Discovery potential of radiative neutralino production at the ILC

Abstract

We study radiative neutralino production e + e − →χ 0 1χ 0 1 γ at the linear collider with longitudinally polarised beams. We consider the Standard Model background from radiative neutrino production e + e − → ννγ, and the supersymmetric radiative production of sneutrinos e + e − →νν * γ, which can be a background for invisible sneutrino decays. We give the complete tree-level formulas for the amplitudes and matrix elements squared. In the Minimal Supersymmetric Standard Model, we study the dependence of the cross sections on the beam polarisations, on the parameters of the neutralino sector, and on the selectron masses. We show that for bino-like neutralinos longitudinal polarised beams enhance the signal and simultaneously reduce the background, such that statistics is significantly enhanced. We point out that there are parameter regions where radiative neutralino production is the only channel to study SUSY particles, since heavier neutralinos, charginos and sleptons are too heavy to be pair-produced in the first stage of the linear collider with √ s = 500 GeV.

Mass bounds on a very light neutralino

“…However due to the large background from radiative neutrino production, e + e − → ννγ , we find that the (theoretical) significance 5 is at best S ≈ 0.1 for L = 100 pb −1 and √ s = 208 GeV [87,88]. In addition, cuts on the photon energy or angle do not enhance the significance, due to similar kinematic distributions of signal and background.…”

“…Three of the present authors [87,88] have recently presented the first complete calculation of the process (3) for a general neutralino, focusing on heavy neutralinos, and analysed the resulting phenomenology at the ILC including beam polarisation. In Sect.…”

Rare meson decays into very light neutralinos

“…Direct searches at past and future e þ e À colliders have been studied in detail in Refs. [20,27,28,30,32,109]. While no bounds on the mass of the lightest neutralino can be obtained from past searches at LEP and B factories, measurements at a future e þ e À linear collider might be able to discover light neutralinos through radiative production, e þ e À !~0 1~0 1 þ .…”

“…[14,[19][20][21], and cosmological implications, see e.g., [18,[22][23][24][25][26]. Light neutralinos have also been discussed in the context of collider searches [15,[27][28][29][30][31][32], as well as electroweak precision observables [18,33] and rare meson decays [18,[34][35][36][37][38]. In a previous paper [18], some of the present authors presented an extensive study of these phenomenological constraints.…”

The electroweak sector of the pMSSM in the light of LHC - 8 TeV and other data

“…This scenario with three invisible sparticles (the LSP, χ 0 2 and the sneutrino) have interesting collider phenomenology [177,178]. In particular at a high energy e + e − collider [179,180] it would lead to a significantly enhanced signal in the single photon + missing energy channel [181] compared to a pMSSM scenario with LSP as the lone carrier of missing energy [182,183].…”