TWO blogging physicists made a stir earlier this year when they divulged rumours that the Higgs boson 鈥� the most-wanted particle in physics 鈥� may have been spotted in Batavia, Illinois. Follow-up results revealed this week leave those hints as tantalising as ever.
In the standard model of particle physics, the hypothetical Higgs boson is needed to give all other particles their mass. More exotic 鈥渟upersymmetric鈥� theories, on the other hand, predict a family of Higgs bosons, each with a different mass. In March, New 杏吧原创 reported that two independent rival groups using the Tevatron accelerator at Fermilab, in Batavia 鈥� the CDF and DZero collaborations 鈥� had detected tentative signals of the lightest supersymmetric Higgs (3 March, p 8).
In Fermilab鈥檚 accelerator, protons and antiprotons are smashed together to create a range of particles, including, perhaps, the elusive Higgs. Physicists sift through the collision debris and scan the energy of the decaying particles for evidence of a particle with the mass of a Higgs. The excitement earlier this year came when the teams spotted a bump in their data, possibly a trace of a particle matching the predicted mass of the lightest Higgs. If it was really there, this particle then seemed to promptly decay into two tau leptons.
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Although further analysis showed the bump was most likely just a random blip in the data, rather than a real event reflecting an actual particle, anything to do with the Higgs has physicists intrigued, says Jason Nielsen, a member of the CDF collaboration based at the University of California, Santa Cruz. 鈥淭he tau result that caused all the excitement was just one half of the picture,鈥� says Nielsen. According to the simplest supersymmetric model, a Higgs should sometimes decay into two tau leptons and at other times decay into two bottom, or b, quarks. 鈥淲e needed to see if there was also a particle with a similar mass decaying into b quarks,鈥� Nielsen says.
The b-decay results are now in. 鈥淲e do see a small bump in about the right mass region,鈥� Nielsen says. Disappointingly, however, the team calculated that the new bump was almost certainly another blip.
Worse still, the DZero group hasn鈥檛 seen any b-quark events at all in this region. 鈥淭his should kill some of the noise around the two-tau result for now,鈥� says Mario Martinez-Perez at the Autonomous University of Barcelona in Spain, who presented the CDF results at the Lepton-Photon conference in Daegu, South Korea, on Monday. However, there is still a chance that the original tau bump was real. There are other supersymmetric models that may predict that the Higgs is more likely to decay into tau leptons than into bottom quarks, Martinez-Perez says.
Nielsen agrees. 鈥淚鈥檓 not sure we鈥檝e fully explored the ramifications of these results in the light of different, more exotic models,鈥� he says.
Results that might resolve the issue are still pouring in from the Tevatron. Crucially for Fermilab, the analysis of these findings could be completed before results start to come in from the Large Hadron Collider, which is due to start up next May at CERN, the European particle physics lab near Geneva, Switzerland. 鈥淔ermilab still has a window of opportunity to chase the Higgs,鈥� says Nielsen. 鈥淚f these candidate Higgs events persist, that really will be interesting.鈥�
鈥淔ermilab still has a window of opportunity to chase the Higgs. If these candidate events persist, that really will be interesting鈥�
