A robust measure of event isotropy at colliders
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Springer
Received: May 7, 2020 Accepted: July 21, 2020 Published: August 19, 2020
Cari Cesarottia and Jesse Thalerb a
Department of Physics, Harvard University, Cambridge, MA 02138, U.S.A. b Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, U.S.A.
E-mail: [email protected], [email protected] 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. Keywords: Jets, QCD Phenomenology ArXiv ePrint: 2004.06125
c The Authors. Open Access, Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP08(2020)084
JHEP08(2020)084
A robust measure of event isotropy at colliders
Contents 1 Introduction
1
2 A robust measure of event isotropy 2.1 Review of Earth mover’s distance 2.2 Energy mover’s distance as a measure of event isotropy 2.3 Comparison to existing event shape observables
3 4 5 9 12 13 15 17
4 Benchmark scenarios: proton-proton colliders 4.1 Top pair production vs. QCD dijet 4.2 Toy model: uniform N -body phase space 4.3 Toy model: quasi-isotropic distributions
19 20 22 23
5 Soft unclustered energy patterns at the LHC 5.1 Model details and analysis strategy 5.2 Results
24 26 29
6 Conclusions and future studies
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A Approximations of event isotropy
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B Events with dijet plus spherical structure
36
C Additional SUEP benchmark scenarios
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1
Introduction
The Large Hadron Collider (LHC) at CERN has enormous potential for discovery, as demonstrated by the first detection of the Higgs boson in 2012 [1, 2]. Other new physics signals near the weak scale may have evaded detection by hiding in unexplored kinematic regimes. The challenge is then to design robust searches for new physics that are sensitive to several possible classes of theories. One promising strategy is to construct observables sensitive to event characteristics that are fundamentally distinct from those arising from the Standard Model (SM). Event shape observables have long provided useful insights into the structure of the SM and the underlying dynamics
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