Search for charged Higgs bosons in $e^+ e^-$ collisions at centre-of-mass energies from 130 to 172 GeV

Abstract The data collected at centre-of-mass energies ranging from 130 to 172 GeV by ALEPH at LEP, corresponding to an integrated luminosity of 27.5 pb −1 , are analysed in a search for pair-produced charged Higgs bosons H ± . Three analyses are employed to select the τ + ν τ τ − ν τ , c s τ − ν τ and c s s c final states. No evidence for a signal is found. Mass limits are set as a function of the branching fraction B (τν) for H ± → τν . Charged Higgs bosons with masses below 52 GeV/ c 2 are excluded at 95% C.L. independently of B (τν) , thus significantly improving on existing limits.