INTERPRETATION of IGEC RESULTS Lucio Baggio, Giovanni Andrea Prodi - - PowerPoint PPT Presentation

INTERPRETATION of IGEC RESULTS

Lucio Baggio, Giovanni Andrea Prodi University of Trento and INFN Italy

• r unfolding gw source parameters

starting point:

• IGEC 1997-2000 results (P.Astone et al., PRD 68 (2003) 022001)

with reference to:

• LIGO S1 burst gw results (B.Abbott et al., gr-qc/0312056)

COMPARISON at a GLANCE

IGEC 1997-2000

• systematic search over many

amplitude thresholds: many data selections many data points

• bound of maximum false

dismissal probability of detection: conservative efficiency is estimated for δ-like waveform results are upper limits on rate of detected burst gws above threshold: rate vs search threshold cumulative Lacking the “unfolding” to gw source parameters (“uninterpreted” results) LIGO S1

• playground data to tune the

search:

• ne data selection
• ne data point
• montecarlo for some specific

source models: efficiency is measured vs gw amplitude for sample waveforms results are upper limits on rate of incoming burst gws: rate vs true amplitudes Source model: sample waveforms incoming at fixed amplitude + directional corrections…

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%

• vercoverage

21

2 10 0 02 ~ / .

S

Hz M converted in burst gw atGalacticCe H nter

−

⋅ ↔

฀

signal amplitude HS= FT[hS ] at 2 900 Hz

UPPER LIMIT on the RATE of BURST GW from the GALACTIC CENTER DIRECTION (2)

• no coincidences found, limited by the observation time

Poisson rate of detected gw [year –1] search threshold

dashed region excluded with probability 90%

• vercoverage
• limited by accidental coincidences
• observation time cuts off: sensitivity cut

1.8 yr -1

UPPER LIMIT on the RATE of BURST GW from the GALACTIC CENTER DIRECTION (3)

• analysis includes all the measured signal amplitudes search threshold

result is cumulative for HM Ht

Poisson rate of detected gw [year –1] search threshold

• systematic search vs threshold Ht many trials (20 /decade)

almost independent results

Poisson rate of incoming gw [year –1] true δ amplitude HS

Case of gw flux of constant amplitude: δ-like signal from GC

Poisson rate of detected δ gw [year –1] search threshold correct each result for the detection efficiency as a function of gw amplitude HS convert in terms of parameters of the source model at HS ≥ 2 Ht efficiency = 1 enough above the threshold at HS ≥ Ht efficiency ≥ 0.25 due to 2-fold observations at threshold

Poisson rate of incoming gw [year –1] true δ amplitude HS

Case of gw flux of constant amplitude: δ-like signal from GC (2)

• complete conservative efficiency estimation for the single data point
• … on all data points
• convert from HS= FT[hS ] at 2 900 Hz to template amplitude parameter

e.g. for a sine-gaussian(850 Hz;Q=9) hrss= 10 Hz 0.5 HS

Remarks

• IGEC time coincidence search provides

a systematic search as a function of common threshold a directional search strategy ⇒ is able to deal with

• detectors with different sensitivities (level & bandwidths)

search with templates search resctricted on the common sensitivity bandwidth

• detectors with different antenna patterns and locations

if gw polarization is modeled or simply linear

• IGEC method is able to assess the false detection probability

Of course, relevant improvements are possible:

• provide measurements of detection efficiency

Monte Carlo injection of selected templates

• feed a further stage of coherent analysis
• effective control of false detections of surveys

1 10 100 1,000 1E-21 1E-20 1E-19 0.60 0.80 0.90 0.95

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

1 10 100 1,000 1E-21 1E-20 1E-19 0.60 0.80 0.90 0.95

search threshold (Hz -1 ) rate (year –1)

• Estimate the distribution of measured coincidences HM Ht (cont.line)

Ht

• Take a model for the distribution of events impinging on the

detector HS Ht (dashed line)

coverage

Poisson rate of detected gw [year –1] search threshold

Case of gw flux of constant amplitude: δ-like signal from GC (3)

• the resulting interpreted upper limit
• convert from

HS= FT[hS ] at 2 900 Hz

to template amplitude parameter e.g. for a sine-gaussian(850 Hz;Q=9) hrss= 10 Hz 0.5 HS

Poisson rate of detected gw [year –1] hrss

Case of gw flux of constant amplitude: comparison to LIGO

• the resulting interpreted upper limit
• convert from

HS= FT[hS ] at 2 900 Hz

to template amplitude parameter e.g. for a sine-gaussian(850 Hz;Q=9) hrss= 10 Hz 0.5 HS

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 Ht
• correct each result for the detection efficiency as a function of gw amplitude HS:

at HS ≥ 2 Ht efficiency = 1 enough above the threshold e.g. at HS ≥ Ht efficiency ≥ 0.25 due to 2-fold observations at threshold

1 2 3 4 5 6 7 8 9 10 6 12 18 24 30 36 42 48 54 60 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 6 12 18 24 30 36 42 48 54 60

amplitude directional sensitivity

2

sin

GC

ϑ

2

sin

GC

ϑ

−

1 2 3 4 5 6 7 8 9 10 6 12 18 24 30 36 42 48 54 60

time (hours) amplitude (Hz-1·10-21) time (hours)

DIRECTIONAL SEARCH: sensitivity modulation

amplitude (Hz-1·10-21)

1 2 3 4 5 6 7 8 9 10 6 12 18 24 30 36 42 48 54 60

1 2 3 4 5 6 7 8 9 10 6 12 18 24 30 36 42 48 54 60 1 2 3 4 5 6 7 8 9 10 6 12 18 24 30 36 42 48 54 60 1 2 3 4 5 6 7 8 9 10 6 12 18 24 30 36 42 48 54 60 1 2 3 4 5 6 7 8 9 10 6 12 18 24 30 36 42 48 54 60 1 2 3 4 5 6 7 8 9 10 6 12 18 24 30 36 42 48 54 60

time (hours)

Resampling statistics by time shifts

amplitude (Hz-1·10-21)

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)

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)

2 4 6 8 10 12 14 16 18 1.0 10.0 100.0

search threshold [10-21/Hz] Ngw many trials ! all upper limits but one: ⇒ testing the null hypothesis

• verall 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

FALSE ALARM RATES

2E-21 1E-20 1E-6 1E-5 1E-4 1E-3 0.01 0.1 1 10 AL-AU AL-AU-NA

false alarm rate [yr

• 1]

common search threshold [Hz

• 1]

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 timing [ms]

UPPER LIMIT on the RATE of BURST GW from the GALACTIC CENTER DIRECTION (3)

• analysis includes all the measured signal amplitudes search threshold

result is cumulative for HM Ht

Poisson rate of detected gw [year –1] search threshold

• systematic search vs threshold Ht many trials (20 /decade)

almost independent results

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

2 2 2

1

i j i j

t t k false dismissal k σ σ − ≤ + ↔ ≤ 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

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

0.2 0.4 0.6 0.8 1 4 8 12 16 20 24

Sin2(θ) Time (h)

← ALLEGRO ←AURIGA -EXPLORER –NAUTILUS ← NIOBE amplitude directional sensitivity factor vs sideral time (hours)

TARGET GW SIGNALS

Fourier amplitude of burst gw

= ⋅ − ( ) ( ) h t H t t δ

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 1997-2000

(days)

EXCHANGED PERIODS of OBSERVATION 1997-2000

fraction of time in monthly bins threshold on burst gw

21 1

6 10 Hz

− −

> ⋅

21 1

3 6 10 Hz

− −

⋅ ÷

21 1

3 10 Hz

− −

< ⋅

ALLEGRO AURIGA NAUTILUS EXPLORER NIOBE

AMPLITUDE DISTRIBUTIONS of EXCHANGED EVENTS

relative counts 10

• 5

10

• 4

10

• 3

10

• 2

10

• 1

1 relative counts 10

• 5

10

• 4

10

• 3

10

• 2

10

• 1

1 NIOBE NIOBE AMP/THR 1 10 NAUTILUS NAUTILUS AMP/THR 1 10 AURIGA AURIGA AMP/THR 1 10 ALLEGRO ALLEGRO AMP/THR 1 10 EXPLORER EXPLORER AMP/THR 1 10

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

POISSON STATISTICS of ACCIDENTAL COINCIDENCES Poisson fits of accidental concidences: χ2 test sample of EX-NA background

• ne-tail probability = 0.71

histogram of one-tail χ2

probabilities for ALL two-fold observations

agreement with uniform distribution

coincidence times are random

1 2 3 4 5 6 7 8 9 10 6 12 18 24 30 36 42 48 54 60

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-1·10-21)

time amplitude time amplitude time amplitude time amplitude

A ∆

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 1997-1999 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 kHz FEM modelled new capacitive transducer: two-modes (1 mechanical+1 electrical)

• ptimized mass

new amplifier: double stage SQUID 200 energy resolution new data analysis: C++ object oriented code frame 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) 031101 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 = x1+x2-x3-x4

Dual detector: the concept

Intermediate frequency range:

• the outer resonator is driven

above resonance,

• the inner resonator is driven

below resonance → phase difference of π 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 √Shh~10-23/√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 > 2x108 K-1 - Mass = 62 tons
• R = 1.44 m - height = 3 m

Molybdenum

• Q/T>2x108 K-1 - Mass = 16 tons
• R = 0.47 m - height = 2.3 m

R&D on readouts: status

• Requirement: ~ 5x10-23 m/√Hz
• Present AURIGA technology: 10-19 m/√Hz

with:

• ptomechanical 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: ~ 5x10-22 m/√Hz.

Critical issues:

• ptomechanical – 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

• ver 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.