The ALICE experiment at the CERN LHC

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

Ion spectroscopy — A diamond characterization tool

The stopping power Delta E and the energy-loss resolution delta E/Delta E of Single-Crystal CVD-Diamond Detectors (SC-DDs) measured with relativistic Heavy Ions (HIs) are interpreted as global quality parameters, characterizing simultaneously crystal texture and carrier-trapping concentrations, as well as the charge-transport properties of intrinsic diamond samples. HI spectra are presented, where spectral lines are obtained similar to the predictions of the Lindhard and Sorensen (LS) theory [J. Lindhard, A.H. Sorensen, Phys. Rev. A 53 (1996) 2443]. The spectroscopic results indicate an almost defect free material, and spatial homogeneity of all parameters relevant to the detector signal (i.e., mass density, dielectric constant, drift mobility and velocity of the charge carriers). Measured and simulated transient current signals generated by relativistic Xe-132 ions are discussed according to theories [A. Many, G. Rakavy, Phys. Rev., 126 (1962) 1980: G. Juska, M. Viliunas. O. Klima, E. Sipek. J. Kocka, Phil, Mag. B 69 (1994) 277; G. Juska, M. Viliunas, K. Arlauskas, J. Kocka, Phys. Rev. B 51 (1994) 16 668] of space-charge limited current (SCLC) transients. The evidence of the spectroscopic results is confirmed by the current-mode studies, and thus indirectly, the potential of the characterization method as well

Diagnostic scheme for the HITRAP decelerator

The HITRAP linear decelerator currently being set up at GSI will provide slow, few keV/u highly charged ions for atomic physics experiments. The expected beam intensity is up to 105 ions per shot. To optimize phase and amplitude of the RF systems intensity, bunch length and kinetic energy of the particles need to be monitored. The bunch length that we need to fit is about 2 ns, which is typically measured by capacitive pickups. However, they do not work for the low beam intensities that we face. We investigated the bunch length with a fast CVD diamond detector working in single particle counting mode. Averaging over 8 shots yields a clear, regular picture of the bunched beam. Energy measurements by capacitive pickups are limited by the presence of intense primary and partially decelerated beam and hence make tuning of the IH-structure impossible. The energy of the decelerated fraction of the beam behind the first deceleration cavity was determined to about 10 % accuracy with a permanent dipole magnet combined with a MCP. Better detector calibration should help reaching the required 1%. Design of the detectors as well as the results of the measurements will be presented