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New mid-infrared period-luminosity (PL) relations are presented for \rrl{}variables in the globular cluster M4 (NGC 6121). Accurate photometry wasobtained for 37 \rrl{} variables using observations from the Infrared ArrayCamera onboard the Spitzer Space Telescope. The dispersion of M4's PL relationsis 0.056, and the uncertainty in the slope is 0.11 mag. Additionally,weestablished calibrated PL relations at 3.6 and 4.5~\micron{} using publishedHubble Space Telescopegeometric parallaxes of five Galactic \rrl{} stars. Theresulting band-averaged distance modulus for M4 is $ \mu = 11.399 \pm 0.007\textrm{(stat)} \pm 0.080 \textrm{(syst)} \pm 0.015 \textrm{(cal)} \pm 0.020\textrm{(ext)}$. The systematic uncertainty will be greatly reduced whenparallaxes of more stars become available from the GAIA mission. Optical andinfrared period-color (PC) relations are also presented, and the lack of a MIRPC relation suggests that \rrl{} stars are not affected by CO absorptionin the4.5~\micron{} band.

On the distance of the globular cluster M4 (NGC 6121) using RR Lyrae stars: II. Mid-infrared period-luminosity relations