Illustration of correlations in the azimuthal angle relative to the direction
of the leading charged jet in the event, chgjet1.
The "toward" region is defined by || < 60 degrees
and |eta| < 1 (includes particles in chgjet1), while the "away" region is defined by
|| > 120 degrees
and |eta| < 1. The "transverse" region is defined by
60 deg <|| <120 deg
and |eta| < 1.
The "toward" region contains the
leading charged particle jet, while the "away" region, on the average, contains the away-side jet.
The "transverse" region is perpendicular to the plane of the hard 2-to-2 scattering and is very sensitive to
the "underlying event" component of the QCD Monte-Carlo models.