magistrsko delo
Luka Senekovič (Author), Peter Križan (Mentor)

Abstract

Pri eksperimentu Belle II v Cukubi na Japonskem iščemo signale t.i. nove fizike v redkih razpadih mezonov B, mezonov D in leptona tau. Pri rekonstrukciji iskanih razpadov iz nastalih končnih produktov, ki jih zaznamo v detektorju Belle II, ima zelo pomembno vlogo identifikacija nabitih delcev, predvsem učinkovito ločevanje med pioni in kaoni v njihovem celotnem kinematskem območju. Eden izmed sistemov v detektorju Belle II, ki je namenjen identifikaciji delcev, je detektor obročev Čerenkova ARICH. Delovanje detektorja ARICH temelji na znani odvisnosti velikosti Čerenkovega kota (t.j. kota med smerjo nabitega delca in smerjo izsevanega fotona) od hitrosti nabitega delca. Z detekcijo Čerenkovih fotonov in rekonstrukcijo Čerenkovega kota tako posredno izmerimo hitrost delca, preko katere lahko ob znani gibalni količini pridemo do njegove mase, ter posledično identitete. Iz detektorskih simulacij in tudi študij na merjenih podatkih se je pokazalo, da pomembno omejitev v učinkovitosti identifikacije povzročajo delci, ki v centralni potovalni komori sicer pustijo sled, vendar zaradi razpada v letu ali sipanja v snovi ne pridejo do detektorja ARICH. V nalogi izboljšamo obstoječo metodo identifikacije delcev, tako, da na podlagi odziva drugih detektorskih sistemov v Belle II (elektronskega kalorimetra) ter števila Čerenkovih fotonov izsevanih v kvarčnem oknu foto-detektorjev ocenimo verjetnost, da delec ni dosegel detektorja ARICH in to možnost vključimo v izračun pričakovanega odziva detektorja pri preletu delca posameznega tipa. Na vzorcu simuliranih podatkov pokažemo, da metoda vidno izboljša učinkovitost identifikacije pionov in kaonov pri gibalnih količinah pod Čerenkovim pragom kaonov (<1.5 GeV/c).

Keywords

Čerenkovo sevanje;identifikacija delcev;fizika detektorjev;detektor Belle II;B-tovarne;fizika okusov;standardni model;nova fizika;kršitev simetrije CP;LFU kršitev;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL FMF - Faculty of Mathematics and Physics
Publisher: [L. Senekovič]
UDC: 539.1
COBISS: 30076931 Link will open in a new window
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Other data

Secondary language: English
Secondary title: Improvement of particle identification method for the Aerogel RICH of the Belle II spectrometer
Secondary abstract: In the Belle II experiment we are searching for signals of phenomena related to the so called new physics, based on the B meson, D meson and tau lepton decays. Particle identification, in the whole kinematic range, plays a major role in the reconstruction of decays, especially the efficient separation of kaons and pions. One of the particle identification key systems is the (Aerogel) Ring Imaging Cherenkov Counter, or ARICH. Its working principle is the known relation between the Cherenkov angle (i.e. the angle between particle trajectory and emitted photon direction) and particle velocity. With the detection of Cherenkov photons and subsequent Cherenkov angle reconstruction indirect measurements of particle velocity are performed. Known velocity and momentum measurement information provide means of particle mass determination, based on which particle identity is determined. Simulations and previous studies of sample data have shown the problematic decays of particles, for which a track is measured in the Central Drift Chamber (CDC), but subsequently fail to reach the ARICH detector, on account of scattering phenomena and in-flight decays. In this thesis the enhancement of current methods, based on information provided by other detector system (ECL calorimeter) and the number of Cherenkov photons emitted in the HAPD detector window, will be discussed. Such information is used to construct a probability criteria that is incorporated into the expected detector response calculation (for a given mass hypothesis). On a simulation data sample a major improvement in identification/separation of kaons and pions is subsequently show in the kinematic area below the kaon Cherenkov threshold of <1.5 Gev/c.
Secondary keywords: Cherenkov radiation;particle identification;detector physics;Belle II;B-factories;flavor physics;Standard model;New physics;CP violation;LFU violation;
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: XIV, 63 str.
ID: 12035116