Suche nach einem diffusen kosmischen Neutrinofluss mit Hilfe von Schauerereignissen im ANTARES Neutrinoteleskop

The ANTARES neutrino telescope is a three-dimensional array of 885 photomultiplier tubes that has been installed in the Mediterranean Sea and that is designed to detect high energy neutrinos from the cosmos. Neutrinos that interact with nucleons in water in deep inelastic scattering processes induce secondary particles, such as muon tracks or hadronic and electromagnetic particle showers, that move faster than the speed of light in water and hence, emit Cherenkov radiation. By measuring the arrival time and the amount of Cherenkov photons at different detector positions the event pattern can be reconstructed, from which conclusions about the energy and the direction of the inducing neutrino can be drawn. Whereas for a long time the charged current interaction of a muon neutrino has been regarded as the golden channel of neutrino astronomy, as the long muon trajectory allows a good angular resolution, it is evident that the study of hadronic showers from neutral current events or electromagnetic showers from charged current interactions of the electron neutrino is a gain of information that must be taken into account, too. Within this work a search for the all-flavour diffuse cosmic neutrino flux using the ANTARES data from 2007-2012 is presented. As first step a reconstruction algorithm has been developed that is able to identify shower events and determine their parameters, such as vertex position, interaction time, shower energy and neutrino direction, by performing a maximum likelihood fit. The fit is based on probability density function tables that have been created from extensive Monte-Carlo simulations. Several approaches have been investigated to distinguish between track-like and shower-like events. Different cuts have been introduced to suppress the background of atmospheric neutrino and muon events. As after the final cuts no significant signal was observed, a 90% confidence upper limit on the diffuse cosmic neutrino flux was evaluated.Das ANTARES Neutrinoteleskop besteht aus einer dreidimensionalen Anordnung von 885 Photomultipliern. Diese wurden in der Tiefsee des Mittelmeers installiert um Tscherenkow-Strahlung nachzuweisen, die von Teilchen emittiert wird, welche in Streuprozessen hoch-energetischer Neutrinos mit Nukleonen im Wasser erzeugt wurden. Aus der Messung der Ankunftszeit und der Menge der Tscherenkow-Photonen kann das Ereignismuster rekonstruiert und die Energie und Richtung des Neutrinos bestimmt werden. Lange Zeit galt die Wechselwirkung eines Myonneutrinos über den geladenen Strom als goldener Kanal der Neutrinoastronomie, da die Rekonstruktion der langen Myonspur eine gute Winkelauflösung ermöglicht. Die Erweiterung der Suche auf hadronische Teilchenschauer aus Wechselwirkungen über den neutralen Strom und elektromagnetische Schauer aus Reaktionen von Elektronneutrinos über den geladenen Strom sind jedoch definitiv eine zusätzliche Informationsquelle, die nicht außer Acht gelassen werden sollte. In dieser Arbeit wird eine Suche nach einem diffusen kosmischen Neutrinofluss aller drei Neutrinogenerationen in den ANTARES Daten von 2007-2012 vorgestellt. Hierzu wurde ein Rekonstruktions-Algorithmus entwickelt, der Schauerereignisse erkennen und deren Eigenschaften, wie Ort, Zeitpunkt, Schauerenergie und Richtung des Neutrinos, bestimmen kann. Dies geschieht mit Hilfe eines Maximum-Likelihood-Fits, der auf Wahrscheinlichkeits-Tabellen beruht, welche aus umfangreichen Monte-Carlo-Simulationen gewonnen wurden. Verschiedene Ansätze zur Unterscheidung von spurartigen und schauerartigen Ereignissen wurden untersucht. Mehrere Schnitte wurden eingeführt um den Untergrund aus atmosphärischen Neutrino- und Myonereignissen zu unterdrücken. Da nach allen Schnitten kein statistisch signifikanter Überschuss an kosmischen Neutrinos beobachtet werden konnte, wurde eine obere Ausschlussgrenze auf den diffusen kosmischen Neutrinofluss bestimmt

Deep-Sea Bioluminescence Blooms after Dense Water Formation at the Ocean Surface

The deep ocean is the largest and least known ecosystem on Earth. It hosts numerous pelagic organisms, most of which are able to emit light. Here we present a unique data set consisting of a 2.5-year long record of light emission by deep-sea pelagic organisms, measured from December 2007 to June 2010 at the ANTARES underwater neutrino telescope in the deep NW Mediterranean Sea, jointly with synchronous hydrological records. This is the longest continuous time-series of deep-sea bioluminescence ever recorded. Our record reveals several weeks long, seasonal bioluminescence blooms with light intensity up to two orders of magnitude higher than background values, which correlate to changes in the properties of deep waters. Such changes are triggered by the winter cooling and evaporation experienced by the upper ocean layer in the Gulf of Lion that leads to the formation and subsequent sinking of dense water through a process known as “open-sea convection”. It episodically renews the deep water of the study area and conveys fresh organic matter that fuels the deep ecosystems. Luminous bacteria most likely are the main contributors to the observed deep-sea bioluminescence blooms. Our observations demonstrate a consistent and rapid connection between deep open-sea convection and bathypelagic biological activity, as expressed by bioluminescence. In a setting where dense water formation events are likely to decline under global warming scenarios enhancing ocean stratification, in situ observatories become essential as environmental sentinels for the monitoring and understanding of deep-sea ecosystem shifts

Deep-Sea Bioluminescence Blooms after Dense Water Formation at the Ocean Surface

<p>The deep ocean is the largest and least known ecosystem on Earth. It hosts numerous pelagic organisms, most of which are able to emit light. Here we present a unique data set consisting of a 2.5-year long record of light emission by deep-sea pelagic organisms, measured from December 2007 to June 2010 at the ANTARES underwater neutrino telescope in the deep NW Mediterranean Sea, jointly with synchronous hydrological records. This is the longest continuous time-series of deep-sea bioluminescence ever recorded. Our record reveals several weeks long, seasonal bioluminescence blooms with light intensity up to two orders of magnitude higher than background values, which correlate to changes in the properties of deep waters. Such changes are triggered by the winter cooling and evaporation experienced by the upper ocean layer in the Gulf of Lion that leads to the formation and subsequent sinking of dense water through a process known as "open-sea convection". It episodically renews the deep water of the study area and conveys fresh organic matter that fuels the deep ecosystems. Luminous bacteria most likely are the main contributors to the observed deep-sea bioluminescence blooms. Our observations demonstrate a consistent and rapid connection between deep open-sea convection and bathypelagic biological activity, as expressed by bioluminescence. In a setting where dense water formation events are likely to decline under global warming scenarios enhancing ocean stratification, in situ observatories become essential as environmental sentinels for the monitoring and understanding of deep-sea ecosystem shifts.</p>

Time series of oceanographic parameters measured at the Lacaze-Duthiers Canyon (LDC) and the open-sea convection region in the Gulf of Lion (LION) from January 2008 to June 2010.

<p>(<b>a</b>) Potential temperature at 500 and 1,000 m depth at the LDC mooring site and (<b>b</b>) from various water depths at the LION site, jointly with (<b>c</b>) salinity at 2,300 m depth, (<b>d</b>) horizontal current speed and (<b>e</b>) vertical current speed from various water depths at the LION site. The four levels of temperature measurements at LION presented here are a sub-set of measurement depths (see Fig. S1). Essentially stable temperatures in the deepest layers in 2008 show that open-sea convection reached only 700 m and did not modify the deep water in the study area. In contrast, strong convection events, reaching 2,300 m depth, occurred during February-March 2009 and 2010 with an abrupt cooling of the upper water column and an increase in temperature and salinity in the deep layers. A concurrent increase in current speed was also noticed in winter 2009 and 2010. The 5-month long data gap in 2009 is due to a damaging of the mooring line during the April 2009 recovery, which induced a postponement of its redeployment to September 2009.</p

Links between bioluminescence, current speed and the modification of the properties of the Western Mediterranean Deep Water (WMDW).

<p>Box-and-whisker plot of median PMT counting rates (log scale) versus current speed classes for salinities higher (red) or lower (grey) than 38.479 for data recorded in (<b>a</b>) 2008, (<b>b</b>) 2009 and (<b>c</b>) between January and June 2010. The salinity threshold of 38.479 is used as a marker of the intrusion of newly formed deep water at the ANTARES site. While bioluminescence increases with current speed, it is also enhanced by the modification of WMDW (red box-plots). The top and bottom of each box-plot represent 75% (upper quartile) and 25% (lower quartile) of all values, respectively. The horizontal line is the median. The ends of the whiskers represent the 10^th and 90^th percentiles. Outliers are not represented. The statistical comparison between the two box-plots (red and grey) in each current class is given by the Kruskal-Wallis test: the observed difference between the two samples is significant beyond the 0.05 (*), the 0.01 (**) and the 0.001 (***) levels. The absence of an asterisk in some current classes indicates that the difference between the two box-plots is not significant. The number of measurements for salinity lower or higher than 38.479 is given in black or in red, respectively. Note the different scales of figures a, b and c.</p