Steer clear of buses, Dr Higgs

A flurry of leaks and rumors about statistical fluctuations that may (or may not) have been observed by CERN's Atlas experiment has rather obscured the more significant particle physics news: the astonishing progress of the Large Hadron Colliders' luminosity ramp this year, which is well ahead of schedule. Recent physics runs have been amassing upward of 20 / pb of data (a measure of the number of particle collisions), with the total collected so far approaching 0.3 / fb. Unless they break the machine again, it seems likely that the official target for the year - 1 / fb - might be exceeded by a factor of 5 or more.

What does this mean? Most obviously, it means that by the end of the year (or soon after, when the data analysis is reported) we ought to know a lot more about the existence, or otherwise, of the Higgs Boson. More precisely, as the figure below from the Atlas collaboration shows, 5 / fb of data would serve to robustly exclude the existence of the Higgs across the entire range of masses where it is thought to be lurking. The green line shows the expected utility of the experiment to rule out the existence of hypothetical Higgs particles of different masses with this much data, with the exclusion being robust where the curve drops below 1 on the vertical axis.

So if the Standard Model Higgs does not exist - which paradoxically might be more interesting than its existence, though perhaps not to Peter Higgs - we'll know by the end of the year. If it does exist, then we'll also likely have firm hints, initially perhaps from ATLAS and CMS failing to do as well "as expected" at ruling out Higgs' of some given mass. An actual discovery might still take a little longer - there's some expectation that the Higgs might have a mass close to the lower limit of 115 GeV, which turns out to be the hardest to detect.

Scientifically, the existence of the Higgs is of only peripheral interest astrophysically (though sociologically I think some cosmologists already fear that their subject may become as frustratingly "successful" as particle physics, where a decade or more of experiments have failed to uncover much that is truly new). Of more direct relevance is the fact that the bounty of 2011 LHC data should also strongly constrain the existence of many types of hypothetical supersymmetric particles, which have long been leading candidates for making up the Universe's dark matter. Strictly speaking, failing to find dark matter at the LHC, or underground, would mean rather little - since while it would serve to exclude some popular models there is no shortage of other candidate dark matter particles that could escape direct detection for now. Still, it would be tremendously comforting to be able to finally root the mysterious dark matter in known physics, while failure to do so would leave a nagging worry that perhaps we have the dark matter / dark energy story more fundamentally wrong than we think.