Reconstruction and identification of hadronic tau decays with CMS at the LHC
The current experimental program of the CMS experiment contains many analyses which look for a lepton in the final state. The decay of Higgs boson into leptons is one of the few decay channels which can be used to observe or exclude a low mass neutral scalar boson that is predicted by the Standard Model as well as by many Beyond SM scenarios. Additionally, the observation of a charged Higgs boson, which for masses below 200 GeV preferably decays into a lepton and a neutrino, would represent a unique clue to both the origin of mass and the deeper symmetries in Nature.
The lepton can be useful also in many other analyses beyond the Higgs sector, e.g. to test the lepton/flavour universality.
Being the heaviest lepton, can decay either to or electron (``leptonic '') or to lighter hadrons (``hadronic ''). Most of the leptons decay hadronically (65 %). In hadronic decays, there is an odd number of charged hadrons possibly accompanied by neutral hadrons (due to charge conservation), forming together so-called jet. Finally, there is always at least one neutrino (two for leptonic modes) among the decay products.
Given that bulk of decays are non-leptonic, the efficient reconstruction and identification of jets is of crucial importance for the CMS physics program.
At CMS, the decay products are reconstructed from Particle Flow (PF) objects. In the PF approach, the information from all sub-detectors is combined to identify and reconstruct all particles from collision, namely charged and neutral hadrons, photons, muons and electrons. The reconstruction starts from jets.
The main reconstruction algorithm at CMS is "Hadron plus strips" (HPS). It combines PF electromagnetic particles into strips (due to broadening of calorimeter depositions from photon conversions) in order to reconstruct candidates. Those are combined with charged hadrons to reconstruct visible decay products.
Several identification criteria are applied to the candidates: isolation (how much momentum is carried by jet constituents that cannot be associated with decay products) and rejection against electrons and muons. All discriminators exist in cut- or MVA-based form and have several working points with different values of reconstruction efficiency and rejection against fake candidates.
The aim of this project is to maintain and improve the performance of the CMS tau reconstruction and identification algorithms.