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Register a new userPinning Down the Invisible Sneutrino at the ILC
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Using the event generator WHIZARD we study in a realistic ILC environment the prospects of measuring properties of sneutrinos that decay invisibly into the lightest neutralino and the neutrino.
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For points in SUSY parameter space where the sneutrino is lighter than the lightest chargino and next-to-lightest neutralino, its direct mass determination from sneutrino pair production process at e+e- collider is impossible since it decays invisibly. In such a scenario the sneutrino can be discovered and its mass determined from measurements of two-body decays of charginos produced in pairs at the ILC. Using the event generator WHIZARD we study the prospects of measuring sneutrino properties in a realistic ILC environment. In our analysis we include beamstrahlung, initial state radiation, a complete account of reducible backgrounds from SM and SUSY processes, and a complete matrix-element calculation of the SUSY signal which encompasses all irreducible background and interference contributions. We also simulate photon induced background processes using exact matrix elements. Radiation effects and the cuts to reduce background strongly modify the edges of the lepton energy spectra from which the sneutrino and chargino mass are determined. We discuss possible approaches to measure the sneutrino mass with optimal precision.
The Standard Model (SM) predicts a branching ratio of the Higgs boson decaying to invisible particles of $mathcal{O}$(0.001), though current measurements have only set upper limits on this value. The small SM-allowed rate can be enhanced if the Higgs boson decays into new particles such as dark matter. Upper limits have been placed on BR(H$rightarrow$inv.) by ATLAS and CMS at $mathcal{O}$(0.1), but the hadron environment limits precision. The ILC `Higgs factory will provide unprecedented precision of this electroweak measurement. Studies of the search for H$rightarrow$invisible processes in simulation are presented with SiD, a detector concept designed for the ILC. Preliminary results for expected sensitivity are provided, as well as studies considering potential systematics limitations.
We make a careful analysis of $W^pmgamma$ production at the LHC, identifying the $W^pm$ through leptonic decays, with a view to exploring the sensitivity of the machine to anomalous $CP$-conserving $WWgamma$ interactions. All the available kinematic variables are used, but we find that the most useful one is the opening angle in the transverse plane between the decay products of the $W^pm$. It is shown that even a simple-minded analysis using this variable can lead to a much greater sensitivity at the LHC than the current constraints on the relevant parameters.
We study the possibility of measuring neutrino Yukawa couplings in the Next-to-Minimal Supersymmetric Standard Model with right-handed neutrinos (NMSSMr) when the lightest right-handed sneutrino is the Dark Matter (DM) candidate, by exploiting a `dijet + dilepton + Missing Transverse Energy signature. We show that, contrary to the miminal realisation of Supersymmetry (SUSY), the MSSM, wherein the DM candidate is typically a much heavier (fermionic) neutralino state, this extended model of SUSY offers one with a much lighter (bosonic) state as DM that can then be produced at the next generation of $e^+e^-$ colliders with energies up to 500 GeV or so. The ensuing signal, energing from chargino pair production and subsequent decay, is extremely pure so it also affords one with the possibility of extracting the Yukawa parameters of the (s)neutrino sector. Altogether, our results serve the purpose of motivating searches for light DM signals at such machines, where the DM candidate can have a mass around the electroweak scale.
The existence of dark matter has been established in astrophysics. However, there are no dark matter candidates in the Standard Model~(SM). If the dark matter particles or their mediator can not interact with SM fermions or gauge bosons, the Higgs boson is the only portal to the dark matter. We present a simulation study to search for invisible decays of the Higgs boson at the ILC with the ILD detector.
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