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We introduce three alternative angular variables-denoted by$\tilde{\omega}_\text{min}$, $\hat{\omega}_\text{min}$, and$\chi_\text{min}$-for QCD multijet event suppression in supersymmetry searchesin events with large missing transverse momentum in proton-proton collisions atthe LHC at CERN. In searches in all-hadronic final states in the CMS and ATLASexperiments, the angle $\Delta\varphi_i$, the azimuthal angle between a jet andthe missing transverse momentum, is widely used to reduce QCD multijetbackground events with large missing transverse momentum, which is primarilycaused by a jet momentum mismeasurement or neutrinos in hadron decays-themissing transverse momentum is aligned with a jet. A related angularvariable-denoted by $\Delta\varphi^*_\text{min}$, the minimum of the azimuthalangles between a jet and the transverse momentum imbalance of the other jets inthe event-is used instead in a series of searches in all-hadronic final statesin CMS to suppress QCD multijet background events to a negligible level. Inthis paper, before introducing the alternative variables, we review thevariable $\Delta\varphi^*_\text{min}$ in detail and identify room forimprovement, in particular, to maintain good acceptances for signal models withhigh jet multiplicity final states. Furthermore, we demonstrate with simulatedevent samples that $\hat{\omega}_\text{min}$ and $\chi_\text{min}$ considerablyoutperform $\Delta\varphi^*_\text{min}$ and $\Delta\varphi_i$ in rejecting QCDmultijet background events and that $\hat{\omega}_\text{min}$ and$\tilde{\omega}_\text{min}$ are also useful for reducing the total standardmodel background events.

Alternative angular variables for suppression of QCD multijet events in new physics searches with missing transverse momentum at the LHC