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Harmonizing discovery thresholds and reporting two-sided confidence intervals: a modified Feldman & Cousins method
Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).ORCID iD: 0000-0002-2011-1889
(English)Manuscript (preprint) (Other academic)
Abstract [en]

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.

Keywords [en]
Data Analysis, Statistics and Probability
National Category
Other Physics Topics
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-163388OAI: oai:DiVA.org:su-163388DiVA, id: diva2:1274351
Note

Submitted to JINST.

Available from: 2018-12-30 Created: 2018-12-30 Last updated: 2019-01-06
In thesis
1. Statistical Modelling and Inference for XENON1T
Open this publication in new window or tab >>Statistical Modelling and Inference for XENON1T
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2019. p. 116
Keywords
Dark matter, direct detection, statistical analysis
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-163390 (URN)978-91-7797-566-3 (ISBN)978-91-7797-567-0 (ISBN)
Public defence
2019-02-25, FA31, Albanova, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript.

Available from: 2019-01-31 Created: 2019-01-06 Last updated: 2019-02-28Bibliographically approved

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arXiv:1809.02024

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Morå, Knut Dundas
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