424 research outputs found
Lepton-Flavor-Dependent Angular Analysis of B→K^{*}ℓ^{+}ℓ^{-}
We present a measurement of angular observables and a test of lepton flavor universality in the B → K∗ ` +` − decay, where ` is either e or µ. The analysis is performed on a data sample corresponding to an integrated luminosity of 711 fb−1 containing 772 × 106 BB¯ pairs, collected at the Υ(4S) resonance with the Belle detector at the asymmetric-energy e +e − collider KEKB. The result is consistent with Standard Model (SM) expectations, where the largest discrepancy from a SM prediction is observed in the muon modes with a local significance of 2.6σ
Triazoles : a new class of precursors for the synthesis of negatively charged carbon nitride derivatives
Carbon nitride polymers were prepared for the first time by the pyrolysis of 3,5-disubstituted-1,2,4-triazole derivatives, namely 3,5-diamino-1,2,4-triazole [1] and 3-amino-1,2,4-triazole-5-thiol [2], in bulk as well as in LiCl/KCl salt melts. The reaction of [1] and [2] in bulk yields condensed heptazine-based polymers, while in LiCl/KCl eutectics it leads to the formation of well-defined potassium poly(heptazine imides), according to the results of 13C NMR and XPS investi-gations, whose formation resembles that of emeraldine salts of polyaniline. The density functional calculations supported the structural model suggested for potassium poly(heptazine imide) polymer. Owing to the specific reaction path, the products obtained from triazoles therefore show electronic properties rather different to known carbon nitrides, such as band gap and conduction and valence bands positions. With the degree of crystallinity of the reference materials, triazole-derived carbon nitrides are characterized by almost complete absence of steady photoluminescence, charge separation and localization upon excitation seems to be improved. As a consequence, photocatalysts prepared from [2] outperform classical carbon nitrides in a model dye degradation reaction and mesoporous graphitic carbon nitride in hydrogen evolution reaction under visible light irradiation. On its turn, [1] can be conveniently used as a co-monomer in order to prepare carbon nitrides with improved visible light absorption
Absolute Energy Calibration of X-ray TESs with 0.04 eV Uncertainty at 6.4 keV in a Hadron-Beam Environment
A performance evaluation of superconducting transition-edge sensors (TESs) in
the environment of a pion beam line at a particle accelerator is presented.
Averaged across the 209 functioning sensors in the array, the achieved energy
resolution is 5.2 eV FWHM at Co (6.9 keV) when the pion beam is
off and 7.3 eV at a beam rate of 1.45 MHz. Absolute energy uncertainty of
0.04 eV is demonstrated for Fe (6.4 keV) with in-situ energy
calibration obtained from other nearby known x-ray lines. To achieve this small
uncertainty, it is essential to consider the non-Gaussian energy response of
the TESs and thermal cross-talk pile-up effects due to charged-particle hits in
the silicon substrate of the TES array.Comment: Accepted for publication in J. Low Temperature Physics, special issue
for the proceedings of the Low Temperature Detectors 16 conferenc
High-resolution high-speed microwave-multiplexed low temperature microcalorimeters for the HOLMES experiment
We present the first performance results obtained with microwave multiplexed Transition Edge Sensors prototypes specifically designed for the HOLMES experiment, a project aimed at directly measuring the electron neutrino mass through the calorimetric measurement of the 163 Ho electron capture spectrum. The detectors required for such an experiment feature a high energy resolution at the Q–value of the transition, around ∼ 2.8 keV, and a fast response time combined with the compatibility to be multiplexed in large arrays in order to collect a large statistics while keeping the pile-up contribution as small as possible. In addition, the design has to be suitable for future ion-implantation of 163 Ho. The results obtained in these tests allowed us to identify the optimal detector design among several prototypes. The chosen detector achieved an energy resolution of (4.5 ± 0.3) eV on the chlorine K α line, at ∼ 2.6 keV, obtained with an exponential rise time of 14 \upmu μ s. The achievements described in this paper pose a milestone for the HOLMES detectors, setting a baseline for the subsequent developments, aiming to the actual ion-implantation of the 163 Ho nuclei. In the first section the HOLMES experiment is outlined along with its physics goal, while in the second section the HOLMES detectors are described; the experimental set-up and the calibration source used for the measurements described in this paper are reported in Sects. 3 and 4, respectively; finally, the details of the data analysis and the results obtained are reported in Sect. 6
Working principle and demonstrator of microwave-multiplexing for the HOLMES experiment microcalorimeters
The determination of the neutrino mass is an open issue in modern particle
physics and astrophysics. The direct mass measurement is the only
theory-unrelated experimental tool capable to probe such quantity. The HOLMES
experiment aims to measure the end-point energy of the electron capture (EC)
decay of Ho with a statistical sensitivity on the neutrino mass as low
as eV/c. In order to acquire the large needed statistics, by
keeping the pile-up contribution as low as possible, 1024 transition edge
sensors (TESs) with high energy and time resolutions will be employed.
Microcalorimeter and bolometer arrays based on transition edge sensor with
thousands of pixels are under development for several space-based and
ground-based applications, including astrophysics, nuclear and particle
physics, and materials science. The common necessary challenge is to develop
pratical multiplexing techniques in order to simplify the cryogenics and
readout systems. Despite the various multiplexing variants which are being
developed have been successful, new approaches are needed to enable scaling to
larger pixel counts and faster sensors, as requested for HOLMES, reducing also
the cost and complexity of readout. A very novel technique that meets all of
these requirements is based on superconducting microwave resonators coupled to
radio-frequency Superconducting Quantum Interference Devices, in which the the
changes in the TES input current is tranduced to a change in phase of a
microwave signal. In this work we introduce the basics of this technique, the
design and development of the first two-channel read out system and its
performances with the first TES detectors specifically designed for HOLMES. In
the last part we explain how to extend this approach scaling to 1024 pixels.Comment: accepted on JINS
Search for and a measurement of the branching fraction for
We search for the decay and measure the
branching fraction for using
121.4~ of data collected at the
resonance with the Belle detector at the KEKB asymmetric-energy
collider. The branching fraction is measured
to be , where is the fraction of
in events. Our result is in good
agreement with the theoretical predictions as well as with a recent measurement
from LHCb. We observe no statistically significant signal for the decay
and set a confidence-level upper
limit on its branching fraction at . This constitutes a
significant improvement over the previous result.Comment: 6 pages, 3 figure
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