Search for Lepton Number Violating Decays B+ -> pi(-)mu(+)mu(+) and B+ -> K-mu(+)mu(+)

A search is performed for the lepton number violating decay B+ -> h(-)mu(+)mu(+), where h(-) represents a K- or a pi(-), using an integrated luminosity of 36 pb(-1) of data collected with the LHCb detector. The decay is forbidden in the standard model but allowed in models with a Majorana neutrino. No signal is observed in either channel and limits of B(B+ -> h(-)mu(+)mu(+)) h(-)mu(+)mu(+)) < 5.8 X 10(-8) are set at the 95% confidence level. These improve the previous best limits by factors of 40 and 30, respectively.