Displaced Vertex Signatures Research Articles

Density dependent displaced vertex signatures as a novel probe of light dark sector scalars at the LHC

Dynamical theories of dark energy predict new degrees of freedom with particular environmental sensitivity to avoid constraints on fifth forces. We show that the similar, yet complementary multi-purpose detector setup of the ATLASand CMS experiments provides a unique opportunity to place sensitivity on such scenarios in a narrow, yet relevant parameter range. Furthermore, our investigation gives rise to a novel phenomenological signature that the LHC experimentscan pursue to exploit their complementary detector design from a BSM perspective.

Long-lived heavy neutral leptons at lepton colliders as a probe of left-right-symmetric models

Left-right symmetric models (LRSM) were proposed to reconcile the apparent parity violation in weak interactions with our intrinsic notion of fundamental parity symmetry. It was quickly realized that LRSM offers a viable framework for explaining neutrino masses by incorporating right-handed neutrinos, N, into its spectrum. In this study, we investigate for the first time the potential of future lepton colliders (including the FCC-ee, CEPC, ILC, CLIC, and a muon collider) to detect signals stemming from N’s, focusing primarily on displaced vertex signals, and on prompt signals to a lesser degree. Our results demonstrate that these signals can effectively probe the characteristic scales of LRSM, providing evidence that would be unobtainable through any other experimental means. Published by the American Physical Society 2024

Jet substructure probe to unfold singlet-doublet dark matter in the presence of non-standard cosmology

We examine the singlet-doublet fermionic dark matter model, where the non-thermal production of the dark matter in light of a non-standard cosmology demands a significantly large interaction rate than the typical radiation-dominated Universe. Despite being a model of freeze-in light dark matter and heavy mediator, the characteristic long-lived particle searches at the collider experiment and the displaced vertex signature do not help in probing such a dark sector since this non-standard interaction mandates nearly prompt decay. We make a counterproposal to probe such signal with di-fat-jets generated from the boosted decays of massive vector bosons and Standard Model Higgs, along with the substantial missing transverse momentum to probe the dark matter at LHC. Interestingly, substructure variables associated with these fat jets have an additional handle to tackle the extensive QCD background as it encodes implicit footmarks of their origin. We adopt the multivariate analysis with the booted decision tree to constrain the measured relic density allowed parameter space of dark matter in the presence of the modified cosmological scenario. Our study shows how the non-trivial expansion affects dark matter production in the early Universe and alters the required search strategies at colliders. This probe provides the best discovery prospect at the HL-LHC for extended parameter space now opened up in the dark sector.

A combined approach to the analysis of space and ground experimental data within a simplified E_6SSM

Within the Exceptional Supersymmetric Standard Model (E_6SSM), we investigate signatures at the Large Hadron Collider (LHC) for a long-lived charged inert higgsino, which is degenerate with the inert neutralino at tree level and a small mass splitting is generated at the loop level, resulting in a lifetime mathcal{O}(0.02) nanoseconds. We focus on the most sensitive search for long-lived charged inert higgsino decays to the lightest neutral inert higgsino dark matter and very soft charged leptons, which are eventually stopped in the detector resulting in a disappearing-track signal. Furthermore, we study the displaced vertex signature of the inert chargino in the case where it is produced via the Z^{prime } portal. We illustrate how difficult it is to construct displaced vertices in this class of models, though some evidence could be gained at the High Luminosity LHC. Finally, we compare the spin independent and spin dependent cross sections of the lightest inert higgsino DM to those of current direct detection experiments, proving that it is possible to gain sensitivity to the active DM component of this scenario in the near future. The combination of these signatures with the one emerging from Z' production and decay via Drell–Yan, which can be characterised as belonging to the E_6SSM via both the cross section and Forward–Backward Asymmetry, could point uniquely to this non-minimal realisation of Supersymmetry.

Displaced vertex and disappearing track signatures in type-III seesaw

We investigate a prospect of probing the type-III seesaw neutrino mass generation mechanism at various collider experiments by searching for a disappearing track and a displaced vertex signature originating from the decay of SU(2)_L triplet fermion (Sigma ). Since Sigma is primarily produced at colliders through the electroweak gauge interactions, its production rate is uniquely determined by its mass. We find that a Sigma particle produces a disappearing track signature from the decay of its charged component, which can be searched at the HL-LHC. Furthermore, we show that if the lightest observed neutrino has a mass of around 10^{-9} eV, the neutral component of {Sigma } can be discovered at the proposed MATHUSLA detector. We also show that the charged component of {Sigma } can be potentially be observed at FCC-he as a displaced vertex signature.

Self-interacting freeze-in dark matter in a singlet doublet scenario

We examine the non-thermal production of dark matter in a scalar extended singlet doublet fermion model where the lightest admixture of the fermions constitutes a suitable dark matter candidate. The dark sector is non-minimal with the MeV scale singlet scalar, which is stable in the Universe lifetime and can mediate the self-interaction for the multi-GeV fermion dark matter mitigating the small scale structure anomalies of the Universe. If the dark sector is strongly coupled to yield a velocity dependent large self-interaction cross section, it undergoes internal dark thermal equilibrium after freeze-in production. We essentially end up with suppressed relic abundance for the fermion dark matter in a traditional radiation dominated Universe. In contrast, the presence of a modified cosmological phase in the early era drives the fermion dark matter to satisfy nearly the whole amount of observed relic. It also turns out that the assumption of an unconventional cosmological history can allow the GeV scale dark matter to be probed at LHC from displaced vertex signature with improved sensitivity.

Long-lived sterile neutrinos at Belle II in effective field theory

Large numbers of τ leptons are produced at Belle II. These could potentially decay into sterile neutrinos that, for the mass range under consideration, are typically long-lived, leading to displaced-vertex signatures. Here, we study a displaced-vertex search in the context of the sterile-neutrino-extended Standard Model Effective Field Theory. The production and decay of the sterile neutrinos can be realized via either the standard active-sterile neutrino mixing or higher-dimensional operators in the effective Lagrangian. We perform Monte-Carlo simulations to estimate the Belle II sensitivities to such interactions. We find that Belle II can probe non-renormalizable dimension-six operators involving a single sterile neutrino up to a few TeV in the new-physics scale.

LHC signatures of sterile neutrinos in a minimal radiative extended seesaw framework

The presence of small neutrino masses and flavour mixings can be accounted for naturally in various models about extensions of the standard model, particularly in the seesaw mechanism models. In this work, we present a minimally extended seesaw framework with two right-handed neutrinos, where the active neutrino masses are derived in the radiative regime. Using the framework it can be shown that within certain mass limits, the light neutrino mass term can approach a form that is similar to its form under type-I seesaw mechanism. Apart from this, we show that the decay width of right-handed neutrinos (produced through the decay of [Formula: see text] boson in a particle collider) is short enough to cause a sufficiently long lifetime for the particles, thus ensuring an observable displacement in the LHC between the production and decay vertices. We comment on the fact that these displaced vertex signatures thus can serve as a means to verify the existence of these right-handed neutrinos in future experiments. Lastly, we line up the possibility of our future work where the vertex signatures of particles greater than the mass of [Formula: see text] boson can be worked upon.

Exploring properties of long-lived particles in inelastic dark matter models at Belle II

The inelastic dark matter model is one kind of popular models for the light dark matter (DM) below O(1) GeV. If the mass splitting between DM excited and ground states is small enough, the co-annihilation becomes the dominant channel for thermal relic density and the DM excited state can be long-lived at the collider scale. We study scalar and fermion inelastic dark matter models for mathcal{O} (1) GeV DM at Belle II with U(1)D dark gauge symmetry broken into its Z2 subgroup. We focus on dilepton displaced vertex signatures from decays of the DM excited state. With the help of precise displaced vertex detection ability at Belle II, we can explore the DM spin, mass and mass splitting between DM excited and ground states. Especially, we show scalar and fermion DM candidates can be discriminated and the mass and mass splitting of DM sector can be determined within the percentage of deviation for some benchmark points. Furthermore, the allowed parameter space to explain the excess of muon (g− 2)μ is also studied and it can be covered in our displaced vertex analysis during the early stage of Belle II experiment.

Exploring color-octet scalar parameter space in minimal R-symmetric models

In this work we study the collider phenomenology of color-octet scalars (sgluons) in minimal supersymmetric models endowed with a global continuous R symmetry. We systematically catalog the significant decay channels of scalar and pseudoscalar sgluons and identify novel features that are natural in these models. These include decays in nonstandard diboson channels, such as to a gluon and a photon; three-body decays with considerable branching fractions; and long-lived particles with displaced vertex signatures. We also discuss the single and pair production of these particles and show that they can evade existing constraints from the Large Hadron Collider, to varying extents, in large regions of reasonable parameter space. We find, for instance, that a 725 GeV scalar and a 350 GeV or lighter pseudoscalar can still be accommodated in realistic scenarios.

Lepton-trijet and displaced vertex searches for heavy neutrinos at future electron-proton colliders

Electron proton (ep) colliders could provide particle collisions at TeV energies with large data rates while maintaining the clean and pile up-free environment of lepton colliders, which makes them very attractive for heavy neutrino searches. Heavy (mainly sterile) neutrinos with masses around the electroweak scale are proposed in low scale seesaw models for neutrino mass generation. In this paper, we analyse two of the most promising signatures of heavy neutrinos at ep colliders, the lepton-flavour violating (LFV) lepton-trijet signature and the displaced vertex signature. In the considered benchmark model, we find that for heavy neutrino masses around a few hundred GeV, the LFV lepton-trijet signature at ep colliders yields the best sensitivity of all currently discussed heavy neutrino signatures (analysed at the reconstructed level) up to now.

Probing long-lived particles at Higgs factories

We study displaced vertex signatures of long-lived particles (LLPs) from exotic Higgs decays in the context of a Higgs-portal model and a neutral-naturalness model at the circular electron positron collider (CEPC) and future circular collider ${e}^{+}\text{ }{e}^{\ensuremath{-}}$ (FCC-ee). Such two models feature two representative mass ranges for LLPs, which show very different behavior in their decay signatures. The Higgs-portal model contains a very light sub-GeV scalar boson stemming from a singlet scalar field appended to the Standard Model. Such a light scalar LLP decays into a pair of muons or pions, giving rise to a distinctive signature of collimated muon-jet or pion-jet, thanks to the sub-GeV mass. On the other hand, the neutral-naturalness model, e.g., folded supersymmetry, predicts the lightest mirror glueball of mass $O(10)\text{ }\text{ }\mathrm{GeV}$, giving rise to long decays with a large transverse impact parameter because of the relatively large mass. Utilizing such distinct characteristics to remove the background, we estimate the sensitivities of searches for light scalar bosons and mirror glueballs at the CEPC and FCC-ee. We find either complementary or stronger coverage compared to the previous results in the similar contexts.

Displaced heavy neutrinos from Z\u2032 decays at the LHC

We study the LHC sensitivity to probe a long-lived heavy neutrino N in the context of Z′ models. We focus on displaced vertex signatures of N when pair produced via a Z′, decaying to leptons and jets inside the inner trackers of the LHC experiments. We explore the LHC reach with current long-lived particle search strategies for either one or two displaced vertices in association with hadronic tracks or jets. We focus on two well-motivated models, namely, the minimal U(1)B−L scenario and its U(1)X extension. We find that searches for at least one displaced vertex can cover a significant portion of the parameter space, with light-heavy neutrino mixings as low as |VlN|2≈ 10−17, and l = e, μ accessible across GeV scale heavy neutrino masses.

Right-handed neutrino dark matter with radiative neutrino mass in gauged B − L model

We study the possibility of right-handed neutrino dark matter (DM) in gauged U(1)B−L×Z2 extension of the standard model augmented by an additional scalar doublet, being odd under the Z2 symmetry, to give rise the scotogenic scenario of radiative neutrino masses. Due to lepton portal interactions, the right-handed neutrino DM can have additional co-annihilation channels apart from the usual annihilations through ZB−L which give rise to much more allowed mass of DM from relic abundance criteria, even away from the resonance region like MDM≈MZB−L/2. This enlarged parameter space is found to be consistent with neutrino mass constraints while being sensitive to direct detection experiments of DM as well as rare decay experiments looking for charged lepton flavour violating decays like μ→eγ. Due to the possibility of the Z2 odd scalar doublet being the next to lightest stable particle that can be sufficiently produced in colliders by virtue of its gauge interactions, one can have interesting signatures like displaced vertex or disappearing charged tracks provided that the mass splitting δM between DM and the next to lightest stable particle (NLSP) is small. In particular, if δM<mτ=1.77 GeV, then we get large displaced vertex signature of NLSP while being consistent with neutrino mass, lepton flavour violation and observed relic density.

Long-lived TeV-scale right-handed neutrino production at the LHC in gauged U(1)X model

A gauged U(1)X extension of the Standard Model is a simple and consistent framework to naturally incorporate three right-handed neutrinos (RHNs) for generating the observed light neutrino masses and mixing by the type-I seesaw mechanism. We examine the collider testability of the U(1)X model, both in its minimal form with the conventional charges, as well as with an alternative charge assignment, via the resonant production of the U(1)X gauge boson (Z′) and its subsequent decay into a pair of RHNs. We first derive an updated upper limit on the new gauge coupling gX as a function of the Z′-boson mass from the latest LHC dilepton searches. Then we identify the maximum possible cross section for the RHN pair-production under these constraints. Finally, we investigate the possibility of having one of the RHNs long-lived, even for a TeV-scale mass. Employing the general parametrization for the light neutrino mass matrix to reproduce the observed neutrino oscillation data, we perform a parameter scan and find a simple formula for the maximum RHN lifetime as a function of the lightest neutrino mass eigenvalue (mlightest). We find that for mlightest≲10−5 eV, one of the RHNs in the minimal U(1)X scenario can be long-lived with a displaced-vertex signature which can be searched for at the LHC and/or with a dedicated long-lived particle detector, such as MATHUSLA. In other words, once a long-lived RHN is observed, we can set an upper bound on the lightest neutrino mass in this model.

Discovering the twin Higgs boson with displaced decays

The Twin Higgs mechanism keeps the scalar sector of the Standard Model (SM) natural while remaining consistent with the non-observation of new colored particles at the Large Hadron Collider (LHC). In this construction the heavy twin Higgs boson provides a portal between the SM particles and the twin sector, but is quite challenging to discover at colliders. In the Fraternal Twin Higgs setup, where light twin quarks are absent, we study a novel discovery channel for the heavy twin Higgs boson by considering its decay to a pair of light Higgs bosons, one of which subsequently decays to glueball states in the twin sector, leading to displaced vertex signatures. We estimate the sensitivity of existing LHC searches in this channel, and assess the discovery potential of the high luminosity (HL) LHC. We show that the glueballs probed by these searches are outside the sensitivity of existing searches for exotic decays of the light Higgs boson. In addition, we demonstrate that the displaced signals we consider probe a region of heavy Higgs masses beyond the reach of prompt signals. We also comment on the possibility of probing the input parameters of the microscopic physics and providing a way to test the Twin Higgs mechanism with this channel.

Low scale type II seesaw: present constraints and prospects for displaced vertex searches

The type II seesaw mechanism is an attractive way to generate the observed light neutrino masses. It postulates a SU(2)L-triplet scalar field, which develops an induced vacuum expectation value after electroweak symmetry breaking, giving masses to the neutrinos via its couplings to the lepton SU(2)L-doublets. When the components of the triplet field have masses around the electroweak scale, the model features a rich phenomenology. We discuss the currently allowed parameter space of the minimal low scale type II seesaw model, taking into account all relevant constraints, including charged lepton flavour violation as well as collider searches. We point out that the symmetry protected low scale type II seesaw scenario, where an approximate “lepton number”-like symmetry suppresses the Yukawa couplings of the triplet to the lepton doublets, is still largely untested by the current LHC results. In part of this parameter space the triplet components can be long-lived, potentially leading to a characteristic displaced vertex signature where the doubly-charged component decays into same-sign charged leptons. By performing a detailed analysis at the reconstructed level we find that already at the current run of the LHC a discovery would be possible for the considered parameter point, via dedicated searches for displaced vertex signatures. The discovery prospects are further improved at the HL-LHC and the FCC-hh/SppC.

Inclusive displaced vertex searches for heavy neutral leptons at the LHC

The inclusion of heavy neutral leptons to the Standard Model particle content could provide solutions to many open questions in particle physics and cosmology. The modification of the charged and neutral currents from active-sterile mixing of neutral leptons can provide novel signatures in Standard Model processes. We revisit the displaced vertex signature that could occur in collisions at the LHC via the decay of heavy neutral leptons with masses of a few GeV emphasizing the implications of flavor, kinematics, inclusive production and number of these extra neutral fermions. We study in particular the implication on the parameter space sensitivity when all mixings to active flavors are taken into account. We also discuss alternative cases where the new particles are produced in a boosted regime.

Long-lived B−L symmetric SSM particles at the LHC

We investigate the collider signatures of neutral and charged long-lived particles (LLPs), predicted by the supersymmetric $B\ensuremath{-}L$ extension of the Standard Model (BLSSM), at the Large Hadron Collider (LHC). The BLSSM is a natural extension of the minimal supersymmetric Standard Model (MSSM) that can account for nonvanishing neutrino masses. We show that the lightest right-handed sneutrino can be the lightest supersymmetric particle (LSP), while the next-to-the LSP (NLSP) is either the lightest left-handed sneutrino or the left-handed stau, which are natural candidates for the LLPs. We analyze the displaced vertex signature of the neutral LLP (the lightest left-handed sneutrino) and the charged tracks associated with the charged LLP (the left-handed stau). We show that the production cross sections of our neutral and charged LLPs are relatively large, namely of order $\mathcal{O}(1)\text{ }\text{ }\mathrm{fb}$. Thus, probing these particles at the LHC is quite plausible. In addition, we find that the displaced dilepton associated with the lightest left-handed sneutrino has a large impact parameter that discriminates it from other SM leptons. We also emphasize that the charged track associated with the left-handed stau has a large momentum with slow moving charged tracks, hence it is distinguished from the SM background, and therefore it can be accessible at the LHC.

Displaced vertex signatures of doubly charged scalars in the type-II seesaw and its left-right extensions

The type-II seesaw mechanism with an isospin-triplet scalar ΔL provides one of the most compelling explanations for the observed smallness of neutrino masses. The triplet contains a doubly-charged component {H}_{{}^L}^{pm pm } , which dominantly decays to either same-sign dileptons or to a pair of W bosons, depending on the size of the triplet vacuum expectation value. However, there exists a range of Yukawa couplings fL of the triplet to the charged leptons, wherein a relatively light {H}_{{}^L}^{pm pm } tends to be long-lived, giving rise to distinct displaced-vertex signatures at the high-energy colliders. We find that the displaced vertex signals from the leptonic decays {H}_{{}^L}^{pm pm}to {ell}_{alpha}^{pm }{ell}_{{}^{beta}}^{pm } could probe a broad parameter space with 10−10 ≲ |fL| ≲ 10−6 and 45.6 GeV<{M}_{H_L^{pm pm }}lesssim 200 GeV at the high-luminosity LHC. Similar sensitivity can also be achieved at a future 1 TeV e+e− collider. The mass reach can be extended to about 500GeV at a future 100TeV proton-proton collider. Similar conclusions apply for the right-handed triplet {H}_{{}^R}^{pm pm } in the TeV-scale left-right symmetric models, which provide a natural embedding of the type-II seesaw. We show that the displaced vertex signals are largely complementary to the prompt same-sign dilepton pair searches at the LHC and the low-energy, high-intensity/precision measurements, such as neutrinoless double beta decay, charged lepton flavor violation, electron and muon anomalous magnetic moments, muonium-antimuonium oscillation and Møller scattering.