First results on bilepton production based on LHC collision data and predictions for run II

The LHC potential for discovering doubly charged vector bileptons is investigated considering the measurable process $pp\to {\mu }^{+}{\mu }^{+}{\mu }^{-}{\mu }^{-}X$. The study is performed assuming different bilepton and leptoquark masses. The process cross section is calculated at leading order using the Calchep package. Combining the calculation with the latest ATLAS experiment results at a center-of-mass energy of 7 TeV, bounds on bilepton masses based on LHC data are derived for the first time. The results exclude bilepton masses in the range of 250 GeV to 500 GeV at 95% C.L., depending on the leptoquark mass. Moreover, minimal LHC integrated luminosities needed for discovering and for setting limits on bilepton masses are obtained for 13 TeV center-of-mass energy. Simulated events are passed through a fast parametric detector simulation using the Delphes package.

Figure 1

Feynman diagrams contributing to bilepton pair production at the LHC.

Figure 2

Upper limits on $\sigma \times Br$. The black solid and dashed lines represent the ATLAS observed and expected limits, respectively. The blue, green, and red lines are the cross section times branching ratio for bilepton production decaying into muons for different values of the leptoquark mass.

Figure 3

Exclusion region on the $M_Y\times M_Q$ plane.

Figure 4

Bilepton width as a function of bilepton mass for three different leptoquark masses.

Figure 5

Cross section for bilepton production at 13 TeV.

Figure 6

Invariant mass distributions for same-sign muon pairs produced by the background and by bilepton decay, assuming an integrated luminosity of $50{\mathrm{fb}}^{-1}$. The open red/blue histograms are two possible positively charged bilepton signals.

Figure 7

Same as Fig. 6, but for negatively charged bileptons.

Figure 8

Minimal integrated luminosity needed for a $5\sigma$ discovery of doubly charged vector bileptons in the four-muon final state.

Figure 9

Upper limits on $\sigma \times Br$, assuming $50{\mathrm{fb}}^{-1}$ of data at 13 TeV.

Figure 10

Minimal integrated luminosity needed to exclude bileptons of a given mass, for three different leptoquark masses.