Majorana Neutrinos in Same-Sign $W^\pm W^\pm$ Scattering at the LHC: Breaking the TeV Barrier
- Fuks, Benjamin et al
- arXiv:2011.02547CP3-20-50DESY 20-186DESY-20-186MCNet-20-24IFJPAN-IV-2021-2VBSCAN-PUB-11-20
 | Diagrammatic representation of same-sign $\ell_i^+\ell_j^+$ production in same-sign $W^+ W^+$ scattering in $pp$ collisions mediated by a Majorana neutrino $N$. Drawn with \texttt{JaxoDraw}~\cite{Binosi:2008ig}. |
 | Upper: As a function of heavy neutrino mass $m_N$ [GeV], the bare cross section $\sigma/\vert V_{\ell N}V_{\ell N}\vert^2$ [fb] for the $W^\pm W^\pm$ signal process at NLO in QCD (purple band), as well as the bare cross sections $\sigma/\vert V_{\ell N}\vert^2$ for the CCDY (black band) and $W\gamma$ fusion (green band) processes at NLO in QCD. Band thickness corresponds to the residual scale uncertainty. Lower: The QCD $K$-factor for each channel. |
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 | : : Kinematic distributions at $\sqrt{s}=13\TeV$ of the same-sign $W^\pm W^\pm \to \mu^\pm \mu^\pm$ signal process at NLO+PS with residual $\mu_r, \mu_f, \mu_s$ uncertainty envelope (band thickness), for $m_N=750\GeV$ (darkest), $1.5\TeV$ (dark), and $5\TeV$ (light), of the (a,c) leading and (b,d) sub-leading $\mu^\pm$ (a,b) transverse momentum $(p_T)$ and (c,d) pseudorapidity $(\eta)$. |
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 | : : Same as figure \ref{fig:wwScattHeavyN_single_lep} but for the (a,c) leading and (b,d) sub-leading jet. |
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 | : : Same as figure \ref{fig:wwScattHeavyN_single_lep} but for the (a) $p_T$ and (b) $\eta$ of the trailing jet $(j_3)$ at LO+PS. |
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 | : : Same as figure \ref{fig:wwScattHeavyN_single_lep} but for the (a) azimuthal separation of the leading same-sign $\mu^\pm\mu^\pm$ pair $\Delta\varphi(\mu_1,\mu_2)$, (b) missing transverse energy $\met$, (c) invariant mass of the leading dijet system $M(j_1,j_2)$, and (d) pseudorapidity difference of the same system $\Delta\eta(j_1,j_2)$. |
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 | : : Same as figure \ref{fig:wwScattHeavyN_single_lep} but for the (a) scalar sum of all jet $p_T$ $(H_T)$, (b) scalar sum of all visible $p_T$ $(X_T)$, (c) ratio $H_T/p_T^{\mu_1}$, (d) ratio $X_T/p_T^{\mu_1}$. |
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 | : : The distribution for (a) $M(j_1,j_2)$ and (b) $p_T^{\mu_2}$ after pre-selection cuts for the signal process assuming representative heavy neutrino masses $m_N=750\GeV$ (darkest cross), $1.5\TeV$ (dark cross), and $5\TeV$ (light cross). Also shown are the inclusive $W^\pm V$ (light), EW $W^\pm W^\pm jj$ (dark), and QCD $W^\pm W^\pm jj$ (darkest) backgrounds, as well as their sum (black cross). |
 | Expected 95\% CL sensitivity at the $\sqrt{s}=13\TeV$ LHC (300 fb$^{-1}$) and HL-LHC (3 ab$^{-1}$) on the squared active-sterile mixing element $\vert V_{\mu N}\vert^2$ as a function of heavy neutrino mass following the $W^{\pm}W^{\pm}\to\mu^\pm\mu^\pm$ analysis described in the text. Also shown are the direct limits $(35.9\invfb)$ set by CMS using the CCDY and $W\gamma$ fusion channels~\cite{Sirunyan:2018mtv}, an extrapolation of the CMS to the HL-LHC, and indirect limits~\cite{Fernandez-Martinez:2016lgt}. |