χ ν l N h h X PL B668 (2008) 185
Introduction • RPB SUSYModels of neutrino mass are interesting as they simultaneously solve the hierarchy problem of SM & they can be experimentally tested in foreseeable future. • Bilinear RPB SUSY model provides a predictive ext. of MSSM as it has relatively few (6) parameters. • All the 6 RPB parameters are determined within tight limits by the observed neutrino masses and mixing angles. • Tiny neutrino masses ensure tiny RPB parameters εi. • Hence the predictions for superparticle prod and decay down to the LSP are practically same as in MSSM. • Moreover LSP decay width and BRs are predicted by the 6 known RPB parameters in terms of the given MSSM parameters. Mukhopadhyaya et al., Joshipura and Vempati, Hirsch and Valle,….
LSP decay length and BRs For relatively light MSSM mass range of our interest the two main decay channels are χ (ν) τ- τ+ τ,b H χ χ χ(ν) τ,b χdecay range r0 =cτ ~1 mm for mχ~ 100 GeV and goes down inversely as mass there after Porod, Hirsch, Ramao, Valle, PRD65(2001)
Three MSSM Points Points I and II have very light SUSY spectra and hence most natural. But they are hard to probe at LHC because while RPB χ decay imply soft missing-pT . For the same reason the TeVatron limit on squark mass does not apply here. Point III corresponds to the typical mSUGRA gaugino spectrum, which can be probed at LHC via the hard leptons coming from cascade decay because of the 2:1 hierarchy between the Wino and Bino (χ) masses. SUSY Signal at UHE Neutrino Telescopes:
CC cross-sections NC cross-sections obtained by substituting zino mass for wino and multiplying by and SUSY cross-sections at least two orders of magnitude smaller.
Gandhi et al PRD58 (1998) ν τ→νh ~100 m Double bang events Learned & Pakvasa:APP3 (1995) N τ X ν N h X
χ l N h h X SUSY Events: χ→ττν decay => Collinear Triple-bang events 2/3rd of Events come from CC => Collinear l = e (shower), μ(track) or τ (4th bang) ν χ→bbν decay =>Double-bang Separated by r (χ) ~ 100 m 2/3rd from CC => Collinear l (distinguishable from SM Bg) Sig BR = (2/3).60%+30%=70% NC:νNνχνν bb 100m gap
ν νττ, τh , τh 100, 200, 500m νττ, τh , τh 20, 40, 100m N All the decay vertices are collinear with the production vertex Only the more energetic τ from the squark decay has a range of ~ 100 m from prod vertex, which can be resolved at IceCube. But including this extra bang does not enhance the BR significantly, though it will enhace the detection efficiency of multi-bang events.
Signal Rate Small & Uncertain(Uncertainty in UHE ν flux) Waxman-Bahcall flux: • Common EG source for UHE ν & CRs. • It accelerates protons to UHE, which interacts with the ambient photon giving • The νs & n escape the confining mag. field. • Source optically thin → n escapes without int with γ & decays outside to give CR protons. • power law of a Fermi engine for ν/CR spectra. (equally distributed into the three flavours by ν oscillation)
The E-2 power law has been questioned by many people, who suggest to treat it instead as a free parameter. AGASA & HiRes Data shows a steepenning of the UHE CR spectrum from E-2 To E-2.54 above E = 3x108 GeV. This coincides with change of CR composition form Heavy nuclei to proton dominance → dominance of EG component at this energy. Ahlers, Anchordoque, Goldberg, Halzen, Ringwald, Weiler, PRD (2005)
Cont to UHE ν flux from optically thick sources (AGN) → no nucleons escapes: Semikoz & Sigl, JCAP (2004); Neronov, Semikoz, & Kalasev, PRL (2002). Aharonian Only decay ν and γ escape. Energy of γ gets degraded in transit. The EGRET flux estimate of diffuse γ → normalization of AGN ν flux ~ 30 times larger than the WB flux at 20 PeV.
Signal Rate: NT = 6x1038 is the no of target nucleons at km3 size water/ice telescope T = 15 years is the total operation time of IceCube Number of Sig events is same as in the MSSM. But unlike the MSSM the bilinear RPB SUSY Signal has a distinctive multi-bang signature at UHE ν telescopes. Number of signal events are admittedly small at IceCube. But it is remarkable to note that IceCube will come at least within striking distance of detecting this SUSY signal. Hopefully it will be followed by a ~ 10 km3 UHE telescope, which can probe this signal effectively.