Abstract
Simplified Models are a useful way to characterize new physics scenarios for the LHC. Particle decays are often represented using non-renormalizable operators that involve the minimal number of fields required by symmetries. Generalizing to a wider class of decay operators allows one to model a variety of final states. This approach, which we dub the $n$-body extension of Simplified Models, provides a unifying treatment of the signal phase space resulting from a variety of signals. In this paper, we present the first application of this framework in the context of multijet plus missing energy searches. The main result of this work is a global performance study with the goal of identifying which set of observables yields the best discriminating power against the largest Standard Model backgrounds for a wide range of signal jet multiplicities. Our analysis compares combinations of one, two and three variables, placing emphasis on the enhanced sensitivity gain resulting from non-trivial correlations. Utilizing boosted decision trees, we compare and classify the performance of missing energy, energy scale and energy structure observables. We demonstrate that including an observable from each of these three classes is required to achieve optimal performance. This work additionally serves to establish the utility of $n$-body extended Simplified Models as a diagnostic for unpacking the relative merits of different search strategies, thereby motivating their application to new physics signatures beyond jets and missing energy.
Highlights
Z(→ ν ν) + jets t t + jets QCDNMC per bin ∼ 4 × 106 ∼ 7 × 106 ∼ 1 × 107 matching scale 60 GeV 60 GeV 60 GeV products are expected to be soft
To develop intuition for a broad set of variables, we will characterize sensitivity using curves which detail the signal efficiency versus background rejection power for a given cut in observable space, often referred to as receiver operating characteristic (ROC) curves
With 50% branching ratio for each decay mode and keep only the events where the gluinos decay asymmetrically. Note that while this procedure is artificial in the case of identical particle production, it is possible to have odd numbers of final state partons in associated production, i.e, if the production channel involves multiple states, see table 1 above for examples
Summary
We will leave exploring the implications of these additional directions in model space to future work Considering these effective operators allows us to focus our study on final states only, while not including information about possible intermediate particles in the gluino decay chain. Their work demonstrates that even though we have chosen to use “gluinos” as our parent particles, the implications of our results are expected to hold in a much wider variety of theories that are dominated by non-zero s-wave production This is part of the justification for the comparison between the distributions provided for our 2-parton results with stop pair production (that subsequently decay yielding t t χ χ) given in appendix C. OSETs and our n-body extended Simplified Models are complementary approaches, and the work of [16] gives many of the detailed arguments for the broad applicability of the choices made here
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