A Novel Tau Signature in Neutrino Telescopes

1. A Novel Tau Signature in Neutrino Telescopes UHE Tau Neutrino Workshop Beijing, China

2. Classic Tau Signature “Double Bang” Learned & Pakvasa 1995 νN interaction Tau lepton track ~50 m/PeV (neglecting energy loss) Tau decay UHE Tau Neutrino Workshop

3. Neutrino flavor n t full flavor ID n e n e (supernovæ) showers vs. tracks n m 9 12 18 21 6 15 Log(ENERGY/eV) Energy Windows by Flavor UHE Tau Neutrino Workshop

4. Alternative Signature “Lollipop” – half double bang Beacom, Bell, Hooper, Pakvasa & Weiler Dim track Stops in a big cascade (starting tracks dominated by BG) UHE Tau Neutrino Workshop

5. Tau Decay Modes Decay modeBranching fraction • τ → ντ + e + νe 17.8% • τ → ντ + X(hadronic) ~65% • τ → ντ + μ + νμ 17.4% double bang / lollipop UHE Tau Neutrino Workshop

6. Energy Losses Particles are detected in neutrino telescopes through energy deposited in the detector stochastic losses ionization • Stochastic energy loss mechanisms: • Bremsstrahlung • pair production • Photonuclear interactions UHE Tau Neutrino Workshop

7. Energy Loss Rates Taus are much dimmer than muons Bremsstrahlung, pair production suppressed by particle mass At E = 1 PeV: 1 EeV: βμ ~ 5 · 10-6 7 · 10-6 βτ ~ 3.5 · 10-7 9 · 10-7 UHE Tau Neutrino Workshop

8. Muons are brighter than taus → track suddenly brightens Can we see it? μ τ

9. Muonic Tau Decay τ → ντ + μ + νμ Muon energy spectrum in the lab frame: where Average muon energy (Perl 1992) UHE Tau Neutrino Workshop

10. Flavor Dependence Muons lose energy by pair production (& brems) Taus lose through photonuclear interactions Dutta, Reno, Sarcevic, and Seckel τ μ UHE Tau Neutrino Workshop

11. (= μ,τ) l Energy Loss Mechanisms l Bremsstrahlung Pair production Photonuclear interactions l γ l EM showers l e+ e- l l hadronic shower UHE Tau Neutrino Workshop

12. Hadronic Light Yield M. Kowalski Hadronic showers emit 65-85% of the light of an electromagnetic shower of the same energy UHE Tau Neutrino Workshop

13. Are Photonuclear Losses Quasi-Continuous? • Very high energy muons emit pairs, brems so frequently they cannot be resolved → Increase overall track brightness • Tau losses dominated by photonuclear interactions – fewer, brighter events • If they blur together, increase track brightness • If they’re distinct, won’t increase “baseline” track brightness (may reduce event rates) UHE Tau Neutrino Workshop

14. Photonuclear Energy Loss Bugaev & Shlepin hard component total photonuclear energy loss soft component UHE Tau Neutrino Workshop

15. Photonuclear Spectra soft component 1 EeV Peak at 10-2El Bugaev & Shlepin hard component 1 EeV 1 PeV 100 PeV 10 PeV 1 PeV = Eshower / Eτ UHE Tau Neutrino Workshop

16. Quasi-Continuous? • Soft component clearly continuous • Hard component: At 1 PeV, → 30 TeV Mean free path ~ 5 km At 1 EeV, mean free path ~ 200 m UHE Tau Neutrino Workshop

17. Brightness Ratio Non-Continuous Quasi-Continuous EeV EeV PeV PeV Ratio: ∆(log10): Detector resolutions (in log10 E): AMANDA: 0.5 ANTARES: 0.3–0.4 (ICRC 2003) (Carr & Hallewell) UHE Tau Neutrino Workshop

18. Low Energy Taus? • 1 TeV tau “track:” 5 cm Impossible! ντ → τ + X μ + νμ + ντ • Two neutrinos take 2/3 the energy → dim track • Compare energy of hadronic shower to energy of muon track? Need to worry about NC/νebackground! MC studies in progress… UHE Tau Neutrino Workshop