Majorana Neutrinos in Same-Sign $W^\pm W^\pm$ Scattering at the LHC: Breaking the TeV Barrier
Benjamin Fuks, Jonas Neundorf, Krisztian Peters, Richard Ruiz, Matthias Saimpert
备注：
Journal version: results unchanged, only minor revisions w.r.t. v1. 31 pages (including three appendices), nine figures (23 png and pdf files), eight tables
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 $pp\toμ^\pmμ^\pm j j$ 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 $\vert V_{μN} \vert^{2}$ 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 $\vert V_{μN} \vert^{2}\gtrsim 0.5~(0.3)$. 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.
Production of heavy Majorana neutrino $N_{e}$ predicted by left-right symmetric extension of the Standard Model at future {\normalsize TeV} scale $ep$ colliders have been considered. In order to estimate potential of $ep$ colliders for $N_{e}$ search we consider back-groundless process $e^{-}p\rightarrow e^{+}X$ which is consequence of Majorana nature of $N_{e}$. It is shown that {\normalsize linac-LHC} and {\normalsize linac-FCC} based $ep$ colliders will cover much wider regions of $N_{e}$ and $W_{R}$ masses than corresponding linear electron-positron colliders.
Vector boson fusion processes become increasingly more important at higher collider energies and for probing larger mass scales due to collinear logarithmic enhancements of the cross section. In this context, we revisit the production of a hypothetic heavy Majorana neutrino $(N)$ at hadron colliders. Particular attention is paid to the fusion process $Wγ\rightarrow N\ell^{\pm}$. We systematically categorize the contributions from an initial state photon in the elastic, inelastic, and deeply inelastic channels. Comparing with the leading channel via the Drell-Yan production $q \bar{q}'\rightarr…
We compare the prospects for observing theories with Majorana or Dirac gauginos at a future 100 TeV proton-proton collider. Calculating the expected discovery and exclusion regions, we find that for heavy gluino masses the squark discovery reach is significantly reduced in Dirac gluino models relative to the Majorana case. However, if the squark and gluino masses are close the reach is similar in both scenarios. We also consider the electroweak fine tuning of theories observable at such a collider, and the impact of existing constraints from flavour and CP violating observables. Models with Ma…
Majorana and pseudo-Dirac heavy neutrinos are introduced into the type-I and inverse seesaw models, respectively, in explaining the naturally small neutrino mass. TeV scale heavy neutrinos can also be accommodated to have a sizable mixing with the Standard Model light neutrinos, through which they can be produced and detected at the high energy colliders. In this paper we consider the Next-to-Leading Order QCD corrections to the heavy neutrino production, and study the scale variation in cross-sections as well as the kinematic distributions with different final states at $14$ TeV LHC and also …
Dirac Vs. Majorana Neutrino Masses From a TeV Interval
我们研究了在[0，πR]区间内紧致化的超对称五维模型中左手中微子质量的性质（Dirac vs. Majorana）和大小，其中夸克和轻子局域在边界上，而规范和希格斯扇区在第五维的大部分中传播.超对称性被Scherk-Schwarz边界条件破缺，电弱破缺通过辐射修正进行。右手中微子在体中传播，并具有一般的五维质量M，它将零模定位在其中一个边界和任意边界项上。我们发现，对于一般边界项，左手中微子具有马约拉纳质量。然而，对于特定的边界配置，左手中微子是狄拉克费米子，因为理论具有守恒的整体U（1）对称性，这防止了轻子数的破坏。中微子质量的大小取决于右手中微子零模的局域化和/或五维中微子汤川耦合的大小。亚电子伏特范围内的左手中微子需要MR~10或汤川耦合~10^{-3}R，这使得五维理论在自然截止之前是微扰的。
Heavy sterile neutrinos with masses below $M_W$ can induce trilepton events at the 14 TeV LHC through purely leptonic $W$ decays of $W^\pm \to e^\pm e^\pm μ^\mp ν$ and $μ^\pm μ^\pm e^\mp ν$ where the heavy neutrino will be in an intermediate state on its mass shell. Discovery and exclusion limits for the heavy neutrinos are found using both Cut-and-Count (CC) and a Multi-Variate Analysis (MVA) methods in this study. We also show that it is possible to discriminate between a Dirac and a Majorana heavy neutrino, even when lepton number conservation cannot be directly tested due to unobservabilit…
Models beyond the Standard Model have been proposed to simultaneously solve the problems of naturalness and neutrino mass, in which heavy Majorana neutrinos and vector-like top partners are usually predicted. A new decay channel of the top partner mediated by the heavy Majorana neutrino can thus appear: $T\to b\,W^{+}\to b\,\ell^{+}\ell^{+}q\bar{q'}$. We study in this paper the observability of this decay process through single production of the top partner at the 14 TeV LHC: $pp\to T/\bar{T}$+jets$\to b/\bar{b}+μ^{\pm}μ^{\pm}$+jets. $2σ$ exclusion bounds on the top partner mass and mixing par…
We discuss an alternative for Baryon-violating six quarks transitions, in the contest of low scale string theory. In particular, with $M_{S}=10÷10^{3}\rm TeV$, such a transition can be mediated by two color-triplets,through a quartic coupling with down-quarks,generated by exotic instantons, in a calculable and controllable way. We show how FCNCs limits on color-triplet massare well compatible with $n-\bar{n}$ oscillation ones. If a $n-\bar{n}$ transition were found, this would be an indirect hint for our model. This would strongly motivate researches of direct channels in proton-proton collide…
As the planning stages for a high energy muon collider enter a more concrete era, an important question arises as to what new physics could be uncovered. A TeV-scale muon collider is also a vector boson fusion (VBF) factory with a very clean background, and as such it is a promising environment to look for new physics that couples to the electroweak (EW) sector. In this paper, we explore the ability of a future TeV-scale muon collider to search for Majorana and Dirac Heavy Neutral Leptons (HNLs) produced via EW bosons. Employing a model-independent, conservative approach, we present an estimat…
Observation of lepton number ($L$) violation by two units at colliders would provide evidence for the Majorana nature of neutrinos. We study signals of $L$-violation in the context of two popular models of neutrino masses, the type-II seesaw model and the Zee model, wherein small neutrino masses arise at the tree-level and one-loop level, respectively. We focus on $L$-violation signals at the LHC arising through the process $pp \to \ell^{\pm}\ell^{\prime \pm}$ + jets within these frameworks. We obtain sensitivity to $L$-violation in the type-II seesaw model for triplet scalar masses up to 700 …
The ATLAS collaboration has recently reported excesses about 2.5 sigma at mass around 2 TeV in the diboson channels, which can be identified with new vector bosons as a hint for the new physics. It is shown that spontaneously broken conformal/scale symmetry prohibits new vector bosons decay to the Higgs, which is contrasted to the popular "equivalence theorem" valid only in a special limit not necessarily relevant to the 2 TeV mass. If the decay $V\to WH/ZH$ is not observed in the ongoing Run II of the LHC, then the 125 GeV Higgs can be a dilaton.
The CMS $e^+ e^- jj$ events of invariant mass near 2 TeV are consistent with a $W'$ boson decaying into an electron and a right-handed neutrino whose TeV-scale mass is of the Dirac type. We show that the Dirac partner of the right-handed electron-neutrino can be the right-handed tau-neutrino. A prediction of this model is that the sum of the $τ^+ e^+ jj$ and $τ^- e^- jj$ signal cross sections equals twice that for $e^+ e^- jj$. The Standard Model neutrinos acquire Majorana masses and mixings compatible with neutrino oscillation data.
The neutrino masses and flavor mixings, which are missing in the Standard Model (SM), can be naturally incorporated in the type-I seesaw extension of the SM with heavy Majorana neutrinos being singlet under the SM gauge group. If the heavy Majorana neutrinos are around the electroweak scale and their mixings with the SM neutrinos are sizable, they can be produced at high energy colliders, leaving characteristic signatures with lepton-number violations. Employing the general parametrization for the neutrino Dirac mass matrix in the minimal seesaw scenario, we perform a parameter scan and identi…
We investigate the search for heavy Majorana neutrinos stemming from a composite model scenario at the upcoming LHC Run II at a center of mass energy of 13 TeV. While previous studies of the composite Majorana neutrino were focussed on gauge interactions via magnetic type transition coupling between ordinary and heavy fermions (with mass $m^*$) here we complement the composite model with contact interactions at the energy scale $Λ$ and we find that the production cross sections are dominated by such contact interactions by roughly two/three orders of magnitude. This mechanism provides therefor…
The Majorana neutrino in type-I seesaw and the pseudo-Dirac neutrinos in the inverse seesaw can have sizable mixings with the light neutrinos in the standard model (SM), through which the heavy neutrinos can be produced at the Large Hadron Collider (LHC). In producing the heavy neutrinos we study a variety of initial states such as quark-quark, quark-gluon and gluon-gluon as well as photon mediated processes. For the Majorana heavy neutrino production we consider same-sign di-lepton plus di-jet as the signal events. Using the recent ATLAS and CMS data at $\sqrt{s}=$ 8 TeV with 20.3 fb$^{-1}$ a…
We consider a TeV scale resonant lepogenesis within type-I seesaw mechanism. We show that a concrete model based on $A_4$ flavor symmetry with a scaling ansatz in the neutrino Dirac mass matrix and a retro-circulant heavy Majorana mass matrix can be realized. The full Yukawa coupling matrix $Y_ν$ can be fully reconstructed from the low energy neutrino oscillations data and the quasi-degenerate heavy Majorara neutrino masses. We have carried out a detailed numerical analysis to constrain the Dirac neutrino mass matrix elements. In particular, it was found that its diagonal elements lie near or …
