Stringy origin of Tevatron <em>Wjj</em> 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 , 3σ 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 ) ⊂ 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. For a given Z ′ mass, the model is quite constrained. Fine tuning three of its free parameters is just sufficient to simultaneously ensure: a small Z – Z ′ mixing in accord with the stringent LEP data on the Z mass; very small (less than 1%) branching ratio into leptons; and a large hierarchy between Z ″ and Z ′ masses. The heavier neutral gauge boson Z ″ is within the reach of LHC.

费米实验室Tevatron的CDF合作组近期观测到的与W玻色子相关联产生的双喷注的不变质量分布，在120 - 160 GeV/c²的双喷注质量范围内显示出超出标准模型预期3σ的过量。我们表明，这种过量是低质量弦理论的一个普遍特征，这是由于一个轻子厌恶的Z′（它是SU(3)胶子的单态伙伴，主要与U(1)重子数耦合）的产生和衰变。在这个框架中，U(1)和SU(3)作为与终止于3个D - 膜堆的开弦相关联的U(3)的子群出现。此外，一个最小模型包含另外两个膜堆以容纳电弱SU(2)⊂U(2)和超荷U(1)。在三个U(1)规范玻色子中，两个重的Z′和Z″通过格林 - 施瓦茨机制获得质量。对于给定的Z′质量，该模型受到相当的约束。对其三个自由参数进行微调刚好足以同时确保：符合关于Z质量的严格LEP数据的小的Z - Z′混合；到轻子的非常小（小于1%）的分支比；以及Z″和Z′质量之间的大的等级差。更重的中性规范玻色子Z″在大型强子对撞机（LHC）的探测范围内。