Authors:	Scavino, Bianca
Title:	Development of Λ baryons reconstruction and its application to the search for a stable hexaquark at Belle II
Online publication date:	17-Aug-2022
Year of first publication:	2022
Language:	english
Abstract:	QCD-motivated models for hadrons predict a wide variety of exotic hadrons, with structures more complex than the quark-antiquark mesons and the three-quark baryons of the ordinary hadron classification. Among these, one of the most intriguing cases refers to the H dibaryon, an elusive six-quark state with the quark content of two Λ baryons first suggested by R. L. Jaffe in 1977. The search for a stable double strange hexaquark, which, in recent years, was put forward to also be a dark matter candidate, is part of the Belle II physics program. In the coming years, a fraction of the Belle II data taking period will be dedicated to run at the energy of the Υ(3S) resonance. This bb̄ resonance decays primarily via three gluons, in which ss̄ quark pairs are produced with roughly the same probability as uū and dƌ pairs, making it particularly well suited for searches for multiquark states with nonzero strangeness. This thesis describes a feasibility study for the search for a stable double strange six-quark state S produced in Υ(3S) decays, Υ(3S) → SΛΛnπ (with n = 0, 2, 4, 6, and 8). The predictions obtained for the channel with n=0 are compared with an existing result from the BaBar collaboration, while the other channels represent a novel measurement. In order to obtain optimal results, an integral part of the work is the optimization of the Belle II tracking package for displaced vertices with a focus on Λ baryon reconstruction, a key element in the stable hexaquark analysis. After the optimization, the algorithms and selections developed for Λ baryons were extensively tested using Belle II data collected at the Υ(4S) resonance. Finally, a look at the future is taken. Given that the beam background level measured at Belle II in the first data taking periods turned out to be higher than initial estimates, the possible effect of increased background on performance deterioration, both on tracking in general and on the hexaquark analysis in particular, is assessed and discussed in detail. The work presented in this thesis is intended to prepare a measurement where the tools and the analysis procedures developed, as well as the critical points observed, will be used on the Υ(3S) Belle II data to set a new limit on the possible observation of such an exotic state.
DDC:	530 Physik 530 Physics
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 08 Physik, Mathematik u. Informatik
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-7508
URN:	urn:nbn:de:hebis:77-openscience-ca4525d4-c352-4a51-bf62-ea02b207ed175
Version:	Original work
Publication type:	Dissertation
License:	In Copyright
Information on rights of use:	http://rightsstatements.org/vocab/InC/1.0/
Extent:	xiii, 158 Seiten, Diagramme
Appears in collections:	JGU-Publikationen