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

2. 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

3. 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

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
August 29, 2006

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

6. 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

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
August 29, 2006

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
August 29, 2006

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

11. 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

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
August 29, 2006

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
August 29, 2006

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

15. 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

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