INR RAS - international collaborations

Particle physics - nonaccelerator experiments

KATRIN is an abbreviation for the KArlsruhe TRItium Neutrino experiment, which is presently being assembled at Karlsruhe Institute of Technology, Germany. KATRIN, launched at 2001, will investigate absolute mass scale of neutrinos that is the most important open issue in neutrino physics. Neutrinos tiny mass is a clear indication for physics beyond the standard model of elementary particle physics. On the largest scales, neutrinos take part in shaping the visible structures in the Universe, as they influence the formation and the distribution of galaxies.
Experimental method is based on 1983 paper by V.M. Lobashev and P.E. Spivak where they invented new type of the electrostatic spectrometer that uses adiabatic magnetic collimation. Experimental set-up that combined new spectrometer with Windowless Gaseous Tritium Source (WGTS) was commissioned in INR at 1994.
Similar spectrometer but with frozen tritium source was build at Mainz University, Germany. Common efforts of two groups achieved neutrino mass limit at 2 eV/c2 level. KATRIN, using the same measurement technique as predecessor experiments, will either improve this limit by one order of magnitude down to 0.2 eV/c2 (90% CL) or discover the actual mass, if it is larger than 0.35 eV/c2. This requires an improvement by two orders of magnitude with respect to key experimental parameters. INR group, an Associated Member of the Helmholtz Alliance for Astroparticle Physics, carry out studies of tiny physical processes in the WGTS necessary to limit final systematic uncertainty.

DOUBLE CHOOZ experiment was created to measure the value of neutrino mixing angle θ13. It is founded on the idea of using two identical detectors for doing relative measurements in reactor antineutrino flux. Double Chooz doing in France (l’Institut national de physique nucleaire et de physique des particules (IN2P3) is one of three experiments of the type like this taking place at present (two others are: Daya Bay (China) and RENO (Korea)). Before 2014 the measurements at Double Chooz were carried out by only one (far) detector but in spite of this the θ13 value was measured and it is appeared to be large enough (about 10 degrees) sin2θ13 = 0.109 ± 0.040. After 2014 we expect to start with near detector and this will allow to increase the accuracy at least factor 2, up to 0.02.
INR RAS takes part in the experiment from the beginning. Our colleagues took part in development of liquid scintillator doped with gadolinium. We have experts group on liquid scintillator taking part in filling the detectors. INR RAS was actively included in testing and installing PMTs in both Double Chooz detectors.
We take part in measurements (doing regular shifts on detector and remotely) and analysis.

The Germanium Detector Array (GERDA) at the National Laboratory Gran Sasso, Italy, has been searching for neutrinoless double beta decay (0ν2β) of the isotope Ge-76.
The Phase I of the experiment was finished in 2013. Data considered in the present analysis have been collected between November 2011 and May 2013 with a total exposure of 21.6 kg.yr. The background index is about 1x10-2 counts/ after pulse shape discrimination.
3 events are observed in the range of (0ν2β) decay region, to be compared to 2.5 expected background counts. No signal is observed and a lower limit T1/2 ≥ 2.1x1025 year is derived for the half-life of neutrinoless double beta decay of Ge-76 (90% C.L.).
The result obtained is the best for Ge-76 0ν2β decay. It solved the intrigue problem of positive 0ν2β decay observation by Klabdor's group (T1/2 = 1.2(+0.37; -0.21)x1025 year) keeping unsolved for more than 10 years.
Russian group has provided delivery, purification , purity measurement and transportation in low background condition of the enriched Ge-76 isotope which is the main basis of the all experiment. Russian participants calculated and found optimal conditions of the experiment. The setup elements were built on the basis of these calculation results.
Russian group took part in all steps of experiment: projection and creation of the setup, arrangement and testaments, and results analysis.

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