Production Of Heavy Neutrinos Research Articles

Hunting for sterile neutrino with future collider signatures

We study the feasibility to observe sterile neutrino at the high energy colliders with direct production channels through e+e−, ep collision, and indirect production channels through decays of heavy meson, baryon and Higgs. For e+e− collision, the e+e−→ν¯eN channel is explored with new signal selection method which tends to be efficient for light mN, the constraints of active-sterile mixing |UeN|2 at the SuperKEKB, CEPC and ILC are expected to reach better lower limits than current experiments. For ep collision, We investigate the heavy sterile neutrino production through a new channel via photon PDF, i.e., e−γ→NW−, hundreds of GeV heavy sterile neutrino can be probe and new limit on mixing is given. For heavy hadrons decay, the lepton-number-violating decays of Λc,Ξc,Ξcc and Λb are explored via an intermediate on-shell Majorana neutrino in GeV scale. The branching fractions and the constraints for |UℓN|2 are given, and hence may put new limits on this mass region. The Higgs→Wμμπ channel is also considered to test massive neutrino within Higgs sector.

Phenomenology of the simplest linear seesaw mechanism

The linear seesaw mechanism provides a simple way to generate neutrino masses. In addition to Standard Model particles, it includes quasi-Dirac leptons as neutrino mass mediators, and a leptophilic scalar doublet seeding small neutrino masses. Here we review its associated physics, including restrictions from theory and phenomenology. The model yields potentially detectable μ → eγ rates as well as distinctive signatures in the production and decay of heavy neutrinos (Ni) and the charged Higgs boson (H±) arising from the second scalar doublet. We have found that production processes such as e+e−→ NN, e−γ → NH− and e+e−→ H+H− followed by the decay chain {H}^{pm}to {ell}_i^{pm }N , Nto {ell}_j^{pm }{W}^{mp } leads to striking lepton number violation signatures at high energies which may probe the Majorana nature of neutrinos.

Probing heavy sterile neutrinos at neutrino telescopes via the dipole portal

The question of how heavy a sterile neutrino can be probed in experiments leads us to investigate the Primakoff production of heavy sterile neutrinos from ultrahigh-energy neutrinos via the magnetic dipole portal. Despite the suppression from the small magnetic moment, the transition is significantly enhanced by tiny t-channel momentum transfers, similar to the resonant production of pions and axions in an external electromagnetic field. Based on the current IceCube measurement of astrophysical neutrinos up to PeV energies, strong constraints can already be derived on the transition magnetic moments of sterile neutrinos up to TeV masses. Moreover, we investigate the sensitivity of future tau neutrino telescopes, which are designed for EeV cosmogenic neutrino detection. We find that sterile neutrino masses as large as 30TeV can be probed at tau neutrino telescopes such as GRAND, POEMMA, and Trinity.

Probing heavy triplet leptons of the type-III seesaw mechanism at future muon colliders

We study the search potential of heavy triplet leptons in a type-III seesaw mechanism at future high-energy and high-luminosity muon colliders. The impact of up-to-date neutrino oscillation results is taken into account on neutrino parameters and the consequent decay patterns of heavy leptons in a type-III seesaw. The three heavy leptons in the Casas-Ibarra parametrization with diagonal unity matrix are distinguishable in their decay modes. We consider the pair production of charged triplet leptons ${E}^{+}{E}^{\ensuremath{-}}$ through both ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ annihilation and vector boson fusion (VBF) processes. The leading-order framework of electroweak parton distribution functions is utilized to calculate the VBF cross sections. The charged triplet leptons can be probed for masses above $\ensuremath{\sim}1\text{ }\text{ }\mathrm{TeV}$. The ${E}^{+}{E}^{\ensuremath{-}}\ensuremath{\rightarrow}ZZ{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ channel can be further utilized to fully reconstruct the three triplet leptons and distinguish neutrino mass patterns. The pair production of heavy neutrinos $N$ and the associated production ${E}^{\ifmmode\pm\else\textpm\fi{}}N$ are only induced by VBF processes and lead to a lepton-number-violating (LNV) signature. We also study the search potential of LNV processes at future high-energy muon colliders with $\sqrt{s}=30\text{ }\text{ }\mathrm{TeV}$.

Heavy neutrinos at the FCC-hh in the U(1)B−L model

We investigate the potential of the 100 TeV future circular collider (FCC-hh) to probe heavy neutrinos. We concentrate in particular on heavy neutrino production via a $U(1)_{B-L}$ $Z'$ gauge boson and contrast the resulting limits with that mediated by Standard Model weak currents. We consider heavy neutrino decays to semi-leptonic as well as fully leptonic final states, particularly with muon flavour, and we show the importance of considering searches both in prompt and displaced decays of the heavy neutrinos. For prompt final states, semi-leptonic modes are more promising due to smaller background and larger yields, and TeV-scale heavy neutrinos with active-sterile mixing compatible with light neutrino mass generation in a seesaw scenario can be probed for a 5 TeV $Z'$ and gauge coupling as low as $g_{B-L} = 10^{-2}$. Displaced vertex searches can extend this range to heavy neutrino masses as low as 10 GeV.

Searching for heavy neutrino in terms of tau lepton at future hadron collider

The tau lepton plays important role in the correlation between the low-energy neutrino oscillation data and the lepton flavor structure in heavy neutrino decay. We investigate the lepton flavor signatures with tau lepton at hadron collider through lepton number violating (LNV) processes. In the Type I Seesaw with U$(1)_{\rm B-L}$ extension, we study the pair production of heavy neutrinos via a $Z'$ resonance. We present a detailed assessment of the search sensitivity to the channels with tau lepton in the subsequent decay of heavy neutrinos. For the benchmark model with $Z'$ only coupled to the third generation fermions, we find that the future circular collider (FCC-hh) can discover the LNV signal with tau lepton for $M_{Z'}$ up to 2.2 (3) TeV with the gauge coupling $g'=0.6$ and the integrated luminosity of 3 (30) ab$^{-1}$. The test on the flavor combinations of SM charged leptons would reveal the specific nature of different heavy neutrinos.

Pair production of heavy neutrinos in next-to-leading order QCD at the hadron colliders in the inverse seesaw framework

The explanation of the small neutrino mass can be depicted using some handsome models like type-I and inverse seesaw where the Standard Model gauge singlet heavy right-handed neutrinos are deployed. The common thing in these two models is a lepton number violating parameter, however, its order of magnitude creates a striking difference between them making the nature of the right-handed heavy neutrinos a major play factor. In the type-I seesaw a large lepton number violating parameter involves the heavy right-handed neutrinos in the form of Majorana fermions while a small lepton number violating parameter being involved in the inverse seesaw demands the pseudo-Dirac nature of the heavy right-handed neutrinos. Such heavy neutrinos are accommodated in these models through the sizable mixings with the Standard Model light neutrinos. In this paper we consider the purely inverse seesaw scenario to study the pair production of the pseudo-Dirac heavy neutrinos followed by their various multilepton decay modes through the leading branching fraction at the leading order and next-to-leading order QCD at the LHC with a center-of-mass energy of 13 TeV and a luminosity of 3000 fb[Formula: see text]. We also consider a prospective 100 TeV hadron collider with luminosities of 3000 fb[Formula: see text] and 30,000 fb[Formula: see text], respectively to study the process. Using anomalous multilepton search performed by the CMS at the 8 TeV with 19.5 fb[Formula: see text] luminosity we show prospective search reaches of the mixing angles for the three lepton and four lepton events at the 13 TeV LHC and 100 TeV hadron collider.

Search for long-lived heavy neutrinos at the LHC with a VBF trigger

The charged current production of long-lived heavy neutrinos at the LHC can use a prompt charged lepton for triggering the measurement of the process. However, in order to fully characterize the heavy neutrino interactions, it is necessary to also probe Higgs or Z mediated neutral current production. In this case the charged lepton is not available, so other means of triggering are required. In this work, we explore the possibility of using a vector boson fusion trigger in the context of a GeV-scale Type I Seesaw model. We consider a minimal model, where both Higgs and Z-mediated contributions produce one heavy neutrino, as well as an extended model where the Higgs can decay into two heavy ones. Both scenarios are tested through displaced dilepton and displaced multitrack jet searches.

Heavy Neutrinos at Large Colliders

In this work we discuss the state of the art of the heavy neutrinos at colliders. The neutrinos in the Standard Model (SM) are considered to be massless which is in contradiction with the evidence from the neutrino oscillations experiments. These cosmological observations established that at least two SM neutrinos have non-zero masses and that individual lepton number is violated. Therefore a strong conclusive first evidence of new physics caused by the neutrino mass mechanism is emerged. In this work we discuss the collider phenomenology of neutrino mass models at the existing (LHC) and next generation large colliders (FCC: ee, hh, eh, ILC and CePC) at different high synergies. It is naturally known that colliders are not sensitive to the SM light neutrinos; however the production of heavy neutrinos is very possible to be detected; giving rise to several signal processes which are categorised by different final state topologies according to theirs physics interests. We will present the state of the art of the heavy neutrinos generated with radiative neutrino mass models and their experimental searches; mainly for Majorana neutrino signals allowing for probing the nature of the Dark Matter candidates at high energy colliders. The focus will be on the well-motivated neutrino mass models which provide an elegant framework to explore new directions in Dark Matter phenomenology at the TeV scale and the future experimental prospects.

Limits on Heavy Neutrinos at NA48/2 and NA62

Large samples of charged kaon decays have been collected by the NA48/2 (2003-2004), the NA62-R[Formula: see text] (2007) and the NA62 (2015) experiments at CERN SPS. This proceedings summarizes upper limits on heavy neutrino production measured by these experiments. The results from the 2015 data analysis at the NA62 experiment are preliminary.

Can we observe the new physics manifestations by the use of ultra-high energy cosmic neutrinos?

Detecting the New physics signals at neutrino telescopes observing ultra high energy cosmic neutrinos is investigated. As an example of the standard model extension the left right symmetric model (LRM) is adopted. The process of the heavy neutrino production in the reactionνe+e−→γ*,W1,2−*,δ˜(−)*→Ne+e−,where W1− is an analog of the SM charged gauge boson, W2− is an additional (compared to the SM) charged gauge boson, and δ˜(−) is a singly charged Higgs boson, is examined. Calculations revealed that the Ne production may be detected by IceCube-Gen2 and ARIANNA only at δ˜(−)-resonance.The processνe+e−→W1−+Z1is considered as well. Analysis demonstrates that again the basic contribution is caused by the diagrams with the virtual δ˜(−) boson in s channel. For example, at mδ˜=173 GeV, the high of the δ˜(−)-resonance peak could reach the value of 90 pb. As a result, detecting the WZ-pair production will be possible only at ARIANNA and it will be confirmation of the existing of the singly charged Higgs boson too.

Production of heavy sterile neutrinos from vector boson decay at electroweak temperatures

In the standard model extended with a seesaw mass matrix, we study the production of sterile neutrinos from the decay of vector bosons at $T\simeq M_{W,Z}$. We derive a general quantum kinetic equation for the production of sterile neutrinos and their effective mixing angles valid in a wide range of temperature, to all orders in interactions of the standard model, and to leading order mixing angle $\theta \ll 1$. Production rates and effective mixing angles depend sensitively on helicity. Positive helicity states interact more weakly with the medium and their effective mixing angle is not modified significantly whereas the mixing angle for negative helicity is strongly suppressed by the medium. If $M_s \lesssim 8.35\,\mathrm{MeV}$, there are fewer states with negative helicity produced than those with positive helicity. There is an MSW resonance in the absence of lepton asymmetry, but is screened by the damping rate, without production enhancement. Negative helicity states freeze-out at $T^-_f\simeq 5\,\mathrm{GeV}$ and positive helicity states freeze-out at $T^+_f \simeq 8\,\mathrm{GeV}$, both distributions are far from thermal. Negative helicity states feature a broader momentum distribution than that for those with positive helicity. Sterile neutrinos produced via vector boson decay do not satisfy the abundance, lifetime and cosmological constraints to be the sole dark matter component in the universe but might solve the $^{7}Li$ problem, albeit at the very edge of the possible parameter space. A heavy sterile neutrino with a mass of a few MeV could decay into light sterile neutrinos, of a few keV in mass, that contribute to warm dark matter. We argue that heavy sterile neutrinos with lifetime $\leq 1/H_0$ reach local thermodynamic equilibrium.

Fully automated precision predictions for heavy neutrino production mechanisms at hadron colliders

Motivated by TeV-scale neutrino mass models, we propose a systematic treatment of heavy neutrino $(N)$ production at hadron colliders. Our simple and efficient modeling of the vector boson fusion (VBF) $W^\pm\gamma\rightarrow N\ell^\pm$ and $N\ell^\pm+nj$ signal definitions resolve collinear and soft divergences that have plagued past studies, and is applicable to other color-singlet processes, e.g., associated Higgs $(W^\pm h)$, sparticle $(\tilde{\ell}^\pm\tilde{\nu_\ell})$, and charged Higgs $(h^{\pm\pm}h^{\mp})$ production. We present, for the first time, a comparison of all leading $N$ production modes, including both gluon fusion (GF) $gg\rightarrow Z^*/h^*\rightarrow N\overset{(-)}{\nu_\ell}$ and VBF. We obtain fully differential results up to next-to-leading order (NLO) in QCD accuracy using a Monte Carlo tool chain linking FeynRules, N{\small LO}CT, and MadGraph5\_aMC@NLO. Associated model files are publicly available. At the 14 TeV LHC, the leading order GF rate is small and comparable to the NLO $N\ell^\pm+1j$ rate; at a future 100 TeV Very Large Hadron Collider, GF dominates for $m_N={300-1500}$ GeV, beyond which VBF takes lead.

Probing the heavy neutrinos of inverse seesaw model at the LHeC

We consider the production of a heavy neutrino and its possible signals at the Large Hadron-electron Collider (LHeC) in the context of an inverse-seesaw model for neutrino mass generation. The inverse seesaw model extends the Standard Model (SM) particle content by adding two neutral singlet fermions for each lepton generation. It is a well motivated model in the context of generating non-zero neutrino masses and mixings. The proposed future LHeC machine presents us with a particularly interesting possibility to probe such extensions of the SM with new leptons due to the presence of an electron beam in the initial state. We show that the LHeC will be able to probe an inverse scenario with much better efficacy compared to the LHC with very nominal integrated luminosities as well as exploit the advantage of having the electron beam polarized to enhance the heavy neutrino production rates.

The case for mixed dark matter from sterile neutrinos

Sterile neutrinos are SU(2) singlets that mix with active neutrinos via a mass matrix, its diagonalization leads to mass eigenstates that couple via standard model vertices. We study the cosmological production of heavy neutrinos via standard model charged and neutral current vertices under a minimal set of assumptions: i) the mass basis contains a hierarchy of heavy neutrinos, ii) these have very small mixing angles with the active (flavor) neutrinos, iii) standard model particles, including light (active-like) neutrinos are in thermal equilibrium. If kinematically allowed, the same weak interaction processes that produce active-like neutrinos also produce the heavier species. We introduce the quantum kinetic equations that describe their production, freeze out and decay and discuss the various processes that lead to their production in a wide range of temperatures assessing their feasibility as dark matter candidates. The final distribution function at freeze-out is a mixture of the result of the various production processes. We identify processes in which finite temperature collective excitations may lead to the production of the heavy species. As a specific example, we consider the production of heavy neutrinos in the mass range Mh ≲ 140 MeV from pion decay shortly after the QCD crossover including finite temperature corrections to the pion form factors and mass. We consider the different decay channels that allow for the production of heavy neutrinos showing that their frozen distribution functions exhibit effects from ``kinematic entanglement'' and argue for their viability as mixed dark matter candidates. We discuss abundance, phase space density and stability constraints and argue that heavy neutrinos with lifetime τ> 1/H0 freeze out of local thermal equilibrium, and conjecture that those with lifetimes τ ≪ 1/H0 may undergo cascade decay into lighter DM candidates and/or inject non-LTE neutrinos into the cosmic neutrino background. We provide a comparison with non-resonant production via active-sterile mixing.

Production of heavy neutrino in next-to-leading order QCD at the LHC and beyond

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 in the context of $100$ TeV hadron collider. The repertoire of the Majorana neutrino is realized through the characteristic signature of the same-sign dilepton pair, whereas, due to a small lepton number violation, the pseudo-Dirac heavy neutrino can manifest the trileptons associated with missing energy in the final state. Using the $\sqrt{s}=8$ TeV, $20.3$ fb$^{-1}$ and $19.7$ fb$^{-1}$ data at the ATLAS and CMS respectively, we obtain prospective scale dependent upper bounds of the light-heavy neutrino mixing angles for the Majorana heavy neutrinos at the $14$ TeV LHC and $100$ TeV collider. Further exploiting a recent study on the anomalous multilepton search by CMS at $\sqrt{s}=8$ TeV with $19.5$ fb$^{-1}$ data, we also obtain the prospective scale dependent upper bounds on the mixing angles for the pseudo-Dirac neutrinos. We thus project a scale dependent prospective reach using the NLO processes at the $14$ TeV LHC.

Higgs production from sterile neutrinos at future lepton colliders

In scenarios with sterile (right-handed) neutrinos that are subject to an approximate "lepton-number-like" symmetry, the heavy neutrinos (i.e. the mass eigenstates) can have masses around the electroweak scale and couple to the Higgs boson with, in principle, unsuppressed Yukawa couplings while accounting for the smallness of the light neutrinos' masses. In these scenarios, the on-shell production of heavy neutrinos and their subsequent decays into a light neutrino and a Higgs boson constitutes a hitherto unstudied resonant contribution to the Higgs production mechanism. We investigate the relevance of this resonant mono-Higgs production mechanism in leptonic collisions, including the present experimental constraints on the neutrino Yukawa couplings, and we determine the sensitivity of future lepton colliders to the heavy neutrinos. With Monte Carlo event sampling and a simulation of the detector response we find that, at future lepton colliders, neutrino Yukawa couplings below the percent level can lead to observable deviations from the SM and, furthermore, the sensitivity improves with higher center-of-mass energies (for identical integrated luminosities).

Improved bounds on the heavy neutrino productions at the LHC

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$^{-1}$ and 19.7 fb$^{-1}$ luminosities, respectively, we obtain direct upper bounds on the light-heavy neutrino mixing angles. For the pseudo-Dirac heavy neutrino production we consider the final sate with tri-lepton plus missing energy as the signal events. Using the recent anomalous multi-lepton search by CMS at $\sqrt{s}=$ 8 TeV with 19.5 fb$^{-1}$ luminosity we obtain upper bounds on the mixing angles. Taking the varieties of initial states into account, the previously obtained upper bounds on the mixing angles have been improved. We scale our results at the 8 TeV LHC to obtain a prospective search reach at the 14 TeV LHC with high luminosities.

Looking for hints of a reconstructible seesaw model at the Large Hadron Collider

We study the production of heavy neutrinos at the Large Hadron Collider (LHC) through the dominant s-channel production mode as well as the vector boson fusion (VBF) process. We consider the TeV scale minimal linear seesaw model containing two heavy singlets with opposite lepton number. This model is fully reconstructible from oscillation data apart from an overall normalization constant which can be constrained from meta-stability of the electroweak vacuum and bounds coming from lepton flavor violation (LFV) searches. Dirac nature of heavy neutrinos in this model implies suppression of the conventional same-sign-dilepton signal at the LHC. We analyze the collider signatures with tri-lepton final state and missing transverse energy as well as VBF type signals which are characterized by two additional forward tagged jets. Our investigation reveals that due to stringent constraints on light-heavy mixing coming from LFV and meta-stability bounds, the model can be explored only for light to moderate mass range of heavy neutrinos. We also note that in case of a positive signal, flavor counting of the final tri-lepton channel can give information about the mass hierarchy of the light neutrinos.

B−Lheavy neutrinos and neutral gauge bosonZ′at the LHC

We explore possible signatures for heavy neutrinos and neutral gauge boson, Z', in TeV scale B-L extension of the Standard Model (BLSM) with inverse seesaw mechanisms at the Large Hadron Collider. We show that due to new decay channels of Z' into heavy/inert neutrinos, the LHC stringent bounds imposed on Z' mass can be significantly relaxed. We analyze the pair production of heavy neutrinos decaying to four leptons plus two neutrinos, four jets plus two leptons, or three leptons plus two jets and one neutrino. We show that the 4l + 2 nu is the most promising decay channel for probing both Z' and heavy neutrinos at the LHC.