Tag archives: particle accelerator

By Tushna Commissariat

Looks like the Large Hadron Collider (LHC) at the CERN particle physics lab had an interesting few days last week, just before everybody left for Easter, and the Internet is now abuzz with rumours of an impending discovery.

But before we get into any of the highly interesting and debatable stuff, let’s look at one thing that has definitely happened at the LHC.

Around midnight on Friday 22 April, the LHC set a new world record for beam intensity when it collided beams with a luminosity of 4.67 × 10³² cm^–2s^–1. This was significantly more than the previous luminosity record of 4.024 × 10³² cm^–2s^–1 held by the US Fermi National Accelerator Laboratory’s Tevatron collider in 2010.

This new beam intensity was achieved after two weeks of planning and readying the collider. The machine is now moving into a phase of continuous physics scheduled to last until the end of the year when, after a short technical stop, the machine will resume running for 2012.

“Beam intensity is key to the success of the LHC, so this is a very important step,” said CERN director Rolf-Dieter Heuer in a statement. “Higher intensity means more data, and more data means greater discovery potential.”

But didn’t I read all about some record being broken by the LHC last year, you ask? Yes, but that was the LHC accelerating its proton beams to 3.5 TeV each, leading to later collisions at 7 TeV. Now it is the beam intensity or the “luminosity” that is record breaking. Luminosity gives a measure of how many collisions are happening in a particle accelerator. So the higher the luminosity, the more particles are likely to collide which is necessary while looking for rare particles like the infamous Higgs boson.

“There’s a great deal of excitement at CERN today,” said CERN’s director for research and scientific computing, Sergio Bertolucci, “and a tangible feeling that we’re on the threshold of new discovery.”

Well, it looks like Bertolucci spoke a tad too soon, as on the same day a leaked memo posted by an anonymous commenter on mathematician Peter Woit’s blog, claimed that certain researchers at the ATLAS experiment at CERN had seen firm evidence for the Higgs particle in recent data.

The memo, though not official by any means, was authored by four ATLAS members who claimed to have seen an excess number of photons produced at energy of 115 GeV that could be caused by the decay of the Higgs particle into photons.

Surprisingly, only a few websites and blogs mentioned the news for the first day or so, before slowly more people seemed to notice this juicy story of physics, Higgs and betrayal!

On 25 April, Nature reported on its blog, an official statement from ATLAS spokeswoman Fabiola Gianotti. Gianotti said “Only official ATLAS results, i.e. results that have undergone all the necessary scientific checks by the collaboration, should be taken seriously.” She went on to say that signals of the kind reported in the memo show up often during data analysis and are later falsified after more detailed scrutiny.

But the damage had already been done as physicists and others began to comment on the legitimacy of the claim made in the memo and the ethics of such an internal memo being posted and talked about online.

As people began to look deeper into the memo, interesting facts began to creep up.

Tommaso Dorigo, from the University of Padova in Italy wrote an initial post on his blog A Quantum Diaries Survivor that turned into a debate and eventually a bet! His post was sceptical from the start and he gave his reasons for why he was sure it as nothing more than a blip in the data, then went on to explain in more detail what other data already exists.

After that, a regular reader of his blog pointed out that the authors of the ATLAS study are actually physicists from Wisconsin, and include a Professor Wu, “who was among those less happy of the decommissioning of LEP [the Large Electron-Positron Collider] at the time when they were claiming a possible Higgs signal at 115 GeV. So maybe these guys have been looking for some confirmation of the 115 GeV Higgs all along”.

Woit too was quick to distance himself from the memo saying that “it should be made clear that, while members of ATLAS work here at Columbia, I have no connection at all to them, and they had nothing to do with this. The source of the abstract posted here anonymously as a comment is completely unknown to me.”

As more people debated and commented over the memo, Dorigo came back to say that he would bet anyone who “has a name and a reputation in particle physics (this is a necessary specification, because I need to be sure that the person taking the bet will honour it) that the signal is not due to Higgs boson decays” and then updated that comment by saying that if he is wrong he would pay $1000 but that if he is right he would be given only $500.

Meanwhile, Channel 4 conducted an interview with Jon Butterworth, a particle physics professor at University College London, who also works at ATLAS. He went on to say the same thing; that nothing would be definitive until it was scrutinized by CERN officially (look above).

So at the end of the day, it looks like the world is going to have to wait a while longer before Higgs boson gets its official post in the Standard Model hall of fame.