Some ideas on advanced Virgo Twins A. Giazotto-INFN Pisa If this is true, one appealing idea could be to build a second Virgo:

Some interesting test on twin beams 1)Direct measurement of Scattered Light Effect on the Sensitivity in TAMA300 Ryutaro Takahashi, Koji Arai, Seiji Kawamura and Michael Smith* National Astronomical Observatory of Japan, Caltech*

Experimental method Vibrate the mid point of the arm using a shaker vertically. 5.6 x 10-6m @776.5Hz 4.7 x 10-6m @788.5Hz Measure the effects due to vibration and sound.

Experimental result 1 (signals of the interferometer)

Results and discussion 776.5Hz 788.5Hz Interferometer 1.2 x 10-17m 0.25 x 10-17m (Background) 0.16 x 10-17m 0.13 x 10-17m Vibration　 <0.1 x 10-17m <0.01 x 10-17m Sound not detected 0.2 x 10-17m Calculation (with 2-m reflection area and optimal phase) 6.3 x 10-17m There is cancellation due to mechanical modes.

Approximate Conclusions from TAMA TAMA Tube: Diam.~40 cm, No Baffles Vibration TF @ 765 Hz : ~10-17/5 10-6=2 10-12 Scale to Virgo Seismic noise in Virgo is expected to be xVirgo~10-7/2 m/Hz1/2 Expected seismic correlated signal in the two beams~ 2 10-12. 10-7/2= 2 10-19/2 m/Hz1/2 Expected reduction due to Baffles~1/10 ~2 10-20/2 m/Hz1/2

2)Preliminary data from 2km and 4km Hanford ITF’s seems to show low correlation.

From LIGO it seems that: Seismic noise correlate up 30 Hz due to suspensions. Switching power supply create bad correlations at 60 Hz harmonics; needed analog power supply and very good groundings. 3) Sound correlate on injection systems due to common housing.

Virgo seems to have an optimal configuration from three relevant points of views: 1) Very good seismic isolation down to 4Hz 2) Buildings for the second ITF may be completely separated from Virgo 1, this reduces a lot sound and e.m. couplings on the two injection systems. 3) Baffles are installed in the vacuum tube 4) We may also design the overall electronics to be powered with analog Power Supply. 5) A problem: overlapped beams may give coincidences due to dust falling in the vacuum pipe.

VIRGO 2 VIRGO1