Safe Jet Vetoes

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 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 $(p_T)$ of the leading charged lepton $\ell$ 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 $\gtrsim95\%$ 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 $p_T$. 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 $m_N = 150-1000$ GeV and the representative active-sterile mixing hypothesis $\vert V_{e4}\vert = \vert V_{\tau 4}\vert$ with $\vert V_{\mu 4}\vert=0$, we find that LHC experiments can probe $\vert V_{e4}\vert^2, \vert V_{\tau 4}\vert^2 \lesssim 6\times10^{-4} - 8\times10^{-3}$, surpassing the global upper limit for $m_N < 450$ GeV, with $\mathcal{L}=3$ ab$^{-1}$ of data at $\sqrt{s}=14$ 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.