119997612
A new technique for the identification of surface contamination in low temperature bolometric experiments
In the framework of the bolometric experiment CUORE, a new and promising technique has been developed in order to control the dangerous contamination coming from the surfaces close to the detector. In fact, by means of a composite bolometer, it is possible to partially overcome the loss of spatial resolution of the bolometer itself and to clearly identify events coming from outside.
119110967
Performances of a large mass ZnSe bolometer to search for rare events
Scintillating bolometers of ZnSe are the baseline choice of the LUCIFER experiment, whose aim is to observe the neutrinoless double beta decay of 82Se. The independent read-out of the heat and scintillation signals allows to identify and reject α particle interactions, the dominant background source for bolometric detectors. In this paper we report the performances of a ZnSe crystal operated within the LUCIFER R&D. We measured the scintillation yield, the energy resolution and the background in the energy region where the signal from 0νDBD decay of 82Se is expected with an exposure of 9.4 kgdays. With a newly developed analysis algorithm we improved the rejection of α events, and we estimated the increase in energy resolution obtained by the combination of the heat and light signals. For the first time we measured the light emitted by nuclear recoils, and found it to be compatible with zero. We conclude that the discrimination of nuclear recoils from β/γ interactions in the WIMPs energy region is possible, but low-noise light detectors are needed.
55610143
From Cuoricino to CUORE: Investigating the inverted hierarchy region of neutrino mass
Cuoricino is a Double Beta Decay experiment operating deep underground, in the Laboratori Nazionali del Gran Sasso, Italy; at a depth of about 3500 m.w.e. The search for the 0νββ of 130Te is carried out with the bolometric technique and an upper limit of 3×1024 y (@ 90%C.L.) is set for this process. Cuoricino represents not only the most sensitive DBD Experiment presently operating but also a prototype for a next generation experiment, CUORE (Cryogenic Underground Observatory for Rare Events). The expected performance and sensitivity, based on Monte Carlo simulations and extrapolations of the present Cuoricino results, indicate that CUORE will be able to test the 0.02-0.05 eV region for the effective neutrino mass, having a high discovery potential in the inverted hierarchy region of the neutrino mass pattern.
118915062
Dark matter search with innovative techniques
120133399
Production, characterization, and selection of the heating elements for the response stabilization of the CUORE bolometers
Abstract One of the critical issues while operating bolometric detectors over periods of time of 1 year or more consists of keeping their response stable within a 0.1% level, despite the unavoidable temperature fluctuations of the cryogenic set-up. By using an energy pulser, which periodically delivers a fixed amount of energy in the absorber, it is possible to stabilize the response of the bolometers. A stabilization technique using heating devices, made up of heavily doped semiconductor material (well above the metal-to-insulator transition), has been developed in the framework of the CUORE experiment. In this paper we describe in detail the procedure for the realization of the heating elements, based on silicon planar technology. We then report on the multi-step low temperature characterization (77 K, 4.2 K, 1.5 K, 35 mK) of the heaters. Finally, an example of achieved stabilization for a CUORE-like detector is reported. The ∼ 1500 heaters tested at ∼ 1.5 K show less than 0.5% change in resistance between 30 μ V and 3 mV, and less than 1% change in value between 50 mK and 800 mK. In particular, the resistance change between 4.2 K and 1.5 K is less than 0.1%.
121148985
Neutrinoless Double-Beta Decay
This paper introduces the neutrinoless double-beta decay (the rarest nuclear weak process) and 
describes the status of the research for this transition, both from the point of view of theoretical 
nuclear physics and in terms of the present and future experimental scenarios. Implications of this 
phenomenon on crucial aspects of particle physics are briefly discussed. The calculations of the nuclear 
matrix elements in case of mass mechanisms are reviewed, and a range for these quantities is proposed 
for the most appealing candidates. After introducing general experimental concepts—such as the 
choice of the best candidates, the different proposed technological approaches, and the sensitivity—we make the point on the experimental situation. Searches running or in preparation are described, providing an organic presentation which picks up similarities and differences. A critical comparison of 
the adopted technologies and of their physics reach (in terms of sensitivity to the effective Majorana 
neutrino mass) is performed. As a conclusion, we try to envisage what we expect round the corner 
and at a longer time scale.
55458894
Lattice quantum electrodynamics for graphene
Abstract The effects of gauge interactions in graphene have been analyzed up until now in terms of effective models of Dirac fermions. However, in several cases lattice effects play an important role and need to be taken consistently into account. In this paper, we introduce and analyze a lattice gauge theory model for graphene, which describes tight binding electrons hopping on the honeycomb lattice and interacting with a three-dimensional quantum U ( 1 ) gauge field. We perform an exact renormalization group analysis, which leads to a renormalized expansion that is finite at all orders. The flow of the effective parameters is controlled thanks to Ward identities and a careful analysis of the discrete lattice symmetry properties of the model. We show that the Fermi velocity increases up to the speed of light and Lorentz invariance spontaneously emerges in the infrared. The interaction produces critical exponents in the response functions; this removes the degeneracy present in the non interacting case and allows us to identify the dominant excitations. Finally, we add mass terms to the Hamiltonian and derive by a variational argument the correspondent gap equations, which have an anomalous non-BCS form, due to the non trivial effects of the interaction.
29885643
Anomalous Behavior in an Effective Model of Graphene with Coulomb Interactions
We analyze by exact Renormalization Group (RG) methods the infrared properties of an effective model of graphene, in which two-dimensional (2D) massless Dirac fermions propagating with a velocity smaller than the speed of light interact with a 3D quantum electromagnetic field. The fermionic correlation functions are written as series in the running coupling constants, with finite coefficients that admit explicit bounds at all orders. The implementation of Ward Identities in the RG scheme implies that the effective charges tend to a line of fixed points. At small momenta, the quasi-particle weight tends to zero and the effective Fermi velocity tends to a finite value. These limits are approached with a power law behavior characterized by non-universal critical exponents.
14496666
Lattice gauge theory model for graphene
The effects of the electromagnetic (em) electron-electron interactions in half-filled graphene are investigated in terms of a lattice gauge theory model. By using exact renormalization group methods and lattice Ward identities, we show that the em interactions amplify the responses to the excitonic pairings associated to a Kekule distortion and to a charge-density wave. The effect of the electronic repulsion on the Peierls-Kekule instability, usually neglected, is evaluated by deriving an exact non BCS gap equation, from which we find evidence that strong em interactions among electrons facilitate the spontaneous distortion of the lattice and the opening of a gap.
337931
The Scaling limit of the energy correlations in non integrable Ising models
We obtain an explicit expression for the multipoint energy correlations of a non solvable two-dimensional Ising models with nearest neighbor ferromagnetic interactions plus a weak finite range interaction of strength �, in a scaling limit in which we send the lattice spacing to zero and the temperature to the critical one. Our analysis is based on an exact mapping of the model into an interacting lattice fermionic theory, which generalizes the one originally used by Schultz, Mattis and Lieb for the nearest neighbor Ising model. The interacting model is then analyzed by a multiscale method first proposed by Pinson and Spencer. If the lattice spacing is finite, then the correlations cannot be computed in closed form: rather, they are expressed in terms of infinite, convergent, power series in �. In the scaling limit, these infinite expansions radically simplify and reduce to the limiting energy correlations of the integrable Ising model, up to a finite renormalization of the parameters. Explicit bounds on the speed of convergence to the scaling limit are derived.
17981665
Absolute stability limit for relativistic charged spheres
We find an exact solution for the stability limit of relativistic charged spheres for the case of constant gravitational mass density and constant charge density. We argue that this provides an absolute stability limit for any relativistic charged sphere in which the gravitational mass density decreases with radius and the charge density increases with radius. We then provide a cruder absolute stability limit that applies to any charged sphere with a spherically symmetric mass and charge distribution. We give numerical results for all cases. In addition, we discuss the example of a neutral sphere surrounded by a thin, charged shell.