A robust measure of event isotropy at colliders

Abstract

We introduce a new event shape observable — event isotropy — that quantifies how close the radiation pattern of a collider event is to a uniform distribution. This observable is based on a normalized version of the energy mover’s distance, which is the minimum “work” needed to rearrange one radiation pattern into another of equal energy. We investigate the utility of event isotropy both at electron-positron colliders, where events are compared to a perfectly spherical radiation pattern, as well as at proton-proton colliders, where the natural comparison is to either cylindrical or ring-like patterns. Compared to traditional event shape observables like sphericity and thrust, event isotropy exhibits a larger dynamic range for high-multiplicity events. This enables event isotropy to not only distinguish between dijet and multijet processes but also separate uniform N-body phase space configurations for different values of N. As a key application of this new observable, we study its performance to characterize strongly-coupled new physics scenarios with isotropic collider signatures.

Spheres to jets tuning event shapes with 5d simplified models

“…3) forn i the unit vector proportional to the three-momentum of the element p i , etc. Note this differs from [26], where the distance measure was proportional to d ij ∼ 1 − cos θ ij . See appendix B of that paper for a discussion of the different distance measures.…”

“…It has a range T ∈ [0.5, 1], where T = 1 corresponds to two back-to-back particles, and T = 0.5 is an isotropic radiation pattern. While thrust has provided essential insight on the perturbative nature of QCD, it is most sensitive to event shape deviations from the two-particle dijet configuration and has less sensitivity in the quasi-spherical regime (see figure 8 of [26]). To complement such standard observables, we also make use of a recently proposed event shape observable, the event isotropy [26].…”

“…While thrust has provided essential insight on the perturbative nature of QCD, it is most sensitive to event shape deviations from the two-particle dijet configuration and has less sensitivity in the quasi-spherical regime (see figure 8 of [26]). To complement such standard observables, we also make use of a recently proposed event shape observable, the event isotropy [26]. Event isotropy is defined using the energy mover's distance (EMD) [27,28].…”

“…The resulting event isotropy distributions are shown in figure 1; the values of I sph 192 are higher than the corresponding plot in ref. [26] because of our choice of distance measure eq. (1.3).…”

Learning physics at future e−e+ colliders with machine

“…It is interesting that most of these event-level observables were originally proposed for the e − e + and e − h events [41] rather than the hh ones [42]. Recently, an observable to measure event isotropy was also proposed [43]. Another class encode the event-level information at different angular scales.…”