IT鈥橲 the sort of thing that keeps particle hunters up at night. What if the Large Hadron Collider only turns up the Higgs boson and nothing else? That nightmare would leave the hunt for new physics at a dead end 鈥� a fate that could perhaps be avoided if the LHC hung onto more of its data.
Physicists celebrate even tentative signs of the Higgs (see 鈥�Still on the run鈥�). Thought to give all other particles mass, the Higgs is the last undiscovered particle in the standard model, our most successful theory for how particles and forces interact.
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The trouble is the standard model is incomplete, since it has nothing to say about gravity or dark matter. Unfortunately, no new particles have been found that might point the way to a more powerful theory (see 鈥�11 particles for 11 physics puzzles鈥�). 鈥淚t could be the situation a year from now that nothing will be found at the LHC other than the Higgs,鈥� says of Tel Aviv University in Israel. 鈥淚n that situation, we won鈥檛 really know what to do next.鈥�
See graphic: 鈥淲here the Higgs could still lie鈥�
At a , last week, Volansky proposed a solution: the LHC, which is at CERN, near Geneva in Switzerland, should save more of its data. The accelerator鈥檚 computers only record data when prompted by certain triggers, which are set for expected outcomes, like the particles produced when the simplest version of the Higgs decays. Volansky says we should look for signs of more exotic 鈥� and unlikely 鈥� physics, such as a new force beyond the four we already know. 鈥淲e should drop our prejudice and look for anything that is possible,鈥� he says. 鈥淚f we won鈥檛 check, we won鈥檛 know.鈥�
Others say it is not possible to save more data without extra funding or processing time. The LHC鈥檚 CMS detector, for example, takes the equivalent of 40 million pictures, each with a resolution of 1 billion pixels, every second. 鈥淪toring all the LHC data is impractical,鈥� says of the University of Wisconsin in Madison, who helped develop the detector鈥檚 trigger system.
, another CMS team member at the University of California, Santa Barbara, agrees. Taking more data for one search means taking less for another. 鈥淭he total will always need to fit in the same bandwidth,鈥� he says.
He adds that the hunt for the Higgs will take priority this year, but that when the LHC fires up again in 2015 after a two-year upgrade, it could start to look for more exotic physics. 鈥淪earching further in overlooked corners can always come later,鈥� Lowette says. 鈥淏andwidth can always be reshuffled in case a new signature gains a high enough priority.鈥�
Still, saving even a little more data would give a 鈥渢aste of exotic events that may encode important information鈥�, Volansky says. 鈥淣o one has told us the answer [to what lies beyond the standard model], so sometimes we have to search in the dark.鈥�
Still On the run鈥�
The most wanted particle in physics is still on the loose.
In December, each of the Large Hadron Collider鈥檚 main detectors, CMS and ATLAS, reported seeing a hint of the Higgs at a mass of about 125 gigaelectronvolts, around 133 times the mass of a proton.
Now one of those groups seems to have lost the scent. At a conference last week in La Thuile, Italy, the ATLAS team reported that the statistical significance of its December signal had weakened on closer inspection.
That signal was based on only two of the Higgs鈥檚 five possible decay routes, or channels 鈥� one that decays into four particles called leptons, and the other into two gamma-ray photons. The new ATLAS result involves the remaining three channels 鈥� when the Higgs decays into two W particles, two tau particles, or a bottom quark and a bottom antiquark.
Those three channels so far show no sign of the Higgs, says Sandra Kortner of the Max Planck Institute for Physics in Munich, Germany. But of Rutgers University in Piscataway, New Jersey, points out that these three channels create some particles that ATLAS cannot detect. That means the channels carry less information about the Higgs than the two from December, which are 鈥渢he ones that will be really convincing over time鈥�, he says.
Indeed, combining all five channels still leaves room for the Higgs, says Kortner. 鈥淲e still need more data to really tell.鈥� If the LHC operates as planned, the Higgs will be pinned down by the end of 2012.
