Prospects for improving the sensitivity of the cryogenic gravitational wave detector KAGRA

Upgrades to improve the sensitivity of gravitational wave detectors enable more frequent detections and more precise source parameter estimation. Unlike other advanced interferometric detectors such as Advanced LIGO and Advanced Virgo, KAGRA requires a different approach for the upgrade since it is the only detector which employs cryogenic cooling of the test masses. In this paper, we describe possible KAGRA upgrades with technologies focusing on different detector bands and compare the impacts on the detection of compact binary coalescences. We show that either fivefold improvement in the $100M_{\odot }–100M_{\odot }$ binary black hole range, a factor of 1.3 improvement in the binary neutron star range, or a factor of 1.7 improvement in the sky localization of binary neutron stars is quite feasible with upgrades that do not require changes in the existing cryogenic or vacuum infrastructure. We also show that twofold broadband sensitivity improvement is possible by applying multiple upgrades to the detector.

Figure 1

Sensitivity curves for the default KAGRA and possible upgrades calculated with the parameters shown in Table 1. Sensitivity curves for Advanced LIGO (aLIGO) and Advanced Virgo (AdV) are also shown for comparison in (a). For other plots, sensitivity curves for the upgrades $\mathrm{A}+$ and $\mathrm{AdV}+$, and default KAGRA are shown. Sensitivity curve data for Advanced LIGO and $\mathrm{A}+$ are taken from Refs. [22, 37], and those for Advanced Virgo and $\mathrm{AdV}+$ are extracted from Ref. [26].

Figure 2

The detection ranges of possible KAGRA upgrades for nonspinning equal-mass binaries. The redshift corrected, sky averaged distance at which gravitational waves can be detected with a signal-to-noise ratio of more than 8 is shown for each upgrade.