State College May 2004 LIGO- Mining for IMBH Gravitational Waves Fabrizio Barone Enrico Campagna Yanbei Chen Giancarlo Cella Riccardo DeSalvo Seiji Kawamura

State College May 2004 LIGO- Pushing the Low Frequency Limit of ground based GWIDs Three limiting noise sources impede GWID at Low Frequency 1.Newtonian Noise (NN, alias Gravity Gradient ) 2.Suspension Thermal Noise (STN) 3.Radiation Pressure Noise (RPN) All three can be reduced by means of an underground interferometer

State College May 2004 LIGO- Is gravity gradient going to stop us? ~70 Hz

State College May 2004 LIGO- Which knobs to turn for low frequency In LG-GWID the first limitation is Newtonian noise, followed by Suspension thermal noise and Radiation pressure noise Example: surface LF-GWID (R.DeSalvo, Class. Quantum Grav. 21 (2004)) 8 Watts laser Fused Silica Mirror 70 Kg mirror Longer suspensions

State College May 2004 LIGO- LF-GWID the lowest frequency feasible surface GW detector Bad seismic day Good seismic day ~30 Hz, possibly 20 Hz

State College May 2004 LIGO- Newtonian Noise NN derives from the varying rock density induced by seismic waves around the test mass It generates fluctuating gravitational forces indistinguishable from Gravity Waves It is composed of two parts, 1.The movement of the rock surfaces or interfaces buffeted by the seismic waves 2.The variations of rock density caused by the pressure waves

State College May 2004 LIGO- Newtonian Noise How to shape the environment’s surface to minimize NN? The dominant term of NN is the rock-to-air interface movement On the surface this edge is the flat surface of ground Ground surface

State College May 2004 LIGO- Cella Cancellation of NN If the cavern housing the suspended test mass is shaped symmetrically along the beam line and around the test mass tilting and surface deformations, the dominant terms of NN, cancel out –(with the exception of the longitudinal dipole moment, which can be measured and subtracted).

State College May 2004 LIGO- Cella Cancellation of NN Pressure seismic waves induce fluctuating rock density around the test mass The result is also fluctuating gravitational forces on the test mass

State College May 2004 LIGO- Cella cancellation of NN Larger caves induce smaller test mass perturbations The noise reduction is proportional to 1/r 3 The longitudinal direction is more important =>elliptic cave

State College May 2004 LIGO- Cella cancellation of NN Reduction factor Cave radius [m] 5 Hz 10 Hz 20 Hz 40 Hz Calculation made for Centered Spherical Cave In rock salt beds Width Length

State College May 2004 LIGO- Newtonian Noise gains Minimal (multiplicative) Gains ≥ 10 2 from lower underground activity ~ 10 4 from symmetry and size of cave Gain in frequency (=> ~1 Hz) Now we can try kissing LISA

State College May 2004 LIGO-. Under Ground Above Ground NN limit The physics, frequency reach

State College May 2004 LIGO- The physics, Universe range 1 101

State College May 2004 LIGO-. Above ground Ad-LIGO: See LIGO document M LF-GWID: See R.DeSalvo, Class. Quantum Grav. 21 S1145-S1154, (2004) G. Conforto, Nucl.Instr.Meth. Vol 518/1-2 pp (2004) Limited by Newtonian Noise Under ground Aspen presentation, LIGO- G R CEGO proposal, LIGO-T R.doc

State College May 2004 LIGO- Reducing the suspension thermal noise Reduce suspension thermal noise with long suspensions Noise ~ 1/√L Suspensions tens of meters long How to shape the facility to allow this?

State College May 2004 LIGO- Vertical cross section A) Upper experimental halls contain all suspension points, readout and control equipment B) Wells (50 to 100 m deep allow for long isolation and suspension wires for LF seismic and STN reduction C) Lower large diameter caves, immune from people’s and seismic Noise reduce the NN

State College May 2004 LIGO- Large symmetric underground halls for NN Longer suspension wires for STN Large mass mirrors for RPN Large beam spots for normal TN How far can we turn the knobs?

State College May 2004 LIGO- For lowest frequencies, turn more the same knobs Suspension Thermal Violin mode

State College May 2004 LIGO- Suspension thermal noise limitations Can make one more step improving the materials (silicon instead of fused silica) getting to 3-4 Hz After that, cryogenics or alternative solutions will be needed

State College May 2004 LIGO- Seismic Attenuation, OK Suspension and Seismic Isolation schematics meter pendula Between all stages 2-3 meter tall Pre-isolator In upper cave LF Vertical filters marionetta Composite Mirror Recoil mass

State College May 2004 LIGO- You have never seen a seismic attenuation filter Gosh, where do you come from? I will show you one!

State College May 2004 LIGO- Filter under test Attenuated Payload wire

State College May 2004 LIGO- Mirror design - a way out A clear no action band is present

State College May 2004 LIGO- Summarizing An underground facility permits to overcome or reduce Newtonian, Suspension Thermal and Radiation Pressure Noise the three limitations for Low Frequency operation of GWIDs Going underground is a very attractive option to explore the IMBH Universe Chinese scientists got interested and have proposed to their government the construction of an underground GW detection facility CEGO

State College May 2004 LIGO-

State College May 2004 LIGO-