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Combining and comparing neutrinoless double beta decay experiments using different nuclei
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
2013 (English)In: Journal of High Energy Physics (JHEP), ISSN 1029-8479, E-ISSN 1126-6708, no 2, 093- p.Article in journal (Refereed) Published
Abstract [en]

We perform a global fit of the most relevant neutrinoless double beta decay experiments within the standard model with massive Majorana neutrinos. Using Bayesian inference makes it possible to take into account the theoretical uncertainties on the nuclear matrix elements in a fully consistent way. First, we analyze the data used to claim the observation of neutrinoless double beta decay in Ge-76, and find strong evidence (according to Jeffrey's scale) for a peak in the spectrum and moderate evidence for that the peak is actually close to the energy expected for the neutrinoless decay. We also find a significantly larger statistical error than the original analysis, which we include in the comparison with other data. Then, we statistically test the consistency between this claim with that of recent measurements using Xe-136. We find that the two data sets are about 40 to 80 times more probable under the assumption that they are inconsistent, depending on the nuclear matrix element uncertainties and the prior on the smallest neutrino mass. Hence, there is moderate to strong evidence of incompatibility, and for equal prior probabilities the posterior probability of compatibility is between 1.3% and 2.5%. If one, despite such evidence for incompatibility, combines the two data sets, we find that the total evidence of neutrinoless double beta decay is negligible. If one ignores the claim, there is weak evidence against the existence of the decay. We also perform approximate frequentist tests of compatibility for fixed ratios of the nuclear matrix elements, as well as of the no signal hypothesis. Generalization to other sets of experiments as well as other mechanisms mediating the decay is possible.

Place, publisher, year, edition, pages
2013. no 2, 093- p.
Keyword [en]
Rare Decays, Statistical Methods, Neutrino Physics
National Category
Physical Sciences
URN: urn:nbn:se:kth:diva-121132DOI: 10.1007/JHEP02(2013)093ISI: 000316273700016ScopusID: 2-s2.0-84875861465OAI: diva2:616886

QC 20130419

Available from: 2013-04-19 Created: 2013-04-19 Last updated: 2013-08-30Bibliographically approved
In thesis
1. Models in Neutrino Physics: Numerical and Statistical Studies
Open this publication in new window or tab >>Models in Neutrino Physics: Numerical and Statistical Studies
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The standard model of particle physics can excellently describe the vast majorityof data of particle physics experiments. However, in its simplest form, it cannot account for the fact that the neutrinos are massive particles and lepton flavorsmixed, as required by the observation of neutrino oscillations. Hence, the standardmodel must be extended in order to account for these observations, opening up thepossibility to explore new and interesting physical phenomena.

There are numerous models proposed to accommodate massive neutrinos. Thesimplest of these are able to describe the observations using only a small numberof effective parameters. Furthermore, neutrinos are the only known existing particleswhich have the potential of being their own antiparticles, a possibility that isactively being investigated through experiments on neutrinoless double beta decay.In this thesis, we analyse these simple models using Bayesian inference and constraintsfrom neutrino-related experiments, and we also investigate the potential offuture experiments on neutrinoless double beta decay to probe other kinds of newphysics.

In addition, more elaborate theoretical models of neutrino masses have beenproposed, with the seesaw models being a particularly popular group of models inwhich new heavy particles generate neutrino masses. We study low-scale seesawmodels, in particular the resulting energy-scale dependence of the neutrino parameters,which incorporate new particles with masses within the reach of current andfuture experiments, such as the LHC.

Abstract [sv]

Standardmodellen för partikelfysik beskriver den stora majoriteten data från partikelfysikexperimentutmärkt. Den kan emellertid inte i sin enklaste form beskrivadet faktum att neutriner är massiva partiklar och leptonsmakerna är blandande,vilket krävs enligt observationerna av neutrinooscillationer. Därför måste standardmodellenutökas för att ta hänsyn till detta, vilket öppnar upp möjligheten att utforska nya och intressanta fysikaliska fenomen.

Det finns många föreslagna modeller för massiva neutriner. De enklaste av dessakan beskriva observationerna med endast ett fåtal effektiva parametrar. Dessutom är neutriner de enda kända befintliga partiklar som har potentialen att vara sinaegna antipartiklar, en möjlighet som aktivt undersöks genom experiment på neutrinolöst dubbelt betasönderfall. I denna avhandling analyserar vi dessa enkla modellermed Bayesisk inferens och begränsningar från neutrinorelaterade experiment och undersöker även potentialen för framtida experiment på neutrinolöst dubbelt betasönderfall att bergänsa andra typer av ny fysik.

Även mer avancerade teoretiska modeller för neutrinomassor har föreslagits, med seesawmodeller som en särskilt populär grupp av modeller där nya tunga partiklargenererar neutrinomassor. Vi studerar seesawmodeller vid låga energier, i synnerhetneutrinoparametrarnas resulterande energiberoende, vilka inkluderar nya partiklarmed massor inom räckh°all för nuvarande och framtida experiment såsom LHC.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xii, 96 p.
Trita-FYS, ISSN 0280-316X ; 2013:50
Neutrino mass, lepton mixing, Majorana neutrinos, neutrino oscillations, neutrinoless double beta decay, statistical methods, Bayesian inference, model selection, effective field theory, Weinberg operator, seesaw models, inverse seesaw, right-handed neutrinos, renormalization group, threshold effects., Neutrinomassor, leptonblandning, Majorananeutriner, neutrinooscillationer, neutrinol¨ost dubbelt betas¨onderfall, statistiska metoder, Bayesisk inferens, modellval, effektiv f¨altteori, Weinbergoperator, seesawmodeller, invers seesaw, högerhänta neutriner, renormeringsgrupp, tröskeleffekter.
National Category
Subatomic Physics
urn:nbn:se:kth:diva-127409 (URN)978-91-7501-854-6 (ISBN)
Public defence
2013-09-13, FB54, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)

QC 20130830

Available from: 2013-08-30 Created: 2013-08-29 Last updated: 2013-08-30Bibliographically approved

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