L. Moneta

ROOT | A C++ Framework for Petabyte Data Storage, Statistical Analysis and Visualization

ROOT is an object-oriented C++ framework conceived in the high-energy physics (HEP) community, designed for storing and analyzing petabytes of data in an efcient way. Any instance of a C++ class can be stored into a ROOT le in a machine-independent compressed binary format. In ROOT the TTree object container is optimized for statistical data analysis over very large data sets by using vertical data storage techniques. These containers can span a large number of les

The design, construction and performance of the ALEPH silicon vertex detector

Abstract The ALEPH silicon vertex detector is the first detector operating in a colliding beam environment that uses silicon strip detectors which provide readout on both sides and hence a three-dimensional point measurement for the trajectory of charged particles. The detector system was commissioned successfully at the e+e− collider LEP at the research centre CERN, Switzerland, during the year 1991 while taking data at the Z0 resonance. The achieved spatial resolution of the complete 73 728 channel device (intrinsic plus alignment) is 12 μm in the r-f view and 12 μm in the z view. The design and construction of the entire detector system are discussed in detail and the experience gained in running the detector will be described with special emphasis on the uses of this novel tracking device for the physics of short-lived heavy particles produced in the decays of the Z0 resonance.

THE NEW ALEPH SILICON VERTEX DETECTOR

The ALEPH collaboration, in view of the importance of effective vertex detection for the Higgs boson search at LEP 2, decided to upgrade the previous vertex detector. Main changes were an increased length (+/- 20 cm), a higher granularity for r phi view (50 mu m), a new preamplifier (MX7 rad hard chip), a polymide (upilex) fan-out on z side to carry the signals from the strips to the front-end electronics outside the fiducial region reducing consequently the passive material in the central region by a factor of two. The detector, the running experience and its performance will be described

Recent results and running experience of the new ALEPH Vertex Detector

A description of the new ALEPH Vertex Detectors (VEDET 91), including the new mechanical structure and the improved data acquisition system, is given. The apparatus consists of two complete layers of silicon detectors with double-sided readout which provide full x,y,z information on the impact points of charge particles. The authors present results on signal-to-noise ratio for minimum ionizing particles and efficiency in hit/track matching. Results on position, impact parameter, and momentum resolution are also shown as measured using high-momentum muons. Preliminary results on single hit and impact parameter resolution show that the detectors and VLSI read-out electronics work as expected, and the performance compares well with previous test beam results and Monte Carlo simulations. Preliminary results on precision vertex reconstruction show a significant improvement in the data analysis which will be fully exploited in studying tau , b and c physics when all statistics are available.<<ETX>>

Operational experience with a large detector system using silicon strip detectors with double sided readout

Abstract A large system of silicon strip detectors with double sided readout has been successfully commissioned over the course of the last year at the e + e − collider LEP. The readout of this 73 728 channel system is performed with custom designed VLSI charge sensitive amplifier chips (CAMEX64A). An overall point resolution of 12 μm on both sides has been acheived for the complete system. The most important difficulties during the run were beam losses into the detector, and a chemical agent deposited onto the electronics; however, the damage from these sources was understood and brought under control. This and other results of the 1991 data-taking run are described with special emphasis on the operational experience.

The CDF online silicon vertex tracker

The CDF Online Silicon Vertex Tracker (SVT) reconstructs 2D tracks by linking hit positions measured by the Silicon Vertex Detector to the Central Outer Chamber tracks found by the eXtremely Fast Tracker (XFT). The system has been completely built and assembled and it is now being commissioned using the first CDF run II data. The precision measurement of the track impact parameter will allow triggering on B hadron decay vertices and thus investigating important areas in the B sector, like CP violation and B(s) mixing. In this paper we briefly review the architecture and the tracking algorithms implemented in the SVT and we report on the performance of the system achieved in the early phase of CDF run II.

MINUIT package parallelization and applications using the RooFit package

The fitting procedures are based on numerical minimization of functions. The MINUIT package is the most common package used for such procedures in High Energy Physics community. The main algorithm in this package, MIGRAD, searches the minimum of a function using the gradient information. For each minimization iteration, MIGRAD requires the calculation of the derivative for each free parameter of the function to be minimized. Minimization is required for data analysis problems based on the maximum likelihood technique. The calculation of complex likelihood functions, with several free parameters, many independent variables and large data samples, can be very CPU-time consuming. Then, the minimization process requires the calculation of the likelihood functions several times for each minimization iteration. In this paper we will show how MIGRAD algorithm and the likelihood function calculation can be easily parallelized using Message Passing Interface techniques. We will present the speed-up improvements obtained in typical physics applications such as complex maximum likelihood fits using the RooFit package.

Construction and performance of the new ALEPH Vertex Detector

A new Silicon Vertex Detector was developed for the ALEPH experiment and first installed for the high energy run at 130 GeV at the end of 1995. The detector has an active length of 40 cm and consists of two concentric layers of silicon wafers with double-sided readout. It extends the angular coverage, has only half the passive material as the former detector in the tracking volume and is radiation hard to cope with the higher level of radiation background expected for the LEP2 phase. The construction and the performance of the detector is described.

Recent developments of the ROOT mathematical and statistical software

Advanced mathematical and statistical computational methods are required by the LHC experiments to analyzed their data. These methods are provided by the Math work package of the ROOT project. An overview of the recent developments of this work package is presented by describing the restructuring of the core mathematical library in a coherent set of C++ classes and interfaces. The achieved improvements, in terms of performances and quality, of numerical methods present in ROOT are shown as well. New developments in the fitting and minimization packages are reviewed. A new graphics interface has been developed to drive the fitting process and new classes are being introduced to extend the fitting functionality. Furthermore, recent and planned developments of integrating in the ROOT environment new advanced statistical tools required for the analysis of the LHC data are presented.

Initial experience with the CDF SVT trigger

The Collider Detector at Fermilab (CDF) Silicon Vertex Tracker (SVT) is a device that works inside the CDF Level 2 trigger to find and fit tracks in real time using the central silicon vertex detector information. SVT starts from tracks found by the Level 1 central chamber fast trigger and adds the silicon information to compute transverse track parameters with offline quality in about . The CDF SVT is fully installed and functional and has been exercised with real data during the spring and summer 2001. It is a complex digital device of more than 100 VME boards that performs a dramatic data reduction (only about one event in a thousand is accepted by the trigger). Diagnosing rare failures poses a special challenge and SVT internal data flow is monitored by dedicated hardware and software. This paper briefly covers the SVT architecture and design and reports on the SVT building/commissioning experience (hardware and software) and on the first results from the initial running.