A non-destructive tomographic measurement technique for application on nuclear fuel assemblies has beendeveloped at the Uppsala University. Using this technique, the rod-by-rod distribution of selectedradioactive isotopes is determined experimentally. In the present work, the numerical technique to reconstruct the activity distribution inside the fuelassemblies has been analyzed. Three iterative reconstruction algorithms have been investigated, ART(Additive Reconstruction Technique), ML (Maximum Likelihood) and ASIRT (Additive SimultaneousIterative Reconstruction Technique). It was found that the ART algorithm is too sensitive to data points where the gamma-ray intensityis low, while ASIRT handles it in the best manner. Furthermore, ASIRT appears to be the most stablealgorithm and produces the best agreement to theoretical data.

Quantum computers, like classical ones, need to be capable of sending informa-tion between different parts of the computer. Spin chains are one viable method of sending qubits while preserving the superposition and entanglement of a state. We use quantum speed limits, which give bounds on how fast non-relativistic quantum systems can evolve, to study simple Heisenberg chains and their efficacy as quantum channels.

The neutron is a valuable tool in many fields of science due to its properties regarding electric charge and magnetic moment. However, these properties also makes it difficult to detect. Through simulation one can optimize the detector environment to best correspond with the needs for a specific experiment. In this project, a detector environment is simulated, consisting of a neutron and gamma point source and one detector for each type of particle. The simulated results were in good agreement with the underlying theory and the simulation can, therefore, be used in future work.

The potential for characterizing the spin and mass of dark matter at the Large Hadron Collider (LHC) given a 5 sigma confidence level discovery has been studied. The search for dark matter is one of the big open question in particle physics as observations predict 84 percent of the matter in the universe to be dark matter, however no detection has been made. In this study two production channels at the LHC of weakly interacting massive particles with different spin have been studied in the framework of a simplified model. The processes if detected have the signature of a mono-jet and missing transverse energy. The assumption made is that the dark matter is a scalar or a Dirac fermion particle and interacts with the top quark and a Beyond the Standard Model color charged mediator via a loop process. The considered mediators are a scalar top partner and a fermionic top partner. The results from recasting conclude that in a narrow region in the mass-mass-plane for the dark matter and the mediator a search is adequate and given a discovery characterization of the spin and mass is possible.

This feasibility study concerns the implementation and analysis of a Higgs pair decaying to two W bosons, with hadronic final states, and to two τ-leptons, one with a leptonic and one with a hadronic final state, hh→ WhadWhad τlepτhad, in the ATLAS detector at the CERN Large Hadron Collider, by adapting the ``CxAOD framework'' software analysis code of the hh→ bbττ analysis. The purpose is to compare the sensitivity of this final state with other di-Higgs analyses in the ATLAS collaboration. Monte Carlo samples are used for the background and signal simulation. A cut based selection is then performed based on several kinematic variables. Finally, a statistical analysis is performed on the MMC mass distribution of the ττ system. The cross section can be limited at the 95 %  confidence level to σexpected < 89.8 fb, compared to the theoretical σSM = 0.19 fb.

Recently, searches for pair production of Higgs bosons in several final states have been carried out by the ATLAS exeperiment at the Large Hadron Collider (LHC). This study focuses on the search for non-resonant di-Higgs production decaying to a final state with two b-jets and two τ-leptons using 36.1 fb-1 of data recorded by the ATLAS detector. The analysis for this process has already been performed. Boosted decision trees (BDTs) are used in the analysis to improve the separation of the signal from background processes and several variables that provide good discrimination between signal and background are used as inputs to the BDT. This study aims to unfold the BDT of the analysis and optimize a cut-based analysis so that the gain from using the BDT can be estimated. Two variables, related to the invariant masses and angular distances of the Higgs boson decay products, are defined and the optimal cuts are found to be Xmττmbb<1.8 and XΔRττΔRbb <4.0. Then, the upper limits on the SM HH production cross section are set when fitting mHH with the cut-based analysis. An expected limit of 0.78 pb, 23 times the SM prediction is obtained when neglecting systematic uncertainties, compared to the limit of 15 times the SM as recomputed when using the BDT. Comparing the two results, the sensitivity is worsened by 50% when not using the BDT.

No description available.

A study for the search for vector-like quarks and a new pseudo Nambu-Goldstone boson(pNGB) scalar at the LHC running at $\sqrt{s} = 13$ TeV is presented. A model based on the composite Higgs model in which the Higgs boson emerges as a composite pNGB together with a new pNGB $\eta$ is considered. Simulations are made on the modelshowing a low ratio between signal to background indicating no significance and a low discovery potential. However, further studies are needed as more channels should be investigated. Moreover, a more sophisticated analysis is needed to properly reject the background and for a more thorough statistical analysis. Even so, results still show potential in the search as there do exist distinct differences between signal and SM background.

I replicated the H/A → τ μ τ had analysis of the MSSM extension to the stan-dard model with the ATLAS experiment. I investigated, using a transformedBDT score for τ -lepton identification with a flat distribution, with more work-ing points than the standard loose, medium and tight, the sensitivity of theanalysis. I then compared for each of the working points and found new signalefficiencies that are more sensitive for this analysis than the standard workingpoints. / I replicated the H/A → τ μ τ had analysis of the MSSM extension to the stan-dard model with the ATLAS experiment. I investigated, using a transformedBDT score for τ -lepton identification with a flat distribution, with more work-ing points than the standard loose, medium and tight, the sensitivity of theanalysis. I then compared for each of the working points and found new signalefficiencies that are more sensitive for this analysis than the standard workingpoints.

The pairing correlation has long been recognized as the dominant many-body correlation beyond the nuclear mean field. Pairing plays an essential role in many nuclear phenomena including the occurrence of a systematic odd-even staggering (OES) of the nuclear binding energy. Pairing interaction plays, in particular, a significant role in the stability of weakly bound nuclei. Therefore it has been one of the most critical topics in nuclear physics because of the weakly bound structure of all newly discovered nuclei. Beyond the line of stability, pairing interaction is not a residual interaction anymore. Its strength can be of the same order of magnitude as the mean field.  In this thesis we have focused on the pairing interaction in atomic nuclei under extreme conditions to investigate the structure of loosely bound nuclei near the dripline; to probe and globally assess different outcomes of various zero-range pairing interactions and their effect on the loosely bound low angular momentum states. How much can density-dependence in zero-range pairing interaction nuclei affect the line of stability? Calculations predict that pure density-dependent pairing interaction so-called surface interaction enhances the collectivity and gives stronger neutron pairing gap in nuclei far from stability, while, the density dependence pairing interaction does not affect the gap for bound nuclei as much. The odd-even staggering of nuclear binding energies has been investigated to estimate the empirical pairing gap. A 3-point formula Δ(3)C (1/2[B(N,Z)+B(N −2,Z)−2B(N −1,Z)]) is advocated in this thesis, which we believe it is more suitable to measure the magnitude of pairing gap in even-even nuclei. The strength of Δ(3)C can be a good indicator of the two-particle spatial correlation. One-quasiparticle energies and binding energy for those odd nuclei, which can be approximated by spherical symmetry, are calculated to obtain binding energy odd-even staggering (OES) in all known semi-magic even-even nuclei. The pairing strength is fitted globally to all available data on the OES of semi-magic nuclei with Z ≥ 8. The difference between different zero-range density-dependent pairing interactions reduces with this global fitted parameter. The difference between the mean pairing gap and the OES gets larger as we get closer to the dripline. At the end of the thesis, a simple model has been developed which shows that when the mean-field becomes shallower the odd-even staggering of charge radii is reduced.This thesis covers results that are not included in the three published papers and some complementary works on the subject. / Parkopplingen i atomkärnan anses vara den dominerande mångkropparskorrelationen efter kärnmedelfältet. Parkoppling i atomkärnan spelar en viktig roll i många kärnfenomen,inklusive förekomsten av en systematisk udda-jämn förskjutning (OES) av bindningsenergin.Hos svagt bundna atomkärnor däremot spelar parkopplingen en signifikant roll för stabiliteten. Det gäller alla de nyupptäckta neutronrika atomkärnor som karakteriseras aven svag bindningsenergi där således parkopplingen blir ett kritiskt fenomen. När vi lämnar stabilitetslinjen och närmar oss linjen av spontan neutronsönderfall är parkopplingeninte längre obetydlig, utan tvärtom spelar en viktig roll för stabiliteten hos atomkärnan.Dess styrka kan vara av samma storleksordning som medelfältet. I denna avhandling har vi fokuserat på parkopplingen i atomkärnor under extrema villkor i syfte att undersöka strukturen hos löst bundna atomkärnor nära linjen för neutronsönderfall; att utforska och globalt bedöma resultaten av olika parkopplingar baserad på en deltakraft (räckvidd noll) och deras effekt på löst bundna tillstånd med lågt rörelsemängdsmoment. Hur mycket kan ett täthetsberoende i parkopplingen påverka stabilitetslinjen? Beräkningarna förutsäger att ren densitetsberoende växelverkan för parkoppling, så kallad ytväxelverkan, ökar kollektiviteten i atomkärnan och ger ett större pargap för neutroner i kärnor långt ifrån stabilitetslinjen,medan densitetsberoende parkoppling påverkar inte gapet för bundna kärnor i samma omfattning.Udda-jämn-spridning av bindningsenergier har undersökts för att hitta storleken på parkopplingens gap. En 3-punktsformel Δ(3)C (1/2[B(N,Z)+B(N −2,Z)−2B(N −1,Z)]) förespråkas i denna avhandling, som vi anser vara mera lämplig för att mäta storleken på pargapet i jämn-jämna kärnor. Storleken på Δ(3)C kan vara en bra indikator på rumskorrelationen mellan två nukleoner. En-kvasipartikelenergi för de udda kärnorna, som kan approximeras med sfärisk symmetri, beräknas för att erhålla udda-jämn spridning (OES) med avseende på bindningsenergin för alla kända semi-magiska jämn-jämna kärnor. Parkopplingsstyrkan är globalt anpassat med all tillgänglig data på OES vad gäller semi-magiska kärnor med Z ≥ 8. Skillnaden mellan olika täthetsberoende parkopplingar med vår växelverkan minskar med dessa globalt anpassade parametrar. Skillnaden mellan det teoretiska genomsnittliga parkopplingsgapet och OES blir större när vi kommer närmare tröskeln för atomkärnans stabilitet. I slutet av avhandlingen har en schematisk modell utvecklats som, genom attgöra medelfältet grundare, reducerar de udda-jämnt spridda laddningsradierna. Avhandlingen innehåller dessutom resultat som inte ingår i de tre publicerade artiklarna samt några kompletterande arbeten om ämnet. / <p>QC 20171114</p>