title: Calculating track-based observables for the LHC.
abstract: By using observables that only depend on charged particles (tracks), one can efficiently suppress pileup contamination at the LHC. Such measurements are not infrared safe in perturbation theory, so any calculation of track-based observables must account for hadronization effects. We develop a formalism to perform these calculations in QCD, by matching partonic cross sections onto new nonperturbative objects called track functions which absorb infrared divergences. The track function Ti(x) describes the energy fraction x of a hard parton i which is converted into charged hadrons. We give a field-theoretic definition of the track function and derive its renormalization group evolution, which is in excellent agreement with the pythia parton shower. We then perform a next-to-leading order calculation of the total energy fraction of charged particles in e+ e-→ hadrons. To demonstrate the implications of our framework for the LHC, we match the pythia parton shower onto a set of track functions to describe the track mass distribution in Higgs plus one jet events. We also show how to reduce smearing due to hadronization fluctuations by measuring dimensionless track-based ratios.
authors.affiliation: Department of Physics, University of California at San Diego, La Jolla, California 92093, USA.
authors.forename: Hsi-Ming
authors.initials: HM
authors.lastname: Chang
authors.affiliation: Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, University of Bern, CH-3012 Bern, Switzerland.
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Procura
authors.affiliation: Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Jesse
authors.initials: J
authors.lastname: Thaler
authors.affiliation: Department of Physics, University of California at San Diego, La Jolla, California 92093, USA.
authors.forename: Wouter J
authors.initials: WJ
authors.lastname: Waalewijn