Friday, April 08, 2011
By Hamish Johnston
Particle physics blogs are buzzing about an innocuous-looking bump in data taken by the CDFexperiment at Fermilab in Chicago – and the possibility that it could be evidence for a new particle.
The unexplained signal was spotted in a study of W and Z boson pairs that are created when protons and antiprotons collide in Fermilab’s Tevatron collider. It appears at about 120–160 GeV /C2in the distribution of jets that are produced in the collisions. The bump has a statistical significance of “three-sigma”, which means that there is a one in 370 chance that the bump is not real.
While that might sound convincing to you and me, particle physicists don’t accept a new result until it has been established at five-sigma – about one in two million chance of not being real. Another problem is that CDF’s sister experiment D0 doesn’t see the bump. Rumours are also circulating thatATLAS at CERN has not seen it.
But if the bump is real, what could it be?
Theoretical physicists are now hard at work trying to explain the bump, and at least one paper – with the intriguing title Technicolor at the Tevatron – has already been posted on the arXiv preprint server. No doubt many more will follow.
What are other physicists saying?
In his blog, Tommaso Dorigo sketches out three possible ways that the bump could be an artefact of how the experiment was done or the data were analyzed. But if the bump is real, he thinks that it could be evidence for a new particle – but not a Higgs boson.
Adam Falkowski seems to agree. “It is not a Higgs; anything Higgsish with 150 GeV mass would prefer decaying to a pair of W bosons rather than to two light jets,” he writes in his blog.
But what about a “non-standard Higgs”? Flip Tanedo explores that possibility in this blog entry.
The story has also captured the imagination of veteran science writer Dennis Overbye in an article in the New York Times. However, most of the leading physicists interviewed by Overbye seem sceptical, yet excited.
Giovanni Punzi from CDF is “strongly thrilled…and cautious at the same time”, New York University’s Neal Weiner says “If it holds up, it’s very big”, and Lisa Randall at Harvard comments “It is definitely interesting, if real”.
We’ll have to wait and see. In the meantime you can read a preprint describing the bump here.