Emma Sian Kuwertz

The XMM Cluster Survey (XCS) is a serendipitous search for galaxy clusters using all publicly available data in the XMM-Newton Science Archive.Its main aims are to measure cosmological parameters and trace the evolution of X-ray scaling relations.In this paper we describe the data processing methodology applied to the 5776 XMM observations used to construct the current XCS source catalogue.A total of 3675 > 4σ cluster candidates with >50 backgroundsubtracted X-ray counts are extracted from a total non-overlapping area suitable for cluster searching of 410 deg 2 .Of these, 993 candidates are detected with >300 background-subtracted X-ray photon counts, and we demonstrate that robust temperature measurements can be obtained down to this count limit.We describe in detail the automated pipelines used to perform the spectral and surface brightness fitting for these candidates, as well as to estimate redshifts from the X-ray data alone.A total of 587 (122) X-ray temperatures to a typical accuracy of <40 (<10) per cent have been measured to date.We also present the methodology adopted for determining the selection function of the survey, and show that the extended source detection algorithm is robust to a range of cluster morphologies by inserting mock clusters derived from hydrodynamical simulations into real XMMimages.These tests show that the simple isothermal β-profiles is sufficient to capture the essential details of the cluster population detected in the archival XMM observations.

This paper presents the design and characterisation of a front-end prototype ASIC for the ATLAS High Granularity Timing Detector, which is planned for the High-Luminosity phase of the LHC. This prototype, called ALTIROC1, consists of a 5$\times$5-pad matrix and contains the analog part of the single-channel readout (preamplifier, discriminator, two TDCs and SRAM). Two preamplifier architectures (transimpedance and voltage) were implemented and tested. The ASIC was characterised both alone and as a module when connected to a 5$\times$5-pad array of LGAD sensors. In calibration measurements, the ASIC operating alone was found to satisfy the technical requirements for the project, with similar performances for both preamplifier types. In particular, the jitter was found to be 15$\pm$1~ps (35$\pm$1~ps) for an injected charge of 10~fC (4~fC). A degradation in performance was observed when the ASIC was connected to the LGAD array. This is attributed to digital couplings at the entrance of the preamplifiers. When the ASIC is connected to the LGAD array, the lowest detectable charge increased from 1.5~fC to 3.4~fC. As a consequence, the jitter increased for an injected charge of 4~fC. Despite this increase, ALTIROC1 still satisfies the maximum jitter specification (below 65~ps) for the HGTD project. This coupling issue also affects the time over threshold measurements and the time-walk correction can only be performed with transimpedance preamplifiers. Beam test measurements with a pion beam at CERN were also undertaken to evaluate the performance of the module. The best time resolution obtained using only ALTIROC TDC data was 46.3$\pm$0.7~ps for a restricted time of arrival range where the coupling issue is minimized. The residual time-walk contribution is equal to 23~ps and is the dominant electronic noise contribution to the time resolution at 15~fC.

The High-Granularity Timing Detector is a detector proposed for the ATLAS Phase II upgrade. The detector, based on the Low-Gain Avalanche Detector (LGAD) technology, will cover the pseudo-rapidity region of 2.4<|η|<4.0 with two end caps on each side and a total area of 6.4 m2. The timing performance can be improved by implanting an internal gain layer that can produce signals with a fast rising edge. It significantly improves the signal-to-noise ratio. The required average timing resolution per track for a minimum ionizing particle is 30 ps at the start and 50 ps at the end of the HL-LHC operation. This is achieved with several layers of LGAD. The innermost region of the detector would accumulate a 1MeV neutron-equivalent fluence up to 2.5× 1015 neq/cm2 including a safety factor of 1.5 before being replaced during the scheduled shutdowns. The addition of this new detector is expected to play an important role in the mitigation of high pile-ups at the HL-LHC. The layout and performance of the various versions of LGAD prototypes produced by Hamamatsu (HPK) have been studied by the ATLAS Collaboration. The breakdown voltages, depletion voltages, inter-pad gaps, collected charge as well as the time resolution have been measured and the production yield of large size sensors has been evaluated.

This paper studies the radiation hardness of low gain avalanche detector (LGAD) developed by the Novel Device Laboratory (NDL) in Beijing and the Institute of High Energy Physics (IHEP) of Chinese Academy of Sciences, in the context of an upgrade project of the ATLAS detector for the high luminosity phase of LHC. NDL LGAD sensors with different layouts, epitaxial resistivity and doping profile were irradiated up to 1.02 × 1015 neq/cm2 by 70 MeV protons at Cyclotron and Radioisotope Center (CYRIC). The timing resolution of NDL LGAD sensors reached 50 ps and the collected charge reached 3 - 4 fC after irradiation.

A High-Granularity Timing Detector (HGTD) is proposed based on the Low-Gain Avalanche Detector (LGAD) for the ATLAS experiment to satisfy the time resolution requirement for the up-coming High Luminosity at LHC (HL-LHC). We report on beam test results for two proto-types LGADs (BV60 and BV170) developed for the HGTD. Such modules were manufactured by the Institute of High Energy Physics (IHEP) of Chinese Academy of Sciences (CAS) collaborated with Novel Device Laboratory (NDL) of the Beijing Normal University. The beam tests were performed with 5 GeV electron beam at DESY. The timing performance of the LGADs was compared to a trigger counter consisting of a quartz bar coupled to a SiPM readout while extracting reference SiPM by fitting with a Gaussian function. The time resolution was obtained as 41 ps and 63 ps for the BV60 and the BV170, respectively.

Abstract The High Granularity Timing Detector (HGTD) will be installed in the ATLAS detector to mitigate pile-up effects during the High Luminosity (HL) upgrade of the Large Hadron Collider (LHC) at CERN. The design of the HGTD is based on the use of Low Gain Avalanche Detectors (LGADs), with an active thickness of 50 μm, that allow to measure with high-precision the time of arrival of particles. The HGTD will improve the particle-vertex assignment by measuring the track time with a resolution ranging from approximately 30 ps at the beginning of the HL-LHC operations to 50 ps at the end. Performances of several unirradiated, as well as neutron- and proton-irradiated, LGAD sensors from different vendors have been measured in beam test campaigns during the years 2018 and 2019 at CERN SPS and DESY. This paper presents the results obtained with data recorded by an oscilloscope synchronized with a beam telescope which provides particle position information within a resolution of a few μm. Collected charge, time resolution and hit efficiency are presented. In addition to these properties, the charge uniformity is also studied as a function of the position of the incident particle inside the sensor pad.

We report on the results of a radiation campaign with neutrons and protons of Low Gain Avalanche Detectors (LGAD) produced by Hamamatsu (HPK) as prototypes for the High-Granularity Timing Detector (HGTD) in ATLAS. Sensors with an active thickness of 50μm were irradiated in steps of roughly 2× up to a fluence of 3×1015neqcm−2. As a function of the fluence, the collected charge and time resolution of the irradiated sensors will be reported for operation at −30 °C.

The use of data-intensive methods for tasks which impact peoples’ lives continues to accelerate. This has resulted in several high-profile, seemingly avoidable, ethical mistakes. Despite this, those with the power to change how data science is developed can lack the incentives, training, or support, to properly consider the impacts of their work. This scrutiny is also not often provided by review boards, whose focus tends to be on the protection of human participants rather than downstream outcomes. Supporting data scientists and technical staff to consider worst-case scenarios, and facilitate discussions with ethics experts and those impacted by their methods, could allow us to work together across disciplinary boundaries to identify and avoid possible negative outcomes. A selected shared vocabulary could overcome two known barriers to such interdisciplinary conversations: a mismatched vocabulary and a lack of an accessible structure for discussions. This paper presents the Data Hazards project, which contains a shared, controlled vocabulary of 11 data ethics issues, presented as ‘labels’ which represent potential negative outcomes of data science work. Similarly to chemical hazard labels, the Data Hazards serve as a warning of a potential risk, and encourage adoption of appropriate safety measures. The labels were co-created as an open-source project, where they will continue to evolve over time with input from various communities. In this paper we present version 1.0.We present the 11 current labels, each consisting of: an image, description, examples of when it applies, and crucially, safety precautions that provide concrete steps to address concerns. The project provides documentation for using these labels that supports technical decision-makers to consider the perspectives of a diverse audience on these issues, through workshops or asynchronously. The ‘alpha’ set of Data Hazards were evaluated through a series of workshops, with participants (N=47). In these workshops participants saw a presentation on one of five data science projects and applied the labels to them before and after a structured reflective discussion. The projects covered a range of data science applications from data collection to natural language processing. Overall, 94% of participants found the labels useful, 92% found the concepts clear, and 72% thought that they were easy to apply to a real project. Most workshop participants (89%) found the reflective discussion format useful, and we include reflections from two project owners on their experience of presenting their work.

A search for squarks and gluinos in nal states with at least two leptons (electrons or muons) is presented. Events are selected using the Razor variables to discriminate between signal and background processes. This analysis is performed over the full 2012 dataset of proton-proton collisions at 8 TeV centre-of-mass energy, totalling an integrated luminosity of 20:3 fb-1 recorded by the ATLAS experiment at the CERN Large Hadron Collider. In the absence of any signicant excess with respect to the Standard Model expectation, exclusion limits are derived in the context of several supersymmetry-inspired simplied model topologies involving the direct production of squarks and gluinos.

A search for supersymmetry in di-lepton final states using the razor variables with the ATLAS detector