27175903
New limits on heavy sterile neutrino mixing in 8B decay obtained with the Borexino detector
If heavy neutrinos with mass $m_{\nu_{H}}\geq$2$ m_e $ are produced in the Sun via the decay ${^8\rm{B}} \rightarrow {^8\rm{Be}} + e^+ + \nu_H$ in a side branch of pp-chain, they would undergo the observable decay into an electron, a positron and a light neutrino $\nu_{H}\rightarrow\nu_{L}+e^++e^-$. In the present work Borexino data are used to set a bound on the existence of such decays. We constrain the mixing of a heavy neutrino with mass 1.5 MeV $\leq m_{\nu_{H}} \le$ 14 MeV to be $|U_{eH}|^2\leq (10^{-3}-4\times10^{-6})$ respectively. These are tighter limits on the mixing parameters than obtained in previous experiments at nuclear reactors and accelerators.
119000964
Measurement of the cosmogenic 11C background with the Borexino Counting Test Facility
Within next year, two organic liquid scintillator detectors, Borexino and KamLAND, will start the measurement of the mono‐energetic 7Be solar neutrino flux in real time. Besides this objective, both of them have the potential to detect neutrinos from the pep fusion reaction and the CNO cycle in the Sun.For this purpose, two conditions are required: an extremely low radioactive contamination level and the efficient identification of the 11C background, produced in reactions induced by the residual cosmic muon flux on 12C. In the process, a free neutron is almost always produced. 11C can be tagged on an event by event basis by looking at the three‐fold coincidence with the parent muon track and the subsequent neutron capture on protons. We tested successfully this coincidence method with the Borexino Counting Test Facility. The results are reported here.Moreover, we discuss on the effective potential of Borexino and KamLAND in detecting pep+CNO neutrinos compared to SNO+, a detector specifically designed fo...
124545258
The Borexino experiment: Test of the purification systems and data analysis in the counting test facility
The work I carried out in the last three years was focused on the development and test of purification systems and data analysis techniques for the Borexino experiment, a detector specifically designed for low energy neutrino spectroscopy. I participated to the study of the adsorption technique based on activated carbons for removing krypton from nitrogen and to the investigation of the purity of nitrogen available on the market. I analyzed the data from the third campaign of the Borexino prototype detector, the Counting Test Facility (CTF), to identify each contamination source in the scintillator and to evaluate the efficiency of the purification system. 11C represents the main background source in the CNO and pep neutrino energy range. I investigated on the possibility to apply the three-fold coincidence technique with the parent muon track and the subsequent neutron capture on protons in Borexino in order to tag and remove 11C nuclides on a one-by-one basis. Furthermore, I implemented and tested such technique on the CTF data.
119181847
Positronium signature in organic liquid scintillators for neutrino experiments
Electron antineutrinos are commonly detected in liquid scintillator experiments via inverse {beta} decay by looking at the coincidence between the reaction products: neutrons and positrons. Prior to positron annihilation, an electron-positron pair may form an orthopositronium (o-Ps) state, with a mean lifetime of a few nanoseconds. Even if the o-Ps decay is speeded up by spin-flip or pick-off effects, it may introduce distortions in the photon emission time distribution, crucial for position reconstruction and pulse shape discrimination algorithms in antineutrino experiments. Reversing the problem, the o-Ps-induced time distortion represents a new signature for tagging antineutrinos in liquid scintillator. In this article, we report the results of measurements of the o-Ps formation probability and lifetime for the most used solvents for organic liquid scintillators in neutrino physics (pseudocumene, linear alkyl benzene, phenylxylylethane, and dodecane). We characterize also a mixture of pseudocumene +1.5 g/l of 2,5-diphenyloxazole, a fluor acting as wavelength shifter. In the second part of the article, we demonstrate that the o-Ps-induced distortion of the scintillation photon emission time distributions represent an optimal signature for tagging positrons on an event by event basis, potentially enhancing the antineutrino detection.
11472516
The classification of flaring states of blazars
Aims. The time evolution of the electromagnetic emission from blazars, in particular high-frequency peaked sources (HBLs), displays irregular activity that has not yet been understood. In this work we report a methodology capable of characterizing the time behavior of these variable objects. Methods. The maximum likelihood blocks (MLBs) is a model-independent estimator that subdivides the light curve into time blocks, whose length and amplitude are compatible with states of constant emission rate of the observed source. The MLBs yield the statistical significance in the rate variations and strongly suppresses the noise fluctuations in the light curves. We applied the MLBs for the first time on the long term X-ray light curves (RXTE/ASM) of Mkn 421, Mkn 501, 1ES 1959+650, and 1ES 2155-304, more than 10 years of observational data (1996-2007). Using the MLBs interpretation of RXTE/ASM data, the integrated time flux distribution is determined for each single source considered. We identify in these distributions the characteristic level, as well as the flaring states of the blazars. Results. All the distributions show a significant component at negative flux values, most probably caused by an uncertainty in the background subtraction and by intrinsic fluctuations of RXTE/ASM. This effect concerns in particular short time observations. To quantify the probability that the intrinsic fluctuations give rise to a false identification of a flare, we study a population of very faint sources and their integrated time-flux distribution. We determine duty cycle or fraction of time a source spent in the flaring state of the source Mkn 421, Mkn 501, 1ES 1959+650 and 1ES 2155-304. Moreover, we study the random coincidences between flares and generic sporadic events such as high-energy neutrinos or flares in other wavelengths.
120536446
Performances and calibrations of the Borexino detector
Borexino is a real-time detector for low energy Solar neutrino spectroscopy installed in the underground laboratories (3800 mwe depth) at Gran Sasso, Italy (LNGS). Borexino is specifically designed to measure the mono-energetic (866 keV) 7Be flux via neutrino-electron elastic scattering in ultra-pure organic scintillation liquid. The separation of signal and background relies on the identification of the Compton-like edge in the recoil electron energy spectrum at 667 keV. The physics potential of Borexino strongly depends on the unprecedented requirements of low level background. The exceptional radio-purity reached by the Borexino, in order to guarantee the success of the experiment, must be complemented with the identification and discrimination of the residual intrinsic contaminants, as well as of the external and cosmogenic backgrounds. Crucial in this respect are the energy and spatial reconstruction capabilities of the detector, which thus require a careful and precise assessment. We report on the Borexino performances after 1 year of data taking in reconstructing event energy and position, in discriminating on the nature of the contaminant with the pulse shape analysis and in the identification of fast coincidences looking at time and space correlations.
16119199
A Note on Superdistributions and Wavefront Set
We present a simple and new method of constructing superdistributions on superspace over a Grassmann-Banach algebra, which close to the de Rham's “currents'' defined as dual objects to differential forms. The paper also contains the extension of the Hörmander's description of the singularity structure (wavefront set) of a distribution to include the supersymmetric case.
13873742
A new derivation of the CPT and spin-statistics theorems in noncommutative field theories
We propose an alternative axiomatic description for noncommutative field theories (NCFT) based on some ideas by Soloviev to nonlocal quantum fields. The local commutativity axiom is replaced by the weaker condition that the fields commute at sufficiently large spatial separations, called asymptotic commutativity, formulated in terms of the theory of analytic functionals. The question of a possible violation of the CPT and spin-statistics theorems caused by nonlocality of the commutation relations [xμ,xν]=iθμν is investigated. In spite of this inherent nonlocality, we show that the modification aforementioned is sufficient to ensure the validity of these theorems for NCFT. We restrict ourselves to the simplest model of a scalar field in the case of only space–space noncommutativity.
119216045
Lorentz and CPT violation in QED revisited: A missing analysis
Abstract We investigate the breakdown of Lorentz symmetry in QED by a CPT violating interaction term consisting of the coupling of an axial fermion current with a constant vector field b , in the framework of algebraic renormalization — a regularization-independent method. We show, to all orders in perturbation theory, that a CPT-odd and Lorentz violating Chern–Simons-like term, definitively, is not radiatively induced by the axial coupling of the fermions with the constant vector b .
119266920
No parity anomaly in massless QED3: A BPHZL approach
Abstract In this Letter we call into question the perturbatively parity breakdown at 1-loop for the massless QED 3 frequently claimed in the literature. As long as perturbative quantum field theory is concerned, whether a parity anomaly owing to radiative corrections exists or not shall be definitely proved by using a renormalization method independent of any regularization scheme. Such a problem has been investigated in the framework of BPHZL renormalization method, by adopting the Lowenstein–Zimmermann subtraction scheme. The 1-loop parity-odd contribution to the vacuum-polarization tensor is explicitly computed in the framework of the BPHZL renormalization method. It is shown that a Chern–Simons term is generated at that order induced through the infrared subtractions — which violate parity. We show then that, what is called “parity anomaly”, is in fact a parity-odd counterterm needed for restauring parity.
120792860
Simple parametrizations of light meson properties in hot or dense matter
Abstract Sophisticated calculations of the dynamics of relativistic heavy-ion collisions often need as input properties of light mesons in medium. In this context simple analytical expressions for these quantities which respect chiral symmetry and low-energy current algebra results are most desirable. In the present work we provide such simple expressions based on a bosonized version of the microscopic NJL model. We also study the pion lifetime in hot and dense matter showing that the ratio τ(π − →μ − + ν μ ) τ(π − →e − + ν e ) changes by a factor about three and thus carries a clear signature of the chiral phase transition.