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Tau lepton identification ($\tau$-ID) is a challenging but important endeavor
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at hadron colliders. Standard Model (SM) Higgs boson searches and many new
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physics scenarios Beyond the Standard Model (BSM) process have discovery
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channels involving taus. In the Standard Model, the Higgs boson Yukawa
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couplings are proportional to mass, resulting in decays to taus ten percent of
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the time for scenearios where the higgs mass is below the diboson threshold.
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In the Minimal Supersymmetric Model (MSSM), the coupling of members of the
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Higgs sector doublet to the tau lepton is enhanced by a factor of $tan\beta$.
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The large mass of the tau makes it unique among the leptons in that can hadron
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final states. These hadronic decays account for approximately 65\% of all tau
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decays and have a signature of small number of collimated pions. The hadronic
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decays are dominated by small number of collimated pions. This signature is
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very similar QCD jet production, which in general has cross sections many
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orders of magnitude larger than signal processes of interest. An additional
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complication at hadron colliders is the presence of underlying event (UE), due
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to secondary interactions in the $pp$ collision. These underlying event
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particles are dominated by large numbers of soft pions which can overlap true
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tau decays.
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The criterion for a successful $\tau$-ID is twofold: the algorithm must have
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high tau efficiency to facilitate searches for rare new physics while
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supressing the common backgrounds found at hadron colliders. This paper will
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focus on novel algorithms designed to identify true hadronic tau decays and
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reject common backgrounds.
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Tau identification in CMS is performed using objects from the ``Particle Flow''
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algorithm. The particle flow algorithm provides a global and unique
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reconstruction of the event. Signals in various subdectors are linked together
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to reconstruct physics objects at particle granularity.
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