Translated material
The first results of the Gerda experiment
On July 16, 2013, at a scientific seminar in the laboratory of Grand Sasso (Italy), the first results of the search for a immune-dual beta (ββ0v) of the GE-76 nucleus using the Gerda-I detector were presented [1]. The next day, the voiced results appeared in the form of an electronic preprint [2] and a week later were reported at the European Conference on High Energy Physics (Stockholm, July 18-24, 2013).
These results were expected by scientists with great interest. The intrigue was due to the fact that one of the tasks of the experiment was to verify the sensational (but, at the same time, and extremely ambiguous) result, obtained and published by several participants in the Heidelberg-Moscow (Mr.) experiment-the so-called Clapdore result (named after one of the leaders of the Clapdor-Claininghusus experiment). First, the collaboration reported not to observe the PP0V decay process in the GE-76 and set the limit for the half-life-T1/2> 1.9x1025 years. Then, several people from this collaboration, led by Clapdor-Clawringusus, announced the observation of ββ0v-decay with a reliability level of 4ѡ (T = 1.2x1025 years). Later, after a more complicated analysis, a result was obtained with the reliability level of 6ѡ: T1/2 = (2.2 ± 0.3) x1025 years. This result leads to fundamental consequences: the lepton number is not preserved, the neutrino has mass, this mass of the Mayran type, and the effective mass is equal to <mv> ~ 0.3 em. However, the scientific community reacted to this result with great distrust and did not accept it. An analysis carried out by independent groups of scientists showed a large number of inaccuracies, contradictions and frank “stretches” of “discovery” made by the authors.
However, the results of the Gerda-I experiment were expected with great interest. This experiment uses a completely new approach to the organization of passive and active protection against the background signal. Serious efforts have been made to minimize the number of structural materials around the semiconductor Germany (HPGE) detectors. In order to reduce the level of the background of the Germany crystal, in a vessel with a liquid argon, which, in turn, is placed in a huge tank with water (with a diameter and height of 10 m) (see Fig. 1). Liquid argon and water passed special cleaning of radioactive impurities. Full weight of HPGE detectors ~ 18 kg. It is interesting to note that the experiment mainly uses HPGE detectors, which were previously used in the experiments of Mr. and Igex. The entire installation is placed in the underground laboratory Grand Sasso (Italy) at a depth corresponding to the water column 3.5 km.
Interest was also fueled by the fact that the collaboration decided to use the so-called “blind analysis”-when the experimental data in the field of ββ0v-decay were unknown until the very last moment. The measurements were started in November 2011 and lasted about a year and a half. Finally, in June 2013, experimental data in the field of 0V mods were opened. And what did we see?
Complete lack of effect! With the expected 2.5 events, 3 events were registered from the background (see Fig. 2). Thus, only the limit was set for the duration of the dual immunitrin beta-decay T1/2> 2.1x1025 years (<MV> <0.2-0.4 EV). This closes the initial result of the Clapdor, but, nevertheless, formally does not exclude its last result (although, the authors themselves do not consider it, considering it obviously high). In fact, the initially planned sensitivity of the Gerda-I experiment was 3x1025 years old. In this case, both results of Clapdor would be closed (which was planned). However, the level of the background was slightly higher than the expected, in addition, two detectors failed and as a result, this did not allow the planned sensitivity. Nevertheless, the Gerda-I experiment has become a new stage in the development of experimental technology for the search for ββ0v-decompade GE-76. The proposed technique showed its performance and effectiveness, and the reached the level of the background was about an order of magnitude lower compared to the previous experiments of Mr. and Igex.
The next stage of the experiment is planned, Gerda-II, in which it is supposed to double the GE-76 mass and significantly reduce the level of the background. The planned sensitivity is about 2x1026 years for 3 years of measurement. The data set will begin, apparently, in early 2014. As a result, the problem associated with the result of the Clapdor will be finally resolved, and a new level of sensitivity in experiments on the search for ββ0v-decay has been achieved.
In conclusion, we note that scientists from several Russian institutes (ITEF, IYAI, Kurchatov Institute, Jin) participate in the Gerda experiment.
Alexander Barabash
ITEF, Moscow
2. Arxiv: 1307.4720