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Študij tetrakvarka Zb s kvantno kromodinamiko na mreži
ID Petković, Jan (Author), ID Prelovšek, Saša (Mentor) More about this mentor... This link opens in a new window

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Abstract
V tem delu teoretično študiramo resonanco Zb, opaženo leta 2011 v detektorju Belle, ki izkazuje tetrakvarkovsko strukturo. Sistem analiziramo s kvantno kromodinamiko na mreži, saj gre za močno interagirajoč sistem v neperturbativnem režimu. Iz razpadnih produktov resonance je mogoče sklepati na kvarkovsko strukturo ˉbbˉdu. Zaradi ogromne razlike mas med kvarki uporabimo Born-Oppenheimerjev približek, kjer težja kvarka ˉb in b v prvem koraku privzamemo za statična. Možna stanja, s katerimi opišemo tetrakvark Zb, razvrstimo v dva tipa. Prvemu ustreza par interagirajočih mezonov B in ˉB, drugemu pa interagirajoča botomonij Υ in pion s tremi najnižjimi vrednostmi gibalne količine, ki so v skladu s simetrijo sistema. Stanja z neničelno gibalno količino piona moramo vključiti v analizo, saj ta še vedno ležijo pod vrednostjo resonanc Zb. Do sedaj tega ni vsebovala še nobena študija. Z izbranimi operatorji numerično izračunamo korelacijske funkcije, iz katerih izluščimo lastne energije sistema kot funkcijo razdalje med težkima kvarkoma. Za interpretacijo energijskega spektra izračunamo lastne energije neinteragirajoče verzije originalnega sistema. Po primerjavi ustreznih lastnih energij opazimo očitno odstopanje v kanalu BˉB, kjer je za majhne razdalje med mezonoma B znaten privlačen potencial. Izluščen potencial nato uporabimo za reševanje Schr\"odingerjeve enačbe za mezona v težiščnem sistemu. Preučimo stanja, ki jih takšen potencial dopušča, ter skušamo rezultate povezati z izmerjenio resonanco Zb.

Language:Slovenian
Keywords:fizika osnovnih delcev, močna interakcija, kvantna kromodinamika na mreži, tetrakvark Zb, Born-Oppenheimerjev približek
Work type:Master's thesis/paper
Typology:2.09 - Master's Thesis
Organization:FMF - Faculty of Mathematics and Physics
Year:2020
PID:20.500.12556/RUL-117100 This link opens in a new window
COBISS.SI-ID:20602371 This link opens in a new window
Publication date in RUL:24.06.2020
Views:1632
Downloads:219
Metadata:XML DC-XML DC-RDF
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PETKOVIĆ, Jan, 2020, Študij tetrakvarka $Z_{b}$ s kvantno kromodinamiko na mreži [online]. Master’s thesis. [Accessed 8 July 2025]. Retrieved from: https://repozitorij.uni-lj.si/IzpisGradiva.php?lang=eng&id=117100
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Secondary language

Language:English
Title:Study of Zb tetraquark with lattice QCD
Abstract:
In this thesis we study the resonance Zb, observed in 2011 at Belle detector, with exotic quark structure. We analyse the system using quantum chromodynamics on lattice, since the system considered is governed by the strong interaction in nonperturbative regime. From decay channels of Zb, it is possible to deduce that the valence quark structure is ˉbbˉdu. A large difference in mass of the valence quarks allows us to use Born-Oppenheimer approximation, where in the first step of the calculation the two heavier quarks ˉb and b are treated as static. Possible states, that we use to describe Zb, are classified into two types. The first set resembles two interacting mesons, B and ˉB. The second one describes bottomonium Υ and a pion with three different smallest values of momenta, that are allowed by the symmetry of the system. States with non-zero pion momenta need to be included, since some of them still lie below or close to the threshold of the Zb resonance. Up to this point no theoretical study has included those states in their analysis. After chossing the operators we compute the correlation function, from which we extract the eigen energies as a function of separation of the two heavy quarks. To make any physical conclusion based of the spectrum, we compute eigenenergies of a non-interacting version of the original system. After comparing the two, we observe a large deviation in the channel BˉB, where for small separations between the two mesons there appears a large binding potential. The extracted potential is then used to solve the Schr\"odinger equation for mesons in the center of mass system. We analyse the states, that are allowed by the potential, and try to connect those with the experimentally observed resonance Zb.

Keywords:particle physics, strong interaction, quantum chromodynamics on lattice, tetraquark Zb, Born-Oppenheimer approximation

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