Detection of high energy cosmic rays with the resonant gravitational wave detectors NAUTILUS and EXPLORER

Abstract

The cryogenic resonant gravitational wave detectors NAUTILUS and EXPLORER, made of an aluminum alloy bar, can detect cosmic ray showers. At temperatures above 1 K, when the material is in the normal conducting state, the measured signals are in good agreement with the values expected based on the cosmic rays data and on the thermo-acoustic model. When NAUTILUS was operated at the temperature of 0.14 K, in superconductive state, large signals produced by cosmic ray interactions, more energetic than expected, were recorded. The NAUTILUS data in this case are in agreement with the measurements done by a dedicated experiment on a particle beam. The biggest recorded event was in EXPLORER and excited the first longitudinal mode to a vibrational energy of ∼ 670 K, corresponding to ∼ 360 TeV absorbed in the bar. Cosmic rays can be an important background in future acoustic detectors of improved sensitivity. At present, they represent a useful tool to verify the gravitational wave antenna performance.

SGR 1806-20 and the gravitational wave detectors EXPLORER and NAUTILUS

“…particle multiplicity measured in the lower part of the cosmic ray detectors. The vibrational energy peaks are correspondently 2.47 K and 1.08 K, several hundred times the background, indicating a total energy of the order of 10 TeV deposited in each bar [23].…”

“…The test validity is performed employing the real signals generated by extensive air showers (EASs) [23], and the filtered data of EXPLORER and NAUTILUS, all relative to the year 2004 [21,28]. Two events were selected, each for the single detector, with highest interaction energy with relative bar, in order to be independent of the noise.…”

“…IV, we evaluate the excess amplitude on the on-source regions of the GW detector data. With this measurement (calibrated using the cosmic ray signals [23], as explained in the Appendix), we exclude the presence of the GW short signal and we establish the upper limit to the amount of isotropic GW energy E GW emitted during the exceptional periods. The second algorithm regards the crosscorrelation function calculated between the EXPLORER and NAUTILUS data streams, as shown in Sec.…”

Analysis of 3 years of data from the gravitational wave detectors EXPLORER and NAUTILUS

“…(ii) cosmic ray showers are known to produce short bursts of excitation in the antennas. The events must not be in coincidence with a shower, as recorded by detectors installed above and below both antennas [16,17]. These two selections veto a very small fraction of the events, usually less than 0.1%.…”

“…In the period considered, however, the refrigerator was not operational, in order to maximize the detector duty cycle. Both detectors are equipped with cosmic ray telescopes, to veto excitations due to large showers [15][16][17]. The two telescopes rely on different technologies (scintillators for Explorer, streamer tubes for Nautilus) but both provide a monitor of comparable effectiveness and a continuous check of the antenna sensitivity [18,19].…”