The past year has been a remarkable one in the search for the Higgs. Not only have the Tevatron experiments made strides to actually rule out a Standard Model Higgs Boson in certain mass regions, but progress has been made in filling in an important gap in our understanding of the Higgs sector. In certain extensions of the Standard Model, supersymmetry is introduced as a way to solve problems of the Standard Model at high energy. While solving some problems, supersymmetry creates some new ones. There have been attempts to solve these problems that do so by adding extra Higgs bosons to the theory. In doing this, they create the possibility for one of the Higgs bosons to be very light, perhaps even accessible at BaBar and Belle.
This possibility was part of the motivation for taking the world’s largest Y(3S) and Y(2S) data samples in 2008 at BaBar. In the past year, we have made remarkable progress as a community toward squeezing the possibility of this light Higgs. The CLEO collaboration fired the first volley shortly after BaBar started taking the Y(2S) data. I discussed those results, and the first results from BaBar, in an earlier post [1]. In the past few weeks, the D0 collaboration and BaBar have presented even more stringent results to the physics community.
D0 did what we always wanted LEP to do: look for h -> a a -> 4leptons, where “h” is the Standard Model higgs boson and “a” is the light Higgs boson. This process was not searched for at LEP, and if the light Higgs boson has a mass below the threshold for producing b-quarks it would have eluded detection at LEP. So D0 went for the gap [2]. They don’t see any evidence for this process, a key prediction of the light Higgs boson scenario in extensions of the Standard Model and minimal supersymmetry.
Attacking the problem from the bottom up (pun intended), BaBar has just released two searches. One is brand new, and searches for Y(3S) -> photon + Higgs [3], where the Higgs decays to a pair of tau leptons. The other is an update of a previous preliminary result (discussed in [1]) looking for the same Higgs decaying to a pair of muons [4]. This update uses both the Y(3S) and Y(2S) meson samples, and makes significant improvements in the results. Both see no evidence for the low mass Higgs boson.
The Higgs Boson has eluded us for decades. As the Tevatron continues to push and the LHC comes online, I wonder how much longer the Higgs can withstand the onslaught of brilliant particle physicists. I guess the only escape for the Higgs is if it doesn’t exist at all. And wouldn’t THAT be interesting.
[1] http://steve.cooleysekula.net/goingupalleys/2009/02/15/lets-go-higgs-hunting/
[3] http://arxiv.org/abs/0906.2219
[4] http://arxiv.org/abs/0905.4539
