The mass production of silicon sensors for the Phase-2 CMS Outer Tracker

The high luminosity upgrade of the Large Hadron Collider (HL-LHC) will create a more challenging and demanding environment for the operation of the CMS detector. The peak instantaneous luminosity of the HL-LHC machine will reach 5 - 7 $\times$ $10^{34}$ $\textrm{cm}^{-2}\textrm{s}^{-1}$, which by the end of its lifetime will have delivered up to 4000 $\textrm{fb}^{-1}$. To cope with these conditions the CMS Tracker will be fully replaced with a more advanced system. The new sub-detector is divided into an Outer Tracker, instrumented by short strips and macro pixels, and a more granular Inner Tracker using pixelated sensors. This report will describe some features of the new Outer Tracker silicon sensors and modules, provide results indicating the quality of the sensors produced to date, as well as the robustness of the sensors against environmental factors such as relative humidity

The large-scale production of silicon sensors for the Phase-2 Upgrade of the CMS Outer Tracker

\par The high-luminosity upgrade of the Large Hadron Collider (LHC) at CERN will introduce a new period of challenges for the high-energy physics community. The increase of the peak instantaneous luminosity of the machine up to 5 $\times$ 10$^{34}$ \si{\centi\meter}^{-2}\si{\second}^{-1} (or 7 $\times$ 10$^{34}$ \si{\centi\meter}^{-2}\si{\second}^{-1} in the ultimate case) will provide with more statistics of the Higgs boson decays and expand the discovery potential especially for rare processes of the standard model or beyond standard model physics. The HL-LHC is expected to deliver an integrated luminosity of 3000 - 4000 \si{\femto\barn}^{-1} by the end of its lifetime. \par The CMS (Compact Muon Solenoid) detector needs to undergo several upgrades in order to fully exploit the increase in luminosity delivered by HL-LHC. This upgrade program is known as the CMS \emph{Phase-2} upgrade. The innermost sub-detector of CMS, the tracking system (CMS Tracker), will be fully replaced with a more advanced detector which is designed to cope with the larger particle rates and the high radiation levels of HL-LHC. \par The Phase-2 Tracker consists of an Inner Tracker (IT) based on pixel sensors and an Outer Tracker (OT) based on strip and macro pixel sensors. The Outer Tracker requires about 26400 new silicon sensors. The production of the Outer Tracker sensors has started since the summer of 2020. \par This thesis describes the basic features of the new Outer Tracker silicon sensors and summarizes the CMS plan to monitor the stability and quality of large-scale production. This plan comprises the electrical characterization of the production sensors and the test structures on a sampled basis. The test structures are developed on the same wafers as the main sensors and they share the same properties. They provide quick access to several sensor parameters, many of which can not be directly measured on the main sensor, such as the flat-band voltage or they require potentially destructive tests, such as the breakdown voltage of coupling oxide. \par To date, the mass production of the Phase-2 Outer Tracker silicon sensors has exceeded 70$\%$ of the total. Hence, a sufficient number of data has been collected in order to characterize the production process. This thesis provides a summary of the evolution of all the measured sensor and wafer parameters over production time. A comparison and a correlation of all the parameters related to the same sensor properties is performed. An emphasis is given on those parameters which reveal trends and inconsistencies over production time. Apart from providing conclusions for the quality of the production sensors, this thesis attempts to prove the importance of process quality control as a tool to spot in-time fabrication process variations and to give a full insight into the wafer properties. \par Moreover, studies are conducted on the robustness of the Outer Tracker production sensors against external factors such as electrostatic charge-up and humidity. The electrostatic charge-up is an effect which concerns a large fraction of the Outer Tracker sensor production. The source of this effect, its impact on the electrical behavior of the production sensors as well as a mitigation strategy as defined by CMS, are presented in this thesis. Also, the impact of high relative humidity on the production sensors is investigated. The role of high relative humidity becomes more crucial during the module assembly stage due to the long exposure of the sensors to the humid environment of the ESD-safe clean rooms. The response of the sensors after a long exposure to humidity is examined and a recovery strategy is defined for those sensors which show a deterioration of their electrical behaviors due to humidity

Silicon sensors for the Phase-2 upgrade of the CMS Outer Tracker; status and early results from the production phase

The high luminosity upgrade of the Large Hadron Collider (HL-LHC) will set new challenges in the operation and performance of the CMS and ATLAS experiments. The peak luminosity of the HL-LHC machine will reach 5 $\text{-}$ 7.5 $\times$ $10^{34}$ cm$^{-2}$s$^{-1}$, which will deliver to the experiments a 10$\text{-}$fold increase in integrated luminosity by the end of its lifetime. The CMS Tracker will have to be fully replaced in order to maintain its excellent performance and to withstand this more demanding environment. The upgraded system is divided into an Outer Tracker, instrumented by short strips and macro-pixels, and a high granularity Inner Tracker using pixels. After several years of research on different sensor options, the baseline for the Outer Tracker sensors has been defined and production of over 24,000 sensors started in 2020. This report will provide a brief overview of the new Outer Tracker silicon sensor features, as well as some initial results regarding the quality of the sensors produced to date

Teeth Eruption Disorders: A Critical Review

Dental eruption refers to the vertical displacement of a tooth from its initial non-functional towards its functional position. Tooth eruption disorders may be expressed in various clinical conditions, which may be grouped as “primary retention” and “secondary retention”. The purpose of this article is to review the literature and the clinical parameters of the various conditions related to tooth eruption disorders. Materials and Methods: The search strategy of this critical review included keywords in combination with MeSH terms in Medline, Scopus, and Cochrane Library until February 2022 and only in English. Results: “Primary Failure of Eruption” (PFE) occurs during the eruption process and includes clinical characteristics of both primary and secondary retention, which make diagnosis difficult. PFE is distinguished by Types I and II. In Type I, the defect in the eruption process occurs in all the relative teeth at the same time, whilst in Type II, the clinical expressions vary in multiple quadrants of the mouth, and the second molars erupt more. The variability of the PFE’s clinical spectrum seems to be connected to a genetic origin. The differential diagnosis among single ankylosis, secondary retention, and PFE is based on the occlusal relationship between the upper and the lower teeth distally, most commonly the first molar, which has not yet fully erupted. The treatment approach depends on many factors and combines surgical and orthodontic techniques

Measurement of the Higgs boson width and evidence of its off-shell contributions to ZZ production [Dataset]

Since the discovery of the Higgs boson in 2012, detailed studies of its properties have been ongoing. Besides its mass, its width - related to its lifetime - is an important parameter. One way to determine this quantity is by measuring its off-shell production, where the Higgs boson mass is far away from its nominal value, and relating it to its on-shell production, where the mass is close to the nominal value. Here, we report evidence for such off-shell contributions to the production cross section of two Z bosons with data from the CMS experiment at the CERN Large Hadron Collider. We constrain the total rate of the off-shell Higgs boson contribution beyond the Z boson pair production threshold, relative to its standard model expectation, to the interval [0.0061, 2.0] at 95% confidence level. The scenario with no off-shell contribution is excluded at a p-value of 0.0003 (3.6 standard deviations). We measure the width of the Higgs boson as Th = 3.2 (+2.4 / -1.7) MeV, in agreement with the standard model expectation of 4.1 MeV. In addition, we set constraints on anomalous Higgs boson couplings to W and Z boson pairs.Peer reviewe

Inclusive nonresonant multilepton probes of new phenomena at s =13 TeV

An inclusive search for nonresonant signatures of beyond the standard model (SM) phenomena in events with three or more charged leptons, including hadronically decaying τ leptons, is presented. The analysis is based on a data sample corresponding to an integrated luminosity of 138 fb-1 of proton-proton collisions at s=13 TeV, collected by the CMS experiment at the LHC in 2016-2018. Events are categorized based on the lepton and b-tagged jet multiplicities and various kinematic variables. Three scenarios of physics beyond the SM are probed, and signal-specific boosted decision trees are used for enhancing sensitivity. No significant deviations from the background expectations are observed. Lower limits are set at 95% confidence level on the mass of type-III seesaw heavy fermions in the range 845-1065 GeV for various decay branching fraction combinations to SM leptons. Doublet and singlet vectorlike τ lepton extensions of the SM are excluded for masses below 1045 GeV and in the mass range 125-150 GeV, respectively. Scalar leptoquarks decaying exclusively to a top quark and a lepton are excluded below 1.12-1.42 TeV, depending on the lepton flavor. For the type-III seesaw as well as the vectorlike doublet model, these constraints are the most stringent to date. For the vectorlike singlet model, these are the first constraints from the LHC experiments. Detailed results are also presented to facilitate alternative theoretical interpretations.ISSN:1550-7998ISSN:0556-2821ISSN:1550-236

Search for resonant production of strongly coupled dark matter in proton-proton collisions at 13 TeV

The first collider search for dark matter arising from a strongly coupled hidden sector is presented and uses a data sample corresponding to 138 fb−1, collected with the CMS detector at the CERN LHC, at s = 13 TeV. The hidden sector is hypothesized to couple to the standard model (SM) via a heavy leptophobic Z′ mediator produced as a resonance in proton-proton collisions. The mediator decay results in two “semivisible” jets, containing both visible matter and invisible dark matter. The final state therefore includes moderate missing energy aligned with one of the jets, a signature ignored by most dark matter searches. No structure in the dijet transverse mass spectra compatible with the signal is observed. Assuming the Z′ boson has a universal coupling of 0.25 to the SM quarks, an inclusive search, relevant to any model that exhibits this kinematic behavior, excludes mediator masses of 1.5–4.0 TeV at 95% confidence level, depending on the other signal model parameters. To enhance the sensitivity of the search for this particular class of hidden sector models, a boosted decision tree (BDT) is trained using jet substructure variables to distinguish between semivisible jets and SM jets from background processes. When the BDT is employed to identify each jet in the dijet system as semivisible, the mediator mass exclusion increases to 5.1 TeV, for wider ranges of the other signal model parameters. These limits exclude a wide range of strongly coupled hidden sector models for the first time. [Figure not available: see fulltext.]ISSN:1126-6708ISSN:1029-847