Search for rare baryonic b decays with the LHCb experiment at the LHC

McCarthy, James (2016). Search for rare baryonic b decays with the LHCb experiment at the LHC. University of Birmingham. Ph.D.

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Abstract

A search was performed for the Λ $_b$ $^0$ →Λ $^0$ η’ and Λ $_b$ $^0$ →Λ $^0$ η decays with the LHCb experiment. The full dataset recorded by LHCb in 2011 and 2012 is used, corresponding to 1.0fb $^-$ $^1$ of proton-proton collision data collected at a centre of mass energy of 7 TeV, and 2.0fb $^-$ $^1$ of data collected at a centre of mass energy of 8 TeV, respectively. The B $^0$ →K $_S$ $^0$ η’ decay is used as a normalisation channel, and a selection is designed and optimised using this decay. By measuring the ratio of the branching fractions for the signal decay to the normalisation decay, many systematic uncertainties cancel out. No significant signal is observed for the Λ $_b$ $^0$ →Λ $^0$ η’ decay, and some evidence is observed for the Λ $_b$ $^0$ →Λ $^0$ η decay with a significance of 3σ. The Feldman-Cousins method is used to make the first measurement of the limit on the branching fractions. The limits are
BF(Λ $_b$ $^0$ →Λ $^0$ η’) < 3.1*10 $^-$ $^6$ at 90% CL.
BF(Λ $_b$ $^0$ →Λ $^0$ η) ε[2.5,22.8]*10 $^-$ $^6$ at 90% CL.