Material Budget Research Articles

HVMUX, a high voltage multiplexing for the ATLAS Tracker upgrade

The HV biasing solution adopted in the current ATLAS detector uses one HV conductor for each sensor. This approach easily allows disabling of malfunctioning sensors without affecting the others, but space constraints and material budget considerations renders this approach impractical for the Upgraded detector. In fact, the increased luminosity of the Upgraded LHC will require more channels in the upgraded ATLAS Tracker, as a result of the finer detector segmentation. Different approaches to bring the HV biasing to the detectors, including the use of a shared HV line to bias several sensors and employing semiconductor switches for the HV routing (HVMUX), have been investigated. Beside the size constraints, particular attention must be paid to the radiation tolerance of any proposed solution, which, for the strips detector, requires proper operation up to fluences of the order of 2⋅ 1015 1MeV neq/cm2 and TID in excess of 300 kGy. In this paper, a description of the proposed HVMUX solution, along with electrical and radiation tests results will be presented and discussed.

Silicon pixel R&D for CLIC

Challenging detector requirements are imposed by the physics goals at the future multi-TeV e+ e− Compact Linear Collider (CLIC). A single point resolution of 3 μm for the vertex detector and 7 μm for the tracker is required. Moreover, the CLIC vertex detector and tracker need to be extremely light weighted with a material budget of 0.2% X0 per layer in the vertex detector and 1–2% X0 in the tracker. A fast time slicing of 10 ns is further required to suppress background from beam-beam interactions. A wide range of sensor and readout ASIC technologies are investigated within the CLIC silicon pixel R&D effort. Various hybrid planar sensor assemblies with a pixel size of 25×25 μm2 and 55×55 μm2 have been produced and characterised by laboratory measurements and during test-beam campaigns. Experimental and simulation results for thin (50 μm–500 μm) slim edge and active-edge planar, and High-Voltage CMOS sensors hybridised to various readout ASICs (Timepix, Timepix3, CLICpix) are presented.

Optimization of thin n-in-p planar pixel modules for the ATLAS upgrade at HL-LHC

The ATLAS experiment will undergo around the year 2025 a replacement of the tracker system in view of the high luminosity phase of the LHC (HL-LHC) with a new 5-layer pixel system. Thin planar pixel sensors are promising candidates to instrument the innermost region of the new pixel system, thanks to the reduced contribution to the material budget and their high charge collection efficiency after irradiation. The sensors of 50-150 μm thickness, interconnected to FE-I4 read-out chips, have been characterized with radioactive sources and beam tests. In particular active edge sensors have been investigated. The performance of two different versions of edge designs are compared: the first with a bias ring, and the second one where only a floating guard ring has been implemented. The hit efficiency at the edge has also been studied after irradiation at a fluence of 1015 neq/cm2. Highly segmented sensors will represent a challenge for the tracking in the forward region of the pixel system at HL-LHC. In order to reproduce the performance of 50x50 μm2 pixels at high pseudo-rapidity values, FE-I4 compatible planar pixel sensors have been studied before and after irradiation in beam tests at high incidence angles with respect to the short pixel direction. Results on the hit efficiency in this configuration are discussed for different sensor thicknesses.

Track reconstruction in the inhomogeneous magnetic field for Vertex Detector of NA61/SHINE experiment at CERN SPS

The heavy-ion programme of the NA61/SHINE experiment at CERN SPS is expanding to allow precise measurements of exotic particles with lifetime few hundred microns. A Vertex Detector for open charm measurements at the SPS is being constructed by the NA61/SHINE Collaboration to meet the challenges of high spatial resolution of secondary vertices and efficiency of track registration. This task is solved by the application of the coordinate sensitive CMOS Monolithic Active Pixel Sensors with extremely low material budget in the new Vertex Detector.A small-acceptance version of the Vertex Detector is being tested this year, later it will be expanded to a large-acceptance version. Simulation studies will be presented. A method of track reconstruction in the inhomogeneous magnetic field for the Vertex Detector was developed and implemented. Numerical calculations show the possibility of high precision measurements in heavy ion collisions of strange and multi strange particles, as well as heavy flavours, like charmed particles.

The Phase1 CMS Pixel detector upgrade

The pixel detector of the CMS experiment will be replaced in an extended end-of-year shutdown during winter 2016/2017 with an upgraded one able to cope with peak instantaneous luminosities beyond the nominal LHC instantaneous luminosity of 1 × 1034 cm−2 s−1. Under the conditions expected in the coming years, which will see an increase of a factor two in instantaneous luminosity, the present system would experience a dynamic inefficiency caused mainly by data losses due to buffer overflows. The Phase I upgrade of the CMS pixel detector, described in this paper, will operate at full efficiency at an instantaneous luminosity of 2 × 1034 cm−2 s−1 and beyond, thanks to a new readout chip. The new detector will feature one additional tracking point both in the barrel and in the forward regions, while reducing the material budget as a result of a new CO2 cooling system and optimised layout of the services. In this paper, the design and the technological choices of the Phase I detector will be reviewed and the status of the construction of the detector and the performance of its components will be discussed.

The ALICE pixel detector upgrade

The ALICE experiment at the CERN LHC is designed to study the physics of strongly interacting matter, and in particular the properties of the Quark-Gluon Plasma, using proton-proton, proton-nucleus and nucleus-nucleus collisions. The ALICE collaboration is preparing a major upgrade of the experimental apparatus to be installed during the second long LHC shutdown in the years 2019–2020. A key element of the ALICE upgrade is the new, ultra-light, high-resolution Inner Tracking System. With respect to the current detector, the new Inner Tracking System will significantly enhance the pointing resolution, the tracking efficiency at low transverse momenta, and the read-out rate capabilities. This will be obtained by seven concentric detector layers based on a Monolithic Active Pixel Sensor with a pixel pitch of about 30×30 μm2. A key feature of the new Inner Tracking System, which is optimised for high tracking accuracy at low transverse momenta, is the very low mass of the three innermost layers, which feature a material budget of 0.3% X0 per layer. This contribution presents the design goals and layout of the upgraded ALICE Inner Tracking System, summarises the R&D activities focussing on the technical implementation of the main detector components, and the projected detector performance.

The STAR PXL detector

The PiXeL detector (PXL) of the STAR experiment at RHIC is the first application of the state-of-the-art thin Monolithic Active Pixel Sensors (MAPS) technology in a collider environment. Designed to extend the STAR measurement capabilities in the heavy flavor domain, it took data in Au+Au collisions, p+p and p+Au collisions at 0√sNN=20 GeV at RHIC, during the period 2014–2016. The PXL detector is based on 50 μm-thin MAPS sensors with a pitch of 20.7 μm. Each sensor includes an array of nearly 1 million pixels, read out in rolling shutter mode in 185.6 μs. The 170 mW/cm2 power dissipation allows for air cooling and contributes to reduce the global material budget to 0.4% radiation length on the innermost layer. Experience and lessons learned from construction and operations will be presented in this paper. Detector performance and results from 2014 Au+Au data analysis, demonstrating the STAR capabilities of charm reconstruction, will be shown.

Ultra-low material pixel layers for the Mu3e experiment

The upcoming Mu3e experiment will search for the charged lepton flavour violating decay of a muon at rest into three electrons. The maximal energy of the electrons is 53 MeV, hence a low material budget is a key performance requirement for the tracking detector. In this paper we summarize our approach to meet the requirement of about 1 ‰ of a radiation length per pixel detector layer. This includes the choice of thinned active monolithic pixel sensors in HV-CMOS technology, ultra-thin flexible printed circuits, and helium gas cooling.

Development of a Detector Control System for the ATLAS Pixel detector in the HL-LHC

The upgrade of the LHC to the HL-LHC requires a new ITk detector. The innermost part of this new tracker is a pixel detector. The University of Wuppertal is developing a new DCS to monitor and control this new pixel detector. The current concept envisions three parallel paths of the DCS. The first path, called security path, is hardwired and provides an interlock system to guarantee the safety of the detector and human beings. The second path is a control path. This path is used to supervise the entire detector. The control path has its own communication lines independent from the regular data readout for reliable operation. The third path is for diagnostics and provides information on demand. It is merged with the regular data readout and provides the highest granularity and most detailed information. To reduce the material budget, a serial power scheme is the baseline for the pixel modules. A new ASIC used in the control path is in development at Wuppertal for this serial power chain. A prototype exists already and a proof of principle was demonstrated. Development and research is ongoing to guarantee the correct operation of the new ASIC in the harsh environment of the HL-LHC. The concept for the new DCS will be presented in this paper. A focus will be made on the development of the DCS chip, used for monitoring and control of pixel modules in a serial power chain.

Upgrade of the ALICE Inner Tracking System

During the long shutdown of the Large Hadron Collider (LHC) in 2019-20 (LS2) the present Inner Tracking System (ITS) of the ALICE experiment based on silicon pixel, silicon drift and silicon strip detectors, will be entirely replaced by a new tracker using novel monolithic silicon pixel chips. This new tracker will significantly enhance heavy flavour measurements, which are out of reach for the present system, e.g. charmed baryons, such as the ΛC, and will allow studying hadrons containing a beauty quark. The new tracker will provide an improved pointing resolution in rϕ and z, decreasing the present values by a factor 3 and 5, respectively, to about 40 μm for a pT of 500 MeV/c. Each of the seven layers will be constructed using 50 μm, respectively 100 μm thin silicon chips on a very light weight carbon fibre based support structure for the innermost and the outer layers. The material budget for the first three layers corresponds to 0.3% X0/layer while the four outer layers will have an average material budget of 1% X0/layer. The innermost layer will be placed at 23 mm radius, compared to presently 39 mm. Furthermore, the readout rate of the new ITS will increase from presently 1 kHz to 50 kHz for Pb-Pb collisions and 400 kHz for p-p collisions, thus matching the expected event rate for Pb-Pb collisions after LS2. This contribution will provide an overview of the upgrade of the ALICE ITS and the expected performance improvement and will present the actual status of the R&D.

How do you like your books: Print or digital? An analysis on print and e-book usage at the Graduate School of Education

ABSTRACTThe shift from physical materials to digital holdings has slowly infiltrated libraries across the globe, and librarians are struggling to make sense of these intangible, and sometimes fleeting, resources. Materials budgets have shifted to accommodate large journal and database subscriptions, single-title article access, and, most recently, e-book holdings. This analysis measures the impact of digital acquisitions in an academic setting during a highly transformative period of library practices. The study finds that both electronic and print books are valuable to the academic research community at the Graduate School of Education (GSE).

A scintillating fibre beam profile monitor for the experimental areas of the SPS at CERN

The CERN Super Proton Synchrotron (SPS) delivers a wide spectrum of particle beams (hadrons, leptons and heavy ions) that can vary greatly in momentum and intensity. The profile and position of these beams are measured using particle detectors. However, the current systems show several problems that limit the quality of such monitoring. We have researched a new monitor made of scintillating fibres read-out with Silicon Photomultipliers (SiPM), which has the potential to perform better in terms of material budget, range of intensities measured and available detector size. In addition, it also has particle counting capabilities, extending its use to spectrometry or Time-Of-Flight measurements. Its radiation hardness is good to guarantee years of functioning. We have successfully tested a first prototype of this detector with different particle beams at CERN, giving accurate profile measurements over a wide range of energies and intensities. It only showed problems during operation with lead ion beams, believed to come from crosstalk between the fibres. Investigations are ongoing on alternative photodetectors, the electronics readout and solutions to the fibre crosstalk.

A review on the research of modern aeolian dust in Central Asia

The Central Asian Arid Zone (CAAZ) located in the temperate desert belt of the Northern Hemisphere is one of the most important sources for global aeolian dust and aerosol. It is widely acknowledged that aeolian dust plays a vital role in the Earth system through participating in the energy and material budget of the planet. Except for the existed natural desert areas, the newly human-induced deserts that originally used to be the bed of terminal lakes (like the Aral Sea, Caspian Sea, Balkhash Lake, etc.) are becoming the much more significant sources for aeolian dust/salt in this region. Dust and associated aerosols have complex impacts on local ecological system and human health for its special chemical composition. In recent years, a slight declining trend of dust storm frequency in the region was reported, which may be explained by the weakened human disturbances in desert areas or climate variations. The dust dynamics in the CAAZ represent considerable variations in both spatial and temporal distribution, which makes it harder to forecast the dust events and mitigate its damages to ecosystems and social economics. Nevertheless, there is not much evidence of its climatic and environmental impacts both on the regional and global scales. Therefore, further related studies and regulation measures in the region are essential and emergent, as well as the strengthening cooperation between the associated countries and organizations.

Single-hit resolution measurement with MEG II drift chamber prototypes

Drift chambers operated with helium-based gas mixtures represent a common solution for tracking charged particles keeping the material budget in the sensitive volume to a minimum. The drawback of this solution is the worsening of the spatial resolution due to primary ionisation fluctuations, which is a limiting factor for high granularity drift chambers like the MEG II tracker. We report on the measurements performed on three different prototypes of the MEG II drift chamber aimed at determining the achievable single-hit resolution. The prototypes were operated with helium/isobutane gas mixtures and exposed to cosmic rays, electron beams and radioactive sources. Direct measurements of the single hit resolution performed with an external tracker returned a value of 110 μm, consistent with the values obtained with indirect measurements performed with the other prototypes.

Thin hybrid pixel assembly fabrication development with backside compensation layer

The ATLAS and CMS experiments will both replace their entire tracking systems for operation at the HL-LHC in 2026. This will include a significantly larger pixel systems, for example, for ATLAS approximately 15m2. To keep the tracker material budget low it is crucial to minimize the mass of the pixel modules via thinning both the sensor and readout chip to about 150μm each. The bump yield of thin module assemblies using solder based bump bonding can be problematic due to wafer bowing during solder reflow at high temperature. A new bump-bonding process using backside compensation on the readout chip to address the issue of low yield will be presented. The objective is to compensate dynamically the stress of the front side stack by adding a compensating layer to the backside of the wafer. A SiN and Al:Si stack has been chosen for the backside layer. The bow reducing effect of applying a backside compensation layer will be demonstrated using the FE-I4 wafer. The world's first results from assemblies produced from readout wafers thinned to 100μm with a stress compensation layer are presented with bond yields close to 100% measured using the FE-I4 readout chip.

The NA62 GigaTracker

The GigaTracker is a hybrid silicon pixel detector built for the NA62 experiment aiming at measuring the branching fraction of the ultra-rare kaon decay K+→π+νν¯ at the CERN SPS. The detector has to track particles in a beam with a flux reaching 1.3MHz/mm2 and provide single-hit timing with 200ps RMS resolution for a total material budget of less than 0.5% X0 per station. The tracker comprises three 60.8mm×27mm stations installed in vacuum (∼10−6mbar) and cooled with liquid C6F14 circulating through micro-channels etched inside a few hundred micron thick silicon plates. Each station is composed of a 200μm thick silicon sensor read out by 2×5 custom 100μm thick ASICs, called TDCPix. Each chip contains 40×45 asynchronous pixels, 300μm×300μm each and is instrumented with 100ps bin time-to-digital converters. In order to cope with the high rate, the TDCPix is equipped with four 3.2Gb/s serialisers sending out the data. We will describe the detector and the results from the 2014 and 2015 NA62 runs.

Feasibility studies for a wireless 60 GHz tracking detector readout

The amount of data produced by highly granular silicon tracking detectors in high energy physics experiments poses a major challenge to readout systems. At high collision rates, e.g. at LHC experiments, only a small fraction of data can be read out with currently used technologies. To cope with the requirements of future or upgraded experiments new data transfer techniques are required which offer high data rates at low power and low material budget.Wireless technologies operating in the 60GHz band or at higher frequencies offer high data rates and are thus a promising upcoming alternative to conventional data transmission via electrical cables or optical fibers. Using wireless technology, the amount of cables and connectors in detectors can be significantly reduced. Tracking detectors profit most from a reduced material budget as fewer secondary particle interactions (multiple Coulomb scattering, energy loss, etc.) improve the tracking performance in general.We present feasibility studies regarding the integration of the wireless technology at 60GHz into a silicon tracking detector. We use spare silicon strip modules of the ATLAS experiment as test samples which are measured to be opaque in the 60GHz range. The reduction of cross talk between links and the attenuation of reflections is studied. An estimate of the maximum achievable link density is given. It is shown that wireless links can be placed as close as 2cm next to each other for a layer distance of 10cm by exploiting one or several of the following measures: highly directive antennas, absorbers like graphite foam, linear polarization and frequency channeling. Combining these measures, a data rate area density of up to 11Tb/(s·m2) seems feasible. In addition, two types of silicon sensors are tested under mm-wave irradiation in order to determine the influence of 60GHz data transmission on the detector performance: an ATLAS silicon strip sensor module and an HV-MAPS prototype for the Mu3e experiment. No deterioration of the performance of both prototypes is observed.

A new timing detector for the CT-PPS project

The CT-PPS detector will be installed close to the beam line on both sides of CMS, 200m downstream the interaction point. This detector will measure forward scattered protons, allowing detailed studies of diffractive hadron physics and Central Exclusive Production. The main components of the CT-PPS detector are a silicon tracking system and a timing system. In this contribution we present the proposal of an innovative solution for the timing system, based on Ultra-Fast Silicon Detectors (UFSD). UFSD are a novel concept of silicon detectors potentially able to obtain the necessary time resolution (∼20ps on the proton arrival time). The use of UFSD has also other attractive features as its material budget is small and the pixel geometries can be tailored to the precise physics distribution of protons. UFSD prototypes for CT-PPS have been designed by CNM (Barcelona) and FBK (Trento): we will present the status of the sensor productions and of the low-noise front-end electronics currently under development and test.

Thin n-in-p planar pixel modules for the ATLAS upgrade at HL-LHC

The ATLAS experiment will undergo a major upgrade of the tracker system in view of the high luminosity phase of the LHC (HL-LHC) foreseen to start around 2025. Thin planar pixel modules are promising candidates to instrument the new pixel system, thanks to the reduced contribution to the material budget and their high charge collection efficiency after irradiation. New designs of the pixel cells, with an optimized biasing structure, have been implemented in n-in-p planar pixel productions with sensor thicknesses of 270μm. Using beam tests, the gain in hit efficiency is investigated as a function of the received irradiation fluence. The outlook for future thin planar pixel sensor productions will be discussed, with a focus on thin sensors with a thickness of 100 and 150μm and a novel design with the optimized biasing structure and small pixel cells (50×50 and 25×100μm2). These dimensions are foreseen for the new ATLAS read-out chip in 65nm CMOS technology and the fine segmentation will represent a challenge for the tracking in the forward region of the pixel system at HL-LHC. To predict the performance of 50×50μm2 pixels at high η, FE-I4 compatible planar pixel sensors have been studied before and after irradiation in beam tests at high incidence angle with respect to the short pixel direction. Results on cluster shapes, charge collection- and hit efficiency will be shown.

The Role of Ocean Tides on Groundwater-Surface Water Exchange in a Mangrove-Dominated Estuary: Shark River Slough, Florida Coastal Everglades, USA

Low-relief environments like the Florida Coastal Everglades (FCE) have complicated hydrologic systems where surface water and groundwater processes are intimately linked yet hard to separate. Fluid exchange within these low-hydraulic-gradient systems can occur across broad spatial and temporal scales, with variable contributions to material transport and transformation. Identifying and assessing the scales at which these processes operate is essential for accurate evaluations of how these systems contribute to global biogeochemical cycles. The distribution of 222Rn and 223,224,226Ra have complex spatial patterns along the Shark River Slough estuary (SRSE), Everglades, FL. High-resolution time-series measurements of 222Rn activity, salinity, and water level were used to quantify processes affecting radon fluxes out of the mangrove forest over a tidal cycle. Based on field data, tidal pumping through an extensive network of crab burrows in the lower FCE provides the best explanation for the high radon and fluid fluxes. Burrows are irrigated during rising tides when radon and other dissolved constituents are released from the mangrove soil. Flushing efficiency of the burrows—defined as the tidal volume divided by the volume of burrows—estimated for the creek drainage area vary seasonally from 25 (wet season) to 100 % (dry season) in this study. The tidal pumping of the mangrove forest soil acts as a significant vector for exchange between the forest and the estuary. Processes that enhance exchange of O2 and other materials across the sediment-water interface could have a profound impact on the environmental response to larger scale processes such as sea level rise and climate change. Compounding the material budgets of the SRSE are additional inputs from groundwater from the Biscayne Aquifer, which were identified using radium isotopes. Quantification of the deep groundwater component is not obtainable, but isotopic data suggest a more prevalent signal in the dry season. These findings highlight the important role that both tidal- and seasonal-scale forcings play on groundwater movement in low-gradient hydrologic systems.