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 laserFused Silica Mirror70 Kg mirrorLonger suspensions

State College May 2004 LIGO-

LF-GWID the lowest frequency feasible surface GW detector

Bad seismic dayGood 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

seismic motion leads to

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).

atilting leads to fluctuating attraction force

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/r3

• The longitudinal direction is more important =>elliptic cave

State College May 2004 LIGO-

Cella cancellation of NN

Reductionfactor

Cave radius [m]

5 Hz10 Hz20 Hz40 Hz

Calculation made forCentered Spherical CaveIn rock salt beds

Width Length

State College May 2004 LIGO-

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

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

10 1

10

State College May 2004 LIGO-

.Above ground

Ad-LIGO: See LIGO document M-0300023-00LF-GWID: See R.DeSalvo, Class. Quantum Grav. 21 S1145-S1154,(2004)

G. Conforto, Nucl.Instr.Meth. Vol 518/1-2 pp 228-232 (2004)

Limited by Newtonian Noise

Under ground

Aspen presentation, LIGO-G040036-00-R

CEGO proposal, LIGO-T040059-00-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

SuspensionThermal

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, OKSuspension and Seismic Isolation

schematics

10-20 meter pendulaBetween all stages

2-3 meter tallPre-isolatorIn uppercave

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-

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

Filter under test

AttenuatedPayloadwire

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-