Identification of very-low transverse momentum muons in the ATLAS experiment

The standard muon identification in the ATLAS experiment is optimized for muons with transverse momentum ($p_{\textrm{T}}$) above 5 GeV. However searches for low mass resonances and many B-physics studies often need to identify muons with lower $p_{\textrm{T}}$, where standard algorithms suffer from large backgrounds originating from sources such as hadron decays in flight. A new LowPt selection has been developed to allow optimal muon identification down to 3 GeV in $p_{\textrm{T}}$ using variables that are sensitive to track kinks in the inner detector and to the imbalance between momentum measured in the inner detector and in the muon spectrometer. The new LowPt identification, analyzed in simulation and in data, shows good efficiencies for muons produced in hard collisions and is effective in rejecting backgrounds.