| 1. |
- Andersen, Jeppe R., et al.
(författare)
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Les Houches 2017: Physics at TeV Colliders Standard Model Working Group Report
- 2018. - 07977
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This Report summarizes the proceedings of the 2017 Les Houches workshop on Physics at TeV Colliders. Session 1 dealt with (I) new developments relevant for high precision Standard Model calculations, (II) theoretical uncertainties and dataset dependence of parton distribution functions, (III) new developments in jet substructure techniques, (IV) issues in the theoretical description of the production of Standard Model Higgs bosons and how to relate experimental measurements, (V) phenomenological studies essential for comparing LHC data from Run II with theoretical predictions and projections for future measurements, and (VI) new developments in Monte Carlo event generators.
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| 2. |
- Andersen, Jeppe R., et al.
(författare)
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Merging high energy with soft and collinear logarithms using HEJ and PYTHIA
- 2018
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2018:9
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Tidskriftsartikel (refereegranskat)abstract
- We present a method to combine the all-order treatment of the High Energy Jets exclusive partonic Monte Carlo (HEJ) with the parton shower of Pythia8, while retaining the logarithmic accuracy of both. This procedure enables the generation of fully realistic and hadronised events with HEJ. Furthermore, the combination of the two allorder treatments leads to improvements in the quality of the description of observables, in particular for regions with disparate transverse scales.
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| 3. |
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| 4. |
- Bierlich, Christian, et al.
(författare)
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Collectivity without plasma in hadronic collisions
- 2018
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 779, s. 58-63
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Tidskriftsartikel (refereegranskat)abstract
- We present a microscopic model for collective effects in high multiplicity proton–proton collisions, where multiple partonic subcollisions give rise to a dense system of strings. From lattice calculations we know that QCD strings are transversely extended, and we argue that this should result in a transverse pressure and expansion, similar to the flow in a deconfined plasma. The model is implemented in the PYTHIA8 Monte Carlo event generator, and we find that it can qualitatively reproduce the long range azimuthal correlations forming a near-side ridge in high multiplicity proton–proton events at LHC energies.
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| 5. |
- Bierlich, Christian, et al.
(författare)
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Diffractive and non-diffractive wounded nucleons and final states in pA collisions
- 2016
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2016:10
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Tidskriftsartikel (refereegranskat)abstract
- 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 model 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 Pythia8.
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| 6. |
- Bierlich, Christian, et al.
(författare)
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Effects of overlapping strings in pp collisions
- 2015
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :3
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Tidskriftsartikel (refereegranskat)abstract
- 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 Pythia8 for hadronization, and comparison to pp minimum bias data, reveals improvement in the description of identified particle spectra.
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| 7. |
- 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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| 8. |
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| 9. |
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| 10. |
- Gras, Philippe, et al.
(författare)
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Systematics of quark/gluon tagging
- 2017
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2017:7
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Tidskriftsartikel (refereegranskat)abstract
- By measuring the substructure of a jet, one can assign it a “quark” or “gluon” tag. In the eikonal (double-logarithmic) limit, quark/gluon discrimination is determined solely by the color factor of the initiating parton (CF versus CA). In this paper, we confront the challenges faced when going beyond this leading-order understanding, using both parton-shower generators and first-principles calculations to assess the impact of higher-order perturbative and nonperturbative physics. Working in the idealized context of electron-positron collisions, where one can define a proxy for quark and gluon jets based on the Lorentz structure of the production vertex, we find a fascinating interplay between perturbative shower effects and nonperturbative hadronization effects. Turning to proton-proton collisions, we highlight a core set of measurements that would constrain current uncertainties in quark/gluon tagging and improve the overall modeling of jets at the Large Hadron Collider.
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| 11. |
- Gustafson, Gösta, et al.
(författare)
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Dipoles in Impact Parameter Space and Rapidity
- 2019
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Ingår i: Multiple Parton Interactions at the LHC. - : WORLD SCIENTIFIC. - 1793-1339. - 9789813227750 - 9789813227774 ; 29, s. 359-376
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Bokkapitel (refereegranskat)abstract
- We describe the DIPSY model for initial state evolution and the implementation of this in an event generator for producing fully exclusive hadronic final states. The model is formulated in impact parameter space and rapidity. Including non-leading and nonlinear effects, it gives a unique picture of fluctuations and correlations in the initial state parton evolutions. It also gives an impact-parameter- dependent description of the final state, allowing for new insights into the hadronization process in dense collision environments.
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| 12. |
- Gustafson, Gösta, et al.
(författare)
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Total, inelastic and (quasi-)elastic cross sections of high energy pA and γ$^{⋆}$ A reactions with the dipole formalism
- 2015
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2015:10
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Tidskriftsartikel (refereegranskat)abstract
- In order to understand the initial partonic state in proton-nucleus and electron-nucleus collisions, we investigate the total, inelastic, and (quasi-)elastic cross sections in pA and gamma-A collisions, as these observables are insensitive to possible collective effects in the final state interactions. We used as a tool the DIPSY dipole model, which is based on BFKL dynamics including non-leading effects, saturation, and colour interference, which we have extended to describe collisions of protons and virtual photons with nuclei. We present results for collisions with O, Cu, and Pb nuclei, and reproduce preliminary data on the pPb inelastic cross section at LHC by CMS and LHCb. The large NN cross section results in pA scattering that scales approximately with the area. The results are compared with conventional Glauber model calculations, and we note that the more subtle dynamical effects are more easily studied in the ratios between the total, inelastic and (quasi-)elastic cross sections. The smaller photon interaction makes the gamma-A collisions more closely proportional to A, and we see here that future electron-ion colliders would be valuable complements to the pA collisions in studies of dynamical effects from correlations, coherence and fluctuations in the initial state in high energy nuclear collisions.
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| 13. |
- Isaxon, Christina, et al.
(författare)
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Contribution of indoor-generated particles to residential exposure
- 2015
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 106, s. 458-466
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Tidskriftsartikel (refereegranskat)abstract
- The majority of airborne particles in residences, when expressed as number concentrations, are generated by the residents themselves, through combustion/thermal related activities. These particles have a considerably smaller diameter than 2.5 mu m and, due to the combination of their small size, chemical composition (e.g. soot) and intermittently very high concentrations, should be regarded as having potential to cause adverse health effects. In this study, time resolved airborne particle measurements were conducted for seven consecutive days in 22 randomly selected homes in the urban area of Lund in southern Sweden. The main purpose of the study was to analyze the influence of human activities on the concentration of particles in indoor air. Focus was on number concentrations of particles with diameters <300 nm generated by indoor activities, and how these contribute to the integrated daily residential exposure. Correlations between these particles and soot mass concentration in total dust were also investigated. It was found that candle burning and activities related to cooking (using a frying pan, oven, toaster, and their combinations) were the major particle sources. The frequency of occurrence of a given concentration indoors and outdoors was compared for ultrafine particles. Indoor data was sorted into non-occupancy and occupancy time, and the occupancy time was further divided into non-activity and activity influenced time. It was found that high levels (above 10(4) cm(-3)) indoors mainly occur during active periods of occupancy, while the concentration during non-activity influenced time differs very little from non-occupancy time. Total integrated daily residential exposure of ultrafine particles was calculated for 22 homes, the contribution from known activities was 66%, from unknown activities 20%, and from background/non-activity 14%. The collected data also allowed for estimates of particle source strengths for specific activities, and for some activities it was possible to estimate correlations between the number concentration of ultrafine particles and the mass concentration of soot in total dust in 10 homes. Particle source strengths (for 7 specific activities) ranged from 1.6.10(12) to 4.5.10(12) min(-1). The correlation between ultrafine particles and mass concentration of soot in total dust varied between 0.37 and 0.85, with an average of 0.56 (Pearson correlation coefficient). This study clearly shows that due to the importance of indoor sources, residential exposure to ultrafine particles cannot be characterized by ambient measurements alone. (C) 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/).
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| 14. |
- Kerbizi, Albi, et al.
(författare)
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Inclusion of the 3P0 model in PYTHIA 8
- 2019
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Konferensbidrag (refereegranskat)abstract
- The spin effects in the hadronization process have been included for the first time in the PYTHIA 8 event generator. The spin effects are limited to the production of pseudo-scalar mesons and are obtained from the propagation of the quark polarization along the fragmentation chain according to the rules of the so-called 3P0 model. The interface between PYTHIA 8 and the package of the 3P0 model is presented together with preliminary results on the Collins and di-hadron asymmetries as obtained from simulations of the transversely polarized semi-inclusive deep inelastic scattering process.
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| 15. |
- Lönnblad, Leif, et al.
(författare)
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Generation of central exclusive final states
- 2016
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 76
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Tidskriftsartikel (refereegranskat)abstract
- We present a scheme for the generation of central exclusive final states in the program. The implementation allows for the investigation of higher-order corrections to such exclusive processes as approximated by the initial-state parton shower in . To achieve this, the spin and colour decomposition of the initial-state shower has been worked out, in order to determine the probability that a partonic state generated from an inclusive sub-process followed by a series of initial-state parton splittings can be considered as an approximation of an exclusive colour- and spin-singlet process. We use our implementation to investigate the effects of parton showers on some examples of central exclusive processes, and we find sizeable effects on di-jet production, while the effects on e.g. central exclusive Higgs production are minor.
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| 16. |
- Lönnblad, Leif
(författare)
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Modelling pp, pA and AA in Pythia8
- 2019
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 208, s. 11003-11003
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We present a new model for generating complete exclusive hadronic final states in high energy collisions involving heavy ions. The model is called Angantyr and is inspired by the old Fritiof model, building on the concept of wounded nucleons.
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