magistrsko delo
Miha Medvešek (Author), Svjetlana Fajfer (Mentor)

Abstract

Uvodoma je predstavljen standardni model (SM), najbolj celovita teorija osnovnih delcev in njihovih interakcij. Vsaka interakcija je zapisana v umeritveni teoriji in za vsako smo zapisali Lagrangian. Podrobno smo opisali poenotenje elektromagnetne in šibke interakcije v elektrošibko, pri kateri se simetrija zlomi. S Higgsovim mehanizmom smo generirali mase umeritvenih bozonov, fermionov in leptonov. Nato smo transformirali stanja fermionov iz šibke (umeritvene) baze v masno bazo pri čemer pride do mešanja okusov, kar je predstavljeno z matriko CKM. Kljub vsemu je SM nepopoln, zato danes potekajo raziskave za njegovo razširitev. V tej nalogi smo kot primer fizike onkraj SM navedli nevtrinske oscilacije, ki so pogojene z masivnimi nevtrini. Drug primer razširitve so hipotetični delci leptokvarki (LQ), ki lahko neposredno sklopijo leptone s kvarki in so bili opisani v tej nalogi. Osredotočili smo se na skalarni LQ $\tilde{R}_2$, ki lahko sklaplja SM fermione z delci, ki imajo kvantna števila desnoročnega nevtrina in jih SM ne opiše. Nadaljnje smo opisali osnovne količine v razpadih elementarnih delcev ter predstavili teoretično ozadje izračuna le-teh. Osrednja tematika te magistrske naloge so razpadi $B_s^0 \rightarrow$ "nevidno", $B^+ \rightarrow K^{+}$ "nevidno" ter $B^+ \rightarrow K^{*+}$ "nevidno" v efektivni teoriji. Za prvi razpad smo izračunali razvejitveno razmerje za skalarni operator in vektorski operator, ki vsebujeta masivne desnoročne nevtrine, nato je bil v interakcijo vključen LQ $\tilde{R}_2$. Raziskali smo odvisnost produkta Yukawinih sklopitev v odvisnosti od mase $\tilde{R}_2$. V primeru razpada $B^+ \rightarrow K^{+}$ "nevidno" in $B^+ \rightarrow K^{*+}$ "nevidno" smo najprej v efektivni teoriji izračunali napoved SM, v katerem "nevidno" predstavljata dva SM nevtrina. Kasneje smo razširili izbor operatorjev, ki vsebujejo masivne desnoročne nevtrine ter vpeljali interakcijo z LQ. Za oba razpada smo poiskali meje za mase LQ $\tilde{R}_2$ in poiskali povezavo z maso desnoročnega nevtrina.

Keywords

fizika osnovnih delcev;standardni model;redki razpadi mezonov B;nova fizika;desnoročni nevtrini;leptokvarki;nevtrinske oscilacije;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL FMF - Faculty of Mathematics and Physics
Publisher: [M. Medvešek]
UDC: 539.12
COBISS: 194205955 Link will open in a new window
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Downloads: 2
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Other data

Secondary language: English
Secondary title: Neutrinos and invisible fermions in rare B meson decays
Secondary abstract: Initially, the Standard model (SM), the most comprehensive theory of fundamental particles and their interactions, is presented. Each interaction is described using the framework of the gauge theory and a Lagrangian is constructed for each of them. The unification of electromagnetic and weak interactions into the electroweak interaction, where symmetry breaking occurs is described in detail. With the Higgs mechanism, masses for gauge bosons, fermions and leptons are generated. A transformation of the states of fermions from the weak (gauge) basis to the mass basis occurs, resulting in flavor mixing which is presented using the CKM matrix. In the following section, physics beyond the SM, citing neutrino oscillations as an example, which require massive neutrinos, is described. Next, we introduced hypothetical particles, leptoquarks (LQ), which can directly couple leptons, and quarks. Our focus was on the scalar LQ $\tilde{R}_2$, which can couple SM fermions with particles that possess the quantum numbers of the right-handed neutrino, which are absent in the Standard model. Furthermore, we described fundamental quantities in the decays of elementary particles and provided the theoretical background for their calculations. The main theme of this master's thesis are the decays $B_s^0 \rightarrow$ "invisible", $B^+ \rightarrow K^{+}$ "invisible", and $B^+ \rightarrow K^{+}$ "invisible" in effective theory. For the first decay, we calculated the branching ratios for a scalar operator and a vector operator containing massive right-handed neutrinos, then we incorporated the interaction with LQ $\tilde{R}_2$. Next, we explored the dependece of Yukawa couplings product on the mass of $\tilde{R}_2$. In the cases of $B^+ \rightarrow K^{+}$ "invisible" and $B^+ \rightarrow K^{+}$ "invisible" we first calculated the SM prediction in the effective theory, where "invisible", represents two SM neutrinos. Later, we expanded the selection of operators that include massive right-handed neutrinos and introduced the interaction with LQ. For both decays, we found limits for the masses of LQ $\tilde{R}_2$ and established a connection with the mass of the right-handed neutrino.
Secondary keywords: physics of elementary particles;Standard Model;rare decays of B mesons;New Physics;right-handed neutrinos;leptoquarks;neutrino oscillations;
Type (COBISS): Master's thesis/paper
Study programme: 0
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Fak. za matematiko in fiziko, Oddelek za fiziko
Pages: 73 str.
ID: 23547781