[en] We present the first direct search for lepton flavour violating muon decay mediated by a new light particle X, μ${}^{+}$→e${}^{+}$X,X→γγ . This search uses a dataset resulting from 7.5×10${}^{14}$ stopped muons collected by the MEG experiment at the Paul Scherrer Institut in the period 2009–2013. No significant excess is found in the mass region 20–45 MeV/c${}^2$ for lifetimes below 40 ps, and we set the most stringent branching ratio upper limits in the mass region of 20–40 MeV/c${}^2$, down to O(10${}^{\text{â<!-- ?? -->}\text{ˆ<!-- ?? -->}\text{’<!-- ??? -->}11}$) at 90% confidence level.

[en] The ATHENA X-ray observatory is the second large-class mission in the ESA Cosmic Vision 2015–2025 science programme. One of the two on-board instruments is the X-IFU, an imaging spectrometer based on a large array of TES microcalorimeters. To reduce the particle-induced background, the spectrometer works in combination with a cryogenic anticoincidence detector (CryoAC), placed less than 1 mm below the TES array. The last CryoAC single-pixel prototypes, namely AC-S7 and AC-S8, are based on large-area (1 ${\text{cm}}^2$) silicon absorbers sensed by 65 parallel-connected iridium TES. This design has been adopted to improve the response generated by the athermal phonons, which will be used as fast anticoincidence flag. The latter sample is featured also with a network of aluminum fingers directly connected to the TES, designed to further improve the athermals collection efficiency. In this paper, we will report the main results obtained with AC-S8, showing that the additional fingers network is able to increase the energy collected from the athermal part of the pulses (from the 6% of AC-S7 up to the 26 % with AC-S8). Furthermore, the finger design is able to prevent the quasiparticle recombination in the aluminum, assuring a fast pulse rising front (L/R limited). In our road map, the AC-S8 prototype is the last step before the development of the CryoAC demonstration model, which will be the detector able to demonstrate the critical technologies expected in the CryoAC development programme.

[en] The ATHENA X-IFU development program foresees to build and characterize an instrument Demonstration Model (DM), in order to probe the system critical technologies before the mission adoption. In this respect, we are now developing the DM of the X-IFU Cryogenic AntiCoincidence Detector (CryoAC), which will be delivered to the Focal Plane Assembly development team for the integration with the TES array. Before the delivery, we will characterize and test the CryoAC DM in our CryoLab at INAF/IAPS. In this paper, we report the main results of the activities performed to improve our cryogenic test setup, making it suitable for the DM integration. These activities mainly consist in the development of a mechanical setup and a cryogenic magnetic shielding system, whose effectiveness has been assessed by FEM simulations and a measurement at warm. The preliminary performance test has been performed by means of the last CryoAC single-pixel prototype, the AC-S8 pre-DM sample.

[en] For the cosmic microwave background, the increase of the sensitivity of present superconducting TES Spiderweb Bolometers can be done coupling them to a large set of modes of the EM radiation inside the cavity. This will require a proper shaping of the horn-cavity assembly for the focal plane of the microwave telescope and the use of large area bolometers. Large area spiderweb bolometers of 8 mm diameter and a mesh size of 250 μm are fabricated in order to couple with approximately the first 20 modes of the cavity at about 140 GHz. These bolometers are fabricated with micro machining techniques from silicon wafer covered with SiO₂ – Si₃N₄ CVD thick films, 0.3 μm and 1 μm respectively. The sensor is a Ti/Au/Ti 3 layer TES sensor with Tc tuned in the 330-380 mK and 2 mK transition width. The TES is electronically coupled to the EM gold absorber that is grown on to the spiderweb mesh in order to sense the temperature of the electron gas heated by the EM radiation. The gold absorber mesh has 5 um beam size over a Si₃N₄ 10 μm beam size supporting mesh. The Si₃N₄ mesh is then fully suspended by means of DRIE back etching of the Si substrate. Here we present the first results of these large area bolometers.

[en] Low temperature detectors operated at about 0.1 K have achieved excellent spectral performances in the soft X-rays, becoming appealing for new challenging measurements with space missions in Astrophysics. In order to exploit their full sensitivity, it is necessary to minimize the background signals generated by the cosmic rays, i.e., high energy protons and light nuclei, that leave sizable amounts of energy in the same spectral window of the astrophysics signals. Detectors for GeV protons and nuclei operating few millimeters from the X-ray detector at 0.1 K can act as anti-coincidence to disentangle the fake signal of cosmic. Fast and large detectors are designed and fabricated. These operate by mixing the fast α-thermal phonon signal with the slow diffusive thermal ones. A greater uniformity in the response should be obtained using large shaped superconducting aluminium films that acts as phonon collectors: the quasi-particles created by high energy phonons diffuse along the film toward a small Ir TES sensor giving out to a fast rise time. Here we present the measurement of an operating prototype of a superconducting anticoincidence detector for the proposed space mission ATHENA+.

[en] We present a detailed description of the electromagnetic filter for the PTOLEMY project to directly detect the Cosmic Neutrino Background (CNB). Starting with an initial estimate for the orbital magnetic moment, the higher-order drift process of $\mathit{E}\times \mathit{B}$ is configured to balance the gradient-$B$ drift motion of the electron in such a way as to guide the trajectory into the standing voltage potential along the mid-plane of the filter. As a function of drift distance along the length of the filter, the filter zooms in with exponentially increasing precision on the transverse velocity component of the electron kinetic energy. This yields a linear dimension for the total filter length that is exceptionally compact compared to previous techniques for electromagnetic filtering. The parallel velocity component of the electron kinetic energy oscillates in an electrostatic harmonic trap as the electron drifts along the length of the filter. An analysis of the phase-space volume conservation validates the expected behavior of the filter from the adiabatic invariance of the orbital magnetic moment and energy conservation following Liouville’s theorem for Hamiltonian systems.

[en] In a microcalorimetric neutrino mass experiment using the radioactive decay of ¹⁶³Ho, the radioactive material must be fully embedded in the microcalorimeter absorber. One option that is being investigated is to implant the radioactive isotope into a gold absorber, as gold is successfully used in other applications. However, knowing the thermal properties at the working temperature of microcalorimeters is critical for choosing the absorber material and for optimizing the detector performance. In particular, it is paramount to understand if implanting the radioactive material in gold changes its heat capacity. We used a bolometric technique to measure the heat capacity of gold films, implanted with various concentrations of holmium and erbium (a byproduct of the ¹⁶³Ho fabrication), in the temperature range 70 mK–300 mK. Our results show that the specific heat capacity of the gold films is not affected by the implant, making this a viable option for a future microcalorimeter holmium experiment

[en] In the last years organic scintillators have been largely investigated in order to achieve high light yield together with good time response. Pure organic compound with high quality crystalline structure can achieve both this goals. Among a large type of organic compound, para-terphenyl (C_1_8H_1_4) have proven to have practical applications as detector medium for particle physics. In this work, the characterization of different sizes high quality mono-crystal p-terphenyl samples is presented. The optical and scintillation properties (emission spectrum, light yield, attenuation length, and decay time) are investigated. Coupling a Silicon PhotoMultiplier-based readout system to the crystal, a small prototype for a high resolution TOF detector was built; the preliminary results, obtained on a 20×30×3 mm"3 sample, with dual-side read-out (Hamamatsu S10931-050P SiPMs) and irradiated with "9"0Sr source, show a time resolution of 35 ps.

[en] The European Research Council has recently funded HOLMES, a new experiment to directly measure the neutrino mass. HOLMES will perform a calorimetric measurement of the energy released in the decay of "1"6"3Ho. The calorimetric measurement eliminates systematic uncertainties arising from the use of external beta sources, as in experiments with beta spectrometers. This measurement was proposed in 1982 by A. De Rujula and M. Lusignoli, but only recently the detector technological progress allowed to design a sensitive experiment. HOLMES will deploy a large array of low temperature microcalorimeters with implanted "1"6"3Ho nuclei. The resulting mass sensitivity will be as low as 0.4 eV. HOLMES will be an important step forward in the direct neutrino mass measurement with a calorimetric approach as an alternative to spectrometry. It will also establish the potential of this approach to extend the sensitivity down to 0.1 eV. We outline here the project with its technical challenges and perspectives

[en] During the 2024–2025 shut-down, the Large Hadron Collider (LHC) will be upgraded to reach an instantaneous luminosity up to 7×10³⁴ cm⁻²s⁻¹. This upgrade of the collider is called High-Luminosity LHC (HL-LHC). ATLAS and CMS detectors will be upgraded to meet the new challenges of HL−LHC: an average of 200 pile-up events in every bunch crossing and an integrated luminosity of 3000 fb⁻¹ over ten years. In particular, the current trackers will be completely replaced. In HL-LHC the trackers should operate under high fluences (up to 1.4 × 10¹⁶ n_eq cm⁻²), with a correlated high radiation damage. The pixel detectors, the innermost part of the trackers, needed a completely new design in the readout electronics, sensors and interconnections. A new 65 nm front-end (FE) electronics is being developed by the RD53 collaboration compatible with smaller pixel sizes than the actual ones to cope with the high track densities. Consequently the bump density will increase up to 4 ·10⁴ bumps/cm². Preliminary results of two hybridization technologies study are presented in this paper. In particular, the on-going bump-bonding qualification program at Leonardo−Finmeccanica is discussed, together with alternative hybridization techniques, as the capacitive coupling for HV-CMOS detectors.