Virgo status

Marie-Anne Bizouard (LAL-Orsay)

on behalf of the Virgo Collaboration

MG 11 - Berlin 2

• Ground based gravitational wave detectors

• Virgo detector commissioning – 2006 ( M. Barsuglia GW1)

• Virgo data analysis – searches and detector characterization (E. Cuoco GW4

C. Palomba GW4)

• Preparation of Virgo future– Virgo+ (N. Man GW2)

– Advanced Virgo

• Short term planning

Outline

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The Virgo Collaboration as in 2006

• CNRS - LAPP - Annecy

• INFN - Firenze/Urbino

• CNRS - LMA/ESPCI – Lyon/Paris

• INFN – Napoli

• CNRS - OCA – Nice

• CNRS - LAL - Orsay

• INFN - Perugia

• INFN - Pisa

• INFN – Roma

2006: NIKHEF – Amsterdam (joining)

Tor Vergata – Roma (just joining)+ EGO (European Gravitational Observatory)

175 physicists / engineers

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TAMA

300 m

Growing ground based interferometers network

4 & 2 km

4 km

3 km

600 m GEO

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Interferometers at a glance

How to detect the path of a GW? measure the displacement of the mirrors induced by the GW

light phase shift measurement Lh

L 2

LLh /

Seismic noise

Thermal noise:vibration of bulk due to non null temperature

Shot noise: quantum fluctuation in the number of detected photons

But: • GW amplitude is small h~10-21 L=3km L=10-18 m• The laser has fluctuations in phase and amplitude• External forces push the mirrors

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Virgo optical layout

Laser Nd:YVO4P=20 W

Input Mode Cleaner cavityLength = 144 m

Recycling

Output Mode Cleaner cavityLength = 4 cm

L=3km

L=3km

P=1kW

A Michelson with 3 partly-transparent mirrorsto form optical cavities to increase the powerinside the arms

Virgo seismic attenuator

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1: longitudinal control

2: angular control

Interferometer controls

• Keep the Fabry Perot cavities in resonance

• Keep the output on the “dark fringe”

Keep the arms’ length constant within 10-12 m

• Avoid high order mode generation(reduction of coupling dark fringe with

frequency noise, power noise,

input beam jitter, beam miscentering, ..)

Reduction of the power fluctuation!

ALIGNMENT

Recycling cavity power

Alignment ON

ITF output port

ITF “locked”

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Interferometer controls

• Complicated scheme!• Controls introduce noise in the dark fringe at low frequency (<100Hz)

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Foreseen sensitivity

Seismic wall

Thermal noise

Shot noise

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Virgo sensitivity curve progresses (as end of 2005)

C7 run (sep. 2005):Best strain h ~ 6 10-22 / Hz1/2

NS/NS maximum range ~ 1.5 Mpc(optimal orientation)

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Noise budget

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Shutdown at end of 2005 – Why?

• Increase the power2005: need to operate with reduced power: 0.7 W instead of 10W because of backscattering light in the Mode Cleaner cavity

Increase a lot the frequency noise

Solution: Faraday isolator on the

injection bench to attenuate the

backscattering light

a new injection bench

Backscattering

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120 mm

R=4100 mm

350 mm

Incident Beam

120 mm

R=4100 mm

350 mm

Incident Beam

Shutdown at end of 2005 – Why?

• Non-monolithic and curved Power Recycling mirror– Curved: because part of the output telescope to match the beam– Non-monolithic: lots of resonances control problems and alignment drifts

• Solution:– Monolithic mirror– Flat mirror

need of a telescope on the injection bench

a new injection bench …

Translations induce misalignment and jitter noise

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New injection bench

Faraday isolator

New parabolic telescope

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Virgo commissioning – new input benchSep 2005 – April 2006

Lots of work:– New scheme of the alignment wrt to the ITF

– Parabolic telescope alignment done

– Beam matching: 95% reached

– Faraday isolator tuned No more backscattering light problem!

7 W entering in the ITF280 W on the BS (sep. 2005: 25W! )

M. Barsuglia GW1

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Virgo commissioning – full power recycled ITFFeb 2006 – until now

We had few problems/difficulties:• Beam matching

• Beam astigmatism

• Beam clipping on detection bench

• Oscillations in signals used for control lock losses!

• Thermal effect in substrate (25W 280W on Beam Splitter mirror) ?

10 hours

Work done on: - demodulation phase tuning - more angular degrees of freedom controlled

Lock stability improved a lot !

Where are we now?

•f>200 Hz: better than one year ago

•f<200 Hz: a lot of work to be done! (dominated by control noise)

…but the noise hunting period just restarted!

See M. Barsuglia in GW1

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The last data taking periods - 2005

Maximal distance for SNR=8, optimally oriented 1.4/1.4 M NS-NS binary

14 days duty cycle: 86% in Science Mode

5 days duty cycle: 65% in Science Mode

C6 July 2005

C7 Sep. 2005

Shorter but better sensitivity

best NS-NS distance range: 1.5 Mpc !

Beyond Andromeda reached!

Sensitivity improvement

Max

imal

dis

tanc

e (M

pc)

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Data analysis in Virgo at a glance

• Virgo search groups– Burst (SN, neutron star and black hole birth, ..) – Binary inspiral (neutron star + black hole)

– Continuous waves (spinning neutron stars)

– Stochastic background (big bang +

background of “standard” GW)

But we don’t have yet the sensitivity to set competitive upper limits …

So C6 & C7 data taking analysis …. more dealing with– pipeline development / tuning

– detector characterization

than with “physics” search or competitive upper limits

More details in E. Cuoco and C. Palomba’s talks

NS EOS, Strong field gravity, GRB models,Binary population … lots of astronomy!

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SNR

Eve

nts

Burst events search

• Burst studies on a single detector: hard!– Events distribution dramatically different from Gaussian

– Vetoes based on auxiliary channels

understand the machine

• Identification of the main source of excess noise for the burst search:

• Vetoes strategy:

Vetoes definition:• excess frequency noise• environmental glitches (air conditioning, air plane, …)

Nice reduction of the burst fake events …but huge dead time: >20%

without veto

with veto

SNR

Eve

nts

Excess noise above 100 Hz due to GW channel coupling with the frequency noise when the North End mirror is tilted

problem of mirror angular control (too loose during C6 &C7)

Fre

quen

cy (

Hz)

Dar

k fr

inge

(w

hite

n)

Time (s)

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• Fake event rejection safety test?– Hardware event injection (force applied on

the mirrors)

( + signal recovery accuracy estimation)

vetoes are safe for the hardware injections, while strongly reducing the event distribution tails !

Before 2 After 2

Hardware GW injections

Hardware GW injections

Inspiral search

• C6/C7 analysis focus: NS-NS search– 2 pipelines developed in Virgo

– Veto studies – Virgo data understanding

• Fake events rejection:1. Veto against “identified” noisy data periods

2. Use of “2” methods to reject fake events

(the 2 checks the compatibility between the signal waveform and the recorded strain)

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Continuous sources search

• All-sky search pipeline: hierarchical + coincidence

• C6 & C7 work goal: – 1kHz band considered (50Hz 1050 Hz)– Production of bank of candidates for C6 and C7 and perform coincidence

– Detection of detector related noise that could bias the analysisExample: 10 Hz disturbance : pulses caused by a video camera

Number of candidates : excess for some frequencies!

Sensitivity obtained : h~10-23 [200-1000 Hz] (Virgo design: h~10-25 @ 200 Hz)

C6: number of candidates before coincidence

Frequency (Hz)

C. Palomba GW4

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f> 300 Hz: Virgo-GEO performs good!

Stochastic background GW search with Virgo

• This search requires cross-correlation between 2 detectors’ output (GW background sensitivity depends on distance and orientation)

• Auriga/Nautilus/Explorer/VirgoScope limited by the bars sensitivity curve

• LHO, LLO, GEO, Virgo– Isotropic background search

– Directional search (sky map luminosity)

(background could be dominated by individual sources!)

• First detectors generation sensitivity: GW ~ 4 x 10-6 advanced detectors needed!

Virgo at design sensitivity : GW < 2 x 10-2

S. Ballmer gr-qc/0510096

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International collaborations

VERY TENTATIVE

• Auriga-RoG-Virgo– Burst search + Stochastic background search

• LSC-Virgo: – Burst + Inspiral : working effort for 2 years (simulated data) + SB just joins

“Physics gain” to add a (non aligned) ITF to LIGO network:

- reconstruction of the source location (need of at least 3 ITF!)

- signal parameters estimation

- detection efficiency enhanced by 50% (burst) or 30% (inspiral)

– Now: discussions about• data exchange agreement (MOU to be signed)

• how to work as a joint data analysis group

• Sketching a tentative joint run planning

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Outline

• Ground based gravitational wave detectors

• Virgo detector commissioning – 2006

• Virgo data analysis – searches and detector characterization

• Preparation of Virgo future– Virgo+

– Advanced Virgo (second generation ITF)

• Short term planning

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• Virgo+

• Advanced Virgo (second generation ITF)

Virgo future preparation

A factor 10 in distance to hit sources in a volume

1000 times larger

LIGO - Virgo

LIGO+ - Virgo+

AdvLIGO - AdvVirgo

Credit: R.Powell

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2008

Now

2007

2009

• Short– Acoustic isolation

– Pre-Mode Cleaner

– Upgrade of the quadrant diode front-end electronics

– New coil drivers (R&D)

• Intermediate– Eddy current dissipation mitigation

– New MC mirror payload

– New DSP electronics (R&D)

– Thermal compensation

• Virgo+ upgrades

Virgo upgrades planning

• Short term– Acoustic isolation

– Pre-Mode Cleaner

– Upgrade of the quadrant diode front-end electronics

– New coil drivers (R&D)

• Intermediate term– Eddy current dissipation mitigation

– New MC mirror payload

– New DSP electronics (R&D)

– Thermal compensation

• Virgo+ upgrades

“Standard” upgrades dedicated to reach the Virgo design sensitivity

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1 10 100 1000 1000010-23

10-22

10-21

10-20

10-19

10-18

(a) Virgo Nominal sensitivity (b) Seismic noise (c) Pendulum thermal noise (d) Mirror thermal noise (e) Shot Noise

h(f) [1/

sqrt(H

z)]

Frequency [Hz]

(a)

(b)

(c)

(d)

(e)

What is Virgo+ project?

shot noise higher power laser!

Last stage of the suspension thermal noise(pendulum mode excited) friction metallic wires clamping wire dissipation

mirror thermal noise (bulk + coating) higher Q new material + coating R&D

Monolithic suspension!

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Virgo+

• Virgo+ upgrades– High power laser amplifier 20W 50W

– Replace all Virgo mirrors with Suprasil 311 fused silica (low losses)

– Improved coatings R&D

– Fused silica monolithic payload

– New DAQ electronics (R&D)

• Compatible with current Virgo optical configuration

• Require a relative short shutdown

N. Man (GW2)

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2 machines for producing and welding fused silica fibers in Cascina:

H2-O2 (Perugia)

CO2 (Glasgow)

Monolithic payload on going activities

Fused silicate fiber H2-O2 pulling machine on site

Dummy mirror to test the monolithic suspension

Fused silica fiber(different technology)

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Virgo+ scientific outreach

1 10 100 1000 1000010-23

10-22

10-21

10-20

10-19

10-18

h(

f) [1

/sqr

t(H

z)]

Frequency [Hz]

50W/2 + new losses model 50W/2 + current mirrors Nominal Virgo 50W/2 + new losses model+FS suspensions Virgo+ with Newtonian Noise

NS-NS signal detection benefitsof the sensitivity improvement at intermediate frequency

Shot noise decrease

Thermal noise decrease

Virgo+ (NN) Mpc

Opt. orientation (average)

NSNS 114 (45.6)

BHBH 584 (234)

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Short term planning - Conclusions

• Commissioning: – Noise hunting phase

– Reduction of control noise sources

In the next weeks: reach LIGO sensitivity at high frequency

Start collecting “Science” data this fall

Soft transition towards long data taking periods for GW searches

• Huge campaign of upgrades : Virgo+ foreseen in 2008

inspiral event rate: gain more than a factor 10!

• Advanced Virgo: design choice by end of 2007