Saturday, September 24, 2011

CERN explains the neutrino experiment

CERN explains the neutrino experiment


Dario Auterio explained in detail the measurement methods and results of the OPERA experiment
Image: CERN In a two-hour webcast Dario Auterio, a physicist at the Institute of Nuclear Physics of Lyon (CNRS), the measurement results and measurement of the OPERA experiment presented in detail, the neutrino a speed of about 0.025 parts per thousand, or about 7.5 km / s certified by the speed of light. If you missed the event can watch the replay of the webcast. (If this server will be overloaded, recommends the CERN groovy gecko webcast or webcast elmundo.es).

The experts present were able to identify at least at first glance does not bug craft, either in the time measurement, distance measurement, even in the analysis. Is everywhere been proceeded with utmost care, she conceded.

Possible interference by the seasons, temperature, moon phases, supernovae, seismic shifts - all questions that were asked Auterio, but which were considered by his remarks or not the cause for this unexpected result may be.

The time is measured with two synchronized via GPS cesium clocks, which were of the Swiss Institute of Metrology (METAS) delivered and calibrated. In addition, the PTB in Braunschweig, the measurement method has cross-checked with portable instruments, and confirmed in measurement accuracy of 2.3 + -0.9 ns. The distance between the deep in the mountains nearby detector at the Gran Sasso tunnel, and the measuring point at CERN in Geneva, was of around 730 km with GPS technology to about 20 cm determined with sufficient accuracy, although with a bit more effort to distance still could determine more precisely . But it would have to for a while the cars in the Gran Sasso tunnel, stopping completely in order to measure the distance to the GPS point on the edge of the motorway tunnel precise way and the scientists wanted to the Italian drivers do not expect, at least not yet.

In the current measurements since 2008, scientists at the coordinates daily measurements, a slight continuous shift could order a few centimeters per year and an earthquake in 2009 represent a jump of 6 inches to the north and east. The 1400-meter cliff overlooking the neutrino detector shield 99.9 percent of the cosmic radiation that would otherwise overlap the measurements.

The duration of a single neutrino can not be measured, however, only the probability distribution in a bundle. From the pre-accelerator (SPS) of the Large Hadron Collider are decoupled by kicker magnets 10.4 microsecond long proton beam of 400 GeV. They modulated the synchrotron frequency of 500 kHz and the radio frequency of 200 MHz. The time structure of the bundle is in a Beam Detector Current Transformer (BCT) with a high-resolution waveform digitizer (WFT) with 1 Gigasamples / s were measured. The protons slam on a 2 m long graphite block with mesons (pions, kaons) are produced. These mesons decay somewhere in the 1,000 m-long vacuum tunnels into muons, muon neutrinos being produced. The exact point you do not know, but since the mesons have nearly the same rate as the neutrino, one can neglect the difference. Over a 18-m-long carbon-iron block, the remaining heavy particles are then intercepted and measure the muons. The neutrinos travel 730 km through the crust convert into a fixed component and tau neutrinos are then collected in the 1500-ton detector. About half of the detected neutrinos react with the rocks of the mountain (external events), the rest with the target (internal events). These different events are then billed separately.

This ultimately results in a shift in the probability distribution over the expected value at light speed of 60.7 ns + / -14.5 ns with a significance of 6.0.

The researchers, this result is itself not safe: "We try not theoretical or phenomenological readings," said her final sentence. But CERN's Chief Heuer has already announced that the existing CERN-side line called OPERA is now come much more important - but you will not forget the search for the particles Higgschen it.

Many more details can be found in the official publication (pdf). Given the crowd of scientists listed in the event of a fall should be divided on the Nobel Prize over a century.

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