Model of the response function of large mass bolometric detectors

Large mass bolometers are used in particle physics experiments to search for rare processes. By operating at low temperature, they are able to detect particle energies from few keV up to several MeV, measuring the temperature rise produced by the energy released. This study was performed on the bolometers of the CUORE experiment. The response function of these detectors is not linear in the energy range of interest, and it changes with the operating temperature. The non-linearity is found to be dominated by the thermistor and its biasing circuit. A method to obtain a linear response is the result of this work. It allows a great simplification of the data analysis.Comment: 7 pages, 13 figures. Changes wrt v1: two columns layout, corrected typos, increase of plot labels font, fixes in bibliograph

An algorithm to linearize the response function of bolometric detectors

Bolometric detectors are used in particle physics experiments to search for rare processes, like neutrinoless double-beta decay and dark-matter interactions. Operating in low-temperature conditions they are able to detect particles energies from few keV up to several MeV, measuring the temperature rise produced by the energy released. We studied the bolometers used in the CUORE experiment. The response function of these detectors is not linear in the energy range of interest: the measurement of the energy is complicated and the shape of the signal depends on the energy itself. The response function changes when the operating temperature changes. The non-linearity is found to be dominated by the thermistor and the biasing circuit used to operate these detectors. An algorithm to obtain a linear response is proposed, introducing new techniques for the data analysis

LUCIFER: Scintillating bolometers for the search of Neutrinoless Double Beta Decay

Abstract The nature of neutrino mass is one of the frontier problems of particle physics. Neutrinoless Double Beta Decay (0 ν DBD) is a powerful tool to measure the neutrino mass and to test possible extensions of the Standard Model. Bolometers are excellent detectors to search for this rare decay, thanks to their good energy resolution and to the low background conditions in which they can operate. The current challenge consists in the reduction of the background, represented by environmental γ ʼs and α ʼs, in view of a zero background experiment. We present the LUCIFER R&D, funded by an European grant, in which the background can be reduced by an order of magnitude with respect to the present generation experiments. The technique is based on the simultaneous bolometric measurement of the heat and of the scintillation light produced by a particle, that allows to discriminate between β and α particles. The γ background is reduced by choosing 0 ν DBD candidate isotopes with transition energy above the environmental γ ʼs spectrum. The prospect of this R&D are discussed

Sources of uncertainties in modelling black carbon at the global scale

Our understanding of the global black carbon (BC) cycle is essentially qualitative due to uncertainties in our knowledge of its properties. This work investigates two source of uncertainties in modelling black carbon: those due to the use of different schemes for BC ageing and its removal rate in the global Transport-Chemistry model TM5 and those due to the uncertainties in the definition and quantification of the observations, which propagate through to both the emission inventories, and the measurements used for the model evaluation. The schemes for the atmospheric processing of black carbon that have been tested with the model are (i) a simple approach considering BC as bulk aerosol and a simple treatment of the removal with fixed 70% of in-cloud black carbon concentrations scavenged by clouds and removed when rain is present and (ii) a more complete description of microphysical ageing within an aerosol dynamics model, where removal is coupled to the microphysical properties of the aerosol, which results in a global average of 40% in-cloud black carbon that is scavenged in clouds and subsequently removed by rain, thus resulting in a longer atmospheric lifetime. This difference is reflected in comparisons between both sets of modelled results and the measurements. Close to the sources, both anthropogenic and vegetation fire source regions, the model results do not differ significantly, indicating that the emissions are the prevailing mechanism determining the concentrations and the choice of the aerosol scheme does not influence the levels. In more remote areas such as oceanic and polar regions the differences can be orders of magnitude, due to the differences between the two schemes. The more complete description reproduces the seasonal trend of the black carbon observations in those areas, although not always the magnitude of the signal, while the more simplified approach underestimates black carbon concentrations by orders of magnitude. The sensitivity to wet scavenging has been tested by varying in-cloud and below-cloud removal. BC lifetime increases by 10% when large scale and convective scale precipitation removal efficiency are reduced by 30%, while the variation is very small when below-cloud scavenging is zero. Since the emission inventories are representative of elemental carbon-like substance, the model output should be compared to elemental carbon measurements and if known, the ratio of black carbon to elemental carbon mass should be taken into account when the model is compared with black carbon observation

Measurements of the Cerenkov light emitted by a TeO2 crystal

Bolometers have proven to be good instruments to search for rare processes because of their excellent energy resolution and their extremely low intrinsic background. In this kind of detectors, the capability of discriminating alpha particles from electrons represents an important aspect for the background reduction. One possibility for obtaining such a discrimination is provided by the detection of the Cerenkov light which, at the low energies of the natural radioactivity, is only emitted by electrons. In this paper, the results of the analysis of the light emitted by a TeO2 crystal at room temperature when transversed by a cosmic ray are reported. Light is promptly emitted after the particle crossing and a clear evidence of its directionality is also found. These results represent a strong indication that Cerenkov light is the main, if not even the only, component of the light signal in a TeO2 crystal. They open the possibility to make large improvements in the performance of experiments based on this kind of material

Operator norm localization property for equi-approximable families of projections

The rigidity problem for uniform Roe algebras was recently positively solved. Before its solution was found, there were positive solutions under the assumption of certain technical geometric conditions. In this paper, we introduce weaker versions of the operator norm localization property (ONL) which turn out to characterize those technical geometric conditions. We use this to obtain new rigidity results for nonmetrizable coarse spaces. As an application, we provide a novel partial answer to a question of White and Willett about Cartan subalgebras of uniform Roe algebras. We also study embeddings between uniform Roe algebras.Comment: 21 page

Formation of secondary organic aerosol from isoprene oxidation over Europe

The role of isoprene as a precursor to secondary organic aerosol (SOA) over Europe is studied with the two-way nested global chemistry transport model TM5. The inclusion of the formation of SOA from isoprene oxidation in our model almost doubles the atmospheric burden of SOA over Europe compared to SOA formation from terpenes and aromatics. The reference simulation, which considers SOA formation from isoprene, terpenes and aromatics, predicts a yearly European production rate of 1.0 Tg SOA yr<sup>−1</sup> and an annual averaged atmospheric burden of about 50 Gg SOA over Europe. A fraction of 35% of the SOA produced in the boundary layer over Europe is transported to higher altitudes or to other world regions. Summertime measurements of organic matter (OM) during the extensive EMEP OC/EC campaign 2002/2003 are better reproduced when SOA formation from isoprene is taken into account, reflecting also the strong seasonality of isoprene and other biogenic volatile organic compounds (BVOC) emissions from vegetation. However, during winter, our model strongly underestimates OM, likely caused by missing wood burning in the emission inventories. Uncertainties in the parameterisation of isoprene SOA formation have been investigated. Maximum SOA production is found for irreversible sticking (non-equilibrium partitioning) of condensable vapours on particles, with tropospheric SOA production over Europe increased by a factor of 4 in summer compared to the reference case. Completely neglecting SOA formation from isoprene results in the lowest estimate (0.51 Tg SOA yr<sup>−1</sup>). The amount and the nature of the absorbing matter are shown to be another key uncertainty when predicting SOA levels. Consequently, smog chamber experiments on SOA formation should be performed with different types of seed aerosols and without seed aerosols in order to derive an improved treatment of the absorption of SOA in the models. Consideration of a number of recent insights in isoprene SOA formation mechanisms reduces the tropospheric production of isoprene derived SOA over Europe from 0.4 Tg yr<sup>−1</sup> in our reference simulation to 0.1 Tg yr<sup>−1</sup>