Casimir meets Poisson: improved quark/gluon discrimination with counting observables
Charged track multiplicity is among the most powerful observables for discriminating quark from gluoninitiated jets. Despite its utility, it is not infrared and collinear (IRC) safe, so perturbative calculations are limited to studying the energy evolution of multiplicity moments. While IRCsafe observables, like jet mass, are perturbatively calculable, their distributions often exhibit Casimir scaling, such that their quark/gluon discrimination power is limited by the ratio of quark to gluon color factors. In this paper, we introduce new IRCsafe counting observables whose discrimination performance exceeds that of jet mass and approaches that of track multiplicity. The key observation is that track multiplicity is approximately Poisson distributed, with more suppressed tails than the Sudakov peak structure from jet mass. By using an iterated version of the soft drop jet grooming algorithm, we can define a “soft drop multiplicity” which is Poisson distributed at leadinglogarithmic accuracy. In addition, we calculate the nexttoleadinglogarithmic corrections to this Poisson structure. If we allow the soft drop groomer to proceed to the end of the jet branching history, we can define a collinearunsafe (but still infraredsafe) counting observable. Exploiting the universality of the collinear limit, we define generalized fragmentation functions to study the perturbative energy evolution ofmore »
 Authors:

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;
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 Harvard Univ., Cambridge, MA (United States). Dept. of Physics
 Reed College, Portland, OR (United States). Physics Dept.
 Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Center for Theoretical Physics
 Publication Date:
 Grant/Contract Number:
 SC0013607; SC0012567; SC0015476
 Type:
 Accepted Manuscript
 Journal Name:
 Journal of High Energy Physics (Online)
 Additional Journal Information:
 Journal Name: Journal of High Energy Physics (Online); Journal Volume: 2017; Journal Issue: 9; Journal ID: ISSN 10298479
 Publisher:
 Springer Berlin
 Research Org:
 Harvard Univ., Cambridge, MA (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
 Sponsoring Org:
 USDOE Office of Science (SC), High Energy Physics (HEP) (SC25)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; jets; QCD phenomenology
 OSTI Identifier:
 1425789
Frye, Christopher, Larkoski, Andrew J., Thaler, Jesse, and Zhou, Kevin. Casimir meets Poisson: improved quark/gluon discrimination with counting observables. United States: N. p.,
Web. doi:10.1007/JHEP09(2017)083.
Frye, Christopher, Larkoski, Andrew J., Thaler, Jesse, & Zhou, Kevin. Casimir meets Poisson: improved quark/gluon discrimination with counting observables. United States. doi:10.1007/JHEP09(2017)083.
Frye, Christopher, Larkoski, Andrew J., Thaler, Jesse, and Zhou, Kevin. 2017.
"Casimir meets Poisson: improved quark/gluon discrimination with counting observables". United States.
doi:10.1007/JHEP09(2017)083. https://www.osti.gov/servlets/purl/1425789.
@article{osti_1425789,
title = {Casimir meets Poisson: improved quark/gluon discrimination with counting observables},
author = {Frye, Christopher and Larkoski, Andrew J. and Thaler, Jesse and Zhou, Kevin},
abstractNote = {Charged track multiplicity is among the most powerful observables for discriminating quark from gluoninitiated jets. Despite its utility, it is not infrared and collinear (IRC) safe, so perturbative calculations are limited to studying the energy evolution of multiplicity moments. While IRCsafe observables, like jet mass, are perturbatively calculable, their distributions often exhibit Casimir scaling, such that their quark/gluon discrimination power is limited by the ratio of quark to gluon color factors. In this paper, we introduce new IRCsafe counting observables whose discrimination performance exceeds that of jet mass and approaches that of track multiplicity. The key observation is that track multiplicity is approximately Poisson distributed, with more suppressed tails than the Sudakov peak structure from jet mass. By using an iterated version of the soft drop jet grooming algorithm, we can define a “soft drop multiplicity” which is Poisson distributed at leadinglogarithmic accuracy. In addition, we calculate the nexttoleadinglogarithmic corrections to this Poisson structure. If we allow the soft drop groomer to proceed to the end of the jet branching history, we can define a collinearunsafe (but still infraredsafe) counting observable. Exploiting the universality of the collinear limit, we define generalized fragmentation functions to study the perturbative energy evolution of collinearunsafe multiplicity.},
doi = {10.1007/JHEP09(2017)083},
journal = {Journal of High Energy Physics (Online)},
number = 9,
volume = 2017,
place = {United States},
year = {2017},
month = {9}
}