The ABC130 barrel module prototyping programme for the ATLAS strip tracker

For the Phase-II Upgrade of the ATLAS Detector, its Inner Detector, consisting of silicon pixel, silicon strip and transition radiation sub-detectors, will be replaced with an all new 100 % silicon tracker, composed of a pixel tracker at inner radii and a strip tracker at outer radii. The future ATLAS strip tracker will include 11,000 silicon sensor modules in the central region (barrel) and 7,000 modules in the forward region (end-caps), which are foreseen to be constructed over a period of 3.5 years. The construction of each module consists of a series of assembly and quality control steps, which were engineered to be identical for all production sites. In order to develop the tooling and procedures for assembly and testing of these modules, two series of major prototyping programs were conducted: an early program using readout chips designed using a 250 nm fabrication process (ABCN-25) and a subsequent program using a follow-up chip set made using 130 nm processing (ABC130 and HCC130 chips). This second generation of readout chips was used for an extensive prototyping program that produced around 100 barrel-type modules and contributed significantly to the development of the final module layout. This paper gives an overview of the components used in ABC130 barrel modules, their assembly procedure and findings resulting from their tests.Comment: 82 pages, 66 figure

Search for Non-pointing and Delayed Photons in pp collisions at √s=13 TeV using the ATLAS detector

This thesis describes the search for displaced photons in the exotic decays of the Standard Model Higgs boson using 139 fb−1 of proton-proton collision data recorded by the ATLAS detector. The signal model involves the decay of the Higgs boson into a pair of long-lived supersymmetric particles, each of which subsequently decay into a photon and a stable supersymmetric particle. The current upper limits on the decays of the Higgs boson to the undetected particles is around 21% making this search extremely relevant. This analysis utilizes the ATLAS electromagnetic calorimeter’s unique capabilities to measure the photon’s direction of flight and its time of arrival. No significant excess was observed compared to theestimated Standard Model background and this null result was used to set 95% confidence level limits on the branching ratio of the Higgs to the pair of long-lived particles for the very first time

Search for Non-pointing and Delayed Photons in pp\it{pp} collisions at s\sqrt{s}=13 TeV using the ATLAS detector

This thesis describes the search for displaced photons in the exotic decays of the Standard Model Higgs boson using 139 fb$^{-1}$ of proton-proton collision data recorded by the ATLAS detector. The signal model involves the decay of the Higgs boson into a pair of long-lived supersymmetric particles, each of which subsequently decay into a photon and a stable supersymmetric particle. The current upper limits on the decays of the Higgs boson to the undetected particles is around 21\% making this search extremely relevant. This analysis utilizes the ATLAS electromagnetic calorimeter's unique capabilities to measure the photon's direction of flight and its time of arrival. No significant excess was observed compared to the estimated Standard Model background and this null result was used to set 95\% confidence level limits on the branching ratio of the Higgs to the pair of long-lived particles for the very first time

Measuring the borders of the active area on silicon strip sensors

Silicon strip sensors for the ATLAS Inner Tracker (ITk) have been designed to provide reliable particle detection in the high-radiation environment of the High-Luminosity Large Hadron Collider. One important design criterion for their development is the minimisation of inactive sensor area (bias ring, guard ring and edge implant surrounding the active sensor area), as inactive sensor areas impact the hermeticity of particle detection inside the detector. In previous measurements of ATLAS silicon strip sensors, the charge collecting area of individual strip implants has been mapped and found to agree well with the sensor strip pitch and strip length. For strip implants next to the sensor bias ring, the extent of their charge collecting area towards the inactive sensor area was previously unknown, which limited the accuracy of both overall detector hermeticity estimates and the position resolution for particle detection at the sensor edge. Therefore, measurements were conducted to map the area of charge collection for sensor strips at the edge of the active sensor area. Using a micro-focused X-ray beam has made it possible to map this shape both within the sensor plane as well as inside the sensor volume. This contribution presents measurements showing the extent of charge collection in the edge strips (with a condition where the AC metal of a strip between the bias ring and the edge strips is being floated) of silicon strip sensors. The edge regions of two generations of ITk strip sensor modules were studied: one module with a short strip (ATLAS12) sensor and ABC130 readout chips and one module a long strip (ATLAS17LS) sensor and ABCstar readout chips

Mapping the in-plane electric field inside irradiated diodes

A significant aspect of the Phase-II Upgrade of the ATLAS detector is the replacement of the current Inner Detector with the ATLAS Inner Tracker (ITk). The ATLAS ITk is an all-silicon detector consisting of a pixel tracker and a strip tracker. Sensors for the ITk strip tracker have been developed to withstand the high radiation environment in the ATLAS detector after the High Luminosity Upgrade of the Large Hadron Collider at CERN, which will significantly increase the rate of particle collisions and resulting particle tracks. During their operation in the ATLAS detector, sensors for the ITk strip tracker are expected to accumulate fluences up to $1.5\cdot10^{15}\,\text{n}_{\text{eq}}/\text{cm}^2$ (including a safety factor of 1.5), which will significantly affect their performance. One characteristic of interest for highly irradiated sensors is the shape and homogeneity of the electric field inside its active area. For the results presented here, diodes with edge structures similar to full size ATLAS sensors were irradiated up to fluences comparable to those in the ATLAS ITk strip tracker and their electric fields mapped using a micro-focused X-ray beam (beam diameter $2\times3$ $\mu$m). This contribution shows the extension and shape of the electric field inside highly irradiated diodes over a range of applied bias voltages. Additionally, measurements of the outline of the depleted sensor areas allow a comparison of the measured leakage current for different fluences with expectations for the corresponding active areas

The ABC130 barrel module prototyping programme for the ATLAS strip tracker

For the Phase-II Upgrade of the ATLAS Detector [1], its Inner Detector, consisting of silicon pixel, silicon strip and transition radiation sub-detectors, will be replaced with an all new 100% silicon tracker, composed of a pixel tracker at inner radii and a strip tracker at outer radii. The future ATLAS strip tracker will include 11,000 silicon sensor modules in the central region (barrel) and 7,000 modules in the forward region (end-caps), which are foreseen to be constructed over a period of 3.5 years. The construction of each module consists of a series of assembly and quality control steps, which were engineered to be identical for all production sites. In order to develop the tooling and procedures for assembly and testing of these modules, two series of major prototyping programs were conducted: an early program using readout chips designed using a 250 nm fabrication process (ABCN-250) [2,2] and a subsequent program using a follow-up chip set made using 130 nm processing (ABC130 and HCC130 chips). This second generation of readout chips was used for an extensive prototyping program that produced around 100 barrel-type modules and contributed significantly to the development of the final module layout. This paper gives an overview of the components used in ABC130 barrel modules, their assembly procedure and findings resulting from their tests

Enriching the physics program of the CMS experiment via data scouting and data parking

International audienceSpecialized data-taking and data-processing techniques were introduced by the CMS experiment in Run 1 of the CERN LHC to enhance the sensitivity of searches for new physics and the precision of standard model measurements. These techniques, termed data scouting and data parking, extend the data-taking capabilities of CMS beyond the original design specifications. The novel data-scouting strategy trades complete event information for higher event rates, while keeping the data bandwidth within limits. Data parking involves storing a large amount of raw detector data collected by algorithms with low trigger thresholds to be processed when sufficient computational power is available to handle such data. The research program of the CMS Collaboration is greatly expanded with these techniques. The implementation, performance, and physics results obtained with data scouting and data parking in CMS over the last decade are discussed in this Report, along with new developments aimed at further improving low-mass physics sensitivity over the next years of data taking

Observation of the J/ψ\psi→\toμ+μ−μ+μ−\mu^+\mu^-\mu^+\mu^- decay in proton-proton collisions at s\sqrt{s} = 13 TeV

International audienceThe J/$\psi$$\to$$\mu^+\mu^-\mu^+\mu^-$ decay has been observed with a statistical significance in excess of five standard deviations. The analysis is based on an event sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment in 2018 and corresponding to an integrated luminosity of 33.6 fb${-1}$. Normalizing to the J/$\psi$$\to$$\mu^+\mu^-$ decay mode leads to a branching fraction [10.1$^{+3.3}_{-2.7}$ (stat) $\pm$ 0.4 (syst) ]$\times$ 10$^{-7}$, a value that is consistent with the standard model prediction

The CMS Statistical Analysis and Combination Tool: COMBINE

International audienceThis paper describes the COMBINE software package used for statistical analyses by the CMS Collaboration. The package, originally designed to perform searches for a Higgs boson and the combined analysis of those searches, has evolved to become the statistical analysis tool presently used in the majority of measurements and searches performed by the CMS Collaboration. It is not specific to the CMS experiment, and this paper is intended to serve as a reference for users outside of the CMS Collaboration, providing an outline of the most salient features and capabilities. Readers are provided with the possibility to run COMBINE and reproduce examples provided in this paper using a publicly available container image. Since the package is constantly evolving to meet the demands of ever-increasing data sets and analysis sophistication, this paper cannot cover all details of COMBINE. However, the online documentation referenced within this paper provides an up-to-date and complete user guide

Search for new physics in high-mass diphoton events from proton-proton collisions at s\sqrt{s} = 13 TeV

International audienceResults are presented from a search for new physics in high-mass diphoton events from proton-proton collisions at $\sqrt{s}$ = 13 TeV. The data set was collected in 2016-2018 with the CMS detector at the LHC and corresponds to an integrated luminosity of 138 fb$^{-1}$. Events with a diphoton invariant mass greater than 500\GeV are considered. Two different techniques are used to predict the standard model backgrounds: parametric fits to the smoothly-falling background and a first-principles calculation of the standard model diphoton spectrum at next-to-next-to-leading order in perturbative quantum chromodynamics calculations. The first technique is sensitive to resonant excesses while the second technique can identify broad differences in the invariant mass shape. The data are used to constrain the production of heavy Higgs bosons, Randall-Sundrum gravitons, the large extra dimensions model of Arkani-Hamed, Dimopoulos, and Dvali (ADD), and the continuum clockwork mechanism. No statistically significant excess is observed. The present results are the strongest limits to date on ADD extra dimensions and RS gravitons with a coupling parameter greater than 0.1