“School of Particles And Accelerator”
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Paper IPM / Particles And Accelerator / 15750  


Abstract:  
In this paper, we explore the constraints that the LHC can place on a massive gauge boson $X$ that predominantly couples to the third generation of fermions. Such a gauge boson arises in scenarios where the $BL$ of the third generation is gauged. We focus on the mass range $10 \leq \mx \lesssim 2\,m_W$, where current constraints are lacking, and develop a dedicated search strategy. For this mass range, we show that $b \bar b \tau^+ \tau^$, where at least one of the $\tau$s decay leptonically is the optimal channel to look for the $X$ at the LHC. The QCD production of $b$ quarks, combined with the cleanliness of the leptons coming from the decay of the $\tau$ allow us to detect $X$ gauge boson with couplings of $\gx \sim(0.0050.01)$, for $\mx < 50 \gev$, and a coupling of $O(0.1)$ for heavier $X$ gauge boson with $100 \fb^{1}$ of integrated luminosity. This is about a factor of 210 improvement over previous constraints coming from the decay of $\Upsilon \to \tau^+ \tau^$. Extrapolating to the full HLLHC luminosity of $3000 \fb^{1}$, the bounds on $\gx$ can be enhanced by another factor of $\sqrt{2}$ for $\mx < 50 \gev$.
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