Michele Punturo INFN Perugia and EGO

ASPERA 2012: GW detectors 1 Talk Outline

 Introduction to the Gravitational Wave (GW) search  Gravitational wave interferometric detectors  Working principles  Current status  Advanced detectors  3rd generation of gravitational wave observatories  The Einstein Telescope

ASPERA 2012: GW detectors 2 General Relativity and GW  GW are predicted by the Einstein General Relativity (GR) theory  Formal treatment of the GW in GR is beyond the scope of this talk and only the aspects important for the GW detection will be considered Einstein field equation links c4 to the effect of the deformation the source of the space-time = − Tµν Gµν (Gµν the deformation tensor) deformation (Tµν Energy- 8πG impulse tensor) Far from the big masses Einstein field equation admits (linear approximation) wave solution (small perturbation of the background  1 ∂ 2  =η + << ⇒ ∇2 −  = geometry) g h with hµν 1  2 2 hµν 0  c ∂t 

ASPERA 2012: GW detectors 3 Gravitational Waves

 Gravitational waves are a perturbation of the space-time 0 0 0 0   geometry 0 h+ h× 0 h(z,t) = ei(ωt−kz)  0 h − h 0 They present two polarizations  × +    0 0 0 0  The effect of GWs on a mass distribution is the modulation of the reciprocal distance of the masses

h× h+

ASPERA 2012: GW detectors 4 Quantify the “deformation”  The amplitude of the space-time deformation is:

21G Where Qµν is the = ⋅  hQµν 4 µν quadrupolar moment cr of the GW source

 Let suppose to have a system of 2 and r is the distance coalescing neutron stars, located in between the detector the Virgo cluster (r~10Mpc): and the GW source h ≈10−21 −10−22 h  δL ≈ ⋅ L  −18 −19 2 0  ⇒ δL ≈10 −10 m 3  L0 ≈10 m

Extremely challenging for the detectors ASPERA 2012: GW detectors 5 But, GWs really exist?  Neutron star binary system: PSR1913+16  Pulsar bound to a “dark companion”, 7 kpc from Earth. -3  Relativistic clock: vmax/c ~10  GR predicts such a system to loose energy via GW emission: orbital period decrease  Radiative prediction of general relativity verified at 0.2% level

Nobel Prize 1993: HulseASPERA and 2012:Taylor GW detectors 6 GW interferometric initial detectors  A network of detectors has been active in the World until few years ago

GEO, Hannover, 600 m

TAMA, Tokyo, 300 m Virgo, Pisa, 3 km (now CLIO)

ASPERA 2012: GW detectors 7 VIRGO

 LAPP – Annecy  LMA – Lyon  INFN – Padova-Trento  NIKHEF – Amsterdam  INFN – Napoli  INFN – Perugia  RMKI - Budapest  OCA – Nice  INFN - Pisa  INFN – Firenze-Urbino  LAL – Orsay  INFN – Roma 1  INFN – Genova  APC – Paris  INFN – Roma 2  INFN – LNF  LKB - Paris  POLGRAV - Warsaw

ASPERA 2012: GW detectors 8 GEO600

ASPERA 2012: GW detectors 9 GW interferometric initial detectors  A network of detectors has been active in the World until few years ago

GEO, Hannover, 600 m

LIGO Hanford, 4 km: 2 ITF on the same site!

TAMA, Tokyo, 300 m Virgo, Cascina, 3 km (now CLIO)

LIGO Livingston, 4 km

ASPERA 2012: GW detectors 10 LIGO Scientific Collaboration

GEO600, Hannover, Germany

LIGO – Hanford, WA

LIGO – Livingston, LA

ASPERA 2012: GW detectors 11 GW interferometric initial detectors  A network of detectors has been active in the World until few years ago

GEO, Hannover, 600 m

LIGO Hanford, 4 km: 2 ITF on the same site!

TAMA, Tokyo, 300 m Virgo, Cascina, 3 km (now CLIO)

LIGO Livingston, 4 km

ASPERA 2012: GW detectors 12 Working principle  The quadrupolar nature of the GW makes the Michelson interferometer a “natural” GW detector h δL ≈ ⋅ L 2 0

2 4 10 ≤L0 ≤10 m in terrestrial detectors

Beam-splitter Mirror

GW signal

4π φGW = L0 ⋅h λ Interference Photodetector 13 ASPERA 2012: GW detectors Real life: complex machine

typical earth crust tidal strain: ~10-4 m Complex optical scheme ~ -14 Complex active control strategy allowed mirror rms motion: 10 m

ASPERA 2012: GW detectors 14 Detector sensitivity  The faint space-time deformation measurement must compete with a series of noise sources that are spoiling the detector sensitivity Seismic filtering: in Virgo pendulum chains to reduce seismic motion 14 Virgo nominal by a factor 10 sensitivity above 10 Hz ~ 8 m

ASPERA 2012: GW detectors 15 Detector sensitivity  The faint space-time deformation measurement must compete with a series of noise sources that are spoiling the detector sensitivity

Optimization of the payload design to minimize the mechanical losses

ASPERA 2012: GW detectors 16 Detector sensitivity  The faint space-time deformation measurement must compete with a series of noise sources that are spoiling the detector sensitivity

Maximization of the injected laser power, to minimize the shot noise

ASPERA 2012: GW detectors 17 Noise budget: real life

Virgo+ noise budget example

ASPERA 2012: GW detectors 18 GW interferometer past evolution past GW interferometer principle working the of Proof assembling Infrastructu realization realization  detector detector Evolution of the GW detectors (VirgoEvolution GW detectors of the example): and re re 2003 infrastructure Same

2008

year Detection distance (a.u.) 19

ASPERA 2012: GW detectors GW interferometer past evolution past GW interferometer principle working the of Proof assembling Infrastructu realization realization Upper Limit physics Limit Upper  detector detector Evolution of the GW detectors (VirgoEvolution GW detectors of the example): and re re 2003 infrastructure Same

2008

year Detection distance (a.u.) 20

ASPERA 2012: GW detectors z GW sources: BS BH-BH r0  Binary systems of massive and compact stellar bodies: r  NS-NS, NS-BH, BH-BH  Source of crucial interest:  We are able to model (roughly) the signal using the (post) Newtonian chirp physics

ASPERA 2012: GW detectors 21 Network of GW detectors  The search for GW signal emitted by a binary system (of neutron star) asks for a network of (distant) detectors  Event reconstruction  Source location in the sky  Reconstruction of polarization components  Reconstruction of amplitude at source and determination of source distance (BNS)  Detection probability increase  Detection confidence increase  Larger uptime  Better sky coverage

ASPERA 2012: GW detectors 22 GW sources: BS z r0  Binary systems of massive and compact stellar bodies: r  NS-NS, NS-BH, BH-BH

1ST GENERATION INTERFEROMETERS COULD DETECT A NS-NS COALESCENCE AS FAR AS VIRGO CLUSTER (15 MPc)

LOW EXPECTED EVENT RATE: 0.01-0.1 ev/yr (NS-NS) ASPERA 2012: GW detectors 23 Scientific runs  A series of runs have been performed by the GW network  As expected, no BS detection so far!

’05 ’06 ’07 ’08 ’09 ’10 ’11 ’12

LIGO S4 S5 AstroWatch S6

GEO

VSR1 VSR2 VSR3 Virgo

But, upper limit physics explored! (PRD 85, 082002 – 2012, 24 Nature 460, 990-994 . 2009) ASPERA 2012: GW detectors GW source: Isolated NS  Not-axisymmetric rotating neutron stars (pulsars) are expected to emit GW at frequency double of the spinning one

38 2 I zz ≈10 kg ⋅m G 2 h ≈ ε ⋅ I ⋅Ω I xx − I yy rc4 zz ε = I zz  The periodicity of the signal allows to increase the SNR integrating for a long time  But Doppler effect correction needed because of the Earth motion determines a computational obstacle to a full blind search  Detection of GW from a NS gives info on the internal structure of the star (ε limit is related to the superfluid/strange matter nature of the star, to the magnetic field, …)

ASPERA 2012: GW detectors 25 GW sources: isolated NS

 Isolated NS are a possible source of GW if they have a 713 671 non-null quadrupolar moment (ellipticity) Crab pulsar ApJ in the Crab nebula al. 2010 -22 Spin-down limit of known NS vs integrated sensitivities (2kpc) 10 et

(tobs=1year, 1%FAP, 10%FDP) LIGO-S5 upper limit: -23 10 Know Pulsar spin down limit <1/4 of the SD limit Virgo nominal sensitivity iLIGO nominal sensitivity in h amplitude 10-24 B. P. Abbott B. P. 10-25 Vela pulsar in its -26

10 nebula (0.3kpc) 737 93

-27 Space-time strain 10 Upper limit ApJ determined in the 10-28 Virgo VSR2 run: ~1/3 of the spin- -29 10 et al. 2011 10 100 1000 down limit Frequency [Hz] Credits: C.Palomba ASPERA 2012: GW detectors 26 J. Abadie GW sources: GRB  Gamma ray bursts are subdivided in 2 classes:  Long (>2s duration): SNe generation mechanism  Short (<2s): BNS coalescence mechanism → GW B.P. Abbot (LSC and Virgo coll), Astr. Jour. 715 (2010), 1438

GRB mainly detected by Swift satellite

 A series (137) of GRB occurred during the LIGO-S5/Virgo-VSR1 run  No detection occurred, but lower limit for the distance of each GRB ASPERA 2012: GW detectors event 27 GW interferometer present evolution  Evolution of the GW detectors (Virgo example):

First detection

a.u .) Initial astrophysics

Proof of the working principle

Upper Limit physics enhanced

detectors Detection distance (

Infrastructu re 2012: GW ASPERA detectors realization Same Same Same and infrastructureinfrastructure infrastructure detector assembling year 2003 2008 2011 2017 28 Advanced detectors  The upgrade to the advanced phase (2nd generation) is just started. The detectors should be back in commissioning in 2014  Advanced are promising roughly a factor 10 in sensitivity improvement: Enhanced LIGO/Virgo+ Virgo/LIGO

108 ly

Adv. Virgo/Adv. LIGO

Credit: R.Powell, B.Berger  This allows a detection distance for coalescing BNS of about 130-200Mpc ASPERA 2012: GW detectors 29 Advanced detectors: BNS detection rates  The detection rate follows the sight distance with a roughly cubic law: 

A BNS detection rate of few tens per year with a limited SNR: detection is assured

et al. (LSC & Virgo), al. (LSC et arXiv:1003.2480; Virgo), &

Abadie 173001 (2010) 27, CQG ASPERA 2012: GW detectors 30 Advanced detectors: pulsars  Better sensitivities, especially at low frequency, will allow to beat the spin-down limit for many pulsars

Credits: C.Palomba

ASPERA 2012: GW detectors 31 Advanced detectors: technologies  Advanced detectors are based on technologies having already proved their effectiveness in laboratory or in partial installation in the enhanced detectors  Low frequency (10-100Hz):  Target BH-BH coalescence, pulsars  Reduction of residual seismic noise (adv.LIGO, through active seismic filtering)  Reduction of suspension thermal noise:  Monolithic fused silica suspensions, pioneered by GEO600, currently installed in Virgo+ (enhanced)  Reduction of radiation pressure noise (heavier test masses)

ASPERA 2012: GW detectors 32 Advanced detectors: technologies  Advanced detectors are based on technologies having already proved their effectiveness in laboratory or in partial installation in the enhanced detectors  Intermediate frequency (80- 500Hz)  Target BS-BS coalescence, pulsars  Reduction of “mirror” thermal noise:  Heavier test masses, larger beams, lower mechanical dissipation coatings  Higher finesse in the Fabry-Perot cavities

ASPERA 2012: GW detectors 33 Advanced detectors: technologies  Advanced detectors are based on technologies having already proved their effectiveness in laboratory or in partial installation in the enhanced detectors  High frequency (300-10000Hz)  Target BNS-BNS coalescence, NS normal modes  Reduction of quantum (shot) noise:  High laser power  Solid state (aLIGO, GEO techn.)  Fiber laser (aVirgo)  Low absorption optics and TCS to reduce the thermal lensing  Signal recycling to tune sensitivity in frequency (GEO600 pioneered technology)

ASPERA 2012: GW detectors 34 New players !  KAGRA  A 2.5 generation detector, under construction in Japan, implementing new (3G) underground and cryogenic technologies in a 3km long site in Kamioka (2018)

ASPERA 2012: GW detectors 35 New players !  KAGRA  A 2.5 generation detector, under construction in Japan, implementing new (3G) underground and cryogenic technologies in a 3km long site in Kamioka (2018)  LIGO-India  The move of aLIGO-H2 to India to improve pointing capabilities of the GW detector network (2018-  AIGO 2020) is almost decided  Attempt to build a GW interferometer in Australia ASPERA 2012: GW detectors 36 rd Precision Astrophysics 3 generation? Cosmology  Evolution of the GW detectors (Virgo example): Limit of the current infrastructures

First detection

a.u .) Initial astrophysics

Proof of the working principle

Upper Limit physics enhanced

detectors Detection distance (

Infrastructu re 2012: GW ASPERA detectors Same realization Same Same Same Infrastructure and infrastructureinfrastructure infrastructure (≥20 years old for Virgo, even more for LIGO & GEO600) detector assembling year 2003 2008 2011 2017 2022 37 GW Astronomy?  Is our target the precision Astronomy with GW detectors?  Let learn from who is doing astronomy now:

“Electro-magnetic” Telescopes

ASPERA 2012: GW detectors 38 E.M. Astronomy  Current e.m. telescopes are mapping almost the entire Universe  Keywords:  Map it in all the WMAP accessible wavelengths 408MHz  See as far as possible  Galaxy UDFy-38135539 in Ultra Deep Field image (Hubble Telescope) ∼ 13.1 Gly Infrared visible

X-ray γ-ray

GRB M. Trenti, Nature 467, 924–925 (21 October 2010) ASPERA 2012: GW detectors 39 GW Astronomy ?  Enlarge as much as possible the frequency range of GW detectors  Pulsar Timing Arrays 408MHz WMAP  10-9-10-6 Hz  Space based detectors (LISA/NGO, DECIGO)  10-5-10-1 Hz Infrared visible  Ground based detectors  1-104Hz  Improve as much as possible the sensitivity to γ-ray increase the detection X-ray volume (rate) and the observation SNR GW ?

GRB ASPERA 2012: GW detectors 40 Beyond Advanced Detectors  Let suppose to gain a factor 10 wrt the Advanced detectors: What could we do?  Astrophysics:  Measure in great detail the physical parameters of the stellar bodies composing the binary systems  NS-NS, NS-BH, BH-BH  Constrain the Equation of State of NS through the measurement  of the merging phase of BNS  of the NS stellar modes  of the gravitational continuous wave emitted by a pulsar NS  Contribute to solve the GRB enigma  Relativity  Compare the numerical relativity model describing the coalescence of intermediate mass black holes  Test General Relativity against other gravitation theories  Cosmology  Measure few cosmological parameters using the GW signal from BNS emitting also an e.m. signal (like GRB)  Probe the first instant of the universe and its evolution through the measurement of the GW stochastic background  Astro-particle:  Contribute to the measure the neutrino mass ASPERA 2012: GW  Constrain the graviton mass measurement detectors

41 The Einstein Telescope  The Einstein Telescope project concluded its conceptual design study phase, FP7-supported by the European Community, in July 2011.

The ET Science Team Participant Country EGO Italy involved more than 220 France scientist interested to the ET INFN Italy science from Europe, MPG Germany Russia, USA, Japan and CNRS France Australia University of Birmingham UK University of Glasgow UK Nikhef NL Cardiff University UK

ASPERA 2012: GW 42 detectors Conceptual Design Document

 ET conceptual design document released:  https://tds.ego- gw.it/ql/?c=7954  ~400 pages describing the main characteristics of the observatory  The main conclusion is the demonstration of the need of a new research infrastructure, allowing the prosecution of the GW observation for decades.

ASPERA 2012: GW detectors 43 How a new infrastructure (and new technologies) pushes ET beyond the 2nd generation?

10-16 Seismic

(Hz)] sqrt h(f) [1/

10-25

1 Hz Frequency [Hz] 10 kHz ASPERA 2012: GW detectors 44 Seismic and Newtonian noises  Virgo and advanced Virgo seismic filtering is already close to the top of the possible performances  Longer suspensions to facilitate the low frequency access  Gravity gradient noise bypasses the seismic filtering

SEISMIC NOISE

NEWTONIAN NOISE Gρ h() f=×⋅ const .0 x () f Hf() 0

ASPERA 2012: GW detectors Credit M.Lorenzini4545 Seismic noise  Virgo and advanced Virgo seismic filtering is already close to the top of the possible performances  Gravity gradient noise bypasses the seismic filtering

 The only way to try to access the 1-10Hz range is to select a site with very low seismic noise  We need to minimize  Seismic noise  Gravity Gradient Noise  Environmental noises (wind, human activities, …)

ASPERA 2012: GW detectors 46 Current GW detectors seismic noise

µ-seism in a very noisy day

ASPERA 2012: GW detectors 47 WP1: Site search:

 Many sites visited in Europe

ASPERA 2012: GW detectors 48 Underground Seismic noise Measurement

Underground sites are the candidates for a very quiet site

ASPERA 2012: GW detectors 49 Baksan Neutrino Observatory

 BNO site is showing an appealing seismic noise  Further measurements proposed in the GW proposal submitted to reply to latest ASPERA R&D call

ASPERA 2012: GW detectors 50 Site selection  Single site selection was not one of the targets of the conceptual design study  Our objective has been  to define the requirements  to understand the relationship between site characteristics, costs and performances  To prepare a list of good candidates  The selection of the site will be performed in a future phase and the scientific and technical arguments will be joint to the “political” and financial aspects

ASPERA 2012: GW detectors 51 Thermal noise

10-16 Seismic

(Hz)] sqrt h(f) [1/

10-25

1 Hz Frequency [Hz] 10 kHz ASPERA 2012: GW detectors 52 Reduction of the thermal noise  Thermal noise reduction is achievable through two handles  Fluctuation dissipation theorem: Minimization of the mechanical losses in the (suspension and test mass) material and optimization of the suspension geometry  Equipartition theorem: reduction of the thermal energy (low temperatures)  Advanced detector are fully exploiting the first “handle”  Third generation will use the second one:  Cryogenics  But impressive developments will be needed in optical materials, laser technologies, coatings, cryo-cooling technologies to achieve the 3G targets

ASPERA 2012: GW detectors 53 Synergies with KAGRA: ELiTES  KAGRA is pioneering the development of an underground infrastructure and of the cryogenic interferometer for GW detection  It is mandatory to profit of all the collaboration possibilities  A 4 years European-Japanese joint project “ELiTES” supported by European Commission under FP7-IRSES is just started  Exchange of scientists focused mainly on cryogenic issues common to ET and KAGRA  First ELiTES general meeting:  3-4 October 2012, hosted by the European Commission delegation in Japan (Tokyo)  AdV-KAGRA meeting appended the 5th of October ASPERA 2012: GW detectors 54 High frequency noise

10-16 Seismic

(Hz)] sqrt h(f) [1/

10-25

1 Hz Frequency [Hz] 10 kHz ASPERA 2012: GW detectors 55 High frequency  High frequency noise reduction requires the suppression of the quantum noise  Brute force approach:  High power in the FP cavities  High power laser  High reflectivity  Thermal lensing issues  Difficult cross-compatibility Shot noise reduction with cryogenics  Parametric instabilities  QND techniques: squeezing  Hyper-Promising (12.7dB @5MHz), 3.4dB in GEO, 2dB in LIGO test  Frequency dependent implementation  New infrastructures ASPERA 2012: GW detectors 56 R&D programme  The success of the Advanced detectors is mandatory and preliminary for the 3G realization  We need  Detection  2G technologies success  But specific 3G technologies must be developed in advance:  3G R&D programme needed (in Europe)  ASPERA R&D call is going timidly in that direction

ASPERA 2012: GW detectors 57 The ET project

 The target of the ET project is to realize in Europe a fundamental Research Infrastructure that could host the Gravitational Wave observatories for decades, opening the GW precision astronomy and implementing the technical evolutions in the detectors composing the observatory  The implementation of the full observatory is diluted in the years and triggered by the first detection  ET studies triggered long term investigations (LIGO3) in US

ASPERA 2012: GW detectors 58 commissioning ET and first detector -commissioning pre Components ET Site and infrastructures infrastructures and ET Site 2012 design ET Conceptual

2013 Hardware production 2014

2015

2016

2017 realisation First interferometers onadvanced First detection 2018

2019 Technical design

2020 Funding ET Observatory 2021

2022 preparation Site

2023

2024 data science First

2025 R&D 2026

2027

202859

2029 END

ASPERA 2012: GW detectors 60 Gravity Gradient noise in AdV  The GGN noise could limit the AdV sensitivity during high seismic activity days:

- 12) - 0073B (GWADW 2012 (GWADW M. Punturo M. Punturo (VIR M.Beker

ASPERA 2012: GW detectors 61 Day/Night variability vs population density

ASPERA 2012: GW detectors 62 Substrates characteristics @ cryo (~10K) temperatures Material adopted in New possible candidate the KAGRA design investigated in the ET Design Study

SiO2 Silicon Sapphire 300K CRYO 300 K CRYO 300 K CRYO Φ 5 10-9 10-7 2 10-8 ~3 10-9 2 10-9 4 10-9 assumed κ - W/(m.K) 1.38 0.13 130 297 @4K 40 110 @4.2K @10K 2330 @10K 1500 @ 12.5K C - 746 1-7@10K 711 0.276 @10K 790 0.1 @ 10K J/(K.Kg) α - 1/K 0.51 10-6 -0.25 10-6 2.54 10-6 4.85 10-10 5.1 10-6 5.7 10-10 @ 10K @10K @10K β - 1/K 8 10-6 1.01 10-6 2.5 10-6 5.8 10-6 1.3 10-5 9 10-8 @20K @30K @30K

Credits: J.Franc et al. ASPERA 2012: GW detectors 63 ET sensitivity (Xylophone strategy)  Implementing all the technologies under study for ET a target sensitivity (ET-B) can be draft

 Doubts on the cross-compatibility of the technologies  Need to simplify the problem  Xylophone strategy

ASPERA 2012: GW detectors 64 Geometry optimization 45° stream and null stream generated by Fully resolve polarizations virtual interferometry

y1 x1 Redundancy L γ=120° L γ=240° 45° x1 y y 1 5 end caverns 1 x 7 end caverns 4×L long tunnels 1 6×L long tunnels

Fully resolve polarizations by virtual interferometry Null stream Redundancy Equivalent to ζ=60° ~3-9 end caverns 3.45×L long tunnels L L’=L/sin(60°)=1.15×L γ=120°

ASPERA 2012: GW detectors (Freise 2009) 65 The infrastructure  Schematic view  Full infrastructure realized  Initial detector(s) implementation  1 detector (2 ITF)  Physics already possible in coincidence with the improved advanced detectors  Progressive implementation  2 detector (4 ITF)  Redundancy and cross- correlation  Full implementation  3 detector (6 ITF)  Virtual interferometry  2 polarizations reconstruction ASPERA 2012: GW detectors 66