In 2017, CMS has installed a new pixel detector with 124M channels that features full 4-hit coverage in the tracking volume (|η|<2.5) and is capable to withstand instantaneous luminosities of ...2ċ1034cm−2s−1 and beyond. By now the detector has been successfully operated for two years in proton and heavy ion collisions. In this time, many improvements of the DAQ system, the detector monitoring capabilities, and silicon property modelling have been made. Very valuable experience has been collected in running a detector with DC-DC powering and CO2 cooling, which are both new core technologies for most of the upcoming detector upgrades at LHC experiments. During the long shutdown of LHC from 2019 to 2021 the CMS pixel detector will be extracted and the modules of the innermost layer that suffered the most from radiation damage will be replaced. At that occasion a better readout chip as well as a new communication chip will be used for these modules, which fixes problems observed during operation. This paper will give an overview of the different improvements that have been made and the challenges that have been faced in the last two years. A special focus will be put on the lessons learned in the light of the design of future detectors. Finally, the planned work on the CMS pixel detector during the LHC shutdown will be outlined.
Polarised electron and positron beams are key ingredients to the physics programme of future linear colliders. Due to the chiral nature of weak interactions in the Standard Model - and possibly ...beyond - the knowledge of the luminosity-weighted average beam polarisation at the e super(+)e super(-) interaction point is of similar importance as the knowledge of the luminosity and has to be controlled to permille-level precision in order to fully exploit the physics potential. The current concept to reach this challenging goal combines measurements from Laser-Compton polarimeters before and after the interaction point with measurements at the interaction point. A key element for this enterprise is the understanding of spin-transport effects between the polarimeters and the interaction point as well as collision effects. We show that without collisions, the polarimeters can be cross-calibrated to 0.1 %, and we discuss in detail the impact of collision effects and beam parameters on the polarisation value relevant for the interpretation of the e super(+)e super(-) collision data.
The International Linear Collider (ILC) is a future electron/positron collider at the energy frontier. Its physics goals are clearly focused on precision measurements at the electroweak scale and ...beyond. Beam energy and beam polarisation are two important beam parameters, which need to be measured and monitored to any possible precision. We discuss in this publication the foreseen concepts of beam energy and beam polarisation measurement at the ILC. Two Compton polarimeters per beam line will determine the beam polarisation. The anticipated precision of this measurement amounts to Delta scriptP/scriptP = 2.5 x 10 super(-3), which is a challenging goal putting highest demands on detector alignment and linearity. Recent detector developments as well as a detector calibration technique are described, which allow for meeting these requirements. The beam energy is measured before and after the interaction point to a targeted precision of Delta E/E = 10 super(-4). Thereby, the two foreseen concepts are introduced: a noninvasive energy spectrometer based on beam position monitors is planned to be operated before the interaction region. Behind, a synchrotron radiation imaging detector will allow not only for measuring the beam energy, but also gives access to the beam energy spread of the (disrupted) beam.
Abstract
The FASER experiment is a new small and inexpensive experiment that is placed 480 meters downstream of the ATLAS experiment at the CERN LHC. FASER is designed to capture decays of new ...long-lived particles, produced outside of the ATLAS detector acceptance. These rare particles can decay in the FASER detector together with about 500–1000 Hz of other particles originating from the ATLAS interaction point. A very high efficiency trigger and data acquisition system is required to ensure that the physics events of interest will be recorded. This paper describes the trigger and data acquisition system of the FASER experiment and presents performance results of the system acquired during initial commissioning.
Polarimetry with permille-level precision is essential for future electron-positron linear colliders. Compton polarimeters can reach negligible statistical uncertainties within seconds of measurement ...time. The dominating systematic uncertainties originate from the response and alignment of the detector which records the Compton scattered electrons. The robust baseline technology for the Compton polarimeters foreseen at future linear colliders is based on an array of gas Cherenkov detectors read out by photomultipliers. In this paper, we will present a calibration method which promises to monitor nonlinearities in the response of such a detector at the level of a few permille. This method has been implemented in an LED-based calibration system which matches the existing prototype detector. The performance of this calibration system is sufficient to control the corresponding contribution to the total uncertainty on the extracted polarisation to better than 0.1%.
A group of Early-Career Researchers (ECRs) has been given a mandate from the European Committee for Future Accelerators (ECFA) to debate the topics of the current European Strategy Update (ESU) for ...Particle Physics and to summarise the outcome in a brief document 1. A full-day debate with 180 delegates was held at CERN, followed by a survey collecting quantitative input. During the debate, the ECRs discussed future colliders in terms of the physics prospects, their implications for accelerator and detector technology as well as computing and software. The discussion was organised into several topic areas. From these areas two common themes were particularly highlighted by the ECRs: sociological and human aspects; and issues of the environmental impact and sustainability of our research.
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