  The J-region asymptotic giant branch (JAGB) method is a new standard candle
based on the constant luminosities of carbon-rich asymptotic giant branch stars
in the J band. The JAGB method is independent of the Cepheid and TRGB distance
indicators. Therefore, we can leverage it to both cross-check Cepheid and TRGB
distances for systematic errors and use it to measure an independent local
Hubble constant. The JAGB method also boasts a number of advantages in
measuring distances relative to the TRGB and Cepheids, several of which are
especially amplified when combined with JWST's revolutionary resolving power.
First, JAGB stars are 1 mag brighter in the NIR than the TRGB, and can be
discovered from single-epoch NIR photometry unlike Cepheids which require
congruent optical imaging in at least 12 epochs. Thus, JAGB stars can be used
to measure significantly farther distances than both the TRGB stars and
Cepheids using the same amount of observing time. Further advantages include:
JAGB stars are easily identified solely via their colors and magnitudes, dust
extinction is reduced in near-infrared observations, and JAGB stars are
ubiquitous in all galaxies with intermediate-age populations. In this paper, we
present a novel algorithm that identifies the optimal location in a galaxy for
applying the JAGB method, so as to minimize effects from crowding. We then
deploy this algorithm in JWST NIRCam imaging of seven SN Ia host galaxies to
measure their JAGB distances, undertaking a completely blind analysis. The
zero-point of this JAGB distance scale is set in the water mega-maser galaxy
NGC 4258. In our CCHP overview paper Freedman et al. (2024), we apply the JAGB
distances measured in this paper to the Carnegie Supernova Program (CSP) SNe Ia
sample, measuring a Hubble constant of H0 = 67.96 +/- 1.85 (stat) km/s/Mpc.
