Tesis sobre el tema "Higgs, LHC, Silicon Detectors"

El Large Hadron Collider (LHC) en la Organización Europea para la Investigación Nuclear (CERN), Ginebra, interrumpirá su operación en 2023 para ser mejorado a High Luminosity LHC (HL-LHC) y proporcionar colisiones entre protones con una energı́a en el centro de masa de √s = 14 TeV con una luminosidad de 1035 cm−2 s−1. ATLAS es uno de los experimentos alojados en el LHC que tendrá que ser mejorado para cumplir los nuevos requisitos impuestos por la mayor luminosidad. Las obras de mejora de ATLAS prevén la sustitución del Inner Detector por un detector de trazas interamente de silicio, el Inner Tracker (ITk), con una granularidad más pequeña y una mayor resistencia a la radiación, y la introducción del High Granularity Timing Detector (HGTD), que proporcionará información temporal de las trazas y de los vértices. Combinando las medidas de ITk y HGTD será posible resolver vértices cercanos en el espacio pero con suficiente separación temporal, lo cual mejora las prestaciones de ATLAS. En esta tesis se investigan dos nuevas tecnologı́as de detectores de silicio para aplicaciones en el HGTD y el ITk, la tecnologı́a de Low Gain Avalanche Detector (LGAD) y la de HV-CMOS. La tecnologı́a LGAD consiste en detectores planares de silicio n-on-p con un implante altamente dopado de tipo p debajo del electrodo de tipo n. Originalmente fue desarrollada para detectores de trazas resistentes a la radiación, pero la segmentación del electrodo demostró afectar al mecanismo de multiplicación y no se ha observado ganancia en los primeros dispositivos. Por otro lado, detectores LGAD delgados han mostrado una resolución temporal de aproximadamente 30 ps y fueron elegidos como de base para los sensores del HGTD. Estudios de sensores LGAD, antes y después de la irradiación, se realizaron por primera vez en el contexto de esta tesis. La tecnologı́a HV-CMOS originalmente aspriaba a producir sensores con pı́xel activo, con la ventaja, en comparación con los dispositivos hı́bridos estándar, de poder optar por el acoplamiento capacitivo. Sin embargo, durante el proceso de IyD, resultó claro que los dispositivos monolı́ticos en tecnologı́a HV-CMOS ofrecen las ventajas más prometedoras: una moderada resistencia a la radiación y la reducción de costos. Esta tesis incluye la caracterización de la primera muestra a escala completa de un chip HV-CMOS para el experimento ATLAS. Actualmente, esta tecnologı́a se tiene en cuenta como una opción de inserción para la capa externa del detector de pı́xeles del ITk.
The Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN), Geneva, will interrupt its operation in 2023 to be upgraded to high luminosity (HL-LHC) and provide proton-proton collisions with a center of mass energy of √s = 14 TeV at a luminosity of 1035 cm−2 s−1. ATLAS, one of the two general purpose experiments at the LHC , will have to be upgraded to meet the new requirements given by the larger luminosity. Among other things the ATLAS upgrade foresees the replacement of the Inner Detector with a full silicon Inner Tracker (ITk), with finer granularity and improved radiation tolerance, and the introduction of the High Granularity Timing Detector (HGTD) that will provide timing information of tracks and vertices. Combining the measurements of ITk and HGTD it will be possible to resolve vertices close in space but separated in time, improving the ATLAS reconstruction performance. In this thesis two novel silicon detector technologies are investigated for applications in the HGTD and ITk, the Low Gain Avalanche Detectors (LGAD) and the HV-CMOS technologies. The LGAD technology consists of planar n-on-p silicon detectors with a highly doped p-type implantation underneath the n-type electrode. It was originally developed for radiation hard tracking detectors but the fine segmentation of the electrode proved to affect the charge multiplication mechanism and no gain has been observed on segmented devices. On the other hand, thin LGAD detectors have shown a time resolution of about 30 ps on the detection of minimum ionizing particles and it was chosen as baseline technology for the HGTD sensors. Studies of LGAD sensors, before and after irradiation were first performed in the context of this thesis. The HV-CMOS technology was originally aimed to provide active pixel sensors with the advantage, compared to the standard hybrid devices, of the AC coupling capability. However, during the R&D effort, it become clear that monolithic HV-CMOS devices offered the most promising advantages: moderate radiation hardness and cost reduction. This thesis includes the characterization of the first full scale HV-CMOS chip prototype for the ATLAS experiment. This technology is currently taken into account as a drop-in option for the outer layer of the ITk pixel detector.

The Standard Model is a mathematical description of the very nature of elementary particles and their interactions, now seen as relativistic quantum fields. A key feature of the theory is the Brout-Englert-Higgs mechanism, responsible for the spontaneous symmetry breaking of the underlying gauge symmetry, and which implies the existence of a neutral Higgs particle. Searches for the Higgs boson were conducted at the Large Electron Positron collider until 2000 and are still ongoing at the Tevatron collider, but the particle has not been not observed. In order to better constrain models with an exotic electroweak symmetry breaking sector, a search for a Higgs boson decaying into a W pair is carried out with the ALEPH detector on 453 pb-1 of data collected at center-of-mass energies up to 209 GeV. The analysis is optimized for the many topologies resulting from the six-fermion final state. A lower limit at 105.8 GeV/c² on the Higgs boson mass in a fermiophobic Higgs boson scenario is obtained. The ultimate machine for the Higgs boson discovery is the Large Hadron Collider, which is being built at CERN. In order to evaluate the physics potential of the CMS detector, the WH associated production of a Higgs boson decaying into a W pair is studied. Performances of data acquisition and its sophisticated trigger system, particle identification and event reconstruction are investigated by performing a detailed analysis on simulated data. Three-lepton final states are shown to provide interesting possibilities. For an integrated luminosity of 100 fb-1, a potential signal significance of more than 5ó is obtained in the mass interval between 155 and 178 GeV/c². The corresponding precision on the Higgs boson mass and partial decay width into W pairs are evaluated. This channel also provides one of the very few possible avenues towards the discovery of a fermiophobic Higgs boson below 180 GeV/c². These studies required many original technical developments, that are also presented.

To extend the physics reach of the LHC, upgrades to the accelerator are planned which will increase the integrated annual luminosity by a factor of 10 (to 250 - 300 fb$^{-1}$/ year). This will increase the occupancy and the radiation damage of the inner trackers. To cope with the elevated occupancy, the ATLAS experiment plans to introduce an all silicon inner tracker for use during High Luminosity LHC (HL-LHC) operation. With silicon, the occupancy can be adjusted by using the appropriate pitch for the pixels/micro-strips. Constraints due to high radiation damage mean that only sensors with electrode configuration designed to read out the electron signal (n-in-p and n-in-n) are considered. The work presented within this thesis has been undertaken as part of the CERN-RD50 and ATLAS Upgrade collaborations. The main focus has been, firstly, on the development of radiation hard silicon detectors and the possible exploitation of the charge multiplication effect observed in irradiated silicon detectors that collect charge via electrons. Secondly, the production and optimisation of n-in-p planar pixel detectors designed specifically for ATLASs new Inner Tracker (ITk). The prototype sensors were produced by Micron Semiconductors Ltd, UK.

Aquesta tesi tracta el desenvolupament de detectors de silici de tecnologia avançada per experiments de Física d'Altes Energies (HEP en anglès). La mida dels detectors de silici per determinar traces en experiments de HEP ha de disminuïr per millorar la resolució espacial en les mesures i millorar l'ocupancia en l'electrònica. Els experiments al CERN hauran de funcionar amb fluencies de fins a 2·10 16 n eq 1cm2 , i els detectors de silici més petits tindran menys atrapament de les parelles electró-forat generats al volum, que porta a un millor comportament sota un medi amb alts nivells de radiació. Aquesta tesi estudia detectors de silici fabricats al CNM-Barcelona per aplicacions de HEP amb dos tipus d'arquitectura nou: 3D i detectors d'allau amb guany moderat (LGAD en anglès). Els detectors 3D afavoreixen la reducció de la mida de la regió buidada dins del detector i permet treballar a voltatges més baixos, mentres que els detectors LGAD tenen guany intern que incrementa la senyal col·leccionada amb un mecanisme de multiplicació. El capítol 1 introdueix els detectors de silici aplicats a HEP. Els capítols 2 i 3 exploren els dissenys de detectors 3D de silici fabricats al CNM-Barcelona. Els detectors 3D de silici van ser introduïts per primera vegada a un experiment de HEP durant el 2013 per una nova capa del experiment ATLAS, la Insertable B-Layer (IBL), i alguns d'aquests detectors han sigut caracteritzats durant aquest treball. Actualment, detectors 3D de silici amb dimensions de píxel més petites seran operatius per noves posades a punt de l'ATLAS, i aquests detectors s'han simulat en aquest treball. El capítol 4 està dedicat a detectors LGAD segmentats i fabricats en oblies epitaxials amb la intenció de disminuïr el gruix dels detectors i augmentar la càrrega col·leccionada amb el mecanisme de multiplicació. Aquesta tesi mostra simulacions tecnològiques, el procés de fabricació, simulació elèctrica i caracterització elèctrica i de càrrega d'aquests detectors.
This thesis presents the development of advanced silicon technology detectors fabricated at CNM-Barcelona for High Energy Physics (HEP) experiments. The pixel size of the tracking silicon detectors for the upgrade of the HL-LHC will have to decrease in size in order to enhance the resolution in position for the measurements and they need to have better occupancy for the electronics. The future experiments at CERN will cope with fluences up to 2·10 16 n eq 1cm2 , and the smaller 3D silicon detectors will have less trapping of the electron-holes generated in the bulk leading to a better performance under high radiation environment. This thesis studies silicon detectors fabricated at CNM-Barcelona applied to HEP experiments with two different kinds of novel projects: 3D and Low Gain Avalanche Detectors (LGAD). The 3D detectors make it possible to reduce the size of the depleted region inside the detector and to work at lower voltages, whereas the LGAD detectors have an intrinsic gain which increase the collected signal with a multiplication mechanism. Chapter 1 introduces the silicon detectors applied to HEP experiments. Chapters 2 and 3 explore the new designs for 3D silicon detectors fabricated at CNM-Barcelona. 3D silicon detectors were first introduced in a HEP experiment in 2013 for a new ATLAS layer, the Insertable B layer (IBL), and some of them are characterized in this work. Now, it is expected that 3D silicon detectors with smaller pixel size will be operative for the next ATLAS upgrade, and they are also simulated in this thesis. Chapter 4 is devoted to segmented LGAD detectors fabricated on epitaxial wafer with the intention to decrease the thickness of the detector and increase the charge collected with the multiplication mechanism. This thesis shows technological simulations, fabrication process, electrical simulations and electrical and charge characterization of those devices.

L'utilisation optimale, dans des applications spécifiques, des Détecteurs Silicium nécessite une connaissance approfondie des phénomènes physiques sous-jacents. Dans ce mémoire, cette idée conductrice est appliquée à deux types de détecteurs : (1) les SiPM et leurs applications en imagerie médicale (2) les détecteurs à pixels planaires (PPS) et leurs applications dans la mise-à-jour du détecteur interne d'ATLAS pour le LHC à haute luminosité. Mon travail personnel sur les SiPM a débuté il y a environ 10 ans. Ainsi la partie (A) de mon HDR rappelle tout d'abord le principe physique de la photodiode à avalanche en mode Geiger (GM-APD), qui constitue la cellule élémentaire d'un SiPM. Puis le fonctionnement du SiPM est développé, avec ses principales caractéristiques physiques, ainsi que les montages expérimentaux mis en œuvre et les mesures de ces paramètres sur les productions des principaux fabricants. La dépendance en température des paramètres des SiPM constitue un inconvénient majeur dans certaines applications, aussi mon travail personnel montre comment on peut en grande partie s'affranchir de cette dépendance, en contrôlant certains paramètres de fonctionnement. Les détecteurs à SiPM présentent des avantages très intéressants au plan électrique, optique, mécanique, etc ..., permettant des applications multiples dans des domaines où une grande surface de détection est requise. Ainsi, les matrices de SiPM sont des composants très attractifs pour des applications d'imagerie médicale. Mon travail dans deux applications de ce type est détaillé : PET à haute résolution pour des petits animaux, et détecteur de radiation portatif pour l'aide à la localisation in situ de tumeurs solides. En parallèle à l'activité SiPM, j'ai été impliquée ces dernières années dans la conception et la caractérisation de nouveaux détecteurs à pixel planaires pour "l'upgrade" de l'expérience ATLAS. La partie (B) de mon HDR expose ainsi les méthodes expérimentales, comme "Secondary Ion Mass Spectrometry (SIMS)" et "Spreading Resistance Profiling" (SRP), utilisées pour la mesure de profils de dopage pour le détecteurs PPS. Je démontre ainsi l'importance de ces mesures pour le contrôle du process de fabrication, et la calibration des simulations TCAD (Technology-Computed Aided Design). Les résultats des simulations prévoyant le comportement des nouveaux détecteurs planaires proposés, avec des caractéristiques géométriques et une résistance aux radiations améliorées, sont présentés.

Durante il mio percorso di dottorato mi sono occupato principalmente dello sviluppo di nuovi sensori a pixel in Silicio per l’upgrade dell’esperimento CMS in vista della fase ad alta luminosità del collisionatore LHC (HL – LHC o LHC fase 2) al CERN, un’attività che avevo già intrapreso per il mio lavoro di tesi magistrale. Questi sensori devono tollerare fluenze di radiazione di alcuni 10^16 neq/cm^2 ad una distanza di circa 3 cm dal punto di interazione. Il programma di R&D portato avanti da un gruppo INFN ATLAS-CMS, in collaborazione con Fondazione Bruno Kessler, riguarda lo sviluppo di sensori planari sottili e 3D su substrati prodotti con la tecnica del Direct Wafer Bonding. L'impiego di questa tecnica permette di attuare tutti i processi di fabbricazione su una sola superficie del wafer, riducendo notevolmente i costi del processo. Lo spessore attivo dei prototipi è di 100 o 130 um per i sensori planari e 130 um per quelli 3D. I primi sensori prodotti hanno pixel delle stesse dimensioni di quelli attualmente in uso in CMS, 100 x 150 um^2. Le dimensioni sono state poi ridotte a 25 x 100 um^2 e 50 x 50 um^2 in modo da aumentare il numero di canali di lettura in vista della maggiore molteplicità di tracce attesa ad HL-LHC. Sono state effettuate numerose campagne di prova su fascio per caratterizzare i sensori planari e quelli 3D, prima e dopo l’irraggiamento a fluenze fino a 1 x 10^16 neq/cm^2. I miei contributi alla caratterizzazione dei prototipi sono riportati in questa tesi e includono anche lo sviluppo di algoritmi dedicati. Dopo circa due anni di lavoro sulla caratterizzazione dei nuovi prototipi ho sviluppato un interesse anche per l’impatto del rivelatore a pixel sul programma di fisica dell’esperimento. All’inizio del mio secondo anno di dottorato mi sono messo in cerca di un’analisi in cui le informazioni del rivelatore a pixel fossero largamente sfruttate. Ho scelto di lavorare alla ricerca della produzione di coppie di bosoni di Higgs nello stato finale con 2 b-jets e 2 leptoni tau. Ho scelto questa analisi sia perchè la ricostruzione delle particelle nello stato finale fa ampio uso delle informazioni di tracce e vertici sia perchè l’analisi trarrà grande benificio dell'incremento della statistica previsto ad HL-LHC, che potrebbe portare ad avere la prima evidenza sperimentale di produzione HH. La ricerca di coppie di bosoni di Higgs ha un ruolo fondamentale nella caratterizzazione di questa particella in quanto rappresenta il canale migliore per la misura della costante di accoppiamento trilineare. Ogni deviazione dalle previsioni teoriche del Modello Standard porterebbe a cambiamenti importanti nella cinematica e nel rateo di produzione di coppie di bosoni di Higgs, il che rende queste ricerche sensibili a effetti di nuova fisica. Lo stato finale bbtau^+tau^- rappresenta uno dei canali più interessanti in questo studio visti il branching ratio elevato e la piccola contaminazione di eventi di fondo. In questa tesi viene descritta la strategia sviluppata per l'analisi dei dati raccolti dall’esperimento CMS durante il Run 2 di LHC (2016 + 2017 + 2018), corrispondenti ad una luminosità integrata di 137 fb^-1. Viene inoltre riportata la sensitività attesa dell'analisi, che include lo studio di due meccanismi di produzione di coppie di bosoni di Higgs: Gluon-Gluon Fusion (GGF) e Vector Boson Fusion (VBF).
My research activity during the PhD has focused mainly on the development of new silicon pixel sensors for the upgrade of the CMS experiment inner tracker in view of the CERN LHC High Luminosity phase (HL-LHC), an activity I started to work on during my master thesis. These sensors must be capable of surviving irradiation fluences up to a few 10^16 neq/cm^2 at ~ 3 cm from the interaction point. The R&D program carried out by an INFN ATLAS-CMS group, in collaboration with Fondazione Bruno Kessler, covers both planar and 3D pixel devices made on substrates obtained by the Direct Wafer Bonding technique. Using this technology, every fabrication process takes place on one side only of the wafer, with consequent cost savings. The active thickness of the planar sensors studied in this thesis is 100 um or 130 um, that of 3D sensors 130 um. Sensors belonging to the first batches have pixel cells with dimensions of 100 x 150 um^2, same as the sensors currently installed in CMS. These dimensions have been reduced to 25 x 100 um^2 and 50 x 50 um^2 in order to cope with the higher track multiplicity expected at HL-LHC. Prototypes of hybrid modules, bump-bonded to different readout chips, have been characterized in beam tests. Results on their performance before and after irradiation up to maximum fluence of ∼ 1 x 10^16 neq/cm^2 are reported in this thesis. After a couple of years working on the characterization of the new prototypes I became interested also on the impact of the pixel detector on the physics program of the experiment. At the beginning of my second year of PhD I started to look for a physics analysis where the information of the pixel detector is largely exploited. I chose to work on the search for double Higgs boson production in final states with 2 b-jets and 2 tau leptons since the reconstruction of the b-jets and tau leptons makes large use of vertexes and tracks information. Another reason why I chose this analysis is that it will benefit from the incremented statistics foreseen at HL-LHC, possibly leading to the first experimental evidence of HH production. Double Higgs searches play a fundamental role in the characterization of the Higgs boson as they represent the favorite channel to measure the Higgs boson trilinear self coupling. Any deviation from the theoretical predictions of the Standard Model would lead to sizable changes in both the kinematics and production rate of HH events, thus making double Higgs searches sensitive to new physics effects. The bbtau^+tau^-final state represents one of the most interesting channels to explore double Higgs production, because of the high branching ratio and the relatively small background contamination. The strategy developed to analyze data collected by the CMS experiment during the LHC Run 2 (2016 + 2017 + 2018), corresponding to an integrated luminosity of 137 fb^-1, is described in this thesis. The expected sensitivity of the analysis, targeting both the Gluon Fusion (GGF) and Vector Boson Fusion (VBF) production channels, is also reported.

Les detecteurs au silicium, dont l'utilisation est prevue dans les futures experiences de physique des hautes energies (lhc au cern) devront soutenir un tres haut niveau de radiation. La defaillance des detecteurs plus exposes est attendue apres quelques annees d'operations. Un grand interet est pourtant devolue a l'etude des changements provoques par les radiations dans les detecteurs et a l'amelioration de la resistance aux radiations de ceux-ci. L'introduction d'impuretes dans le cristal de silicium peut influencer la tenue aux radiations. Les impuretes forment des complexes avec les defauts primaires induits par les radiations. Ces complexes peuvent etre electriquement actifs ou inactifs. Dans ce dernier cas, les defauts n'affectent pas les proprietes electriques du detecteur. Une grande concentration d'impuretes qui forment des complexes inactifs peut reduire la vitesse de degradation des detecteurs. Les plus importants parametres electriques qui changent en fonction de la fluence sont la densite effective de dopage, le courant inverse et l'efficacite de collection de charge. Cette these presente une etude detaillee des changements de ces parametres en fonction de la fluence hadronique et du temps apres les irradiations, pour des cristaux de silicium contenant differentes teneurs en impuretes. Le role de l'o, c et sn sur la tenue aux radiations est evalue. L'etude a ete faite en utilisant comme detecteur de simples diodes (p#+-n-n#+). Certains changements des caracteristiques electriques de ces diodes apres des forts niveaux d'irradiation ne peuvent pas etre expliques par la theorie de la jonction p-n d'un semi-conducteur. Un modele de distribution du champ electrique est propose pour expliquer les proprietes de collection de charge des detecteurs irradies.

The ALICE experiment at CERN has planned an upgrade of the Inner Tracking System (ITS), named ITS3, for the LHC Long Shutdown 3, in 2025. The cornerstone of the upgrade is a new CMOS pixel sensor built in 65 nm technology and in bent-cylindrical configuration, replacing the inner layers of the existing detector, the ITS2. The ITS3 will reach much better tracking and vertexing performance, thanks to the improved spatial resolution and the much reduced material budget with respect to the previous Inner Tracking System. The aim of this thesis is to report on the analysis of the data collected at beam tests on new ALPIDE chips (used for ITS2, based on Monolithic Active Pixel Sensor, MAPS) which have been bent in a cylindrical configuration as foreseen for the ITS3. This is the first bending proof of concept for a silicon detector. In particular, data from beam test taken in 2020 have been studied through a data analysis framework that I have personally written to accomplish this task; the complexity of the data analysis is driven by the fact that each ALPIDE chip has a total of 1024x512 pixel MAPS and by the bent geometry of the sensor. In this thesis, the promising performances obtained by studying the sensor total efficiency and spatial resolution in different experimental configurations will be presented and discussed.

Le trajectographe interne (ITk) de l'expérience ATLAS sera amélioré pour la nouvelle phase de prise de données du grand collisionneur de hadrons du CERN à haute luminosité (HL-LHC) en 2026. Le HL-LHC fonctionnera avec l’énergie nominale de collision est de 14 TeV et la luminosité instantanée maximale de 7,5 x (10)34 cm(−2) s(−1), cinq fois plus élevée qu’à présent. La luminosité accrue se traduira par des niveaux de rayonnement et des débits de données environ dix fois plus élevés. Afin de faire face aux exigences d’ATLAS en termes d’intensite du rayonnement, de vitesse de lecture et de granularité au HL-LHC, le remplacement de l’actuel ATLAS Inner Tracker (ITk) est nécessaire. Deux capteurs CMOS épuisés à grande échelle dans la technologie LF de 150 nm, appelés LF-CPIX et LF-MONOPIX, ont été développés dans le cadre de la mise à niveau ATLAS Inner Tracker (ITK) pour le LHC à haute luminosité. Le travail présenté ici montre la caractérisation de ces trois prototypes, avec des contributions concernant le développement de la configuration, le calibrage source 55 Fe et 90 Sr, les modifications du microprogramme FPGA et le développement de programmes de test. L’enquête sur la dureté du rayonnement pour l’électronique et les composants du capteur a été une préoccupation majeure. Nous montrerons les résultats concernant les caractérisations de ces prototypes dans les performances de laboratoire du CPPM, ainsi que les résultats de multiples campagnes de rayonnement conduites à l’installation de protons IRRAD de 24 GeV du CERN, afin d’étudier les effets de la perte d’énergie non ionisante (NIEL) et du Dose ionisante (TID) sur les prototypes
The Inner Tracker (ITk) system of the ATLAS experiment will be upgraded for the 2026 High Luminosity Large Hadron Collider (HL-LHC) run. The HL-LHC will operate with a center of mass energy of 14 TeV and a peak instantaneous luminosity five times higher than at present. The increased luminosity will result in roughly ten times higher radiation levels and data rates. To cope with the ATLAS requirements in terms of radiation hardness, readout speed and granularity at the HL-LHC, the replacement of the present ATLAS Inner Tracker (ITk) is needed. Two large-scale depleted CMOS sensors in the 150 nm LF-technology called LF-CPIX and LF-MONOPIX, developed in the framework of the ATLAS Inner Tracker (ITK) upgrade for High Luminosity LHC. The work presented here shows the characterization for these three prototypes, with contributions concerning the setup development, 55Fe and 90Sr source calibration, modifications of the FPGA firmware and development of test programs. A main concern was the investigation on the radiation hardness for both the electronics and the sensor parts. We will show results concerning characterizations for these prototypes in the laboratory performance at CPPM, as well as results in multiple radiation campaigns performed at the 24 GeV IRRAD proton facility at CERN, to study the effects of Non-Ionizing Energy Loss (NIEL) and Total Ionizing Dose (TID) on the prototypes

The second decade of Large Hadron Collider operations, from about 2020 onwards, envisages a remarkable increase in collider instantaneous luminosity, one order of magnitude above the project one. This luminosity increase presents several challenges to the LHC experiments. The present Tracker of the Compact Muon Solenoid experiment must be replaced with a system providing excellent tracking quality at higher luminosities, as well as Tracking Trigger inputs to the existing "Level 0" CMS Trigger system at the full 40 MHz bunch-crossing rate. The minimal requirements for a Tracking Trigger would be the capability to confirm the presence of high-pT tracks associated with Calorimeter and/or Muon Level 0 Triggers. The ability to provide effective isolation criteria may also be required, and would in any case substantially improve the Trigger performance. Maintaining the data rates generated by Tracking Trigger inputs within a manageable bandwidth requires sensor modules able to locally sparsify the data. Measuring at detector module level the track direction in the transverse plane, and hence deriving its transverse momentum, is the most promising solution to provide such a detector-embedded data reduction feature. These so-called "pT-modules"' would only transmit to the Level 1 Trigger "stubs", pairs of correlated hits in two closely separated sensors, derived by tracks with pT above a given threshold. To exemplify, a 2 GeV/c threshold would cut data rate of more than a factor 10, hence providing a data rate well within the capabilities of present data links. The pT-modules design discussed in this work consists of two, closely spaced segmented silicon sensors, featuring both pattern hit correlation across the module and a single hit position resolution high enough to compute stubs with the required accuracy to resolve track directions despite a lever arm of about only 1 mm. A concept Tracker layout, the so-called "Long Barrel", consisting in an Outer Tracker completely built out of pT-modules, has been proposed. The Long Barrel Tracker is particularly flexible in simulation studies of Tracking Trigger as it allows for information from several layers of the Tracker to be combined in a projective geometry. For this reason, it is meant as a testing ground to compare the performance of different designs and configurations. The Long Barrel layout also allows the generation of even more structured Trigger Objects such as "tracklets", consisting of pairs of stubs in opportunely paired layers, which can in turn be used as seeds to generate "Level 1 tracks", including even more stubs. The choice of stacked sensors for pT-modules has been recently strengthened by test beam results obtained with novel prototypes of Monolithic Active Pixel Sensors and reported in this thesis. The developement of Tracking Trigger simulations is also presented as a major step towards the design of a realistic Trigger capable Tracker upgrade. A particular challenge for the Trigger system is given by tau leptons produced in many rare processes searched at the LHC. The performance of a Tracking Trigger on final states with tau leptons will be crucial at very high luminosities and is presented at the and of this document as the natural step forward in the work on the subject.
Durante il secondo decennio di operazioni al Large Hadron Collider, a partire dall'anno 2020, è previsto un notevole aumento della luminosità istantanea del collisionatore, di un ordine di grandezza superiore rispetto a quella di progetto. Questa luminosità presenta numeose sfide per gli esperimenti a LHC. Il Tracciatore attualmente impiegato nell'esperimento Compact Muon Solenoid dovrà essere rimpiazzato con un sistema in grado di garantire una tracciatura di qualità eccellente ad alte luminosità e, allo stesso tempo, fornire informazioni utili per l'attuale "Livello 0" del sistema di Trigger a CMS, alla frequenza di collisioni di 40 MHz. Le richieste minime per un Trigger basato sul Tracciatore sono la capacità di confermare la presenza di tracce ad alto pT associate a Trigger di Livello 0 ottenuti con i Calorimetri o i rivelatori di muoni. La capacità di fornire criteri efficaci di isolazione può essere ulteriormente richiesa e in ogni caso migliorerebbe significativamente le prestazioni del Trigger. Il rateo dei dati associati con la generazione nel Tracciatore di informazione di Trigger può essere mantenuto in una larghezza di banda sufficientemente maneggevole richiedendo che i moduli sensitivi siano in grado di ridurre localmente i dati. I principali candidati per una simile riduzione locale del rateo i dati sono caratterizzati dalla capacità di fornire la direzione della traccia nel piano trasverso, oltre alla sua posizione, da cui poter dedurre la quantità di moto della traccia stessa. Questi "pT-modules" trasmetterebbero di conseguenza al Trigger di primo livello degli abbozzi di traccia ("stub") generati da particelle con pT al di sopra di 2 GeV/c. La scelta di una simile soglia permetterebbe la riduzione dei dati di un fattore superiore a 10, consentendo quindi un rateo facilmente tollerabile. I moduli di Trigger possono essere realizzati con due sensori di silicio paralleli leggermente separati, caratterizzati da una risoluzione sulla misura del singolo punto d'impatto tale che gli stub, ottenuti tramite correlazione tra i punti misurati nel modulo, possano fornire un'adeguata misura della direzione della traccia, nonostante il braccio di leva sia dell'ordine del millimetro. Un'ipotetica configurazione per il Tracciatore, composto da "lunghi barili", che prevede un Tracciatore esterno realizzato totalmente con moduli di Trigger, è stata proposta. Essa è particolarmente flessibile negli studi di simulazione per il Trigger realizzato con il Tracciatore giacché consente di combinare tra loro, tramite proiezioni geometriche, le informazioni provenienti da diversi strati del Tracciatore. Pertanto è un campo di prova per confrontare le prestazioni di diverse concezioni e diverse configurazioni. Il Tracciatore proposto permette anche la generazione di oggetti più articolati degli stub per il Trigger, come ad esempio le "tracklet", che consistono in coppie di stub opportunamente associate tra loro, le quali possono a loro volta essere usate come punto di partenza per la costruzione di Tracce di Primo Livello. La scelta di moduli di Trigger realizzati con sensori accoppiati è rafforzata da risultati recenti ottenuti con dei prototipi innovativi di rivelatori a Pixel Monolitici durante dei test sotto fascio riportati in questa tesi. Lo sviluppo di simulazioni per un Trigger con il Tracciatore è anch'esso presentato come un significativo progresso verso la progettazione di un nuovo Tracciatore realistico e capace di fornire informazioni utili per il Trigger. Particolarmente impegnativo è lo sforzo per un Trigger che selezioni i leptoni tau prodotti in numerosi processi rari di interesse per gli esperimenti a LHC. Le prestazioni di un Trigger con il Tracciatore su stati finali contenenti leptoni tau saranno fondamentali a luminosità molto elevate e sono illustrate alla fine di questo documento, come naturale prosecuzione del lavoro descritto.

The Large Hadron Collider (LHC) is the largest circular accelerator ever build, allowing collisions at a center-of-mass energy of 13 TeV. The Phase-2 of the LHC, known as High Luminosity LHC (HL-LHC), is going to start in 2027. With HL-LHC, the Compact Muon Solenoid (CMS) experiment will gather an integrated luminosity up to 4000 fb^{-1} in 10 years, making it possible to study rare events of the Standard Model (SM) or to search for processes beyond it. The CMS experiment will be upgraded between 2025 and 2027 to cope with the higher luminosity: especially in the regions near the collision point, unprecedented requirements in terms of radiation resistance and granularity need to be met. The first part of this Thesis focuses on the upgrade of the CMS silicon tracker, whose inner section will be made of pixel detectors. The characteristics of the new tracker will be extremely important in the future analysis to be carried out in CMS during Phase-2. For the new Phase, pixel sensors of new conception have been considered, in which the electrodes (p+ and n+) penetrate deep into the silicon from the same side of the sensor: these new pixels are referred as `3D' for their characteristic of having columnar implants as deep as the active thickness of the sensor, while the more conventional planar `2D' pixels have superficial implants of small thickness. Thanks to this structure, 3D sensors can have excellent performance even with high radiation damage, making them suitable for the use in the inner layers of the future CMS tracker. Due to the cutting edge technology needed to produce these sensors, their use for a large scale experiment has only recently become feasible. However, the production processes are more complex than those of planar sensors, and this affects costs and production effciency. Therefore, 3D sensors have been taken into consideration only for the inner layers of the tracker, while planar sensors will be used in the other layers. In this Thesis, a complete characterisation of 3D and planar pixel detectors is presented. The studies are performed at the INFN and CERN laboratories and in several test beam experiments at DESY. My work was crucial for the characterisation of the detectors both before and after irradiation, to verify that both the sensor and the readout chip are able to resist the high fuences expected at the HL-LHC with a minimum loss of performance. The studies I made demonstrated that planar pixel detectors reach a hit detection effciency of over 99% at a bias voltage of 600 V after an irradiation corresponding the fuence expected after ten years of operations of HL-LHC. 3D pixel detectors have not been tested to these fuences yet (new test beams in the near future will target their characterisation), but are expected to reach similar effciencies with far lower bias voltages, around 150 V. Having high efficiencies at relatively low bias voltages leads to a lower power consumption and reduces the susceptibility to sparking issues with respect to planar sensors. Both of these features are invaluable in the inner tracker environment. Among the studies presented in this Thesis, the spatial resolution of 3D and planar pixel detectors was thoroughly evaluated. Non-irradiated 3D and planar pixel detectors have shown remarkable spatial resolution, down to 2 µm or 5 µm depending on the pixel pitch. The results presented in this Thesis will contribute significantly to the choice of the pixel sensors to be used in the future CMS Inner Tracker. The second part of this Thesis focuses on the measurement of the Vector Boson Fusion (VBF) Higgs production mechanism in the H->WW decay channel. A particle consistent with the SM Higgs boson was observed in 2012 by the CMS and ATLAS collaborations at the LHC. After the discovery, precision on the measure- ment of this new particle properties and interactions has progressed as more data were collected. Currently, all production processes have been observed in one or more decay channels or via combination of several decay channels, with no significant deviations with respect to the SM prediction. However, the VBF mechanism, being at the heart of the electroweak symmetry breaking, needs to be studied with ever-improving analysis techniques while waiting for additional data to reduce the statistical uncertainty. Such a rare process is sensitive to new physics phenomena and allows to set stringent constraints on the compatibility of the Higgs boson itself with the SM. The cross section for the VBF mechanism in proton-proton collisions at a center of mass energy of 13 TeV has been measured by CMS in several Higgs decay channels. The H->WW decay, thanks to its large branching ratio, is ideal for the observation of this production process. The most recent CMS analysis in the H ! WW decay channel, however, mainly focused on the measurement of the global production cross section: the analysis was not optimized with respect to the VBF production mode. In this Thesis, a multivariate analysis was implemented in order to enhance the sensitivity of the measurement of the VBF mechanism in the H->WW decay channel. In particular, a Deep Neural Network (DNN) was developed in order to isolate the signal events from the background, which is mainly composed by top quarks events, non-resonant WW and gluon fusion Higgs boson production mechanism. The DNN yields four scores for each event, corresponding to the degree of compatibility either with the signal or one of the main backgrounds. These scores are then combined and used in the fitting procedure. This innovative approach was necessary because one of the main backgrounds of this analysis is another Higgs production process, therefore making it diffcult to tackle this analysis in a simple signal versus background paradigm. This study is based on the whole Run-2 dataset, collected from 2016 to 2018 with the CMS experiment. The VBF Higgs production mechanism is observed with a significance of 3.6 standard deviations, resulting in the first evidence of this production mechanism in the WW decay channel with the CMS experiment. Moreover, the measured cross section is compatible with the Standard Model within one standard deviation. This work established an analysis strategy that will be used for the LHC Run-3 and possibly beyond it.