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A new measurement of the neutrino asymmetry parameter B in neutron decay, the angular correlation between neutron spin and anti-neutrino momentum, is presented. The result, B=0.9802(50), agrees with the Standard Model expectation and earlier measurements, and permits improved tests on ``new physics'' in neutron decay.
Using data collected with the LHCb detector in proton–proton collisions at a centre-of-mass energy of 7 TeV, the semileptonic decays B¯s0→Ds*Xμ-v¯ and B¯s0→D0K+Xμ-v¯ are detected. Two structures are observed in the D0K+ mass spectrum at masses consistent with the known Ds1+(2536) and Ds2*(2573)+ mesons. The measured branching fractions relative to the total B¯s0 semileptonic rate are B(B¯s0→Ds2*+Xμ-v¯)/B(B¯s0→D0→Xμ-v¯)=(3.3±1.0±0.4)%, B(B¯s0→Ds1*+Xμ-v¯)/B(B¯s0→D0→Xμ-v¯)= (5.4±1.2±0.5)%, where the first uncertainty is statistical and the secon...
A search for the decays View the MathML source and B0→μ+μ− is performed with 0.37 fb−1 of pp collisions at View the MathML source collected by the LHCb experiment in 2011. The upper limits on the branching fractions are View the MathML source and B(B0→μ+μ−)<3.6×10−9 at 95% confidence level. A combination of these results with the LHCb limits obtained with the 2010 dataset leads to View the MathML source and B(B0→μ+μ−)<3.2×10−9 at 95% confidence level.
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