Iskanje nove fizike v redkih razpadih mezona $D^0\rightarrow \text{“nevidno”}$

Novosel, Anja (author), Fajfer, Svjetlana (mentor)

Po kratkem povzetku osnovnih delcev v standardnem modelu, bomo predstavili umeritvene teorije, ki predstavljajo interakcije. Podrobneje si bomo pogledali model elektrošibke interakcije z vključenim Higgsovim mehanizmom, ki generira mase šibkim bozonom $W$ in $Z$. Določili bomo tudi masne člene fermionov, kjer bomo z biunitarno transformacijo diagonalizirali masne matrike. Nato bomo razložili mešanje fermionov in GIM mehanizem. Pri obravnavi nove fizike bomo najprej definirali razvejitveno razmerje, količino, ki jo bomo kasneje uporabili za primerjavo teoretične napovedi z eksperimentom. Opisali bomo tudi, kako z uporabo efektivne teorije polja raziskujemo prispevke nove fizike. Potem bomo predstavili leptokvarke, ki nastopajo v eni možnih razširitev standardnega modela. Kasneje bomo v efektivni teoriji obravnavali prispevke nove fizike v redkih razpadih mezona $D^0\rightarrow \text{“nevidno”}$, kjer se bomo osredotočili na končna stanja, ki vsebujejo nevtrine. Obravnavali bomo samo prispevke kratkih razdalj, ki so v standardnem modelu zaradi GIM mehanizma zelo potisnjeni. V standardnem modelu nastopajo samo levoročni nevtrini, medtem ko se v modelih nove fizike pojavijo tudi masivni desnoročni nevtrini. Iz procesov $D^0\rightarrow \bar{\nu}_R\nu_R$ in $D^0-\bar{D}^0$ bomo omejili sklopitve leptokvarka $\bar{S}_1$ s fermioni. Na koncu bomo izračunali vrednost razvejitvenega razmerja za proces $D^0\rightarrow \pi^0\bar{\nu}_R\nu_R$.

• Language: Slovenian
• Keywords: razpadi mezona D, desnoročni nevtrini, nova fizika
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FMF - Faculty of Mathematics and Physics
• Year: 2019
• PID: 20.500.12556/RUL-112893
• COBISS.SI-ID: 3384932
• Publication date in RUL: 19.11.2019

NOVOSEL, Anja, 2019, Iskanje nove fizike v redkih razpadih mezona $D^0\rightarrow \text{“nevidno”}$ [online]. Master’s thesis. [Accessed 7 April 2025]. Retrieved from: https://repozitorij.uni-lj.si/IzpisGradiva.php?lang=eng&id=112893

Secondary language

• Language: English
• Title: Searching for New Physics in rare decays of meson $D^0 \rightarrow \text{“invisible”}$

Abstract

After short review of the Standard Model elementary particles, we present interactions as gauge theories. We take a closer look at the model of electroweak interactions with included Higgs mechanism, which generates masses of weak bosons $W$ and $Z$. We determine mass terms for fermions, where we diagonalise mass matrices with biunitary transformation. After we explain mixing of fermions and GIM mechanism. When considering New Physics we first define branching fraction, which we use to compare theoretical prediction with experimental value. We describe how can we explore New Physics contributions by using Effective Theory approach. Later we present model containing leptoquarks as one of possible extensions of the Standard Model. Afterwards we analyse New Physics contributions in rare decays $D^0\rightarrow \text{“invisible”}$ using Effective Theory approach, where we focus on neutrinos in final state. We consider especially short distance contributions, which are highly suppressed in the Standard Model due to the GIM mechanism. In the Standard Model we have only left-handed neutrinos, while in New Physics models also right-handed neutrinos can emerge. We constrain couplings of leptoquark $\bar{S}_1$ with fermions from processes $D^0\rightarrow \bar{\nu}_R\nu_R$ and $D^0-\bar{D}^0$. At the end we calculate branching fraction for $D^0\rightarrow \pi^0\bar{\nu}_R\nu_R$.

• Keywords: D meson decays, right-handed neutrinos, New Physics