Gutenberg Open Science: Search for π0 --> invisible decays with the NA62 experiment

Please use this identifier to cite or link to this item: http://doi.org/10.25358/openscience-5911

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DC Field	Value	Language
dc.contributor.author	Peruzzo, Letizia	-
dc.date.accessioned	2021-05-19T08:48:48Z	-
dc.date.available	2021-05-19T08:48:48Z	-
dc.date.issued	2021	-
dc.identifier.uri	https://openscience.ub.uni-mainz.de/handle/20.500.12030/5920	-
dc.description.abstract	The search for new physics beyond the Standard Model is one of the most active fields in particle physics. Complementary to direct searches for new processes at high-energy scale, $\mathcal{O}(\text{TeV})$, rare or forbidden Standard Model decays are investigated to look for deviations from the predictions. The NA62 experiment at the CERN SPS, designed for the measurement of the ultra-rare decay $K^+ \rightarrow \pi^+ \nu \bar{\nu}$, investigates new-physics contributions in the kaon and pion sector. The highly efficient, hermetic photon-veto system makes NA62 a perfect apparatus for a high-sensitivity search for $\pi^o$ decays into invisible particles. In a fraction of data collected by NA62 in 2017, about $8.4 \times 10^9$ $\pi^o$ mesons have been tagged by the reconstruction of the second most-abundant $K^+$ decay, $K^+ \rightarrow \pi^+ \pi^o (\gamma)$. The background rejection inefficiency for visible $\pi^o$ decays, ranging from $\mathcal{O}(10^{-8})$ to $\mathcal{O}(10^{-9})$, is estimated by the combination of single-photon detection efficiencies measured in data and Monte Carlo simulations of $K^+ \rightarrow \pi^+ \pi^o (\gamma)$ decays, a novel experimental technique with respect to that used in the most sensitive previous experimental result. The analysis is performed with the blind technique for a cut-based signal region. The $\pi^+$ momentum range is optimized to have the best sensitivity for the estimated upper limit on the $\pi^o \rightarrow invisible$ branching ratio in absence of a signal. In the signal region with $\pi^+$ momentum between 25 and 40~GeV/$c$, a total of about $4 \times 10^9$ tagged $\pi^o$ mesons are collected out of which 12 events survive the signal selection criteria. Given an estimated rejection inefficiency of $( 2.8^{+5.9}_{-2.1} ) \times 10^{-9}$, no signal is observed beyond the expected background fluctuations. The resulting upper limit on the branching ratio is \begin{displaymath} \mathrm{BR}(\pi^o \rightarrow invisible) \leq 4.4 \times 10^{-9} \end{displaymath} at 90\% confidence level, which improves on the previous best limit by a factor of 60. As a by-product of the analysis, the decay $K^+ \rightarrow \pi^+ X$ is investigated, where $X$ is a neutral particle escaping detection with a mass in the range 109--155~MeV/$c^2$. Model-dependent scenarios are investigated with the assumption that $X$ is an axion-like particle with dominant fermion couplings or a dark scalar with mixing with the Standard Model Higgs.	en_GB
dc.language.iso	eng	de
dc.rights	InCopyright	*
dc.rights.uri	http://rightsstatements.org/vocab/InC/1.0/	*
dc.subject.ddc	530 Physik	de_DE
dc.subject.ddc	530 Physics	en_GB
dc.title	Search for π0 --> invisible decays with the NA62 experiment	en_GB
dc.type	Dissertation	de
dc.identifier.urn	urn:nbn:de:hebis:77-openscience-7082af54-1c89-4e69-97e2-0ead33d7517d3	-
dc.identifier.doi	http://doi.org/10.25358/openscience-5911	-
jgu.type.dinitype	doctoralThesis	en_GB
jgu.type.version	Original work	de
jgu.type.resource	Text	de
jgu.date.accepted	2021-03-12	-
jgu.description.extent	xiv, 174, xvii Seiten, Illustrationen, Diagramme	de
jgu.organisation.department	FB 08 Physik, Mathematik u. Informatik	de
jgu.organisation.year	2020	-
jgu.organisation.number	7940	-
jgu.organisation.name	Johannes Gutenberg-Universität Mainz	-
jgu.rights.accessrights	openAccess	-
jgu.organisation.place	Mainz	-
jgu.subject.ddccode	530	de
jgu.organisation.ror	https://ror.org/023b0x485
Appears in collections:	JGU-Publikationen

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