### Abstract

The decays (Formula presented.) and (Formula presented.) are studied with the ATLAS detector at the LHC using a dataset corresponding to integrated luminosities of 4.9 and 20.6 fb^{-1} of pp collisions collected at centre-of-mass energies (Formula presented.) TeV and 8 TeV, respectively. Signal candidates are identified through (Formula presented.) and (Formula presented.) decays. With a two-dimensional likelihood fit involving the (Formula presented.) reconstructed invariant mass and an angle between the (Formula presented.) candidate momenta in the muon pair rest frame, the yields of (Formula presented.) and (Formula presented.), and the transverse polarisation fraction in (Formula presented.) decay are measured. The transverse polarisation fraction is determined to be (Formula presented.) = 0.38 \pm 0.23 \pm 0.07(Formula presented.), and the derived ratio of the branching fractions of the two modes is (Formula presented.), where the first error is statistical and the second is systematic. Finally, a sample of (Formula presented.) decays is used to derive the ratios of branching fractions (Formula presented.) and (Formula presented.) = 10.4 \pm 3.1 \pm 1.5 \pm 0.6(Formula presented.), where the third error corresponds to the uncertainty of the branching fraction of (Formula presented.) decay. The available theoretical predictions are generally consistent with the measurement.

Original language | English (US) |
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Article number | 4 |

Pages (from-to) | 1-24 |

Number of pages | 24 |

Journal | European Physical Journal C |

Volume | 76 |

Issue number | 1 |

DOIs | |

Publication status | Published - Jan 1 2016 |

Externally published | Yes |

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### ASJC Scopus subject areas

- Physics and Astronomy (miscellaneous)
- Engineering (miscellaneous)

### Cite this

*European Physical Journal C*,

*76*(1), 1-24. [4]. https://doi.org/10.1140/epjc/s10052-015-3743-8