ITA: Il Modello Standard (MS) della fisica delle particelle elementari assume che l’accoppiamento elettrodebole tra i leptoni e i bosoni di gauge sia indipendente dalla famiglia leptonica a meno di correzioni dovute alla massa. Tale proprietà è conosciuta come Universalità Leptonica (Lepton Flavour Universality o LFU). I decadimenti semileptonici di adroni b sono laboratori ideali per testare la LFU attraverso il confronto tra i rapporti di diramazione dei decadimenti nel cui stato finale sono coinvolti un leptone τ o un leptone μ: R(Hc) = B(Hb → Hcτν)/ B(Hb → Hcμν), dove Hb e Hc sono rispettivamente l’adrone b da cui si origina il decadimento e l’adrone c prodotto nel decadimento. Risultati sperimentali su test di LFU sono stati ottenuti dalle collaborazioni Belle, Babar e LHCb e mostrano tensioni con le predizioni del MS di circa 3.4σ quando si considera la combinazione delle misure di R(D) and R(D∗). Questa tesi, sfruttando l’abbondanza di adroni b prodotti in LHCb e le caratteristiche del rivelatore, documenta gli studi preliminari per la misura di R(Ds) richiedendo nello stato finale un leptone τ che decade in 3 pioni carichi. I dati analizzati per questi studi sono stati raccolti da LHCb nel 2012, sono relativi a collisioni protone protone con energia nel centro di massa pari a 8TeV, e corrispondono ad una luminosità integrata di 2 fb^{−1}. Data la richiesta di misure sempre più precise per testare ulteriormente il MS, l’esperimento LHCb è stato sottoposto ad un upgrade per essere in grado di operare alla luminosità di circa 2×10^33cm^{−2}s^{−1} dall’inizio del Run3 nel 2022. Per fronteggiare la sfida di una luminosità istantanea aumentata di cinque volte rispetto al Run2 e alla necessità di acquisire i dati ad una frequenza di 40 MHz, i rivelatori di fotoni e l’intera catena di elettronica di entrambi i sottorivelatori Ring Imaging CHerenkov sono stati sostituiti. Questa tesi descrive, inoltre, i protocolli di controllo qualità, i test effettuati sulla nuova optoelettronica, e le attività di istallazione e messa in opera dei nuovi sottorivelatori.

The Standard Model (SM) of particle physics assumes that the couplings between leptons and the electroweak gauge bosons are independent of the lepton flavour up to a correction due to the mass. This property is known as Lepton Flavour Universality (LFU). Ideal laboratories to test the LFU are the b-hadron semileptonic decays which can be studied through the ratios of branching fractions between decays with the τ lepton and the ones with the μ lepton in the final state: R(Hc) =B(Hb → Hcτν)/B(Hb → Hcμν), with Hb and Hc the b−hadron which originates the decay and the c−hadron produced in the decay respectively. Experimental results on LFU tests have been obtained by Belle, BaBar and LHCb collaborations and show tension with the SM prediction of about 3.4σ when considering the combination of the measurement of R(D) and R(D∗). Exploiting the abundance of the b-hadron produced in the LHCb environment and the features of the detector, that allow to reconstruct the b-hadron decay vertex with high precision and to perform particle identification, this thesis documents the preliminary studies for the measurement of R(Ds) using the τ decaying in 3 charged pions. The data sample used for the studies corresponds to an integrated luminosity of 2 fb^{−1} of proton-proton collision events at a centre-of-mass energy of 8 TeV collected by the LHCb experiment in 2012. Given the request of high precision measurements to further test the SM in many other sectors, the LHCb experiment is currently being upgraded to be able to operate at a luminosity of about 2×10^33cm^{−2}s^{−1} from the start of Run3 in 2022. To cope with the challenge of a five-fold increased instantaneous luminosity, and the need to read-out the full LHCb detector at a rate of 40 MHz, the photon detectors and the electronics chain of both the Ring Imaging CHerenkov (RICH) detectors have been replaced. This thesis also describes the quality assurance and test protocols on the new opto-electronics and reports of the commissioning activities.

Test of Lepton Flavour Universality using the B_s^0→D_s^- τ^+ ν_τ with 3 prongs τ^+ decays and validation of the new opto-electronics for the RICH Upgrade at the LHCb experiment

GIUGLIANO, Carmen
2022-06-29T00:00:00+02:00

Abstract

The Standard Model (SM) of particle physics assumes that the couplings between leptons and the electroweak gauge bosons are independent of the lepton flavour up to a correction due to the mass. This property is known as Lepton Flavour Universality (LFU). Ideal laboratories to test the LFU are the b-hadron semileptonic decays which can be studied through the ratios of branching fractions between decays with the τ lepton and the ones with the μ lepton in the final state: R(Hc) =B(Hb → Hcτν)/B(Hb → Hcμν), with Hb and Hc the b−hadron which originates the decay and the c−hadron produced in the decay respectively. Experimental results on LFU tests have been obtained by Belle, BaBar and LHCb collaborations and show tension with the SM prediction of about 3.4σ when considering the combination of the measurement of R(D) and R(D∗). Exploiting the abundance of the b-hadron produced in the LHCb environment and the features of the detector, that allow to reconstruct the b-hadron decay vertex with high precision and to perform particle identification, this thesis documents the preliminary studies for the measurement of R(Ds) using the τ decaying in 3 charged pions. The data sample used for the studies corresponds to an integrated luminosity of 2 fb^{−1} of proton-proton collision events at a centre-of-mass energy of 8 TeV collected by the LHCb experiment in 2012. Given the request of high precision measurements to further test the SM in many other sectors, the LHCb experiment is currently being upgraded to be able to operate at a luminosity of about 2×10^33cm^{−2}s^{−1} from the start of Run3 in 2022. To cope with the challenge of a five-fold increased instantaneous luminosity, and the need to read-out the full LHCb detector at a rate of 40 MHz, the photon detectors and the electronics chain of both the Ring Imaging CHerenkov (RICH) detectors have been replaced. This thesis also describes the quality assurance and test protocols on the new opto-electronics and reports of the commissioning activities.
FIORINI, Massimiliano
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11392/2491050
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