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INTERNATIONAL GRAVITATIONAL EVENT COLLABORATION: OBSERVATION SUMMARY

INTERNATIONAL GRAVITATIONAL EVENT COLLABORATION: OBSERVATION SUMMARY. Giovanni Andrea Prodi University of Trento and INFN Italy 2 nd GWPW, Penn State, Nov.6 th , 2003. IGEC observations in 1997-2000: exchanged data multiple detector analysis background of accidental coincidences

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INTERNATIONAL GRAVITATIONAL EVENT COLLABORATION: OBSERVATION SUMMARY

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  1. INTERNATIONAL GRAVITATIONAL EVENT COLLABORATION:OBSERVATION SUMMARY Giovanni Andrea Prodi University of Trento and INFN Italy 2nd GWPW, Penn State, Nov.6th, 2003 • IGEC observations in 1997-2000: • exchanged data • multiple detector analysis • background of accidental coincidences • upper limits and their interpretation

  2. International Gravitational Event Collaboration http://igec.lnl.infn.it ALLEGRO group: ALLEGRO (LSU)http://gravity.phys.lsu.edu Louisiana State University, Baton Rouge - Louisiana AURIGA group: AURIGA (INFN-LNL) http://www.auriga.lnl.infn.it INFN of Padova, Trento, Ferrara, Firenze, LNL Universities of Padova, Trento, Ferrara, Firenze IFN- CNR, Trento – Italia NIOBE group: NIOBE (UWA) http://www.gravity.pd.uwa.edu.au University of Western Australia, Perth, Australia ROG group: EXPLORER (CERN) http://www.roma1.infn.it/rog/rogmain.html NAUTILUS (INFN-LNF) INFN of Roma and LNF Universities of Roma, L’Aquila CNR IFSI and IESS, Roma - Italia

  3. PRD 68 (2003) 022001 astro-ph/0302482

  4. DETECTORS almost parallel detectors

  5. Resonant Bars vibration insulation f low T pre-amplifier q Bar electromechanical transducer tuned to the lowest longitudinal mode L The planar gravitational wave impinging on the bar with an angle  excites its longitudinal mechanical mode, with amplitude proportional to sin2() The detector is sensitive in a narrow frequency range near the resonance (~900Hz) Typical 1997-2000 bandwidths ~ 1 Hz

  6. DIRECTIONAL SENSITIVITY The achieved sensitivity of bar detectors limits the observation range to sources in the Milky Way. The almost parallelorientation of the detectors guarantees a good coverage of the Galactic Center •  ALLEGRO • AURIGA -EXPLORER –NAUTILUS •  NIOBE amplitude directional sensitivity factor vs sideral time (hours)

  7. OBSERVATION TIME 1997-2000 (days) threshold on burst gw TARGET GW SIGNALS Detectable signals: transients withflat Fourier amplitude at the detector frequencies (900 Hz) Fourier amplitude of burst gw each detector applies an exchange threshold on measured H arrival time

  8. threshold on burst gw EXCHANGED PERIODS of OBSERVATION 1997-2000 ALLEGRO AURIGA EXPLORER NAUTILUS NIOBE fraction of time in monthly bins

  9. efficiency of detection fluctuations of false alarms maximize the chances of detectioni.e. the ratio MULTIPLE DETECTOR ANALYSIS network is needed to estimate (and reduce) the false alarms time coincidence search among exchanged triggers time window is set according to timing uncertainties by requiring a conservative false dismissal by Tchebyscheff inequality false alarms k • measure the false alarms: • time shifts  resampling the stochastic processes so that: • gw sources are off (as well as any correlated noise) • statistical properties are preserved (max shift ~ 1 h) • independent samples (min shift > largest time window ~ few s)

  10. AMPLITUDE DISTRIBUTIONS of EXCHANGED EVENTS normalized to each detector threshold for trigger search ·typical trigger search thresholds: SNR 3ALLEGRO, NIOBE SNR 5 AURIGA, EXPLORER, NAUTILUS The amplitude range is much wider than expected: non modeled outliers dominate at high SNR

  11. DIRECTIONAL SEARCH: sensitivity modulation amplitude directional sensitivity amplitude (Hz-1·10-21) time (hours) amplitude (Hz-1·10-21) time (hours)

  12. Resampling statistics by time shifts amplitude (Hz-1·10-21) time (hours) We can approximately resample the stochastic process by time shift. in the shifted data the gw sources are off, along with any correlated noise Ergodicity holds at least up to timescales of the order of one hour. The samples are independent as long as the shift is longer than the maximum time window for coincidence search (few seconds)

  13. POISSON STATISTICS of ACCIDENTAL COINCIDENCES Poisson fits of accidental concidences: 2 test sample of EX-NA background one-tailprobability = 0.71 agreement with uniform distribution  coincidence times are random histogram of one-tail2 probabilities for ALL two-fold observations

  14. mean • timing [ms] mean rate of events [ yr -1] FALSE ALARM RATES dramatic improvement by increasing the detector number: 3-fold or more would allow to identify the gw candidate

  15. Setting confidence intervals IGEC approach is frequentistic in that it computes the confidence level or coverage as theprobability that the confidence interval contains the true value unified in that it prescribes how to set a confidence interval automatically leading to a gw detection claim or an upper limit based on maximum likelyhood confidence intervals (different from Feldman & Cousins) false dismissal is under control (but detection efficiency is only lower-bounded) estimation of the probability of false detection (many attempts made to enhance the chances of detection)

  16. UPPER LIMIT on the RATE of BURST GWfrom the GALACTIC CENTER DIRECTION Poisson rate of detected gw [year –1] dashed region excluded with probability  90% overcoverage search threshold • signal template = -like gw from the Galactic Center direction signal amplitudeHS= FT[hS ]at  2 900 Hz

  17. UPPER LIMIT on the RATE of BURST GWfrom the GALACTIC CENTER DIRECTION (2) Poisson rate of detected gw [year –1] search threshold • analysis includes all themeasured signal amplitudes  search threshold •  result is cumulativefor HM Ht • systematic searchvsthresholdHtmany trials(20 /decade) • almost independent results

  18. TESTING the NULL HYPOTHESIS • testing the null hypothesis • overall false alarm probability • 33% for 0.95 coverage • 56% for 0.90 coverage • at least one detection in the set • in case • NO GW are in the data many trials ! all upper limits but one: NULL HYPOTHESIS WELL IN AGREEMENT WITH THE OBSERVATIONS

  19. UPPER LIMIT on the RATE of BURST GWfrom the GALACTIC CENTER DIRECTION (3) dashed region excluded with probability  90% overcoverage Poisson rate of detected gw [year –1] 1.8 yr -1 search threshold • no coincidences found, limited by the observation time • limited by accidental coincidences • observation time cuts off: sensitivity cut

  20. Take a model for the distribution of events impinging on the detector HS Ht (dashed line) • Estimate the distribution of measured coincidencesHM Ht (cont.line) • Compare with IGEC results to set confidence intervals on gw flux parameters rate (year –1) rate (year –1) search threshold (Hz -1 ) search threshold (Hz -1 ) HOW to UNFOLD IGEC RESULTSin terms of GW FLUX at the EARTH coverage Ht

  21. e.g. at HSHt efficiency  0.25 due to 2-fold observations at threshold at HS 2 Ht efficiency = 1enough above the threshold Case of gw flux of constant amplitude: comparison with LIGO results • IGEC sets an almost independent result per each tried thresholdHt • correct each result for the detection efficiency as a function of gw amplitude HS: Poisson rate of detected gw [year –1] search threshold

  22. Poisson rate of detected gw [year –1] search threshold Case of gw flux of constant amplitude: comparison with LIGO results (2) • the resulting interpreted upper limit • convert from HS= FT[hS ]at  2 900 Hzto template amplitude parameter • e.g. for a sine-gaussian(850 Hz;Q=9) hrss= 10 Hz 0.5 HS

  23. Data selection at work Duty time is shortened at each detector in order to have efficiency at least 50% A major false alarm reduction is achieved by excluding low amplitude events. amplitude (Hz-1·10-21) time (hours)

  24. FALSE ALARM REDUCTIONby amplitude selection of events consequence: selected events have consistent amplitudes

  25. Auto- and cross-correlation of time series (clustering)  Auto-correlation of time of arrival on timescales ~100s  No cross-correlation

  26. UPGRADE of the AURIGA resonant bar detector Previous set-up during 1997-1999 observations current set-up for the upcoming II run • beginning cool down phase • at operating temperature by November

  27. AURIGA II run LHe4 vessel Al2081 holder Electronics wiring support Main Attenuator Thermal Shield Sensitive bar Compression Spring Transducer

  28. AURIGA II run:upgrades new mechanical suspensions: attenuation > 360 dB at 1 kHz FEM modelled new capacitive transducer: two-modes (1 mechanical+1 electrical) optimized mass new amplifier: double stage SQUID 200  energy resolution new data analysis: C++ object oriented code frame data format

  29. initial goal of AURIGA II: improving amplitude sensitivity by factor 10 over IGEC results

  30. FUTURE PROSPECTS we are aiming at

  31. DUAL detectors estimated sensitivity at SQL: • Science with HF GW • BH and NS mergers and ringdown • NS vibrations and instabilities • EoS of superdense matter • Exp. Physics of BH Mo Dual16.4 tonheight 2.3 m Ø 0.94m SiC Dual 62.2 tonheight 3 m Ø 2.9m T~0.1 K , Standard Quantum Limit • Only very few noise resonances in bandwidth. • Sensitive to high frequency GW in a wide bandwidth. • PRD 68 (2003) 1020XX in press • PRL 87 (2001) 031101

  32. • High cross section materials • (up to 100 times larger than Al5056 used in bars) New concepts - new technologies: • No resonant transducers: measure differential motion of massive cylindrical resonators • Mode selective readout: Forget if you want bandwidth measured quantity: X = x1+x2-x3-x4

  33. Dual detector: the concept below both resonances: the masses are driven in-phase → phase difference is null 2 nested masses: • Intermediate frequency range: • the outer resonator is driven above resonance, • the inner resonator is driven below resonance • → phase difference of p In the differential measurement: → the signals sum up → the readout back action noise subtracts above both resonances: the masses are driven out-of-phase → phase difference is null

  34. Differential measurement strategy • Average the deformation of the resonant masses over a wide area: reduce thermal noise contribution from high frequency resonant modes which do not carry the gravitational signal • Readout with quadrupolar symmetry: ‘geometrically selective readout’ that rejects the non-quadrupolar modes bandwidth free from acoustic modes not sensitive to gw. Example: - capacitive readout - The current is proportional to:

  35. Dual Detector with √Shh~10-23/√Hz in 1-5 kHz range • Molybdenum • Q/T>2x108 K-1 - Mass = 16 tons • R = 0.47 m - height = 2.3 m • Silicon Carbide (SiC) • Q/T > 2x108 K-1 - Mass = 62 tons • R = 1.44 m - height = 3 m Feasibility issues • Detector: • Massive resonators( > 10 tons ) • Cooling • Suspensions • Low loss and high cross-section materials • Readout: • Selective measurement strategy • Quantum limited • Wide area sensor • Displacement sensitivity

  36. R&D on readouts: status • Requirement: ~ 5x10-23m/√Hz • Present AURIGA technology: 10-19 m/√Hz • with: • optomechanical readout - based on Fabry-Perot cavities • capacitive readout - based on SQUID amplifiers Foreseen limits of the readout sensitivity: ~ 5x10-22m/√Hz. Critical issues: optomechanical – push cavity finesse to current technological limit together with Watts input laser power capacitive – push bias electric field to the current technological limit Develop non-resonant devices to amplify the differential deformation of the massive bodies.

  37. Idea to relax requirements on readout sensitivity: mechanical amplifiers • based on the elastic deformation of monolithic devices • well known for their applications in mechanical engineering. GOAL: Amplify the differential deformations of the massive bodies over a wide frequency range. Requirements: * Gain of at least a factor 10. * Negligible thermal noise with respect to that of the detector.

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