiment One of the lead-ion collisions, as seen by the ALICE experiment

The Large Hadron Collider has successfully created a "mini-Big Bang" by smashing together lead ions instead of protons.

The scientists working at the enormous machine on Franco-Swiss border achieved the unique conditions on 7 November.

The experiment created temperatures a million times hotter than the centre of the Sun.

The LHC is housed in a 27km-long circular tunnel under the French-Swiss border near Geneva.

Up until now, the world's highest-energy particle accelerator - which is run by the European Organization for Nuclear Research (Cern) - has been colliding protons, in a bid to uncover mysteries of the Universe's formation.

Proton collisions could help spot the elusive Higgs boson particle and signs of new physical laws, such as a framework called supersymmetry.

But for the next four weeks, scientists at the LHC will concentrate on analysing the data obtained from the lead ion collisions.

This way, they hope to learn more about the plasma the Universe was made of a millionth of a second after the Big Bang, 13.7 billion years ago.

One of the accelerator's experiments, ALICE, has been specifically designed to smash together lead ions, but the ATLAS and Compact Muon Solenoid (CMS) experiments have also switched to the new mode.

'Strong force'

David Evans from the University of Birmingham, UK, is one of the researchers working at ALICE.

He said that the collisions obtained were able to generate the highest temperatures and densities ever produced in an experiment.

"We are thrilled with the achievement," said Dr Evans.

ALICE experiment, CERN The ALICE experiment has been designed specifically for lead ion collisions

"This process took place in a safe, controlled environment, generating incredibly hot and dense sub-atomic fireballs with temperatures of over ten trillion degrees, a million times hotter than the centre of the Sun.

"At these temperatures even protons and neutrons, which make up the nuclei of atoms, melt resulting in a hot dense soup of quarks and gluons known as a quark-gluon plasma."

Quarks and gluons are sub-atomic particles - some of the building blocks of matter. In the state known as quark-gluon plasma, they are freed of their attraction to one another. This plasma is believed to have existed just after the Big Bang.

He explained that by studying the plasma, physicists hoped to learn more about the so-called strong force - the force that binds the nuclei of atoms together and that is responsible for 98% of their mass.

After the LHC finishes colliding lead ions, it will go back to smashing together protons once again.

They hunt it here, they hunt it there, those researchers seach it everywhere. Is it in heaven? Is it in hell? That damned elusive Higgs boson particle.(Apologies to The Scarlet Pimpernel)

From the BBC today:

LHC 'has two years to find Higgs'

 

Researchers working at the Large Hadron Collider have said they expect to discover the Higgs boson particle by the end of 2012.

If the LHC does not turn up evidence of the Higgs during this run, physicists say they may have to significantly alter their views of physical laws.

The Higgs boson particle explains why other particles have mass, but it has not yet been observed by physicists.

The LHC is housed in a 27km-long tunnel under the French-Swiss border.

It smashes together proton particles travelling at close to the speed of light in a bid to uncover secrets of the Universe.

According to Professor Tom LeCompte of the Argonne National Laboratory, US, who works at the LHC: "The most likely place for the Higgs to be is in a very good place for us to discover it in the next two years."

The LHC has now restarted after its winter shut down - and is about to embark on a run of work that could make or break the current view of how the Universe was formed.

The most widely accepted theory of particle physics requires the existence of the Higgs - and the detection of this particle is one of the LHC's main objectives.

If the collider does not detect the Higgs within two years, researchers say they will know that it does not exist - at least in the form required by the Standard Model, the framework which was devised to explain the behaviour of fundamental particles.

"The Higgs is one model of many," according to Professor LeCompte.

"It's a model that we like. It's simple, its elegant, but it's entirely possible that there is something else beyond the Higgs that does its job instead, and what we may discover is instead of the Higgs itself we may discover something much more interesting.

"There could be multiple Higgses or there could be something completely different doing the same job as the Higgs in a completely different way."

But he adds that not finding the Higgs may be more exciting than finding it - because researchers may have to modify their current view of sub-atomic physics.

"If we don't see it after this two year run it means that something is perhaps not the way that we think it is, either the Higgs search itself had to be amended in some way or some of its indirect evidence may be pointing us in the wrong direction," said Professor LeCompte.

From the BBC yesterday:

 

Higgs speculation is 'premature'

 

Speculation about a dramatic finding in the search for the elusive Higgs boson particle is premature, experts say.

An internal note leaked on the web reveals that a group of researchers at the Large Hadron Collider (LHC) has detected a signal compatible with the sought-after particle.

A spokesman for Cern, which runs the LHC, confirmed the note was authentic.

But he told the BBC it had not been held up to proper scientific scrutiny and could turn out to be a false alarm.

The Higgs boson is of huge importance to the widely accepted theory of physics, known as the Standard Model.

It is the sub-atomic particle which explains why all other particles have mass.

However, despite decades trying, no-one, so far, has detected it.

The result under discussion originates from four members of the Atlas collaboration. Atlas is one of two "multi-purpose" experiments at the LHC designed to search for the Higgs, and some 3,000 physicists are working on the project.

 

'First stage'

Some observers have argued that the note could be a hoax, but Dr James Gillies, director of communications at Cern in Geneva, told BBC News: "It's genuine, but what it comes from is a note written by a very small group of people in a large collaboration.

"There will be working groups for individual physics topics... within those working groups small teams of people will write notes for scrutiny by their colleagues.

"If those notes survive scrutiny, which is often not the case... then the next stage in the peer review process is for them to go out to the collaboration as a whole. If they survive that, then the collaboration will say: 'we've got something to go out to external peer review'."

Dr Gillies added: "What was leaked was the first stage in that process... at this stage we can't take it seriously and these things do come and go quite often."

The LHC is designed to smash together proton particles at close to light-speed in a bid to uncover new physics. Experiments such as Atlas look for "events" that could be associated with the production of new particles.

The Atlas researchers targeted a mass region of 115 gigaelectronvolts (GeV), where Higgs candidates had previously been observed by the LHC's predecessor - the Large Electron Positron (LEP) collider.

They observed a so-called "resonance", an effect which can be associated with the presence of sub-atomic particles.

But the number of events seen by the researchers was about 30 times greater than would be expected.

The note was originally posted on the Not Even Wrong physics blog by an anonymous user.

Another anonymous user on the blog commented: "Anything, especially garbage, can be published as a 'com' note. It's internal to the Atlas collaboration, not reviewed by anyone, not approved."

From the BBC today:

 

Large Hadron Collider results excite scientists

 

The Large Hadron Collider (LHC) has picked up tantalising fluctuations which might - or might not - be hints of the sought-after Higgs boson particle.

But scientists stress caution over these "excess events", because similar wrinkles have been detected before only to disappear after further analysis.

Either way, if the sub-atomic particle exists it is running out of places to hide, says the head of the European Organization for Nuclear Research (Cern), which runs the LHC.

He told BBC News the collider had now ruled out more of the "mass range" where the Higgs might be.

The new results are based on analyses of one inverse femtobarn of data, gathered as the vast machine smashes beams of protons together at close to light-speed.

Scientists from two different experiments (Atlas and CMS) based at the LHC are scouring the wreckage of these collisions.

One of their primary goals is to search for hints of the Higgs, which is the last missing piece in the Standard Model - the most widely accepted theory of particle physics.

Without the Higgs, physicists cannot explain why particles have mass. But despite the best efforts of scientists working on both sides of the Atlantic to detect it experimentally, the boson remains a theoretical sub-atomic particle.

Statistics of a 'discovery'

 
  • Particle physics has an accepted definition for a "discovery": a five-sigma level of certainty
  • The number of sigmas (or standard deviations) is a measure of how unlikely it is that an experimental result is simply down to chance rather than a real effect
  • Similarly, tossing a coin and getting a number of heads in a row may just be chance, rather than a sign of a "loaded" coin
  • The "three sigma" level represents about the same likelihood of tossing more than eight heads in a row
  • Five sigma, on the other hand, would correspond to tossing more than 20 in a row
  • A five-sigma result is highly unlikely to happen by chance, and thus an experimental result becomes an accepted discovery

Rolf-Dieter Heuer, director-general of Cern, said the amount of data gathered was a factor of 20 greater than had been amassed at the same time last year.

"With one inverse femtobarn, you cannot cover the entire mass region which is allowed for the Higgs boson," Professor Heuer told me.

"However, the experiments can now - unfortunately - exclude quite a large part of this allowed mass region."

Physicists think the Higgs will most probably be found in the low-mass region - between 114 GeV (gigaelectronvolts) and 140 GeV. While the gigaelectronvolt is a unit of energy, in particle physics, mass and energy can be interchanged because of Einstein's equivalence idea (E=MC2).

Professor Heuer said that searches at low masses had picked up small fluctuations "here and there", but that this was expected because physicists were analysing small numbers across a number of different "channels".

"The whole thing becomes more interesting the more data we collect," he explained.

News of the surplus of interesting events - seen by both the Atlas and CMS teams - were outlined at the European Physical Society's HEP 2011 conference here in Grenoble, France.

One candidate noted by the Atlas team occurs at the higher mass of 250 GeV and has reached the 2.8 sigma level of certainty. A three-sigma result means there is roughly a 1 in 1,000 chance that the result is attributable to some statistical quirk in the data.

Five sigma means there is about a one-in-one-million chance that the "bump" is just a fluke and is the level generally required for a formal discovery.

Another Atlas fluctuation occurs between 130 GeV and 150 GeV and is at the 2.5-sigma level.

Professor Dave Charlton, who works on the Atlas experiment at the LHC, called the excess of events "intriguing".

But the particle physicist from the University of Birmingham, UK, told BBC News these "could go up to three sigma, or they could disappear".

HEP 2011 runs until 29 July in Grenoble.

From the BBC today:

 

LHC@home allows public to help hunt for Higgs particle

 

The Large Hadron Collider team will be tapping into the collective computing power of the public to help it simulate particle physics experiments.

Among other pursuits, the effort could help uncover the Higgs boson.

The effort, dubbed LHC@home 2.0, is a vastly updated version of a 2004 effort to enlist the public's computers to simulate beams of protons.

Advances in home computers now allow simulations of the enormously more complex particle collisions themselves.

The LHC facility is the world's most powerful "atom smasher", occupying an underground, 27km ring beneath the Swiss-French border.

"Volunteers can now actively help physicists in the search for new fundamental particles that will provide insights into the origin of our Universe, by contributing spare computing power from their personal computers and laptops," read a statement from Cern, the European Organization for Nuclear Research which runs the LHC.

'Fundamental principles'

Along with the grandeur of the accelerator itself came an unprecedented computing infrastructure to handle the 15 million gigabytes of data produced at the LHC each year.

The Worldwide Large Hadron Collider Computing Grid is a 100m-euro network designed to handle the flood of data and distribute it to scientists worldwide.

The LHC@home project will complement this network by splitting up the gargantuan task of simulating the collisions, feeding those computer simulations back to the scientists for comparison.

"By looking for discrepancies between the simulations and the data, we are searching for any sign of disagreement between the current theories and the physical Universe," says the LHC@home 2.0 website.

"Ultimately, such a disagreement could lead us to the discovery of new phenomena, which may be associated with new fundamental principles of nature."

The project is just the latest in an increasingly long line of "citizen science" projects in which the power of the public's home computers is put to use in solving scientific problems; the search for extra-terrestrial intelligence and the fabulously complex process of protein folding are both subjects of such distributed computing projects.

From the BBC:

 

Higgs boson range narrows at European collider

 

Scientists at the Large Hadron Collider say a signal that suggested they might have seen "hints" of the long-sought Higgs boson particle has weakened.

New results to be presented this week at a conference in India all but eliminate the mid-range where the Higgs - if it exists - might be found.

Physicists will now search for the boson at lower and higher energy ranges.

It is much more difficult to detect new particles in these ranges, however.

Nonetheless, LHC researchers still believe they will either have found the Higgs by the end of next year or confirmed that it does not exist in the form proposed by the current theory of subatomic particles and their interactions, called the Standard Model.

"These are exciting times for particle physics," said Sergio Bertolucci, the research director at the European Organization for Nuclear Research (Cern), which runs the LHC.

"Discoveries are almost assured within the next 12 months. If the Higgs exists, the LHC experiments will soon find it. If it does not, its absence will point the way to new physics."

The Higgs particle was postulated by physicists in 1964 to explain how other sub-atomic particles have mass. It remains the only major particle in the Standard Model yet to be observed, and its discovery or elimination is one of the LHC's chief objectives.

The collider is a giant accelerator machine housed in a 27km-long (17 miles) circular tunnel under the French-Swiss border.

Two beams of proton particles are fired around this subterranean "ring" and smashed together at crossing points.

Big detectors are located at these points to look for new particles in the sub-atomic wreckage of the collisions.

Last month, scientists reported at the Europhysics meeting in Grenoble, France, that the collisions were throwing up some intriguing results.

The data presented at the meeting showed what physicists described as "excess events" across the search area - or mass region - where the Higgs has been predicted to be found. The most significant of these was a surplus of unusual particle events at a mass of 140-145 gigaelectronvolts (GeV).

Since the results were presented, the amount of data collected by the two detectors being used to find the Higgs has more than doubled, according to Fabiola Gianotti, who speaks for the Atlas Collaboration, one of the teams searching for the Higgs.

"Thanks to the superb performance of the LHC, we have recorded a huge amount of new data over the last month," she said. "This has allowed us to make very good progress in our understanding of the Standard Model and in the search for the Higgs boson and new physics."

Guido Tonelli, speaking for the other group at the LHC involved in the search, CMS, described the LHC's performance as "fantastic".

What is an electronvolt?

 
  • Charged particles tend to speed up in an electric field, defined as an electric potential - or voltage - spread over a distance
  • One electron volt (eV) is the energy gained by a single electron as it accelerates through a potential of one volt
  • It is a convenient unit of measure for particle accelerators, which speed particles up through much higher electric potentials
  • The first accelerators only created bunches of particles with an energy of about a million eV
  • The LHC can reach beam energies a million times higher: up to several teraelectronvolts (TeV)
  • This is still only the energy in the motion of a flying mosquito
  • But LHC beams include trillions of these particles, each travelling at more than 99.99% of the speed of light

 

"Whatever the final verdict on the Higgs, we're now living in very exciting times for all involved in the quest for new physics," he commented.

An updated assessment, to be discussed at the Lepton Photon Conference in Mumbai, shows the excess events appear to be melting away, and along with them much premature excitement.

It is often the case in particle physics that one will see an excess building up when the data sample is small, but as one moves on the excess will be either reinforced or diminished; and what seems to be happening now is that the excess is diminishing.

The physicists are used to this - but under the glare of media scrutiny in what may turn out to be the biggest science story of the century so far, every twist and turn of this thrilling project is seized upon and pored over by reporters.

So what happens next?

According to James Gilles, the director of communication for Cern, it is now that the real work starts.

"In some mass areas, the Higgs is much easier to see than in others so in some mass areas it was always going to be easier to find it or exclude it quite quickly," he told BBC News.

"And now what we're being left with is the harder part; the regions where it's harder for us to see and harder to pick out the signal from the background."

The ranges left after these results suggest that the Higgs is either quite a light particle, below about 145 GeV, or a heavy one, above 466 GeV. A couple of islands in the middle, around 250 GeV, have not been fully excluded yet.

According to Cern, Atlas and CMS have excluded the existence of a Higgs over most of the mass region 145 to 466 GeV with 95% certainty.

For the researchers at the LHC, this is now the endgame in their search for the Higgs. But it is a search that could still take many months.

Announced today - per the BBC website:

 

LHC results put supersymmetry theory 'on the spot'

 

Results from the Large Hadron Collider (LHC) have all but killed the simplest version of an enticing theory of sub-atomic physics.

Researchers failed to find evidence of so-called "supersymmetric" particles, which many physicists had hoped would plug holes in the current theory.

Theorists working in the field have told BBC News that they may have to come up with a completely new idea.

Data were presented at the Lepton Photon science meeting in Mumbai.

They come from the LHC Beauty (LHCb) experiment, one of the four main detectors situated around the collider ring at the European Organisation for Nuclear Research (Cern) on the Swiss-French border.

According to Dr Tara Shears of Liverpool University, a spokesman for the LHCb experiment: "It does rather put supersymmetry on the spot".

The experiment looked at the decay of particles called "B-mesons" in hitherto unprecedented detail.

If supersymmetric particles exist, B-mesons ought to decay far more often than if they do not exist.

There also ought to be a greater difference in the way matter and antimatter versions of these particles decay.

The results had been eagerly awaited following hints from earlier results, most notably from the Tevatron particle accelerator in the US, that the decay of B-mesons was influenced by supersymmetric particles.

LHCb's more detailed analysis however has failed to find this effect.

 

Bitten the dust

This failure to find indirect evidence of supersymmetry, coupled with the fact that two of the collider's other main experiments have not yet detected supersymmetic particles, means that the simplest version of the theory has in effect bitten the dust.

The theory of supersymmetry in its simplest form is that as well as the subatomic particles we know about, there are "super-particles" that are similar, but have slightly different characteristics.

The theory, which was developed 20 years ago, can help to explain why there is more material in the Universe than we can detect - so-called "dark matter".

According to Professor Jordan Nash of Imperial College London, who is working on one of the LHC's experiments, researchers could have seen some evidence of supersymmetry by now.

"The fact that we haven't seen any evidence of it tells us that either our understanding of it is incomplete, or it's a little different to what we thought - or maybe it doesn't exist at all," he said.

 

Disappointed

The timing of the announcement could not be worse for advocates of supersymmetry, who begin their annual international meeting at Fermilab, near Chicago, this weekend.

Dr Joseph Lykken of Fermilab, who is among the conference organisers, says he and others working in the field are "disappointed" by the results - or rather, the lack of them.

"There's a certain amount of worry that's creeping into our discussions," he told BBC News.

The worry is that the basic idea of supersymmetry might be wrong.

"It's a beautiful idea. It explains dark matter, it explains the Higgs boson, it explains some aspects of cosmology; but that doesn't mean it's right.

"It could be that this whole framework has some fundamental flaws and we have to start over again and figure out a new direction," he said.

 

Down the drain

Experimental physicists working at the LHC, such as Professor Nash, say the results are forcing their theoretical colleagues to think again.

"For the last 20 years or so, theorists have been a step ahead in that they've had ideas and said 'now you need to go and look for it'.

"Now we've done that, and they need to go scratch their heads," he said.

That is not to say that it is all over for supersymmetry. There are many other, albeit more complex, versions of the theory that have not been ruled out by the LHC results.

These more complex versions suggest that super-particles might be harder to find and could take years to detect.

Some old ideas that emerged around the same time as supersymmetry are being resurrected now there is a prospect that supersymmetry may be on the wane.

One has the whimsical name of "Technicolor".

According to Dr Lykken, some younger theoretical physicists are beginning to develop completely novel ideas because they believe supersymmetry to be "old hat" .

"Young theorists especially would love to see supersymmetry go down the drain, because it means that the real thing is something they could invent - not something that was invented by the older generation," he said.

And the new generation has the backing of an old hand - Professor George Smoot, Nobel prizewinner for his work on the cosmic microwave background and one of the world's most respected physicists.

"Supersymmetry is an extremely beautiful model," he said.

"It's got symmetry, it's super and it's been taught in Europe for decades as the correct model because it is so beautiful; but there's no experimental data to say that it is correct."

Bringing things up to date - from the BBC:

 

'Moment of truth' approaching in Higgs boson hunt

 

In recent months, news headlines have been dominated by one story from the world of particle physics - those befuddling faster-than-light neutrinos.

Such is the interest in those speedy sub-atomic particles that developments in the search for the elusive Higgs boson - usually covered at every twist and turn by journalists - have been all-but eclipsed.

Earlier this month, physicists announced results of a combined search for the Higgs by the Atlas and CMS experiments at the Large Hadron Collider (LHC).

Their analysis, presented at a meeting in Paris, shows that physicists have now covered a large chunk of the search area in detail, ruling out a broad part of the mass range where the boson could be lurking.

An even more important milestone in the Higgs hunt beckons in December.

The Higgs explains why other particles have mass, making it crucial to our understanding of the Universe. But it has never been observed by experiments.

 

Small window

Researchers have now excluded the possibility that the Higgs (in its conventional form) will be found between the masses of 141 gigaelectronvolts (GeV) and 476 GeV.

Statistics of a 'discovery'

 
  • Particle physics has an accepted definition for a "discovery": a five-sigma level of certainty
  • The number of standard deviations, or sigmas, is a measure of how unlikely it is that an experimental result is simply down to chance rather than a real effect
  • Similarly, tossing a coin and getting a number of heads in a row may just be chance, rather than a sign of a "loaded" coin
  • The "three sigma" level represents about the same likelihood of tossing more than eight heads in a row
  • Five sigma, on the other hand, would correspond to tossing more than 20 in a row
  • Unlikely results can occur if several experiments are being carried out at once - equivalent to several people flipping coins at the same time
  • With independent confirmation by other experiments, five-sigma findings become accepted discoveries

Finding the Higgs boson at a mass of 476 GeV or more is considered highly unlikely.

This means that physicists are now focussing their hunt on the remaining "low mass" range - a small window between 114 GeV and 141 GeV.

Within that window, there is an intriguing "excess" in observations - a Higgs hint, perhaps - that stands out at 120 GeV.

But as fluctuations go, this one is relatively weak - at around the two-sigma level of certainty.

This roughly equates to a one in 22 chance that the observation is down to chance. A five sigma level is needed for a formal discovery.

There is also a broader "excess" above that mass. And it must be stressed that such hints may come and go.

But there is an even more intriguing possibility: that the boson may not exist at all, at least in its simplest form.

This is the version of the Higgs that conforms to the Standard Model, the framework drawn up to explain how the known particles - from the quarks to the W and Z bosons to the neutrinos - interact.

In this "zoo" of particles, the Higgs remains hidden in the long grass of its enclosure, invisible to the prying eyes of visitors.

 

Beginning of the end

The search by the LHC has already moved on from the data presented earlier this month.

Teams of scientists at the facility on the Franco-Swiss border have been busy analysing a whopping five inverse femtobarns of data collected by the LHC's experiments up to October this year.

The Atlas and CMS collaborations will present independent analyses of this data set at a seminar in Geneva on 13 December. The respective teams have not had the time to combine their results, as they did for the Paris seminar.

They might see completely different things.

Or, more promisingly, they could both see a fluctuation at around the same mass - as they did when researchers presented findings at the Europhysics meeting in Grenoble, France, in July.

"If you look at the data, it's about five times as much as was presented at the summer conferences," said Dr James Gillies, director of communications at Cern (the Geneva-based organisation that operates the LHC).

"It's possible to exclude much more of the available range for the Higgs.

"It's possible - but I think extraordinarily unlikely - to exclude the Higgs definitively. It's possible that there will be signs something is there.

 

What is an inverse femtobarn?

 
  • The "barn" is a unit of area used in particle collider physics
  • It derives from the measure of a uranium atom's nucleus - comparatively large among atoms, or as physicists joked, "as big as a barn"
  • A femtobarn is a millionth of a billionth of a barn
  • That's just 0.000000000000000000000000000000000000001 square centimetres
  • The inverse femtobarn is a measure of how many particles have smashed into one another in an area equal to one femtobarn

"But what's not possible is to give a definitive discovery announcement, on the status of the analysis, given the time they've had."

Either way, scientists are waiting with bated breath for the December seminar, which will - at the very least - mark the beginning of the end for the Higgs race.

"We are pushing very hard to present preliminary results on the entire statistics," said Dr Guido Tonelli, spokesperson for the CMS collaboration.

He told BBC News that with five inverse femtobarns of data, the researchers will have sufficient sensitivity that "if there is something, we should see first hints. If there is nothing we should see no excess".

"It is the first yes or no. It will very likely not be conclusive - to be really sure at the highest confidence level, we might need to combine the data [from Atlas and CMS] again and collect additional data next year.

"But we are entering a phase where it will be very interesting - this I know."

 

'Uneasy rumour'

The rumour mill is already churning vigorously, and is likely to enter overdrive as the December seminar approaches.

The blogger known as Jester recently proffered a Soviet-inspired analogy: "An uneasy rumour is starting among the working class and the lower-ranked party officials.

"Is the first secretary dead? Or on life support? Or, if he's all right, why he's not showing in public?"

A definitive statement about the Higgs is likely to come next year.

The suggestion that particle physicists have been chasing a chimera for decades is one that some will not want to contemplate. But others regard as a more exciting possibility.

A no-show would open up a new era of activity in particle physics - one focussed on finding an alternative theory to patch up the hole in the Standard Model left by the excision of the Higgs.

Indeed, there is already a substantial body of work on alternatives to the Standard Model Higgs.

As Prof Rolf-Dieter Heuer, director-general of Cern, says, either scenario would represent "a tremendous discovery".

And one particle physicist speaking at the Europhysics conference this year summed it up thus: "God forbid that all we find at the LHC is the Standard Model Higgs and no new physics."

Today's announcement. From the BBC:

 

LHC: Higgs boson 'may have been glimpsed'

 

The most coveted prize in particle physics - the Higgs boson - may have been glimpsed, say researchers reporting at the Large Hadron Collider (LHC) in Geneva.

The particle is purported to be the means by which everything in the Universe obtains its mass.

Scientists say that two experiments at the LHC see hints of the Higgs at the same mass, fuelling huge excitement.

But the LHC does not yet have enough data to claim a discovery.

Finding the Higgs would be one of the biggest scientific advances of the last 60 years. It is crucial for allowing us to make sense of the Universe, but has never been observed by experiments.

This basic building block of the Universe is a significant missing component of the Standard Model - the "instruction booklet" that describes how particles and forces interact.

The Higgs boson

  • The Higgs is a sub-atomic particle that is predicted to exist, but has not yet been seen
  • It was proposed as a mechanism to explain mass by six physicists, including Peter Higgs, in 1964
  • It imparts mass to other fundamental particles via the associated Higgs field
  • It is the last missing member of the Standard Model, which explains how particles interact

Two separate experiments at the LHC - Atlas and CMS - have been conducting independent searches for the Higgs. Because the Standard Model does not predict an exact mass for the Higgs, physicists have to use particle accelerators like the LHC to systematically look for it across a broad search area.

At a seminar at Cern (the organisation that operates the LHC) on Tuesday, the heads of Atlas and CMS said they see "spikes" in their data at roughly the same mass: 124-125 gigaelectronvolts (GeV).

"The excess may be due to a fluctuation, but it could also be something more interesting. We cannot exclude anything at this stage," said Fabiola Gianotti, spokesperson for the Atlas experiment.

Guido Tonelli, spokesperson for the CMS experiment, said: "The excess is most compatible with a Standard Model Higgs in the vicinity of 124 GeV and below, but the statistical significance is not large enough to say anything conclusive.

"As of today, what we see is consistent either with a background fluctuation or with the presence of the boson."

 

'Exciting'

Prof Rolf-Dieter Heuer, director-general of Cern, told BBC News: "Such signals can come and go… Although there is correspondence between the two experiments, we need more solid numbers."

None of the spikes seen by the experiments is at much more than the "two sigma" level of certainty.

A level of "five sigma" is required to claim a discovery, meaning there is less than a one in a million chance the data spike is down to a statistical fluke.

Another complicating factor is that these tantalising hints consist only of a handful of events among the billions of particle collisions analysed at the LHC.

Professor Rolf-Dieter Heuer, director-general of Cern told BBC News: "We can be misled by small numbers, so we need more statistics," but added: "It is exciting."

If it exists, the Higgs is very short-lived, quickly decaying - or transforming - into more stable particles. There are several different ways this can happen, which provides scientists with different routes to search for the boson.

They looked at particular decay routes for the Higgs that produce only a handful of events, but have the advantage of having less background noise in the data. This background noise consists of random combinations of events, some of which can look like Higgs decays.

Other decay modes produce more events - which are better for statistical certainty - but also more background noise. Prof Heuer said physicists were "squeezed" between these two options.

Prof Stefan Soldner-Rembold, from the University of Manchester, called the quality of the LHC's results "exceptional", adding: "Within one year we will probably know whether the Higgs particle exists, but it is likely not going to be a Christmas present."

The simple fact that both Atlas and CMS seem to be seeing a data spike at the same mass has been enough to cause enormous excitement in the particle physics community.

Announced today (from the BBC):

 

LHC claims new particle discovery

 

Cern scientists reporting at conferences in the UK and Geneva claim the discovery of a new particle consistent with the Higgs boson.

The particle has been the subject of a 45-year hunt to explain how matter attains its mass.

Both of the two Higgs-hunting experiments at the Large Hadron Collider have reached a level of certainty worthy of a "discovery".

More work will be needed to be certain that what they see is a Higgs, however.

The CMS team claimed they had seen a "bump" in their data corresponding to a particle weighing in at 125.3 gigaelectronvolts (GeV) - about 133 times heavier than the proton at the heart of every atom.

The result announced at Cern, home of the LHC in Geneva, was met with applause.

The CMS team claimed that by combining two of its data sets, they had attained a confidence level just at the "five-sigma" point - about a one-in-3.5 million chance that the signal they see would appear if there were no Higgs particle.

However, a full combination of the CMS data brings that number just back to 4.9 sigma - a one-in-2 million chance.

Joe Incandela, spokesman for CMS, was unequivocal.

"The results are preliminary but the five-sigma signal at around 125 GeV we're seeing is dramatic. This is indeed a new particle," he told the Geneva meeting.

Atlas results were even more promising.

"We observe in our data clear signs of a new particle, at the level of five sigma, in the mass region around 126 GeV," said Fabiola Gianotti, spokeswoman for the Atlas experiment at the LHC.

 

Massive problem

Anticipation had been high and rumours were rife before the announcement.

Indications are strong, but it remains to be seen whether the particle the team reports is in fact the Higgs - those answers will certainly not come on Wednesday.

A confirmation would be one of the biggest scientific discoveries of the century; the hunt for the Higgs has been compared by some physicists to the Apollo programme that reached the Moon in the 1960s.

Two different experiment teams at the LHC observe a signal in the same part of the "search region" for the Higgs - at a rough mass of 125 Gigaelectronvolts (GeV).

Hints of the particle, revealed to the world by teams at the LHC in December 2011, have since strengthened markedly.

The $10bn LHC is the most powerful particle accelerator ever built: it smashes two beams of protons together at close to the speed of light with the aim of revealing new phenomena in the wreckage of the collisions.

The Atlas and CMS experiments, which were designed to hunt for the Higgs at the LHC, each detect a signal with a statistical certainty of more than 4.5 sigma.

Five sigma is the generally accepted benchmark for claiming the discovery of a new particle. It equates to a one in 3.5 million chance that there is no Higgs and the "bump" in the data is down to some statistical fluctuation.

Statistics of a 'discovery'

 
  • Particle physics has an accepted definition for a discovery: a "five-sigma" (or five standard-deviation) level of certainty
  • The number of sigmas measures how unlikely it is to get a certain experimental result as a matter of chance rather than due to a real effect
  • Similarly, tossing a coin and getting a number of heads in a row may just be chance, rather than a sign of a "loaded" coin
  • A "three-sigma" level represents about the same likelihood as tossing eight heads in a row
  • Five sigma, on the other hand, would correspond to tossing more than 20 in a row
  • Independent confirmation by other experiments turns five-sigma findings into accepted discoveries

Prof Stefan Soldner-Rembold, from the University of Manchester, told BBC News earlier this week: "The evidence is piling up... everything points in the direction that the Higgs is there."

The Higgs is the cornerstone of the Standard Model - the most successful theory to explain the workings of the Universe.

But most researchers now regard the Standard Model as a stepping stone to some other, more complete theory, which can explain phenomena such as dark matter and dark energy.

Once the new particle is confirmed, scientists will have to figure out whether the particle they see is the version of the Higgs predicted by the Standard Model or something more exotic.

Scientists will look at how the Higgs decays or - transforms - into other, more stable particles after being produced in collisions at the LHC.

"We'll look at how often it decays into a pair of photons, how often it decays into Z bosons, how often it decays into W bosons," said Dr Tara Shears, from the University of Liverpool.

"It could match what the Standard Model predicts, but if there are deviations, that means there is new physics at work. That would be the first glimpse through the window at what lies beyond our current understanding."

Well, full marks for your ‘persistance’ here with the ‘science’ content on this site El Loro!

I can see that since my last post here the ‘link’ to ‘science content’ here has all but ‘dissapeared’. My thanks for your attempt at keeping this ‘link’ extant, however, it would seem that the ‘site population’ would rather discuss ‘other things’. BTW. Regards to ‘MUF......’.

I was ‘directed here’ by a link from ‘another site’ commenting upon my past activities, and I was surprised to discover the lack of scientific alacrity. When one considders that this site ‘absorbed’ a ‘lot of’ the ‘science content’ from the ‘C4 Eve site’ it leaves a ‘bitter taste’!

Best regards, Ray Dart.

Extremely Fluffy Fluffy Thing said, 08 March 2015 00:40.

 

"Unfortunately the majority of contributors to the science subjects drifted away reasonably soon after we moved here. Those of us left either don't know enough in depth, don't have the time, or are discouraged by the lack of interest."

 

I can well understand that EFFT. The 'format' for 'posting' here is so different to what posters were comfortable with at the C4 Eve site. I've recently been 'copy-pasting' into 'MS Notepad' for post construction, then copy-pasting into 'Open Office' 'Writer' for uploading onto a site. It works for 'Word Press' sites and may well work for this site, we'll see if this post works. However, 'Word Pro' (my preference for a word processor) seemed unusable for me and 'Notepad' is restrictive on 'character diversity'. That does seem to be the major 'downside' to posting here.

 

If you 'know your stuff', you need to be able to 'explain it' properly.

 

"I always enjoyed reading 'your' debates on C4 around various science subjects."

 

Although I'm flattered by this response (my comments were 'rarely' 'liked'), are you trying to 'enlist'?

 

Best regards, Ray Dart.

 

PS. Yes, I link my true identity with my avatar now. Why not, I'm only an engineer.

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