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Register a new userSearching for heavy neutrino in terms of tau lepton at future hadron collider
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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.
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We discuss the future prospects of heavy neutrino searches at next generation lepton colliders. In particular, we focus on the planned electron-positron colliders, operating in two different beam modes, namely, $e^+e^-$ and $e^-e^-$. In the $e^+e^-$ beam mode, we consider various production and decay modes of the heavy neutrino ($N$), and find that the final state with $e+2j+{E!!!/}_T$, arising from the $e^+e^-to N u$ production mode, is the most promising channel. However, since this mode is insensitive to the Majorana nature of the heavy neutrinos, we also study a new production channel $e^+e^-to Ne^pm W^mp$, which leads to a same-sign dilepton plus four jet final state, thus directly probing the lepton number violation in $e^+e^-$ colliders. In the $e^-e^-$ beam mode, we study the prospects of the lepton number violating process of $e^-e^-to W^-W^-$, mediated by a heavy Majorana neutrino. We use both cut-based and multivariate analysis techniques to make a realistic calculation of the relevant signal and background events, including detector effects for a generic linear collider detector. We find that with the cut-based analysis, the light-heavy neutrino mixing parameter $|V_{eN}|^2$ can be probed down to $sim 10^{-4}$ at 95% C.L. for the heavy neutrino mass up to $400$ GeV or so at $sqrt s=500$ GeV with $100 rm{fb}^{-1}$ of integrated luminosity. For smaller mixing values, we show that a multivariate analysis can improve the signal significance by up to an order of magnitude. These limits will be at least an order of magnitude better than the current best limits from electroweak precision data, as well as the projected limits from $sqrt s=14$ TeV LHC.
We have considered the physics opportunities of future lepton-hadron colliders and how these opportunities might be realized in a possible polarized eRHIC facility and an e-p collider as part of a staged or final version VLHC. We evaluated the physics priorities based on experience at HERA and, using simulated data for e-p collisions with sqrt(s) > 1 TeV, showed how detector designs would be impacted by the physics.
We investigate the prospects for the discovery of massive color-octet vector bosons at the CERN Large Hadron Collider with $sqrt{s} = 14$ TeV. A phenomenological Lagrangian is adopted to evaluate the cross section of a pair of colored vector bosons (colorons, $tilde{rho}$) decaying into four colored scalar resonances (hyper-pions, $tilde{pi}$), which then decay into eight gluons. We include the dominant physics background from the production of $8g,7g1q, 6g2q$, and $5g3q$, and determine the masses of $tilde{pi}$ and $tilde{rho}$ where discovery is possible. For example, we find that a 5$sigma$ signal can be established for $M_{tilde{pi}} alt 495$ GeV ($M_{tilde{rho}} alt 1650$ GeV). More generally we give the reach of this process for a selection of possible cuts and integrated luminosities.
The LHCb Collaboration recently gave an update on testing lepton flavour universality with $B^+ rightarrow K^+ ell^+ ell^-$, in which a 3.1 standard deviations from the standard model prediction was observed. The g-2 experiment also reports a 3.3 standard deviations from the standard model on muon anomalous magnetic moment measurement. These deviations could be explained by introducing new particles including leptoquarks. In this paper, we show the possibility to search for heavy spin-1 leptoquarks at a future TeV scale muon collider by performing studies from three channels: 1) same flavour final states with either two bottom or two light quarks, 2) different flavour quark final states, and 3) a so-called VXS process representing the scattering between a vector boson and a leptoquark to probe the coupling between leptoquark and tau lepton. We conclude that a 3 TeV muon collider with $3~{ab^{-1}}$ of integrated luminosity is already sufficient to cover the leptoquark parameter space in order to explain the LHCb lepton flavour universality anomaly.
We investigate a potential of discovering lepton flavor violation (LFV) at the Large Hadron Collider. A sizeable LFV in low energy supersymmetry can be induced by massive right-handed neutrinos, which can explain neutrino oscillations via the seesaw mechanism. We investigate a scenario where the distribution of an invariant mass of two hadronically decaying taus ($tauhtauh$) from $schizero{2}$ decays is the same in events with or without LFV. We first develop a transfer function using this ditau mass distribution to model the shape of the non-LFV $tauhmu$ invariant mass. We then show the feasibility of extracting the LFV $tauhmu$ signal. The proposed technique can also be applied for a LFV $tauh e$ search.
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