LSND

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LSND ( Liquid scintillator Neutrino Detector , Engl. For "liquid scintillator neutrino detector") was a physical experiment at Los Alamos National Laboratory . It was used to investigate neutrino oscillations and ran from 1993 to 1998. The result was interpreted as an indication of previously unknown sterile neutrinos outside the standard model of particle physics , but was highly controversial from the start.

The experiment

LSND was on the 800 MeV - linear accelerator of LAMPF ( Los Alamos Meson Physics Facility , English "Lot Alamos- for. Mesons system -Physics") connected. The protons of the beam hit a water target . The collision produced pions that came to rest in the target and disintegrated into muons and neutrinos, with the muons also disintegrating while emitting further neutrinos. The neutrinos reached the detector through a shield that held up the remains of other particles. This was a 8.3 m long and 5.7 m diameter cylinder with a filling of 167 t of mineral oil . Here the neutrinos could react with protons, electrons and atomic nuclei. The resulting scintillation and Cherenkov light were detected by photomultipliers . The detector was 30 m away from the target, which is a very short distance for oscillation experiments.

Result

Due to the reactions in the target, the neutrino beam should mainly consist of muon-antineutrinos and have an electron-antineutrino portion of at most . In order to observe a neutrino oscillation, an increased number of events for reactions that were only possible with electron antineutrinos was searched for. In fact, the LSND collaboration came to the conclusion that it had measured a significantly increased proportion of such events. The observation of a neutrino oscillation on such a short flight path cannot be explained in the context of the usual oscillation theories and other experiments, which is why so-called sterile neutrinos, a fourth type of neutrino without a weak charge and leptonic partner, have been postulated as the simplest explanation.

Controversy and control experiments

Due to the fact that the results contradicted other experiments and the current theory, it was often assumed that the LSND results were statistically insignificant, incorrectly evaluated or just measurement errors. The KARMEN experiment from 1999 to 2001 could not confirm the results, but could not exclude them with certainty due to incompatible parameters. This finally succeeded in 2007 with MiniBooNE , whose first publications KARMEN confirmed and excluded the LSND explanation by means of sterile neutrinos. For the LSND results either alternative explanations have to be found or experimental errors have to be assumed.

literature

  • Kai Zuber: Neutrino Physics , Institute of Physics Publishing, Bristol and Philadelphia 2004, ISBN 0-7503-0750-1 - Chapter 8.7.1
  • Athanassopoulos et al. : "The Liquid Scintillator Neutrino Detector and LAMPF Neutrino Source", Nucl. Instrum. Meth. A 388 (1997) 149-172. ( available online at arxiv.org , PDF file, 624 KB)

Web links