Tell-tale signature? These four jets of quarks may come from the decay of a Higgs boson. Credit: CERN

Physicists at the European Laboratory for Particle Physics (CERN) near Geneva believe that a new analysis of their recent observations indicates an increased probability that they have witnessed the transitory creation of their current Holy Grail — the Higgs boson.

Although they do not rule out the possibility that there may be another explanation for the events they have observed, the analysis helped physicists last week to convince CERN's director-general, Luciano Maiani, to extend the operation of its Large Electron–Positron (LEP) collider by a month.

LEP was to have been switched off at the end of this month to allow construction to start on its successor, the Large Hadron Collider (LHC). Keeping LEP running for an extra month will cost SFr7 million (US$4 million). This will be found by shuffling CERN's existing budget, although Maiani says it will not disrupt LHC's schedule, or increase its cost.

Scientists working on LEP's four detector experiments had requested a temporary reprieve because their pooled results had pinpointed five ‘events’ that could be interpreted as evidence for the existence of the elusive particle. The Higgs boson is thought to be produced when electrons and positrons collide at an energy of around 115 giga-electron volts (see Nature 407, 118; 2000).

Re-analysis of the results shortly before last week's decision had produced a fivefold reduction in the odds — to 1 in 1,000 — that the observed decay patterns, or ‘signatures’, are random events. But these odds are still four orders of magnitude too high for physicists to say that the existence of Higgs has been demonstrated conclusively.

LEP's temporary reprieve will allow its scientists to double the amount of data they can collect from particle collisions at the high energy levels that LEP was originally designed to achieve. If the signatures of the boson continue to be seen, the confidence limits will have been increased by two orders of magnitude.

“We are excited,” says Tiziano Camporesi, head of LEP's DELPHI experiment. But he points out that the observations still have to be confirmed not only with a higher degree of confidence, but also in a way that is consistent across all detector experiments and all decay modes of the particles involved in the collisions. So far, no events have been seen in other decay modes apart from those involving the creation of quarks.

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