Search

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 about 670 K, corresponding to about 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., Comment: submitted to Astroparticle Physics

Many experiments have searched for supersymmetric WIMP dark matter, with null results. This may suggest to look for more exotic possibilities, for example compact ultra-dense quark nuggets, widely discussed in literature with several different names. Nuclearites are an example of candidate compact objects with atomic size cross section. After a short discussion on nuclearites, the result of a nuclearite search with the gravitational wave bar detectors Nautilus and Explorer is reported. The geometrical acceptance of the bar detectors is 19.5 $\rm m^2$ sr, that is smaller than that of other detectors used for similar searches. However, the detection mechanism is completely different and is more straightforward than in other detectors. The experimental limits we obtain are of interest because, for nuclearites of mass less than $10^{-5}$ g, we find a flux smaller than that one predicted considering nuclearites as dark matter candidates. Particles with gravitational only interactions (newtorites) are another example. In this case the sensitivity is quite poor and a short discussion is reported on possible improvements., published on Astroparticle Physics Sept 25th 2016 replaced fig 15

We report here the preliminary results of the search for gravitational wave bursts from the 2003 run of the EXPLORER–NAUTILUS experiment. The total common measuring time was 149 days. The detectors had a typical noise spectral amplitude of about 2 × 10−21 Hz−1/2, a bandwidth of the order of 10 Hz and a very good stability. We derive a new upper limit for the GW burst rate, of the order of 0.02 events/day for hRSS ≥ 2 × 10−19, and discuss the implication of this result with respect to the results obtained with the 2001 run.

We have analysed three data sets, each two days long, of the EXPLORER resonant bar detector. We have searched for continuous gravitational-wave signals from spinning neutron stars. Our data analysis technique was based on the maximum likelihood detection method. We briefly describe the theoretical methods that we used in our search and we present results of the search. The main outcome of our analysis is an upper limit of 1 × 10 −22 for the dimensionless amplitude of a continuous gravitational-wave signal. The upper limit is for any source location in the sky, any polarization of the wave and for signals of frequency from 921.00 Hz to 921.76 Hz and with spin down from −2.36 × 10 −8 Hz s −1 to +2.36 × 10 −8 Hz s −1 .

We have fabricated and characterized a superconducting planar gradiometer sensitive to the second‐order spatial derivative of the magnetic field. Our device has been patterned on a 12.8×12.8 mm silicon chip on which the sensitive area of the gradiometer and the SQUID inductance are generated by the same four 0.5‐mm‐square holes. We measured the sensitivity both in flux‐locked‐loop (FLL) and in open‐loop mode. With the second method we used another dc‐SQUID as amplifier and in this case we obtained the best noise performance. The gradiometer sensitivity was 18 fT/cm2 √Hz. The magnetic isoflux line distribution generated by a dipolar source was measured by the gradiometer in FLL mode.

Two dedicated and distinct tests of the effects of Nitrogen and Oxygen contaminations in liquid Argon (LAr) have been performed within the WArP R&D program. Purpose of the tests is to detect the reduction of the LAr scintillation light emission as a function of the amount of the contaminant injected in the Argon volume. The rate constant of the light quenching process induced by Nitrogen in LAr has been found to be k ( N 2 ) = 0.11 μ s - 1 ppm - 1 (part per million), while the rate constant for Oxygen has been found to be k ′ ( O 2 ) = 0.54 ± 0.03 μ s - 1 ppm - 1 . Direct PMT signals acquisition allowed to extract with high precision the main characteristics of the scintillation light emission in pure and contaminated LAr. In particular, the decreasing behavior in lifetime and relative amplitude of the slow component is found to be appreciable from O (1 ppm) of Nitrogen concentrations and from O (0.1 ppm) of Oxygen concentrations.

Following a previously found correlation between the gravitational-wave detectors and the Mont Blanc particle detector, we have searched for a similar correlation between the data of the experiments mentioned in the title. We have found that both the Kamioka and the IMB data have a correlation with the gravitational-wave data that occurs with the same characteristics and at the same time of that already found with Mont Blanc. This correlation extends for a period of one or two hours centred at the hour 2∶45 UT of 23 February 1987. It shows that the particle detector signals are delayed with respect to the gravitational-wave detector signals by (1.2±0.5) s. The probability that the additional correlation due to Kamioka and IMB is only accidental is estimated of the order of 10−3 or 10−4.

A simple mathematical model is reported for a dilution refrigerator coupled to a large cryostat. The model is used to determine the equilibrium temperatures of the various intermediate shields of the cryostat between 1.2 and 0.1 K. Requirements are derived for the circulating 3He flow and the heat load on the shields, that are relevant for large, ultra-low temperature cryostats such as those being developed for gravitational wave research. Agreement between model predictions and preliminary data gathered with the dilution refrigerator on a test cryostat is excellent.

We review the state of operation of the two cryogenic resonant antennas of the ROG Group, with updated statistics on observation time and data quality. We also mention some preliminary results from joints searches with other gravitational detectors. Finally, the present a brief overview of the development work into advanced readouts, that could increase the peak sensitivity and the bandwidth of our apparata

We report on the present status of the resonant gravitational waves detectors EXPLORER and NAUTILUS operated by the ROG collaboration at CERN and at the INFN Prascati National Laboratories respectively. EXPLORER has been operating in continuous data taking for three years. NAUTILUS during 2002 underwent a partial overhaul of its read-out electronics. The results obtained since May 2003 show a considerable improvement in the performances of the apparatus. Both the detectors exhibit an unprecedented useful bandwidth: in over 30 Hz their spectral sensitivities are better than 10~/ \/Hz with a duty cycle only limited by cryogenic operations.

We report on the present scientific run (04-05) of the two detectors EXPLORER and NAUTILUS. The 04-05 run of the two detectors started in March 2004. The strain sensitivity is about 7 x 10(-22) Hz(-1/2) and the bandwidth is about 5 Hertz. The sensitivity for 1 ms bursts is h = 3 x 10(-19).

We present the result of a search for coincidences among the triggers found in the analysis of three 2-day-long stretches of data from the EXPLORER bar detector. The data were searched for nearly periodic gravitational waves from rapidly rotating neutron stars in our Galaxy. In this paper we propose a numerical procedure to search for coincidences and we present a theoretical formula for the expected number of coincidences. Our numerical analysis revealed no double and consequently no triple coincidences among the triggers from the three data sets. The results are in agreement with the expected number of coincidences that we estimate by our theoretical formula.

The statistical association between the output of the Gravitational Wave (GW) detectors EXPLORER and NAUTILUS and a list of Gamma Ray Bursts (GRBs) detected by the satellite experiments BATSE and BeppoSAX has been analyzed using cumulative algorithms. GW detector data collected between 1991 and 1999 have been correlated to the GRB flux peak times. The cumulative analysis of a large number of GRBs (387) allows to push the upper bound for the corresponding GW burst amplitude down to $h = 2.5\cdot10^{-19}$., Comment: 10 pages, 6 figures; minor corrections, added references. Accepted for publication in Phys. Rev. D

Gamma ray bursts (GRBs) likely arise from the collapse of very massive objects or from the coalescence of compact binary systems. In both cases, also a burst of gravitational waves (GWs) should be emitted. The observation of a large number of GRB events gives the possibility of a systematic analysis of the GW detector data when searching for an association between the two emissions. Data collected by the resonant cryogenic detectors, EXPLORER and NAUTILUS, between 1991 and 1999, have been correlated with the GRB events. The analysis excludes the presence of a signal of amplitude h ? 5.4 ? 10?19, if we allow a time delay between GW burst and GRB within 10 s.

Resonant gravitational wave detectors with an observation bandwidth of tens of hertz are a reality: the antenna Explorer, operated at CERN by the ROG collaboration, has been upgraded with a new read-out. In this new configuration, it exhibits an unprecedented useful bandwidth: in over 55 Hz about its frequency of operation of 919 Hz the spectral sensitivity is better than 10^{-20} /sqrt(Hz) . We describe the detector and its sensitivity and discuss the foreseable upgrades to even larger bandwidths., 4 pages- 4 figures Acceted for publication on Physical Review Letters

The resonant-mass gravitational wave detector NAUTILUS, operated by the ROG collaboration at the INFN Frascati National Laboratories, is in continuous data taking since June 1998 with peak sensitivity of \( h \simeq 3 \cdot 10^{ - 22} Hz^{ - {1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} \). It has recently proven to be capable of recording signals due to the passage of cosmic rays. The results of the latest coincidence analyses between the NAUTILUS data and the cosmic ray signals measured by detectors located above and below NAUTILUS are reported.

The EXPLORER gravitational wave detector has been recently improved. The antenna has been equipped with a new read-out. The use of a new transducer, characterized by a very small gap, and a dc-Squid with a high coupling, led to a better sensitivity and a larger bandwidth. In the first six months of the year 2000, an effective temperature of 3 mK and a bandwidth of almost 8 Hz were reached. Further improvements are expected. The new experimental configuration appears also very promising for use in the ultra-cryogenic antenna NAUTILUS.

The Explorer gravitational wave detector is cooled by a very large superfluid helium bath (1000–2000 I). It exhibits a dramatic drop in noise level, reaching the expected Brownian level, when the liquid helium bath is cooled through the superfluid transition. This is most likely due to the suppression of extra noise related to helium boil-off and thermoacoustic oscillations. This behaviour has been monitored, with the detector gathering data while being cooled. The data and some possible interpretations are reported.

NAUTILUS started its second run of continuous data taking in june 1998. The measured strain sensitivity at the two resonances is 410−22/Hz over a bandwidth of 1 Hz and better than 310−20/Hz over a band of about 25 Hz, with a duty cycle mainly limited by cryogenic operations. A summary of the most recent results obtained with the NAUTILUS data is given.

The passage of cosmic rays has been observed to excite mechanical vibrations in the resonant gravitational wave detector NAUTILUS operating at temperature of 100 mK. A very significant correlation (more than ten standard deviations) is found.

The International Gravitational Event Collaboration, IGEC, is a coordinated effort by research groups operating gravitational wave detectors working towards the detection of millisecond bursts of gravitational waves. Here we report on the current IGEC resonant bar observatory, its data analysis procedures, the main properties of the first exchanged data set. Even though the available data set is not complete, in the years 1997 and 1998 up to four detectors were operating simultaneously. Preliminary results are mentioned., 8 pages, 2 figures, 3 tables; Proceeding of the GWDAW'99. Submitted to the International Journal of Modern Physics

We report on our progresses in the design and construction of the suspension system for a 3 kHz spherical detector. The plan for our SFERA project is to build a small cryogenic spherical detector by the year 2001.

Recently significant advancements have been made towards the realization of a large spherical gravitational wave detector. Research and development activities have already begun in several countries. We present here the main features and capabilities of a spherical gravitational wave detector. In particular, we discuss the interaction between a spherical antenna and cosmic rays that may require a large detector to be placed underground.

We have measured the Josephson radiation emitted at millimeter‐wave frequencies by a long Josephson junction dc‐current biased on Fiske steps of the current‐voltage characteristic. Our measurements demonstrate that differences between dynamic excitation generating Fiske steps and fluxon oscillations giving rise to zero‐field steps in long junctions may exist. The radiation, whose maximum measured frequency is 240 GHz, is generated by an in‐line junction and detected on a chip by a small planar tunnel junction. From measurements of Shapiro steps amplitude and photon‐assisted tunneling steps we find that the coupled radiation has a power tunability of 350 nW and the maximum coupled power is 20 nW in a 30‐Ω normal‐state resistance tunnel junction.

A dedicated test of the effects of Nitrogen contamination in liquid Argon has been performed at the INFN-Gran Sasso Laboratory (LNGS, Italy) within the WArP R&D program. A detector has been designed and assembled for this specific task and connected to a system for the injection of controlled amounts of gaseous Nitrogen into the liquid Argon. The purpose of the test is to detect the reduction of the Ar scintillation light emission as a function of the amount of the Nitrogen contaminant injected in the Argon volume. A wide concentration range, spanning from similar to 10(-1) ppm up to similar to 10(3) ppm, has been explored. Measurements have been done with electrons in the energy range of minimum ionizing particles (gamma-conversion from radioactive sources). Source spectra at different Nitrogen contaminations are analyzed, showing sensitive reduction of the scintillation yield at increasing concentrations. Direct PMT signal acquisition exploiting high time resolution by fast waveform recording allowed high precision extraction of the main characteristics of the scintillation light emission in contaminated LAr. In particular, the decreasing behavior in lifetime and relative amplitude of the slow component is found to be appreciable starting from O(1 ppm) of Nitrogen concentrations. The rate constant of the quenching process induced by Nitrogen in liquid Ar has been found to be k(Q)(N(2)) = 0.11 +/- 0.01 mu s(-1) ppm(-1), consistent with a previous measurement of this quantity but with significant improvement in precision. On the other hand, no evidence for absorption by N(2) impurities has been found up to the higher concentrations here explored.

We discuss here the use of a mechanical suspension for the new generation of resonant gravitational wave antennas, cooled at temperatures below 0.1 K. The crucial problem of these detectors is the isolation from all external mechanical vibrations in the presence of the unavoidable solid thermal link with a dilution refrigerator. Measurements of the mechanical transfer function performed with two types of suspension‐thermal link configurations are reported. This study has led to the design of the suspension and thermal link of the first ultralow temperature antenna of the Rome group ‘‘Nautilus.’’

The somatosensory homunculus has been identified during stimulation of median (at wrist and elbow), femoral, tibial and pudendal nerves of the left hemibody via the neuromagnetic imaging technique. The somatic representations of different body districts have been localized in the somatosensory cortex, by means of an equivalent dipole localization algorhythm. Dipole locations agree with the well-known somatotopic organization obtained with invasive techniques. The proposed method is, therefore, an important investigating tool for studies on normal and diseased subjects.

The coupling of millimeter-wave radiation from a long Josephson junction to a small-area junction is discussed. The coupling is obtained by means of thin-film technology and the design parameters allowing radiation coupling are discussed. Since the frequency of the oscillator radiation is smaller than the plasma frequency of the detector junction, the latter shows evidence of chaotic dynamics in the current-voltage characteristic. However, very stable zero-crossing bias steps appear for high values of the applied radiation power. The tunability of the oscillator power allows measuring the dependence of the detector critical current on the external radiation to be measured; from this measured dependence and from the observed amplitude of the photon-assisted tunneling steps it is estimated that maximum coupled power is the range of tens of nanowatts.

We report on the operation of the resonant gravitational wave (g.w.) detector Explorer of the Rome group (M = 2300 kg, T =2 :6 K, located at CERN) at the time of the gamma-ray burst GRB 980425 (April 25.90915 UT, 1998), which is probably associated with the supernova SN 1998bw .W e present the data of the detec- tor (with sensitivity hc =8 10 19 for a1m s pulse), and use the BeppoSAX data to estimate the initial time of the GRB: a basic parameter for any correlation analysis. The g.w. data exhibit no signicant time signature around the GRB 980425. We wish to remark the impor- tance to make use, in spite of the present low sensitiv- ity, of the data collected with g.w. detectors, that can be regarded as active observatories, in coincidence with the BeppoSAX data.

The behavior of a pair of aluminum ’’Dayem’’ bridges in a magnetic field is reported. The quantum interference properties of the supercurrents are found biasing the links with an ac current and measuring its mean square voltage as a function of an external magnetic field. The shape of the so‐obtained curve remains the same in a relatively large range of temperature: 6×10−3< (Tc−T)/Tc

The quality factorQ of a small gravitational-wave antenna has been measured between 4.2 and 1.1 K. The dependence ofQ onT can be fitted by an expression linear in 1/T as well as by the formulaQ=Q0 exp [Δe/kT]. In the latter case, one finds Δe≈7·10−5eV.

In two previous papers we have presented evidence for a correlation between a part of the background of a gravitational-wave antenna (M=390 kg) and the free oscillations of the Earth. These results are suggestive of a similar study of the forced oscillations of the Earth. In this paper we present the results of the Fourier analysis for periods between ℱ=100 and 1667 min of the data collected on the occasion of two runs: one in 1978, the other in 1980. They show a few frequencies, some of which are in very good agreement with tidal frequencies. The probability for these «overlappings» to be accidental is of the order of 10−2 or less.

In November 1985 the gravitational-wave antenna of the Rome group, installed at CERN, has started operating. It consists of a 5056 aluminium cilinder 3 m long, 2270 kg heavy, cooled at 4.2 K. The antenna vibrations are detected by means of a resonant capacitive transducer that together with the bar makes a two-coupled-oscillator system. The low-noise amplification is obtained with a d.c. SQUID amplifier. The frequencies of the two resonant modes are:v-=907.116 Hz andv+=923.083 Hz, with merit factorsQ−=3.2·106 andQ+=5.6·106. The sensitivity to short gravitational bursts, expressed in terms of effective noise temperature, is 18 mK. This corresponds to a change in the metric tensor whose Fourier transform isH=1.1·10−21 Hz−1. For monochromatic waves the antenna is sensitive (SNR=1) toh∼2·10−25 in a band width of about 1/3 Hz, with a three months integration time.

The intermediate gravitational-wave antenna ofM=390 kg and ν0=1795 Hz has been operated at 4.2 K in the Laboratorio Plasma Spazio of CNR from June 10 to July 18, 1978. The data collected during more than 50% of the time show an effective temperature of 1.5 K on the average, with periods of the order of a few hours during which it goes below 1 K. This corresponds to an instrumental sensitivity of 2 GPU=200 J/m2·Hz. The observed difference between observed and computed equivalent temperature is due to disturbances of mechanical and thermal origin which we believe can be further reduced.

A new method for measurements of ultralow currents in the audio‐frequency range (from dc up to over 104 Hz) has been developed. The combined use of a ferromagnetic current transformer and of a superconducting flux transformer together with a rf‐biased SQUID allows measurements of currents as low as 10−14 A. A detailed circuital analysis and considerations on the input impedance of the device are presented. The agreement between predictions and experiments is quite good. The measured noise level beyond the low‐frequency region keeps at values typical of commercial SQUID’s.

Some levitation tests using superconducting coils on superconducting sheets are reported. These tests are used to provide preliminary data for the design of a levitation system for a gravitational antenna. Levitation tests on a small 60 kg bar are also reported. An empirical relation which enables displacement to be predicted as a function of the geometrical size, the weight, and the number of Ampere-turns of the coils is obtained from these tests.

Magnetic methods for localizing evoked neural activity in the human brain have been used to search for evidence of a functional organization in primary somatosensory cortex. We have found that in response to median nerve stimulation the deduced source for the evoked component with a latency of 45 ms lies at a depth in the central sulcus that depends on stimulus repetition rate, whereas the sources of the 20 ms and 24 ms components lie at a fixed depth. Moreover we have identified this 45 ms component with the dominant sinusoidal feature characteristic of steady state response.

To detect gravitational waves it is necessary to separate the signals due to these waves from thermal noise in the antenna. A possible way of achieving this would be to operate at liquid helium temperatures. The behaviour of aluminium bar antenna was studied at liquid helium temperatures with particular reference to Q values.

New measurements obtained at the University of Rome by means of a cryogenic gravitational-wave antenna of massM=24.4 kg operated atT=4.5 and 1.5 K are reported. The operation was interrupted after 90 hours of data taking, mainly during successive nights, although the antenna could continue to function very satisfactorily for a much longer time. The rate of disturbances is so small that it can be easily eliminated by coincidences with other antennas. The overall effective temperature obtained with an appropriate data analysis algorithm atT=1.5 K isT eff∼=0.79 K. This value is mostly due to the noise temperature of the FET preamplifier which constitutes the main limiting factor to the sensitivity of present gravitational-wave resonant antennas.

A small‐area Josephson tunnel junction is pumped by the radiation emitted by a long Josephson junction dc biased on a zero‐field singularity. Josephson constant voltage steps are observed in the current‐voltage characteristic of the small junction at voltages of ±150 μV corresponding to the fundamental frequency of emission of the oscillator. The radiation also gives rise to quasiparticle steps around the gap‐sum voltage of the small junction. From the measured current amplitude of the steps we estimate that the maximum power coupled to the small junction is about 90 nW.

A novel approach to neuromagnetic data analysis is presented. This technique is aimed at studying synchronised spontaneous activity (SSA) and has been used to resolve two different signals from one single evoked response, providing evidence for two possibly distinct sources. The data presented are consistent with a model that permits the generators of spontaneous activity to be synchronized by sensory stimuli.

Neuromagnetic measurements in the visual and somatosensory modalities reveal that, following repetitive stimulation, the brain persists in emitting synchronized after-discharges in the form of oscillations with highly specific spectral composition. In the visual modality, this rhythmic activity is centered at the frequency of the resting alpha rhythm and it is most readily induced by stimulation of the same frequency. This suggests that the phenomenon is due to synchronization of the generators responsible for the natural rhythms by the steady-state stimulation and that these generators behave as resonant oscillators. The phenomenon could then be referred to as Synchronized Spontaneous Activity (SSA). The discovery of this phenomenon has important implications for modelling the dynamics of normal evoked and spontaneous cerebral activity as well as for the understanding of pathological conditions such as photically induced epilepsies.

Sensory stimulation at certain frequencies was shown to elicit EEG and MEG (MagnetoEncephaloGraphic) responses persisting longer than one second after the stimulation. Such responses have been described as a consequence of a process of synchronization of bioelectrical spontaneous activities in the brain with a specific frequency content, but otherwise uncorrelated (Narici et a1 1987a).

Recent neuromagnetic studies indicate that suitable kinds of sensory stimulation can elicit enhanced responses correlated with underlying spontaneous activity, and that the study of these responses can shed light on the present preliminary results of a totally noninvasive neuromagnetic study on the spatial structure of these enhanced responses (in the somatosensory and visual modalities). Using the spatially discriminating capability of the neuromagnetic method, they provide evidence of the generation of these responses from the same sources responsible for the natural rhythms. >