Some Dipole Shower Studies

Parton showers have become a standard component in the description of high-energy collisions. Nowadays most final-state ones are of the dipole character, wherein a pair of partons branches into three, with energy and momentum preserved inside this subsystem. For initial-state showers a dipole picture is also possible and commonly used, but the older global-recoil strategy remains a valid alternative, wherein larger groups of partons share the energy--momentum preservation task. In this article we introduce and implement a dipole picture also for initial-state radiation in PYTHIA, and compare with the existing global-recoil one, and with data. For the case of Deeply Inelastic Scattering we can directly compare with matrix element expressions and show that the dipole picture gives a very good description over the whole phase space, at least for the first branching.Comment: 31 pages, 17 figures and 3 table

Parton Shower Algorithms - Possible Improvements

In this Master thesis, two directions have been explored to improve the current parton shower algorithm of the event generator Pythia. Firstly, three choices of transverse-momentum-ordered evolution variable have been studied for final-state radiation in order to allow more flexibility within the algorithm. These three choices turn out to be valid but they lead to more technical implementations than the default evolution variable. Secondly, a new approach, involving colour dipoles, has been set up to deal locally with recoils in initial-state radiation. It is a complementary procedure to the one present in the current version of Pythia, which is based on global recoils. This new procedure has been implemented and compared to the default one through some simulations. The use of the dipole framework leads to a smooth combination of initial-state radiation and final-state radiation. Some specific cases, such as deep inelastic scattering, are better described with this new approach. The matching between Feynman graphs and parton shower also benefits from this framework.Standardmodellen är det teoretiska ramverk som beskriver partikelväxelverkningar på subatomär nivå. För att bekräfta teorins förutsägelser behöver experimentella data samlas in. I partikelfysik kan information om hur partiklar produceras och växelverkar med varandra erhållas genom att accelerara partiklar till höga energier och sedan låta dem kollidera. Detta är skälet att partikelkolliderare har byggts de senaste årtiondena. De data som samlats in genom dessa experiment har bekräftat att standardmodellen ger en mycket rimlig beskrivning av det mesta av de observerade fenomenen. Olyckligtvis kan vissa experimentella observationer inte förklaras enbart med standardmodellen. Detta motiverar forskare att söka efter utvidgningar av standardmodellen eller efter helt nya teorier. Nuförtiden används kolliderare inte enbart för att validera modeller utan också att samla experimentella antydningar om vilka riktningar som skall utforskas. I detta sammanhang planeras kolliderare för de kommande årtiondena. Eftersom det är dyrt och komplicerat att bygga en kolliderare så är det användbart att simulera vad som kan tänkas inträffa i förväg. Med sådana simuleringar kan framtida resultat förutses. Datorprogram som gör detta kallas händelsegeneratorer och baseras på sannolikhetsmässiga ansatser. Mer i detalj kan en simulering starta med två inkommande partiklar. Dessa partiklar växelverkar sedan och producerar nya partiklar. Varje sådan möjlig växelverkan karakteriseras av en viss sannolikhet att inträffa. De nya partiklarna kan växelverka igen, alternativt sönderfalla, vilket leder fram mot ett sluttillstånd. Hela processen, från de inkommande partiklarna till slutpartiklarna, kallas en händelse. För att en simulering skall ge relevanta förutsägelser måste många händelser genereras. Resultaten måste överensstämma med existerande experimentella data, inom ramen för statistiska överväganden och gjorda approximationer. Därför blir händelsegeneratorer en förbindelselänk mellan teori och experiment. De måste uppfylla teorins krav och också reproducera experimentella observationer. Det pågår ett ständigt arbete att förbättra effektivitet och precision av dessa generatorer. Några förbättringsriktningar utforskas i denna avhandling

Combining single and double parton scatterings in a parton shower

From Springer Nature via Jisc Publications RouterHistory: received 2020-08-11, accepted 2020-09-04, collection 2020-10, registration 2020-10-01, pub-electronic 2020-10-01, online 2020-10-01Publication status: PublishedAbstract: Double parton scattering (DPS) processes in which there is a perturbative “1 → 2” splitting in both protons overlap with loop corrections to single parton scattering (SPS). Any fundamental theoretical treatment of DPS needs to address this double-counting issue. In this paper, we augment our Monte-Carlo simulation of DPS, dShower, to be able to generate kinematic distributions corresponding to the combination SPS+DPS without double counting. To achieve this, we formulate a fully-differential version of the subtraction scheme introduced in Diehl et al. (JHEP 06 (2017) 083). A shower is attached to the subtraction term, and this is combined with the dShower DPS shower along with the usual SPS shower. We perform a proof-of-concept study of this new algorithm in the context of Z0Z0 production. Once the subtraction term is included, we verify that the results do not depend strongly on the artificial “DPS-SPS demarcation” scale ν. As part of the development of the new algorithm, we improve the kinematics of the 1 → 2 splitting in the DPS shower (and subtraction term), allowing the daughter partons to have a relative transverse momentum. Several reasonable choices for the transverse profile in the 1 → 2 splitting are studied. We find that many kinematic distributions are not strongly affected by the choice, although we do observe some differences in the region where the transverse momenta of both bosons are small

Data visualization instructional design

This is a Master Thesis research project

A Monte-Carlo Simulation of Double Parton Scattering

In this work, a new Monte-Carlo simulation of double parton scattering (DPS) at parton level is presented. The simulation is based on the QCD framework developed recently by M. Diehl, J. R. Gaunt and K. Schonwald. With this framework, the dynamics of the $1\to2$ perturbative splittings is consistently included inside the simulation, with the impact-parameter dependence taken into account. The simulation evolves simultaneously two hard systems from a common hard scale down to the hadronic scale. The evolution is performed using an angular-ordered parton shower which is combined with a set of double parton distributions that depend explicitly on the inter-parton distance. An illustrative study is performed in the context of same-sign WW production at the LHC, with the quark content of the proton being limited to three flavours. In several distributions we see differences compared to DPS models in Herwig, Pythia, and the DPS "pocket formula".In this work, a new Monte-Carlo simulation of double parton scattering (DPS) at parton level is presented. The simulation is based on the QCD framework developed recently by M. Diehl, J. R. Gaunt and K. Schönwald. With this framework, the dynamics of the 1 → 2 perturbative splittings is consistently included inside the simulation, with the impact-parameter dependence taken into account. The simulation evolves simultaneously two hard systems from a common hard scale down to the hadronic scale. The evolution is performed using an angular-ordered parton shower which is combined with a set of double parton distributions that depend explicitly on the inter-parton distance. An illustrative study is performed in the context of same-sign WW production at the LHC, with the quark content of the proton being limited to three flavours. In several distributions we see differences compared to DPS models in Herwig, Pythia, and the DPS “pocket formula”

Pondering the reading of visual representations

We follow a theoretical approach to define the concept of reading visualizations. In the past, researchers often assessed readability based on the cognitive processes at work during an individual's engagement with a visual representation. The commonly used term "reading" in these studies, however, often lacks consistency: sometimes it refers solely to the extraction of textual information, while in other instances it is limited to the interpretation of visual signals such as patterns, color gradients, or object sizes. We argue that there exists a gap in the literature for a comprehensive, unifying definition of reading that would potentially broaden the horizons of design spaces and analytical frameworks in our field. To address this issue, we discuss models of reading text and how they can potentially relate to visualization reading

Open Questions about the Visualization of Sociodemographic Data

International audienceThis paper collects a set of open research questions on how to visualize sociodemographic data. Sociodemographic data is a common part of datasets related to people, including institutional censuses, health data systems, and human-resources fles. This data is sensitive, and its collection, sharing, and analysis require careful consideration. For instance, the European Union, through the General Data Protection Regulation (GDPR), protects the collection and processing of any personal data, including sexual orientation, ethnicity, and religion. Data visualization of sociodemographic data can reinforce stereotypes, marginalize groups, and lead to biased decision-making. It is, therefore, critical that these visualizations are created based on good, equitable design principles. In this paper, we discuss and provide a set of open research questions around the visualization of sociodemographic data. Our work contributes to an ongoing refection on representing data about people and highlights some important future research directions for the VIS community. A version of this paper and its fgures are available online at osf.io/a2u9c

PREVis: Perceived Readability Evaluation for Visualizations

International audienceWe developed and validated an instrument to measure the perceived readability in data visualization: PREVis. Researchers and practitioners can easily use this instrument as part of their evaluations to compare the perceived readability of different visual data representations. Our instrument can complement results from controlled experiments on user task performance or provide additional data during in-depth qualitative work such as design iterations when developing a new technique. Although readability is recognized as an essential quality of data visualizations, so far there has not been a unified definition of the construct in the context of visual representations. As a result, researchers often lack guidance for determining how to ask people to rate their perceived readability of a visualization. To address this issue, we engaged in a rigorous process to develop the first validated instrument targeted at the subjective readability of visual data representations. Our final instrument consists of 11 items across 4 dimensions: understandability, layout clarity, readability of data values, and readability of data patterns. We provide the questionnaire as a document with implementation guidelines on osf.io/9cg8j. Beyond this instrument, we contribute a discussion of how researchers have previously assessed visualization readability, and an analysis of the factors underlying perceived readability in visual data representations