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Proceedings supplement for conference poster at Neutrino 2010, Athens, Greece.
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The front-end electronics of the ATLAS hadronic calorimeter (Tile Cal) is housed in a unit, called {it PMT-Block}. The PMT-Block is a compact instrument comprising a light mixer, a PMT together with its divider and a {it 3-in-1} card, which provides shaping, amplification and integration for the signals. This instrument needs to be qualified before being assembled on the detector. A PMT-Block test bench has been developed for this purpose. This test bench is a system which allows fast, albeit accurate enough, measurements of the main properties of a complete PMT-Block. The system, both hardware and software, and the protocol used for the PMT-Blocks characterisation are described in detail in this report. The results obtained in the test of about 10000 PMT-Blocks needed for the instrumentation of the ATLAS (LHC-CERN) hadronic Tile Calorimeter are also reported.
Double Chooz main target is to measure Theta13 oscillation parameter by comparing reactor neutrino fluxes in two identical detectors located respectively at 400 m and 1 km away from the 2 Chooz reactor cores. The far detector is now under construction, while we have just completed the design phase of the near one. In this report I will discuss the detector principle, sensitivity and its present construction status.
We describe a muon track reconstruction algorithm for the reactor anti-neutrino experiment Double Chooz. The Double Chooz detector consists of two optically isolated volumes of liquid scintillator viewed by PMTs, and an Outer Veto above these made of crossed scintillator strips. Muons are reconstructed by their Outer Veto hit positions along with timing information from the other two detector volumes. All muons are fit under the hypothesis that they are through-going and ultrarelativistic. If the energy depositions suggest that the muon may have stopped, the reconstruction fits also for this hypothesis and chooses between the two via the relative goodness-of-fit. In the ideal case of a through-going muon intersecting the center of the detector, the resolution is ~40 mm in each transverse dimension. High quality muon reconstruction is an important tool for reducing the impact of the cosmogenic isotope background in Double Chooz.
Modern precision neutrino experiments like Double Chooz require a highly efficient trigger system in order to reduce systematic uncertainties. The trigger and timing system of the Double Chooz experiment was designed according to this goal. The Double Chooz trigger system is driven by the basic idea of triggering on multiple thresholds according to the total visible energy and additionally triggering on the number of active photomultiplier tubes (PMTs) in the detector. To do so, the trigger system continuously monitors the analogue signals from all PMTs in the detector. The amplitudes of these PMT-signals are summed for groups of certain PMTs (group signals) and for all PMTs (sum signal), respectively. The group signals are discriminated by two thresholds for each input channel and four thresholds for the sum signal. The resulting signals are processed by the trigger logic unit which is implemented in a FPGA. In addition to the proper trigger, the trigger system provides a common clock signal for all subsequent data acquisition systems to guarantee a synchronous readout of the Double Chooz detectors. The present design of the system provides a high flexibility for the applied logic and settings, making it useful for experiments other than Double Chooz. The Double Chooz trigger and timing system was installed and commissioned in 2011. This article describes the hardware of the trigger and timing system. Furthermore the setup, implemented trigger logic and performance of the trigger and timing system for the Double Chooz experiment is presented.
The Double Chooz experiment measures the neutrino mixing angle $theta_{13}$ by detecting reactor $bar{ u}_e$ via inverse beta decay. The positron-neutron space and time coincidence allows for a sizable background rejection, nonetheless liquid scintillator detectors would profit from a positron/electron discrimination, if feasible in large detector, to suppress the remaining background. Standard particle identification, based on particle dependent time profile of photon emission in liquid scintillator, can not be used given the identical mass of the two particles. However, the positron annihilation is sometimes delayed by the ortho-positronium (o-Ps) metastable state formation, which induces a pulse shape distortion that could be used for positron identification. In this paper we report on the first observation of positronium formation in a large liquid scintillator detector based on pulse shape analysis of single events. The o-Ps formation fraction and its lifetime were measured, finding the values of 44$%$ $pm$ 12$%$ (sys.) $pm$ 5$%$ (stat.) and $3.68$ns $pm$ 0.17ns (sys.) $pm$ 0.15ns (stat.) respectively, in agreement with the results obtained with a dedicated positron annihilation lifetime spectroscopy setup.
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