Observatoire de neutrinos | EPFL Graph Search

thumb|Intérieur de , un détecteur de neutrinos lancé en 2002. Un observatoire de neutrinos est un dispositif permettant de détecter les neutrinos. En raison de la très faible interaction des neutrinos avec la matière, ces dispositifs doivent être très étendus pour en détecter un nombre significatif. De tels observatoires sont souvent construits sous terre, pour isoler le détecteur des rayons cosmiques et autres rayonnements d'arrière-plan. Types De nombreuses méthodes de détection ont été inventées. Au Super-Kamiokande, un important volume d'eau, ceinturé de photomultiplicateurs qui surveillent l'effet Vavilov-Tcherenkov, qui se produit quand un neutrino crée un électron ou un muon en entrant dans l'eau. L'observatoire de neutrinos de Sudbury est similaire, mais utilise de l'eau lourde. D'autres détecteurs utilisent de grandes quantités de chlore (comme l'expérience Homestake) ou de gallium (comme les expériences SAGE et Gallex) dans lesquelles on recherche respectivemen

High-Speed Wireline Link Design

Hazar Yüksel

High-speed serial links are a crucial application of semiconductor technology and have been the enabler of the scaling of computing systems. The increasing data-rate requirements of these links have only been partially satisfied by advancements in process technologies. Implementing serial links operating at a data rate of more than 25 Gb/s thus requires constantly inventing smarter algorithms, architectures, power-management techniques, and new standards. The Viterbi algorithm (VA), an attractive solution for symbol detection in the presence of intersymbol interference (ISI) and noise, minimizes the error probability in detecting the whole symbol sequence, instead of a single symbol as in decision-feedback equalization. The bit-error-rate (BER) performance of the VA is thus better than that of symbol-by-symbol detectors because the VA does not cancel the ISI, but rather uses the information embedded therein to maximize the reliability of its decisions. However, implementing a maximum-likelihood sequence detector (MLSD) realizing the VA may be prohibitive because design specifications regarding area, latency, power consumption, and speed may not be satisfied concurrently. Suboptimal solutions, such as feed-forward and decision-feedback equalizers (DFEs), may therefore be chosen instead of MLSDs due to their lower implementation complexity. A reduced-state sequence detector (RSSD) reduces the implementation complexity of the MLSD with negligible performance degradation by exploiting set-partitioning principles and embedded per-survivor decision feedback. A sliding-block or systolic-array Viterbi detector (VD) breaks the speed bottleneck in sequence-detector implementations by parallelizing the operation of the VA. In this thesis, we implement a 56-Gb/s four-level pulse-amplitude-modulation (4-PAM) DFE to demonstrate the feasibility of a multi-level analog-to-digital-converter (ADC)-based symbol-by-symbol detector in terms of achievable area, BER, energy-efficiency, latency, and speed figures comparable to those of analog solutions. Furthermore, to improve the BER figures, we implement a 25.6-Gb/s 4-PAM reduced-state sliding-block VD to demonstrate the feasibility of a multi-level sequence detector in terms of achievable area, energy-efficiency, latency, and speed figures comparable to those of symbol-by-symbol detectors. Moreover, we develop a sliding-block VA with optimized unequal synchronization and survivor path memory lengths to reduce its implementation complexity, latency, and power consumption. An increase in speed is thereby achieved at the same implementation complexity, BER, latency, and power consumption. We then develop a novel VD with embedded per-survivor decision feedback, whose longest path contains only one adder, to increase its speed significantly. Next, we propose a concatenated-coding scheme using an outer Reed—Solomon code and a four-dimensional (4-D) 5-PAM inner trellis-coded-modulation (TCM) scheme to achieve signal-to-noise-ratio gains without bandwidth expansion. Finally, we implement a 70-Gb/s 4-D 5-PAM systolic-array TCM decoder with eight states, which includes an inverse Tomlinson—Harashima precoder, to demonstrate the feasibility of a multi-level ADC-based sequence decoder in terms of achievable speed figures comparable to those of sequence detectors.

EPFL2017

Measurement of sound speed vs. depth in South Pole ice for neutrino astronomy

Xiaoxia Bai

We have measured the speed of both pressure waves and shear waves as a function of depth between 80 and 500 m depth in South Pole ice with better than 1% precision. The measurements were made using the South Pole Acoustic Test Setup (SPATS), an array of transmitters and sensors deployed in the ice at the South Pole in order to measure the acoustic properties relevant to acoustic detection of astrophysical neutrinos. The transmitters and sensors use piezoceramics operating at similar to 5-25 kHz. Between 200 m and 500 m depth, the measured profile is consistent with zero variation of the sound speed with depth, resulting in zero refraction, for both pressure and shear waves. We also performed a complementary study featuring an explosive signal propagating vertically from 50 to 2250 m depth, from which we determined a value for the pressure wave speed consistent with that determined for shallower depths, higher frequencies, and horizontal propagation with the SPATS sensors. The sound speed profile presented here can be used to achieve good acoustic source position and emission time reconstruction in general, and neutrino direction and energy reconstruction in particular. The reconstructed quantities could also help separate neutrino signals from background. (C) 2010 Elsevier B.V. All rights reserved.

2010

Measurement Of The Anisotropy Of Cosmic-Ray Arrival Directions With Icecube

Xiaoxia Bai, Shirit Cohen, Levent Demirörs, Mathieu Ribordy, Matthias Wolf

We report the first observation of an anisotropy in the arrival direction of cosmic rays with energies in the multi-TeV region in the Southern sky using data from the IceCube detector. Between 2007 June and 2008 March, the partially deployed IceCube detector was operated in a configuration with 1320 digital optical sensors distributed over 22 strings at depths between 1450 and 2450 m inside the Antarctic ice. IceCube is a neutrino detector, but the data are dominated by a large background of cosmic-ray muons. Therefore, the background data are suitable for high-statistics studies of cosmic rays in the southern sky. The data include 4.3 billion muons produced by downward-going cosmic-ray interactions in the atmosphere; these events were reconstructed with a median angular resolution of 3 degrees and a median energy of similar to 20 TeV. Their arrival direction distribution exhibits an anisotropy in right ascension with a first-harmonic amplitude of (6.4 +/- 0.2 stat. +/- 0.8 syst.) x 10(-4).

2010

High-Speed Wireline Link Design

Hazar Yüksel

EPFL2017