Flavor universality in elementary particle processes at low and high energies

Korajac, Arman (author), Fesel Kamenik, Jernej (mentor)

Persistent indications of lepton flavor universality violation observed in bottom-quark transitions have motivated a plethora of models addressing the relevant deviations from the expected Standard Model (SM) result. This dissertation focuses on different strategies of observing flavor non-universal patterns in diverse Beyond the Standard Model realizations. We utilize simultaneously high-energy and low-energy data to constrain the parameter space of models addressing such issues and propose novel search strategies at present and at future colliders. Specifically, we propose an analysis of extracting New Physics (NP) information from collider searches targeting events with high missing transverse energy (MET) values and tagged $b$-jets as signatures. In the context of the Standard Model Effective Field Theory (SMEFT), we show that such an analysis imposes constraints on the SMEFT operators that are comparable in magnitude to those obtained via high-$p_T$ dilepton searches. Afterwards, we compare our results with the exclusion bounds derived from low-energy experiments, specifically including the decays $\Upsilon(1S) \to $ invisibles and $B \to K^{(\ast)} \nu \bar{\nu}$. Additionally, our attention is linked towards light-generation quarks, with a particular emphasis on investigating CP violation within the SMEFT. The studied inclusion of the singlet and triplet left-handed semileptonic operators for the first two quark generations leads to contributions in semileptonic and leptonic decays of $K, D$ mesons, pions, and nuclear beta decay. We implement the flavor covariant description in the low-energy couplings, identify universal CP phases of New Physics and give an explicit description of up- and down-quark transitions simultaneously. As a result, we can predict the maximal effects of such flavored NP in $D$ decays from stringent $K$ decay constraints and vice-versa. Furthermore, a long-standing candidate for the explanation of charged-current $B$-anomalies is a TeV-scale $U_1 \sim \left(\mathbf{3}, \mathbf{1}, 2/3\right)$ leptoquark, mainly coupled to the third generation. We study its production by lepton-quark fusion at the Large Hadron Collider, considering next-to-leading-order effects from its interactions with gluons and photons. We derive high-energy bounds on the parameters of the 4321 Lagrangian using the most recent resonant leptoquark production search performed by the CMS Collaboration. We also employ recent advances in $b$, $c$, and $s$ quark tagging together with novel statistical analysis techniques within the context of the FCC-ee collider environment. We show that it is possible to place phenomenologically relevant bounds on flavor-violating Higgs and $Z$ decays to quarks using these methods. We show that searches for $h\to bs, cu$ decays at FCC-ee can probe new parameter space not excluded by indirect, low-energy searches.

• Language: English
• Keywords: beyond the Standard Model, New Physics, flavor-violating processes, collider studies, dineutrino couplings, low-energy theory, CP violation, leptoquarks, FCC
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FMF - Faculty of Mathematics and Physics
• Year: 2024
• PID: 20.500.12556/RUL-156396
• COBISS.SI-ID: 192034563
• Publication date in RUL: 23.05.2024

Secondary language

• Language: Slovenian
• Title: Univerzalnost okusov v procesih osnovnih delcev pri nizkih in visokih energijah

Abstract

Vztrajni znaki kršitve univerzalnosti leptonskih okusov, opaženi pri prehodih kvarka $b$, so spodbudili množico modelov, ki prilagajajo odstopanja od pričakovanega rezultata standardnega modela (SM) z eksperimentalnimi meritvami. Ta disertacija se osredotoča na različne strategije opazovanja kršitve univerzalnosti okusov v različnih upodobitvah fizike onkraj standardnega modela. Istočasno uporabljamo visokoenergijske in nizkoenergijske podatke, da omejimo parameterski prostor modelov, ki obravnavajo takšna vprašanja, in predlagamo nove strategije iskanja pri sedanjih in prihodnjih trkalnikih. Natančneje, predlagamo analizo pridobivanja informacij o novi fiziki (NP) iz iskanj v trkalniku, ki ciljajo na dogodke z visokimi manjkajočimi vrednostmi prečne energije (MET) in označenimi curki $b$. V kontekstu teorije efektivnega polja standardnega modela (SMEFT) pokažemo, da taka analiza nalaga operaterjem SMEFT omejitve, ki so po velikosti primerljive s tistimi, pridobljenimi iz dvoleptonskih eksperimentov z visoko vrednostjo transverzalne gibalne količine $p_T$. Nato svoje rezultate primerjamo z izključitvenimi mejami, pridobljenimi iz nizkoenergijskih poskusov $\Upsilon(1S) \to $ nevidno in $B \to K^{(\ast)} \nu \bar{\nu}$. Poleg tega se osredotočamo na prvo in drugo generacijo kvarkov, s posebnim poudarkom na raziskovanju kršitve CP znotraj SMEFT. Raziskana vključitev singletnih in tripletnih levoročnih semileptonskih operaterjev za prvi dve generaciji kvarkov vodi do prispevkov v semileptonskih in leptonskih razpadih mezonov $K, D$, pionov in jedrskega beta razpada. Implementiramo t.i. kovariantni opis okusa v nizkoenergijskih povezavah, identificiramo univerzalne CP faze Nove fizike in podamo ekspliciten opis prehodov kvarkov navzgor in navzdol hkrati. Posledično lahko predvidimo maksimalne učinke takšne Nove fizike pri razpadih mezona $D$ glede na stroge omejitve razpada mezona $K$ in obratno. Dolgoletni kandidat za razlago $B$-anomalij nabitega toka je leptokvark $U_1 \sim (\mathbf{3}, \mathbf{1}, 2/3)$ na skali TeV, večinoma sklopljen do tretje generacije. Preučujemo njegovo proizvodnjo s fuzijo leptona in kvarka na velikem hadronskem trkalniku, pri čemer upoštevamo učinke z gluoni in fotoni na eni zanki. Izpeljemo visokoenergijske meje parametrov lagrangiana 4321 z uporabo najnovejšega iskanja proizvodnje resonančnih leptokvarkov, ki ga je opravila kolaboracija CMS. Uporabljamo tudi nedavni napredek pri označevanju kvarkov $b$, $c$ in $s$ skupaj z novimi tehnikami statistične analize v okviru okolja trkalnika FCC-ee. Pokažemo, da je mogoče s temi metodami postaviti fenomenološko pomembne meje za Higgsove razpade in razpade bozona $Z$ na kvarke različnih generacij. Pokažemo, da lahko iskanja razpadov $h\to bs, cu$ pri FCC-ee preiščejo nov prostor parametrov, ki ni izključen s posrednimi, nizkoenergijskimi iskanji.

• Keywords: fizika onkraj Standardnega Modela, Nova fizika, kršitev okusne simetrije, analiza na trkalnikih, dvonevtrinske sklopitve, efektivne teorije pri nizkih energijah, CP kršitev, leptokvarki, FCC