The Virgo interferometer for Gravitational Wave detection and its upgrade Francesco Fidecaro The First Galileo-Xu Guangqi Meeting Shanghai, October 26, 2009

2 Outline The Virgo Collaboration The European Gravitational Observatory The Virgo interferometer The LSC Virgo agreement Performance Upgrades

3 The Virgo Collaboration Early efforts –Brillet (optics) –Giazotto (suspensions) Collaboration started in 1992 LAPP Annecy EGO Cascina Firenze-Urbino Genova Napoli OCA Nice NIKHEF Amsterdam LAL Orsay LMA Lyon – ESPCI Paris APC Paris Perugia Pisa Roma La Sapienza Roma Tor Vergata Trento-Padova Warsaw RMKI Budapest (observers) LKB Paris (observers) 18 groups About 200 authors

4 GW interferometers Isolated/suspended mirrors: –  z at 10 Hz ~ m –  z at 100 Hz ~ m Differential measurement to cancel phase noise Effective L ~ 10 2 km = 1  m Effective power ~ 1 kW ~  Measurement noise ~ rad for a 1 s measurement Record a signal, if high SNR there is a large information content L Light source

5 The Virgo interferometer

6 Issues in sensitivity (Virgo example) h ~ 3 x Hz 10 Hz h ~ 7 x Hz 100 Hz 200  m fused silica suspension fibre pioneered by Glasgow/GEO600 Mirror coating Mirror thermal lensing compensation for high power Seismic attenuation

7 Virgo site in Cascina

8 The European Gravitational Observatory PURPOSE The Consortium shall have as its purpose the promotion of research in the field of gravitation in Europe. In this connection and in particular, the Consortium pursues the following objectives: –ensures the end of the construction of the antenna VIRGO, its operation, maintenance and the upgrade of the antenna as well as its exploitation; –ensures the maintenance of the related infrastructures, including a computer centre and promotes an open co-operation in R&D; –ensures the maintenance of the site; –carries out any other research in the field of gravitation of common interest of the Members; –promotes the co-operation in the field of the experimental and theoretical gravitational waves research in Europe; –promotes contacts among scientists and engineers, the dissemination of information and the provision of advanced training for young researchers.

9 EGO 5 year renewal approved this year Current members: CNRS, INFN participating equally to budget (ca 10 M€ / year) Management: –EGO Council and its President –EGO Director –Board of auditors –Currently 48 staff, EGO Scientific Director, Adminstrative Head Scientific and Technical Advisory Committee –Experts of the field or of related questions VESF:Virgo-EGO Scientific Forum –Implementation of one of the EGO purposes –Gathers people interested in gravitational waves and their detection

10 World wide GW network: LV agreement “Among the scientific benefits we hope to achieve from the collaborative search are: –better confidence in detection of signals, better duty cycle and sky coverage for searches, and better source position localization and waveform reconstruction. In addition, we believe that the intensified sharing of ideas will also offer additional benefits.” Collaborations keep their identities and independent governance

11 LV Agreement (I) “All data analysis activities will be open to all members of the LSC and Virgo Collaborations, in a spirit of cooperation, open access, full disclosure and full transparency with the goal of best exploiting the full scientific potential of the data.” Joint committees set up to coordinate data analysis, review results, run planning, and computing. The makeup of these committees decided by mutual agreement between the projects. Joint publication of observational data whether data from Virgo, or LIGO (GEO) or both

12 LV Agreement (II) “Author lists are to be separately established according to the rules ofeach collaboration, and maintained by them. When papers are published, the author lists will be combined in a manner established by mutual agreement between the collaborations.” Joint collaboration meetings 4 times/year alternating between Europe and US Bi-weekly meeting of LIGO and Virgo leadership Organization of joint data analysis described in detail in 7 page attachment to MOU

13 The low frequency strategy

14 Noise in mass position

15 Seismic isolation Super-attenuators: multi- stage passive seismic isolation system (many exchanges of visits with UWA group) Inverted pendulum: large amplitude low frequency motion for tidal control Mechanical filters in 6 dof Hierarchical actuation: F0, marionetta, mirror MODEL marionetta mirror

16 marionetta mirror Superattenuator performance Excitation at top Use Virgo sensitivity and stability Integrate for several hours Upper limit for TF at 32 Hz:1, In some configurations a signal was found, but also along a direction perpendicular to excitation: compatible with magnetic cross talk

17 The optics strategy

18 Coating facility – LMA Lyon ESPCI Paris Dedicated investment by Virgo Large area coating Metrology Corrective coating procedure

19 Virgo mirror performance Coating Nature and Clear aperture (mm) RMS Wavefront (nm) Average Absorption (ppm) Average Scattering (ppm) Transmission Side ASide BSide ASide B North End Mirror - HR  330 mm 3.9  150 mm 3.8  150 mm 0.67  150 mm 4  150 mm 42.9 ppm West End Mirror- HR  330 mm 2.8  150 mm 3.4  150 mm 0.69  150 mm 6.5  150 mm 38.3 ppm North Input Mirror HR  200 mm AR  200 mm 2.6  60 mm 3.8  60 mm 1.25  60 mm 5  60 mm % West Input Mirror AR  200 mm HR  200 mm 2.6  60 mm 2.5  60 mm 1.20  60 mm 8  60 mm % Recycling Mirror 2006 HR  200 mm AR  200 mm 1.4  60 mm 1.08  60 mm 0.54  100 mm 8  60 mm 5.13 % Beam Splitter n°1 AR  210 mm HR  210 mm 3.9  100 mm 5.4  120 mm 1.35 center 5.5  100 mm 49.8 %

20 Upgrades from VSR1 (2007) to VSR2 ( )

Virgo+ upgrade: injection system New laser amplifier (LZH): up to 50 W (25 W at interferometer input)‏ New pre-mode-cleaner Remotely tunable in-vacuum Faraday Isolator Heavier input-mode-cleaner end-mirror

Phase camera Beam scanned on pinhole detector, signal demodulated to separate carrier and sidebands Located on dark fringe before output-mode-cleaner (B1p)‏ Extensively used, but more as 'amplitude camera' –TCS fine alignment, 'cold interferometer' experiments –Mirror cool-down experiments to measure coating absorption field amplitude phase between fields

High power operation Power increased in steps from 8 W (VSR1) to 17 W now –limited by mismatching of reference cavity due to thermal effects No major problems with interferometer stability Some alignments loops more critical Quadrature signals (B1_ACq or B5_ACq) kept close to zero using slow servos on TCS power Currently about 1.5 W on both mirrors: interferometer similar to 8W 'Cold interferometer' with about 2x 6W –More optical gain, ideal frequency stabilization TF, but TCS too noisy without TCSwith TCS

Virgo+ upgrade: electronics Replaced real-time fiber links: more flexible signal routing Replaced old RIOs by real-time PC: much more computing power New ADCs: from 16 to 18 bit New quadrants read-out electronics for alignment

Virgo+ upgrade: infrastructure Replaced complete wiring of main power and grounding in central building Replaced and doubled UPS Replaced 15 kV transformer New hot water pipes Lowered speed of air-conditioning

26 Noise understanding Noise sources and coupling are well understood Low frequency shows more structures Noise reduction in advanced detectors achieved with proper design Virgo+ in 2010: fused silica suspensions and higher Finesse –risk reduction for Advanced detectors

27 Virgo sensitivity progress VSR1: May 18-Sep month continuous data taking simultaneously with LIGO Analysis in progress

28 Virgo & LIGO:

29 Very latest sensitivity Calibration lines moved Environmental noise

Stability Robust interferometer –95% Science Mode duty cycle (if no commissioning is made) –Good sensitivity Stable horizon: Mpc ( Ns-Ns) - averaged (now Mpc) Mpc (10-10 BH-BH) - averaged –fluctuating with input mirror etalon effect Low glitch rate: factor 10 lower than VSR1 Taking data since July 7 th with 80% duty cycle in science mode and locks alasting days Preparing for installation of monolithic suspensions

31 Data Analysis

32 Joint LIGO/Virgo Search for GRBs Gamma Ray Bursts (GRBs) - brightest EM emitters in the sky –Long duration (> 2 s) bursts, high Z  progenitors are likely core-collapse supernovae –Short duration (< 2 s) bursts, distribution about Z ~ 0.5  progenitors are likely NS/NS, BH/NS, binary merger –Both progenitors are good candidates for correlated GW emissions! 212 GRBs detected during S5/VSR1 –137 in double coincidence (any two of LIGO Hanford, LIGO Livingston, Virgo) No detections, we place lower limits on distance assuming E GW = 0.01 M  c 2

33 VSR2 sensitivity for CW searches Targeted searches. Vela

34 Compatible with some ‘exotic’ EOS Marginally compatible with standard EOS (Vela spin-down limit in ~80 days) may improve on Crab VSR2 sensitivity Spin-down limit can be beaten for a few pulsars

35 Monolithic fused silica suspension

36 SENSITIVITY GOAL 36 State-of-the-art coating used in the model (room for further improvement) Conservative assumptions on suspension thermal noise At low frequency Virgo+ is anticipating AdV

37 Silica anchors Silica Clamps on the marionette Coupling to the mirror flats with New Ears Silicate bonding Steel box to host the upper silica clamp on the marionetta Monolithic Suspensions Clamp design

38 Fiber production validated Implemented the fiber welding with the laser on the lower and upper silica clamps; original pulling machine by our Glasgow colleagues CO 2 Upper cone 1.5 mm rod Lower “anchor” CO 2 Silica wires production

39 Payload Suspension

40  Transportation test):  On the dummy payload  Mechanical vibration monitored with accelerometers  The test was successful: no broken fibers until the January 2009 Crash Test : see movie on YouTube  (search monolithic crash), fiber robustness tested m/s 2 Resistance to shocks, pollution, humidity

41 Dummy Mirror suspended in Perugia labs; The aim is to measure the wire mechanical losses with the new clamping system; Silica wires installation on the marionette Dummy payload and C tool Steel box for the silica upper clamps Feb. ‘09 - Dummy suspension for losses measurements

42 Dummy payload installation in the vacuum chamber Legs Shadow meter Silica wires installation on the mirror Silica anchors glued on the ears ES actuators for pendulum and violin modes Mechanical losses measurements with dummy mirror Dummy mirror suspended with silica wires in vacuum chamber to measure the wire mechanical losses The assembled system is positioned on very stiff legs attached to the ground to decrease recoils;

43 Feb. ‘09 - Dummy suspension for losses measurements Measurements are ongoing Currently the measured Q is 4*10 6 which is the expected value for the structure recoil losses (at this level we are not dominated by excess losses!!!) Dummy payload installation in the vacuum chamber Legs Shadow meter ES actuators for pendulum and violin modes PRELIMINARY LOWER LIMIT

44 Longitudinal controls: noise budget November 2007 May 2008

45 Environmental noises studies Investigations to understand the sources and the path to dark fringe  Coupling (paths) to dark fringe - diffused light from in air optical benches - diffused light related to Brewster window - beam jitter on injection bench  Sources of environmental noise: - air conditioning - electronic racks Laser Brewster window End benches External bench Injection bench Detection suspended bench Beam jitter DAQ room Worked in parallel on: -reduction of coupling -reduction of environmental noise Elec racks

46 Diffused light: noise budget Noise from diffused light: before mitigations (March 27 th ) Noise from diffused light: before mitigations (May 6 th ) Diffused light globally reduced by a factor ~3 More improvements planned: - More investigations on optics - Better beam dumps - Reduce the motion of benches: all benches have horizontal resonances ~10-20Hz  Resonance dampers in preparation

47 Summary After many years of blood, sweat and tears, Virgo is now working very well The low frequency region appears to be well understood and other project will be able to profit from the experience; Not only seismic, but all environmental noise has to be mitigated We look forward trying to push further down the noise with the monolithic suspensions as it could give to the LV network a Poisson rate for NSNS coalescences of more than one event per year.

48 The Fluctuation-Dissipation Theorem