Abstract
In models with colored particle mathcal {Q} that can decay into a dark matter candidate X, the relevant collider process pprightarrow mathcal {Q}bar{mathcal {Q}}rightarrow Xbar{X},+,jets gives rise to events with significant transverse momentum imbalance. When the masses of mathcal {Q} and X are very close, the relevant signature becomes monojet-like, and Large Hadron Collider (LHC) search limits become much less constraining. In this paper, we study the current and anticipated experimental sensitivity to such particles at the High-Luminosity LHC at sqrt{s}=14 TeV with mathcal {L}=3 ab^{-1} of data and the proposed High-Energy LHC at sqrt{s}=27 TeV with mathcal {L}=15 ab^{-1} of data. We estimate the reach for various Lorentz and QCD color representations of mathcal {Q}. Identifying the nature of mathcal {Q} is very important to understanding the physics behind the monojet signature. Therefore, we also study the dependence of the observables built from the pprightarrow mathcal {Q}bar{mathcal {Q}} + j process on mathcal {Q} itself. Using the state-of-the-art Monte Carlo suites MadGraph5_aMC@NLO+Pythia8 and Sherpa, we find that when these observables are calculated at NLO in QCD with parton shower matching and multijet merging, the residual theoretical uncertainties are comparable to differences observed when varying the quantum numbers of mathcal {Q} itself. We find, however, that the precision achievable with NNLO calculations, where available, can resolve this dilemma.
Highlights
The nature of dark matter (DM) remains one of the outstanding mysteries in the particle physics today
Using the state-of-theart Monte Carlo suites MadGraph5_aMC@next-to-leading order (NLO)+Pythia8 and Sherpa, we find that when these observables are calculated at NLO in QCD with parton shower matching and multijet merging, the residual theoretical uncertainties are comparable to differences observed when varying the quantum numbers of Q itself
To further demonstrate the comparability of the MG5_aMC@NLO+PY8 and Sherpa curves, we show in Fig. 9b the same quantities plotted in Fig. 9a for pTj1,cut > 200 GeV but overlaid with the individual, unmerged pp → TpTp + j samples
Summary
The nature of dark matter (DM) remains one of the outstanding mysteries in the particle physics today. If a compressed scenario is realized in nature, one can experimentally resolve the soft, i.e., low pT , visible decays of Q by recoiling against a relatively hard, i.e., high pT , electroweak or QCD radiation that, in its own right, is sufficiently energetic to satisfy trigger criteria Can one readily include potentially important O(αs) corrections to cross sections normalizations, but parton showers augment fixed order predictions with resummed corrections to at least the leading logarithmic (LL) level As a consequence, such observables like the associated jet multiplicity in the monojet process, an exclusive observable that is critical to search strategies, is automatically modeled at LO+LL accuracy.
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