Saturday, July 11, 2015

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Deutsches Elektronen-Synchrotron
A Research Centre of the Helmholtz Association
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IceCube: A Next Generation Neutrino-Telescope


IceCube is a cutting-edge next generation neutrino telescope, at the South Pole, several thousands of meters below the surface of the Antarctic ice cap. With 5160 optical sensors distributed over a cubic kilometer of ice, IceCube is the biggest particle detector world-wide. At a first view, the South Pole may appear a strange site for deploying such an instrument. But there are crucial advantages that outweight the remoteness of the site. The Polar ice is about 3 km deep, the level of background light is extremely small, it is sufficiently transparent. That makes it an ideal medium to detect the faint light signals emitted by charged particles produced by high-energy neutrinos. The necessary infrastructure on site is provided by the renovated Amundsen-Scott station.

The successful deployment and operation of the AMANDA neutrino telescope laid the ground to get support for the IceCube project. AMANDA recorded more than six thousand high-energy neutrinos. The sky map of these neutrinos did not yet provide evidence for point sources. Most of these neutrinos, if not all, must have been produced in the Earth's atmosphere, as products of collisions between cosmic rays and air molecules. No spectacular discoveries have been made so far, but AMANDA has substantially contributed to the present detection limits on candidates for dark matter, on the flux of magnetic monopoles and on the neutrino flux from various potential point sources inside and outside our galaxy. AMANDA has clearly demonstrated that the polar ice is a suitable medium for a large neutrino telescope and the analysis of AMANDA data has proven the science potential of such a detector.
IceCube is about 30 times bigger and thus substantially more sensitive than AMANDA. The deployment of all 5160 optical sensors was completed in December 2010. During the construction phase the deployed parts of the detector produce already high-quality data. The 677 optical modules of AMANDA were integrated into the IceCube array. In 2009 AMANDA was decommissioned. The schematic sketch shows the dimension of the three detectors. Just like AMANDA, IceCube is deployed in vertical strings. Each IceCube string comprises 60 optical as well as their power-supply and the cables for the signal readout. The modules at one string are equally spaced at a distance of 17 m. Each string was lowered into a vertical hole, drilled with pressurized hot water, such that the instrumented volume of the detector spans a depth range between 1450 and 2450 m. A total of 86 holes was drilled, 78 of them are regularly distributed over a surface of a square kilometer, the distance between two holes being 125 m. The other 8 holes are for the dense Deep Core detector in the center of IceCube. Here the horizontal string spacing is 72 m and the vertical sensor spacing 7 m.
The optical sensors of IceCube are so sensitive that they respond even to a single photon. Still inside the optical modules, the photon signals are amplified, converted into electrical pulses and then translated into digital signals. Therefore, each module has its own mini-computer as well as a precision clock to measure the arrival time of the photons to an accuracy of 5 nanosecond (5*10-9sec). From the depth, the digitized light signals are sent over kilometer-long cables to the central data acquisition system in the South Pole station.

The contributions of DESY to the IceCube project are the following:

  • Production and test of 1250 of the more than 5000 optical modules
  • development and manufacturing of electronic components for the data acquisition system
  • software development for the data analysis
  • development and test of new methods of particle detection
  • European TIER1 center for data archiving and analysis
  • Data analysis
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