Precision Muon Tracking Detectors for High-Energy Hadron Colliders

Small-diameter muon drift tube (sMDT) chambers with 15 mm tube diameter are a cost-effective technology for high-precision muon tracking over large areas at high background rates as expected at future high-energy hadron colliders including HL-LHC. The chamber design and construction procedures have been optimized for mass production and provide sense wire positioning accuracy of better than 10 ?m. The rate capability of the sMDT chambers has been extensively tested at the CERN Gamma Irradiation Facility. It exceeds the one of the ATLAS muon drift tube (MDT) chambers, which are operated at unprecedentedly high background rates of neutrons and gamma-rays, by an order of magnitude, which is sufficient for almost the whole muon detector acceptance at FCC-hh at maximum luminosity. sMDT operational and construction experience exists from ATLAS muon spectrometer upgrades which are in progress or under preparation for LHC Phase 1 and 2

Construction and Test of New Precision Drift-Tube Chambers for the ATLAS Muon Spectrometer

ATLAS muon detector upgrades aim for increased acceptance for muon triggering and precision tracking and for improved rate capability of the muon chambers in the high-background regions of the detector with increasing LHC luminosity. The small-diameter Muon Drift Tube (sMDT) chambers have been developed for these purposes. With half of the drift-tube diameter of the MDT chambers and otherwise unchanged operating parameters, sMDT chambers share the advantages of the MDTs, but have an order of magnitude higher rate capability and can be installed in detector regions where MDT chambers do not fit in. The chamber assembly methods have been optimized for mass production, minimizing construction time and personnel. Sense wire positioning accuracies of 5 ?micons have been achieved in serial production for large-size chambers comprising several hundred drift tubes. The construction of new sMDT chambers for installation in the 2016/17 winter shutdown of the LHC and the design of sMDT chambers in combination with new RPC trigger chambers for replacement of the inner layer of the barrel muon spectrometer are in progress

Precision Muon Tracking at Future Hadron Colliders with sMDT Chambers

Small-diameter muon drift tube (sMDT) chambers are a cost-effective technology for high-precision muon tracking. The rate capability of the sMDT chambers has been extensively tested at the Gamma Irradiation Facility at CERN in view of expected rates at future high-energy hadron colliders. Results show that it fulfills the requirements over most of the acceptance of muon detectors. The optimization of the read-out electronics to further increase the rate capability of the detectors is discussed. Chambers of this type are under construction for upgrades of the muon spectrometer of the ATLAS detector at high LHC luminosities. Design and construction procedures have been optimized for mass production while providing a precision of better than 10 micrometers in the sense wire positions and the mechanical stability required to cover large areas.Comment: 5 pages, 12 figures; conference proceedings for IEEE NSS & MIC conference, San Diego, 201

High Rate Proton Irradiation of 15mm Muon Drifttubes

Future LHC luminosity upgrades will significantly increase the amount of background hits from photons, neutrons and protons in the detectors of the ATLAS muon spectrometer. At the proposed LHC peak luminosity of 5*10^34 1/cm^2s, background hit rates of more than 10 kHz/cm^2 are expected in the innermost forward region, leading to a loss of performance of the current tracking chambers. Based on the ATLAS Monitored Drift Tube chambers, a new high rate capable drift tube detecor using tubes with a reduced diameter of 15mm was developed. To test the response to highly ionizing particles, a prototype chamber of 46 15mm drift tubes was irradiated with a 20 MeV proton beam at the tandem accelerator at the Maier-Leibnitz Laboratory, Munich. Three tubes in a planar layer were irradiated while all other tubes were used for reconstruction of cosmic muon tracks through irradiated and non-irradiated parts of the chamber. To determine the rate capability of the 15mm drift-tubes we investigated the effect of the proton hit rate on pulse height, efficiency and spatial resolution of the cosmic muon signals

Optimisation of the Read-out Electronics of Muon Drift-Tube Chambers for Very High Background Rates at HL-LHC and Future Colliders

In the ATLAS Muon Spectrometer, Monitored Drift Tube (MDT) chambers and sMDT chambers with half of the tube diameter of the MDTs are used for precision muon track reconstruction. The sMDT chambers are designed for operation at high counting rates due to neutron and gamma background irradiation expected for the HL-LHC and future hadron colliders. The existing MDT read-out electronics uses bipolar signal shaping which causes an undershoot of opposite polarity and same charge after a signal pulse. At high counting rates and short electronics dead time used for the sMDTs, signal pulses pile up on the undershoot of preceding background pulses leading to a reduction of the signal amplitude and a jitter in the drift time measurement and, therefore, to a degradation of drift tube efficiency and spatial resolution. In order to further increase the rate capability of sMDT tubes, baseline restoration can be used in the read-out electronics to suppress the pile-up effects. A discrete bipolar shaping circuit with baseline restoration has been developed and used for reading out sMDT tubes under irradiation with a 24 MBq 90Sr source. The measurements results show a substantial improvement of the performance of the sMDT tubes at high counting rates

Performance of Drift-Tube Detectors at High Counting Rates for High-Luminosity LHC Upgrades

The performance of pressurized drift-tube detectors at very high background rates has been studied at the Gamma Irradiation Facility (GIF) at CERN and in an intense 20 MeV proton beam at the Munich Van-der-Graaf tandem accelerator for applications in large-area precision muon tracking at high-luminosity upgrades of the Large Hadron Collider (LHC). The ATLAS muon drifttube (MDT) chambers with 30 mm tube diameter have been designed to cope with and neutron background hit rates of up to 500 Hz/square cm. Background rates of up to 14 kHz/square cm are expected at LHC upgrades. The test results with standard MDT readout electronics show that the reduction of the drift-tube diameter to 15 mm, while leaving the operating parameters unchanged, vastly increases the rate capability well beyond the requirements. The development of new small-diameter muon drift-tube (sMDT) chambers for LHC upgrades is completed. Further improvements of tracking efficiency and spatial resolution at high counting rates will be achieved with upgraded readout electronics employing improved signal shaping for high counting rates

Antiferromagnetic interlayer exchange coupling across an amorphous metallic spacer layer

By means of magneto-optical Kerr effect we observe for the first time antiferromagnetic coupling between ferromagnetic layers across an amorphous metallic spacer layer. Biquadratic coupling occurs at the transition from a ferromagnetically to an antiferromagnetically coupled region. Scanning tunneling microscopy images of all involved layers are used to extract thickness fluctuations and to verify the amorphous state of the spacer. The observed antiferromagnetic coupling behavior is explained by RKKY interaction taking into account the amorphous structure of the spacer material.Comment: Typset using RevTex, 4 pages with 4 figures (.eps

Performance of the new amplifier-shaper-discriminator chip for the ATLAS MDT chambers at the HL-LHC

The Phase-II Upgrade of the ATLAS Muon Detector requires new electronics for the readout of the MDT drift tubes. The first processing stage, the Amplifier-Shaper-Discriminator (ASD), determines the performance of the readout for crucial parameters like time resolution, gain uniformity, efficiency and noise rejection. An 8-channel ASD chip, using the IBM 130 nm CMOS 8RF-DM technology, has been designed, produced and tested. The area of the chip is 2.2 x 2.9 square mm size. We present results of detailed measurements as well as a comparision with simulation results of the chip behaviour at three different levels of detail

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements