G. Steinbrück

The impact of electron hole plasmas on silicon sensor performance was studied with a multi-channel Transient Current Technique (mTCT) setup. Electron hole densities of up to 1016 cm−3 (equivalent to 105 focused 12 keV photons) were created with sub-ns lasers (660 and 1015 nm) and the time resolved current pulses of segmented sensors (4 channels simultaneously) were read out by a 2.5 GHz oscilloscope. Measurements for strip sensors of 280μm thickness and 80μm pitch as well as 450μm thickness and 50μm pitch were carried out showing an increase of the charge collection time and an increase of the charge spread (charge cloud explosion) with increased charge carrier density. These effects were studied as a function of the applied bias voltage and electron hole density. It was shown that for the current AGIPD sensor design plasma effects in p-in-n sensors of 450μm thickness are negligible if at least 500 V bias is applied.

Abstract The high-luminosity upgrade of the LHC brings unprecedented requirements for real-time and precision bunch-by-bunch online luminosity measurement and beam-induced background monitoring. A key component of the CMS Beam Radiation, Instrumentation and Luminosity system is a stand-alone luminometer, the Fast Beam Condition Monitor (FBCM), which is fully independent from the CMS central trigger and data acquisition services and able to operate at all times with a triggerless readout. FBCM utilizes a dedicated front-end application-specific integrated circuit (ASIC) to amplify the signals from CO 2 -cooled silicon-pad sensors with a timing resolution of a few nanoseconds, which enables the measurement of the beam-induced background. FBCM uses a modular design with two half-disks of twelve modules at each end of CMS, with four service modules placed close to the outer edge to reduce radiation-induced aging. The electronics system design adapts several components from the CMS Tracker for power, control and read-out functionalities. The dedicated FBCM23 ASIC contains six channels and adjustable shaping time to optimize the noise with regards to sensor leakage current. Each ASIC channel outputs a single binary high-speed asynchronous signal carrying time-of-arrival and time-over-threshold information. The chip output signal is digitized, encoded, and sent via a radiation-hard gigabit transceiver and an optical link to the back-end electronics for analysis. This paper reports on the updated design of the FBCM detector and the ongoing testing program.

The LHC is planning an upgrade program which will bring the luminosity up to about 7.5×1034cm−2s−1 in 2027, with the goal of delivering an integrated luminosity of 3000 or even 4000 fb−1 by the end of 2037. This High Luminosity phase, HL-LHC, will present new challenges of higher data rates and unprecedented radiation levels for the pixel detector. A fluence of 2.3×1016neq/cm2, or equivalently 12 MGy, is expected for the inner layer of the CMS Inner Tracker (IT) for 3000 fb−1 of integrated luminosity. To maintain or even improve the performance of the present system, new technologies have to be exploited for the so-called Phase-2 upgrade. Among them is the future version of front-end chips in 65 nm CMOS technology by the CERN RD53 Collaboration, which supports small pixel sizes of 50 × 50 or 100×25μm2 and low pixel charge thresholds (≈1000 e−). Thin planar n-in-p type silicon sensors with a thickness of the active layer of 150 μm, segmented into pixel sizes of 100×25μm2 or 50×50μm2, will be used throughout most of the IT. They have been shown to allow for a good detector resolution that is much more stable with respect to radiation damage compared to the Phase-1 detector. CMS has launched several R&D submissions for the development of suitable planar silicon sensors at Hamamatsu Photonics K.K. and FBK Trento. We present results for measurements on such prototype sensors bump bonded to the RD53A prototype chip developed by the RD53 Collaboration at CERN. Different pixel cell designs are compared and evaluated in beam tests at CERN, DESY and FNAL for spatial resolution and hit efficiency at various track angles before and after irradiation. As an example, hit efficiencies of 99% at vertical incidence were reached after irradiation to 5×1015neq/cm2, which corresponds to the layer 2 lifetime fluence of the CMS IT.

Results of an extensive R&D program aiming at radiation hard, small pitch, 3D pixel sensors are reported. The CMS experiment is supporting this R&D in the scope of the Inner Tracker upgrade for the High Luminosity phase of the CERN Large Hadron Collider (HL-LHC). In the HL-LHC the Inner Tracker will have to withstand an integrated fluence up to 2.3×1016neq/cm2. A small number of 3D sensors were interconnected with the RD53A readout chip, which is the first prototype of 65 nm CMOS pixel readout chip designed for the HL-LHC pixel trackers. In this paper results obtained in beam tests before and after irradiation are reported. The irradiation of a single chip module was performed up to a maximum equivalent fluence of about 1×1016neq/cm2. The analysis of the collected data shows excellent performance: the spatial resolution in not irradiated sensors can reach about 3 to 5 μm, for inclined tracks, depending on the pixel pitch. The measured hit detection efficiencies are close to 99% measured both before and after the above mentioned irradiation fluence.

The positions of the silicon modules of the CMS tracker will be known to O(100 μm) from survey measurements, mounting precision and the hardware alignment system. However, in order to fully exploit the capabilities of the tracker, these positions need to be known to a precision of a few μm. Only a track-based alignment procedure can reach this required precision. Such an alignment procedure is a major challenge given that about 50000 geometry constants need to be measured. Making use of the novel χ2 minimization program Millepede II an alignment strategy has been developed in which all detector components are aligned simultaneously and all correlations between their position parameters taken into account. Different simulated data, such as Z0 decays and muons originated in air showers were used for the study. Additionally information about the mechanical structure of the tracker, and initial position uncertainties have been used as input for the alignment procedure. A proof of concept of this alignment strategy is demonstrated using simulated data.

During the high luminosity phase of the LHC starting around 2020 (HL-LHC), the machine is expected to deliver an instantaneous luminosity of 5·10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">34</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . A total of 3000 fb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> of data is foreseen to be delivered, hereby increasing the discovery potential of the LHC experiments significantly. However, the radiation dose of the inner tracking systems will be severe, requiring new radiation hard sensors for the CMS tracker. Up to now, typically p-in-n float-zone devices with a thickness of at least 300 micrometers have been used for silicon strip detectors at CMS and other experiments. However, the signal-to-noise ratio for sensors implemented in this technology would be severely reduced for the inner layers of the tracker at the HL-LHC. Many measurements are described in literature, performed on a variety of silicon materials and technologies, but they are often hard to compare, because they were done under different conditions. To systematically compare the properties of different silicon materials and design choices and identify a solution suited for the upgrade, CMS has initiated a large irradiation and measurement campaign. Several test structures and sensors have been designed and implemented on 18 different combinations of wafer materials, thicknesses and production technologies. The structures are electrically characterized before and after irradiation with different fluences of neutrons and protons, corresponding to the expected fluences at different radii of the outer tracker after 3000 fb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The tests performed include studies with β-sources, lasers and beam tests. In this talk, results from the ongoing campaign are presented.

The positions of the silicon modules of the CMS tracker will be known to 0(100 μm) from survey measurements, mounting precision and the hardware alignment system. However, in order to fully exploit the capabilities of the tracker, these positions need to be known to a precision of a few μm. Only a track-based alignment procedure can reach this required precision. Such an alignment procedure is a major challenge given that about 50.000 geometry constants need to be measured. Making use of the novel χ2 minimization program Millepede II an alignment strategy has been developed in which all detector components are aligned simultaneously and all correlations between their position parameters taken into account. Tracks from different sources such as Z0 decays and cosmic ray muons, plus information about the mechanical structure of the tracker, and initial position uncertainties have been used as input for the alignment procedure. A proof of concept of this alignment strategy is demonstrated using simulated data.

A new pixel detector for the CMS experiment was built in order to cope with the instantaneous luminosities anticipated for the Phase~I Upgrade of the LHC. The new CMS pixel detector provides four-hit tracking with a reduced material budget as well as new cooling and powering schemes. A new front-end readout chip mitigates buffering and bandwidth limitations, and allows operation at low comparator thresholds. In this paper, comprehensive test beam studies are presented, which have been conducted to verify the design and to quantify the performance of the new detector assemblies in terms of tracking efficiency and spatial resolution. Under optimal conditions, the tracking efficiency is $99.95\pm0.05\,\%$, while the intrinsic spatial resolutions are $4.80\pm0.25\,\mu \mathrm{m}$ and $7.99\pm0.21\,\mu \mathrm{m}$ along the $100\,\mu \mathrm{m}$ and $150\,\mu \mathrm{m}$ pixel pitch, respectively. The findings are compared to a detailed Monte Carlo simulation of the pixel detector and good agreement is found.

The topic of the paper is the position reconstruction from signals of segmented detectors. With the help of a simple simulation, it is shown that the position reconstruction using the centre-of-gravity method is strongly biased, if the width of the charge (or e.g. light) distribution at the electrodes (or photo detectors) is less than the read-out pitch. A method is proposed which removes this bias for events with signals in two or more read-out channels and thereby improves the position resolution. The method also provides an estimate of the position–response function for every event. Examples are given for which its width as a function of the reconstructed position varies by as much as an order of magnitude. A fast Monte Carlo program is described which simulates the signals from a silicon pixel detector traversed by charged particles under different angles, and the results obtained with the proposed reconstruction method and with the centre-of-gravity method are compared. The simulation includes the local energy-loss fluctuations, the position-dependent electric field, the diffusion of the charge carriers, the electronics noise and charge thresholds for clustering, A comparison to test-beam-data is used to validate the simulation.

In this work, charge collection profiles of non-irradiated and irradiated 150 µm thick p-type pad diodes were measured using a 5.2 GeV electron beam traversing the diode parallel to the readout electrode. Four diodes were irradiated to 1 MeV neutron equivalent fluences of 2, 4, 8, and 12 × 1015 cm−2 with 23 MeV protons. The Charge Collection Efficiency profiles as a function of depth are extracted by unfolding the data. The results of the measurements are compared to the TCAD device simulation using three radiation damage models from literature which were tuned to different irradiation types and fluences.

We present a measurement of the electron angular distribution parameter $\alpha_2$ in $W \to e\nu$ events using data collected by the D0 detector during the 1994{1995 Tevatron run. We compare our results with next-to-leading order perturbative QCD, which predicts an angular distribution of ($1 \pm \alpha_1 cos \theta^* + \alpha_2 cos^2 \theta^*$), where $\theta^*$ is the angle between the charged lepton and the antiproton in the Collins- Soper frame. In the presence of QCD corrections, the parameters $\alpha_1$ and $\alpha_2$ become functions of $p^W_T$ , the W boson transverse momentum. We present the first measurement of $\alpha_2$ as a function of $p^W_T$ . This measurement is of importance, because it provides a test of next-to-leading order QCD corrections which are a non-negligible contribution to the W mass measurement

We describe a trigger preprocessor to be used by the DØ experiment for selecting events with tracks from the decay of long-lived particles. This Level 2 impact parameter trigger utilizes information from the Silicon Microstrip Tracker to reconstruct tracks with improved spatial and momentum resolutions compared to those obtained by the Level 1 tracking trigger. It is constructed of VME boards with much of the logic existing in programmable processors. A common motherboard provides the I/O infrastructure and three different daughter boards perform the tasks of identifying the roads from the tracking trigger data, finding the clusters in the roads in the silicon detector, and fitting tracks to the clusters. This approach provides flexibility for the design, testing and maintenance phases of the project. The track parameters are provided to the trigger framework in 25μs. The effective impact parameter resolution for high-momentum tracks is 35μm, dominated by the size of the Tevatron beam.

The Central European Consortium designed and prototyped generic test structures (TS) in a R&D study to allow standard monitoring of the process quality of silicon sensors of any given vendor. Furthermore, some novel signal routing strategies for silicon sensors have been applied on the wafers to achieve an implementation of a pitch adapter directly in the sensor, either in the first metal layer or in a second additional metal routing layer. These improvements would allow to connect the readout chip directly to the sensor, omitting an additional pitch adapter. The on-sensor pitch adapter would be reflected by a substantial material budget saving which would be of special interest for the tracking detectors at the super-LHC. After a first batch of improved TS was produced in 2007, a second batch of enhanced TS and additional sensors, with integrated pitch adapters, has been produced by the Institute of Electron Technology in Warsaw, Poland. Some improvements of the TS and the designs of the sensors will be shown. Afterwards a selection of measurements on TS and sensors will be discussed as well as a testbeam and its first results.

The CMS experiment intends to exchange the pixel detector for the high luminosity phase of the Large Hadron Collider (HL-LHC). Therefore, a large R&D effort has been started in order to develop sensors capable of withstanding the expected extremely high radiation damage. The targeted integrated luminosity of 3000 fb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , estimated for 10 years of operation at the design center-of-mass energy of 14 TeV, translates into an equivalent NIEL (Non-Ionizing Energy Loss) of 2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> neq cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> and an IEL (Ionizing Energy Loss) dose in the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> of 5 MGy at the expected position of the innermost pixel detector layer. The CMS collaboration has undertaken two sensor R&D programs on thin n-in-p planar and 3D silicon sensor technologies. To cope with the increase in instantaneous luminosity, the pixel area has to be reduced to approximately 2500 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> to keep the occupancy at the percent level. Suggested pixel cell geometries to match this requirement are 50 × 50 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> or 25 × 100 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , leaving little space for design choices and a possible biasing scheme. Monte Carlo studies comparing the hit resolution for these two scenarios are presented. CMS has initiated the production of test-sensors with the envisaged pixel geometries. Status, progress, and prospects of this effort are discussed.

Abstract As a result of the high luminosity phase of the SLHC, for CMS a tracking system with very high granularity is mandatory and the sensors will have to withstand an extreme radiation environment of up to 10 16  part/ 2 . On this basis, a new geometry with silicon short strip sensors (strixels) is proposed. To understand their performances, test geometries are developed whose parameters can be verified and optimized using simulation of semiconductor structures. We have used the TCAD-ISE (SYNOPSYS package) software in order to simulate the main electrical parameters of different strip geometries, for p-in-n-type wafers.

The LHC is planning an upgrade program which will bring the luminosity up to about 7.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">34</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> in 2026, with the goal of an integrated luminosity of 3000 fb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> by the end of 2037. This High Luminosity scenario, HL-LHC, will present new challenges of higher data rates and unprecedented radiation levels for the CMS Inner Tracker (IT): Φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eq</sub> = 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , and 10 MGy, are expected at the inner layer of the pixel detector for 3000 fb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> integrated luminosity. To maintain or even improve the performance of the present vertex detector, new technologies have to be fully exploited for the so-called Phase-2 upgrade. Among them is the future version of front-end chips in 65-nm CMOS by the CERN RD53 Collaboration which supports small pixel sizes of 50 × 50 or 25 ×100 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and lower charge thresholds ≈ 1000 e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> ).Thin planar n-in-p type silicon sensors (of thickness 100-150 μm), segmented into pixel sizes of 25 × 100 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> or 50 × 50 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , are expected to allow for a good detector resolution that is expected to be more robust with respect to radiation damage compared to the Phase-1 detector. For the innermost detector layer, the option to use 3D silicon sensors is pursued, offering intrinsically higher radiation resistance because of the combination of a short charge collection distance with relatively thick sensors.CMS has launched several R&D submissions for the development of suitable silicon sensors at HPK photonics and FBK Trento (planar), and FBK Trento and CNM (3D sensors). We will present results for measurements on such prototype sensors bump bonded to the ROC4Sens R&D readout chip from PSI, Switzerland, and to the RD53A prototype chip, developed by the RD53 Collaboration at CERN. Different pixel cell designs are compared and evaluated in testbeams at DESY and CERN for charge collection, efficiency and spatial resolution before and after irradiation.

In this article we summarize the impact of misalignment of tracking detectors and muon systems on physics measurements. Studies from the ATLAS, CMS, and LHCb collaborations are presented.

During the high luminosity phase of the LHC starting around 2025 (HL-LHC), the machine is expected to deliver an instantaneous luminosity of 5 · 1034 cm-2s-1. A total of 3000 fb-1 of data is foreseen to be delivered, hereby increasing the physics potential of the LHC experiments significantly. However, this fivefold increase in luminosity compared to the design luminosity of the LHC will lead to a higher track multiplicity in the silicon tracking detectors of the experiments, and to severe radiation levels. In order to maintain physics capability, CMS will build a completely new tracking detector comprising a pixel detector and an outer tracker. Furthermore, information from the outer tracker will be used in the first level trigger of CMS to ensure a sufficient trigger rejection. For this purpose, CMS will use so-called pT modules which will provide a momentum measurement at the module level. These modules consist of two back-to-back strip sensors for the outer layers, and a strip sensor and a macro-pixel sensor for the inner layers, respectively. This paper will introduce the concept of pT modules and give an overview of the ongoing research and development activities concerning radiation hard silicon sensor materials.

While the tracking detectors of the ATLAS and CMS experiments have shown excellent performance in Run 1 of LHC data taking, and are expected to continue to do so during LHC operation at design luminosity, both experiments will have to exchange their tracking systems when the LHC is upgraded to the high-luminosity LHC (HL-LHC) around the year 2024. The new tracking systems need to operate in an environment in which both the hit densities and the radiation damage will be about an order of magnitude higher than today. In addition, the new trackers need to contribute to the first level trigger in order to maintain a high data-taking efficiency for the interesting processes. Novel detector technologies have to be developed to meet these very challenging goals. The German groups active in the upgrades of the ATLAS and CMS tracking systems have formed a collaborative "Project on Enabling Technologies for Silicon Microstrip Tracking Detectors at the HL-LHC" (PETTL), which was supported by the Helmholtz Alliance "Physics at the Terascale" during the years 2013 and 2014. The aim of the project was to share experience and to work together on key areas of mutual interest during the R&amp;D phase of these upgrades. The project concentrated on five areas, namely exchange of experience, radiation hardness of silicon sensors, low mass system design, automated precision assembly procedures, and irradiations. This report summarizes the main achievements.

This chapter contains sections titled: The Standard Model at Born Level The Gain from Additional Precision Measurements Constraints from Precision Data References

Pixelated silicon detectors are state-of-the-art technology to achieve precise tracking and vertexing at collider experiments, designed to accurately measure the hit position of incoming particles in high rate and radiation environments. The detector requirements become extremely demanding for operation at the High-Luminosity LHC, where up to 200 interactions will overlap in the same bunch crossing on top of the process of interest. Additionally, fluences up to 2.3 10^16 cm^-2 1 MeV neutron equivalent at 3.0 cm distance from the beam are expected for an integrated luminosity of 3000 fb^-1. In the last decades, the pixel pitch has constantly been reduced to cope with the experiment's needs of achieving higher position resolution and maintaining low pixel occupancy per channel. The spatial resolution improves with a decreased pixel size but it degrades with radiation damage. Therefore, prototype sensor modules for the upgrade of the experiments at the HL-LHC need to be tested after being irradiated. This paper describes position resolution measurements on planar prototype sensors with 100x25 um^2 pixels for the CMS Phase-2 Upgrade. It reviews the dependence of the position resolution on the relative inclination angle between the incoming particle trajectory and the sensor, the charge threshold applied by the readout chip, and the bias voltage. A precision setup with three parallel planes of sensors has been used to investigate the performance of sensors irradiated to fluences up to F_eq = 3.6 10^15 cm-2. The measurements were performed with a 5 GeV electron beam. A spatial resolution of 3.2 +\- 0.1 um is found for non-irradiated sensors, at the optimal angle for charge sharing. The resolution is 5.0 +/- 0.2 um for a proton-irradiated sensor at F_eq = 2.1 10^15 cm-2 and a neutron-irradiated sensor at F_eq = 3.6 10^15 cm^-2.

Many physics topics to be studied by the D0 experiment during Run II of the Fermilab Tevatron ppbar collider give rise to final states containing b--flavored particles. Examples include Higgs searches, top quark production and decay studies, and full reconstruction of B decays. The sensitivity to such modes has been significantly enhanced by the installation of a silicon based vertex detector as part of the DO detector upgrade for Run II. Interesting events must be identified initially in 100-200 microseconds to be available for later study. This paper describes custom electronics used in the DO trigger system to provide the real--time identification of events having tracks consistent with the decay of b--flavored particles.

The CMS experiment at the Large Hadron Collider at CERN is in the last phase of its construction. The harsh radiation environment at LHC will put strong demands in radiation hardness to the innermost parts of the detector. To assess the performance of irradiated silicon microstrip detector modules, a testbeam was conducted at the Testbeam 22 facility of the DESY research center. The primary objective was the signal-to-noise measurement of fully irradiated CMS Tracker modules to ensure their functionality up to 10 years of LHC operation. The paper briefly summarises the basic setup at the facility and the hardware and software used to collect and analyse the data. Some interesting subsidiary results are shown, which confirm the expected behaviour of the detector with respect to the signal-to-noise performance over the active detector area and for different electron energies. The main focus of the paper are the results of the signal-to-noise over reverse bias voltage measurements for CMS Tracker Modules which were exposed to different radiation doses.

Many physics topics to be studied by the D0 experiment during Run II of the Fermilab Tevatron ppbar collider give rise to final states containing b--flavored particles. Examples include Higgs searches, top quark production and decay studies, and full reconstruction of B decays. The sensitivity to such modes has been significantly enhanced by the installation of a silicon based vertex detector as part of the DO detector upgrade for Run II. Interesting events must be identified initially in 100-200 microseconds to be available for later study. This paper describes custom electronics used in the DO trigger system to provide the real--time identification of events having tracks consistent with the decay of b--flavored particles.

Pixelated silicon detectors are state-of-the-art technology to achieve precise tracking and vertexing at collider experiments, designed to accurately measure the hit position of incoming particles in high rate and radiation environments. The detector requirements become extremely demanding for operation at the High-Luminosity LHC, where up to 200 interactions will overlap in the same bunch crossing on top of the process of interest. Additionally, fluences up to 2.3 10^16 cm^-2 1 MeV neutron equivalent at 3.0 cm distance from the beam are expected for an integrated luminosity of 3000 fb^-1. In the last decades, the pixel pitch has constantly been reduced to cope with the experiment's needs of achieving higher position resolution and maintaining low pixel occupancy per channel. The spatial resolution improves with a decreased pixel size but it degrades with radiation damage. Therefore, prototype sensor modules for the upgrade of the experiments at the HL-LHC need to be tested after being irradiated. This paper describes position resolution measurements on planar prototype sensors with 100x25 um^2 pixels for the CMS Phase-2 Upgrade. It reviews the dependence of the position resolution on the relative inclination angle between the incoming particle trajectory and the sensor, the charge threshold applied by the readout chip, and the bias voltage. A precision setup with three parallel planes of sensors has been used to investigate the performance of sensors irradiated to fluences up to F_eq = 3.6 10^15 cm-2. The measurements were performed with a 5 GeV electron beam. A spatial resolution of 3.2 +\- 0.1 um is found for non-irradiated sensors, at the optimal angle for charge sharing. The resolution is 5.0 +/- 0.2 um for a proton-irradiated sensor at F_eq = 2.1 10^15 cm-2 and a neutron-irradiated sensor at F_eq = 3.6 10^15 cm^-2.

We present the first measurement of the electron angular distribution parameter α 2 in W → e ν events in proton-antiproton collisions as a function of the W boson transverse momentum. Our analysis is based on data collected using the DØ detector during the 1994–1995 Fermilab Tevatron run. We compare our results with next-to-leading order perturbative QCD, which predicts an angular distribution of (1 ± α 1 cos θ * + α 2 cos 2 θ * ), where θ * is the polar angle of the electron in the Collins-Soper frame and α 1 and α 2 are functions of [Formula: see text], the W boson transverse momentum. This measurement provides a test of next-to-leading order QCD corrections which are a non-negligible contrbution to the W boson mass measurement.

Results of the analysis from data taken during a 1997 testbeam at Fermilab are presented. The performance of Si microstrip detectors are studied which will be used in the Silicon Tracker that is part of the upgrade of the DO detector currently under way. Special consideration is given to modeling of the drift of charge clusters in a magnetic field.