Possible sneutrino-pair signatures with R-parity breaking

Abstract

If sneutrinos are the lightest supersymmetry partners and R-parity is not conserved, the process e + e − →νν can have striking signatures due to the decay modes ν → ℓ + ℓ ′− orν → qq ′ . We present cross section formulas and discuss event rates and detection at the upgraded e + e − collider LEP. Four-lepton signals should be detectable up to sneutrino massm ν = 80 GeV and maybe beyond; four-jet signals should be detectable up tom ν = 70 GeV, but would probably be obscured thereafter by W W background.Searches for supersymmetry (SUSY) particles depend considerably on the identity of the lightest SUSY partner (LSP), usually believed to be a neutralino [1]. if approximately degenerate sneutrinosν α are the LSP and decay by RPV processes. We ignore single-SUSY-particle production [7,10], that can in principle take place with a lower threshold via RPV interactions, because the latter are either known [7,8] or suspected to have much much smaller couplings than the gauge couplings which control Eq.(1).Sneutrino pair production proceeds via t-channel exchange of charginos χ+ R → ν eν e only) and via s-channel Z exchange, that together give the helicity amplitudesHere θ is the CM polar scattering angle, m χ + i are the chargino masses (i = 1 is the lightest), while cos 2 γ R is the mixing probability of the wino component in the lightest chargino; β = 1 − 4m 2 ν /s is the sneutrino CM velocity, s and t are the usual invariant squares of energy and momentum transfer, θ W is the weak angle. The differential cross section is then defined by dσ/d cos θ = Σ|M| 2 β/(128πs); we note that it contains an overall factor sin 2 θ , favoring wide angles with good experimental acceptance, well away from the beam-pipe. as in many models). We note thatν eνe production is considerably enhanced aboveν µνµ andν τντ production, due to the chargino-exchange contribution (with constructive interference). Adding all three flavors, Fig.1 indicates about 500 (75) events per 100 pb −1 luminosity at √ s = 190 GeV, form ν = 50 (80) GeV, which should be enough to establish a clear signal in this mass range and possibly beyond, modulo detection efficiency and background questions discussed below.If a sneutrino is the LSP, it can only decay by RPV. With the particle content of the minimal SUSY-SM (MSSM), the most general gauge-and SUSY-invariant Lagrangian includes the following terms that can mediate sneutrino decays[6]where L i and E λ ijk ⇒ν i → ℓ

R-Parity-violating supersymmetry

“…The partial widths ofν i 's when decaying via λ ijk LLĒ or λ ′ ijk LQD are given (neglecting lepton and quark masses) by [437]:…”

R-parity-violating supersymmetric Yukawa couplings: A mini-review

“…Refs. [28,29] The main message that can be read from the above analyses is that the pair production cross section of charginos are sigificantly higher than those of the sfermions (and also higher than neutralino pair production cross section) and, therefore, even after paying the price of losing events while imposing the kinematic cuts during cascades following the decays of the charginos, required number of events still manage to survive resembling the 4-jet excess. But, most importantly, before speculating further, one should wait and see whether these anomalous events stand the test of time!…”

A Search for Pair Production of the LSP <span class="cmr-10">˜</span> <span class="cmmi-10">ν</span>_{<span class="cmmi-7">τ</span>} at the CLIC via RPV Decays

“…As it was shown in [2], the LEP data allows "right" sneutrino to be the LSP. In addition, R-parity violation allowing decays of LSP sneutrino to ordinary SM particles leads to potentially rich phenomenology at high energy colliders [3][4][5][6][7][8][9]. R-parity is represented by R = (−1)…”