Template banks to search for low-mass binary black holes in advanced gravitational-wave detectors

Abstract

Coalescing binary black holes (BBHs) are among the most likely sources for the Laser Interferometer Gravitational-Wave Observatory (LIGO) and its international partners Virgo and KAGRA. Optimal searches for BBHs require accurate waveforms for the signal model and effectual template banks that cover the mass space of interest. We investigate the ability of the second-order post-Newtonian TaylorF2 hexagonal template placement metric to construct an effectual template bank, if the template waveforms used are effective one-body waveforms tuned to numerical relativity (EOBNRv2). We find that by combining the existing TaylorF2 placement metric with EOBNRv2 waveforms, we can construct an effectual search for BBHs with component masses in the range $3{M}_{\ensuremath{\bigodot}}\ensuremath{\le}{m}_{1}$, ${m}_{2}\ensuremath{\le}25{M}_{\ensuremath{\bigodot}}$. We also show that the (computationally less expensive) TaylorF2 post-Newtonian waveforms can be used in place of EOBNRv2 waveforms when $M\ensuremath{\lesssim}11.4{M}_{\ensuremath{\bigodot}}$. Finally, we investigate the effect of modes other than the dominant $l=m=2$ mode in BBH searches. We find that for systems with $({m}_{1}/{m}_{2})\ensuremath{\le}1.68$ or inclination angle $\ensuremath{\iota}\ensuremath{\le}0.31$ or $\ensuremath{\iota}\ensuremath{\ge}2.68$ radians, there is no significant loss in the total possible signal-to-noise ratio due to neglecting modes other than $l=m=2$ in the template waveforms. For a source population uniformly distributed in spacial volume, over the entire sampled region of the component-mass space, the loss in detection rate (averaged over a uniform distribution of inclination angle and sky-location/polarization angles) remains below $\ensuremath{\sim}11%$. For binaries with high mass ratios and $0.31\ensuremath{\le}\ensuremath{\iota}\ensuremath{\le}2.68$, including higher-order modes could increase the signal-to-noise ratio by as much as 8% in Advanced LIGO. Our results can be used to construct matched-filter searches in Advanced LIGO and Advanced Virgo.