Characterization of silicon detectors for the phase 2 upgrade of the CMS experiment of LHC

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Φυσική και Τεχνολογικές Εφαρμογές

Ανιχνευτές πυριτίου για την αναβάθμιση των πειραμάτων στο HL-LHC

The Large Hadron Collider (LHC) at the European Nuclear Research Council in Geneva is scheduled to undergo a major luminosity upgrade after its ten-year lifespan to maximize its potential for scientific discovery. The Compact Muon Solenoid is one of two large general-purpose detectors that contributed to the recent discovery of the Higgs boson and many other physics results in particle physics. Its innermost part is called the Tracker, and it is a high-precision instrument that measures the trajectories of the created particles. It consists of silicon detectors with high spatial resolution and high-speed capabilities. With a total area of more than 200 square meters, it is the largest detector of its kind ever built. The increase in instantaneous luminosity in the upgraded LHC will lead to a very high increased track density at the interaction points of the colliding beams and, thus, also to a much more hostile radiation environment. Consequently, a major upgrade and redesign of the sensors and readout electronics are required. The upgrades will be done in 2 phases, and the upgraded LHC is expected to be fully operational in 2026. In Phase 2, there will be major changes to the Inner Pixel Detector and the Outer Tracking system with new detector units. CMS has developed a quality assurance plan to ensure that all sensors meet technical specifications and monitor their manufacturing process and manufacturing stability. The PQC contacts custom-made test structures produced on the same wafer as the silicon sensors that will be installed in the CMS experiment, so they share the same properties and materials. These test structures provide access to key parameters related to sensor manufacturing quality, including parameters not directly accessible to the sensors, and, together with sensor quality control, are the main processes of the Outer Tracker sensor quality assurance plan for the Phase-2 upgrade. This thesis describes the quality control process and the extraction procedure of the relevant parameters. The first results from the production phase are also presented. In addition to experimental measurements, simulations are integral to confirm the results. Numerical simulation of semiconductor devices' manufacturing process and electrical characteristics offers a fast and inexpensive way to check device designs and manufacturing processes. Simulations are crucial for device structure optimization and detector development. Various test structures related to PQC were simulated using the TCAD (Technology Computer-Aided Design) Sentaurus suite and compared with experimental results. Also, this work includes simulations of silicon sensor capacitances using TCAD simulations as well as a program that solves the 2D, and 3D Laplace equation developed at the Detector Instrumentation laboratory of NCSR Demokritos. In addition, extensive radiation testing is required to evaluate the radiation resistance of the sensors. In the upgraded Outer Tracker of the CMS experiment, the expected radiation dose will be from 10 to 750 kGy, depending on the distance from the beam. This thesis presents radiation studies on test structures with gamma photons from a Cobalt-60 source, complementary to already performed X-ray and particle radiation studies.Ο Μεγάλος Επιταχυντής Αδρονίων (LHC) στο ευρωπαϊκό οργανισμό πυρηνικών ερευνών στη Γενεύη έχει προγραμματιστεί να υποβληθεί σε σημαντική αναβάθμιση φωτεινότητας μετά τη διάρκεια ζωής των δέκα ετών λειτουργίας του, προκειμένου να μεγιστοποιήσει το δυναμικό επιστημονικής ανακάλυψης. Το Compact Muon Solenoid είναι ένας από τους δύο μεγάλους ανιχνευτές γενικού σκοπού που συνέβαλε στην πρόσφατη ανακάλυψη του μποζονίου Higgs και πολλών άλλων αποτελεσμάτων της φυσικής στη σωματιδιακή φυσική. Το πιο εσωτερικό μέρος του ονομάζεται Tracker και είναι όργανο υψηλής ακρίβειας που μετρά τις τροχιές των δημιουργούμενων σωματιδίων. Αποτελείται από ανιχνευτές πυριτίου με υψηλή χωρική ανάλυση και δυνατότητες υψηλής ταχύτητας. Με συνολική επιφάνεια άνω των 200 τετραγωνικών μέτρων, είναι ο μεγαλύτερος ανιχνευτής αυτού του είδους που κατασκευάστηκε ποτέ. Η αύξηση της φωτεινότητας στον αναβαθμισμένο LHC θα οδηγήσει σε αυξημένη πυκνότητα τροχιάς στα σημεία αλληλεπίδρασης των συγκρουόμενων δεσμών και, ως εκ τούτου, σε ένα πολύ πιο απαιτητικό περιβάλλον ακτινοβολίας. Κατά συνέπεια, απαιτείται σημαντική αναβάθμιση και επανασχεδιασμό των αισθητήρων και των ηλεκτρονικών ανάγνωσης. Οι αναβαθμίσεις θα γίνουν σε 2 φάσεις και ο αναβαθμισμένος LHC αναμένεται να είναι πλήρως λειτουργικός το 2026. Στη Φάση 2, θα υπάρξουν σημαντικές αλλαγές στον Inner Pixel Detector και στο Outer Tracking σύστημα με νέες ανιχνευτικές μονάδες.Το CMS έχει αναπτύξει ένα σχέδιο διασφάλισης ποιότητας για να εξασφαλίσει ότι όλοι οι αισθητήρες πληρούν τις τεχνικές προδιαγραφές και να για να παρακολουθεί τη διαδικασία παραγωγής και τη σταθερότητα κατασκευής τους. Το PQC έρχεται σε επαφή με ειδικά κατασκευασμένες τεστ δομές που παράγονται στο ίδιο wafer με τους αισθητήρες πυριτίου που θα εγκαταστάθηκαν στο πείραμα CMS, με αποτέλεσμα να μοιράζονται τις ίδιες ιδιότητες και υλικά. Αυτές οι τεστ δομές παρέχουν πρόσβαση σε βασικές παραμέτρους σχετικά με την ποιότητα κατασκευής των αισθητήρων, συμπεριλαμβανομένων των παραμέτρων που δεν είναι άμεσα προσβάσιμες στους αισθητήρες και, μαζί με τον ποιοτικό έλεγχο των αισθητήρων, αποτελούν τις κύριες διαδικασίες του σχεδίου διασφάλισης ποιότητας των αισθητήρων του Outer Tracker για την αναβάθμιση Phase-2. Στην εργασία αυτή περιγράφεται η διαδικασία ποιοτικού ελέγχου και η διαδικασία εξαγωγής των σχετικών παραμέτρων. Παρουσιάζονται επίσης τα πρώτα αποτελέσματα από τη φάση παραγωγής.Εκτός από τις πειραματικές μετρήσεις, οι προσομοιώσεις είναι αναπόσπαστο κομμάτι για την επιβεβαίωση των αποτελεσμάτων. Η αριθμητική προσομοίωση της διαδικασίας κατασκευής και των ηλεκτρικών χαρακτηριστικών των συσκευών ημιαγωγών προσφέρει έναν γρήγορο και μη δαπανηρό τρόπο ελέγχου των σχεδίων και των διαδικασιών κατασκευής των συσκευών. Οι προσομοιώσεις είναι ζωτικής σημασίας για τη βελτιστοποίηση της δομής της συσκευής και την ανάπτυξη ανιχνευτών. Διάφορες δομές δοκιμής που σχετίζονται με το PQC προσομοιώθηκαν χρησιμοποιώντας τη σουίτα TCAD (Technology Computer-Aided Design) Sentaurus και συγκρίθηκαν με πειραματικά αποτελέσματα. Επιπλέον, αυτή η εργασία περιλαμβάνει προσομοιώσεις χωρητικοτήτων αισθητήρων πυριτίου χρησιμοποιώντας προσομοιώσεις TCAD καθώς και ένα πρόγραμμα το οποίο λύνει τη δισδιάστατη και τρισδιάστατη εξίσωση Laplace που αναπτύχθηκε στο Εργαστήριο Οργάνων Ανιχνευτών του ΕΚΕΦΕ Δημόκριτος.Εκτός από τον ποιοτικό έλεγχο των δομών δοκιμής, απαιτούνται εκτενείς δοκιμές ακτινοβολίας για την αξιολόγηση της αντοχής στην ακτινοβολίας των αισθητήρων. Στο αναβαθμισμένο Outer Tracker του πειράματος CMS, η αναμενόμενη δόση ακτινοβολίας θα είναι από 10 έως 750 kGy, ανάλογα με την απόσταση από τη δέσμη. Αυτή η εργασία παρουσιάζει μελέτες ακτινοβολίας σε δοκιμαστικές δομές με φωτόνια γάμμα από μια πηγή Cobalt-60, συμπληρωματικές σε ήδη πραγματοποιηθείσες μελέτες ακτινοβολίας ακτίνων Χ και σωματιδίων

Cobalt-60 gamma irradiation of silicon test structures for high-luminosity collider experiments

During the era of the High Luminosity LHC (HL-LHC) the devices in the experiments will be subjected to increased radiation levels with fluxes of neutrons and charged hadrons in the inner detectors reaching up to approximately $\mathrm{2.3\times10^{16}\:n_{eq}/cm^2}$ and total ionization doses up to around 1.2 Grad. A systematic program of radiation tests with neutrons and charged hadrons is being carried out by the CMS and ATLAS Collaborations in order to cope with the higher luminosity of HL-LHC and the associated increase in the pile-up events and radiation fluxes. In this work, results from a complementary radiation study with $^{60}$Co-\upgamma photons are presented. The doses are equivalent to those that the outer layers of the silicon tracker systems of the two experiments will be subjected to. The devices in this study are p-type diodes and MOS capacitors

Beam Test Performance of Prototype Silicon Detectors for the Outer Tracker for the Phase-2 Upgrade of CMS

A new CMS tracker detector will be installed for operation at the High Luminosity LHC\,(HL-LHC). This detector comprises modules with two closely spaced parallel sensor plates and front-end ASICs capable of transmitting tracking information to the CMS Level-1\,(L1) trigger at the 40\,MHz beam crossing rate. The inclusion of tracking information in the L1 trigger decision will be essential for selecting events of interest efficiently at the HL-LHC. The CMS Binary Chip\,(CBC) has been designed to read out and correlate hits from pairs of tracker sensors, forming so-called track stubs. For the first time, a prototype irradiated module and a full-sized module, both equipped with the version 2 of the CBC, have been operated in test beam facilities. The efficiency of the stub finding logic of the modules for various angles of incidence has been studied. The ability of the modules to reject tracks with transverse momentum less than $2~\mathrm{GeV}$ has been demonstrated. For modules built with irradiated sensors, no significant drop in the stub finding performance has been observed. Results from the beam tests are described in this paper

Measurement of the double-differential inclusive jet cross section in proton-proton collisions at s\sqrt{s} = 5.02 TeV

International audienceThe inclusive jet cross section is measured as a function of jet transverse momentum $p_\mathrm{T}$ and rapidity $y$. The measurement is performed using proton-proton collision data at $\sqrt{s}$ = 5.02 TeV, recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 27.4 pb$^{-1}$. The jets are reconstructed with the anti-$k_\mathrm{T}$ algorithm using a distance parameter of $R$ = 0.4, within the rapidity interval $\lvert y\rvert$$\lt$ 2, and across the kinematic range 0.06 $\lt$$p_\mathrm{T}$$\lt$ 1 TeV. The jet cross section is unfolded from detector to particle level using the determined jet response and resolution. The results are compared to predictions of perturbative quantum chromodynamics, calculated at both next-to-leading order and next-to-next-to-leading order. The predictions are corrected for nonperturbative effects, and presented for a variety of parton distribution functions and choices of the renormalization/factorization scales and the strong coupling $\alpha_\mathrm{S}$

Two-particle Bose-Einstein correlations and their Lévy parameters in PbPb collisions at sNN\sqrt{s_\mathrm{NN}} = 5.02 TeV

Two-particle Bose-Einstein momentum correlation functions are studied for charged-hadron pairs in lead-lead collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV. The data sample, containing 4.27$\times10^{9}$ minimum bias events corresponding to an integrated luminosity of 0.607 nb$^{-1}$, was collected by the CMS experiment in 2018. The experimental results are discussed in terms of a L\'evy-type source distribution. The parameters of this distribution are extracted as functions of particle pair average transverse mass and collision centrality. These parameters include the L\'evy index or shape parameter ($\alpha$), the L\'evy scale parameter ($R$), and the correlation strength parameter ($\lambda$). The source shape, characterized by $\alpha$, is found to be neither Cauchy nor Gaussian, implying the need for a full L\'evy analysis. Similarly to what was previously found for systems characterized by Gaussian source radii, a hydrodynamical scaling is observed for the L\'evy $R$ parameter. The $\lambda$ parameter is studied in terms of the core-halo model.Comment: Submitted to Physical Review C. All figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/HIN-21-011 (CMS Public Pages

Measurement of the double-differential inclusive jet cross section in proton-proton collisions at s\sqrt{s} = 5.02 TeV

International audienceThe inclusive jet cross section is measured as a function of jet transverse momentum $p_\mathrm{T}$ and rapidity $y$. The measurement is performed using proton-proton collision data at $\sqrt{s}$ = 5.02 TeV, recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 27.4 pb$^{-1}$. The jets are reconstructed with the anti-$k_\mathrm{T}$ algorithm using a distance parameter of $R$ = 0.4, within the rapidity interval $\lvert y\rvert$$\lt$ 2, and across the kinematic range 0.06 $\lt$$p_\mathrm{T}$$\lt$ 1 TeV. The jet cross section is unfolded from detector to particle level using the determined jet response and resolution. The results are compared to predictions of perturbative quantum chromodynamics, calculated at both next-to-leading order and next-to-next-to-leading order. The predictions are corrected for nonperturbative effects, and presented for a variety of parton distribution functions and choices of the renormalization/factorization scales and the strong coupling $\alpha_\mathrm{S}$

Measurement of inclusive and differential cross sections for single top quark production in association with a W boson in proton-proton collisions at s \sqrt{s} = 13 TeV

International audienceMeasurements of the inclusive and normalised differential cross sections are presented for the production of single top quarks in association with a W boson in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data used were recorded with the CMS detector at the LHC during 2016–2018, and correspond to an integrated luminosity of 138 fb$^{−1}$. Events containing one electron and one muon in the final state are analysed. For the inclusive measurement, a multivariate discriminant, exploiting the kinematic properties of the events is used to separate the signal from the dominant $\textrm{t}\overline{\textrm{t}}$ background. A cross section of $79.2\pm 0.9{\left(\textrm{stat}\right)}_{-8.0}^{+7.7}\left(\textrm{syst}\right)\pm 1.2\left(\textrm{lumi}\right)$ pb is obtained, consistent with the predictions of the standard model. For the differential measurements, a fiducial region is defined according to the detector acceptance, and the requirement of exactly one jet coming from the fragmentation of a bottom quark. The resulting distributions are unfolded to particle level and agree with the predictions at next-to-leading order in perturbative quantum chromodynamics.[graphic not available: see fulltext

Search for stealth supersymmetry in final states with two photons, jets, and low missing transverse momentum in proton-proton collisions at s\sqrt{s} = 13 TeV

International audienceThe results of a search for stealth supersymmetry in final states with two photons and jets, targeting a phase space region with low missing transverse momentum ($p_\text{T}^\text{miss}$), are reported. The study is based on a sample of proton-proton collisions at $\sqrt{s}$ =13 TeV collected by the CMS experiment, corresponding to an integrated luminosity of 138 fb$^{-1}$. As LHC results continue to constrain the parameter space of the minimal supersymmetric standard model, the low $p_\text{T}^\text{miss}$ regime is increasingly valuable to explore. To estimate the backgrounds due to standard model processes in such events, we apply corrections derived from simulation to an estimate based on a control selection in data. The results are interpreted in the context of simplified stealth supersymmetry models with gluino and squark pair production. The observed data are consistent with the standard model predictions, and gluino (squark) masses of up to 2150 (1850) GeV are excluded at the 95% confidence level