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Title: Implementing NLO DGLAP evolution in parton showers

Abstract

Here, we present a parton shower which implements the DGLAP evolution of parton densities and fragmentation functions at next-to-leading order precision up to effects stemming from local four-momentum conservation. The Monte-Carlo simulation is based on including next-to-leading order collinear splitting functions in an existing parton shower and combining their soft enhanced contributions with the corresponding terms at leading order. Soft double counting is avoided by matching to the soft eikonal. Example results from two independent realizations of the algorithm, implemented in the two event generation frameworks Pythia and Sherpa, illustrate the improved precision of the new formalism.

Authors:
ORCiD logo [1];  [2];  [3]
  1. SLAC National Accelerator Lab., Menlo Park, CA (United States)
  2. Durham Univ., Durham (United Kingdom)
  3. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1407421
Report Number(s):
SLAC-PUB-16965
Journal ID: ISSN 1029-8479; PII: 6851; TRN: US1703148
Grant/Contract Number:
AC02-76SF00515
Resource Type:
Journal Article: 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: 10; Journal ID: ISSN 1029-8479
Publisher:
Springer Berlin
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; Jets; QCD Phenomenology

Citation Formats

Hoche, Stefan, Krauss, Frank, and Prestel, Stefan. Implementing NLO DGLAP evolution in parton showers. United States: N. p., 2017. Web. doi:10.1007/JHEP10(2017)093.
Hoche, Stefan, Krauss, Frank, & Prestel, Stefan. Implementing NLO DGLAP evolution in parton showers. United States. doi:10.1007/JHEP10(2017)093.
Hoche, Stefan, Krauss, Frank, and Prestel, Stefan. Fri . "Implementing NLO DGLAP evolution in parton showers". United States. doi:10.1007/JHEP10(2017)093. https://www.osti.gov/servlets/purl/1407421.
@article{osti_1407421,
title = {Implementing NLO DGLAP evolution in parton showers},
author = {Hoche, Stefan and Krauss, Frank and Prestel, Stefan},
abstractNote = {Here, we present a parton shower which implements the DGLAP evolution of parton densities and fragmentation functions at next-to-leading order precision up to effects stemming from local four-momentum conservation. The Monte-Carlo simulation is based on including next-to-leading order collinear splitting functions in an existing parton shower and combining their soft enhanced contributions with the corresponding terms at leading order. Soft double counting is avoided by matching to the soft eikonal. Example results from two independent realizations of the algorithm, implemented in the two event generation frameworks Pythia and Sherpa, illustrate the improved precision of the new formalism.},
doi = {10.1007/JHEP10(2017)093},
journal = {Journal of High Energy Physics (Online)},
number = 10,
volume = 2017,
place = {United States},
year = {Fri Oct 13 00:00:00 EDT 2017},
month = {Fri Oct 13 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
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  • We present a parton shower which implements the DGLAP evolution of parton densities and fragmentation functions at next-to-leading order precision up to effects stemming from local four-momentum conservation. The Monte-Carlo simulation is based on including next-to-leading order collinear splitting functions in an existing parton shower and combining their soft enhanced contributions with the corresponding terms at leading order. Soft double counting is avoided by matching to the soft eikonal. Example results from two independent realizations of the algorithm, implemented in the two event generation frameworks Pythia and Sherpa, illustrate the improved precision of the new formalism.
  • We present a phenomenological study of the current status of the application of our approach of exact amplitude-based resummation in quantum field theory to precision QCD calculations, by realistic MC event generator methods, as needed for precision LHC physics. We discuss recent results as they relate to the interplay of the attendant IR-improved DGLAP-CS theory of one of us and the precision of exact NLO matrix-element matched parton shower MC’s in the Herwig6.5 environment as determined by comparison to recent LHC experimental observations on single heavy gauge boson production and decay. The level of agreement between the new theory andmore » the data continues to be a reason for optimism. In the spirit of completeness, we discuss as well other approaches to the same theoretical predictions that we make here from the standpoint of physical precision with an eye toward the (sub-)1% QCD⊗EW total theoretical precision regime for LHC physics. - Highlights: • Using LHC data, we show that IR-improved DGLAP-CS kernels with exact NLO Shower/ME matching improves MC precision. • We discuss other possible approaches in comparison with ours. • We propose experimental tests to discriminate between competing approaches.« less
  • Within the framework of generalized factorization of higher-twist contributions to semi-inclusive cross sections of deeply inelastic scattering (DIS) off a large nucleus, multiple parton scattering leads to an effective medium-modified fragmentation function and the corresponding medium-modified DGLAP evolution equations. We extend the study to include gluon multiple scattering and induced quark-antiquark production via gluon fusion. We numerically solve these medium-modified DGLAP (mDGLAP) evolution equations and study the scale (Q{sup 2}), energy (E), length (L), and jet transport parameter (q) dependence of the modified fragmentation functions for a jet propagating in a uniform medium with finite length (a 'brick' problem). Wemore » also discuss the concept of parton energy loss within such mDGLAP evolution equations and its connection to the modified fragmentation functions. With a realistic Wood-Saxon nuclear geometry, we calculate the modified fragmentation functions and compare them to experimental data on DIS off large nuclei. The extracted jet transport parameter at the center of a large nucleus is found to be q{sub 0}=0.024+-0.008 GeV{sup 2}/fm.« less