A Novel Tau Signature in Neutrino Telescopes (astro-ph/0608486) 2nd Workshop on TeV Particle Astrophysics Madison, Wisconsin August 29, 2006

Classic Tau Signature “Double Bang” νN interaction Tau lepton track Learned & Pakvasa 1995 νN interaction Tau lepton track ~50 m/PeV (neglecting energy loss) Tau decay TeV Astro II August 29, 2006

Windows for Flavor ID double bang Neutrino flavor t n m Log(ENERGY/eV) (supernovæ) showers vs. tracks full flavor ID Neutrino flavor n m t e Log(ENERGY/eV) 12 18 15 6 21 9 double bang TeV Astro II August 29, 2006

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 August 29, 2006

Tau Decay Modes Decay mode Branching fraction τ → ντ + e + νe 17.8% τ → ντ + X (hadronic) ~65% τ → ντ + μ + νμ 17.4% double bang / lollipop TeV Astro II August 29, 2006

Energy Losses Particles are detected in neutrino telescopes through energy deposited in the detector ionization stochastic losses Stochastic energy loss mechanisms: Bremsstrahlung pair production Photonuclear interactions TeV Astro II August 29, 2006

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

Muonic Tau Decay τ → ντ + μ + νμ Muon energy spectrum in the lab frame: where Average muon energy (Perl 1992) TeV Astro II August 29, 2006

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 August 29, 2006

Photonuclear Loss Models Depend on parton density f’ns, nuclear shadowing TeV Astro II August 29, 2006

Energy Loss Mechanisms ( = μ,τ) l Bremsstrahlung Pair production Photonuclear interactions l γ l EM showers l e+ e- l l hadronic shower TeV Astro II August 29, 2006

Hadronic Light Yield M. Kowalski Hadronic showers emit 65-85% of the light of an electromagnetic shower of the same energy TeV Astro II August 29, 2006

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 August 29, 2006

Brightness Ratio track length typical neutrino telescope track energy resolution σ(log10 E) ≈ 0.3 TeV Astro II August 29, 2006

Low Energy Taus? ντ → τ + X (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/νe background! MC studies in progress… TeV Astro II August 29, 2006

Tagging Low Energy Taus? Etrack ντ? νμ CC NC and νe Eshower TeV Astro II August 29, 2006