The NA62 experiment is an experiment at the SPS accelerator at the European nuclear research center CERN, which is currently in the construction phase. The aim of the experiment is to study the extremely rare decay of the kaon into a pion and two neutrinos (). The first scheduled recording of data is provided for 2014. It will be the first experiment in the world at this time, the kaon decays will study with this extremely small decay probability ( magnitude 10-10). Speaker of the NA62 experiment is Augusto Ceccucci.
The investigation of the kaon decay provides an excellent opportunity to test the standard model of particle physics with high precision because of its rarity. Under this model, the probability of this decay is predicted very accurately. Deviates from the measurement result from the predicted result, this is a signal for physics beyond the standard model ( " New Physics "). In addition, with the measurement of the matrix element | be determined with high accuracy of the CKM matrix | Vtd.
NA62 is a so-called "fixed target" experiment. This means that accelerated particles impinge on a stationary target. In NA62 accelerated protons strike from the SPS accelerator at a resting Berylliumdraht. In the collision occur, among other kaons, which decay along the approximately 275 -meter-long experiment. The NA62 experiment is located underground in the North Area (hence the abbreviation NA) of the SPS accelerator.
The great challenge of the experiment is the extreme rarity of the decay to be examined. It must be produced kaons in 1013 to measure 100 of the sought decays. This number of kaons is the number of stars in 50 galaxies similar to our Milky Way. The measurement requires an efficient suppression of all other possible decays of the kaon. This so-called background is suppressed by a factor of 1012, that is filtered to become. These different detector systems cooperate in NA62.
The individual sub-detectors of the NA62 experiment are designed and built by research groups throughout Europe. In Germany, the working group "Experimental Particle and Astroparticle Physics" (ETAP ) at the Johannes Gutenberg University Mainz is involved. Currently finished detector components at CERN already be installed. The following is an overview of the detectors and their function used should be given.
Identification of the kaon and determination of the pulse
In the collision of protons with the Berylliumdraht the kaons represent only a small portion of the particles generated dar. Essentially incur additional protons and pions. To assign a daughter later measured kaon, the kaons must be identified by the production. This is achieved by the so-called CEDAR. CEDAR is a hydrogen-filled tube. Particles passing through the hydrogen, emit Cherenkov radiation. This radiation is reflected by mirrors at the end of Cedars a diaphragm. The arrangement of aperture and mirrors is chosen so that only produced by kaon Cherenkov radiation is incident on the aperture.
For the investigation of the decay knowing the pulse of the kaon is required. This is determined by the GigaTracker (GTK ). This sub-detector consists of three units (GTK 1-3), between which there are magnets. By means of the Lorentz force caused by the curvature of the path of the pulse of the kaon can be determined. The individual stations each consist of 18,000 silicon detectors with dimensions of 300 microns x 300 microns.
Identification of the pion and the determination of the pulse
Only the pion from the decay wanted the kaon into a pion and two neutrinos can be seen in the following detectors. The neutrino can not be measured directly because of their physical properties in this experiment. The momentum of the pion and other charged particles by means of a spectrometer consisting of four straw detectors and a magnet determined. Two of the straw detectors are located outside the magnet and determine the position of the charged particles. The magnet deflects the charged particles and the position is determined in the following straw detectors again. As in the measurement in GigaTracker can be closed from the curvature of the web to the momentum of the charged particles. Behind the spectrometer is a ring imaging Cherenkov detector ( RICH ) detector. The 17 -meter-long detector is filled with neon gas. There the Cherenkov effect is exploited to identify the pions again. The resulting radiation cone is reflected by mirrors at the end of the detector at 2000 photomultiplier read out the light. From the size of the measured particles, the rings can be identified.
To filter out this decay from all possible decays of the kaon, detectors must be able to recognize the ground. These detectors are called veto detectors because they recognize certain decays and these will not be recorded as a result. In the NA62 experiment two veto systems are used, the photo - veto and muon veto system. Since the sought decay emits no photons or muons, such decays can be rejected if any of these particles is detected.
Photo- veto detectors
The object of the photo- detectors to detect decay, produce one or more photons. Various detectors used to ensure complete coverage area. The Large Angle Veto ( LAV ) consists of twelve stations that are positioned along the decay path of kaons. In the stations lead glass is installed, in which the photons are detected via Cherenkov radiation. The LAV is for large emission angle of photons from 8.5 to 50 mrad responsible. The mean angular range of 1 to 8.5 mrad is covered by the liquid krypton calorimeter. This detector has been used in the previous experiment NA48. The liquid krypton calorimeter is a homogeneous calorimeter, which can by photon induced electromagnetic showers completely in the cylindrical volume with a surface area of 5.3 m and a depth of 127 cm register. The small -angle calorimeter (SAC) is located at the end of the experiment structure to detect photons within a very small solid angle (mrad less than 1) is radiated. A magnet in front of the SAC shape deflects charged particles, so that the uncharged photons strike the detector and can be registered there.
Muon veto detectors
The muon veto system comprises three detectors, which include, but are positioned at the end of the experiment only structure of SAC, one behind the other. The first two muon veto detectors ( MUV1 and MUV2 ) are hadronic calorimeter, which should distinguish pions due to the size of the particle showers produced by muons. The calorimeter made of iron and Szintillatorlagen. Charged particles generate light in the scintillator, which is read out. The Szintillatorlagen are segmented so that you can determine the size of the particle showers produced. The third muon veto detector ( MUV3 ) is separated by a 80 cm thick iron block of the first two muon veto detectors. Muons can this iron block happen while pions hadronically interact and get stuck in the block. MUV3 the scintillator consisting of a layer to be read out by photomultiplier tubes. Each watched signal is identified as muon decay and not stored for further analysis.