A Novel Tau Signature in Neutrino Telescopes

1. A Novel Tau Signature in Neutrino Telescopes (astro-ph/0608486) 2nd Workshop on TeV Particle Astrophysics Madison, Wisconsin

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

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) Windows for Flavor ID double bang TeV Astro II

4. Alternative Signature “Lollipop” – half of a double bang Beacom, Bell, Hooper, Pakvasa & Weiler Relatively dim track Stops in a big cascade (starting tracks dominated by BG) TeV Astro II

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 TeV Astro II

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 TeV Astro II

7. Muons are brighter than taus → track suddenly brightens Can we see it? μ τ (D. Cowen)

8. Muonic Tau Decay τ → ντ + μ + νμ Muon energy spectrum in the lab frame: where Average muon energy (Perl 1992) TeV Astro II

9. dE/dx Flavor Dependence Muons lose energy by pair production & brems Taus lose a lot in photonuclear interactions Dutta, Reno, Sarcevic, and Seckel τ μ TeV Astro II

10. Photonuclear Loss Models Depend on parton density f’ns, nuclear shadowing TeV Astro II

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 TeV Astro II

12. Hadronic Light Yield M. Kowalski Hadronic showers emit 65-85% of the light of an electromagnetic shower of the same energy TeV Astro II

13. Put It All Together • Fraction of tau energy carried by muon • Relative energy loss rates for tau, muon • dE/dx roughly 7x higher for muon than for tau, at fixed lepton energy • Relative light yields for photonuclear energy loss vs. bremsstrahlung, pair production • Flat ratio of 75% assumed TeV Astro II

14. Brightness Ratio track length typical neutrino telescope track energy resolution σ(log10 E) ≈ 0.3 TeV Astro II

15. Low Energy Taus? (suggestion John Beacom) • 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… TeV Astro II

16. Tagging Low Energy Taus? Etrack ντ? νμCC NC and νe Eshower TeV Astro II