Abstract

Central jet vetoes are powerful tools for reducing QCD background in measurements and searches for electroweak and colorless, new physics processes in hadron collisions. In this letter, we report the key findings of a new philosophy to designing searches for such phenomena at hadron colliders, one designed and centered around a dynamical jet veto instead of a static veto applied independently of other selection criteria. Specifically, we investigate the theoretical and phenomenological consequences of setting the jet veto scale to the transverse momentum (pT) of the leading charged lepton ℓ in multi-lepton processes on an event-by-event basis. We consider the case of a TeV-scale heavy neutrino N decaying to the trilepton final state and find the following: (i) Perturbative uncertainties associated with the veto greatly reduce due to tying the veto scale to the hard process scale. (ii) The signal efficiency for passing the veto jumps to ≳95% and exhibits little-to-no dependence on the neutrino mass scale. (iii) Top quark and “fake” lepton rejection capabilities also improve compared to only vetoing heavy flavor-tagged jets above a fixed pT. This results in an increased sensitivity to active–sterile neutrino mixing by approximately an order of magnitude over the LHC's lifetime. For a Dirac neutrino with mass mN=150–1000 GeV and the representative active–sterile mixing hypothesis |Ve4|=|Vτ4| with |Vμ4|=0, we find that LHC experiments can probe |Ve4|2,|Vτ4|2≲6×10−4–8×10−3, surpassing the global upper limit for mN<450 GeV, with L=3 ab−1 of data at s=14 TeV. Due to the color structures of the heavy N production mechanisms considered, we argue that our results hold broadly for other color-singlet processes.

Highlights

  • Jet vetoes, i.e., the rejection of events with jets above a transverse momentum threshold, are incredibly powerful tools for reducing QCD backgrounds in measurements and searches for electroweak (EW) and colorless new physics processes at hadron colliders

  • We demonstrate that they can be successfully used in a broad class of experimental searches, including searches for new high-mass particles as well as events with τ leptons decaying hadronically

  • We find an impressive improvement over traditional, fixed-possessing transverse momenta (pT) jet vetoes

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Summary

Introduction

I.e., the rejection of events with jets above a transverse momentum threshold (pVTeto), are incredibly powerful tools for reducing QCD backgrounds in measurements and searches for electroweak (EW) and colorless new physics processes at hadron colliders. For final states with multiple charged leptons, pp → n + X , ∈ {e, μ, τ }, we set on an event-by-event basis the value of pVTeto to be the pT of the leading (highest pT ) charged lepton Dynamical jet vetoes, such as the one we propose, have been considered previously in the context of EW boson production [17,18,19], but only for computational convenience. (iii) Top quark and “fake” lepton rejection capabilities improve compared to only vetoing heavy flavor-tagged jets To illustrate these results, we have investigated the production in proton collisions of a hypothetical, heavy colorless particle, namely a heavy neutrino (N), that decays to a trilepton final state. For a more extensive collection of results, we refer readers to Ref. [25]

Simplified heavy neutrino model
Computational setup
Heavy neutrino signal process
Safe jet vetoes
Top quark production
EW triboson production
EW diboson production
Fake leptons
Results and outlook
Summary and conclusion
Full Text
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