Strip Tracker Research Articles

Alignment of the CMS silicon strip tracker during stand-alone commissioning

The results of the CMS tracker alignment analysis are presented using the data from cosmic tracks, optical survey information, and the laser alignment system at the Tracker Integration Facility at CERN. During several months of operation in the spring and summer of 2007, about five million cosmic track events were collected with a partially active CMS Tracker. This allowed us to perform first alignment of the active silicon modules with the cosmic tracks using three different statistical approaches; validate the survey and laser alignment system performance; and test the stability of Tracker structures under various stresses and temperatures ranging from +15 °C to −15 °C. Comparison with simulation shows that the achieved alignment precision in the barrel part of the tracker leads to residual distributions similar to those obtained with a random misalignment of 50 (80) μm RMS in the outer (inner) part of the barrel.

Performance studies of the CMS Strip Tracker before installation

In March 2007 the assembly of the Silicon Strip Tracker was completed at the Tracker Integration Facility at CERN. Nearly 15% of the detector was instrumented using cables, fiber optics, power supplies, and electronics intended for the operation at the LHC. A local chiller was used to circulate the coolant for low temperature operation. In order to understand the efficiency and alignment of the strip tracker modules, a cosmic ray trigger was implemented. From March through July 4.5 million triggers were recorded. This period, referred to as the Sector Test, provided practical experience with the operation of the Tracker, especially safety, data acquisition, power, and cooling systems. This paper describes the performance of the strip system during the Sector Test, which consisted of five distinct periods defined by the coolant temperature. Significant emphasis is placed on comparisons between the data and results from Monte Carlo studies.

Stand-alone cosmic muon reconstruction before installation of the CMS silicon strip tracker

The subsystems of the CMS silicon strip tracker wereintegrated and commissioned at the Tracker Integration Facility(TIF) in the period from November 2006 to July 2007. As part of thecommissioning, large samples of cosmic ray data were recorded undervarious running conditions in the absence of a magnetic field.Cosmic rays detected by scintillation counters were used to triggerthe readout of up to 15 % of the final silicon strip detector, andover 4.7 million events were recorded. This document describes thecosmic track reconstruction and presents results on the performanceof track and hit reconstruction as from dedicated analyses.

Status of the CMS Silicon Strip Tracker and commissioning results

The main subsystems of the CMS Silicon Strip Tracker were assembled together in a dedicated large clean room at CERN prior to their installation in the CMS collision hall. Following the integration of the Tracker a long commissioning period took place, during which up to 15% of the silicon modules were operated and read out simultaneously at different temperatures. Some of the achievements of the commissioning phase are discussed in details like Tracker noise performance, signal-to-noise measurements, and hit reconstruction efficiency. The Tracker was inserted in CMS in December 2007 and the commissioning of the full Tracker started. A description of the commissioning procedure followed at CMS and the actual status of the Tracker are presented.

The CMS Tracker Detector Control System

The Compact Muon Solenoid DCS (CMS) Silicon Strip Tracker is by far the largest detector ever built in micro-strip technology. It has an active surface area of 198 m 2 consisting of 15,148 silicon modules with 9,316,352 readout channels read via 75,376 Analog Pipeline Voltage (APV) front-end chips and a total of 24,244 sensors. The Detector Control System (DCS) for the Tracker is a distributed control system that operates ∼2000 power supplies for the silicon modules and also monitors its environmental sensors. The DCS receives information from about 10 3 environmental probes (temperature and humidity sensors) located inside the detector's volume and values from these probes are driven through the Programmable Logic Controllers (PLC) of the Detector Safety System (DSS). A total of 10 5 parameters are read out from the dedicated chips in the front-end electronics of the detector via the data acquisition system, and a total of 10 5 parameters are read from the power supply modules. All these parameters are monitored, evaluated and correlated with the detector layout; actions are taken under specific conditions. The hardware for DCS consists of 10 PCs and 10 PLC systems that are continuously running the necessary control and safety routines. The DCS is a fundamental tool for the Tracker operation and its safety.

The CMS experiment at the CERN LHC

The Compact Muon Solenoid (CMS) detector is described. Thedetector operates at the Large Hadron Collider (LHC) at CERN. It wasconceived to study proton-proton (and lead-lead) collisions at acentre-of-mass energy of 14 TeV (5.5 TeV nucleon-nucleon) and atluminosities up to 1034 cm−2 s−1 (1027 cm−2 s−1). At the core of the CMS detector sits ahigh-magnetic-field and large-bore superconducting solenoidsurrounding an all-silicon pixel and strip tracker, a lead-tungstatescintillating-crystals electromagnetic calorimeter, and abrass-scintillator sampling hadron calorimeter. The iron yoke of theflux-return is instrumented with four stations of muon detectorscovering most of the 4π solid angle. Forward samplingcalorimeters extend the pseudorapidity coverage to high values(|η| ⩽ 5) assuring very good hermeticity. The overalldimensions of the CMS detector are a length of 21.6 m, a diameter of14.6 m and a total weight of 12500 t.

Track reconstruction of cosmic ray real data with the CMS Silicon Strip Tracker

The CMS tracking system consists of a silicon pixel vertex detector and a surrounding silicon microstrip detector. The system is currently going through final assembly stage. As the construction goes on, big parts of the detector are being powered, controlled and readout as a whole. A cosmic ray trigger has been setup, thus providing the first real events recorded in the CMS tracker. Reconstruction was performed with three track finder algorithms; we will talk about the Combinatorial Track Finder, which is based on the Kalman Filter technique for both trajectory building and track fitting. A dedicated algorithm for cosmic ray track's seeding has been developed, together with useful tools for the tracking performance analysis; the exercise has been very useful for the understanding and the improvement of the tracking algorithm.

The construction of the CMS Silicon Strip Tracker Inner Barrel and Disks

In the last year the CMS Silicon Tracker Inner Barrel has been tested, each shell and disk individually, assembled in the two halves, shipped to CERN, dressed with the final services and finally integrated together with the Outer Barrel and the Endcaps. These steps will be briefly described together with the results of the tests performed at each step to monitor the status of the detector and of the cosmic run of a fraction of the CMS Silicon Tracker which is, at the time of this conference, on-going.

Data acquisition software for the CMS strip tracker

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.

Monitoring the CMS strip tracker readout system

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 data acquisition monitoring of the Strip Tracker uses both the data acquisition and the reconstruction software frameworks in order to provide real-time feedback to shifters on the operational state of the detector, archiving for later analysis and possibly trigger automatic recovery actions in case of errors. Here we review the proposed architecture of the monitoring system and we describe its software components, which are already in place, the various monitoring streams available, and our experiences of operating and monitoring a large-scale system.

Local reconstruction software for the CMS silicon strip tracker

CMS has a two level trigger system. The first stage is hardware based and provides fast trigger decisions up to a rate 100 kHz. The second stage, known as the High-Level Trigger, is entirely software based and required to provide a trigger decision within 40 ms and a rejection factor of a thousand to achieve a write-to-disk rate of 100 Hz. One of the most CPU-intensive tasks within the High-Level Trigger is the reconstruction of tracking hits using raw data from the strip tracker. This study profiles the performance of these reconstruction algorithms. Even at low luminosities, the average processing time is 5.5 s, which already exceeds the HLT budget. A new schema, optimised for speed and performance, has been developed to reconstruct hits within regions-of-interest only. For the entire sub-detector, hit reconstruction times are reduced to 140 ms. Since only 10 % of High-Level Trigger events are expected to require track reconstruction, the average contribution per event is then ∼14 ms i.e. 30 % of the full budget. Regional reconstruction is tested over Z0 → e+e− events, by unpacking in η-ϕ windows of 0.16 × 0.16 around seeds identified in the calorimeter. In this case, only 2 ± 1 % of the silicon strip tracker raw data is reconstructed in 5 ± 3 ms (or an average contribution per event of 0.5 ms) whilst maintaining 99 % of the original dielectron trigger efficiency.

The CMS tracker operation and performance at the Magnet Test and Cosmic Challenge

During summer 2006 a fraction of the CMS silicon strip tracker wasoperated in a comprehensive slice test called the Magnet Test andCosmic Challenge (MTCC). At the MTCC, cosmic rays detected in the muonchambers were used to trigger the readout of all CMS sub-detectors inthe general data acquisition system and in the presence of the 4 Tmagnetic field produced by the CMS superconducting solenoid. Thisdocument describes the operation of the Tracker hardware and softwareprior, during and after data taking. The performance of the detectoras resulting from the MTCC data analysis is also presented.

Track reconstruction of real cosmic muon events with CMS tracker detector

The CMS Silicon Strip Tracker (SST) construction has been completed on March 2007. From then to July 2007 the SST has gone through of a long series of tests, involving the cosmic ray data taking. Track reconstruction has been performed with three track finders. We will talk about the so called Combinatorial Track Finder, one of the default CMS track finders, and about its generalization to the cosmic ray case. For the first time this algorithm has been run on real data, both online and offline. Tracking performances on simulated and real data will be discussed.

A novel Si strip array to investigate reaction and decay mechanisms

The performance of a novel set-up of double-sided silicon micro-strip detectors (DSSD) developed for the GSI-R3B project (reaction studies with relativistic radioactive beams) is presented. The set-up was used in an experiment aimed at measuring the two-proton decay of 19Mg. This experiment required to record simultaneously protons and the residual nuclei with good position and energy resolution. Our experimental results show that both protons and heavy ions ranging from Z=2 up to Z=12 can be identified with good signal-to-noise ratio and high energy and spatial resolution. This allowed to reconstruct 2- and 3-particle vertices with high precision, opening the possibility to measure lifetimes of very short-lived nuclei and to obtain precise angular correlations of the outgoing particles. This detection system serves as a prototype for the R3B recoil detector, which will be composed of a two-layer Si strip tracker.

Overview and status of the CMS silicon strip tracker

The CMS experiment at the LHC features the largest Silicon Strip Detector ever built. The impact of the operating conditions and physics requirements on the design choices of the CMS Silicon Tracker is reviewed. The readiness of the Silicon Strip Tracker for the tentatively scheduled CMS commissioning in Summer 2008 is briefly described.

The construction of the CMS Silicon Strip Tracker

The CMS Silicon Strip tracker is a very large scale tracker entirely based on silicon strip detectors technology. The integration of modules, electronics, mechanics and services has been completed within the last eighteen months; first large standalone sub-structures (shells, disks, rods, petals depending on the tracker subdetector) have been integrated and verified; then they have been brought together into the final configuration. The CMS silicon tracker design and its construction is reviewed with particular emphasis on the procedures and quality checks deployed to successfully assembly several silicon strip modules and all ancillary components into these large sub-structures. An overview of the results and the lesson learned from the tracker integration are given, also in terms of failure and damage rates.

CMS Tracker Integration: monitoring the process quality

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.

Module production for the CMS Tracker: Problems and achieved quality

The construction of the CMS Inner Tracker is nearing completion. The various components are being mounted on the large structures and by the end of 2006 the tracker assembly will be finished at CERN. The basic elements of the strip tracker are the silicon sensor modules. In total about 15,000 modules of various geometries have been built by a large collaboration of institutes. This paper will explain the design and the semi-automatic assembly procedures. The major problems which appeared during this production are discussed. The final section gives an overview of the obtained results.

Construction of the CMS silicon strip tracker

In the last year the CMS experiment has constructed and integrated the largest ever build full Silicon Strip Tracker. The CMS Tracker collaboration set up a unique scheme of quality control to ensure the necessary high quality of all of the 15,148 modules and their super structures. The applied scheme of quality control revealed several problems, which escaped the initial R&D phase, ranging from corrosion effects on the silicon, capton and via problems on the front end hybrids up to aging conductive glue connections. An overview of the construction and qualification experience is given, discussing the major steps which result in the unique experimental device, which the CMS Tracker is currently commissioning.

The CMS Silicon Strip Tracker: Experience in integration and commissioning

The CMS Silicon Strip Tracker (SST) is now in its final installation phase. All the various subsections are now at CERN and are either undergoing final assembly or being tested with cosmic rays. The CMS schedule foresees to lower the whole SST by summer 2007 so that it can be cabled and be ready in time for the first beams provided by the LHC. The fruitful completion of this project (ongoing now for more than 10 years) will be thanks to an enormous effort by hundreds of people from many institutions in the design and construction phase of the detector. Yet it is now that the biggest effort is needed in bringing all pieces together and ensuring that they work to specification, in other words, integration and commissioning. This paper will focus on some of the points that have come up during integration of the sub-assemblies and some of the issues that have had to be addressed to ensure that the SST performs according to specifications.