This paper discusses the effects of radiation damage to SiPMs on the performances of plastic scintillator counters with series-connected SiPM readout, focusing on timing measurements. The ...performances of a counter composed of a 120×40×5mm3 scintillator tile read out by two sets of six SiPMs from AdvanSiD connected in series attached on the short sides are presented, for different combinations of SiPMs at various levels of irradiation. Firstly, six SiPMs were equally irradiated with electrons from 90Sr sources up to a fluence of Φe−≈3×1012cm−2. The timing resolution of the counter gradually deteriorated by the increase in dark current. The dark current and the deterioration were reduced when the counter was cooled from 30 °C to 10 °C. Secondly, 33 SiPMs were irradiated with reactor neutrons. The fluence levels ranged from Φeq≈8.7×108cm−2 to Φeq≈5.5×1013cm−2. The characteristics of counters read out by series-connected SiPMs with non-uniform damage levels were investigated. The signal pulse height, the time response, and the timing resolution depend on the hit position in the counter when SiPMs’ irradiation is not uniform.
We have developed a new laser-based time calibration system for highly segmented scintillator counters like the MEG II pixelated Timing Counter (pTC), consisting of 512 centimetre-scale scintillator ...counters read out by silicon photomultipliers (SiPMs). It is difficult to apply previous laser-based calibration methods for conventional metre-scale Time-Of-Flight detectors to the MEG II pTC from the implementation and the accuracy points of view. This paper presents a new laser-based time calibration system which can overcome such difficulties. A laser pulse is split into each scintillator counter via several optical components so that we can directly measure the time offset of each counter relative to the laser-emitted time. We carefully tested all the components and procedures prior to the actual operation. The laser system was installed into the pTC and thoroughly tested under the real experimental condition. The system showed good stability and being sensitive to any change of timing larger than ∼10ps. Moreover, it showed an uncertainty of 48ps in the determination of the time offsets, which meets our requirements. The new method provides an example of the implementation of a precise timing alignment for the new type of detectors enabled by the advance of SiPM technology.
A high resolution Timing Counter for the MEG II experiment De Gerone, M.; Bevilacqua, A.; Biasotti, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2016, Letnik:
824
Journal Article
Recenzirano
The development of a Timing Counter detector designed for the MEGII upgrade of the MEG experiment, which strives to improve the sensitivity on the μ+→e+γ decay of an order of magnitude, is presented. ...It is based on two sets of counters (sectors) arranged on a semi-cylindrical structure; each sector consists of 256 counters. Each counter consists of tile of fast scintillator with a dual-side read-out based on SiPM arrays in series connection. The high granularity has two advantages: optimized size for achieving high resolution (75ps) for the single counter, and a signal e+ crosses several counters, so that resolution improves by averaging multiple time measurements. A prototype has been built and tested both in BTF and PSI facilities in order to prove the multi-hit scheme in MEG-like beam conditions. A 35ps resolution with eight hits has been obtained with a e+ beam at 100kHz. The first sector will be tested in the MEG II pre-engineering run planned at the end of 2015.
The MEG II experiment (Baldini et al., 2018) 1 is designed to improve the sensitivity to the μ+→e+γ decay. A crucial component is the Pixelated Timing Counter (pTC), dedicated to the measurement of ...the positron time to reduce the combinatorial background (Cattaneo et al., 2014; Nishimura et al., 2016) 3,4. The detector consists of 512 scintillation counters, each performing a precise measurement of the positron crossing time. This approach requires that the time offsets of the counters are calibrated and regularly monitored over the lifetime of the experiment. The pTC time calibration and monitor system will use a laser diode to deliver pulses to each pixel. The system components have been tested in laboratory, the results demonstrate that a calibration and monitoring resolution satisfying the requirements is within reach.
The MEG II experiment is designed to improve by an order of magnitude the sensitivity of 4.2×10−13 reached by MEG on the search for μ+→e+γ decay. A pixelated Timing Counter (pTC) has been developed ...to improve the time resolution by measuring the positron time information independently with several counters. We constructed and installed the pTC and performed commissioning runs at the πE5 beam line at PSI. A resolution of 38.5 ps is obtained with commissioning run data.
The MEGII Timing Counter will measure the positron time of arrival with a resolution of ~ 30ps relying on two arrays of scintillator pixels read out by 6144 Silicon Photomultipliers (SiPMs) from ...AdvanSiD. They are characterised, measuring their breakdown voltage, to assure that the gains of the SiPMs of each pixel are as uniform as possible, to maximise the pixel resolution. Gain measurements have also been performed.
•Characterisation of SiPMs for MEG-II Timing Counter is illustrated.•SiPMs breakdown voltage and gain measurement are reported.•The criterion for the choice of each single pixel SiPMs is explained.
Flavour violating muon decays Mori, T.; Ootani, W.
Progress in particle and nuclear physics,
11/2014, Letnik:
79
Journal Article
Recenzirano
We review experimental searches for flavour violating muon decays that are strongly suppressed to negligible levels in the standard model but are predicted to occur at measurable rates in many of the ...proposed new physics scenarios. Present and future experimental programs are presented and discussed together with newly developed experimental techniques that enable these experiments to explore extremely rare processes.
PDF
