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The Next Round of Hadronic Generator Tuning Heavily Based on Identified Particle Data

K. Hamacher, M. Weierstall

TL;DR

This work leverages 750k hadronic Z decays measured by DELPHI to tightly constrain hadronization models. By fitting JETSET (PS and ME), ARIADNE, and HERWIG to both inclusive distributions and identified-particle data from LEP, the authors derive optimized parameter sets and quantify uncertainties and correlations. The strategy combines a quadratic analytic expansion with MINUIT χ² minimization to efficiently explore high-dimensional parameter space, revealing systematic differences among models and the pivotal role of identified-particle data in constraining fragmentation. Overall, ARIADNE offers the best description of event shapes, while all models require careful treatment of heavy-quark fragmentation and resonance production to reproduce identified-particle spectra. These tunings improve the reliability of hadronization modeling for LEP-era analyses and inform future Monte Carlo development.

Abstract

Event shape and charged particle inclusive distributions determined from 750 000 hadronic Z events measured with the DELPHI detector at LEP are presented. The statistical and systematic precision of this data allows for a decisive confrontation with Monte Carlo models of the hadronization process and a better understanding of the structure of the Z hadronic final state. Improved tunings of the JETSET, ARIADNE and HERWIG parton shower models and the JETSET matrix element model are obtained by fitting the models to identified particle distributions from all LEP experiments and the DELPHI data presented. The description of the data distributions by the models is critically reviewed with special importance attributed to identified particles.

The Next Round of Hadronic Generator Tuning Heavily Based on Identified Particle Data

TL;DR

This work leverages 750k hadronic Z decays measured by DELPHI to tightly constrain hadronization models. By fitting JETSET (PS and ME), ARIADNE, and HERWIG to both inclusive distributions and identified-particle data from LEP, the authors derive optimized parameter sets and quantify uncertainties and correlations. The strategy combines a quadratic analytic expansion with MINUIT χ² minimization to efficiently explore high-dimensional parameter space, revealing systematic differences among models and the pivotal role of identified-particle data in constraining fragmentation. Overall, ARIADNE offers the best description of event shapes, while all models require careful treatment of heavy-quark fragmentation and resonance production to reproduce identified-particle spectra. These tunings improve the reliability of hadronization modeling for LEP-era analyses and inform future Monte Carlo development.

Abstract

Event shape and charged particle inclusive distributions determined from 750 000 hadronic Z events measured with the DELPHI detector at LEP are presented. The statistical and systematic precision of this data allows for a decisive confrontation with Monte Carlo models of the hadronization process and a better understanding of the structure of the Z hadronic final state. Improved tunings of the JETSET, ARIADNE and HERWIG parton shower models and the JETSET matrix element model are obtained by fitting the models to identified particle distributions from all LEP experiments and the DELPHI data presented. The description of the data distributions by the models is critically reviewed with special importance attributed to identified particles.

Paper Structure

This paper contains 28 sections, 6 equations, 41 figures, 54 tables.

Table of Contents

  1. Introduction
  2. Detector and Data Analysis
  3. Monte Carlo Models
  4. JETSET 7.3 / 7.4 Parton Shower
  5. JETSET 7.4 Matrix Elements
  6. ARIADNE 4.06
  7. HERWIG 5.8c
  8. Fit of Monte Carlo Models to Experimental Data
  9. Choice of Distributions
  10. Strategy of the Fit
  11. JETSET & ARIADNE
  12. HERWIG
  13. Comparison of Models to Data
  14. Summary
  15. Definition of Variables
  16. ...and 13 more sections

Figures (41)

  • Figure 1: Sensitivity single track variables
  • Figure 2: Sensitivity to event shape variables
  • Figure 3: Distribution of $\xi_p$ and the scaled momentum $x_p$
  • Figure 4: Distribution of the Rapidity $y_T$ and the Rapidity $y_S$
  • Figure 5: Distribution of $p^{in}_{t}$ with respect to the Thrust axis
  • ...and 36 more figures