magistrsko delo
Mitja Šadl (Author), Svjetlana Fajfer (Mentor)

Abstract

Standardni model, kot teorija osnovnih interakcij, izjemno dobro opisuje elektromagnetne, šibke in močne interakcije osnovnih delcev. Kljub uspešnosti obstajajo pomanjkljivosti teorije, kot sta opis nevtrinskih mas in izvor temne snovi. Ni jasno, zakaj v naravi nastopajo ravno tri generacije fermionov in zakaj je električni naboj kvantiziran. Marsikoga moti tudi veliko število prostih parametrov. Obstajajo poskusi enotnega opisa vseh treh interakcij v teorijah velikega poenotenja, ki bi lahko rešile marsikateri problem standardnega modela. V takšnih teorijah je proton pogosto nestabilen, saj te napovejo interakcije, ki kršijo ohranitev barionskega kvantnega števila in povzročajo razpad protona. Posredniki teh interakcij so leptokvarki, hipotetični bozoni, ki kvarke spreminjajo v leptone in obratno. V tem delu obravnavamo leptokvark $S_1$, ki nima spina, je singlet elektrošibke simetrije in nosi električni naboj $1/3$. Z njim bi bilo možno razložiti razliko v meritvah razpadnega časa nevtrona, hkrati pa povzroči razpad protona. V delu najprej naredimo pregled standardnega modela in njegovih razširitev. Od slednjih obravnavamo teorije velikega poenotenja in najpreprostejši model $SU(5)$, ki sodi mednje. Potem naredimo klasifikacijo leptokvarkov. Sledi opis meritev razpadnega časa tako nevtrona kot protona. Nato opravimo račune razpadnih širin $\Gamma(p\to e^+\pi^0)$, $\Gamma(p\to e^+\gamma)$ in $\Gamma(n\to \chi\gamma)$, s katerimi s pomočjo meritev razpadnega časa nevtrona in protona ter kršitve atomske parnosti preverimo razmerje sklopitvenih konstant in mase leptokvarka $m_{S_1}$. Na koncu napovemo vrednost $m_{S_1}$ in podamo novo omejitev na $\tau(p\to e^+\gamma)$.

Keywords

fizika osnovnih delcev;fizika onkraj standardnega modela;nova fizika;leptokvarki;razpadi nukleonov;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL FMF - Faculty of Mathematics and Physics
Publisher: [M. Šadl]
UDC: 539.1
COBISS: 3348836 Link will open in a new window
Views: 551
Downloads: 133
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Other data

Secondary language: English
Secondary title: Scalar leptoquark in nucleon decays
Secondary abstract: The Standard Model, a theory of elementary interactions, describes very well electromagnetic, weak and strong interactions of elementary particles. Despite the success, there are some shortcomings like the description of neutrino mass and the origin of dark matter. It is unclear, why there are exactly three fermion families and why the electric charge is quantized. It is also unpleasant to have a theory with so many free parameters. There are attempts to describe all the three forces uniformly in the Grand Unified Theories. They could solve some of the Standard-Model problems. Some of them allow proton to be unstable. This is because they predict interactions that violate baryon number conservation and therefore force the proton to decay. The force carriers of these interactions are leptoquarks. They are hypothetical bosons that transform quarks into leptons and vice versa. I this thesis the leptoquark $S_1$ is considered. This leptoquark has electric charge $1/3$, no spin and is a singlet of the electroweak interaction. He could explain why there are discrepancies between neutron lifetime measurements of different methods. At the same time, leptoquark $S_1$ makes proton unstable. In the beginning, an overview of the Standard Model is made, followed by a description of Grand Unified Theories and the $SU(5)$ model, the simplest representative of them. Next, a classification of leptoquarks is made. Then measurements of the neutron and proton lifetimes are described. What follows, are the derivations of decay widths $\Gamma(p\to e^+\pi^0)$, $\Gamma(p\to e^+\gamma)$ and $\Gamma(n\to \chi\gamma)$. The results are used together with neutron and proton lifetime and atomic parity violation measurements to check the ratio between the $S_1$ coupling constants and its mass $m_{S_1}$. In the end, we estimate the value of $m_{S_1}$ and propose a new bound on $\tau(p\to e^+\gamma)$.
Secondary keywords: physics of elementary particles;physics beyond the Standard Model;new physics;leptoquarks;nucleon decays;
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: 66 str.
ID: 11212353