Abstract
We revisit the sensitivity to non-resonant, heavy Majorana neutrinos $N$ in same-sign $W^\pm W^\pm$ scattering at the $\sqrt{s}=13$ TeV LHC and its high-luminosity upgrade. As a benchmark scenario, we work in the context of the Phenomenological Type I Seesaw model, relying on a simulation up to next-to-leading order in QCD with parton shower matching. After extensively studying the phenomenology of the $pp\to\mu^\pm\mu^\pm j j$ process at the amplitude and differential levels, we design a simple collider analysis with remarkable signal-background separation power. At 95\% confidence level we find that the squared muon-heavy neutrino mixing element $\vert V_{\mu N} \vert^{2}$ can be probed down to about $0.06-0.3 ~ (0.03-0.1)$ for $m_N = 1-10~{\rm TeV}$ with $\mathcal{L}=300$ fb$^{-1}~(3$ ab$^{-1})$. For heavier masses of $m_N = 20~{\rm TeV}$, we report sensitivity for $\vert V_{\mu N} \vert^{2}\gtrsim 0.5~(0.3)$. The $W^\pm W^\pm$ scattering channel can greatly extend the mass range covered by current LHC searches for heavy Majorana neutrinos and particularly adds invaluable sensitivity above a few hundred GeV. We comment on areas where the analysis can be improved as well as on the applicability to other tests of neutrino mass models.
Highlights
Following the discovery of neutrino oscillations [1,2], uncovering the origin of neutrinos’ tiny masses and their large mixing angles are among the most pressing questions in particle physics today [3,4]
At 95% confidence level we find that the squared muon-heavy neutrino mixing element jVμNj2 can be probed down to about 0.06–0.3(0.03–0.1) for mN 1⁄4 1–10 TeV with L 1⁄4 300 fb−1ð3 ab−1Þ
For the pp → μÆμÆjj collider signature with forward jettagging and simple selection cuts, we find that jVμNj2 ≳ 0.06–0.3ð0.03 − 0.1Þ can be probed at 95% confidence level (C.L.) for mN 1⁄4 1–10 TeV with L 1⁄4 300 fb−1 (3 ab−1)
Summary
Following the discovery of neutrino oscillations [1,2], uncovering the origin of neutrinos’ tiny masses and their large mixing angles are among the most pressing questions in particle physics today [3,4]. Hadron Collider (LHC) are supported by a number of signatures, including searches for dijet resonances [10,11], many-lepton final states [12,13,14,15,16,17], and LN-violating lepton pairs [13,18,19,20], but rely mostly on mechanisms mediated by its quark-antiquark ðqq Þ high center-of-mass aennneihrgilyatiðopnffis[ffiÞ2,1]t.hHe oLwHevCer,isduaelstoo effectively an electroweak (EW) boson collider [22,23,24] This in turn opens a multitude of complementary channels. V we explore extensively the phenomenology of the WÆWÆ → lÆi lÆj signal process at the amplitude and differential levels Technical derivations and details on software modifications are reported in Appendixes A, B, and C
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