The ALICE experiment is one of the four approved experiments to be run at the Large Hadron Collider (LHC) which is on the way to be built at CERN in Geneva (Switzerland). The Inner Tracking System (ITS) of the ALICE detector is the vertex detector. It is made of six layers of silicon detectors of three kinds: Silicon Pixel Detectors (SPD), Silicon Drift Detectors (SDD), and Silicon Strip Detectors (SSD). More information on the ALICE experiment and on the ITS can be found in the ALICE Technical Proposal and in the ITS Technical Design Report (huge 160 Mb Postscript file). The interested reader can also have a look at the Technical Design Reports' page here.

This is a web page to organize the software distribution of the ALICE ITS Off-line Group lead by:

ITS Off-line Software Coordinator: Roberto Barbera ­ http://www.ct.infn.it/~barbera

ITS Off-line Software Librarian: Bjørn S. Nilsen ­ http://www.physics.ohio-state.edu/~nilsen

The ITS code, as part of the whole ALICE Off-line code (called Aliroot), is based on the ROOT framework completely developed in a C++ Object Oriented technology. More information on the global structure of the code and on the organisation of the Alice Off-line Project can be found in the official home-page. You can even interactively browse the class index of the code itself starting from here (ITS specific classes are named AliITSxxxx).

General scheme

A logical scheme of the ITS Off-line Software is depicted here. Aliroot is used to create hits and store them in the file galice.root. This file is read by the package ITSSIM which is in charge of creating DIGITS with the slow simulator (taking into account noise, thresholds and electronic response) or directly POINTS with the fast simulator (gaussian randomization of the hits with sigma values of the spatial resolution coming both from slow simulations and test beams). DIGITS should be as close as possible to the experimental data we plan to get from the real detector. DIGITS and POINTS are usualy written out on a ROOT files for further analysis. The package ITSRECO reads the DIGITS in and performs the cluster finding to determine POINTS coming from the slow simulation. POINTS are then read by ITSTRACK package which performs the track finding necessary for further physical analyses. All ITS entities (HITS, DIGITS (clusters), POINTS, TRACKS, and so on) can be read by the visualization package ITSDISPLAY on the same basis as the experimental data when they will come out.

Geometry

Three different ITS geometries are available in the current version of the Aliroot code. Version 1 is the so-called "coarse" geometry consisting of six cylinders. Version 3 is an old detailed version originally hand coded in GEANT3 style and then translated in ROOT style (thanks to Federico Carminati) and represents part of the geometry defined in the ALICE technical proposal. Version 5 is the current detailed version, the only one currently maintained for which the reconstruction software is being developed. Pictorial views of the various ITS geometries will be linked to this page very soon.

The implementation of the detailed geometry (version 5) of the ITS into AliRoot is driven by a semi-automatic procedure which converts the CAD files from the ITS engineers (see below) to two ASCII files read by AliRoot during the simulation phase. These are: ITSgeometry_5.tme (Sep 28 1999), which contains the information about the materials the ITS volumes are made of, and ITSgeometry_5.euc (Nov 2 1999), which contains the information about the geometrical definition (size and thickness), the position and the rotation matrix of the various ITS volumes in the global reference frame. A third geometry file, ITSgeometry_5.det (Dec 8 1999), is then created from ITSgeometry_5.euc (Nov 2 1999) and contains the detector database necessary for the reconstruction phase. Each of the 20*4+40*4+6*14+8*22+23*34+26*38=2270 sensitive detectors of the ITS is described by 12 numbers. The three detector identifiers layer, ladder, and detector numbers (layer number ranges from 1-6; the ladder number ranges from 1-20, 1-40, 1-14, 1-22, 1-34, 1-38 depending on the layer number value; and the detector number ranges from 1-4, 1-4, 1-6, 1-8, 1-23, 1-26 also depending on the layer number value [in this last geometry]). The three coordinates of the centers of the detector in the global reference frame, and the 6 angles "a la GEANT3.12" describing the rotations of the local reference axes of the detector with respect to the global ones (see the GEANT3 manual for more details). In order to see how the ITS modules have been named from these layer, ladder and detector numbers, look at the Silicon Pixel Detectors (front and side view), the Silicon Drift Detectors (front and side view) and the Silicon Strip Detectors (front and side view). In each figure, (x,y,z) refer to the global reference system while (x',y',z') refer to the local reference system.

Software to be released with the official release of Aliroot 3.02 updated for compatibility with HP Unix and fixed typos in the geometry files. ITScode_3.02Db.tar.gz Comments about changes to the code. ITS code Aliroot 3.02 release notes The CAD files used to create the geometry defined for the ITS in Aliroot. CAD Files

For latest documentation click here

ITS Software Latest Release January 14 2000. ITS_code_012400.tar.gz Incomplete comments about changes and proposed changes in this distributions. ITS code 012400 Unreleased notes The CAD files used to create the geometry defined for this ITS release (same as for Official Release). CAD Files

Roberto Barbera and Santo Vanadia's module, point, and related classes.

Sylwester Radomski's point classes.

This is a collection of code fragments contributed by different groups that should be considered for use and inclusion in this or future releases of the ITS code.

Clustering Algorithms

Oil Spot ­ Catania contributed clustering algorithm

Hoshen Koppelman ­ Ohio State contributed clustering algorithm

Piergiorgio Cerello ­ Torino contributed clustering algorithm

Likelyhood ­ Ohio State E896 SDD clustering algorithm

This web page is bound to be missing many people and their contributions. Please send additional information to the Web Page author(s) . Thank you for your comments and/or suggestions from Jason Hubbell and Bjørn S. Nilsen.

This page is always under construction. Come and visit often to see news and updates.

Page maintained by: Jason Hubbell and Bjørn S. Nilsen.
Back to: ALICE home, Off-line home