111334701
A DEPFET pixel matrix system for the ILC vertex detector
Abstract The DEPFET detector offers radiation detection and amplification jointly by embedding a field effect transistor into fully depleted silicon. Due to the excellent noise performance ( ENC = 2.2 e - for single pixel at room temperature and 6 μ s shaping time) and the high spatial resolution of the device ( 4.3 μ m at 22 keV using 50 × 50 μ m 2 pixels), the DEPFET concept is attractive for X-ray astronomy, for biomedical application and for tracking in particle physics. For the vertex detector of a future TeV-scale linear collider, like the proposed ILC (International Linear Collider), a highly granulated pixel system operated row-wise with line rates of 20 MHz at a noise level below 100 e - is needed. Addressing these requirements, improved DEPFET sensors with 22 × 36 μ m 2 pixel size have been fabricated. A prototype system has been developed that uses dedicated chips for steering and readout of a 64 × 128 DEPFET pixel matrix. Due to the current based readout mode provided by the readout chip, a thousand times faster matrix operation than achieved so far is possible. The performance of the single components of the system will be summarized and first results obtained with the entire system will be presented.
73653251
Imaging performance of a DEPFET pixel Bioscope system in Tritium autoradiography
Abstract A Bioscope system based on a 64 × 64 -matrix of DEPFET pixels has been developed for real-time digital autoradiography in biomedical applications. It provides very good energy and spatial resolution at the same time. The DEPFET pixel cells consist of p -channel JFETs integrated into the high-ohmic n -silicon substrate. This leads to a very low noise performance at room temperature. Two dedicated ASIC chips have been developed for steering and readout of the pixel matrix. The measured system noise of ( 69 ± 4 ) e - at 35 ∘ C is mostly due to sensor leakage current and can be largely reduced by cooling or a faster readout. The spatial resolution is examined by measurements with a laser as well as with a dedicated test chart and is determined to be ( 6.7 ± 0.7 ) μ m for 6 keV-X-rays and 4.3 ± 0.8 μ m for 22 keV-X-rays. The measurements are compared to simulation results with different reconstruction algorithms. Due to the thin entrance window at the detector backside and the low noise performance, a detection of low-energy β -emitters such as 3H is possible. Measurements with 3H-labeled biological samples were taken. The ability of the DEPFET pixel Bioscope to separate different radiolabels in the same sample is demonstrated by a measurement with 3H and 14C.
120274396
Timing properties of an avalanche diode for single photon counting
A new concept for a silicon single photon counter has been developed at the Semiconductor Laboratory of the Max-Planck-Institute for Physics. The concept combines the principles of a drift diode and an avalanche diode. The electron which is generated by an incoming photon has to drift to the small avalanche region and avalanche breakdown will take place. The detector is operated in Geiger mode. In order to provide high efficiency and good timing properties, the electrons have to be focussed properly with short time jitter. Therefore, drift and timing properties have been investigated using simulations.
108645383
The ATLAS Silicon Pixel Sensors
Abstract Prototype sensors for the ATLAS silicon pixel detector have been developed. The design of the sensors is guided by the need to operate them in the severe LHC radiation environment at up to several hundred volts while maintaining a good signal-to-noise ratio, small cell size, and minimal multiple scattering. The ability to be operated under full bias for electrical characterization prior to attachment of the readout integrated circuit electronics is also desired.
34283775
Tracking and level-1 triggering in the forward region of the ATLAS muon spectrometer at sLHC
In the endcap region of the ATLAS Muon Spectrometer (η  >  1) precision tracking and Level-1 triggering are performed by different types of chambers. Monitored Drift Tube chambers (MDT) and Cathode Strip Chambers (CSC) are used for precision tracking, while Thin Gap Chambers (TGC) form the Level-1 muon trigger, selecting muons with high transverse momentum (pT). When by 2018 the LHC peak luminosity of 1034 cm−2s−1 will be increased by a factor of ~ 2 and by another factor of ~ 2–2.5 in about a decade from now (``SLHC''), an improvement of both systems, precision tracking and Level-1 triggering, will become mandatory in order to cope with the high rate of uncorrelated background hits (``cavern background'') and to stay below the maximum trigger rate for the muon system, which is in the range of 10–20 % of the 100 kHz rate, allowed for ATLAS. For the Level-1 trigger of the ATLAS Muon Spectrometer this means a stronger suppression of sub-threshold muons in the high-pT trigger as well as a better rejection of tracks not coming from the primary interaction point. Both requirements, however, can only be fulfilled if spatial resolution and angular pointing accuracy of the trigger chambers, in particular of those in the Inner Station of the endcap, are improved by a large factor. This calls for a complete replacement of the currrently used TGC chambers by a new type of trigger chambers with better performance. In parallel, the precision tracking chambers must be replaced by chambers with higher rate capability to be able to cope with the intense cavern background. In this article we present concepts to decisively improve the Level-1 trigger with newly developed trigger chambers, being characterized by excellent spatial resolution, good time resolution and sufficiently short latency. We also present new types of precision chambers, designed to maintain excellent tracking efficiency and spatial resolution in the presence of high levels of uncorrelated background hits, as generated by γ and neutron conversions.
19809846
Development of Fast High-Resolution Muon Drift-Tube Detectors for High Counting Rates
Abstract Pressurized drift-tube chambers are efficient detectors for high-precision tracking over large areas. The Monitored Drift-Tube (MDT) chambers of the muon spectrometer of the ATLAS detector at the Large Hadron Collider (LHC) reach a spatial resolution of 35 μ m and almost 100% tracking efficiency with 6 layers of 30 mm diameter drift tubes operated with an Ar:CO 2 (93:7) gas mixture at 3 bar and a gas gain of 20 000. The ATLAS MDT chambers are designed to cope with background counting rates due to neutrons and γ rays of up to about 300 kHz per tube which will be exceeded for LHC luminosities larger than the design value of 10 34  cm −1  s −1 . Decreasing the drift-tube diameter to 15 mm while keeping the other parameters, including the gas gain, unchanged reduces the maximum drift time from about 700 to 200 ns and the drift-tube occupancy by a factor of 7. New drift-tube chambers for the endcap regions of the ATLAS muon spectrometer have been designed. A prototype chamber consisting of 12 times 8 layers of 15 mm diameter drift tubes of 1 m length has been constructed with a sense wire positioning accuracy of 20 μ m . The 15 mm diameter drift-tubes have been tested with cosmic rays in the Gamma Irradiation Facility at CERN at γ counting rates of up to 1.85 MHz.
110325204
Upgrade of the Readout Electronics of the ATLAS MDT Detector for SLHC
Simulation predicts a high level of ionizing radiation in the ATLAS experimental hall during LHC operation. This radiation will act as a source of background signals to the four subsystems of the ATLAS muon detector. We present the performance of the Monitored Drift Tube detector (MDT) under these background conditions and discuss the consequences for the much higher background rates at SLHC with respect to tracking efficiency, resolution and readout bandwidth. For rates beyond the expected LHC levels, we discuss options to improve the performance of detector and electronics.
15731595
Stringy Instantons and Yukawa Couplings in MSSM-like Orientifold Models
Type IIA orientifold constructions with intersecting D6-branes and their IIB duals in terms of magnetized D9/D7-branes constitute one of the most promising avenues for the construction of semirealistic MSSM-like compactifications. One generic problem with these constructions is that there are many Yukawa couplings, which vanish due to additional U(1) symmetries in the theory. In this paper, we consider a number of such settings and study under what conditions stringy instanton effects can give rise to non-perturbative contributions to the Yukawa couplings, so that all perturbatively forbidden terms are induced. We find specific settings in which Yukawa couplings for all fermions are indeed obtained. For some cases we provide specific local examples of rigid O(1) instantons within the T6/2 × 2' toroidal orientifold with torsion that gives rise to the required amplitudes. A potential problem in these settings is that the same instantons, providing for Yukawa coupling contributions, may give rise to too large μ-terms for the Higgs multiplets. We show how this problem may be overcome in explicit models with a doubled Higgs system.
119295158
Performance of Drift-Tube Detectors at High Counting Rates for High-Luminosity LHC Upgrades
Abstract 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 drift-tube (MDT) chambers with 30 mm tube diameter have been designed to cope with γ and neutron background hit rates of up to 500 Hz/cm 2 . Background rates of up to 14 kHz/cm 2 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.
109933860
Upgrade of the ATLAS Muon Trigger for the SLHC
The outer shell of the ATLAS experiment at the LHC consists of a system of toroidal air-core magnets in order to allow for the precise measurement of the transverse momentum (pT) of muons, which in many physics channels are a signature of interesting physics processes [1,2]. For the precise determination of the muon momentum Monitored Drift Tube chambers (MDT) with high position accuracy are used, while for the fast identification of muon tracks chambers with high time resolution are used, able to select muons above a predefined pT threshold for use in the first Level of the ATLAS triggering system (Level-1 trigger). When the LHC peak luminosity of 1034 cm−2s−1 will be increased by a factor of 4–5 in about a decade from now (''SLHC''), an improvement of the selectivity of the ATLAS Level-1 triggering system will be mandatory in order to cope with the maximum allowed trigger rate of 100 kHz. For the Level-1 trigger of the ATLAS muon spectrometer this means an increase of the pT threshold for single muons. Due to the limited spatial resolution of the trigger chambers, however, the selectivity for tracks above ~ 20 GeV/c is insufficient for an effective reduction of the Level-1 rate. We describe how the track coordinates measured in the MDT precision chambers can be used to decisively improve the selectivity for high momentum tracks. The resulting increase in latency will also be discussed.
120584442
Modelling of the space-to-drift-time relationship of the ATLAS monitored drift-tube chambers in the presence of magnetic fields
Abstract The ATLAS muon spectrometer uses tracking chambers consisting of up to 5 m long drift tubes filled with Ar : CO 2 ( 93 : 7 ) at 3 bar. The chambers are run in a average toroidal magnetic field of 0.4 T created by 8 air core coils. They provide a track-point accuracy of 40 μ m if the space-to-drift-time relationship r ( t ) is known with 20 μ m accuracy. The magnetic field B influences the electron drift inside the tubes: the maximum drift time t max = 700 ns increases by ≈ 70 ns / T 2 B 2 . B varies by up to ± 0.4 T along the tubes of the chambers mounted near the magnet coils which translates into a variation of t max of up to 45 ns. The dependence of r ( t ) on B must be taken into account. Test-beam measurements show that the electron drift in case of B ≠ 0 can be modelled with the required accuracy by a Langevin equation with a friction term which is slightly non-linear in the drift velocity.