The thesis presents the results of years of work dedicated to the development, commissioning and testing of the NA62 GigaTracker data acquisition and control systems as well as analysis of the data for alignment and quality checking. The GigaTracker beam detector is part of the NA62 experiment at CERN-SPS. The experiment is proposed to provide an accurate measurement of the K+→π+νν rare decay branching ratio. Flavour changing transitions, the understanding of which is one of the most important objective in particle physics, are described by the Standard Model by means of the CabibboKobayashi-Maskawa (CKM) unitary matrix. Present experimental data on hadron weak decays are in agreement with Standard Model predictions within theoretical and experimental uncertainties. Nevertheless new physics contributions cannot be ruled out since in most cases theoretical errors on decay amplitudes are elevated due to long-distance non-perturbative contributions. The K+→π+νν however belongs to a limited class of decays in which the matrix elements can be extracted from experimentally well measured decay branching ratios. As a consequence the K+→π+νν branching ratio can be determined with an extremely high accuracy, allowing to determine the possible presence of contributions beyond the Standard Model. The NA62 experiment aims to collect about 100 K+→π+νν events with a signal to background ratio of S/B ≈ 10/1 in 2 years of data taking using the decay in-flight of a 75 GeV/c kaon beam. The latest Standard Model prediction for the K+→π+νν branching ratio is BR(K+→π+νν) = (7.81+0.80 −0.71 ± 0.29) × 10−11 whilst the only experimental result, based on 7 events, comes from the BNL E787/E949 collaborations and gives BR(K+→π+νν) = (1.73+1.15 −1.05)×10−10 . The presence, in the final state, of two undetectable neutrinos imposes an experimental strategy based on precise timing, kinematic rejection, hermetic vetoes and particle identification to suppress the overwhelming background. A crucial role in timing and kinematic rejection is performed by the beam spectrometer named GigaTracker. It consists of three stations of hybrid silicon pixels sensors with an overall resolution of 150 ps (RMS) on time, σ(pK)/pK ∼ 0.2% on momentum and ∼ 16 μrad on direction of the track. In addition the system will operate under a high rate of particles i.e. 0.75 GHz in total, with a peak of intensity around the centre of 1.3 MHz/mm2 . Each GigaTracker station is read out continuously by 10 on-detector chips connected to the same number of off-detector boards where the event data are stored waiting the trigger decision. The trigger-matched output from an entire station is estimated to reach ∼ 900 MB/s. A small farm of sub-detector PCs hosts the data acquisition software and the control software, both developed and maintained by the author; the first organizes data and performs higher level trigger matching, while the second controls and configure the front-end and off-detector electronics as well as the data acquisition software itself. The layout of the thesis is the following: in the first chapter an overview of the physics motivations behind the BR(K+→π+νν) measurement, present experimental status and a description of the NA62 experimental strategy to perform such measurement is given; the second chapter contains a characterization of the NA62 detector; in the third chapter a detailed overview of the crucial components of the GigaTracker such as the sensor, read-out electronics and cooling system is carried out; fourth chapter contains a description of the data acquisition and control software characteristics and follows the commissioning of the GigaTracker’s data acquisition system during the first three years of NA62 data taking; finally in the fifth chapter the work on the analysis of the GigaTracker’s data is reported, with studies on alignment and quality checking.

Development and Commissioning of the GigaTracker Data Acquisition and Control Systems for the NA62 Experiment at CERN

GAMBERINI, ENRICO
2017

Abstract

The thesis presents the results of years of work dedicated to the development, commissioning and testing of the NA62 GigaTracker data acquisition and control systems as well as analysis of the data for alignment and quality checking. The GigaTracker beam detector is part of the NA62 experiment at CERN-SPS. The experiment is proposed to provide an accurate measurement of the K+→π+νν rare decay branching ratio. Flavour changing transitions, the understanding of which is one of the most important objective in particle physics, are described by the Standard Model by means of the CabibboKobayashi-Maskawa (CKM) unitary matrix. Present experimental data on hadron weak decays are in agreement with Standard Model predictions within theoretical and experimental uncertainties. Nevertheless new physics contributions cannot be ruled out since in most cases theoretical errors on decay amplitudes are elevated due to long-distance non-perturbative contributions. The K+→π+νν however belongs to a limited class of decays in which the matrix elements can be extracted from experimentally well measured decay branching ratios. As a consequence the K+→π+νν branching ratio can be determined with an extremely high accuracy, allowing to determine the possible presence of contributions beyond the Standard Model. The NA62 experiment aims to collect about 100 K+→π+νν events with a signal to background ratio of S/B ≈ 10/1 in 2 years of data taking using the decay in-flight of a 75 GeV/c kaon beam. The latest Standard Model prediction for the K+→π+νν branching ratio is BR(K+→π+νν) = (7.81+0.80 −0.71 ± 0.29) × 10−11 whilst the only experimental result, based on 7 events, comes from the BNL E787/E949 collaborations and gives BR(K+→π+νν) = (1.73+1.15 −1.05)×10−10 . The presence, in the final state, of two undetectable neutrinos imposes an experimental strategy based on precise timing, kinematic rejection, hermetic vetoes and particle identification to suppress the overwhelming background. A crucial role in timing and kinematic rejection is performed by the beam spectrometer named GigaTracker. It consists of three stations of hybrid silicon pixels sensors with an overall resolution of 150 ps (RMS) on time, σ(pK)/pK ∼ 0.2% on momentum and ∼ 16 μrad on direction of the track. In addition the system will operate under a high rate of particles i.e. 0.75 GHz in total, with a peak of intensity around the centre of 1.3 MHz/mm2 . Each GigaTracker station is read out continuously by 10 on-detector chips connected to the same number of off-detector boards where the event data are stored waiting the trigger decision. The trigger-matched output from an entire station is estimated to reach ∼ 900 MB/s. A small farm of sub-detector PCs hosts the data acquisition software and the control software, both developed and maintained by the author; the first organizes data and performs higher level trigger matching, while the second controls and configure the front-end and off-detector electronics as well as the data acquisition software itself. The layout of the thesis is the following: in the first chapter an overview of the physics motivations behind the BR(K+→π+νν) measurement, present experimental status and a description of the NA62 experimental strategy to perform such measurement is given; the second chapter contains a characterization of the NA62 detector; in the third chapter a detailed overview of the crucial components of the GigaTracker such as the sensor, read-out electronics and cooling system is carried out; fourth chapter contains a description of the data acquisition and control software characteristics and follows the commissioning of the GigaTracker’s data acquisition system during the first three years of NA62 data taking; finally in the fifth chapter the work on the analysis of the GigaTracker’s data is reported, with studies on alignment and quality checking.
PETRUCCI, Ferruccio Carlo
GIANOLI, Alberto
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/2488014
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