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

International Gravitational Event Collaboration igec.lnl.infn.it ALLEGRO group:ALLEGRO (LSU) Louisiana State University, Baton Rouge - Louisiana AURIGA group:AURIGA (INFN-LNL) INFN of Padova, Trento, Ferrara, Firenze, LNL Universities of Padova, Trento, Ferrara, Firenze IFN- CNR, Trento – Italia NIOBE group:NIOBE (UWA) University of Western Australia, Perth, Australia ROG group:EXPLORER (CERN) NAUTILUS (INFN-LNF) INFN of Roma and LNF Universities of Roma, L’Aquila CNR IFSI and IESS, Roma - Italia

PRD 68 (2003) astro-ph/

DETECTORS almost parallel detectors

Resonant Bars The planar gravitational wave impinging on the bar with an angle  excites its longitudinal mechanical mode, with amplitude proportional to sin 2 (  ) Bar   pre-amplifier electromechanical transducer tuned to the lowest longitudinal mode low T vibration insulation L The detector is sensitive in a narrow frequency range near the resonance (~900Hz) Typical bandwidths ~ 1 Hz

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

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

EXCHANGED PERIODS of OBSERVATION fraction of time in monthly bins threshold on burst gw ALLEGRO AURIGA NAUTILUS EXPLORER NIOBE

MULTIPLE DETECTOR ANALYSIS efficiency of detection fluctuations of false alarms maximize the chances of detection i.e. the ratio 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 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) by Tchebyscheff inequality

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

amplitude directional sensitivity time (hours) amplitude (Hz -1 · ) time (hours) DIRECTIONAL SEARCH: sensitivity modulation amplitude (Hz -1 · )

time (hours) Resampling statistics by time shifts amplitude (Hz -1 · ) 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)

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

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

Setting confidence intervals IGEC approach is frequentistic in that it computes the confidence level or coverage as the probability 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)

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

UPPER LIMIT on the RATE of BURST GW from the GALACTIC CENTER DIRECTION (2) analysis includes all the measured signal amplitudes  search threshold  result is cumulative for H M  H t Poisson rate of detected gw [year –1 ] search threshold systematic search vs threshold H t  many trials (20 /decade) almost independent results

many trials ! all upper limits but one:  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 NULL HYPOTHESIS WELL IN AGREEMENT WITH THE OBSERVATIONS TESTING the NULL HYPOTHESIS

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

search threshold (Hz -1 ) rate (year –1 ) HOW to UNFOLD IGEC RESULTS in terms of GW FLUX at the EARTH Compare with IGEC results to set confidence intervals on gw flux parameters search threshold (Hz -1 ) rate (year –1 ) Estimate the distribution of measured coincidences H M  H t (cont.line) HtHt Take a model for the distribution of events impinging on the detector H S  H t (dashed line) coverage

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

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 H S = FT[h S ] at   2  900 Hz to template amplitude parameter e.g. for a sine-gaussian(850 Hz;Q=9) h rss = 10 Hz 0.5 H S

time (hours) 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 · )

FALSE ALARM REDUCTION by amplitude selection of events consequence: selected events have consistent amplitudes

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

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

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

new mechanical suspensions: attenuation > 360 dB at 1 kHzFEM 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 codeframe data format AURIGA II run: upgrades

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

FUTURE PROSPECTS we are aiming at

DUAL detectors estimated sensitivity at SQL: 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) Science with HF GW BH and NS mergers and ringdown NS vibrations and instabilities EoS of superdense matter Exp. Physics of BH Mo Dual 16.4 ton height 2.3 m Ø 0.94m SiC Dual 62.2 ton height 3 m Ø 2.9m T~0.1 K, Standard Quantum Limit

New concepts - new technologies: measure differential motion of massive cylindrical resonators No resonant transducers: Mode selective readout: High cross section materials (up to 100 times larger than Al5056 used in bars) measured quantity: X = x 1 +x 2 -x 3 -x 4

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

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

Dual Detector with √S hh ~ /√Hz in 1-5 kHz range Readout: Selective measurement strategy Quantum limited Wide area sensor Displacement sensitivity Detector: Massive resonators ( > 10 tons ) Cooling Suspensions Low loss and high cross-section materials Feasibility issues Silicon Carbide (SiC) Q/T > 2x10 8 K -1 - Mass = 62 tons R = 1.44 m - height = 3 m Molybdenum Q/T>2x10 8 K -1 - Mass = 16 tons R = 0.47 m - height = 2.3 m

R&D on readouts: status Requirement: ~ 5x m/√Hz Present AURIGA technology:  m/√Hz with: optomechanical readout - based on Fabry-Perot cavities capacitive readout - based on SQUID amplifiers Develop non-resonant devices to amplify the differential deformation of the massive bodies. Foreseen limits of the readout sensitivity: ~ 5x m/√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

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