Ξ−¯ Ξ triggered K/(π^+ + π^−) yield ratio: unveiling the microscopic hadronization mechanism

Abstract

This thesis investigates the K±/(π+ + π−) yield ratio near Ξ − ¯Ξ pairs in pp collisions at mid-rapidity (|η| < 1) to distinguish between two competing models of strangeness enhancement: the rope hadronization model, implemented in PYTHIA, and the canonical statistical hadronization model, implemented in Thermal-FIST. The results from both models show strong agreement with experimental data from the ALICE Collaboration for strangeness enhancement in strange hadron-to-pion yields. By analyzing (K+ +K−) and (K±) yields normalized to (π++π−) near Ξ and ¯ Ξ separately, the study tries to distinguish the microscopic and macroscopic mechanisms of hadronization. A clear distinction is observed in the K/π ratios near Ξ − ¯ Ξ pairs at low multiplicities. PYTHIA predicts higher K/π yields than Thermal-FIST. At high multiplicities, PYTHIA shows a lower K+/π and K−/π yields than Thermal-FIST, where Thermal-FIST shows a gradual rise in strangeness enhancement. The findings suggest that further refinement in rapidity ranges and larger datasets are needed to clarify the distinctions between the models. This work contributes to understanding the underlying frameworks of strangeness production in high-energy collisions.

Popular Abstract

Physicists have spent much of the past 5 decades smashing particles together, at nearly the speed of light, to understand the fundamental rules that define the universe in which we live. These high-energy collisions, conducted in particle accelerators such as the Large Hadron Collider (LHC) at CERN, create a cascade of new particles. A part of these new particles contain "strange" quarks, which are an exotic type of matter that are not typically found in ordinary atoms that make up the known universe. 'Strangely' enough, in 2016, the ALICE Collaboration found that colliding high-energy protons, which together with neutrons form the atomic nucleus, produce more strange quarks than expected. This opened up a new mystery in physics known as strangeness enhancement.

Two theories lead to explain this mystery. One, called the Quark-Gluon-Plasma (QGP) statistical hadronization model, suggests that collision events briefly transform the event into a high-density 'soup-like' state where quarks and gluons mirror what existed moments just after the Big Bang. The other, known as the rope hadronization model or aptly called the Lund model, argues that the collision events producing new particles arise from colour fields or strings stretching and breaking, forming new particles. Multiple strings overlapping are together called a 'rope'.

Due to the difficulty in theoretically describing the experiments, phenomenology is used to reconstruct final-state particles from collision events. My thesis investigates the distinction the Lund and QGP models using PYTHIA (for the Lund model) and Thermal-FIST (for the QGP model) event generators. By comparing the results of these simulations with real experimental data from the ALICE Collaboration, we can understand which model better explains the strangeness enhancement.

In my thesis, we propose that the key distinction between the statistical model and the rope hadronization model is macroscopic versus the microscopic interactions of infinitesimally small particles. As the statistical model expects a quark-gluon-plasma to form, the model predicts strangeness enhancement via providing the probability distributions of all allowed final particles after the collisions; therefore, the model looks into the collision event macroscopically. The rope hadronization model, on the other hand, looks into the collision event as microscopic string breaks and forms new particles while still upholding current fundamental rules of physics. We believe that looking deeper into a chosen particle-antiparticle interaction in the collision event and analyzing the strange quarks that come from it would pose a valid argument for distinguishing the two models. This distinction in strangeness enhancement, along with further streamlined experiments from the ALICE Collaboration, may help posit a better understanding of the mysteries that currently lie in particle physics and may bring us one step closer to unlocking the fundamental nature of our known universe.

The appearance of strange quarks in high-energy collisions is a puzzle that challenges our understanding of the fundamental laws of physics. By testing competing theories with advanced simulations, we aim to determine whether strangeness enhancement in high-energy proton-proton collisions is caused by the Quark-Gluon-Plasma or by breaking tiny color strings. As my research continues, we move closer to solving this mystery.

• author: Rabbani, Rayan
• supervisor: Christian Bierlich
• organization: Particle and nuclear physics; Department of Physics
• course: FYSK04 20251
• year: 2025
• type: M2 - Bachelor Degree
• subject: Physics and Astronomy
• keywords: QGP, rope hadronization, string fragmentation, pp collisions, ALICE experiments, ALICE Collaboration, PYTHIA, Thermal-FIST, statistical hadronization, strangeness enhancement, k/pi, k-to-pi, Xi, Cascading particles, strange hadrons, multistrange hadrons, strange mesons, strange particles
• language: English
• id: 9207615
• date added to LUP: 2025-07-07 09:51:05
• date last changed: 2025-07-07 09:51:05