We develop the search strategy for a heavy Majorana neutrino via the lepton number violation signal process $p\, e^- \to μ^+ jjj$ at future electron-proton colliders. The signal and dominant standard model background events are generated with the fast detector simulation. We apply the pre-selection criteria and perform the multi-variate analysis based on machine-learning to reject the background. Distributions of representative kinematic observables are presented for both signal and background processes and effects on final limits are compared by inputting two different set of observables when performing multi-variate analysis. The 2- and 5-$σ$ limits on the mixing parameter $|V_{\ell N}|^2$ are predicted for the heavy neutrino mass $m_N$ in the range of 10$-$1000 GeV. At the LHeC (FCC-eh) with an electron beam energy of 60 GeV, a proton beam energy of 7 (50) TeV and an integrated luminosity of 1 (3) ab$^{-1}$, the mixing parameter $|V_{\ell N}|^2$ can be constrained to be below $\sim 3.0~(1.0) \times 10^{-6}$ for $m_N$ around $\mathcal{O}(100)$ GeV at 2-$σ$ level. The limits are much stronger than the current experiment limits at the LHC for $m_N$ above 30 GeV. The positron signal final state and the effect of long-lived cases of heavy neutrinos are also checked and commented.
Right-handed (RH) Majorana neutrinos play a crucial role in understanding the origin of neutrino mass, the nature of dark matter and the mechanism of matter-antimatter asymmetry. In this work, we investigate the observability of heavy Majorana neutrino through the top quark neutrinoless double beta decay process $t \to b \ell^+ \ell^+ j j$ at hadron colliders. By performing detector level simulation, we demonstrate that our method can give stronger limits on the light-heavy neutrino mixing parameters $|V_{eN, μN}|$ in the mass range of 15 GeV $< m_N <$ 80 GeV than other existing collider bound…
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.
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…
The heavy singlet Majorana neutrinos are introduced to generate the neutrino mass in the so-called phenomenological type-I seesaw mechanism. The phenomena induced by the heavy Majorana neutrinos are important to search for new physics. In this paper, we explore the heavy Majorana neutrino production and decay at future $e^{-}p$ colliders. The corresponding cross sections via $W$ and photon fusion are predicted for different collider energies. Combined with the results of the heavy Majorana neutrino production via single $W$ exchange, this work can provide helpful information to search for heav…
We explore model-independent collider constraints on light Majorana dark matter particles. We find that colliders provide a complementary probe of WIMPs to direct detection, and give the strongest current constraints on light DM particles. Collider experiments can access interactions not probed by direct detection searches, and outperform direct detection experiments by about an order of magnitude for certain operators in a large part of parameter space. For operators which are suppresssed at low momentum transfer, collider searches have already placed constraints on such operators limiting th…
We perform a comprehensive and model-independent analysis for characterizing the spin and dynamical structure of the production of a non-diagonal pair of Majorana particles with different masses and arbitrary spins, $e^-e^+\to X_2 X_1$, followed by a sequential two-body decay, $X_2\to Z X_1$, of the heavier particle $X_2$ into a $Z$ gauge boson and the lighter particle $X_1$ escaping undetected at high-energy $e^+e^-$ colliders. Standard leptonic $Z$-boson decays, $Z\to \ell^-\ell^+$ with $\ell=e$ or $μ$, are employed for precisely diagnosing the $Z$ polarization influenced by the production a…
We discuss the potential to observe lepton number violation (LNV) in displaced vertex searches for heavy neutral leptons (HNLs) at future lepton colliders. Even though a direct detection of LNV is impossible for the dominant production channel because lepton number is carried away by an unobservable neutrino, there are several signatures of LNV that can be searched for. They include the angular distribution and spectrum of decay products as well as the HNL lifetime. We comment on the perspectives to observe LNV in realistic neutrino mass models and argue that the dichotomy of Dirac vs Majorana…
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…
The existence of Majorana neutrinos must lead to lepton-number violating processes, and the Majorana nature of neutrinos can only be experimentally verified via lepton-number violating processes. We propose a new approach to search for Majorana neutrinos at future electron-positron colliders by exploiting this feature. We investigate the $ΔL = 2$ like-sign dilepton production and find that lepton colliders with different center-of-mass energies have comparative advantages in resonant production of a Majorana neutrino in either light neutrino mass range or heavy mass range. At the future Circul…
A general feature of TeV-scale radiative seesaw models, in which tiny neutrino masses are generated via loop corrections, is an extended scalar (Higgs) sector. Another feature is the Majorana nature; e.g., introducing right-handed neutrinos with TeV-scale Majorana masses under the discrete symmetry, or otherwise introducing some lepton number violating interactions in the scalar sector. We study phenomenological aspects of these models at collider experiments. We find that, while properties of the extended Higgs sector of these models can be explored to some extent, the Majorana nature of the …
Heavy neutral leptons (HNLs) are hypothetical particles able to explain several puzzles of fundamental physics, first and foremost - neutrino oscillations. Being sterile with respect to Standard Model interactions, these particles admit Majorana masses, allowing for violation of the total lepton number. Lepton number violating (LNV) processes thus become a key signature of HNLs, pursued by many experiments. In this work, we demonstrate that if HNLs are the sole origin of neutrino masses, destructive interference between Majorana states suppresses the same-sign di-lepton signal. In the phenomen…
The nonzero neutrino mass can be a signal for new physics beyond the standard model. To explain the tiny neutrino mass, we can extend the standard model with right-handed Majorana neutrinos in a low-scale seesaw mechanism, while the CP violation effect can be induced due to the CP phase in the interference of heavy Majorana neutrinos. The existence of heavy Majorana neutrinos may lead to lepton number violation processes, which can be used as a probe to search for the signal of heavy Majorana neutrinos. In this paper, we focus on the CP violation effect related to two generations of heavy Majo…
Collider signals of heavy Majorana neutrino mass origin are studied in the minimal Left-Right symmetric model, where their mass is generated spontaneously together with the breaking of lepton number. The right-handed triplet Higgs boson $Δ$, responsible for such breaking, can be copiously produced at the LHC through the Higgs portal in the gluon fusion and less so in gauge mediated channels. At $Δ$ masses below the opening of the $VV$ decay channel, the two observable modes are pair-production of heavy neutrinos via the triplet gluon fusion $gg \to Δ\to NN$ and pair production of triplets from…
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…
A significant benchmark for discovery at a proton-proton collider is the sensitivity to a dijet resonance, X, the intermediate state of the s-channel process $pp \rightarrow X \rightarrow 2\mbox{ jets}$. To probe the highest resonance masses, hadron collider experiments have used the classic technique of searching for bumps in the mass spectrum of two individually resolved jets. In this Snowmass 2021 study, we explore the search sensitivity to multiple benchmark models of dijet resonances at current and future proton-proton colliders. We present the expected masses for $5σ$ discovery and 95\% …
We study the possibility of future $e^{+}e^{-}$ colliders to disentangle different new physics contributions to the production of heavy sterile Majorana neutrinos in the lepton number violating channel $e^{+}e^{-}\rightarrow l^{+} l^{+}+ 4 jets$, with $l=e, μ, τ$. This is done investigating the final anti-tau polarization trails and initial beam polarization dependence of the signal on effective operators with distinct Dirac-Lorentz structure contributing to the Majorana neutrino production and decay, which parameterize new physics from a higher energy scale. We find both analyses could well d…
We investigate the resonant production of color octet muons in order to explore the discovery potential of the FCC-based μp colliders. It is shown that search potential of μp colliders essentially surpass potential of the LHC and would exceed that of FCC pp collider.
The measurement of hard scattering processes, meaning those with energy scales of more than a few GeV, is the main method by which physics is being explored and extended by the experiments at the Large Hadron Collider. We review the principal measurements made so far, and what they have told us about physics at the energy frontier.
Recently proposed Future Circular Collider based muon-proton colliders will allow investigating lepton-hadron interactions at the highest center-of-mass energy. In this study, we investigate the potential of these colliders for a four-fermion contact interactions search. Regarding the constructive and destructive interferences of contact interactions, we estimated discovery, observation, and exclusion limits on the compositeness scale for the left-left, right-right, left-right, and right-left helicity structures. This study's findings show that the FCC-based μp colliders have great potential f…
We investigate the signatures at the Large Hadron Collider of a minimal model where the dark matter particle is a Majorana fermion that couples to the Standard Model via one or several coloured mediators. We emphasize the importance of the production channel of coloured scalars through the exchange of a dark matter particle in the t-channel, and perform a dedicated analysis of searches for jets and missing energy for this model. We find that the collider constraints are highly competitive compared to direct detection, and can even be considerably stronger over a wide range of parameters. We al…
Neutrinos in the Standard Model (SM) are considered to be massless which is in contradiction with the evidence from the neutrino oscillation data. These experiments established that at least two SM neutrinos have non-zero masses and that individual lepton numbers are violated. This is strong evidence of new physics beyond the SM that should be responsible for generating non zero mass for the neutrinos. In this work, we study the collider phenomenology of an extension of the SM where neutrinos are generated radiatively at three-loop. We show that the production of same-sign dilepton at lepton c…
We present a summary of results for SUSY Simplified Model searches at future proton colliders: the 14 TeV LHC as well as a 33 TeV proton collider and a 100 TeV proton collider. Upper limits and discovery significances are provided for the gluino-neutralino (for both light and heavy flavor decays), squark-neutralino, and gluino-squark Simplified Model planes. Events are processed with the Snowmass combined detector and Standard Model backgrounds are computed using the Snowmass samples. We place emphasis on comparisons between different collider scenarios, along with the lessons learned regardin…
We study double parton scattering (DPS) processes involving electroweak gauge bosons at the 13 TeV and 100 TeV proton-proton colliders. Specifically, we focus on three DPS channels: $W$-boson plus two jets ($W\otimes jj$), $Z$-boson plus two jets ($Z\otimes jj$), and same-sign $W$ pair production ($W^\pm\otimes W^\pm$). We demonstrate that the $Z\otimes jj$ process, which has not been paid too much attentions, is the best channel for measuring effective cross section $σ_{\rm eff}$. The accuracy of $σ_{\rm eff}$ measurement in the three DPS channels, especially the $W^\pm\otimes W^\pm$ producti…
We present experimental sensitivity for the production of a fourth-generation Majorana neutrino ($N$) via an s-channel $Z$ boson $Z\to NN \to W\ell W\ell$ at hadron colliders. This channel has not been studied for the Tevatron dataset with $\int \mathcal{L}=5 $ fb$^{-1}$, where we find that a single experiment could significantly extend current 95% C.L. mass lower limits, to $m_N>175$ GeV$/c^2$, or report $3σ$ evidence for the $N$ if $m_N<150$ GeV$/c^2$. With 5 fb$^{-1}$, a single LHC experiment at $\sqrt{s}=10$ TeV could expect t o set a 95% C.L. mass lower limits of $m_N>300$ GeV$/c^2$, or r…
We study the expected experimental mass distributions of dijet resonances from excited quarks in proton-proton collisions at energies $\sqrt{s}=$ 13, 14, 27, 100, 300, and 500 TeV. We explore in detail the expected shapes at both the generator and experimental levels, and identify within the distributions the effects of the excited quark natural width, parton momentum distributions of the proton, radiation, and experimental resolution. We present both differential and cumulative probability distributions as a function of dijet mass, and the signal acceptance of a window in dijet mass centered …
A gauged U$(1)$ extension of the Standard Model (SM) is a simple and anomaly free framework where three generations of Majorana type right-handed neutrinos (RHNs) are introduced to generate light neutrino mass and flavor mixings through the seesaw mechanism. We investigate such models at different hadron and lepton colliders via $Z^\prime$ induced Majorana type RHNs pair production. We derive bounds on U$(1)$ gauge coupling $(g^\prime)$ comparing the model cross sections with experimentally observed data for different $Z^\prime$ mass $(M_{Z^\prime})$ and RHNs mass $(M_N)$. Using these limits w…
Based on current CERN infrastructure, an electron--proton collider is proposed at a centre-of-mass energy of about 9 TeV. A 7 TeV LHC bunch is used as the proton driver to create a plasma wakefield which then accelerates electrons to 3\,TeV, these then colliding with the other 7 TeV LHC proton beam. Although of very high energy, the collider has a modest projected integrated luminosity of $10-100$ pb$^{-1}$. For such a collider, with a centre-of-mass energy 30 times greater than HERA, parton momentum fractions, $x$, down to about $10^{-8}$ are accessible for photon virtualities, $Q^2$, of 1 Ge…
We discuss the possibility of observing multi-lepton signals at the Large Hadron Collider (LHC) from the production and decay of heavy Standard Model (SM) singlet neutrinos added in extensions of SM to explain the observed light neutrino masses by seesaw mechanism. In particular, we analyze two `smoking gun' signals depending on the Dirac or Majorana nature of the heavy neutrino: (i) for Majorana case, the same-sign di-lepton signal which can be used as a probe of lepton-number violation, and (ii) for Dirac case, the tri-lepton signal which conserves lepton number but may violate lepton flavor…
We outline the opportunities to study the production of the Standard Model bosons, $W^\pm$, $Z^0$ and $H^0$ at "low" energies at fixed-target experiments based at possible future ultra-high-energy proton colliders, \ie\ the High-Energy LHC, the Super proton-proton Collider and the Future Circular Collider -- hadron-hadron. These can be indeed made in conjunction with the proposed future colliders designed to reach up to $\sqrt{s}=100$ TeV by using bent crystals to extract part of the halo of the beam which would then impinge on a fixed target. Without disturbing the collider operation, this te…
The SPD experiment at the future NICA collider at JINR (Dubna, Russia) aims to investigate the nucleon spin structure and polarization phenomena in collisions of longitudinally and transversely polarized protons and deuterons at $\sqrt{s}$ up to 27 GeV and luminosity up to 10$^{32}$ cm$^{-2}$ s$^{-1}$. Measurement of asymmetries in the Drell-Yan pairs, charmonium and prompt photon production can provide an access to the full set of leading twist TMD PDFs in nucleons. The experimental setup is planned as a universal 4$π$ detector for a wide range of physics tasks.
A theoretical model describing neutron-proton scattering developed by Majorana as early as in 1932, is discussed in detail with the experiments that motivated it. Majorana using collisions' theory, obtained the explicit expression of solutions of wave equation of the neutron-proton system. In this work two different models, the unpublished one of Majorana and the contemporary work of Massey, are studied and compared.
In this study, main parameters of Super proton-proton Collider (SppC) based lepton-proton colliders are estimated. For electron beam parameters, highest energy International Linear Collider (ILC) and Plasma Wake Field Accelerator-Linear Collider (PWFA-LC) options are taken into account. For muon beams, 1.5 TeV and 3 TeV center of mass energy Muon Collider parameters are used. In addition, ultimate $μ$p collider which assumes construction of additional 50 TeV muon ring in the SppC tunnel is considered as well. It is shown that $L_{ep}$ $\sim$ $10^{32}$ $cm^{-2}s^{-1}$ can be achieved with moder…
We discuss spin physics, Guido Altarelli's contribution to it, and what we still have to learn. We set out in particular a programme for incorporating constraints from semi-inclusive data into global fits of polarized PDFs, and discuss the need for the EIC to increase the precision and kinematic coverage of current measurements.
We describe various studies relevant for top physics at future circular collider projects currently under discussion. We show how highly-massive top-antitop systems produced in proton-proton collisions at a center-of-mass energy of 100 TeV could be observed and employed for constraining top dipole moments, investigate the reach of future proton-proton and electron-positron machines to top flavor-changing neutral interactions, and discuss top parton densities.
We study the Lepton number violating like-sign dilepton processes $h_1 h_2 \to l^\pm l^{\prime \pm} jj X$ and $h_1 h_2 \to l^\pm l^{\prime \pm} W^\pm X$, mediated by heavy GeV scale Majorana neutrinos. We focus on the resonantly enhanced contributions with a nearly on-mass-shell Majorana neutrino in the s-channel. We study the constraints on like-sign dilepton production at the Tevatron and the LHC on the basis of the existing experimental limits on the masses of heavy neutrinos and their mixings $U_{αN}$ with $α= ν_{e}, ν_μ, ν_τ$. Special attention is paid to the constraints from neutrinoless…
We investigate the prospects for discovering charginos and neutralinos at a future $pp$ collider with $\sqrt{s} = 100$ TeV. We focus on models where squarks and sleptons are decoupled -- as motivated by the LHC data. Our initial study is based on models where Higgsinos form the main component of the LSP and $W$-inos compose the heavier chargino states ($M_2 > μ$), though it is straightforward to consider the reverse situation also. We show that in such scenarios $W$-inos decay into $W^\pm$, $Z$ and $h$ plus neutralinos almost universally. In the $W Z$ channel we compare signal and background i…
