We introduce three alternative angular variables-denoted by
ω~min, ω^min, and
χmin-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 Δφi, 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 Δφmin∗, 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 Δφmin∗ 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 ω^min and χmin considerably
outperform Δφmin∗ and Δφi in rejecting QCD
multijet background events and that ω^min and
ω~min are also useful for reducing the total standard
model background events.Comment: 32 pages, 18 figure