Search for anomalous production of prompt same-sign lepton pairs and pair-produced doubly charged Higgs bosons with $\sqrt{s} = 8$ TeV $pp$ collisions using the ATLAS detector

The ATLAS collaboration
JHEP 03 (2015) 041, 2015.

Abstract (data abstract)
CERN-LHC. A low-background inclusive search for new physics in events with same-sign dileptons is presented. The search uses proton-proton collisions corresponding to 20.3 fb$^{-1}$ of integrated luminosity taken in 2012 at a centre-of-mass energy of 8 TeV with the ATLAS detector at the LHC. Pairs of isolated leptons with the same electric charge and large transverse momenta of the type $e^{\pm}e^{\pm}, e^{\pm}\mu^{\pm}$, and $\mu^{\pm}\mu^{\pm}$ are selected and their invariant mass distribution is examined. No excess of events above the expected level of Standard Model background is found. The results are used to set upper limits on the cross sections for processes beyond the Standard Model. Limits are placed as a function of the dilepton invariant mass within a fiducial region corresponding to the signal event selection criteria. Exclusion limits are also derived for a specific model of doubly charged Higgs boson production. The fiducial region in this analysis is defined as - 2e, 2mu or emu - both leptons have the same charge - ptLepton(leading) > 25 GeV; ptLepton(subleading) > 20 GeV - |etaLepton|<2.5 for muons; |etaLepton|<1.37 or 1.52 < |etaLepton| < 2.47 for electrons - Sum pt of charged tracks in DeltaR=0.3 / ptLepton < 0.07 for muons; Sum pt of charged tracks in DeltaR=0.3 / ptLepton < 0.1 for electrons; - same-sign lepton pari with mll > 15 GeV - mll excluded between 70 and 110 GeV for electrons - no opposite-sign same-flavour pair with |mll-mZ| < 10 GeV To measure the fiducial efficiencies MC events are taken from the following processes - doubly-charged Higgs (pair produced) with masses between 100 GeV and 1 TeV - diquark (S$_{DQ}$) production with charge $\pm$ 2/3 or $\pm$ 4/3 in the Zee-Babu mode, which decay into 2 same-sign leptoquarks (S$_{LQ}$), decaying subsequently into a same-sign lepton pair. diquark masses between 2.5 TeV and 3.5 TeV and leptoquark masses between 1 TeV and 1.4 TeV are considered. - Right-handed W$_R$ bosons decaying into a lepton and a Majorana neutrino N$_R$, with N$_R$ subsequently decaying into a lepton and two jets, for W$_R$ masses between 1 TeV and 2 TeV, and N$_R$ masses between 250 GeV and 1.5 TeV. - Pair production of $b\prime$ chiral quarks, decaying either exclusively into Wt or decaying into Wq, q being an up-type quark, with a 33% branching ratio in each quark channel, for $b\prime$ masses between 400 GeV and 1 TeV. The lowest fiducial efficiency, which is subsequently used in the limits, is 48%, 50% and 46% in the $e^{\pm}e^{\pm}, e^{\pm}\mu^{\pm}$ and $\mu^{\pm}\mu^{\pm}$ channel respectively.

  • Table 1

    Data from Table 5


    Expected and observed numbers of isolated same-sign lepton pairs in the $e^{\pm}e^{\pm}, e^{\pm}\mu^{\pm}$ and $\mu^{\pm}\mu^{\pm}$ channel for various cuts on...

  • Table 2

    Data from Table 6


    Expected and observed numbers of positively or negatively charged lepton pairs for various cuts on the dilepton invariant mass, $m(\ell...

  • Table 3

    Data from Table 8


    Upper limit at 95% CL on the fiducial cross section for $\ell^{\pm} \ell^{\pm}$ pairs from non-SM signals. The expected limits...

  • Table 4

    Data from Table 9


    Lower limits at 95% CL on the mass of $H_{\mathrm{L}}^{\pm \pm}$ and $H_{\mathrm{R}}^{\pm \pm}$ bosons, assuming a 100% branching ratio...

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