Color-Reconnection Effects on the nMPI-Nch Conditional Multiplicity Fluctuations in PYTHIA 8 pp Collisions

Abstract

Color reconnection (CR) changes both the mean and the dispersion of charged-particle multiplicity in pp collisions. We study the conditional distribution P(Nch | nMPI = m) at fixed PYTHIA interaction count for sqrt(s) = 2.76, 7, and 13 TeV, using charged particles in |eta| < 0.8 and 0.15 < pT < 20 GeV/c. CR is switched on or off while the remaining tune parameters are held fixed. Enabling CR reduces the conditional mean by a larger fraction than the standard deviation. The absolute width therefore decreases, while the coefficient of variation increases in every retained matched MPI bin. This ordering also holds in independent 13 TeV samples with Monash, A14, and CMS CP5. Comparisons with ALICE mean-transverse-momentum data and simulated activity estimators relate these conditional fluctuations to experimentally accessible final-state observables.

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BibTeX RIS

BibTeX

@misc{sarkar2026colorreconnection,
  title = {{Color-Reconnection Effects on the nMPI-Nch Conditional Multiplicity Fluctuations in PYTHIA 8 pp Collisions}},
  author = {Subir Sarkar and Kalyan Dey},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.37511},
  eprint = {2610.37511},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.37511},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - Color-Reconnection Effects on the nMPI-Nch Conditional Multiplicity Fluctuations in PYTHIA 8 pp Collisions
AU  - Subir Sarkar
AU  - Kalyan Dey
PY  - 2026
DA  - 2026/10/28
PB  - arXiv
DO  - 10.48550/arxiv.2610.37511
UR  - https://arxiv.org/abs/2610.37511
AB  - Color reconnection (CR) changes both the mean and the dispersion of charged-particle multiplicity in pp collisions. We study the conditional distribution P(Nch | nMPI = m) at fixed PYTHIA interaction count for sqrt(s) = 2.76, 7, and 13 TeV, using charged particles in |eta| < 0.8 and 0.15 < pT < 20 GeV/c. CR is switched on or off while the remaining tune parameters are held fixed. Enabling CR reduces the conditional mean by a larger fraction than the standard deviation. The absolute width therefore decreases, while the coefficient of variation increases in every retained matched MPI bin. This ordering also holds in independent 13 TeV samples with Monash, A14, and CMS CP5. Comparisons with ALICE mean-transverse-momentum data and simulated activity estimators relate these conditional fluctuations to experimentally accessible final-state observables.
ER  -

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