Mining for imbh gravitational Waves Fabrizio Barone



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tarix15.08.2018
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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








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