Double Chooz
The Double Chooz experiment, the particular nature of neutrinos is examined to transform itself from one variety to another ( neutrino oscillation ). The experiment is operated in the framework of an international collaboration in France at the Chooz nuclear power plant, in which - as in any nuclear reactor - produced by beta decay antineutrinos in large numbers. To determine the conversion probability of two identical detectors in 400 and 1050 meters are built to the reactor. Neutrinos have a very low reaction probability, is from 2010 measured about 5 years to detect neutrinos and enough to measure the small conversion probability for the first time, or derive upper limits for this process.
This experiment is the successor of the Chooz experiment, which also detected neutrinos at the Chooz nuclear power plant. The original Chooz experiment could determine the precise upper limit to 2012 for the conversion probability of electron neutrinos, which is referred to as. From Double Chooz it was hoped that an even greatly improved border or even an accurate value. A first -presented in November 2011 results indicated a non-zero transition probability. This statistically not significant Note later proved to be consistent with the significant results of the competing experiments Daya Bay and RENO shortly thereafter.
Concept of the Double Chooz experiment
The radioactive decay of fission products in the nuclear reactor provides as a byproduct of anti- electron neutrinos that fly in all directions. One of two detectors is positioned relatively close to the reactor. The antineutrinos have not had the opportunity to transform themselves into a different variety to the near detector. The second detector, however, is placed at a greater distance, to be more likely in the transformations. The detectors can only measure the anti- electron neutrinos produced in the reactor. If you measure so as expected by the dilution in the far detector distance less neutrinos, one can assume that the anti- electron neutrinos have been partially converted to a different type. From the number of neutrino events in the far detector compared to the near detector you close to how big the conversion probability is.
Neutrinos have no electrical charge and can therefore be difficult to establish. In the case of the Double Chooz experiment, the neutrino detection via the inverse beta decay, in which an anti- electron neutrino converts a proton into a neutron and a positron happens:
The resulting positron scintillation light generated in the detector. In order to detect the neutron is added to the liquid scintillator gadolinium that the neutron captures with high probability, thereby passes into an excited state. The excited Gadoliniumkern can then proceed with the emission of gamma radiation in the ground state, which again leads to the production of scintillation light. The light is then registered by the photomultiplier tubes.
Detector principle
The detector consists of several parts that perform specific tasks. At the core of the detector, the neutrino reactions are to be detected in a liquid scintillator. In this case, a neutrino strikes a proton and there are a neutron and a positron ( the antiparticle of the electron). Both reaction products are detected in order to obtain a well-defined neutrino signal: The positron annihilates with an electron from the surrounding environment, producing two high-energy photons. To capture the neutron containing gadolinium scintillator. It also creates high -energy photons that occur somewhat delayed for positron signal. Liquid scintillator in the detector, the inner volumes of the two energy of the photons will be gradually converted to visible light obtained in the end. This light is detected by means of photomultiplier tubes. Photomultiplier are devices which can convert single photons in the visible region into an electrical signal. The outer part of the detector used to shield from natural radioactive radiation from the environment. The fourth volume is used for active background suppression. Especially cosmic muons, which can interfere with the measurement, will be recognized in this part of the detector.
Results so far
On the LowNu conference in Seoul 2011 first results of the Double Chooz experiment were presented in November. The most probable value of θ13 was thus:
The probability that no oscillation was present ( θ13 = 0), was after the first results of just 7.9 %, corresponding to a statistical significance of 1.7 standard deviations. Double Chooz was thus the first reactor neutrino experiment, suggesting the oscillation of electron antineutrinos on short distances. On 8 March 2012, the Daya Bay collaboration with a significance of more than five standard deviations published the first measurement of the mixing angle θ13 through the discovery threshold. Daya Bay was for the mixing angle the value of 0.092, a result of the Double Chooz consistent measurement.
In June 2012, the Double Chooz collaboration announced an improved measurement based on a larger data set. The updated value of the mixing angle is given depends on the analytical approach with 0.109 or 0.170, increases the significance to 2.9 standard deviations.
Further measurements with larger statistics and in particular the data of the near detector to further reduce the measurement uncertainties.
Institutes from Germany
In addition to numerous other institutes from France, USA, Japan, Spain, Russia and Brazil also five German institutes are involved in Double Chooz:
- Eberhard Karls University of Tübingen
- Max Planck Institute for Nuclear Physics in Heidelberg
- Rheinisch- Westfälische Technische Hochschule Aachen
- Technical University of Munich