Oscilacije neutralnih kaona i narušenje CP simetrije

master's thesis

• Title (english): Oscillations of neutral kaons and violation of CP symmetry
• Author: Nora Miljanić
• Mentor: Davor Horvatić (mentor)
• Committee member: Davor Horvatić (predsjednik povjerenstva)
• Committee member: Ivica Friščić (član povjerenstva)
• Committee member: Maja Planinić (član povjerenstva)
• Committee member: Damir Bosnar (član povjerenstva)
• Committee member: Katarina Jeličić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2022-09-27, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

Kaoni su pseudoskalarni mezoni koje jaka sila drži na okupu. U ovom će radu glavni fokus biti na raspadu kaona slabim interakcijama, a slabe interakcije narušavaju očuvanje okusa kvarkova, konjugaciju naboja i paritet. Dovode do miješanja okusa te omogućuju kaonske oscilacije. Fitch i Cronin su 1964. godine napravili eksperiment u kojem su otkrili CP narušenje na neutralnim kaonima. Prilikom izvođenja eksperimenta mjerilo se vrijeme raspada neutralnih kaona što je dovelo do zaključka da se K^0 i K¯^0 sastoje od superpozicije dvaju različitih stanja, različitih vremena poluraspada. Ta stanja nazvana su K_1 i K_2 te su ona svojstvena stanja CP simetrije. Stanje K_1 raspada se na dva piona te je ono kraćeg vremena života od stanja K_2 koje se raspada na tri piona. Prema vremenima života, K_1 i K_2 pridijeljene su nove oznake K_S i K_L. Eksperiment je dokazao da se K_1,2 i K_S,L ne podudaraju u potpunosti. Na detektoru se očekivalo dobiti samo raspade u tri piona od doprinosa K_L, no uočeno je 45 raspada od ukupno 22700 raspada na dva piona. Time je dokazano CP narušenje u prirodi čime je dan odgovor na neka od bitnih pitanja u svijetu fizike. Upravo je CP narušenje jedno od triju Sakharovljevih uvjeta koja trebaju biti zadovoljena da se stvori postojeća asimetrija materije i antimaterije u prirodi odgovorna za svijet kakav danas poznajemo.

Abstract (english)

Kaons are pseudoscalar mesons held together by a strong force. In this paper, the main focus will be on the decay of kaons by weak interactions, and weak interactions violate the conservation of quark flavour, charge conjugation and parity. They lead to the mixing of flavours and enable kaon oscillations. In 1964, Fitch and Cronin did an experiment in which they discovered CP perturbation on neutral kaons. During the experiment, the decay time of neutral kaons was measured, which led to the conclusion that Kˇ0 and K¯^0 consist of a superposition of two different states with different half-lives. These states are called K_1 and K_2, and they are the eigenstates of CP symmetry. State K_1 decays into two pions and has a shorter lifetime than state K_2, which decays into three pions. According to the lifetimes, K_1 and K_2 are assigned new labels K_S and K_L . The experiment proved that K_1,2 and K_S,L do not match completely. On the detector, it was expected to obtain only three-pion decays from the K_L contribution, but 45 decays were observed out of a total of 22,700 two-pion decays. This proved CP violation in nature, which answered some important physics questions. The CP violation is one of the three Sakharov conditions that must be satisfied to create the existing asymmetry of matter and antimatter in nature responsible for the world as we know it today.

• Keywords: standardni model; pseudoskalarni mezoni; zakoni sačuvanja; diskretne transformacije; CP simetrija; kaoni; oscilacije stranosti; bariogeneza
• Keywords (english): standard model; pseudoscalar mesons; conservation laws; discrete transformations; CP symmetry; kaons; strangeness oscillations; baryogenesis
• Language: croatian
• URN:NBN: urn:nbn:hr:217:562389
• Study programme: Title: Physics; specializations in: Education; Course: Education; Study programme type: university; Study level: integrated undergraduate and graduate; Academic / professional title: magistar/magistra edukacije fizike (magistar/magistra edukacije fizike)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2022-10-20 07:59:17