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…