A new neutrino puzzle?

Measuring neutrino interactions with nucleons at the Fermilab Tevatron, the NuTeV collaboration has reported a tantalizing three-standard-deviation discrepancy with the Standard Model of particle theory. The group directed intense beams of high-energy muon neutrinos and antineutrinos at the 700-ton NuTeV target-detector and measured the ratios of neutral-current to charged-current interactions. The result translates into a value of 0.2277 ± 0.0016 for sin² θ _W, the key mixing parameter of electroweak unification. By contrast, the world average of sin² θ _W from measurements of the masses and decays of the heavy Z⁰ and W^± bosons that mediate the weak interactions is 0.2227 ± 0.0004. The discrepancy, hinted at in earlier CERN data on Z⁰ decay to neutrinos, may be telling us of new particles or interactions that might guide particle theory beyond the confines of the Standard Model. (G. P. Zeller et al. , http://xxx.lanl.gov/abs/hep-ex/0110059 .)