Naslov (eng)

Radiative W boson decay studies and the upgrade of the ATLAS muon spectrometer readout system: doctoral dissertation : doctoral dissertation

Autor

Bakoš, Evelin, 1994-

Doprinosi

de Groot, Nicolo, 1959-
Pellegrino, Antonio
Vranješ, Nenad, 1964-
Beenakker, Wim
Latas, Duško, 1962-
Vranješ Milosavljević, Marija, 1990-
Burić, Maja, 1975-

Opis (eng)

This thesis incorporates three research topics, all related to the ATLAS detector atthe Large Hadron Collider (LHC) at CERN. The first topic covers the contribution tothe Data Acquisition (DAQ) of ATLAS, precisely the implementation of the MDT ReadOut Driver (MROD) functionality to the Front-End Link eXchange (FELIX) readoutsystem of the ATLAS detector. The second topic represents the search for the rareradiative decay of W boson to meson and a photon, analyzing data already collectedwith ATLAS during Run 2. The third topic outlines two machine learning algorithmsto identify D mesons from radiative W boson decays at the LHC.ATLAS is one of the general purpose detector placed on the LHC. ATLAS consistof many layers of sub-detectors which are designed to detect the different particles.The outermost layer of ATLAS, the muon spectrometer is made from four detectionsystems, each one exploiting different technologies. The major part of the muonspectrometer consist of Monitored Drift Tube (MDT) chambers which measures theproperties (momentum, angular distributions, electric charge) of muons.Within the DAQ system, during the previous data-taking periods the MDT cham-bers were readout via the MDT Read Out Driver (MROD). This readout system isdependent on MROD cards, which will reach end of their lifetime during Run 3.Since repairing the broken MROD cards or ordering new ones is not possible, anew implementation is needed which will use the new FELIX system. As part ofthe system, the swROD implements data fragment building and formatting. An addi-tional module of the swROD, the CSMProcessor has been developed, which mimicsthe MROD building mechanism and incorporated the sub-detector specific settingswhich allows the configuration of the different MDT chambers, stores informationabout them, like their number or position. Multiple tests have been performed usingthe CSMProcessor, and the results show that the modified FELIX readout chain willbe able to process the increased data rates in Run 3.Using ATLAS, many experimental validations have been performed to investi-gate the accuracy and applicability of the Standard Model (SM). To test the SM asthoroughly as possible, searches for not (yet) detected decays and more precisemeasurements are necessary. Radiative decays of the W boson to W → M γ,where M is a meson, are sensitive to the coupling of the W boson with the pho-ton and, more importantly, probe the strongly coupled Quantum Chromodynamics(QCD) regime. The search for the W → ργ, where a W boson decaying to a ρ me-son and a photon, and other rare decays are experimentally challenging, due to themultijet background, which consists of hadronized quarks and gluons. No search forthe W → ργ has been performed so far, so no previous bounds exist.During the decay the ρ meson and the γ are decaying ”back-to-back”, sharingthe momentum of the W boson. Since the lifetime of the ρ meson is short, it de-cays further to charged and a neutral π meson. Due to the nature of the ρ meson,iABSTRACTisolated prompt ρ and a τ lepton decaying hadronically with exactly one chargedand one neutral pion are indistinguishable within the detector, therefore the algo-rithm used to detect the τ candidate can be used to identify the ρ meson withoutany modification. After the initial trigger and object selection, processes with thesame or similar final states are considered as background. The main sources ofbackground are events involving inclusive photon + jet and dijet processes, wherea track is reconstructed within a hadronic jet. This background cannot be reliablymodelled with Monte Carlo (MC) simulation due to the complicated mixture of con-tributing processes. Instead, this contribution to the total background is modelledwith a data-driven non-parametric approach. To extract the limit on the branchingfractions of the B (W → ργ) a binned maximum-likelihood is performed to the se-lected events. The search provides a limit of B (W → ργ) < 6.29 × 10−6 at 95%confidence level. This limit can be further improve if we include the search in thetrack-plus-photon final state where the ρ meson is identified as a track. Due to thedifferent triggers and selection criteria, the tau-plus-photon and track-plus-photonfinal state are orthogonal, therefore the selected events can be combined in the finalfit. This approach provides, for the first time, a limit of B (W → ργ) < 5.17 × 10−6 at95% confidence level.Reducing the background processes is also possible using the meson proper-ties. However, it is possible to construct many of different variables, which makes itdifficult to make a proper selection and measure their usefulness. To make thingseasier a machine learning algorithm can be developed specifically for meson tag-ging. One way to do this is to list many high-level variables, and using deep neuralnetwork create a classification algorithm, which is able to distinguish between signaland background mesons originating from quarks and gluons. An other approachis to develop a convolutional neural network using low level variables, such as themomentum of the particle and the energy deposited in the calorimeter. However, wecan reach the best results if we combine the two exploiting the advantage of bothmodels.The developed algorithm based on these models is able to identify jets orig-inating from Ds mesons in radiative W decays and shows a good efficiency of 47%for signal with a 100 times rejection of jets from quarks and gluons. This presentsan opportunity to improve measurements related to Ds mesons, particularly in thecontext of the rare decays.

Opis (srp)

Ova teza obuhvata tri teme koje se odnose na istraˇzivanja na detektoru ATLAS naVelikom sudaraˇcu hadrona (LHC) u CERN-u. Prva tema pokriva doprinos sistemuza prikupljanje podataka (Data Acquisition (DAQ)) detektora ATLAS, konkretno im-plementaciju MDT Read Out Driver (MROD) funkcionalnosti u Front-End Link eX-change (FELIX) sistem oˇcitavanja. Druga tema predstavlja potragu za retkim radija-tivnim raspadom W bozona na mezon i foton. Analizirani su podaci iz proton-protonsudara na energiji √s = 13 TeV prikupljenih pomo´cu detektora ATLAS tokom Run 2perioda (2015-2018). Tre´ca tema opisuje dva algoritma maˇsinskog uˇcenja za iden-tifikaciju D mezona nastalih u radijativnim raspadima W bozona na LHC-u.ATLAS je jedan od dva detektora opˇste namene na LHC-u. Sastoji se od viˇsepod-detektora koji su dizajnirani da detektuju tragove naelektrisanih ˇcestica, elek-trone, fotone i dˇzetove, kao i mione. Kombinuju´ci navedene podatke mogu se mer-iti energije i uglovne raspodele navedenih objekata i odrediti znak naelektrisanjanaelektrisanih ˇcestica. Takodje, mogu´ce je identifikovati hadronske raspade tau lep-tona i dˇzetove koji potiˇcu od b- ili c-kvarkova, a moˇze se meriti nedostaju´ca energija.Najudaljeniji pod-detektor ATLAS-a, mionski spektrometar, napravljen je od ˇcetirisistema za detekciju, od kojih svaki koristi razliˇcite tehnologije. Najve´ci deo mion-skog spektrometra ˇcine Monitored Drift Tube (MDT) komore.U okviru sistema DAQ, tokom prethodnih perioda uzimanja podataka, MDT ko-more su oˇcitavane preko MDT Read Out Driver-a (MROD). Ovaj sistem oˇcitavanjazavisi od MROD kartica, koje ´ce dosti´ci kraj svog ˇzivotnog veka tokom Run 3.Poˇsto popravka MROD kartica ili naruˇcivanje novih nije mogu´ca, potrebna je im-plementacija koja ´ce koristiti novodizajnirani sistem za oˇcitavanje podataka FELIX.Kao deo sistema, software ROD (swROD) implementira izgradnju i formatiranje frag-menata podataka. Razvijen je modul swROD-a, CSMProcessor, koji oponaˇsa meh-anizam izgradnje MROD-a i ugradjuje specifiˇcna podeˇsavanja pod-detektora kojaomogu´cavaju konfiguraciju razliˇcitih MDT komora, ˇcuvanje informacije o njima, kaoˇsto su njihov broj ili poloˇzaj. Viˇse testova je obavljeno koriˇs´cenjem CSMProcessor-a,a rezultati pokazuju da ´ce modifikovani sistem za oˇcitanja FELIX moˇze da obradipove´cane brzine prenosa podataka tokom Run 3.Jedna od osnovnih tema istraˇzivanja na eksperimentu ATLAS je testiranje Stan-dardnog modela (SM). Jedan od mogu´cih testova SM-a ˇcine potrage za (joˇs) neotkri-venim raspadima gradijentnih (kao i Higsovog) bozona. Radijativni raspad W bo-zona W → M γ (gde je M mezon) osetljiv je na sprezanje W bozona sa fotonimai, ˇsto je joˇs vaˇznije, omogu´cava ispitivanje reˇzima jako spregnute kvantne hromodi-namike. Potraga za W → ργ, gde se W bozon raspada na ρ mezon i foton, i drugiretki raspadi su eksperimentalno izazovni, zbog velikog fona koji postiˇce iz produk-cije dˇzetova. Na hadronskim sudaraˇcima do sada ovaj kanal raspada nije izuˇcavan,tako da ne postoje prethodne granice za faktor grananja W → ργ.iiiSA ˇZETAKTokom raspada, ρ mezon i γ se raspadaju ”back-to-back”, dele´ci impuls W bo-zona. Poˇsto je vreme ˇzivota ρ mezona kratko, on se dalje raspada na naelektrisanei neutralne π mezone. Zbog prirode ρ mezona, izolovani ρ i tau lepton (koji se ras-pada hadronski sa jednim naelektrisanim i jednim neutralnim pionom) se ne mogueksperimentalno razlikovati, pa se algoritam koji se koristi za detekciju tau moˇze sekoristiti za identifikaciju ρ mezona bez bilo kakvih modifikacija. Nakon inicijalnogtrigera i selekcije ˇcestica, procesi sa istim ili sliˇcnim konaˇcnim stanjima se sma-traju za fon. Glavni izvori fona su dogadjaji koji ukljuˇcuju inkluzivne procese foton+ dˇzet i didˇzet, gde se tragovi ˇcestica rekonstruiˇsu unutar hadronskog dˇzeta. Ovajfon se ne moˇze pouzdano modelovati Monte Carlo (MC) simulacijama, ve´c se ko-riste data-driven tehnike. Da bi se izraˇcunao limit na faktor grananja B (W → ργ)koriˇs´cen je pristup zasnovan na metodu maksimalne verodostojnosti. Dobijen jelimit od B (W → ργ) < 6.29 × 10−6 na nivou poverenja 95% sa uraˇcunatim sistem-atskim greˇskama. Ovo ograniˇcenje se moˇze dodatno poboljˇsava ako se u analizuukljuˇci konaˇcno stanje trag-plus-foton gde je ρ mezon identifikovan kao trag unutardetektora. Zbog razliˇcitih kriterijuma selekcije dogadjaji iz dva navedena konaˇcnastanja su statistiˇcki nezavisni, pa se izabrani dogadjaji mogu kombinovati. Konaˇcnidobijeni B (W → ργ) < 5.17 × 10−6 na nivou poverenja 95%.Suzbijanje fonskih procesa u identifikaciji mezona koji sadrˇze charm kvark semoˇze ostvariti koriˇs´cenjem razliˇcitih svojstava ovih mezona. Mogu´ce je konstruisativeliki broj varijabli, ˇsto oteˇzava pravi izbor i merenje njihove efikasnosti. Stoga jerazvijen algoritam zasnovan na tehnici maˇsinskog uˇcenja. Prvi izuˇcavani pristup jeprimena duboke neuronske mreˇze za kreiranje klasifikacionog algoritma koji je ustanju da razlikuje Ds od mezona koji potiˇcu od kvarkova i gluona. Drugi pristupje da se razvije konvoluciona neuronska mreˇza koriste´ci varijable niskog nivoa, kaoˇsto su impuls ˇcestice i deponovana energija u kalorimetrima. Optimalan rezultat sepostiˇze kombinovanjem dve navedene neuronske mreˇze. Dobijeni algoritam je ustanju da identifikuje dˇzetove koji potiˇcu iz Ds mezona u radijativnim W raspadimasa efikasnoˇs´cu 47% za signal i faktorom potiskivanja dˇzetova iz kvarkova i gluonaod 100. Pokazano je da se na taj naˇcin na LHC-u mogu poboljˇsati merenja vezanaza Ds mezone, posebno u kontekstu retkih raspada.

Opis (srp)

Physics - High energy physics / Fizika - Fizika visokih energija Datum odbrane: 15.01.2025.

Jezik

srpski

Datum

2024

Licenca

Ovo delo je licencirano pod uslovima licence
Creative Commons CC BY-NC-ND 3.0 AT - Creative Commons Autorstvo - Nekomercijalno - Bez prerada 3.0 Austria License.

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Predmet

OSNO - Opšta sistematizacija naučnih oblasti, Elementarne čestice. Fizika polja. Fizika visokih energija

ATLAS detector; muon spectrometer; data acquisition system; standard model QCD processes; W boson rare decays; jet tagging; machine learning

OSNO - Opšta sistematizacija naučnih oblasti, Elementarne čestice. Fizika polja. Fizika visokih energija

ATLAS detektor; mionski spektrometar; sistem za prikupljanje podataka; QCD procesa standardnog modela; retkih raspada W bozona; džet tagging; mašinsko učenje