Hadronisation Models and Colour Reconnection

Enhanced production of hadrons with $s$-quark content has been observed in $pp$ collisions at LHC, and earlier in collisions of heavy nuclei. We review the string hadronisation formalism and correc- tions from rope hadronisation and colour reconnection, corrections that takes place in such dense environments, and are able to correctly describe data. Since such corrections are very sensitive to the modelling of transverse proton structure, we investigate two such models, and compare to final states. Finally we describe how such corrections can also give a possible explanation to collective phenomena observed in small systems.Comment: Conference proceedings DIS2016. 6 pages, 3 figure

Rope Hadronization and Strange Particle Production

Rope Hadronization is a model extending the Lund string hadronization model to describe environments with many overlapping strings, such as high multiplicity pp collisions or $AA$ collisions. Including effects of Rope Hadronization drastically improves description of strange/non-strange hadron ratios as function of event multiplicity in all systems from $e^+ e^-$ to $AA$. Implementation of Rope Hadronization in the MC event generators DIPSY and Pythia8 is discussed, as well as future prospects for jet studies and studies of small systems.Comment: Conference proceedings for Strangeness in Quark Matter 201

Diffractive and non-diffractive wounded nucleons and final states in pA collisions

We review the state-of-the-art of Glauber-inspired models for estimating the distribution of the number of participating nucleons in pA and AA collisions. We argue that there is room for improvement in these models when it comes to the treatment of diffractive excitation processes, and present a new simple Glauber-like model where these processes are better taken into account. We also suggest a new way of using the number of participating, or wounded, nucleons to extrapolate event characteristics from pp collisions, and hence get an estimate of basic hadronic final-state properties in pA collisions, which may be used to extract possible nuclear effects. The new method is inspired by the Fritiof model, but based on the full, semi-hard multiparton interaction model of Pythia 8.Comment: 50 pages, 13 figure

Soft modifications to jet fragmentation in high energy proton-proton collisions

The discovery of collectivity in proton-proton collisions, is one of the most puzzling outcomes from the two first runs at LHC, as it points to the possibility of creation of a Quark-Gluon Plasma, earlier believed to only be created in heavy ion collisions. One key observation from heavy ion collisions is still not observed in proton-proton, namely jet-quenching. In this letter it is shown how a model capable of describing soft collective features of proton-proton collisions, also predicts modifications to jet fragmentation properties. With this starting point, several new observables suited for the present and future hunt for jet quenching in small collision systems are proposed.Comment: 7 pages, 7 figures, 1 table, updated to the published versio

PINK AND DUDE CHEFS: IMPACT OF A NUTRITION AND CULINARY EDUCATION PROGRAM WITH MIDDLE SCHOOL STUDENTS IN AN AFTERSCHOOL SETTING

The epidemic of adolescent obesity has become one of the greatest public health concerns in the United States. Approximately 20.5% of adolescents of both sexes aged 12-19 years are considered obese. Higher rates of obesity are evident in ethnic minority and lower income status children with the highest prevalence among Hispanic/Latino and Black populations. The causes for obesity are multifactorial in nature and highlight disparities nationwide. These factors include socioeconomic status, education, environment, availability and access to fresh fruits and vegetables, and behavior patterns. Successful intervention methods that have reduced the impact of adolescent obesity have incorporated nutrition knowledge and culinary skill building into afterschool programs. Pink and Dude Chefs, a 12-lesson nutrition education and culinary skills afterschool program targeted toward middle school students, aims to improve nutrition knowledge and dietary behavior in low income and minority populations. Based off of evidence-based curriculum, the program focuses on culinary fundamentals while incorporating nutrition lessons about macronutrients, micronutrients, label reading, kitchen safety, and USDA guidelines. Research assistants from California Polytechnic State University, San Luis Obispo and Vanderbilt University in Tennessee, were trained to implement each lesson. The program took place at Mesa Middle School in Arroyo Grande, CA; Shandon, CA; and two sites in Nashville, TN from Spring 2014 to Fall 2014. Thirty-two middle school students participated in the study aged 11-14 years. Questionnaires were used to measure fruit and vegetables preferences, nutrition knowledge, and fruit and vegetable intake. Results indicate that participants’ fruit and vegetable preferences, nutrition knowledge and fruit and vegetable intake all increased. However, statistical significance was only achieved with nutrition knowledge, likely due to small sample size. If programs such as Pink and Dude Chefs show promise for decreasing risk for obesity, the public health impact could improve long-term health outcomes for adolescents and mitigate obesity related consequences

Dipole evolution: perspectives for collectivity and gamma*A collisions

The transverse, spatial structure of protons is an area revealing fundamental properties of matter, and provides key input for deeper understanding of emerging collective phenomena in high energy collisions of protons, as well as collisions of heavy ions. In this paper eccentricities and eccentricity fluctuations are predicted using the dipole formulation of BFKL evolution. Furthermore, first steps are taken towards generation of fully exclusive final states of $\gamma^*$A collisions, by assessing the importance of colour fluctuations in the initial state. Such steps are crucial for the preparation of event generators for a future electron-ion collider. Due to the connection between an impact parameter picture of the proton structure, and cross sections of ep and pp collisions, the model parameters can be fully determined by fits to such quantities, leaving results as real predictions of the model.Comment: 54 pages, 20 figures, replacement corresponding to published versio

Hadronic Rescattering in pA and AA Collisions

In a recent article we presented a model for hadronic rescattering, and some results were shown for pp collisions at LHC energies. In order to extend the studies to pA and AA collisions, the Angantyr model for heavy-ion collisions is taken as the starting point. Both these models are implemented within the general-purpose Monte Carlo event generator Pythia, which makes the matching reasonably straightforward, and allows for detailed studies of the full space--time evolution. The rescattering rate is significantly higher than in pp, especially for central AA collisions, where the typical primary hadron rescatters several times. We study the impact of rescattering on a number of distributions, such as pT and eta spectra, and the space--time evolution of the whole collision process. Notably rescattering is shown to give a significant contribution to elliptic flow in XeXe and PbPb, and to give a nontrivial impact on charm production.Comment: 38 pages, 16 figure

Effects of Overlapping Strings in pp Collisions

In models for hadron collisions based on string hadronization, the strings are usually treated as independent, allowing no interaction between the confined colour fields. In studies of nucleus collisions it has been suggested that strings close in space can fuse to form "colour ropes". Such ropes are expected to give more strange particles and baryons, which also has been suggested as a signal for plasma formation. Overlapping strings can also be expected in pp collisions, where usually no phase transition is expected. In particular at the high LHC energies the expected density of strings is quite high. To investigate possible effects of rope formation, we present a model in which strings are allowed to combine into higher multiplets, giving rise to increased production of baryons and strangeness, or recombine into singlet structures and vanish. Also a crude model for strings recombining into junction structures is considered, again giving rise to increased baryon production. The models are implemented in the DIPSY MC event generator, using PYTHIA 8 for hadronization, and comparison to pp minimum bias data, reveals improvement in the description of identified particle spectra.Comment: 48 pages, 22 figure

The dynamic hadronization of charm quarks in heavy-ion collisions

The PYTHIA8/ANGANTYR model for heavy ion collisions was recently updated with a mechanism for \textit{global colour reconnection}. The colour reconnection model used is QCD colour algebra inspired and enhances baryon production due to the formation of string junctions. In this paper, we present updates to the junction formation and string fragmentation mechanisms, connected to heavy quark fragmentation. This allows for the simulation of heavy quark fragmentation, using junction formation, in heavy ion collisions. The framework is validated for proton collisions, and we show results for charm baryon production in proton-lead collisions.Comment: 20 pages, 10 figure

The Angantyr model for Heavy-Ion Collisions in PYTHIA8

We present a new model for building up complete exclusive hadronic final states in high energy nucleus collisions. It is a direct extrapolation of high energy pp collisions (as described by PYTHIA), and thus bridges a large part of the existing gap between heavy ion and high energy physics phenomenology. The model is inspired by the old Fritiof model and the notion of wounded nucleons. Two essential features are the treatment of multi-parton interactions and diffractive excitation in each NN sub-collision. Diffractive excitation is related to fluctuations in the nucleon partonic sub-structure, and fluctuations in both projectile and target are here included for the first time. The model is able to give a good description of general final-state properties such as multiplicity and transverse momentum distributions, both in pA and AA collisions. The model can therefore serve as a baseline for understanding the non-collective background to observables sensitive to collective behaviour. As PYTHIA does not include a mechanism to reproduce the collective effects seen in pp collisions, such effects are also not reproduced by the present version of Angantyr. Effects of high string density, shown to be able to reproduce e.g. higher strangeness ratios and the ridge in pp, will be added in future studiesComment: 57 pages, 26 figures. Updated corresponding to published versio