Physics

The possibility to reduce the background due to cosmic ray charged particles by the use of magnetic field in the ground based low energy particle detectors is explored. The degree of reduction of cosmic rays as a function of the magnetic field strength and its depth is quantified.

In this work, carbon 14 C and Tritium were considered as possible background source in the XENON1T experiment. The simulation results show that if 14 C is located in dust particles with a characteristic size of tens of micrometers, then its beta spectrum is softened and can contribute to the low-background part of the spectrum (up to 20 keV) of the XENON1T experiment. In addition, it has been shown that the tritium spectrum is also significantly distorted due to the threshold effect and the form in which tritium is living in xenon. Comparison of the simulation results with experimental data allowed us to estimate the activity level of 14 C at about 1500 decays / t / year, which gives the level of organic impurities containing 14 C at the level of 2x10 −13 g/g. In the case of tritium background, spectrum distortions are already caused by nanoparticles. Wherein the shape of the spectrum from tritium sitting on the surface of the dust fits better into the experimental data than the spectrum from pure tritium. In addition, since the dust absorbs part of the decays, the total amount of tritium in xenon can be several times greater than assuming a background from pure tritium in xenon (the factor strongly depends on the size of the dust particles).

This manuscript presents a data-processing technique which improves the accuracy and precision of absorption-spectroscopy measurements by isolating the molecular absorbance signal from errors in the baseline light intensity (Io) using cepstral analysis. Recently, cepstral analysis has been used with traditional absorption spectrometers to create a modified form of the time-domain molecular free-induction decay (m-FID) signal which can be analyzed independently from Io. However, independent analysis of the molecular signature is not possible when the baseline intensity and molecular response do not separate well in the time domain, which is typical when using injection-current-tuned lasers (e.g., quantum cascade lasers) and other light sources with pronounced intensity tuning. In contrast, the method presented here is applicable to all light sources since it determines gas properties by least-squares fitting a simulated m-FID signal to the measured m-FID signal in the time domain. This method is insensitive to errors in the estimated Io which vary slowly with optical frequency and, therefore, decay rapidly in the time domain. The benefits provided by this method are demonstrated via scanned-wavelength direct-absorption measurements acquired with a distributed-feedback (DFB) quantum-cascade laser (QCL). The wavelength of a DFB QCL was scanned across CO's P(0,20) and P(1,14) absorption transitions at 1 kHz to measure the gas temperature and concentration of CO. Measurements were acquired in a gas cell and in an ethylene-air flame at 1 atm. The measured spectra were processed using the new m-FID-based method and two traditional methods which rely on inferring the baseline error within the spectral-fitting routine. The m-FID-based method demonstrated superior accuracy in all cases and a measurement precision that was 1.5 to 10 times smaller than that provided using traditional methods.

The PADME experiment at the LNF Beam Test Facility searches for dark photons produced in the annihilation of positrons with the electrons of a fix target. The strategy is to look for the reaction e + + e − →γ+ A ′ , where A ′ is the dark photon, which cannot be observed directly or via its decay products. The electromagnetic calorimeter plays a key role in the experiment by measuring the energy and position of the final-state γ . The missing four-momentum carried away by the A ′ can be evaluated from this information and the particle mass inferred. This paper presents the design, construction, and calibration of the PADME's electromagnetic calorimeter. The results achieved in terms of equalisation, detection efficiency and energy resolution during the first phase of the experiment demonstrate the effectiveness of the various tools used to improve the calorimeter performance with respect to earlier prototypes.

Far-infrared Transition Edge Sensors (TESs) are being developed for the SAFARI grating spectrometer on the cooled-aperture space telescope SPICA. In support of this work, we have devised a cryogenic (90 mK) test facility for carrying out precision optical measurements on ultra-low-noise TESs. Although our facility is suitable for the whole of the SAFARI wavelength range, 34-230 μ m, we focus on a representative set of measurements at 60-110 μ m using a device having a Noise Equivalent Power (NEP) of 0.32 aW/ Hz − − − √ . The system is able to perform a range of measurements: (i) Dark electrical characterisation. (ii) Optical efficiency with respect to a partially coherent beam having a modal composition identical to that of an ideal imaging telescope. (iii) Optical saturation and dynamic range. (iv) Fast optical transient response to a modulated thermal source. (v) Optical transient response in the presence of high-level background loading. We describe dark measurements to determine the operating characteristics of a TES, and then compare predicted optical behaviour with measured optical behaviour. By comparing electrical and optical transient response, we were able to observe thermalisation in the device. We comment on the challenge of eliminating stray light.

The Extreme Energy Events (EEE) experiment, dedicated to the study of secondary cosmic rays, is arguably the largest detector system in the world implemented by Multigap Resistive Plate Chambers. The EEE network consists of 60 telescopes distributed over all the Italian territory; each telescope is made of three MRPCs and allows to reconstruct the trajectory of cosmic muons with high efficiency and optimal angular resolution. A distinctive feature of the EEE network is that almost all telescopes are housed in High Schools and managed by groups of students and teachers, who previously took care of their construction at CERN. This peculiarity is a big plus for the experiment, which combines the scientific relevance of its objectives with effective outreach activities. The unconventional location of the detectors, mainly in standard classrooms of school buildings, with heterogeneous maintenance conditions and without controlled temperature and dedicated power lines, is a unique test field to verify the robustness, the low aging characteristics and the long-lasting performance of MRPC technology for particle monitoring and timing. Finally, it is reported how the spatial resolution, efficiency, tracking capability and stability of these chambers behave in time.

The Muon Telescope is a muography experiment for imaging volcanoes in Colombia. It consists of a scintillator tracking system and a water Cherenkov detector used for particle deposited energy measurement. The MuTe operates autonomously in high altitude environments where the temperature gradient reaches up to 10 ??C. In this work, we characterize the breakdown voltage, gain, and noise of the telescope silicon photomultipliers for temperature variations spanning 0 to 40 ??C. We demonstrated that the discrimination threshold for the MuTe hodoscope must be above 5 pe to avoid contamination due to the SiPM dark count, crosstalk, and afterpulsing. We also assess the MuTe counting rate depending on day-night temperature variations.

This article reports the characterization of two High Purity Germanium detectors performed by extracting and comparing their efficiencies using experimental data and Monte Carlo simulations. The efficiencies were calculated for pointlike γ -ray sources as well as for extended calibration sources. Characteristics of the detectors such as energy linearity, energy resolution, and full energy peak efficiencies are reported from measurements performed on surface laboratories. The detectors will be deployed in a γ -ray assay facility that will be located in the first underground laboratory in Mexico, Laboratorio Subterráneo de Mineral del Chico (LABChico), in the Comarca Minera UNESCO Global Geopark

Silicon Photo-Multipliers (SiPMs) are semiconductor-based photo-detectors with performances similar to the traditional Photo-Multiplier Tubes (PMTs). An increasing number of experiments dedicated to particle detection in colliders, accelerators, astrophysics, neutrino and rare-event physics involving scintillators are using SiPMs as photodetectors. They are gradually substituting PMTs in many applications, especially where low voltages are required and high magnetic field is present. Hamamatsu Photonics K.K., one of leading producers of photo-detectors, in the last year introduced the S14160 series of SiPMs with improved performances. In this work, a characterization of these devices will be presented in terms of breakdown voltages, pulse shape, dark current and gain. Particular attention has been dedicated to the analysis of the parameters as function of temperature.

Silicon photomultipliers (SiPMs) have a low radioactivity, compact geometry, low operation voltage, and reasonable photo-detection efficiency for vacuum ultraviolet light (VUV). Therefore it has the potential to replace photomultiplier tubes (PMTs) for future dark matter experiments with liquid xenon (LXe). However, SiPMs have nearly two orders of magnitude higher dark count rate (DCR) compared to that of PMTs at the LXe temperature ( ∼ 165 K). This type of high DCR mainly originates from the carriers that are generated by band-to-band tunneling effect. To suppress the tunneling effect, we have developed a new SiPM with lowered electric field strength in cooperation with Hamamatsu Photonics K. K. and characterized its performance in a temperature range of 153 K to 298 K. We demonstrated that the newly developed SiPMs had 6--54 times lower DCR at low temperatures compared to that of the conventional SiPMs.