Stefano Mersi

This paper deals with an investigation of the trapping mechanisms and the “pumping” process on a device based on polycrystalline Chemical Vapor Deposited (CVD) diamond, recently tested as particle tracker. Photoconductivity measurements have been carried out during monochromatic illumination from near IR to above bandgap, while thermally stimulated current measurements have been used to detect a main defect level near band-edge. The results have been compared with charge collection distance measurements, highlighting the passivation effects of some trap levels due to irradiation. Based on these data we suggest a band-gap and trap-state model for CVD diamond presently used in particle physics experiments. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Abstract Due to its excellent electrical and physical properties, silicon carbide can represent a good alternative to Si in applications like the inner tracking detectors of particle physics experiments (RD50, LHCC 2002–2003, 15 February 2002, CERN, Ginevra). In this work p + /n SiC diodes realised on a medium-doped (1×10 15  cm −3 ), 40 μm thick epitaxial layer are exploited as detectors and measurements of their charge collection properties under β particle radiation from a 90 Sr source are presented. Preliminary results up to 900 V reverse bias voltage show a good collection efficiency of 1700e − and a collection length (ratio between collected charge and generated e–h pairs/μm) equal to the estimated width of the depleted region. Preliminary simulations on Schottky diodes have been carried out using the ISE-TCAD DESSIS simulation tool. Experimental results were reproduced well.

We propose a quantitative model of electronic transport on the basis of a conductivity characterization of diamond-based sensors exposed to $\ensuremath{\beta}$ radiation. Some of the investigated samples have been irradiated with neutron up to a fluence of $2\ifmmode\times\else\texttimes\fi{}{10}^{15}∕{\mathrm{cm}}^{2}$. Radiation-induced current measurements have been performed to study the trapping and recombination of deep defect levels in the diamond band gap. We present a quantitative analysis of the passivation of deep traps and the release of carriers during thermal fading between consecutive exposures. We determine the density of trap states per unit volume and per unit energy and their capture cross sections. We also evaluate the modification of these parameters after neutron irradiation. Our analysis gives the cross sections of the traps involved in our measurements with an accuracy of 20--50%, which is far better than that attainable with thermal spectroscopy. Our results on the capture cross section of the recombination centers agree with relevant works presented in literature on natural IIa diamond. We propose that some defects are of the same nature in chemical vapor deposition diamond, but their concentration is far lower in the state-of-the-art material. We also study a modification of the trap level distribution after neutron irradiation. Finally we propose a rationale for the improvement obtained in recent years in the performances of top quality polycrystalline diamond sensors.

Abstract We performed a study of charge collection distance (CCD) on medium to high-quality prototypes of diamond sensors prepared by Chemical Vapor Deposition (CVD). We studied the Charge Collection Efficiency in these materials supposing that it is limited by the presence of a recombination level and a distribution of trap levels centered at 1.7 eV from the band-edge. We also supposed that the exposition to ionizing radiation can make the trap levels ineffective (pumping effect). We have shown that these assumptions are valid by correlating the CCD to the pumping efficiency. Moreover, we have shown that the pumping efficiency is bias-dependent. We have explained our experimental results assuming that trapped carriers generate an electric field inside the diamond bulk.

The CMS silicon strip tracker, providing a sensitive area of approximately 200 m2 and comprising 10 million readout channels, has recently been completed at the tracker integration facility at CERN. The strip tracker community is currently working to develop and integrate the online and offline software frameworks, known as XDAQ and CMSSW respectively, for the purposes of data acquisition and detector commissioning and monitoring. Recent developments have seen the integration of many new services and tools within the online data acquisition system, such as event building, online distributed analysis, an online monitoring framework, and data storage management. We review the various software components that comprise the strip tracker data acquisition system, the software architectures used for stand-alone and global data-taking modes. Our experiences in commissioning and operating one of the largest ever silicon micro-strip tracking systems are also reviewed.

Silicon carbide is a promising wide-gap material because of its excellent electrical and physical properties, which are very relevant to technological applications. In particular, silicon carbide can represent a good alternative to Si in applications like the inner tracking detectors of particle physics experiments [1]. In this work p+/n SiC diodes realized on a medium doped (1×1015 cm -3), 40 µm thick epitaxial layer are exploited as detectors and measurements of their charge collection properties under beta particle radiation from Sr90 source are presented. Preliminary results till 900 V reverse voltage show a good collection efficiency of 1700 e- and a collection length (ratio between collected charges and generated e-h pairs/µm) equal to the estimated width of the depleted region.

Major LHC upgrades planned around 2020 are expected to increase the delivered instantaneous luminosity above 1034 cm-2s-1 while keeping the bunch spacing at 25 ns, or even increasing it. In order to cope with the higher pileup, the CMS collaboration is planning to build a completely new tracking system, which will probably implement also trigger capabilities. In order to identify the best possible design, a tool was developed (tkLayout) to generate layouts, make an estimate of the material budget and even provide an a priori estimate of the tracking performance. tkLayout can be used to optimize a given layout concept, or to compare the performance of different approaches. tkLayout is not specific to CMS, thus it can be used to design upgrades for other experiments. The technology of tkLayout is presented and results for several layout designs discussed.

The performance of the tracker of the CMS experiment, comprising of a pixel and a strip detector, has so far been excellent, as reflected in the wealth of physics results produced so far.However, the foreseen increases of both the instantaneous as well as the integrated luminosity by the LHC during the next ten years will necessitate a series of upgrades of the CMS tracking detector.In 2016-17 the pixel detector will be exchanged, and around 2022 the whole tracker will need to be replaced, in order to be able to cope with an instantaneous luminosity of 5 × 10 34 cm -2 s -1 and an integrated luminosity of 3000 fb -1 , as expected for the High Luminosity LHC (HL-LHC).Experience at high luminosity hadrons collider experiments shows that tracking information enhances the trigger rejection capabilities while retaining high efficiency for interesting physics events.The design of a tracking based trigger for the HL-LHC is an extremely challenging task, and requires the identification of high-momentum particle tracks as a part of the Level 1 Trigger.The present status of this project is summarized, including the future tracker layout, the design of module prototypes, and the status of the front-end electronic components.Preliminary results of a simulated tracker layout equipped with stacked modules are discussed in terms of p T resolution and triggering capabilities.

Tracker Inner Barrel half-cylinders and Tracker Inner Disks of the CMS tracker have been integrated in three INFN sites. Integrated structures are submitted to an extensive set of tests whose main aim is to validate the functioning of the structures in CMS-like conditions. The tests have furthermore proven to be a great opportunity to study several aspects of the performance in detail. In this note the tests are described in some detail and an overview of the results is presented.

The Compact Muon Solenoid (CMS) experiment plans to replace its strip tracker system with a completely new Outer Tracker system to cope with the higher luminosity, compared to Run 2 operation, provided by the HL-LHC.This CMS Phase-2 Outer Tracker will be build up from two types of modules both consisting out of two parallel silicon sensors separated by a few millimetres.To read out the two types of modules four Outer Tracker specific custom chips are required.This proceeding introduces the module concept, goes into more detail on the data path, discusses the test system (OT-µDTC) designed for testing prototypes based on these ASICs and gives examples of test results obtained with this test system.

An upgrade program is planned for the LHC which will smoothly bring the luminosity up to or above 5×1034 cm−2 s−1 sometimes after 2020, to possibly reach an integrated luminosity of 3000 fb−1 at the end of that decade. In this ultimate scenario, called Phase-2, when LHC will reach the High Luminosity phase (HL-LHC), CMS will need a completely new Tracker detector, in order to fully exploit the highly-demanding operating conditions and the delivered luminosity. The new Tracker should have also trigger capabilities. To achieve such goals, R&D activities are ongoing to explore options and develop solutions that would allow including tracking information at Level-1. The design choices for the CMS pixel and outer tracker upgrades are discussed along with some highlights of the R&D activities and expected detector performance.

This paper reports the design, fabrication and characterization of single-sided silicon microstrip sensors with integrated biasing resistors and coupling capacitors, produced for the first time in India. We have first developed a prototype sensor on a four-inch wafer. After finding suitable test procedures for characterizing these AC coupled sensors, we fine-tuned various process parameters in order to produce sensors of the desired specifications.

This is a Technical Scope of Work (TSW) between the Fermi National Accelerator Laboratory (Fermilab) and the experimenters of the CMS Pixel group, which consists of individuals from the Bristol University, CERN, Fermilab, Rutherford Laboratory (UK), and National Taiwan University who have committed to participate in beam tests to be carried out during the 2013 - 2014 Fermilab Test Beam Facility program. The TSW is intended solely for the purpose of recording expectations for budget estimates and work allocations for Fermilab, the funding agencies and the participating institutions. It reflects an arrangement that currently is satisfactory to the parties; however, it is recognized and anticipated that changing circumstances of the evolving research program will necessitate revisions. The parties agree to modify this TSW to reflect such required adjustments. Actual contractual obligations will be set forth in separate documents. This TSW fulfills Article 1 (facilities and scope of work) of the User Agreements signed (or still

The CMS Silicon Strip Tracker is the largest detector of its kind ever operated, with a silicon surface area of about 200 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The Silicon Strip Tracker is the sub-detector with the highest number of detector modules within the CMS experiment. Given the complexity of the device, a variety of tools were developed and are used to determine the status of the detector in real time and allow for data qualification and corrective actions when needed. In this paper we describe the monitoring techniques that are used to safely operate the detector and assess the state of its calibration.

The CMS Silicon Strip Tracker is the largest detector of its kind ever operated, with about 200 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of silicon surface. The Silicon Strip Tracker it is the sub-detector with the highest number of detector modules within CMS. Given the complexity of the device, a variety of tools was developed and is used to measure the status of the detector in real time and allow for data qualification and corrective actions when needed. In this paper we describe the monitoring techniques that are used to safely operate the detector and assess the state of its calibration.

The consolidation and upgrade of the LHC accelerators complex is expected to yield a progressive increase in peak luminosity L, exceeding the value of L = 1034 cm−2 s−1 (original design figure) after about 5 years of operation, to eventually reach values close to L = 1035 cm−2 s−1 (the so-called Super-LHC). All the experiments will have to make some upgrades to be able to operate at Super-LHC. This article makes a short review of the CMS tracker sub-detector research activities in this direction: we will show the time framework of the evolution plan of LHC, what are the limiting factors of the present-day detector and which requirements come from the luminosity upgrade. We will also describe the main results of the research activities already in place in the field of: sensors, power supply, cooling, layout design and simulations.

The CMS Silicon Strip Tracker at the LHC comprises a sensitive area of approximately 200 m2 and 10 million readout channels. Its data acquisition system is based around a custom analogue front-end chip. Both the control and the readout of the front-end electronics are performed by off-detector VME boards in the counting room, which digitise the raw event data and perform zero-suppression and formatting. The data acquisition system uses the CMS online software framework to configure, control and monitor the hardware components and steer the data acquisition. The first data analysis is performed online within the official CMS reconstruction framework, which provides many services, such as distributed analysis, access to geometry and conditions data, and a Data Quality Monitoring tool based on the online physics reconstruction.

The CMS experiment at LHC features the largest Silicon Strip Tracker (SST) ever built. This detector is composed of about 15000 modules, thus the potential problems of the system comes from its complexity. This article covers the tests performed during the tracker integration, describing their motivations in terms of process quality assurance.