Posts Tagged ‘LHC

LHC collides protons with lead ions for the first time

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Protons collide with lead nuclei, sending a shower of particles through the ALICE detector. The ATLAS, CMS and LHCb experiments also recorded collisions this morning (Image: ALICE/CERN

At 1.26am today the Large Hadron Collider (LHC) collided protons with lead ions for the first time.

The switch to colliding different types of particle, rather than like with like, presents technical challenges. “First of all, the collisions are asymmetric in energy which presents a challenge for the experiments,” says accelerator physicist and lead-ion team leader John Jowett. “At the accelerator level we don’t really see the difference in particle size but the difference in the beam size and the fact that the beam sizes change at different rates may affect how they behave in collisions.”

There are further challenges. The LHC usually accelerates two beams of protons in opposite directions – from 0.45 TeV to 4 TeV – before they collide at a total energy of 8 TeV. Radiofrequency (RF) cavities – accelerator components containing electromagnetic fields that kick particles forwards – provide the energy but also keep the two beams in strict synchrony, by kicking backwards when appropriate.

A problem arises because the separate rings for the two beams are contained within a single magnet – a system that ties the momentum of one beam to the momentum of the other, so a lead nucleus, containing 82 protons, is accelerated from 36.9 to 328 TeV, or from 0.18 to 1.58 TeV per proton or neutron.

To account for differences between protons and the heavy lead ions, the RF cavities need to be tuned to different frequencies for each beam. This keeps both particle types on stable central orbits inside their respective rings during injection and acceleration. Similar situations have caused instabilities in other colliders.

Radiofrequency cavities in the LHC tunnel had be retuned to accelerate protons and lead ions (Image: CERN)

“The RF systems of the two rings can be locked together only at top energy before collisions, when the small speed difference that still remains can be absorbed by shifts of the orbits that are acceptably small,” says Jowett. The beams then have to be further adjusted, again by the RF system, so that collisions take place inside detectors, where experiments take physics data. Much detailed work has gone on behind the scenes to prepare LHC systems for this new operational cycle.

This week’s short run will give the experiments a first taste of proton-nucleus collisions before the main run in January to February 2013, the last LHC physics before the accelerator is shut down for maintenance. This will give the experiments vital data to benchmark the lead-lead collision data taken in 2010 and 2011 and also open up exploration of new physics topics.
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Written by physicsgg

September 13, 2012 at 11:27 am

Posted in High Energy Physics

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Hadron Collider is a work of art

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AN EXHIBITION of textiles inspired by the Large Hadron Collider goes on show at the Old Fire Station Gallery next week.

The quilts and framed pieces are the work of local artist Kate Findlay who has a studio in Henley and teaches art at St Mary’s School on St Andrew’s Road.

She has recently shown artwork at the NEC in Birmingham and international scientists have expressed an interest in the unusual pieces. She became interested in the collider, which is buried underground in Switzerland, when she first saw images of it.

She said: “I was struck by the amazing colours and patterns.

“Physicists set out to build this machine for the purpose of studying subatomic particle activity, but it also happens to be a spectacularly beautiful and awesome object.

“I wanted to celebrate some of that beauty and symmetry in my work. As time has gone by, and I’ve continued to work on pieces inspired by the machine, I found myself trying to understand more about the physics too, and to bring this into my work.”

Kate began the series in 2008 and is still producing new pieces.

The exhibition runs from Thursday, August 30 to Tuesday, September 4 and is open every day from 10am to 5pm. For more information about her work, go to website
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Written by physicsgg

August 28, 2012 at 10:58 am

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Physicists unveil plans for ‘LEP3’ collider at CERN

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A group of physicists from Switzerland, Japan, Russia, US and the UK has proposed using the tunnel that currently houses the Large Hadron Collider (LHC) at the CERN particle-physics lab near Geneva for a dedicated machine to study the Higgs boson. The facility, dubbed LEP3, is named after CERN’s previous accelerator, the Large Electron–Positron Collider (LEP), which used to exist in the LHC tunnel before being shut down in 2000. In a preliminary study submitted to the European Strategy Preparatory Group, LEP3’s backers say that the machine could be constructed within the next 10 years.
The plans for LEP3 come just weeks after physicists working at CERN reported that they had discovered a new particle that bears a striking resemblance to a Higgs boson, as described by the Standard Model of particle physics. The ATLAS experiment measured its mass at around 125 GeV and the CMS experiment at 126 GeV.
LEP3 would operate at 240 GeV and comprise two separate accelerator rings that would smash electrons and positrons rather than protons and protons, as with the LHC. In their study, the 20 authors call the concept for LEP3 “highly interesting” and that it deserves more detailed study. “Now is the right moment to get this on the table,” says theorist John Ellis from Kings College London in the UK, who is an author of the preliminary study and hopes that it will trigger debate among physicists as to how to study the new boson in detail.
Tunnel vision
LEP3 is designed to be installed in the LHC tunnel and serve the two LHC’s general-purpose detectors – ATLAS and CMS. If LEP3 is to be built, it will have to fight off two rival proposals for a future collider to study the Higgs – the International Linear Collider (ILC) and the Compact Linear Collider (CLIC). But Ellis says that one advantage of LEP3 is that the tunnel to house it is already built and the collider would use the existing infrastructure, such as cryogenics equipment, thus making LEP3 more cost-effective. LEP3 would also use conventional electromagnets to accelerate particles rather than the accelerating superconducting cavities that will be employed by the ILC.
Which collider is built to succeed the LHC will depend on what the LHC discovers in the next couple of years after it has run at its full design energy of 14 TeV. If it turns out that the LHC finds only the Higgs, then Ellis says there would be a strong case for LEP3. But if more particles are discovered by the LHC – such as supersymmteric particles – it would make sense to consider the other two proposals. “LEP3 could be a more secure option than the ILC if only a Higgs is discovered,” Ellis told “But, of course, it would be foolish to choose anything now, given that the LHC has not hit full energy yet.”
CERN plans to run the LHC into the 2030s after it has undergone a major upgrade in energy and luminosity in the coming decade. However, Ellis thinks that it may even be possible for the LHC and LEP3 to cohabit for a short time. “It would not be ideal, but it could be something to think about,” says Ellis. “If the LHC does not discover anything beyond the Higgs, then would you keep running it for years?”
“Little scope”
Yet some disagree that LEP3 represents the best way to study the Higgs, adding that a decision would have to be made between building LEP3 and running the high-luminosity upgrade to the LHC in the 2020s. “They both have an excellent physics case, but somehow LEP3 presents less chance of a huge breakthrough,” says one leading CERN researcher who prefers not to be named. “[The LHC upgrade] has precision measurements as well as discovery reach to offer.”
That view is shared by linear-collider director Lyn Evans, who told that he thinks it is unlikely that the proposal for LEP3 will get very far. “The first job is to fully exploit the LHC and all its upgrades,” says Evans, who led the construction of the LHC. “This is at least a 20 year programme of work, so I think that it is very unlikely that the LHC will be ripped out and replaced by a very modest machine with little scope apart from studying the Higgs.”
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Written by physicsgg

August 9, 2012 at 7:39 pm

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Answering your Higgs questions

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Scientists at the Large Hadron Collider (LHC) announced the discovery of a Higgs-like boson on July 4 – but what does that mean? What’s a Higgs boson? And how can a particle be like a Higgs? Read on to learn more about the new particle and how it fits into our world.

The following questions were asked on Twitter on 4 July 2012, the day CERN announced the discovery of a new particle with a mass of approximately 126 GeV.


How many Higgs bosons are there?

In the Standard Model there is just one, but many theories predict more. For example, supersymmetry predicts at least five. Supersymmetry also predicts other supersymmetric scalar particles. Models in which the Higgs is composite with internal constituents suggest that it would be accompanied by an infinite number of other composite particles, in which the constituents are arranged in different ways.

What are the key features of this newly discovered boson that would identify it as the Standard Model Higgs?

The decay rates of the new boson could help to identify it as the Standard Model Higgs. The Standard Model predicts certain rates of decay, and, if this boson matches the expected rates, it would offer solid evidence that it is this Higgs. Also, the Standard Model Higgs should have a specific value of spin. If the spin of the new boson differs from predictions, it might be a sign of new physics.

Do you envision a time when we will be able to manipulate Higgs to do things, as we do electrons, perhaps to vary mass?

As a scientist, one should never say never, but it is not clear how it could be done. It would require achieving the same energy density as in collisions at the LHC, but over a large region of space.

What is the difference between the Higgs boson and the Higgs field? Is the field composed of Higgs bosons?

The Higgs field stretches out through the whole of the universe. A massless particle would just glide through, not interacting with the field. A heavier particle would collect more mass. It’s like a skier skimming over the top of a field of snow. The snow would barely be affected, but someone with just boots on would sink deeply into the snow. The Higgs field is the area of snow, while the Higgs bosons are the snowflakes that make up the snow covering the ground.

See video: What is the Higgs boson?

Where do the researchers go from here and how are theories relating to the theoretical dark matter affected?

We need to check whether the new particle has the essential features expected for a Higgs boson. Once we know more about the properties of this boson, we can move forwards. In many theories, including supersymmetry and some composite models, one of the particles associated with the Higgs may make up the astrophysical dark matter. Within these theories, measuring the mass and other properties of the Higgs boson can help to pin down the nature of dark matter.


Is the LHC adapted for the discovery of particles not predicted by theory? If yes how, and in which direction?

Yes. The LHC is a search-and-discovery machine. It uses composite particles (protons) as projectiles so the actual energy liberated (to be used for making new particles) in any given collision spans a wide range, covering the mass range of potential new particles. The ATLAS and CMS detectors are also multipurpose, able to detect all long-lived particles emanating from a collision, including those that arise from decays of heavier, perhaps new, particles. Papers published already by the collaborations include searches for new particles with masses of the order of 1-2 TeV. When the LHC increases in collision energy to 13-14 TeV in 2015 these searches can be extended to much higher energies.

How much data will be needed to isolate the nature of this new particle and possibly identify it as the Higgs boson?

It is very early days! The number of Higgs-boson candidates identified so far is of the order of tens. This is sufficient to be able to understand some basic properties, but not enough to determine details. For example, we know that its spin value must be an integer, but not 1, so does it have spin 0, as expected, or spin 2, say? It’s not yet possible to determine in which of many theories this particle fits. It certainly has properties consistent with the predicted Standard Model Higgs boson but these are very similar (with the current statistics) to the lightest neutral supersymmetric (SUSY) Higgs boson. And some SUSY models predict five Higgs-like bosons! By the end of 2012, the data samples of ATLAS and CMS should at least double, and this should point the way to which theory fits best. But it may be several more years before we understand the details – and indeed this new boson may not fit precisely into any current theory.

The discovery of the Higgs has been hailed as completing the Standard Model. What happened to the graviton?

The graviton has never been a component of the Standard Model. The gravitational force, for which the graviton is the postulated force-carrier, is far too weak to influence the quantum world. Some exotic theories, such as string theory, are attempting to unify all four known forces, but as yet there are no testable quantities.

Assuming the upcoming analysis of the boson turns out to show that it is the expected Higgs, what will be the LHC’s next task (What will the LHC look for now)?

The analysis of the newly discovered boson will certainly take many years. The amount of data so far accumulated is around 2% of that expected for the lifetime of the LHC (until around the year 2022). So this is just the beginning of the story.

Moreover, there are still many unanswered questions that are being tackled in parallel to the origin of mass that the Higgs boson addresses. For example, we know that 96% of the universe is not baryonic matter (the stuff we, the planets and the stars are made of); the nature of this dark matter and dark energy may be elucidated by ATLAS and CMS. And where has all the antimatter – assuming that it was created in equal amounts to normal matter at the time of the big bang – gone? This is something that LHCb in particular is tackling, as well as ATLAS and CMS. The ALICE collaboration plans to study quark-gluon plasma, believed to be present in the moments after the big bang, as it expends and cools, observing how it progressively gives rise to the particles that constitute the matter of our universe today.

But perhaps the most fascinating possibility is that the experiments at the LHC will discover things that we have not even contemplated, something new and unusual that pushes our knowledge forwards in ways we simply cannot predict.

Does today’s announcement mark the triumph of supersymmetry, or make it more likely?

Neither. It is far too early to determine whether the new boson belongs to supersymmetry, the Standard Model or something else.

How many particles were used and collided when this particle was found?

500 trillion – that’s a million million particles!

Future research

If the Higgs boson is discovered will that mean the end of CERN and its work?

Not at all. Once the Higgs boson is officially discovered, there are more questions. Scientists will continue to study the boson to figure out the way it works, as well as how it fits into current models as predicted, or if it has other aspects that may point to new physics.

CERN’s researchers conduct many more studies beyond the search for the Higgs. There are experiments looking for extra dimensions, dark matter and completely new physics. CERN also houses an antimatter facility. There, scientists are studying the properties of antimatter to figure out why, if antimatter and matter were produced in equal amounts during the big bang, there’s more matter in the universe now.

Do you think the public will maintain an interest in the Higgs boson as you continue to explore its properties?

We hope so. Once we know enough about the Higgs-like boson to confirm that it either is the Standard Model Higgs boson or it isn’t, there will be studies to examine exactly how the boson interacts with other particles – giving us more clues to the origin of mass and the beginning of the universe. And if this new boson is not the Standard Model Higgs boson, that’s a sign of new physics beyond the Standard Model. It’s an exciting time, and everyone should stay tuned.

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Written by physicsgg

July 27, 2012 at 4:33 pm

Posted in High Energy Physics

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Boson-spotter’s guide helps you decode the Higgs

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The elusive Higgs boson, or something very close, has finally been spotted at CERN’s Large Hadron Collider near Geneva, Switzerland. The next challenge is to pin down whether the new particle is the boson physicists were expecting or some other beast.

One of the first things physicists want to know about the new particle is itsspin, a quantum property that is analogous to the angle of the axis of rotation of a particle. They also want to know whether it has parity, a property most easily explained as whether a particle is identical to its mirror image – or more like your left and right hands. Perhaps most importantly, they will investigate seeming deviations in the rates that the Higgs decays to certain particles compared with the predictions of the standard model of particle physics.

All these things will help determine whether the new particle merely completes the standard model, offers hints to an elegant, more comprehensive extension – supersymmetry – or demands something else totally new.

You can read more about all this – and what it means for physics – in our special report: Beyond the Higgs. To help make sense of the different options, and to illustrate just what the different possibilities are, we drew up the flowchart below:

It’s not clear when we’ll have answers to the questions – the best-case estimates say by the end of the year. In the meantime, take pleasure in the fact that almost anything is still possible.

Written by physicsgg

July 12, 2012 at 2:48 pm

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Higgs Boson Music: What Might Quarks Sound Like?

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Using a data “sonification” process, researchers at the pan-European GÉANT network have created melodies from the results of the Atlas experiment at the Large Hadron Collider – the experiment that found the so-called ‘God Particle’

Written by physicsgg

July 11, 2012 at 7:40 pm

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The man who built the LHC

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By Alice Lighton

The Large Hadron Collider (LHC) in Geneva is the arguably most famous experiment on Earth. It’s also, by many measures, the largest; a particle collider 27km in circumference and 100m underground, it took 16 years to build and cost £6bn.

The LHC was built to answer some of the burning questions facing particle physicists. Within the massive tunnels, protons travelling at near-light-speed collide with each other, and the physicists examine the resulting debris to try to work out what is going on. Hundreds of researchers scour the data for evidence of the Higgs boson, embraced by the media as “the God particle”. The Higgs, if it is found, would explain why everything around us has mass.

Professor Jon Butterworth, head of Physics at UCL, is, more excited by the prospect of the LHC failing to find the Higgs. The Higgs is at the centre of modern physics, and if the Higgs doesn’t exist, he says “there is no kind of neat little theory waiting to slot into place”. Instead, physics could go almost anywhere. “There’s about a thousand flowers blooming” in theorists minds, said Butterworth.

Constant updates from the LHC on how the hunt for the Higgs is progressing fill the middle pages of newspapers, but we rarely consider the nuts and bolts of the LHC. How do you even begin to build such a vast machine?

The man who was charged with making the LHC a physical reality is Dr Lyn Evans, a Welsh physicist who has worked at the LHC’s home, the European Centre for Nuclear Research (Cern), for around 40 years. He is a typical academic; thoughtful, forthright and slightly scruffy.

Funnily enough, Evans – the man at the helm of the foremost physics experiment of our time – didn’t start out as a physicist. He switched from chemistry at university because “physics was more interesting, and easier.”

Forty years on, he stands by that view, and he is now highly respected in academic circles. In 2010 he received the highest honour in British science when he was elected a fellow of the Royal Society. The august institution nominates only a handful of fellows a year. Evans was honoured not only for his work on the LHC, but also on a previous particle accelerator at Cern, the Super Proton Synchotron (SPS). He enabled the SPS to run at ten times the energy it was originally designed for, paving the way for the discovery of some of the particles that make up the Standard Model of physics.

Evans doesn’t regard building the LHC as simply a physics or an engineering challenge. Digging a 27km circle under the Swiss Alps then filling it with high-tech equipment threw up a myriad of surprises. “Building the LHC… you have to be able to handle anything,” says Evans. After 16 years of work, Evans can claim success. He has built a machine that works; now it is up to physicists to do their experiments.  Results are flowing in from the collider and detectors, and the building works were only marginally over budget – by less than 25 per cent, which Evans describes as “perfectly acceptable” for a high-tech project. But even though he has fulfilled his brief without major incident, Evans reckons that “If I knew [16 years ago] what I know now I would never have started.”

Evans was in charge of constructing the main tunnel of the LHC, through which protons whizz at 99.9999 per cent of the speed of light. Two beams of protons are fired in opposite directions,and then travel round and round the tunnel for a whole day. In caverns at various points along the tunnel are four giant detectors, where protons collide and measurements take place. Two of these detectors, CMS and Atlas, are charged with finding the Higgs boson.  CMS and Atlas were built independently, so that each provides a check on the results of the other. The detectors themselves were designed and constructed by teams of scientists in universities around the world, and then were assembled by Evans’ team in caverns 100m below the ground.

This was no mean feat. One detector in particular, CMS, presented some rather unusual challenges. “When we were preparing that site we came across something that you never want when you’re starting a civil engineering project… Roman ruins,” says Evans. Work stopped for six months while the archaeologists excavated a 4th Century AD Roman villa. While less dramatic than the search for the Higgs, Evans enjoys the nuggets of history the archaeological dig revealed. “The villa is perfectly aligned with the fields today… the land registry in this region was laid out by the Romans and remains to this day.” Also uncovered were coins from Ostia (in Italy), Lyons and London. Even in the 4th Century AD, Cern was an international hub.

But the trouble didn’t end when the dig finished. In a move some might describe as foolhardy, the CMS detector is sited below an underground river. Evans’ engineers knew the river’s course, but digging a cavern through flowing water required some lateral thinking. Rather than going around the river, they decided to simply stop it.  “It was much more difficult than we had anticipated,” says Evans. Engineers sunk pipes down to 50m below the surface which were then pumped full of liquid nitrogen at -77oC.  The liquid nitrogen “[froze the water in] the ground, making it all ice down to 50m”. Then diggers removed the frozen earth, and CMS was lowered in. “That was quite exciting,” says Evans, with exemplary British reserve.

Freezing a river was certainly a creative way to lower CMS into position, but Evans doesn’t regard it as the biggest technical challenge he faced. The protons in the LHC originate in an old linear collider, and would travel in a straight line were it not for intense magnetic fields from supermagnets in the tunnels. The supermagnets control the direction of the proton’s flight path. Like a Ferrari travelling at 300mph, protons moving at only a few kph less than the speed of light are difficult to bend round corners. Supermagnets have been used for years in MRI scanners, but none of these could produce the high fields needed in the LHC. “When we started we didn’t have a single superconducting magnet that worked,” Evans recalls. “[Not] even a small model, a foot long.”

Sixteen years on, and the LHC uses 2000 supermagnets, each 14 metres long. Supermagnets only work at very low temperatures, and work better the colder they are, so each is filled with liquid helium at -271oC .

Liquid helium is a tricky substance to handle – as Evans puts it, “ nobody in their right mind would deal with that”. A bizarre quantum mechanical effect, superfluidity, means that all the liquid in a pipe can leak from just a tiny crack. A leak underground is therefore a nightmare scenario. There is only one entrance to the 27km tunnel wide enough to lift a magnet out, and manoeuvring them in the dark tunnel is a slow process. Each magnet had to be tested at the operating temperature of -271oC before being lowered into the tunnel. Cooling and re-warming each magnet takes over a week, so magnets were built and tested for 24 hours a day, seven days a week, for 50 weeks of the year. So far thanks to careful welding of joints, only relatively minor setbacks have occurred.

Most notorious among setbacks is the electrical connection that fizzled out shortly after the LHC switch-on in 2008. The tunnel contains around 10,000 electrical connections, each with a one in 10,000 chance of failing. The statistics were uncannily precise – shortly after being fired up for the first time, one of the connections failed, shutting down the LHC for several months.

At least one setback in this ambitious project was probably inevitable. The collider was designed not only to find the Higgs boson, but probe questions around where we came from and why we are here – how did the big bang lead to the Universe? Why is there matter? What are we made of? Physicists have been asking these questions for years. But when construction started, the technology didn’t exist to make the LHC a reality. Evans had to develop the tools he needed. The technology is therefore new, and built-to-purpose.

While the main tunnel was all under Evans’s control the detectors were built in bits by over 150 institutions. “When you’re in the LHC and you don’t like something, you can do something about it, but if an institute in Siberia is not producing the goods, you’ve got no control at all over them, ” said Evans. Despite this fragmented approach, the detectors worked. They slotted into place perfectly.

Industrialists and business people tend to be surprised that this behemoth of engineering has succeeded with academics at the helm. Professor Butterworth recalls showing an industrialist around the nearly-complete Atlas detector. “When he walked in the room and he didn’t say anything for about 15 seconds – which was the quietest he’d been all day.”

Remarkable scientific and technological achievements have been achieved with limited money. According to Evans, the budget of Cern has been constant in real terms for the past forty years. The same philosophy might not work in industry, driven by profit. “The only reason it works is the will of the people, that they really want to do the science from this.”

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Written by physicsgg

July 7, 2012 at 7:23 am

Posted in High Energy Physics, TECHNOLOGY

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Large Hadron Collider – 60 Minutes and Fred Watson

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Written by physicsgg

June 25, 2012 at 9:16 am

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