Measurement of hadronic tau decay identification efficiency using W->taunu events

A study to determine the hadronic tau identification efficiency with W->taunu events is reported, using data collected with the ATLAS detector, corresponding to a luminosity of 34 pb-1. Two approaches were used. In the ``tag & probe'' method, the tag-side is the missing transverse energy and the probe-side is the hadronic tau candidate. The track multiplicity spectrum is fitted simultaneously before and after applying tau identification, hence determining the efficiency. The second technique assumes that the W->taunu production cross section is known and compares expected yields to what is measured in data. The results are consistent with MC predictions and with each others. The estimated scale factor to the MC prediction is consistent with 1 within uncertainties, which are dominated by statistics for the tag & probe and by systematics for the cross section approach.