Optimal location of two laser-interferometric detectors for gravitational wave backgrounds at 100 MHz

Recently, observational searches for a gravitational wave background (GWB) have been developed and given constraints on the energy density of a GWB in a broad range of frequencies. These constraints have already resulted in the rejection of some theoretical models of relatively large GWB spectra. However, at 100 MHz, there is no strict upper limit from direct observation, though an indirect limit exists due to ⁴He abundance due to big-bang nucleosynthesis. In our previous paper, we investigated the detector designs that can effectively respond to GW at high frequencies, and found that the configuration, a so-called synchronous-recycling interferometer is best at these sensitivities. In this paper, we investigated the location and orientation dependence of two synchronous-recycling interferometers in detail, and derived the optimal location of the two detectors and the cross-correlation sensitivity to GWB. We found that the sensitivity is nearly optimized and hardly changed if two coaligned detectors are located in a range of 0.2m.