Why is the Conclusion of the GERDA Experiment not Justified ?

TL;DR

The GERDA experiment's initial results are inconclusive due to low statistics, higher background levels, and unresolved background lines, making its conclusion on neutrinoless double beta decay unjustified at this stage.

Contribution

This paper critically evaluates the GERDA experiment's first results, highlighting issues with background reduction, energy resolution, and statistical significance compared to previous experiments.

Findings

GERDA's background levels are higher than those of HEIDELBERG-MOSCOW.

GERDA's current half-life limit is lower than the previous experiment.

Further data collection is needed for a justified conclusion.

Abstract

The first results of the GERDA double beta experiment in Gran Sasso were recently presented. They are fully consistent with the Heidelberg-Moscow experiment, but because of its low statistics cannot proof anything at this moment. It is no surprise that the statistics is still far from being able to test the signal claimed by the HEIDELBERG-MOSCOW experiment. The energy resolution of the coaxial detectors is a factor of 1.5 worse than in the HEIDELBERG-MOSCOW experiment. The original goal of background reduction to 10^{-2}counts/kgykeV, or by an order of magnitude compared to the HEIDELBERG-MOSCOW experiment, has not been reached. The background is only a factor 2.3 lower if we refer it to the experimental line width, i.e. in units counts/kgy energy resolution. With pulse shape analysis (PSA) the background in the HEIDELBERG-MOSCOW experiment around Q_{\beta\beta} is 4x10^{-3} counts/kgykeV \cite{HVKK-IVK-MPhLA2006}, which is a factor of 4 (5 referring to the line width) lower than that of GERDA with pulse shape analysis. The amount of enriched material used in the GERDA measurement is 14.6kg, only a factor of 1.34 larger than that used in the HM experiment. The background model is oversimplified and not yet adequate. It is not shown that the lines of their background can be identified. GERDA has to continue the measurement further ~5years, until they can responsibly present an understood background. The present half life limit presented by GERDA of T_{1/2}^{0\nu} > 2.1 x 10^{25} y (90% confidence level, i.e. 1.6sigma)) is still lower than the half-life of T_{1/2}^{0\nu} = 2.23^{{+0.44}_{-0.31}} x 10^{25} y \cite{HVKK-IVK-MPhLA2006} determined in the HEIDELBERG-MOSCOW experiment.