Monday, November 20, 2006

A very small false alarm, with a fruity finish, and notes of lavender and lilac

Monica, my co-director, has made use of one of the internet's strengths. She has set up what I think of as an editorial assistant robot. This robot scours the internet to find articles and happenings of interest to her and to us: anything to do with the Higgs boson, Fermilab, the Tevatron, CERN, and other things. She's finely tuned this robot to send stuff our way that seems relevant to our story. She periodically sends highlights of the robot's findings to me.

Yesterday she sent along something that made me sit up in my chair and blink, cup of coffee in my hand. The article, from The New Scientist, was entitled "Fleeting Particle has Shades of Higgs." If that wasn't enough, the subhead really got my attention:

"The world's most wanted particle, the Higgs, may have already appeared under our very noses without anyone noticing."

Ulp. Huh?

What's more, the article was saying that someone named German Valencia, working at Iowa State University, was re-analyzing data already taken from Fermilab (!) from 1997-1999.

I'll just paste in the article here:

The world's most wanted particle, the Higgs, may have already appeared under our very noses without anyone noticing.

The hypothetical Higgs boson, which is thought to give all other particles their mass, was first proposed in the 1960s as part of the standard model of particle physics. Other models known as "supersymmetric" theories, which posit a heavy counterpart for every particle in the standard model, predict the existence of many different Higgs bosons, each with a different mass. It is the lightest one of these that may have already been produced, according to physicist German Valencia at Iowa State University in Ames, Iowa.

Valencia and colleagues re-analysed data collected between 1997 and 1999 by the HyperCP experiment at Fermilab in Batavia, Illinois. HyperCP was designed to monitor the decay of exotic particles in order to understand why the universe is filled with matter rather than antimatter. Valencia's team focused on the decay of a particle known as sigma into a proton, a muon and an antimuon . According to the standard model, the muon-antimuon pair should have energies that lie between 210 and 240 megaelectronvolts (MeV). But in the three events seen by the HyperCP experiment, they always had the same energy of 214 MeV.

Calculations using the standard model show that the probability of three decay events all generating a muon- antimuon pair with the same energy is about 0.008. "That's pretty low," says Valencia.

A more likely possibility, he says, is that the sigma decayed to a proton and another intermediate particle with a mass of 214 MeV. This intermediate particle then decayed into the muon-antimuon pair, fixing the pair's energy at that value. So what was that mystery particle? The Iowa team's calculations suggest it could be the lightest Higgs boson predicted by one theory of supersymmetry ( ).

"We were obviously very excited that the conditions matched the lightest Higgs," says Valencia. "But it's easy to say 'this could be the Higgs'. The tough part is explaining why this Higgs hasn't popped up in other particle physics accelerators."

To address this, the team calculated the probability of the light Higgs being produced from the decay of particles such as kaons and B-mesons, which have been widely studied at accelerator experiments, including those at CERN in Switzerland and SLAC in California. They found that the nature of the interaction of the Higgs with those particles made the production of the light Higgs highly unlikely.

Dan Kaplan, a member of the HyperCP collaboration at the Illinois Institute of Technology in Chicago, which was not intended to help search for the Higgs, is intrigued. However, he says that more work is needed to confirm the claim. Unfortunately, the HyperCP experiment cannot be repeated, because the proton beam used in the experiment has been shut down. "Three events aren't enough to get them to start it up again, so there's zero chance of rerunning the experiment," says Kaplan.

Another possibility is to re-analyse the old HyperCP data for overlooked decay processes, including any that might rule out the Higgs. Kaplan says, "I'm inspired to suggest to my colleagues that we look into this data again."

Valencia hopes that the Large Hadron collider being built at CERN will look for the production of the light Higgs through a number of processes that his team has described. "We hope our results will inspire new searches to confirm or refute that this is the Higgs," he says.

At this point I started to get a little suspicious. We've been interviewing no less than 10 experimental and theoretical physicists working AT Fermilab, not somewhere in Iowa, and I figured that if there was any sniff of the Higgs in previous data they would probably know something about it. So after writing back to Monica I sent of the following message to Rob Roser, John Conway, Robin Erbacher, Ben Kilminster, and Mark Oreglia (familiar names to my regular readers), all experimental physicists working at Fermilab except Dr. Oreglia, who was our first contact and who teaches at the University of Chicago.

Interestingly, my email started up a little mini-conference online between these five. Rob wrote back first, saying he hadn't read this article. Robin said the same thing. Then Ben asked if someone could send the article around. Mark said he hadn't heard of it, which made him suspect it was not sensational news. He found the article and sent it around, and asked the others how to explain to us, the filmmakers, why they don't "jump up and down when they see an article like this!" He gave a quick answer: the article mentioned only 3 events, which is very underwhelming in the world of science (in an earlier post somewhere I mention the fact that scientists hate exceptions and love trends). Then he goes on to say the schema in the paper sounds a bit contrived.

Then Ben chimed in to say that "First of all, this Higgs is not the one we are looking for." He goes on to say that the group who wrote this paper is describing a Higgs that would result from a model of the universe that there is no evidence for, instead of from the model that everyone else uses (the Standard Model). This Higgs, the one from the paper, would have a mass 500 times smaller than the one they are looking for at the Tevatron. In short, from what I can understand from Ben's reply, is that the "evidence" of this Higgs could actually exist well within the margins of experimentation. Almost as though it were part of a "plus or minus 1%" that you might expect from very complicated mathmatical figuring. Turns out that the possibility of this result just occuring without any meaning at all are 1 in 100. His conclusion is that it's not convincing, and is merely a curiosity that should be studied more. When it gets in the neighborhood of the odds of 1 in 10,000 that it could be random, then it might become more significant.

Ben made a link to a paper that he analyzed in order to come to his conclusions. I'm going to link to it here, mainly so that non-scientists reading this blog (perhaps most of you) can experience the interesting sensation of reading something in your native tongue that is completely incomprehensible. I believe the gist of it has to do with the fact that since the Higgs is so fleeting, it really can be detected only by what it leaves behind after it disappears, sort of like trying to identify who was at a party by sniffing the lingering smell of perfume the next morning. This paper is trying to make the case that this particular lingering smell belongs to the Higgs, even though it's a different smell than what people have been looking for. Did you know that smells are described in words such as "note" and "timbre" and "pitch?" Some smells are considered heavy, some light --- it sounds like the Higgs perfume this article was searching for was "pitched" light, with perhaps a fruity finish, with notes of lavender and lilac, and the Higgs perfume the Tevatron is searching for is pitched low, with a rooty, musty aroma, with notes of chocolate and leather.

Thinking of the Higgs boson as a perfume-wearing party patron is what happens when you turn non-scientists loose on things they don't fully understand, but greatly admire. Any scientists reading this, 1. please accept my apologies and 2. write in and correct the madness.