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Virgo status
Marie-Anne Bizouard (LAL-Orsay)
on behalf of the Virgo Collaboration
Outline
• Ground based gravitational wave detectors
• Virgo detector commissioning – 2006
• Virgo data analysis –
searches and detector characterization
• Preparation of Virgo future
– Virgo+
– Advanced Virgo
( M. Barsuglia GW1)
(E. Cuoco
GW4
C. Palomba
GW4)
(N. Man
GW2)
• Short term planning
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The Virgo Collaboration as in 2006
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CNRS - LAPP - Annecy
INFN - Firenze/Urbino
CNRS - LMA/ESPCI – Lyon/Paris
INFN – Napoli
CNRS - OCA – Nice
+ EGO (European Gravitational Observatory)
CNRS - LAL - Orsay
INFN - Perugia
INFN - Pisa
INFN – Roma
2006: NIKHEF – Amsterdam (joining)
Tor Vergata – Roma (just joining)
175 physicists / engineers
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Growing ground based interferometers network
4 & 2 km
600 m
GEO
3 km
300 m
4 km
TAMA
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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
h
 light phase shift measurement
But:
• GW amplitude is small h~10-21
L=3km
• The laser has fluctuations in phase and amplitude
• External forces push the mirrors
 L=10-18 m
L 
2
L
Seismic noise
h  L / L
Shot noise:
quantum fluctuation in the
number of detected photons
Thermal noise:
vibration of bulk due to
non null temperature
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Virgo optical layout
L=3km
Input Mode Cleaner cavity
Length = 144 m
Laser Nd:YVO4
P=20 W
Recycling
L=3km
P=1kW
Output Mode Cleaner cavity
Length = 4 cm
A Michelson with 3 partly-transparent mirrors
to form optical cavities to increase the power
inside the arms
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Virgo seismic attenuator
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Interferometer controls
1: longitudinal control
ITF output port
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Keep the Fabry Perot cavities in resonance
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Keep the output on the “dark fringe”
ITF “locked”
Keep the arms’ length constant within 10-12 m
2: angular control
Recycling cavity power
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Avoid high order mode generation
(reduction of coupling dark fringe with
frequency noise, power noise,
input beam jitter, beam miscentering, ..)
Alignment ON
Reduction of the power fluctuation!
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T7
Interferometer controls
• Complicated scheme!
• Controls introduce noise in
the dark fringe at low
frequency (<100Hz)
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Foreseen sensitivity
Thermal noise
Seismic wall
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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
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(optimal orientation)
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Noise budget
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Shutdown at end of 2005 – Why?
• Increase the power
2005: 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
Backscattering
Solution: Faraday isolator on the
injection bench to attenuate the
backscattering light
a new injection bench
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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
350 mm
350 mm
120 mm
120 mm
R=4100 mm
R=4100 mm
• Solution:
– Monolithic mirror
– Flat mirror
Incident
Incident
Beam
Beam
Translations induce
misalignment and jitter noise
need of a telescope on the injection bench
a new injection bench …
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New injection bench
Faraday isolator
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New parabolic telescope
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Virgo commissioning – new input bench
Sep 2005 – April 2006
Lots of work:
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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!
M. Barsuglia GW1
7 W entering in the ITF
280 W on the BS (sep. 2005: 25W! )
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Virgo commissioning – full power recycled ITF
Feb 2006 – until now
We had few problems/difficulties:
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Beam matching
See M. Barsuglia in GW1
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Beam astigmatism
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Beam clipping on detection bench
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Oscillations in signals used for control  lock losses!
•Work
Thermal
effect in substrate (25W  280W on Beam Splitter mirror) ?
done on:
- demodulation phase tuning
- more angular degrees of freedom controlled
Lock stability improved a lot !
10 hours
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!
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The last data taking periods - 2005
C6 July 2005
Maximal distance (Mpc)
Maximal distance for SNR=8, optimally oriented 1.4/1.4 M NS-NS binary
14 days
C7 Sep. 2005
5 days
duty cycle: 86% in Science Mode
duty cycle: 65% in Science Mode
Shorter but better sensitivity
best NS-NS distance range: 1.5 Mpc !
Beyond Andromeda reached!
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Data analysis in Virgo at a glance
NS EOS,
Strong field gravity,
GRB models,
..) Binary population
… lots of astronomy!
• Virgo search groups
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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
More details in
E. Cuoco and C. Palomba’s talks
than with “physics” search or competitive upper limits
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Burst events search
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Events distribution dramatically different from Gaussian
Vetoes based on auxiliary channels
 understand the machine
Events
• Burst studies on a single detector: hard!
Frequency (Hz)
SNR
Vetoes definition:
Excess noise above 100 Hz due to GW channel coupling
• excess frequency noise
with the frequency noise when the North End mirror is tilted
without veto
• environmental glitches
(air conditioning, air plane, …)
 problem of mirror angular control
with veto
Time (s)
(too loose during C6 &C7)
Nice reduction of the burst fake events …
but huge dead time: >20%
Events
Dark fringe (whiten)
• Identification of the main source of excess noise for the burst search:
• Vetoes strategy:
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SNR
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Inspiral search
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C6/C7 analysis focus: NS-NS search
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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
Hardware GW injections
(the 2 checks the compatibility between the
signal waveform and the recorded strain)
Before 2
After 2
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Fake event rejection safety test?
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Hardware GW injections
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 !
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Continuous sources search
• All-sky search pipeline: hierarchical + coincidence
• C6 & C7 work goal:
C. Palomba GW4
– 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 analysis
Example: 10 Hz disturbance : pulses caused by a video camera
C6: number of candidates before coincidence
Number of candidates : excess for some frequencies!
Sensitivity obtained : h~10-23
(Virgo design:
h~10-25
[200-1000 Hz]
@ 200 Hz)
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Frequency (Hz)
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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/Virgo
Scope limited by the bars sensitivity curve
Virgo at design sensitivity : WGW < 2 x 10-2
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LHO, LLO, GEO, Virgo
– Isotropic background search
S. Ballmer gr-qc/0510096
– Directional search (sky map luminosity)
(background could be dominated by individual sources!)
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First detectors generation sensitivity: WGW ~ 4 x 10-6
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f> 300 Hz: Virgo-GEO performs good!
advanced detectors needed!
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International collaborations
• Auriga-RoG-Virgo
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Burst search + Stochastic background search
• LSC-Virgo:
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Burst + Inspiral : working effort for 2 years (simulated data)
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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 future preparation
• Virgo+
• Advanced Virgo (second generation ITF)
LIGO - Virgo
LIGO+ - Virgo+
AdvLIGO - AdvVirgo
A factor 10 in distance
to hit sources in a volume
1000 times larger
Credit: R.Powell
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Virgo upgrades planning
Now
• Short term
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Acoustic isolation
Pre-Mode Cleaner
Upgrade of the quadrant diode front-end electronics
New coil drivers (R&D)
• Intermediate term
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Eddy current dissipation mitigation
New MC mirror payload
New DSP electronics (R&D)
Thermal compensation
• Virgo+ upgrades
2007
2008
2009
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What is Virgo+ project?
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h(f) [1/sqrt(Hz)]
Last stage of the suspension thermal noise
(pendulum mode excited)
friction
metallic wires
clamping
wire dissipation
 Monolithic suspension!
(a) Virgo Nominal sensitivity
(b) Seismic noise
(c) Pendulum thermal noise
(d) Mirror thermal noise
(e) Shot Noise
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(b)
-21
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(d)
-22
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(a)
(e)
(c)
-23
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1
10
100
1000
10000
Frequency [Hz]
shot noise  higher power laser!
mirror thermal noise (bulk + coating)  higher Q new material
+ coating R&D
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Virgo+
• Virgo+ upgrades
– High power laser amplifier 20W 50W
N. Man
(GW2)
– 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
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Monolithic payload on going activities
2 machines for producing and welding fused silica fibers in Cascina:
H2-O2 (Perugia)
(different technology)
Fused silica fiber
CO2 (Glasgow)
Fused silicate fiber H2-O2 pulling machine on site
Dummy mirror to test the monolithic suspension
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Virgo+ scientific outreach
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h(f) [1/sqrt(Hz)]
Thermal noise decrease
50W/2 + new losses model
50W/2 + current mirrors
Nominal Virgo
50W/2 + new losses model+FS suspensions
Virgo+ with Newtonian Noise
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Shot noise decrease
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-23
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1
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100
1000
10000
Frequency [Hz]
Virgo+ (NN) Mpc
Opt. orientation
NS-NS signal detection
benefits(average)
of the sensitivity improvement at
NSNS
intermediate
frequency114 (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
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