This week, too bad the b is not for boson

The LHCb experiment is designed to measure B mesons...but here is a W boson candidate event. Before we see it, the W decays into a muon and a neutrino. LHCb cannot detect the neutrino, but the muon is very visible: in the end view to the left, the muon shows up as a thick white track pointing downward from the center (ending in green dots that indicate "muon hits" in the muon detection system). Based on conservation of momentum, what do you think is the direction of the unseen neutrino? In the 3D view to the right, the muon track is red and the blue dots are muon hits.

Copyright CERN for the benefit of the LHCb Collaboration

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Taken on June 17, 2010