| 1. |
- Aprile, E., et al.
(författare)
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Effective Field Theory and Inelastic Dark Matter Results from XENON1T
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this work we expand on the XENON1T nuclear recoil searches and study the individual signals of Dark Matter interactions from operators up to dimension-eight in a Chiral Effective Field Theory (ChEFT) as well as a model of inelastic Dark Matter using data from the two science runs of the detector totalling 1 tonne*year exposure. For these analyses we extended the region of interest from [4.9, 40.9]keVnr to [4.9, 54.4]keVnr to enhance our sensitivity for signals that peak at nonzero energies. We show that the data is consistent with a background only hypothesis, with small excesses in the models which peak between 20 and 50keVnr, obtaining a maximum local discovery significance of 1.7 for the VVs ChEFT model for a WIMP mass of 70GeV/c2, and 1.8 for an iDM particle of 50GeV/c2 with a mass splitting of 100keV/c2. For each model we report 90% confidence level upper limits. We also report limits on three benchmark models of WIMP interaction using ChEFT for which we investigate the effect of isospin breaking interactions, reporting up to 6 orders of magnitude weaker limits with respect to the isospin conserving case driven by cancellations in the expected rate.
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| 2. |
- Morå, Knut Dundas, 1989-
(författare)
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A Search for Dark Matter Lines with H.E.S.S. II
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Most of the matter in the universe, ~80% is thought to be dark matter- particles that have small or no interactions with standard model particles. Dark matter is an integral part of the current understanding of cosmology, and leaves signs in the movements of stars and galaxies, as well as the Cosmic Microwave Background. The erakly interacting massive particle (WIMP) is a well-studied dark matter model that would be expected to have a mass around the weak scale, 100 GeV. WIMPs annihilating in the galactic center could give rise to mono- energetic gamma-rays in addition to a more extended spectrum. This thesis details a search for a dark matter line in a region 1.5° west of the galactic center using the High Energy Stereoscopic System (H.E.S.S.) imaging air Cherenkov telescope. The inclusion of a fifth telescope in the array enabled the analysis to extend the HESS energy range down to 100 GeV for a spectral line search. At 130 GeV, a limit of 1.38 10^-27 cm^3/s on the velocity-weighted cross-section at 95% confidence limit could be set using15.2 hours of data. The analysis is the first paper using all five telescopes of H.E.S.S. II. The main subject of the thesis has been in optimization of this analysis as well as future H.E.S.S. pointings.
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| 3. |
- Morå, Knut Dundas, 1989-
(författare)
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Harmonizing discovery thresholds and reporting two-sided confidence intervals : a modified Feldman & Cousins method
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- When searching for new physics effects, collaborations will often wish to publish upper limits and intervals with a lower confidence level than the threshold they would set to claim an excess or a discovery. However, confidence intervals are typically constructed to provide constant coverage, or probability to contain the true value, with possible overcoverage if the random parameter is discrete. In particular, that means that the confidence interval will contain the 0-signal case with the same frequency as the confidence level. This paper details a modification to the Feldman-Cousins method to allow a different, higher excess reporting significance than the interval confidence level.
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| 4. |
- Morå, Knut Dundas, 1989-
(författare)
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Statistical Modelling and Inference for XENON1T
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A great number of astrophysical observations suggests that of the matter in our universe, only a sixth is made up of known matter. The rest, named dark matter, has not been successfully identified. This thesis presents the analysis and statistical inference that was used by the XENON1T collaboration to conduct a search for a particular dark matter candidate; weakly interacting massive particles (WIMPs). XENON1T is a dual-phase time projection chamber that can detect particles scattering in a 2 tonne target of liquid xenon with deposited recoil energies above ~3 keV. This is low enough to observe the elastic recoil between a WIMP and a xenon nucleus for WIMP masses >5 GeV c-2.The results presented in this thesis use 278.8 days of data, with an analysis mass of 1.3 tonne. XENON1T uses models for backgrounds and signals within this volume to construct a combined likelihood for two science data-taking periods as well as calibration data-sets. Fits to simulated data-sets were used to calibrate and validate the confidence interval construction. In addition, analysis choices were evaluated both to optimize the discovery power and expected sensitivity of the search, and to improve the robustness of the analysis. No significant excess was observed in the search for a spin-independent WIMP-nucleon interaction for any WIMP masses between 6 GeV c-2 and 104 GeV c-2 for the 1 ton-year exposure. This analysis produced the strongest constraint on the spin-independent WIMP-nucleon cross-section so far, with a minimum of 4.1 10-47 cm2 for a 30 GeV c-2 WIMP.
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