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We use flux-transmission correlations in \Lya forests to measure the imprintof baryon acoustic oscillations (BAO). The study uses spectra of 157,783quasars in the redshift range $2.1\le z \le 3.5$ from the Sloan Digital SkySurvey (SDSS) Data Release 12 (DR12). Besides the statistical improvements onour previous studies using SDSS DR9 and DR11, we have implemented numerousimprovements in the analysis procedure, allowing us to construct a physicalmodel of the correlation function and to investigate potential systematicerrors in the determination of the BAO peak position. The Hubble distance,$\DHub=c/H(z)$, relative to the sound horizon is $\DHub(z=2.33)/r_d=9.07 \pm0.31$. The best-determined combination of comoving angular-diameter distance,$\DM$, and the Hubble distance is found to be$\DHub^{0.7}\DM^{0.3}/r_d=13.94\pm0.35$. This value is $1.028\pm0.026$ timesthe prediction of the flat-\lcdm model consistent with the cosmic microwavebackground (CMB) anisotropy spectrum. The errors include marginalization overthe effects of unidentified high-density absorption systems and fluctuations inultraviolet ionizing radiation. Independently of the CMB measurements, thecombination of our results and other BAO observations determine the open-\lcdmdensity parameters to be $\om=0.296 \pm 0.029$, $\ol=0.699 \pm 0.100$ and$\Omega_k = -0.002 \pm 0.119$.

Measurement of BAO correlations at $z=2.3$ with SDSS DR12 \lya-Forests