A modified cluster-hadronization model

TL;DR

This work presents a modified cluster-hadronization model implemented in SHERPA that introduces soft colour reconnection, explicit diquark spin treatment, and a flavour-dependent, mass-based separation between cluster and hadron regimes. Gluon splitting into q qbar or diquark–antidiquark pairs and a detailed flavour-spin weighting scheme expand the allowed hadronization channels and improve baryon production modeling. Preliminary results for e+e- annihilation into light quarks at the Z0 pole show reasonable agreement with PYTHIA and HERWIG and data, with color reconnection reducing cluster masses and modest impacts on multiplicities and spectra. The study outlines ongoing extensions to heavy-quark hadronization and remnant fragmentation for broader collider applicability, signaling a path toward more universal hadronization in SHERPA.

Abstract

A new phenomenological cluster-hadronization model is presented. Its specific features are the incorporation of soft colour reconnection, a more general treatment of diquarks including their spin and giving rise to clusters with baryonic quantum numbers, and a dynamic separation of the regimes of clusters and hadrons according to their masses and flavours. The distinction between the two regions automatically leads to different cluster decay and transformation modes. Additionally, these aspects require an extension of individual cluster-decay channels that were available in previous versions of such models.

Figures (7)

• Figure 2: Direct and crossed flavour arrangement and colour flow guaranteeing colour neutrality for each final-state configuration in cluster two-body decays.
• Figure 3: Primary cluster-mass distribution in electron--positron annihilation events that evolve into light-quark and gluon jets at the $Z^0$ pole. The SHERPA$\alpha$ result is shown with (solid line) and without (dashed line) colour-reconnection (CR) model.
• Figure 4: Predicted multiplicity distribution of charged particles in $e^+e^-$ annihilation for light-quark and gluon jets at the $Z^0$ pole. The SHERPA$\alpha$ result is compared with the default PYTHIA-6.1($uds$) and HERWIG-6.1($uds$) predictions.
• Figure 5: Scaled momentum distribution of charged particles for $E_{\mathrm{cm}}=91.2\ \mathrm{GeV}$ in $e^+e^-$ annihilation considering only the light-quark sector. The SHERPA$\alpha$ prediction is compared with experimental light-quark data provided by the OPAL, DELPHI and SLD collaborations, and to the PYTHIA-6.1($uds$) and HERWIG-6.1($uds$) outcomes, using their default settings. Concerning the mean value $\langle x^{uds}_p\rangle$ of the distributions, only the HERWIG-6.1($uds$) prediction is consistent with the OPAL measurement of $\langle x^{uds}_p\rangle=0.0630\pm0.0003(\mathrm{stat.})\pm0.0011 (\mathrm{syst.})$ given in Ackerstaff:1998hz.
• Figure 6: $\xi^{uds}_p=\ln(1/x^{uds}_p)$ distribution of charged particles for $E_{\mathrm{cm}}=91.2\ \mathrm{GeV}$ in $e^+e^-$ annihilation, considering the light-quark sector only. The SHERPA$\alpha$ prediction is presented together with experimental $uds$ data provided by the OPAL collaboration, and with results from default PYTHIA-6.1($uds$) and default HERWIG-6.1($uds$).