arXiv subjects

Javira Altmann

Publications and source records attributed to Javira Altmann.

5 recordsLinked to original sources

arXiv2026

Strangeness enhancement in pp collisions from string closepacking in Pythia 8.3

Measurements at LHC show an increased production of strange hadrons with charged multiplicity in pp collisions, which is not described by the Lund String Model (with the Monash tune) implemented in PYTHIA. This work investigates string closepacking, a mechanism invoked during hadronization where overlapping strings create a background field that increases the effective string tension. This reduces strangeness suppression, effectively enhancing production. The model also incorporates an option for "popcorn destructive interference", which suppresses baryon production, to address the non-strange $p/\pi$ ratio, utilizing color algebra arguments; and an option for "strange junctions", which enhances strangeness specifically within the baryon sector. The Trieste tunes of this model to LHC data are presented. The closepacking model is in qualitative agreement with many of the salient particle ratios, although the $\Xi_c/D$ ratio and the shape of $p_\perp$ spectra remain challenging to account for. Overall, the closepacking model with the Trieste tunes provides a competitive description of enhanced strangeness production in pp collisions, improving upon existing PYTHIA models while avoiding excessive proton yields.

hep-ph↗

arXiv2025

Closepacking effects on strangeness and baryon production at the LHC

Data from the LHC show a rise in strange-hadron production with charged-particle multiplicity in pp collisions. The Monte-Carlo event generator PYTHIA, using its default Monash tune, instead predicts constant strangeness. We investigate a mechanism invoked during hadronization called string closepacking, where overlapping strings generate a background field, here assumed to be predominantly aligned with the beam axis. This increases the effective string tension, reducing strangeness suppression and thus enhancing strangeness production. We tune this model to LHC data and contrast it with several alternatives. We comment specifically on the challenge of simultaneously describing the non-strange p/pi ratio, and introduce a mechanism which may act to suppress it. Many of the salient particle-production ratios can be qualitatively described by this model, although the XiC/D ratio and the shape of pT spectra remain challenging to account for.

hep-ph↗

arXiv2025

Sudakov evolution without unitarity

We present a method for sampling singular functions defined on (nested) multi-particle phase spaces, based on a generalisation of parton-shower phase-space generation techniques. At the heart of the method are three key ingredients: 1) the Sudakov sampling by which shower-style calculations sweep across phase space in an ordered manner, from hard to soft; 2) the sequential nesting of multiparticle phase spaces; and 3) the factorisations obeyed by singular multiparton amplitudes on the edges of these phase spaces. We demonstrate a C++ implementation of the proposed algorithm, dubbed Sunshine, for hadronic Z decays, and use it to test the tree-level accuracy of the Vincia sector shower through $\mathcal{O}(\alpha_s^2)$.

hep-ph↗

arXiv2024

String Junctions Revisited

Recent measurements at the LHC have revealed heavy-flavour baryon fractions much larger than those observed at LEP, with e.g., LambdaC+/D0 and LambdaB0/B0 reaching ~ 0.5 at low pT. One scenario that has been at least partly successful in predicting observed trends is QCD colour reconnections with string junctions. In previous work, however, the limit of a low-pT heavy quark was not well defined. We reconsider the string equations of motion for junction systems in this limit, and find that the junction effectively becomes bound to the heavy quark, a scenario we refer to as a "pearl on a string". We extend string-junction fragmentation in Pythia with a dedicated modelling of this limit for both light- and heavy-quark "pearls".

hep-ph↗

arXiv2024

QCD challenges from pp to AA collisions -- 4th edition

This paper is a write-up of the ideas that were presented, developed and discussed at the fourth International Workshop on QCD Challenges from pp to AA, which took place in February 2023 in Padua, Italy. The goal of the workshop was to focus on some of the open questions in the field of high-energy heavy-ion physics and to stimulate the formulation of concrete suggestions for making progresses on both the experimental and theoretical sides. The paper gives a brief introduction to each topic and then summarizes the primary results.

hep-ex↗