Abstract
New particles beyond the Standard Model might be produced with a very high boost, for instance if they result from the decay of a heavier particle. If the former decay hadronically, then their signature is a single massive fat jet which is difficult to separate from QCD backgrounds. Jet substructure and machine learning techniques allow for the discrimination of many specific boosted objects from QCD, but the scope of possibilities is very large, and a suite of dedicated taggers may not be able to cover every possibility — in addition to making experimental searches cumbersome. In this paper we describe a generic model-independent tagger that is able to discriminate a wide variety of hadronic boosted objects from QCD jets using N -subjettiness variables, with a significance improvement varying between 2 and 8. This is in addition to any improvement that might come from a cut on jet mass. Such a tagger can be used in model-independent searches for new physics yielding fat jets. We also show how such a tagger can be applied to signatures over a wide range of jet masses without sculpting the background distributions, allowing to search for new physics as bumps on jet mass distributions.
Highlights
Discrimination of top quarks and W/Z hadronic decays from QCD jets, they may not be able to identify fat jets arising from the decay of BSM boosted particles
If the former decay hadronically, their signature is a single massive fat jet which is difficult to separate from QCD backgrounds
The generic anti-QCD taggers we have developed in this work provide an alternative to usual taggers in LHC searches for new physics in the boosted regime, with the main advantage being their broad sensitivity to multi-pronged boosted signatures
Summary
The generic anti-QCD taggers we have developed in this work provide an alternative to usual taggers in LHC searches for new physics in the boosted regime, with the main advantage being their broad sensitivity to multi-pronged boosted signatures. [54], which looks for XH decays of a heavy resonance, selecting H → bb for the Higgs boson and a two-pronged decay X → qqfor X, with a set of overlapping mass windows for the new particle X and a standard tagger D2(β=1) In this case, a generic tagger could be used to provide sensitivity to X → qqbut to other topologies as well. We have demonstrated that an approach based on standardising along the principal component axes gives satisfactory results in simulation, which is implemented by building a ‘transformation map’ in the two-dimensional plane of mJ and pT J , using Monte Carlo simulation of the QCD background This map relates the N -subjettiness variables τN(β) to the PCA-scaled ones τNPCA(β), which are the inputs to the tagger. This will constitute a leap forward in new physics searches at the energy frontier, and is well worth the effort
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