1,929 research outputs found
The Mass of the Higgs Boson
Abstract Within the Standard Model of particle physics, there was only one undiscovered fundamental particle. This was the Higgs boson. In July 2012, the announcement was made that a Higgs like particle had been discovered by the ATLAS Collaboration and the CMS Collaboration at CERN. The aim of this Bachelorâs thesis was to use data collected by the ATLAS detector facility to estimate the mass of the Higgs boson. The estimation was done with consideration to one decay channel, namely when the Higgs boson decays into two Z bosons, and each Z boson subsequently decays into two muons of opposite charge. Setting constraints on the four-muon system kinematical data yielded a selection of possible Higgs candidates. A histogram was created of the invariant masses of the possible Higgs bosons. The masses of the intermediate step Z bosons were also put in a histogram. Next, an estimation of the background processes was made by forming new four-muon systems, by combining Z bosons from different events. This yielded a mass spectrum that was later normalized to the same integral as the original resulting mass spectrum. Finally, the estimated background was subtracted from the original results, to yield a histogram without background. Both the results with and without the estimated background subtracted displayed a prominent peak in the mass range 120 GeV/c2 â 125 GeV/c2. When the background was subtracted, the amplitude of this peak was about twice the amplitude of any other bin, and it was one of the few bins that did not include the âzero events registeredâ value within its error bars. This is a strong indication that a particle with a mass within this range was detected, and the range is exceptionally close to the mass of the Higgs boson reported by the ATLAS and CMS Collaborations; 126 GeV/c2.Att Söka efter Higgs-Bosonen Den dittills oupptĂ€ckta Higgs-bosonen upptĂ€cktes förra Ă„ret pĂ„ CERN i Schweiz. Denna partikel har en central roll i partikelfysiken, och var dĂ€rför oerhört viktig att upptĂ€cka. DĂ„ den lever vĂ€ldigt kort tid gĂ„r den inte att detektera direkt. Detta arbete söker finna massan hos Higgs-bosonen, och anvĂ€nder sig dĂ„ av fallet dĂ„ den sönderfaller till fyra myoner. Higgs-bosonen var lĂ€nge den sista oupptĂ€ckta partikeln i partikelfysikens standardmodell. Men i juli förra Ă„ret (2012) annonserades det frĂ„n CERN (Schweiz) att man med stor sannolikhet tror att man har funnit den. UpptĂ€ckten skedde med de tvĂ„ olika och oberoende detektorsystemen ATLAS och CMS. I standardmodellen, den modell som beskriver det allra mest fundamentala inom fysiken, har Higgs-bosonen en oerhört viktig roll. Det Ă€r nĂ€mligen vĂ€xelverkan mellan en partikel och Higgs-bosonen som ger den partikeln en massa. Utan Higgs-bosonen skulle standardmodellen falla sönder, och dĂ€rför var det vĂ€ldigt viktigt att hitta denna boson. Bosonen i sig gĂ„r inte att detektera, dĂ„ den sönderfaller sĂ„ pass fort (efter ungefĂ€r 10â22 s). DĂ€rmed mĂ„ste sönderfallsprodukterna detekteras. Det finns mĂ„nga möjliga sĂ€tt som Higgs-bosonen kan sönderfalla, och i det hĂ€r arbetet ligger fokus pĂ„ den sönderfallskedja som, via tvĂ„ stycken Z-bosoner, avslutas med fyra stycken myoner. I projektet analyseras proton-proton-kollisioner som givit upphov till fyra myoner, och blivit uppmĂ€tta med ATLAS-detektorn vid CERN. FrĂ„n de uppmĂ€tta energierna och rörelsemĂ€ngderna hos dessa myoner kan man avgöra vilken massa partikeln som skapade dem hade. Dock kan Ă€ven andra processer i en kollision mellan protoner ge upphov till fyra myoner. Dessa gĂ„r inte att sĂ€rskilja frĂ„n de myoner som har skapats av en Higgs-boson, och kommer ocksĂ„ att tas med i analysen. En sĂ„ kallad bakgrund skapas i mĂ€tdatan, av myoner som egentligen inte hör hemma dĂ€r. För att hantera detta kan man applicera vissa kriterier pĂ„ myonerna som detekteras. MĂ„nga av dessa minskar bakgrunden i mĂ€tningarna, medan andra kompenserar för ofullkomligheter i detektorerna. För att uppskatta hur stor bakgrund som finns kvar görs i vanliga fall en simulation av en stor mĂ€ngd kollisioner, och frĂ„n detta avgörs hur stor andel av myonerna som kom frĂ„n en Higgs-boson, och hur mĂ„nga som kom ifrĂ„n nĂ„got annat. Denna metod Ă€r alldeles för omfattande för detta arbete, sĂ„ uppskattningen görs pĂ„ ett annat sĂ€tt. I detta projekt hade man, för varje event, definierat fyra myoner som parvis hĂ€rstammade frĂ„n varsin Z-boson, ifrĂ„n samma kollisions-vertex. För att uppskatta en bakgrund av oberoende par av Z-bosoner (oberoende par av myonpar) skapade man nya system av fyra myoner genom att kombinera tvĂ„ myonpar frĂ„n tvĂ„ olika event. DĂ€rmed erhölls nya system av fyra parvis oberoende myoner, alltsĂ„ tvĂ„ oberoende Z-bosoner. Detta ger en bra uppskattning av de bakgrundsprocesser som bestĂ„r av just tvĂ„ oberoende Z-bosoner, vilket Ă€r den övervĂ€gande majoriteten av bakgrunden. Projektets resultat visar starka indikationer pĂ„ att Higgs-bosonen har en massa mellan 120 och 125 GeV/c2. Detta resultat stĂ€mmer vĂ€l överens med de resultat som publicerats av ATLAS-kollaborationen, dĂ€r Higgs-bosonen Ă€r sagd att ha en massa pĂ„ 126 GeV/c2
Western Rock Lobster Fishery - Ecological risk assessment 2005 report.
The first two parts of the document provide background on the western rock lobster fishery and its governance. The third and fourth parts outline reporting requirements for the Ecologically Sustainable Development process and the specifics of the risk assessment process applied here. These sections are based substantially on reports written earlier by the Department of Fisheries and distributed to participants in the risk assessment process. They have been edited here to include only the details that were pertinent to this risk assessment. Parts 5, 6 and 7 provide the outcomes of the hazard elicitation workshop with stakeholders and the subsequent risk assessments conducted by the experts
A Neutrino Detector Design
Abstract Today, the neutrino oscillation is very well established by experiment. It is described by a theoretical framework similar to that of quark mixing. Here is included a CP violating phase, delta_CP, which is the only known possible source of CP violation in the lepton sector. So far, delta_CP is completely unconstrained by experiment, and the determination of the value of delta_CP could further the search for an explanation of the matter-antimatter asymmetry observed in the Universe today. Therefore, many next generation experiments are in development to measure delta_CP. One of the experiments under evaluation is the ESSnuSB; a proposed high intensity neutrino beam produced at the European Spallation Source (the ESS). The ESS facility, now under construction in Lund, Sweden, would need to be upgraded in order to produce the high intensity neutrino beam. Neutrino oscillations in the nu_mu to nu_e channel could then be studied by the use of a megaton water Cherenkov detector separated from the beam source by some hundred kilometres. The phase delta_CP would thereby be determined by measuring the asymmetry between the oscillation probabilities of neutrinos and antineutrinos. The precision of this experiment would be improved by characterising the beam close to the production point. This would be achieved by the use of a kiloton water Cherenkov detector, denoted as the Near Detector (ND), which is studied in this thesis. Firstly, concrete design recommendations for the near detector of the ESSnuSB should be found through simulations. Secondly, a set of algorithms should be developed that reconstructs the properties of a neutrino event vertex from the simulated detector response. It is essential that a muon neutrino event can be separated from an electron neutrino event, as the purpose of the ESSnuSB is to detect the transition from one flavour to the other. The near detector is foreseen to be cylindrical in shape, with radius R_ND and length L_ND, and located at a distance z_ND from the neutrino beam production point. It will be filled with water and have photon detectors placed on the inner surface. In this project, several limits have been put on the design parameters of the ESSnuSB ND. ⹠The radius of the near detector: 2*R_ND > 2 m, R_ND 3 m. ⹠The distance between the neutrino beam production and the near detector: zND > 200 m. ⹠The detector must have a spatial resolution smaller than 10 cm. ⹠The detector must have a time resolution shorter than 100 ps. Additionally, a set of reconstruction algorithms was developed for a simplified detector environment, and the flavour identification algorithm was found to have a misidentification rate of 0.3%.Att Detektera en Neutrino I dagens Universum Àr allting vi kan se; alla varelser, alla planeter och alla stjÀrnor, uppbyggda av materia. Trots detta tror man att det i Big Bang skapades lika mycket antimateria som materia, men att all denna antimateria pÄ nÄgot sÀtt har försvunnit. Ett steg pÄ vÀgen att förklara detta kan vara att undersöka vissa skillnader mellan neutriner och antineutriner, vilket Àr de minsta och mest svÄrdetekterade partiklarna man idag kÀnner till. Denna skillnad kan Äterfinnas i hur fort neutrinerna och antineutrinerna oscillerar, alltsÄ hur fort de skiftar mellan att vara en av tre olika sorter (elektron-neutrino, myon-neutrino och tauon-neutrino). Ett av de projekt som Àr föreslagna för att undersöka detta Àr forskningsanlÀggningen ESSnuSB, vilket skulle vara ett tillÀgg till ESS-anlÀggningen i Lund. Vid ESSnuSB skulle man dÄ generera en strÄle av neutriner som sedan skulle passera genom jorden till en gruva i Mellansverige, ca 500 km ifrÄn punkten dÀr de genererats. I gruvan ska dÄ en sÄ kallad fjÀrrdetektor placeras, en enorm vattentank med ljusmÀtare pÄ insidan, i syfte att detektera de neutriner som nÄr den. Utöver fjÀrrdetektorn behöver man Àven ha placerat en sÄ kallad nÀrdetektor i nÀra anslutning till punkten dÀr neutrinerna produceras. NÀrdetektorn kommer att vara en vattenfylld cylinderformad tank med ljusmÀtare pÄ insidan, och ligga i samma riktning som neutrinostrÄlen. Den kommer att vara placerad nÄgonstans mellan 50 och 500 m ifrÄn neutrinernas produktionspunkt, och kommer pÄ insidan vara klÀdd med en stor mÀngd ljusdetektorer. Med hjÀlp av nÀrdetektorn kan man kontrollera att neutrinostrÄlen har de egenskaper som man tror strax efter dess produktion. Syftet med det examensarbete som utförts var tudelat. För det första ska konkreta rekommendationer tas fram för hur nÀrdetektorn ska utformas, d.v.s. begrÀnsningar i bl.a. dess storlek och placering. För det andra ska en algorithm utvecklas som kan avgöra vilken sort en neutrino har nÀr den registreras i detektorn. Detta Àr mycket viktigt, dÄ man vill finna övergÄngen, eller oscillationen, frÄn en sort till en annan. Dessa tvÄ mÄl nÄs genom att simulera hur detektorn beter sig nÀr den registrerar en neutrino. Examensarbetet har visat att nÀrdetektorn mÄste uppfylla följande villkor för att kunna detektera neutriner pÄ ett tillfredsstÀllande sÀtt: ⹠NÀrdetektorn bör ha en diameter betydligt större Àn 2 m, exempelvis 8 m. ⹠NÀrdetektorn bör vara betydligt lÀngre Àn 3 m, exempelvis 10 m. ⹠NÀrdetektorn bör vara placerad lÀngre ifrÄn neutrinernas produktionspunkt Àn 200 m. ⹠NÀrdetektorn bör dessutom vara placerad lÀngre ifrÄn produktionspunkten Àn 25 gÄnger dess diameter, pÄ grund av strÄlens spridning. ⹠Ljusdetektorerna pÄ insidan av nÀrdetektorn bör kunna upplösa avstÄnd pÄ minst 10 cm. ⹠Ljusdetektorerna pÄ insidan av nÀrdetektorn bör kunna upplösa tidsskillnader pÄ minst 100 ps. Utöver detta har en algoritm utvecklats som kan identifiera vilken sort av neutrino som detekteras. Denna algorithm ger en felidentifikation för endast 0.3% av detektionerna. Detta examensarbete utgör dÀrmed den första studien som gjorts pÄ utformningen av nÀrdetektorn för ESSnuSB, och lÀgger sÄledes grunden för vidare utveckling av denna detektor
Rodent Dental Microwear Texture Analysis as a Proxy for Fine-Scale Paleoenvironment Reconstruction
Dental microwear texture analysis (DMTA) of fossil fauna has become a valuable tool for dietary inference and paleoenvironment reconstruction. Most of this work has utilized larger taxa with larger home ranges. These studies may result in broader-scale habitat inferences that could mask the details of complex mosaic habitats. Rodent DMTA offers an opportunity to work at finer spatial scales because most species have smaller home ranges. Rodents are also keystone species within their ecosystems, abundant, ubiquitous, and found in many fossil deposits. These attributes make them excellent proxies for environmental reconstructions. However, the application of DMTA to rodents remains relatively new. Furthermore, many rodent species are dietary generalists, and individuals available for study in museum collections lack detail on feeding behavior, which makes it difficult to develop strong dietary associations with microwear patterns. The same holds for limited environmental metadata associated with such samples.
This dissertation sought to explore the efficacy of rodent DMTA as a proxy for fine-scale paleoenvironment reconstruction and to establish a baseline of extant incisor and molar textures with detailed metadata associations to aid in future comparisons to fossil taxa. The biomonitoring project at Kolomela Mine, located within South Africaâs Northern Cape, provided an ideal opportunity with which to conduct this research. Stomach content analyses conducted on 214 muroid specimens caught within the Kolomela properties examined diets by species, location, and month. These analyses indicated that the Kolomela rodent community mainly consumed grass seed despite the presence of other foodstuff within stomachs.
A confocal profiler scanned high resolution casts to provide microwear textures for 198 incisors and 175 molars, from which SSFA and ISO parameter data were derived. Statistical tests explored the effects of diet, taxon, and habitat attributes on the central tendencies of these parameters, as well as effects by tooth form. Incisor microwear textures seemed to possess a stronger environmental signal than that of molars, with analyses indicating significant variation by species, macrohabitat, microhabitat, burrowing behavior, soil, and land cover classification. These results suggested that while soil characteristics had a strong influence on parameter central tendencies, incisor microwear textures seem to result from complex interactions with habitat characteristics.
Molar microwear did not parse the considered dietary categories, likely because all individuals had diets dominated by grass seed that swamped any diet signal reflecting the food elements of each group. Significant variation in parameter central tendencies by both species and burrowing behavior were believed to be the result of differing molar topography between Gerbillinae and Murinae specimens. Analyses also separated molar microwear from different dust levels, which indicated that perhaps an environmental signal can be parsed, at least when diets are homogeneous and controlled for. Finally, molar and incisor microwear textures were significantly different from one another, presumably due to a) different roles in food acquisition and process, b) different rates in gross wear and surface turnover, and c) different degrees of interaction with exogenous grit and the outside environment. These results suggest that both tooth types should be considered in future paleoenvironment reconstructions
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