  We present synthesis and $^{75}$As-nuclear quadrupole resonance (NQR)
measurements for the noncentrosymmetric superconductor CaPtAs with a
superconducting transition temperature $T_c$ of $\sim 1.5$ K. We discovered two
different forms of CaPtAs during synthesis; one is a high-temperature
tetragonal form that was previously reported, and the other is a
low-temperature form consistent with the orthorhombic structure of CaPtP.
According to the $^{75}$As-NQR measurement for superconducting tetragonal
CaPtAs, the nuclear spin-lattice relaxation rate $1/T_1$ has an obvious
coherence peak below $T_c$ and does not follow a simple exponential variation
at low temperatures. These findings indicate that CaPtAs is a multigap
superconductor and a large $s$-wave component.
