A Search for Indications of Majorana Neutrinos in Same-sign Dimuon Events at the ATLAS Detector

Abstract The current Standard Model cannot explain many properties of the neutrino, including its mass. Models exist where a postulated heavy Majorana neutrino will give rise to the observed small neutrino mass currently observed. This thesis presents a search for indications of Majorana neutrinos with focus on finding heavy neutrinos and W_R-bosons predicted by the Left-Right Symmetric Model. Proton-proton collision data collected by the ATLAS detector in 2012 is used, with an integrated luminosity of 0.84 inverse femtobarn at a center-of-mass energy of 8 TeV. The main analysis channel consists of a final state with two same-sign muons and two quarks with high transverse momentum and low missing transverse energy. Due to insufficient data and a lacking Standard Model background analysis no clear conclusion is drawn regarding the particle nature of the neutrino nor the existence of new particles. The general analysis framework this thesis provides could however be of use for further studies in the same field.Frågan om vad världen egentligen består av har sysselsatt filosofer och vetenskapsmän i århundraden, och svaren har varit allt från de fyra elementen till atomer. När atomen delades i början av 1900-talet samtidigt som fler och fler nya slags partiklar observerades växte partikelfysiken fram. Partikelfysik är studien av de minsta beståndsdelarna i universum, de så kallade elementarpartiklarna. Teorin som beskriver dessa och hur de påverkar varandra kallas standardmodellen och har visat sig vara oerhört bra på att beskriva verkligheten. Dess stora ögonblick var när Higgspartikeln, en partikel som varit teoretisk förutsagt av standardmodellen sedan länge, hittades 2012. Ett antal frågor består dock som standardmodellen i sin nuvarande form inte kan besvara. Dessa inkluderar vad som döljer sig bakom de mystiska begreppen mörk materia och mörk energi, samt hur man kan kombinera gravitationen med de övriga krafterna som påverkar partiklarna. Ett annat problem gäller neutrinon, en elementarpartiklen som visat sig vara svår att förstå sig på. Jämfört med de flesta elementarpartiklar saknar neutrinon elektrisk laddning, vilket innebär att det är väldigt liten sannolikhet för den att växelverka med andra partiklar. Även om den inte är ovanlig är den nästintill osynlig: Varje ögonblick passar miljontals neutrinos genom oss utan att vi märker av någonting. Även om man på senare tid har lyckats med konststycket att bygga tillförlitliga neutrinodetektorer så är dess beteende fortfarande spöklikt, vilket gör att många av dess egenskaper fortfarande är okända. Vad man däremot vet är att den har massa, även om denna massa är mycket mindre än massan för de andra elementarpartiklarna. Detta är ett stort problem för standardmodellen då dess nuvarande formulering förutsätter att neutrinon är masslös. Varje elementarpartikel har en motsvarande antipartikel, men unikt för neutrinon är att det finns en möjlighet att den saknar en antipartikel. En partikel som inte har en motsvarande antipartikel kallas en Majoranapartikel. Det går att visa att om det finns Majorananeutrinos så kan det innebära att de neutrinos vi observerar har massa. Det är därmed viktigt att ta reda på om neutrinon är en Majoranapartikel eller inte. Trots att neutrinon är svår att observera direkt finns det sätt att undersöka detta genom att använda partikelacceleratorer. Genom att skjuta partiklar i väldigt höga hastigheter mot varandra möjliggör man interaktioner som inte är möjliga vid vanliga, låga energier. Genom att analysera vilka partiklar som bildas vid en partikelkollision och hur de rör sig kan man dra slutsatser om hur de fundamentala krafterna fungerar och vilka egenskaper de olika elementarpartiklarna har. Syftet med denna uppsatts är att leta efter Majorananeutrinos genom att använda kollisionsdata insamlat av ATLAS-detektorn vid LHC (Large Hadron Collider). I LHC kollideras två protoner i enorma hastigheter, vilket resulterar i stora mängder olika partiklar skapas. Majorananeutrinos borde ge upphov till att vissa partiklar skapas i kombination med varandra, och om dessa kombinationer observeras i högre grad än förväntat är det en tecken på att neutrinon är en Majoranapartikel. Att beräkna vilka kombinationer som är förväntade är dock komplicerat att göra korrekt. Det resultat som presenteras är därmed svårt att tolka, men väldigt få händelser som matchade Majorananeutrinos observerades och alla kunde förklaras av andra processer. Det är därför troligt att inga indikationer på Majorananeutrinos observeras. Själva metoden som användes vid analysen fungerade däremot bra, och att göra en liknande studie vid högre acceleratorenergier är både möjligt och intressant

Extending Social Resource Exchange to Events of Abundance and Sufficiency

This article identifies how scarcity, abundance, and sufficiency influence exchange behavior. Analyzing the mechanisms governing exchange of resources constitutes the foundation of several social-science perspectives. Neoclassical economics provides one of the most well-known perspectives of how rational individuals allocate and exchange resources. Using Rational Choice Theory (RCT), neoclassical economics assumes that exchange between two individuals will occur when resources are scarce and that these individuals interact rationally to satisfy their requirements (i.e., preferences). While RCT is useful to characterize interaction in closed and stylized systems, it proves insufficient to capture social and psychological reality where culture, emotions, and habits play an integral part in resource exchange. Social Resource Theory (SRT) improves on RCT in several respects by making the social nature of resources the object of study. SRT shows how human interaction is driven by an array of psychological mechanisms, from emotions to heuristics. Thus, SRT provides a more realistic foundation for analyzing and explaining social exchange than the stylized instrumental rationality of RCT. Yet SRT has no clear place for events of abundance and sufficiency as additional motivations to exchange resources. This article synthesize and formalize a foundation for SRT using not only scarcity but also abundance and sufficiency

Social lens or inherently social phenomenon? The study of food in Swedish sociology

Sociology's tendency to branch into applied scientific disciplines is regularly debated. This debate focuses either on the organisation of sociology in academic institutions or on how the content of sociologically informed interdisciplinary research diverges from disciplinary sociology. This article bridges these debates in a study of the sociology of food in Sweden. The aim is to analyse how Swedish food sociology reflects the tension between disciplinary sociology and interdisciplinary research. The data comprise the doctoral dissertations and post-PhD career paths of Swedish sociologists whose dissertations are about food. The article finds that these dissertations treat food either as an inherently social phenomenon or as a social lens (i.e. a social phenomenon viewed as instrumental for analysing something else). Second, it is found that sociologists whose dissertations treated food as an inherently social phenomenon were more likely to pursue careers in food sociology but also to hold affiliations outside of sociology departments. The article concludes that the academic locus of Swedish food sociology is organised outside sociology departments but that its approaches are not necessarily any less sociological. Thus, the analysis questions the basis for arguments that interdisciplinary research represents a threat to the critical and analytical core of sociology

The key aspects of innovation-oriented regional industrial and economic policy

Integration processes taking place in the economy, the new requirements to enhance the effectiveness of production during international competition as well as the need to ensure the social conditions lead to the development and implementation of innovation-oriented regional industrial and economic policy, which in its turn, requires adopting substantial organizational and economic recommendations

In Situ Bioremediation through Mulching of Soil Polluted by a Copper–Nickel Smelter

Received for publication September 8, 2000. Bioremediation of a heavy metal–polluted soil was investigated in a 3-yr field experiment by adding mulch to a polluted forest floor. The mulch consisted of a mixture of compost and woodchips. The remediation treatment decreased the toxicity of the soil solution to bacteria as determined by the [3H]-thymidine incorporation technique, that is, by measuring the growth rate of soil bacteria extracted from unpolluted humus after exposing them to soil solution containing heavy metals from the experimental plots. Canonical correlation analysis was performed in order to identify the chemical and microbiological changes in the soil. The pH of the mulched organic layer increased by one unit. The concentration of complexed Cu increased and that of free Cu2+ decreased in the soil solution from the mulch treatment. According to basal respiration and litter decomposition, microbial activity increased during the 3 yr following the remediation treatment. The [3H]-thymidine incorporation technique was also used to study the growth rate and tolerance of bacteria to Cu. The bacterial growth rate increased and the Cu tolerance decreased on the treated plots. The structure of the microbial community, as determined by phospholipid fatty acid (PLFA) analysis, remained unchanged. The results indicate that remediation of the polluted soil had occurred, and that adding a mulch to the forest floor is a suitable method for remediating heavy metal–polluted soil

Heated soil-water extract effect on bacterial growth: pH or toxic compounds?

Fire-induced soil changes influence indirectly on soil microbial response, mainly due to pH increases and organic matter alterations. Nevertheless, field studies include overlapped effects and it is difficult distinguish the real origin of microbial response. In this work we have performed a laboratory experiment focus on the study of heated soil-water extract effect on bacterial growth, trying to isolate pH and soluble organic carbon alterations induced by heating soil at different temperatures. Bacterial growth was estimated by 3H-leucine incorporation technique which allows isolate bacterial activity response to an alteration. Different heated treatments were applied to unaltered forest soil samples, to simulate moderate (heating at 300 oC) or high (heating at 500 oC) intensity fire. In order to isolate possible pH changes effect, the experience was repeated adding pH buffers to bring the extract to the unaltered soil pH. Preliminary results show bacterial growth inhibition in both heated treatment compared to bacterial growth of the same bacterial suspension incubated with water. The reestablishment of pH improve the bacterial growth of samples incubated in heated soil-water extract, with a more marked effect on incubation soil-water extract from soil heated at 500 oC. These results evidence the importance of pH changes on low pH adapted bacterial community and the presence of other factors presents in the soluble fraction that are limiting bacterial proliferation

A prototype-based resonance model of rhythm categorization

Categorization of rhythmic patterns is prevalent in musical practice, an example of this being the transcription of (possibly not strictly metrical) music into musical notation. In this article we implement a dynamical systems' model of rhythm categorization based on the resonance theory of rhythm perception developed by Large (2010). This model is used to simulate the categorical choices of participants in two experiments of Desain and Honing (2003). The model accurately replicates the experimental data. Our results support resonance theory as a viable model of rhythm perception and show that by viewing rhythm perception as a dynamical system it is possible to model central properties of rhythm categorization