Download - A Novel Tau Signature in Neutrino Telescopes
April 25, 2006
Doug Cowen, Tyce DeYoung, Soeb Razzaque
A Novel Tau Signature in Neutrino Telescopes
UHE Tau Neutrino WorkshopBeijing, China
April 25, 2006UHE Tau Neutrino Workshop
Classic Tau SignatureClassic Tau Signature
“Double Bang”Learned & Pakvasa 1995
νN interaction
Tau lepton track ~50 m/PeV
(neglecting energy loss)
Tau decay
April 25, 2006UHE Tau Neutrino Workshop
Energy Windows by Flavor
Energy Windows by Flavor
(supernovæ) showers vs. tracks
full flavor ID
Neutrino flavor
e
Log(ENERGY/eV)
12 18156 219
e
April 25, 2006UHE Tau Neutrino Workshop
Alternative SignatureAlternative Signature
“Lollipop” – half double bangBeacom, Bell, Hooper, Pakvasa & Weiler
Dim track
Stops in a big cascade(starting tracks dominated by BG)
April 25, 2006UHE Tau Neutrino Workshop
Tau Decay ModesTau 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
April 25, 2006UHE Tau Neutrino Workshop
Energy LossesEnergy Losses
Edx
dE
ionization stochastic losses
Particles are detected in neutrino telescopes through energy deposited in the detector
Stochastic energy loss mechanisms:
• Bremsstrahlung• pair production• Photonuclear interactions
ee
April 25, 2006UHE Tau Neutrino Workshop
Energy Loss Rates Energy Loss Rates
Taus are much dimmer than muonsBremsstrahlung, 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
Muons are brighter than taus
τ
μ
→ track suddenly brightensCan we see it?
April 25, 2006UHE Tau Neutrino Workshop
Muonic Tau DecayMuonic Tau Decay
τ → ντ + μ + νμ
Muon energy spectrum in the lab frame:
where
Average muon energy
E
Ex
5943
1 23 xxdx
dn
EE 35.0
(Perl 1992)
April 25, 2006UHE Tau Neutrino Workshop
Flavor DependenceFlavor Dependence
Muons lose energy by pair production (& brems)
Taus lose through photonuclear interactionsμ τ
Dutta, Reno, Sarcevic, and Seckel
April 25, 2006UHE Tau Neutrino Workshop
Energy Loss MechanismsEnergy Loss Mechanisms
Bremsstrahlung
Pair production
Photonuclear interactions
ll
ll
ll
γ
e+
e-
hadronicshower
( = μ,τ)l
EMshowers
April 25, 2006UHE Tau Neutrino Workshop
Hadronic Light YieldHadronic Light Yield
Hadronic showers emit 65-85% of the light of an electromagnetic shower of the same energy
M. Kowalski
April 25, 2006UHE Tau Neutrino Workshop
Are Photonuclear Losses Quasi-Continuous?
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)
April 25, 2006UHE Tau Neutrino Workshop
Photonuclear Energy Loss
Photonuclear Energy Loss
softcomponent
total photonuclearenergy loss
hardcomponent
Bugaev & Shlepin
April 25, 2006UHE Tau Neutrino Workshop
Photonuclear SpectraPhotonuclear Spectrasoft component
hard component
1 EeV
1 PeV
10 PeV
100 PeV
1 EeV
1 PeV
Peak at10-2 El
Bugaev & Shlepin
= Eshower / Eτ
April 25, 2006UHE Tau Neutrino Workshop
Quasi-Continuous?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
)103(~
8.5
1058.0
2
7
dv
dv
Ehard
hard
Peak
kmTeV/
April 25, 2006UHE Tau Neutrino Workshop
Brightness RatioBrightness Ratio
4.3–6.1 2.5–5.0 5.2–6.9 4.1–6.9
0.63–0.79 0.40–0.70 0.72–0.84 0.61–0.84
Quasi-Continuous Non-Continuous
PeV EeV PeV EeV
Ratio:
∆(log10):
Detector resolutions (in log10 E):AMANDA: 0.5ANTARES: 0.3–0.4(Carr & Hallewell)
(ICRC 2003)
April 25, 2006UHE Tau Neutrino Workshop
Low Energy Taus?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/νe background!
MC studies in progress…