Mining for imbh gravitational Waves Fabrizio Barone

Mining for IMBH Gravitational Waves

• Fabrizio Barone

• Enrico Campagna

• Yanbei Chen

• Giancarlo Cella

• Riccardo DeSalvo

• Seiji Kawamura

Pushing the Low Frequency Limit of ground based GWIDs

• Three limiting noise sources impede GWID at Low Frequency

• Newtonian Noise (NN, alias Gravity Gradient)
• Suspension Thermal Noise (STN)
• Radiation Pressure Noise (RPN)

• All three can be reduced by means of an underground interferometer

Is gravity gradient going to stop us?

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

LF-GWID the lowest frequency feasible surface GW detector

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,

• The movement of the rock surfaces or interfaces buffeted by the seismic waves
• The variations of rock density caused by the pressure waves

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

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).

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

Cella cancellation of NN

• Larger caves induce smaller test mass perturbations

• The noise reduction is proportional to 1/r3

• The longitudinal direction is more important =>elliptic cave

Cella cancellation of NN

• Cave radius [m]

Newtonian Noise gains

• Minimal (multiplicative) Gains

• ≥ 102 from lower underground activity

• ~ 104 from symmetry and size of cave

• Gain 101.5 in frequency (=> ~1 Hz)

• Now we can try kissing LISA

The physics, frequency reach

The physics, Universe range

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?

Vertical cross section

How far can we turn the knobs?

• Large symmetric underground halls for NN

• Longer suspension wires for STN

• Large mass mirrors for RPN

• Large beam spots for normal TN

For lowest frequencies, turn more the same knobs

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

Seismic Attenuation, OK Suspension and Seismic Isolation schematics

You have never seen a seismic attenuation filter

• Gosh, where do you come from?

• I will show you one!

Mirror design - a way out

• A clear no action band is present

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