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The OPERA neutrino experiment, based on the use of a massive nuclear emulsion detector, requires the development of a new generation of fast automatic microscopes for emulsion scanning and image analysis to reconstruct tracks of elementary particles. The ongoing progress in the technology of image acquisition and analysis (CCD and CMOS cameras, frame grabbers, very fast processors), as well as in mechanics and optics, allow the realization of systems with high performance. R&D programs are going on in Japan and in Europe. The prototype of automatic microscope realized in the framework of the European R&D program is presently under test. Together with the present''s achievements, we report about the perspectives for a further increase in scanning speed. [Copyright &y& Elsevier]

In the context of the Ptolemy project, the need for a site with a rather low cosmogenic induced background led us to measure the differential muon flux inside the bunker of Monte Soratte, located about 50 km north of Rome (Italy). The measurement was performed with the Cosmic Ray Cube (CRC), a portable tracking device. The simple operation of CRC was crucial to finalize the measurement, as it was carried out in a site devoid of scientific equipment and during the COVID-19 lockdown. The muon flux measured at the Soratte hypogeum is about two orders of magnitude lower than the flux observed on the surface, suggesting the use of the Soratte bunker for hosting astroparticle physics experiments in which a low environmental background is required. [ABSTRACT FROM AUTHOR]

Results are given on tests of large particle trackers for the detection of neutrino interactions in long-baseline experiments. Module prototypes have been assembled using TiO2-doped polycarbonate panels. These were subdivided into cells of ∼1 cm2 cross-section and 6 m length, filled with liquid scintillator. A wavelength-shifting fibre inserted into each cell captured a part of the scintillation light emitted when a cell was traversed by an ionizing particle. Two different fibre-readout systems have been tested: an optoelectronic chain comprising an image intensifier and an electron-bombarded CCD (EBCCD); and a hybrid photodiode (HPD). New, low-cost liquid scintillators have been investigated for applications in large underground detectors. Testbeam studies have been performed using a commercially available liquid scintillator. The number of detected photoelectrons for minimum-ionizing particles crossing a module at different distances from the fibre readout end was 6–12 with the EBCCD chain and a mirror at the non-readout end; 4–10 with the HPD and no mirror. The light-attenuation lengths in the fibres were ∼9.4 m with the EBCCD and ∼6.4 m with the HPD. The detector response to electron showers has also been measured. After ten radiation lengths of lead, the transverse position of the incoming electron was determined with a precision of a few millimetres for electrons of 4 GeV, and with a precision of 1.5–2.0 cm for electrons of 1 GeV. [Copyright &y& Elsevier]

The Cosmic Ray Cube is a portable tracking device conceived for outreach activities allowing a direct scientific experience for secondary school students. In the context of the PTOLEMY project, the detector was used to measure the differential muon flux inside the bunker of Monte Soratte, a suitable location at about 50 km north of Rome (Italy). Its simple operation was crucial to finalise the measurements, carried out during the Covid-19 lockdown in a site devoid of scientific equipment. The fine scanning of the differential muon rate highlights the details of the mountain above the bunker providing a map of the thickness of the rock which surrounds the detector. The result shows a muon flux at the Soratte hypogeum of about two orders of magnitude lower than the one observed on the surface. [ABSTRACT FROM AUTHOR]

Nuclear emulsion films are a tracking device with unique space resolution. Their use in nowadays large-scale experiments relies on the availability of automated microscope operating at very high speed. In this paper we describe the features and the latest improvements of the European Scanning System, a last-generation automated microscope for emulsion scanning. In particular, we present a new method for the recovery of tracking inefficiencies. Stacks of double coated emulsion films have been exposed to a 10 GeV/c pion beam. Efficiencies as high as 98% have been achieved for minimum ionising particle tracks perpendicular to the emulsion films and of 93% for tracks with tan ( θ ) ≃ 0.8 . [ABSTRACT FROM AUTHOR]

This paper describes the design and performance of a computer controlled emulsion Plate Changer for the automatic placement and removal of nuclear emulsion films for the European Scanning System microscopes. The Plate Changer is used for mass scanning and measurement of the emulsions of the OPERA neutrino oscillation experiment at the Gran Sasso lab on the CNGS neutrino beam. Unlike other systems it works with both dry and oil objectives. The film changing takes less than 20 s and the accuracy on the positioning of the emulsion films is about 10 μ m . The final accuracy in retrieving track coordinates after fiducial marks measurement is better than 1 μ m . [ABSTRACT FROM AUTHOR]

Nuclear emulsion is a perfect choice for a detector for directional DM search because of its high density and excellent position accuracy. The minimal detectable track length of a recoil nucleus in emulsion is required to be at least 100 nm, making the resolution of conventional optical microscopes insufficient to resolve them. Here we report about the R&D on a super-resolution optical microscope to be used in future directional DM search experiments with nuclear emulsion as a detector media. The microscope will be fully automatic, will use novel image acquisition and analysis techniques, will achieve the spatial resolution of the order of few tens of nm and will be capable of reconstructing recoil tracks with the length of at least 100 nm with high angular resolution. [ABSTRACT FROM AUTHOR]

Abstract: There are two key approaches in our CERN RD 39 Collaboration efforts to obtain ultra-radiation-hard Si detectors: (1) use of the charge/current injection to manipulate the detector internal electric field in such a way that it can be depleted at a modest bias voltage at cryogenic temperature range (⩽150K), and (2) freezing out of the trapping centers that affects the CCE at cryogenic temperatures lower than that of the liquid nitrogen (LN2) temperature. In our first approach, we have developed the advanced radiation hard detectors using charge or current injection, the current injected diodes (CID). In a CID, the electric field is controlled by injected current, which is limited by the space charge, yielding a nearly uniform electric field in the detector, independent of the radiation fluence. In our second approach, we have developed models of radiation-induced trapping levels and the physics of their freezing out at cryogenic temperatures. [Copyright &y& Elsevier]

Abstract: The use of nuclear emulsions in very large physics experiments is now possible thanks to the recent improvements in the industrial production of emulsions and to the development of fast automated microscopes. In this paper the hardware performances of the European Scanning System (ESS) are described. The ESS is a very fast automatic system developed for the mass scanning of the emulsions of the OPERA experiment, which requires microscopes with scanning speeds of in an emulsion volume of thickness. [Copyright &y& Elsevier]

Abstract: We report on the development of an automated scanning system for nuclear emulsions aiming at very precise spatial and angular measurements. An accuracy of in position was achieved with the emulsion films used for the measurement. An accuracy of 0.4mrad was achieved for tracks penetrating orthogonally the emulsion films while an accuracy of 1mrad was obtained for tracks inclined by about 300mrad with respect to the perpendicular direction. This result shows unprecedented position and angular resolutions achieved by automated measurements. [Copyright &y& Elsevier]

Abstract: The CERN RD39 Collaboration is developing super-radiation hard cryogenic Si detectors for applications in experiments of the LHC and the future LHC Upgrade. Radiation hardness up to the fluence of 1016neq/cm2 is required in the future experiments. Significant improvement in the radiation hardness of silicon sensors has taken place during the past years. However, 1016neq/cm2 is well beyond the radiation tolerance of even the most advanced semiconductor detectors made by commonly adopted technologies. Furthermore, at this radiation load the carrier trapping will limit the charge collection depth to the range of 20–30μm regardless of the depletion depth. The key of our approach is freezing the trapping that affects Charge Collection Efficiency (CCE). [Copyright &y& Elsevier]

Measurements of the atmospheric flux of muons and other charged particles have been performed at the external site of the Gran Sasso Laboratory (LNGS, Italy, 1000 m a.s.l.), in view of the OPERA experiment. Scintillation counters and nuclear emulsion plates have been used. Rates and angular distributions at several depths of Fe shielding are presented and compared with Monte Carlo simulations. [Copyright &y& Elsevier]

RD39 collaboration develops new detector techniques for particle trackers, which have to withstand fluences up to 1016 cm−2 of high-energy particles. The work focuses on the optimization of silicon detectors and their readout electronics while keeping the temperature as a free parameter. Our results so far suggest that the best operating temperature is around 130 K. We shall also describe in this paper how the current-injected mode of operation reduces the polarization of the bulk silicon at low temperatures, and how the engineering and materials problems related with vacuum and low temperature can be solved. [Copyright &y& Elsevier]

The recovery of the charge collection efficiency (CCE) at low temperatures, the so-called ”Lazarus effect”, was studied in Si detectors irradiated by fast reactor neutrons, by protons of medium and high energy, by pions and by gamma-rays. The experimental results show that the Lazarus effect is observed: (a) after all types of irradiation; (b) before and after space charge sign inversion; (c) only in detectors that are biased at voltages resulting in partial depletion at room temperature. The experimental temperature dependence of the CCE for proton-irradiated detectors shows non-monotonic behaviour with a maximum at a temperature defined as the CCE recovery temperature. The model of the effect for proton-irradiated detectors agrees well with that developed earlier for detectors irradiated by neutrons. The same midgap acceptor-type and donor-type levels are responsible for the Lazarus effect in detectors irradiated by neutrons and by protons. A new, abnormal “zigzag”-shaped temperature dependence of the CCE was observed for detectors irradiated by all particles (neutrons, protons and pions) and by an ultra-high dose of γ-rays, when operating at low bias voltages. This effect is explained in the framework of the double-peak electric field distribution model for heavily irradiated detectors. The redistribution of the space charge region depth between the depleted regions adjacent to p+ and n+ contacts is responsible for the “zigzag”- shaped curves. It is shown that the CCE recovery temperature increases with reverse bias in all detectors, regardless of the type of radiation. [Copyright &y& Elsevier]

We present the first automated momentum measurement in an Emulsion Cloud Chamber, consisting of multiple sandwiches of lead plates and nuclear emulsion sheets. The measurement is based on the detection of the multiple Coulomb scattering analysed by the so-called angular method. A 3X0 chamber was exposed to 2, 3 and 4 GeV/c π−. A pion momentum resolution of 36% at 4 GeV/c, 35% at 3 GeV/c and 28% for 2 GeV/c was achieved. [Copyright &y& Elsevier]

It has been recently observed that heavily irradiated silicon detectors, no longer functional at room temperature, “resuscitate” when operated at temperatures below 130 K. This is often referred to as the “Lazarus effect”. The results presented here show that cryogenic operation represents a new and reliable solution to the problem of radiation tolerance of silicon detectors. [Copyright &y& Elsevier]