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We present a detailed analysis of the pre-main-sequence (PMS) population ofthe young star cluster Westerlund~2 (Wd2), the central ionizing cluster of theHII region RCW 49, using data from a high resolution multi-band survey with theHubble Space Telescope. The data were acquired with the Advanced Camera forSurveys in the F555W, F814W, and F658N filters and with the Wide Field Camera 3in the F125W, F160W, and F128N filters. We find a mean age of the region of1.04+-0.72 Myr. The combination of dereddened F555W and F814W photometry incombination with F658N photometry allows us to study and identify stars withH_alpha excess emission. With a careful selection of 240 bona-fide PMS H_alphaexcess emitters we were able to determine their H_alpha luminosity, which has amean value L(H_alpha)=1.67 x 10^{-31} erg s^{-1}. Using the PARSEC 1.2Sisochrones to obtain the stellar parameters of the PMS stars we determined amean mass accretion rate \dot M_acc=4.43 x 10^{-8} M_sun yr^{-1} per star. Acareful analysis of the spatial dependence of the mass-accretion rate suggeststhat this rate is ~25% lower in center of the two density peaks of Wd2 in closeproximity to the luminous OB stars, compared to the Wd2 average. This rate ishigher with increasing distance from the OB stars, indicating that the PMSaccretion disks are being rapidly destroyed by the far-ultra-violet radiationemitted by the OB population.

A High-Resolution Multiband Survey of Westerlund 2 With the Hubble Space Telescope. II. Mass accretion in the Pre-Main Sequence Population