  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 searches
in events with large missing transverse momentum in proton-proton collisions at
the LHC at CERN. In searches in all-hadronic final states in the CMS and ATLAS
experiments, the angle $\Delta\varphi_i$, the azimuthal angle between a jet and
the missing transverse momentum, is widely used to reduce QCD multijet
background events with large missing transverse momentum, which is primarily
caused by a jet momentum mismeasurement or neutrinos in hadron decays-the
missing transverse momentum is aligned with a jet. A related angular
variable-denoted by $\Delta\varphi^*_\text{min}$, the minimum of the azimuthal
angles between a jet and the transverse momentum imbalance of the other jets in
the event-is used instead in a series of searches in all-hadronic final states
in CMS to suppress QCD multijet background events to a negligible level. In
this paper, before introducing the alternative variables, we review the
variable $\Delta\varphi^*_\text{min}$ in detail and identify room for
improvement, in particular, to maintain good acceptances for signal models with
high jet multiplicity final states. Furthermore, we demonstrate with simulated
event samples that $\hat{\omega}_\text{min}$ and $\chi_\text{min}$ considerably
outperform $\Delta\varphi^*_\text{min}$ and $\Delta\varphi_i$ in rejecting QCD
multijet background events and that $\hat{\omega}_\text{min}$ and
$\tilde{\omega}_\text{min}$ are also useful for reducing the total standard
model background events.
