magistrsko delo
Aljaž Hvala (Author), Jernej Kamenik (Mentor)

Abstract

Na trkalniku elektronov in pozitronov LEP je izmerjena vrednost asimetrije naprej-nazaj v procesu $e^{+} e^{-} \to Z \to b \bar{b}$, znatno odstopala od teoretičnih napovedi znotraj standardnega modela osnovnih delcev in interakcij. Omenjena asimetrija je po teoretičnih izračunih sorazmerna z razliko kvadratov sklopitvenih konstant bozona $Z$ z levo- in desnoročnimi kvarki $b$ ($g^{2}_{Lb}-g^{2}_{Db}$). V magistrski nalogi smo raziskali, kako bi lahko na trkalnikih hadronov, kot je Veliki hadronski trkalnik (LHC), definirali opazljivke, ki so senzitivne na isto razliko kvadratov sklopitvenih konstant. Obravnavali smo tvorbo bozona $Z$ in njegov razpad v par $b \bar{b}$. V vodilnem redu kvantne perturbacijske teorije smo na partonskem nivoju izračunali celotni in diferencialni sipalni presek za proces $q \bar{q} \to Z \to b \bar{b}$ v odvisnosti od kota med smermi potovanja kvarka $q$ in kvarka $b$ v težiščnem sistemu. Ker v eksluzivni tvorbi bozona $Z$ v (simetričnih) trkih protonov asimetrije naprej-nazaj ne moremo definirati, smo obravnavali tudi bolj inkluzivne procese, v katerih se tvorijo dodatni hadronski curki. Zanimale so nas kotne porazdelitve razpadnih produktov bozona $Z$ glede na smeri vpadnih partonov ter dodatnih hadronskih curkov na partonskem nivoju. Iz njih smo na partonskem nivoju izluščili količino, ki je senzitivna na $g^{2}_{Lb}-g^{2}_{Db}$. Na podoben način bi lahko določili $g^{2}_{Lb}-g^{2}_{Db}$ tudi po prehodu na hadronski nivo.

Keywords

fizika osnovnih delcev;bozoni;bozon Z;kvarki b;asimetrija naprej-nazaj;hadronski trkalniki;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL FMF - Faculty of Mathematics and Physics
Publisher: [A. Hvala]
UDC: 539.120
COBISS: 157770499 Link will open in a new window
Views: 9
Downloads: 4
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Other data

Secondary language: English
Secondary title: Interactions between $Z$ boson and $b$ quarks at hadron colliders
Secondary abstract: The measured value of the forward-backward asymmetry in the process $e^{+} e^{-} \to Z \to b \bar{b}$ at the electron-positron collider LEP significantly deviated from the theoretical predictions given by the Standard Model of elementary particles and interactions. According to the theoretical calculation, this asymmetry is proportional to the difference of the squared coupling constants of the boson $Z$ with left- and right-handed $b$ quarks ($g^{2}_{Lb}-g^{2}_{Db}$). In this master thesis, we were searching for observables at hadron colliders, such as the Large Hadron Collider (LHC), which are sensitive to the same difference of the coupling constants. We have investigated the $Z$ boson production and decay into a $b \bar{b}$ pair. At the leading order in quantum perturbation theory, we have calculated, at parton level, the total and differential cross section for the process $q \bar{q} \to Z \to b \bar{b}$ depending on the angle between the $q$ quark and $b$ quark momenta in the center-of-mass reference frame. In exclusive production of the $Z$ boson in (symmetric) collisions of protons, the forward-backward asymmetry is undefined. We have considered more inclusive processes, where additional hadron jets are formed. We were interested in the angular distributions of the $Z$ boson's decay products with respect to the momenta of the incoming partons and additional hadron jets at the parton level. We have then defined and calculated an observable at parton level sensitive to $g^{2}_{Lb}-g^{2}_{Db}$. In a similar way it would be also possible to obtain sensitivity to $g^{2}_{Lb}-g^{2}_{Db}$ at the hadron level.
Secondary keywords: physics of elementary particles;bosons;Z boson;b quarks;forward-backward asymmetry;hadron colliders;
Type (COBISS): Master's thesis/paper
Study programme: 0
Thesis comment: Univ. v Ljubljani, Fak. za matematiko in fiziko, Oddelek za fiziko
Pages: 43 str.
ID: 19872204