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In the manuscript, a 3.8yr optical quasi-periodic oscillations (QPOs) isreported in blue quasar SDSS J132144+033055 (=\obj) at $z=0.269$, based on16.3yr-long light curve from both CSS and ZTF directly described by asinusoidal function. The 3.8yr QPOs can be confirmed through the GeneralizedLomb-Scargle periodogram with confidence level higher than 5$\sigma$, throughproperties of the phase-folded light curve and the WWZ technique. Moreover, thecollected Pan-STARRS light curves well follow the sinusoidal function describedbest fitting results to the CSS and ZTF light curves. The optical QPOs stronglyindicate a central binary black hole (BBH) system in \obj, with expected spaceseparation smaller than 0.018pc, through the estimated upper limit of total BHmass $3.3\times10^9{\rm M_\odot}$ through the correlation between BH mass andcontinuum luminosity. Meanwhile, we check disk precession applied to explainthe optical QPOs. However, under the disk precession assumption, the determinedoptical emission regions from central BH have sizes about $37{\rm R_G}$ similaras the sizes $35{\rm R_G}$ of the expected NUV emission regions through thecorrelation between disk size and BH mass, indicating the disk precession isnot preferred. And due to undetected radio emissions, jet precession can beruled out. Furthermore, only 0.1\% probability can determined as the QPOsmis-detected through CAR process randomly created light curves related tointrinsic AGN activities, re-confirming the optical QPOs with significancelevel higher than 3$\sigma$. Therefore, combining long-term light curves fromCSS and ZTF can lead to more QPOs candidates in the near future.

A 3.8yr optical quasi-periodic oscillations in blue quasar SDSS J132144+033055 through combined light curves from CSS and ZTF