Tag archives: LHC
By James Dacey
I must confess that I was not aware of this partnership, and I must admit it’s not a partnership I would have seen coming. CERN has teamed up with the organization behind the Eurovision Song Contest, in awarding grants to two multimedia companies to develop content that can spark the scientific curiosity of “tweens”.
Okay, let’s back up a second and define a few terms in this equation. Tweens are described by CERN as children aged 8 to 12; not quite teenagers but no longer big babies either. My teacher friends will shoot me down in flames for this cod-pedology but I guess this age group is old enough to be excited by science but not yet old enough to start truly engaging with scientific concepts.
By Hamish Johnston
Recently I had the pleasure of speaking to CERN’s Steve Myers who is supervising the herculean task of upgrading the superconducting magnets that guide protons around the Large Hadron Collider (LHC).
By James Dacey
It may have become a household name in recent years, but for many the Large Hadron Collider is still a mysterious behemoth lurking somewhere beneath Switzerland. Or is it France?
A new exhibition will seek to bring the technology and the sense of scientific discovery of the LHC to those who have not made the trip to the facility itself. Collider: step inside the world’s greatest experiment will open on 13 November at the Science Museum in London, and run for six months.
By Tushna Commissariat
Are you suffering from particle-collider withdrawal symptoms now that the LHC has begun its long shutdown? If so, you will be pleased to learn that you can focus your attention elsewhere.
The International Linear Collider Collaboration has posted an updated version of its 2013 Technical Design Report on the arXiv preprint server. It’s a short and sweet overview of the collider’s design, including “detailed descriptions of the accelerator baseline design for a 500 GeV e+e llinear collider, the R&D program that has demonstrated its feasibility, the physics goals and expected sensitivities, and the description of the ILD and SiD detectors and their capabilities”.
By James Dacey
My colleague, Hamish Johnston, has just returned from a trip to CERN, where he was granted access to the insides of the Large Hadron Colider (LHC), which is currently being upgraded. He has shared some great photos from his trip on the Physics World Facebook page, including some snaps of the interior of the detector experiments.
By Hamish Johnston at CERN
Today I had the immense good fortune of seeing the insides of the CMS detector at CERN.
The huge detector was pulled open and I could see all the various layers that are used to track the vast numbers of particles that are produced when protons collide at the Large Hadron Collider.
Unlike earlier photos of the detector that were taken when it was being built, the beamline is still intact as it passes through the CMS – a plain black conduit suspended many metres above the floor. You can see the beamline poking out from the centre of the detector in the photo on the right.
Imperial College’s Jim Virdee was our tour guide, and he told us how several military technologies from the former Soviet Union have been put to good use in the detector. These include brass shell casings that were melted down to make components for the detector.
By Hamish Johnston
If you are a fan of astronomy and the comedian David Mitchell, the Open University has a treat for you. Mitchell and the OU have made a series of 12 short animated videos about the physics of the cosmos.
By Hamish Johnston
It’s been quite a rollercoaster ride for physicists working on the Large Hadron Collider (LHC) at CERN. When the collider was first switched on in 2008 it suffered a major explosion when a superconducting connector failed – and was shut down for over a year for repairs. Then in 2010 the LHC began taking data and the excitement about the imminent discovery of the Higgs boson grew and grew – and then on 4 July last year, CERN physicists announced the discovery of a Higgs-like particle.
The graph shows the distribution of the “w-jj excess” as seen by the CDF experiment (Courtesy: Punzi/Fermilab)
By Tushna Commissariat
Two months ago, in early April, the particle-physics community was rife with speculation and excitement over a “bump” – a possible new particle – in the data that Fermilab’s CDF experiment was looking at. On Monday 30 May Giovanni Punzi, a CDF collaborator, presented an update on what is now referred to the “ W-jj” bump, as a part of his talk at the 23rd Rencontres de Blois Particle Physics and Cosmology conference currently being held in France. The update says that the bump is seen in more recent data with an even larger statistical significance.
At the time, CDF was looking for slightly rare di-boson pairs – W bosons produced in association with another W or a Z boson. It noted a bump between 120 and 160 GeV /C2 in the jets produced in the collisions with a statistical significance of about “three-sigma”, which meant that the result would not be considered valuable until a “five-sigma” statistical significance could be established. The new data, however, have established a significance that is officially “closer to five sigma” (unconfirmed sources suggest it is as close as 4.8) and that “it was not just a statistical fluctuation” and that it is now a “serious issue for CDF to understand this”, according to Punzi.
Interestingly, Punzi’s slides also say that it is almost impossible that bump is due to the Standard Model top-quark background, as suggested by some theoretical papers, as that would imply that previous measurements for SM top-quark background had huge errors. The next step forward would be if CDF’s sister experiment D0 or the LHC’s ATLAS or CMS experiments, none of which have found the bump in their data so far, manage to detect it.
This updated result has seen a variety of responses from physicists.
Adam Falkowski, who writes the Resonaances blog, seems rather jubilant. “In a collider experiment, such a huge departure from a Standard Model prediction is happening for the first time in the human history,” he writes. “I don’t have to stress how exciting it is.”
Peter Woit, author of the Not Even Wrong blog, feels that while a five-sigma significance is important, problems with background modelling might thwart the result. “The signal is being extracted from a huge background, so a small misunderstanding of the background could be its cause.” Only a detection of the same result by another experiment would make the case more compelling, according to him.
Tommaso Dorigo, a blogger and CDF collaborator, is still sceptical of the result and chalks it up to bad background modelling, like Woit. “No, it is not the Higgs. And it is not a new particle. It is, in my humble opinion, a problem in the modelling of backgrounds, one which was unnoticed before only because it is small enough to have escaped previous attempts at “tuning” the simulations.”, he writes in his blog.
So while it seems like we the path to “new physics” is full of “bumps”, the field of particle physics is a rather exciting one right now! Take a look at the slides Punzi used for his talk here.
Rolf-Dieter Heuer talking to journalists at the Royal Society, London.
(Courtesy: Tushna Commissariat)
By Tushna Commissariat
The Large Hadron Collider (LHC) at CERN has had its share of good and bad press over the past few years. Controversy and rumours abounded when the machine was switched on in September 2008. The mood then turned quickly to disappointment when its magnets failed and finally to euphoria when the first beams collided at 7 TeV in March 2010.
This week, a meeting to discuss the LHC and all things related was held at the Royal Society in London. The “Physics at the High Energy Frontier – the Large Hadron Collider Project” meeting took place on 16–17 May and saw leading lights of the project come together to discuss the collider and its future.
I was at the meeting for the second day, when a press briefing was held where CERN director Rolf-Dieter Heuer, plus Fabiola Gianotti and Guido Tonelli of the ATLAS and CMS experiments respectively, answered all of the questions that the Higgs-hungry reporters could throw at them!
The three speakers described how the collider has “surpassed all expectations” – experimental and computational. Talking about how the LHC is the very essence of global co-operation, Tonelli stressed that “no country could have done it as a stand-alone”. Heuer boasted that every year about 1000 students get their PhDs thanks to the LHC, while just the ATLAS experiment involves about 3000 researchers.
Explaining how things work at the LHC, Tonelli said, “We [experimental scientists] try to test the theory without prejudice. We ask our friends the theorists to come up with something that we can observe.” The collider has already produced the top quark in Europe for the first time and now it is poised to begin a regime of “new physics”, to look for supersymmetry (SUSY), multiple dimensions, matter–antimatter disparity and, of course, the Higgs boson.
The Higgs…or something else?
“We will have an answer to the Shakespeare question for the Higgs – ‘To be or not to be’ – by the end of 2012” declared a confident Heuer. While he did show a great deal of enthusiasm about discovering the Higgs, Heuer was also keen to point out that not finding the particle would be a great result in itself. “Not finding [the Higgs] when it does not exist is a success,” he exclaimed. “If it does not exist, we need to find something else that takes up the job of the Higgs and gives mass to elementary particles,” he added.
The LHC will run until the end of 2012 without any major breaks and Heuer is confident that it will decide the fate of the Higgs by the end of this run. “Physics will not be the same after 2012.” declared Tonelli. “It will change the view of the world.”
One of the first questions, asked by BBC reporter Pallab Ghosh, was about the recent ”leak” of an unconfirmed sighting of the Higgs by ATLAS. A sighting that was later denied by a paper released by the ATLAS team and in interviews with physicists on various media channels.
“Unfortunately we live in a world of WikiLeaks, so it leaked!” said a grinning Gianotti. On a more serious note, she explained that such leaked results have not undergone the scientific scrutiny that is necessary, and hence are almost always insubstantial.
“The CERN management was not amused by the leak” said Heuer. He went on to ask journalists not to believe leaked results in the future. “Don’t trust it on first sight” he said. Although Heuer’s displeasure was clear, the leak did put the LHC back in the public eye after a few quiet months. Also, the media interest did provide the public with a rare insight into the vetting process that all scientific discoveries undergo. So perhaps the CERN management should lighten up and enjoy the renewed interest in the LHC!
Rolf-Dieter Heuer giving a talk about the future of the LHC at the Royal Society, London. (Courtesy: Tushna Commissariat)
Bumps and jumps
When asked about the Higgs-like ‘bumps’ seen at other experiments like the Tevatron and CERN’s Large Electron Positron Collider (LEP) the panel had mixed replies. The Tevatron bump was dismissed by Gianotti and Tonelli, as they both explained that it was too small, statistically speaking, and was only seen by one of the Tevatron’s two detectors. Would the LHC have a look for the Tevatron signal? “No”, was their reply.
However, “interesting events” seen at 115 GeV by the LEP just before its closure in 2000 are of interest to them. While Heuer did say that it is very difficult to determine if it was anything more than a “hint”, the LHC will be looking for the Higgs at that energy soon.
The International Liner Collider – a possible successor to the LHC – is another project that Heuer is excited about. He feels that CERN, with the LEP and now the LHC under its belt, would be the perfect host for the collider. “I think CERN has huge potential, not only on the human side, but on its experience side. We have all the instruments. So I see CERN in a very good position.” he said.
But what about the money? “If you have an excellent science case, you will get the money. Don’t ask for the money until you have the science figured out.” he said. He pointed out that, compared to the US, in Europe the politics of funding are more stable and for that reason CERN would be a better host.
Right: prototype microwave cavity for the ILC, illuminated for a “Science Night” in Hamburg. (Courtesy: DESY)