Recent experimental results concerning heavy systems (Pb+Au, Pb+Ag, Pb+Al, Gd+C, Gd+U, Xe+Sn, …) obtained at GANIL with the INDRA and NAUTILUS 4π arrays will be presented. The study of reaction ...mechanisms has shown the dominant binary and highly dissipative character of the process. The two heavy and excited fragments produced after the first stage of the interaction can decay into various decay modes from evaporation to multifragmentation including fission. However, deviations from this simple picture have been found by analyzing angular and velocity distributions of light charged particles, and fragments. Indeed, there is a certain amount of matter in excess emitted between the two primary sources suggesting either the existence of a mid-rapidity source similar to the one observed in the relativistic regime (participants) or a strong deformation induced by the dynamics of the collision (neck instability). This last possibility has been suggested by analyzing in detail the angular distributions of the fragments. More precisely, we observe an isotropic component which is compatible with the prediction of statistical models and a second one corresponding to breakup aligned with the recoil direction of the projectile like source which should be compared with the predictions of dynamical calculations based on microscopic transport models.
Four different combinations of 9644Ru and 9640Zr nuclei, both as projectile and target, were investigated at the same bombarding energy of 400A MeV using a 4pi detector. The degree of isospin mixing ...between projectile and target nucleons is mapped across a large portion of the phase space using two different isospin-tracer observables, the number of measured protons and the tritium to 3He yield ratio. The experimental results show that the global equilibrium is not reached even in the most central collisions. Quantitative measures of stopping and mixing are extracted from the data. They are found to exhibit a quite strong sensitivity to the in-medium ( n,n) cross section used in microscopic transport calculations.
Ageing tests on the low-resistivity RPC for the ALICE dimuon arm Arnaldi, R.; Baldit, A.; Barret, V. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2003, Letnik:
508, Številka:
1-2
Journal Article
Spatial resolution of RPC in streamer mode Arnaldi, R.; Baldit, A.; Barret, V. ...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment,
09/2002, Letnik:
490, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
In the framework of an R&D program on the ALICE dimuon trigger system, the spatial resolution of Resistive Plate Chambers working in streamer mode has been investigated during beam tests. Preliminary ...studies with cosmic rays had evidenced a dependence of the charge profile to the high voltage and to the gas mixture. However, the spatial resolution measured from the beam tests is only slightly varying with the high voltage and is close to the expected value
w/
12
where w is the strip pitch, for strips of 1 and
2
cm
width. The probability to fire a strip as a function of the distance from the strip to the particle impact has been measured for various high voltages. A simple parametrisation of this probability has been achieved. This allows to predict, under various working condition, the cluster size distributions for RPCs with different strip widths and also to account for the effect of the particle incident angle.
TONNERRE: an array for delayed-neutron decay spectroscopy Buţă, A; Martin, T; Timiş, C ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2000, Letnik:
455, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The design and construction of an array for delayed-neutron decay spectroscopy is presented. The array is composed of 32 plastic scintillator (BC400) modules each of which provide for time-of-flight ...(energy) and position measurements. The intrinsic detection efficiency is 30% at
E
n=2 MeV and the resolution δ
E
n/
E
n∼10% (FWHM). The array can cover a total solid angle of up to 50% of 4π. Details of studies performed to optimize the performances of the individual modules are reported, as well as source testing and in-beam commissioning.
The trigger setup of the dimuon arm of ALICE, the dedicated Heavy-Ion Experiment at LHC, is based on Resistive Plate Chambers (RPCs). This gaseous detector can be operated either in streamer or in ...avalanche mode, each mode having its own advantages and drawbacks. Using conventional discrimination techniques, like single threshold or constant fraction discriminator, the time resolution is better in avalanche mode (commonly
1
ns
) unless the RPC is operated in streamer mode at quite high running voltages which is not suitable. Since we propose to operate the RPCs in streamer mode in ALICE, we have studied a new discrimination technique in order to improve the time resolution in this mode. With this method, a comparable timing quality as one of the avalanche modes is typically obtained, as soon as the applied voltage is sufficient for the RPC to reach the full efficiency. This is an important progress not only for the ALICE trigger but also because the RPC detector is widely used in streamer mode.
ALICE, the experiment dedicated to the study of heavy ion collisions at LHC, will be equipped with a forward spectrometer to identify heavy quarkonium states from their decay into muons. The trigger ...system of the spectrometer consists of four planes of resistive plate chambers, front-end and fast-decision electronics. It is designed to reconstruct muon tracks in a large background environment and to provide a fast trigger signal to the spectrometer. We present results from the test of a trigger prototype that have been carried out with the muon beam of the CERN/SPS at the Gamma Irradiation Facility (GIF). The track finding efficiency as well as the robustness of the system to the uncorrelated background induced on the detector by the GIF source are discussed. Special emphasis is put on timing aspects which are crucial at LHC. A self-consistent method for timing optimization and monitoring is proposed. The findings, although specific to ALICE, are relevant to any muon trigger system operating at LHC.
The mass distributions of baryon resonances populated in near-central collisions of Au on Au and Ni on Ni are deduced by defolding the $p_t$ spectra of charged pions by a method which does not depend ...on a specific resonance shape. In addition the mass distributions of resonances are obtained from the invariant masses of $(p, \pi^{\pm})$ pairs. With both methods the deduced mass distributions are shifted by an average value of -60 MeV/c$^2$ relative to the mass distribution of the free $\Delta(1232)$ resonance, the distributions descent almost exponentially towards mass values of 2000 MeV/c^2. The observed differences between $(p, \pi^-)$ and $(p, \pi^+)$ pairs indicate a contribution of isospin $I = 1/2$ resonances. The attempt to consistently describe the deduced mass distributions and the reconstructed kinetic energy spectra of the resonances leads to new insights about the freeze out conditions, i.e. to rather low temperatures and large expansion velocities.
The ALICE dimuon trigger: overview and electronics prototypes Arnaldi, R; Baldit, A; Barret, V ...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment,
12/2000, Letnik:
456, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
ALICE is the LHC experiment (2005) dedicated to the study of heavy ion collisions. Amongst the ALICE sub-detectors, the muon spectrometer will investigate the dimuon production from heavy resonance ...(J/
ψ,
ϒ) decays, which is believed to be a promising signature of the Quark Gluon Plasma (QGP) formation. For maximum efficiency of the spectrometer, a dedicated dimuon trigger is presently built. The detector part itself is based on resistive plate chambers (RPCs) operated in streamer mode and is the topic of another contribution to this conference. This paper gives the principle and the simulated performances of the trigger and is also focussed on the description of the electronics prototypes and future developments. The RPCs are read-out by
X and
Y orthogonal strips: the front-end chips are presently developed. The signals are sent to the trigger electronics which basically performs a
p
t cut on the tracks to reduce the background. A prototype of fast (decision time 200 ns) programmable electronics working in a pipelined mode at 40 MHz has been built and tested. This prototype handles simultaneously 160 digital information from the strips. The tests of the trigger card have required the construction of a pattern generator (160 bits at 40 MHz).
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