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| 2. |
- Bierlich, Christian, et al.
(författare)
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The Angantyr model for heavy-ion collisions in Pythia8
- 2018
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2018:10
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Tidskriftsartikel (refereegranskat)abstract
- 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 studies.
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| 3. |
- Bierlich, Christian, et al.
(författare)
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The dynamic hadronization of charm quarks in heavy-ion collisions
- 2024
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Ingår i: European Physical Journal C. - 1434-6044. ; 84:3
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Tidskriftsartikel (refereegranskat)abstract
- The Pythia8/Angantyr model for heavy ion collisions was recently updated with a mechanism for 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.
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| 4. |
- Islam, Shadli, et al.
(författare)
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Ab-initio Calculation of Nonlinear Optical Susceptibilities in Germanium Quantum Dots
- 2019
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Ingår i: 2018 IEEE 13TH NANOTECHNOLOGY MATERIALS AND DEVICES CONFERENCE (NMDC). - 2378-377X. - 9781538610169 ; , s. 113-116
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Konferensbidrag (refereegranskat)abstract
- Using Time Independent Density Functional Theory (TIDFT) implemented in SIESTA (R) we calculated the 2nd order and 3rd order nonlinear optical susceptibilities of small Germanium Quantum Dots (GeQD). We observe that the symmetry breaking due to surface termination enhances chi((2)) up to 299.1 pm/V which promises a strong Second Harmonic Generation (SHG) in GeQDs. Diagonal components for chi((2)) tensor are 52.5, 11.2, 299.1 pm/V, for xxx, yyy and zzz, respectively. The 3rd order susceptibility, chi((3)), is within the range of (0.2-0.4) x 10(-18) m(2)/V-2 which is close to the reported experimental values of bulk Germanium. This study suggests possibilities of enhancing SHG in GeQDs through symmetry breaking via strain and surface termination/reconstruction as well as suitability of this fast and less-computationally intensive Density Functional Theory (DFT)-based method in predicting nonlinear optical susceptibilities of nano structures.
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| 5. |
- Lönblad, Leif, et al.
(författare)
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A spatially constrained QCD colour reconnection in pp , p A , and AA collisions in the Pythia8/Angantyr model
- 2023
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Ingår i: European Physical Journal C. - 1434-6044. ; 83:7
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Tidskriftsartikel (refereegranskat)abstract
- We present an updated version of the QCD-based colour reconnection model in Pythia8, where we constrain the range in impact parameter for which reconnections are allowed. In this way, we can introduce more realistic colour reconnections in the Angantyr model for heavy ion collisions, where previously only reconnections within separate nucleon sub-collisions have been allowed. We investigate how the new impact parameter constraint influences final states in pp collisions, and retune parameters of the multi-parton interaction parameters in Pythia to compensate so that minimum bias data are reproduced. We also study multiplicity distributions in p A collisions and find that, in order to counteract the loss in multiplicity due to the introduction of global colour reconnections, we need to modify some parameters in the Angantyr model while keeping the parameters tuned to pp fixed. With Angantyr we can then extrapolate to AA collisions without further parameter tuning and retaining a reasonable description of the basic multiplicity distributions.
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| 6. |
- Lönnblad, Leif, et al.
(författare)
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Baryon correlations in Pythia
- 2023
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Ingår i: European Physical Journal C. - 1434-6044. ; 83:12
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Tidskriftsartikel (refereegranskat)abstract
- We present the results from our investigation of angular correlations between baryons pairs in the Pythia8 event generator. We show how colour reconnection models and hadronization mechanisms influence such angular correlations and in particular address the effect of gluons on the baryon production mechanism in the Lund string fragmentation model. We conclude by discussing the new theoretical ideas in comparison with the ALICE pp collision results for the baryon angular correlations. We propose a hypothesis for suppressing baryons produced in gluon jets and show how that may influence the angular correlations.
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| 7. |
- Shah, Harsh
(författare)
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Developing the Angantyr model and extending colour reconnection for heavy-ion collisions in Pythia
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is composed of four papers, the first two show the attempts made to extend the Pythia event generator to simulate heavy-ion collision events. The other two papers show methods to improve the hadronization mechanism in the Pythia model for a bettter agreement with the experimental data of pp and heavy-ion collisions.Paper I introduces a new model named Angantyr for heavy-ion collision events simulation using the Pythia machinery. We developed a technique for sophisticated stacking of the pp-like sub-collisions, so that the Pythia model can simulate pA and AA type heavy-ion collision events. We show that the Angantyr model can reproduce the general distributions of the produced particles in pp and heavy-ion collision events.Paper II extends the QCD inspired colour reconnection mechanism in Pythia by introducing spatial constrains and extends the hadronization mechanism involving junction systems. The extended QCD colour reconnection model is used to improve the integration of the stacked pp-like sub-collisions as a single heavy-ion event in the Angantyr model by introducing a global colour reconnection. We show that the upgraded model can reporduce the general distribution of the produced particles in pp collision events and qualitatively in heavy-ion collision events. We also show that the model can reproduce the strangeness enhancement like feature in the baryon sector even though the model has no special treatment for the strangeness enhancement.Paper III investigates the baryon angular correlations and the hadronization mechanism using Pythia. It high-lights the need for improvement in the string fragmentation mechanism to reproduce the baryon angular correlations. We propose a hypothesis for the jets sub-structure studies as an outcome of our investigation.Paper IV improves the formation of junction like setups in the QCD inspired colour reconnection and the fragmentation of the junction configurations in the string fragmentation. We show that the changes made in this paper improves the charm baryons production rate in pp and heavy-ion collision events.
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| 8. |
- Shah, Harsh
(författare)
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The Angantyr model for heavy-ion physics in PYTHIA8
- 2019. - 1
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Ingår i: Hot Quarks 2018—Workshop for Young Scientists on the Physics of Ultrarelativistic Nucleus-Nucleus Collisions. - Basel Switzerland : MDPI. ; 10
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Konferensbidrag (refereegranskat)
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