ALICE (A Large Ion Collider Experiment) is a general-purpose, heavy-ion detector at the CERN LHC which focuses on QCD, the strong-interaction sector of the Standard Model. It is designed to address the physics of strongly interacting matter and the quark-gluon plasma at extreme values of energy density and temperature in nucleus-nucleus collisions. Besides running with Pb ions, the physics programme includes collisions with lighter ions, lower energy running and dedicated proton-nucleus runs. ALICE will also take data with proton beams at the top LHC energy to collect reference data for the heavy-ion programme and to address several QCD topics for which ALICE is complementary to the other LHC detectors. The ALICE detector has been built by a collaboration including currently over 1000 physicists and engineers from 105 Institutes in 30 countries. Its overall dimensions are 161626 m3 with a total weight of approximately 10 000 t. The experiment consists of 18 different detector systems each with its own specific technology choice and design constraints, driven both by the physics requirements and the experimental conditions expected at LHC. The most stringent design constraint is to cope with the extreme particle multiplicity anticipated in central Pb-Pb collisions. The different subsystems were optimized to provide high-momentum resolution as well as excellent Particle Identification (PID) over a broad range in momentum, up to the highest multiplicities predicted for LHC. This will allow for comprehensive studies of hadrons, electrons, muons, and photons produced in the collision of heavy nuclei. Most detector systems are scheduled to be installed and ready for data taking by mid-2008 when the LHC is scheduled to start operation, with the exception of parts of the Photon Spectrometer (PHOS), Transition Radiation Detector (TRD) and Electro Magnetic Calorimeter (EMCal). These detectors will be completed for the high-luminosity ion run expected in 2010. This paper describes in detail the detector components as installed for the first data taking in the summer of 2008.

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The ALICE experiment at the CERN LHC

ALICE is a general-purpose heavy-ion detector designed to study the physics of strongly interacting matter and the quark-gluon plasma in nucleus-nucleus collisions at the LHC at a center of mass energy of 5.5 TeV/nucleon. It is currently under construction and will be ready for data taking at LHC turn-on in 2007. The collaboration currently includes more than 900 physicists, both from nuclear physics and high-energy physics, from over 70 institutions in 27 countries.

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The alice experiment at the CERN LHC

The design, construction, and commissioning of the ALICE Time-Projection Chamber (TPC) is described. It is the main device for pattern recognition, tracking, and identification of charged particles in the ALICE experiment at the CERN LHC. The TPC is cylindrical in shape with a volume close to 90 m(3) and is operated in a 0.5T solenoidal magnetic field parallel to its axis. In this paper we describe in detail the design considerations for this detector for operation in the extreme multiplicity environment of central Pb-Pb collisions at LHC energy. The implementation of the resulting requirements into hardware (field cage, read-out chambers, electronics), infrastructure (gas and cooling system, laser-calibration system), and software led to many technical innovations which are described along with a presentation of all the major components of the detector, as currently realized. We also report on the performance achieved after completion of the first round of stand-alone calibration runs and demonstrate results close to those specified in the TPC Technical Design Report. (C) 2010 CERN for the benefit of the ALICE collaboration. Published by Elsevier B.V. All rights reserved. (Less)

The ALICE TPC, a large 3-dimensional tracking device with fast readout for ultra-high multiplicity events

In this paper we present the front end electronics for the time projection chamber (TPC) of the ALICE experiment. The system, which consists of about 570000 channels, is based on two basic units: (a) an analogue ASIC (PASA) that incorporates the shaping-amplifier circuits for 16 channels; (b) a mixed-signal ASIC (ALTRO) that integrates 16 channels, each consisting of a 10-bit 25-MSPS ADC, the baseline subtraction, tail cancellation filter, zero suppression and multi-event buffer. The complete readout chain is contained in front end cards (FEC), with 128 channels each, connected to the detector by means of capton cables. A number of FECs (up to 25) are controlled by a readout control unit (RCU), which interfaces the FECs to the data acquisition (DAQ), the trigger, and the detector control system (DCS). A function of the final electronics (1024 channels) has been characterized in a test that incorporates a prototype of the ALICE TPC as well as many other components of the final set-up. The tests show that the system meets all design requirements. Originally conceived and optimized for the time projection chamber (TPC) of the ALICE experiment, its architecture and programmability make this system suitable for the readout of a wider class of detectors.

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The ALICE TPC front end electronics

A specialized system of target and detector was developed at Jefferson Lab to provide new access to information about neutron structure from electron–neutron interactions. It allows identification and measurement of spectator protons produced in e - d → e - p s X scattering events. The detector is a radial time-projection chamber optimized for the acceptance of low-momentum protons. Gas gain is provided by three cascaded curved Gas Electron Multipliers (GEMs), the first application of GEMs in any configuration other than flat. This article provides details about the development and construction of the detector, its performance, and the analysis of the data from the successful running of its first physics experiment.

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BoNus : Development and use of a radial TPC using cylindrical GEMs

The ALTRO (ALICE TPC Read Out) chip is a mixed-signal integrated circuit designed to be one of the building blocks of the readout electronics for gas detectors. Originally conceived and optimised for the Time Projection Chamber (TPC) of the ALICE experiment at the CERN LHC, its architecture and programmability makes it suitable for the readout of a wider class of gas detectors. In one single chip, the analogue signals from 16 channels are digitised, processed. compressed and stored in a multi-acquisition memory. The Analogue-to-Digital converters embedded in the chip have a 10-bit dynamic range and a maximum sampling rate in the range of 20 to 40 MHz. After digitisation, a pipelined hardwired processor is able to remove from the input signal a wide range of systematic and non- systematic perturbations, related to the non-ideal behaviour of lite detector, temperature variation of the electronics, environmental noise, etc. Moreover. the processor is able to suppress the signal tail within 1 /spl mu/s after the pulse peak with 0.1% accuracy thus narrowing the pulses to improve their identification. The signal is then compressed by removing all data below a programmable threshold, except for a specified number of pre- and post-samples around each peak. This produces non-zero data packets. Eventually, each data packet is marked with its time stamp and size - so that the original data can be reconstructed afterwards and stored in lite multi-acquisition memory that has a readout bandwidth of 300 Mbyte/sec. This paper addresses the algorithms of lite implemented digital functions and the performance of the ALTRO chip on measured data.

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A.J. de Parga

Papers

The ALTRO chip: a 16-channel A/D converter and digital processor for gas detectors