Search for Vector-mediated Dark Matter at the LHC with Proton Tagging.

We investigate production of fermionic dark matter $\chi$ via $pp \to p\gamma p \to p j \chi \bar{\chi}X$ mediated by a leptophobic spin-1 particle, where one of the protons remains intact and is tagged by forward detectors. We find that the masses of $\chi$ and $Y$ are severely constrained when $Y$ interacts with $\chi$ and quarks through the vector couplings. We show that the dark matter search in this production channel has sensitivity for the mediator mass $m_Y \lesssim 1.4~\mathrm{TeV}$ at the 14 TeV LHC with the integrated luminosity $L_{\rm{int}} = 3000~$$\rm{fb}^{-1}$. The lower mass bound on the dark matter is $m_\chi \gtrsim 550~\mathrm{GeV}$ at the mediator mass $m_Y=1.2~\mathrm{TeV}$.