IT鈥橲 first blood to the massive Atlas detector at the Large Hadron Collider. Just days after the physics programme started, Atlas has reported its first detection of W boson particles.
W bosons have been seen at other colliders, but before any of the detectors at the LHC can attempt to discover new particles they must 鈥渞ediscover鈥� established ones. It is 鈥渁n excellent sign鈥� to spot the particles so soon, says Fabiola Gianotti, who heads the Atlas team. 鈥淚t demonstrates that both the LHC accelerator and Atlas work extremely well.鈥�
W bosons decay almost instantly into leptons and neutrinos. On two occasions since the machine began collisions at 7 teraelectronvolts last month, the leptons 鈥� either a positron or a muon 鈥� have been detected in Atlas鈥檚 calorimeter and muon chambers. Neutrinos do not interact with the detector, but their presence was inferred from the imbalance of the decay鈥檚 total momentum 鈥� its 鈥渕issing energy鈥� (see diagram).FIG-mg27564001.jpg
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The detection is interesting in its own right as new particles, such as the Higgs boson, have been predicted to decay into W bosons, says Atlas physicist Andreas Hoecker. 鈥淲 bosons are really very central.鈥�
David Barney, a member of the rival CMS detector collaboration, points to an 鈥渆lement of healthy competition between the two big general-purpose detectors鈥�. He says that many interesting events will be needed from both detectors to produce a complete picture.
