Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 2004.00524

Recursive fragmentation of a polarized quark

Albi Kerbizi
View original source ↗Read source document ↗Export metadata ↓

Abstract

The thesis is devoted to the study of the fragmentation process of polarized quarks, and in particular of the Collins effect used for the extraction of the quark transversity distribution. The aim is to include the spin degree of freedom in the hadronization part of Monte Carlo event generators by using the string+${}^3P_0$ model. The model is reviewed here and the relevant functions have been written in a form suitable for a Monte Carlo implementation. Two main variants of the model for pseudoscalar meson production are formulated and both of them have been implemented in stand alone Monte Carlo programs. After tuning one single parameter, the simulation results are compared with the measured Collins and dihadron transverse spin asymmetries showing a satisfactory qualitative agreement. Given this encouraging outcome, one of them has been interfaced with the hadronization part of the PYTHIA event generator. The quark transversity distribution has been implemented in the generator allowing to simulate for the first time the polarized SIDIS process. The comparison of the simulated transverse spin asymmetries with the experimental data is found to be very promising. As final development, vector meson production and decays have been included in a consistent way with the rules of quantum mechanics. The effect of vector meson production on transverse spin asymmetries has been studied in detail with a stand alone Monte Carlo program showing that the new model is a promising and powerful model for the description of the polarized quark fragmentation process.

Explore related subjects

hep-ph

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Albi Kerbizi. 2020-04-01. Recursive fragmentation of a polarized quark. https://arxiv.org/abs/2004.00524

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

The Physics of Herwig 7

We present the physics foundations and recent developments of Herwig 7, the modern successor of the original HERWIG and Herwig++ series. Herwig 7 provides a flexible and systematically improvable framework for the simulation of high-energy lepton and hadron collisions, with particular emphasis on QCD and EW effects. Hard scattering processes are generated within the automated Matchbox framework, which integrates external amplitude providers, supports tree-level, next-to-leading-order (NLO) and loop-induced matrix elements, and implements subtraction schemes, multi-channel phase-space sampling, dynamic scale choices and both POWHEG- and MC@NLO-type matching algorithms. Consistent multijet merging at LO and NLO is provided, enabling precise predictions across a wide range of SM processes. Parton radiation is simulated using two complementary showers: an angular-ordered shower incorporating QCD coherence and the heavy-quark dead-cone effect, and a dipole shower optimised for NLO matching and multijet merging. Higher-order corrections are included through matrix-element corrections and dedicated reweighting techniques, while QED and EW radiation are treated using a YFS formalism and EW showering algorithms. The modelling of non-perturbative physics employs an advanced cluster hadronization framework with improved cluster formation, fission and decay, as well as colour reconnection models, heavy-quark effects and interfaces to alternative hadronization schemes. An extended eikonal multiple-partonic-scattering model, incorporating semi-hard and soft components together with diffractive interactions, enables realistic descriptions of minimum-bias and underlying-event data. Herwig 7 thus represents a versatile event generator, providing a coherent, modular and extensible platform for Standard Model and beyond-the-Standard-Model collider phenomenology at current and future facilities.

hep-ph↗
arXiv2026

Tensor Decomposition for Energy-Momentum Correlation Functions

We establish the general functional form of the energy-momentum-tensor two-point function in Euclidean coordinate space at zero and finite temperature. The full correlation function is first decomposed into its fundamental tensorial structures based on the remaining rotational symmetry. We use energy-momentum conservation to derive differential relations between the resulting component functions. Using these constraints, the full set of component functions of the correlator can finally be represented in the form of a smaller set of spectral functions. Finally, we show how to use these techniques for more efficient future lattice investigations.

hep-ph↗
arXiv2026

Why fluctuations of conserved charges in the confining regime above $T_{ch}$ behave as if the quarks were free?

Some cumulants of the fluctuations of conserved charges soon above the chiral crossover behave as if the quarks were free. This was taken by many as evidence of deconfinement. At the same temperatures the mesonic correlators reveal the chiral spin and SU(4) symmetries, indicating that the propagating degrees of freedom are massless quarks connected into color singlets by the chromoelectric confining string. These correlators are qualitatively different from the free quark gas. Here we clarify the reason for the difference. The conserved quark number densities do not propagate in time but do propagate in spatial directions. The mesonic propagators calculated in full QCD differ radically from the free quark loop (quark gas) above T_ch. In contrast, the quark number density spatial propagator in full QCD at T > 220 MeV is very close to the free quark loop. In other words, the conserved charges do not see confinement, in contrast to the mesonic correlators. This is consistent with the well understood quark-hadron duality at T=0 in e^+e^- -> hadrons, where at invariant masses above 2 GeV the cross-section in the confining regime is represented by the free quark loop plus small perturbative corrections. All these features above T_ch but below the deconfinement temperature T_d can be combined within the following microscopic picture of the stringy fluid matter. It is a medium of the overlapping strongly interacting color singlet clusters. The quark interchanges between the clusters, required by Paili principle, make the quarks quasifree, which is reflected in fluctuations of conserved charges.

hep-ph↗