The Mu2e calorimeter consists of 1348 undoped CsI crystals coupled to two large area UV-extended Silicon Photomultipliers (SiPMs). A modular and custom SiPM layout, a 3×2 matrix of 6×6 mm2 monolithic ...SiPMs, has been developed to satisfy the Mu2e requirements. As well as ensuring the performances needed for the muon-to-electron conversion search, these photosensors have to guarantee a good reliability while operating maintenance-free in the Mu2e hostile environment: any failure can only be replaced during a long technical shut-down scheduled once a year. After testing prototypes from different vendors, we selected Hamamatsu and the final production of about 4000 pieces is now ongoing. A detailed Quality Assurance (QA) program is then mandatory to minimize the risk of an unexpected further degradation in the performances. The QA process for each photosensor includes a first visual inspection and the subsequent characterization of each of its monolithic cells by means of an automatized test station, able to measure the breakdown voltage, the gain and the dark current. For each production batch (∼300 pieces), 5 devices are exposed to a neutron fluency up to ∼1.4×1011 1 MeV (Si) eq. n/cm2; others 15 devices are undergone an accelerated aging in order to verify the Mean Time To Failure (MTTF) of the batch. A summary of the QA and the results for the firsts 4 production batches are presented in the paper.
The Mu2e experiment at Fermilab will search for the charged-lepton flavor violating neutrino-less conversion of a negative muon into an electron in the field of an aluminum nucleus. The Mu2e detector ...is composed of a tracker, an electromagnetic calorimeter and an external veto for cosmic rays. The calorimeter plays an important role in providing excellent particle identification capabilities and a fast online trigger filter, while aiding the track reconstruction capabilities. Calorimeter requirements are to provide a large acceptance for 0∼10 MeV electrons and reach: i) a time resolution better than 0.5 ns; ii) an energy resolution better than 10%; and iii) a position resolution of 1 cm. The calorimeter consists of two disks, each one made of 674 pure CsI crystals. Each crystal is readout by two large area 2×3 arrays of UV-extended SiPMs of 6×6 mm2 dimensions. A large scale prototype (Module-0) has been tested at an electron beam. We report here the tests done to finalize the calorimeter design, the results obtained with Module-0 and the status of production. At this time, the performance characteristics of 85% of the crystals and all of the SiPMs have been measured. The calorimeter engineering drawings have been completed and the large mechanical components are under fabrication. Analog and digital electronics have been prototyped and tested with irradiation dose. Their serial production is being organized. The calorimeter assembly phase is planned for mid-2020.
The Mu2e experiment at Fermilab will search for Charged Lepton Flavor Violating conversion of a muon to an electron in an atomic field. The Mu2e detector is composed of a tracker, an electromagnetic ...calorimeter and an external system, surrounding the solenoid, to veto cosmic rays. The calorimeter plays an important role to provide: a) excellent particle identification capabilities; b) a fast trigger filter; c) an easier tracker track reconstruction. Two disks, located downstream of the tracker, contain 674 pure CsI crystals each. Each crystal is read out by two arrays of UV-extended SiPMs. The choice of the crystals and SiPMs has been finalized after a thorough test campaign. A first small scale prototype consisting of 51 crystals and 102 SiPM arrays has been exposed to an electron beam at the BTF (Beam Test Facility) in Frascati. Although the readout electronics were not final, results show that the current design is able to meet the timing and energy resolution required by the Mu2e experiment.
The Mu2e experiment at Fermilab searches for the charged-lepton flavor violating neutrino-less conversion of a negative muon into an electron in the field of an aluminum nucleus. The dynamics of such ...a process is well modeled by a two-body decay, resulting in a monoenergetic electron with an energy slightly below the muon rest mass (104.967 MeV). The calorimeter of this experiment plays an important role to provide excellent particle identification capabilities and an online trigger filter while aiding the track reconstruction capabilities. The baseline calorimeter configuration consists of two disks each made with ∼ 700 undoped CsI crystals read out by two large area UV-extended Silicon Photomultipliers. These crystals match the requirements for stability of response, high resolution and radiation hardness. In this paper we present the final calorimeter design.
The Mu2e experiment at FNAL aims to measure the charged-lepton flavor violating neutrinoless conversion of a negative muon into an electron. The conversion results in a monochromatic electron with an ...energy slightly below the muon rest mass (104.97 MeV). The calorimeter should confirm that the candidates reconstructed by the extremely precise tracker system are indeed conversion electrons while performing a powerful μ/e particle identification. Moreover, it should also provide a high level trigger for the experiment independently from the tracker system. The calorimeter should also be able to keep functionality in an environment where the background delivers a dose of ~ 10 krad/year in the hottest area and to work in the presence of 1 T axial magnetic field. These requirements translate in the design of a calorimeter with large acceptance, good energy resolution O(5%) and a reasonable position (time) resolution of ~ < 1 cm (<0.5ns). The baseline version of the calorimeter is composed by two disks of inner (outer) radius of 351 (660) mm filled by 1860 hexagonal BaF2 crystals of 20 cm length. Each crystal is readout by two large area APD's. In this paper, we summarize the experimental tests done so far as well as the simulation studies in the Mu2e environment.
The Mu2e crystal calorimeter Happacher, F.
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The Mu2e Experiment at Fermilab will search for coherent, neutrino-less conversion of negative muons into electrons in the field of an Aluminum nucleus, μ−+Al→e−+Al. Data collection start is planned ...for the end of 2021. The dynamics of such charged lepton flavour violating (CLFV) process is well modelled by a two-body decay, resulting in a mono-energetic electron with an energy slightly below the muon rest mass. If no events are observed in three years of running, Mu2e will set an upper limit on the ratio between the conversion and the capture rates Rμe=μ−+A(Z,N)→e−+A(Z,N)/μ−+A(Z,N)→νμ−+A(Z−1,N) of ≤6×10−17 (@ 90% C.L.). This will improve the current limit of four order of magnitudes with respect to the previous best experiment. Mu2e complements and extends the current search for μ→eγ decay at MEG as well as the direct searches for new physics at the LHC . The observation of such CLFV process could be clear evidence for New Physics beyond the Standard Model. Given its sensitivity, Mu2e will be able to probe New Physics at a scale inaccessible to direct searches at either present or planned high energy colliders. To search for the muon conversion process, a very intense pulsed beam of negative muons (∼1010μ/sec) is stopped on an Aluminum target inside a very long solenoid where the detector is also located. The Mu2e detector is composed of a straw tube tracker and a CsI crystals electromagnetic calorimeter. An external veto for cosmic rays surrounds the detector solenoid. In 2016, Mu2e has passed the final approval stage from DOE and has started its construction phase. An overview of the physics motivations for Mu2e, the current status of the experiment and the required performances and design details of the calorimeter are presented.
The Mu2e experiment at Fermilab searches the neutrino-less conversion of the muon into electron in the field of an Aluminum nucleus. If such a process will be observed, it will be a proof of the ...charged-lepton-flavor-violation (cLFV), otherwise Mu2e will set an upper limit of R mu e < 6 x 10 super(-17) 90% C.L. (which represents an improvement by 3-4 order of magnitude over the existing limit). The Mu2e detector apparatus consists of a magnetic spectrometer, devoted to the measurement of the electrons momentum, and an electromagnetic calorimeter (EMC) which provides an independent measurement of the electron energy, time and position, used for validating or rejecting candidate tracks selected by the tracking system. In this paper, we describe the baseline project of the EMC and present results in terms of performances and R&D.
Understanding the energy resolution terms for LYSO based calorimeters with APD readout at low energy (< 500 MeV) is relevant both for the completion of the KLOE-2 experiment, at DAΦNE, and for the ...design of the Mu2e calorimeter. In this work, we present a dedicated comparison between experimental data, taken in 2011 at the MAMI tagged photon beam facility with a crystal matrix prototype, and a full Geant-4 simulation of this detector. The crystal prototype matrix consisted of 9 2×2 × 15 cm3 LYSO crystals read-out by 10×10 mm2 Hamamatsu avalanche photodiodes (APD) surrounded by 8 PbWO4 crystals read-out by Bialkali photomultipliers for outer leakage recovery granting a total transverse coverage of 3 Rm. An energy resolution of ∼5.4 at 100 MeV has been achieved. A fit to the energy dependence of the resolution provides the following parametrization: σE/E 2.1 /E1/4 ⊕ 3.6 , where the sum is in quadrature. The noise term is completely negligible as expected by the reduced level of the electronic noise achieved. The constant term is still leakage dominated.
Detectors for new energy frontier experiments require excellent spatial, time, and energy resolutions to resolve the structure of collimated high-energy jets. In a future Muon Collider, the ...beam-induced backgrounds represent the main challenge for detector design and event reconstruction. Our proposal – Crilin – consists in a semi-homogeneous Cherenkov electromagnetic calorimeter based on PbF2 crystals with surface-mount UV-extended Silicon Photomultipliers readout.
The PADME experiment, at the Laboratori Nazionali di Frascati (LNF), in Italy, will search for invisible decays of the hypothetical dark photon via the process e+e−→γA′, where the A′ escapes ...detection. The dark photon mass range sensitivity in a first phase will be 1 to 24 MeV. We report here on performance measurements and simulation studies of a prototype of the Small-Angle Calorimeter, a component of PADME’s detector dedicated to rejecting 2- and 3-gamma backgrounds. The crucial requirement is a timing resolution of less than 200 ps, which is satisfied by the choice of PbF2 crystals and the newly released Hamamatsu R13478UV photomultiplier tubes (PMTs). We find a timing resolution of 81 ps (with double-peak separation resolution of 1.8 ns) and a single-crystal energy resolution of 10% at 550 MeV with light yield of 2.05 photo-electrons per MeV, using 100 to 400 MeV electrons at the Beam Test Facility of LNF. We also propose the investigation of a two-PMT solution coupled to a single PbF2 crystal for higher-energy applications, which has potentially attractive features.
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