Stringy origin of Tevatron Wjj anomaly

The invariant mass distribution of dijets produced in association with W bosons, recently observed by the CDF Collaboration at Tevatron, reveals an excess in the dijet mass range 120-160 GeV/c^2, 3\sigma beyond Standard Model expectations. We show that such an excess is a generic feature of low mass string theory, due to the production and decay of a leptophobic Z', a singlet partner of SU(3) gluons coupled primarily to the U(1) baryon number. In this framework, U(1) and SU(3) appear as subgroups of U(3) associated with open strings ending on a stack of 3 D-branes. In addition, a minimal model contains two other stacks to accommodate the electro-weak SU(2) \in U(2) and the hypercharge U(1). Of the three U(1) gauge bosons, the two heavy Z' and Z'' receive masses through the Green-Schwarz mechanism. This model contains a free parameter which controls the Z-Z' mixing and can be chosen to simultaneously ensure three phenomenologically desirable features: small Z-Z' mixing permitting low Z' mass in the 120-160 GeV/c^2 range; very small (less than 1\%) branching ratio into electrons; and a large hierarchy between Z'' and Z' masses.