List of previous students

Nicola Orlando
Faten Hariri
Emma Kuwertz
Spyridon Argyropoulo
Sabrina Sacerdoti
Simone Amoroso
Jesper Roy Christiansen
Nathan Hartland
Christian Roehr
Benjamin Watt
Philip Ilten
Nishita Desai
Sercan Sen
Miroslav Myska
Sudha Ahuja
Holger Schulz
Avi Gershan
Aleksander Kusina
Magdalena Slawinska
Flavia Dias
Kenneth Wraight
Irais Bautista Guzman
Sparsh Navin
Paolo Francavilla
Riccardo Di Sipio
Seyi Latunde-Dada
Devdatta Majumder
Martijn Gosselink
Christopher Bignamini
Marek Schönherr
Michal Deak
Noam Hod
Florian Bechtel
Jonathan Ferland
Manuel Bähr
Alexander Flossdorf
Piergiulio Lenzi

The MCnet short-term project aimed at implementing modifications to the conventional string fragmentation framework in the Pythia event generator. In the current form of the fragmentation, strings are stretched between quark-antiquark pairs. As a pair moves apart the string may break up by producing a new pair of a quark and antiquark which receive opposite and compensating kicks in transverse momentum according to a Gaussian distribution, independently of their flavour. One exploration of a possible non-universality was to introduce a flavour dependance, such that strange quarks and diquarks receive a larger transverse momentum.

A new model for generating the transverse momentum of hadrons during the string fragmentation process has been implemented in Pythia. It is inspired by thermodynamics and based on an exponential suppression of the hadronic transverse mass. It therefore naturally suppresses heavier hadrons with respect to lighter hadrons but they obtain a higher average transverse momentum.

A simple model to take the close-packing of strings into account has been added. By making the generation of the transverse momentum dependent on the environment, hadrons in events with large multiplicities obtain more transverse momentum.

As a last addition a simple model for hadron rescattering has been implemented, where hadron pairs are allowed to scatter off each other dependent on their rapidity difference.

The modified predictions have been tested and validated with toy model studies as well as by comparing to LHC data, such as identified particle spectra. The newly introduced parameters have been tuned to achieve an improved description of data.

The studies resulted in an article: N. Fischer and T. Sjöstrand, Thermodynamical String Fragmentation [arXiv:1610.09818 [hep-ph], MCnet-16-40]