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Tau Neutrinos in IceCube. Advantages of tau neutrinos Tau neutrino signatures in IceCube Or: Double Bangs Are Just the Tip of the Iceberg Results from initial “toy” Monte Carlo studies. 1 PeV n t  t X, t  mnn. Advantages of Tau Neutrinos.

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Tau neutrinos in icecube
Tau Neutrinos in IceCube

  • Advantages of tau neutrinos

  • Tau neutrino signatures in IceCube

    • Or: Double Bangs Are Just the Tip of the Iceberg

  • Results from initial “toy” Monte Carlo studies

1 PeV nttX, tmnn

D. Cowen/Penn State


Advantages of tau neutrinos
Advantages of Tau Neutrinos

  • At high energies (E > ~1 TeV), nt are a virtually background-free source of cosmological neutrinos

    • Sources of nt which will give negligibly small fluxes:

      • atmospheric nt from atmospheric ne and/or nm`oscillations

        • oscillations small at these energies

      • “prompt” atmospheric nt from charm decay

    • Only faraway accelerators that produce neutrinos as ne:nm:nt::1:2:0 can, through neutrino oscillations, produce appreciable numbers of tau neutrinos at IceCube

      • flux ratio at earth is ~1:1:1

  • Tau flavor is a very clean tag for cosmological neutrino origin

D. Cowen/Penn State


More advantages of tau neutrinos
More Advantages of Tau Neutrinos

  • Energy resolution

    • can be comparable to that of ne

  • Pointing resolution

    • can be comparable to that of nm

  • Acceptance

    • varies from ~2p to ~4p, depending on tau decay channel

      • tau neutrino regeneration in the earth allows UHE nt to penetrate and emerge at ~1014-15 eV

        • leads to 4p acceptance at E(nt) < ~1014-15 eV

  • Rich set of signatures allows for

    • better background rejection

    • self-consistency checks

      • e.g., measurements of the same neutrino flux with different systematics

D. Cowen/Penn State


Quick overview of icecube
Quick Overview of IceCube

  • Over 70 strings, L~1km, total V~1km3

    • 60 Digital Optical Modules (DOMs) per string

    • Deployed at depths of 1450-2450m at South Pole

    • Completion slated for 2011

  • Currently have 9 strings deployed

    • partially surrounding AMANDA; eventually will completely surround

    • in principle already sensitive to some nt channels

  • [see talk by K. Hanson for more details about IceCube detector]

D. Cowen/Penn State


Capabilities of icecube doms
Capabilities of IceCube DOMs

  • Each DOM, a standalone computer, has

    • built-in set of digitizers (very important for detection of tau neutrinos)

      • fast ones: 3 different gain levels, ~3ns sampling period, ~400ns depth

        (128 samples)

      • slow one: 25ns sampling period,

        6.4ms depth (256 samples)

    • built-in, remotely

      programmable, calibration

      light source (can be used to

      simulate tau neutrinos)

    • few nanosecond time resolution

      • distinguish light pulses from

        individual nt–induced cascades

D. Cowen/Penn State


Tau neutrino signatures in icecube overview
Tau Neutrino Signatures in IceCube: Overview

nt

nt

t

t

nt

t

nt

t

nt

t

m

DOM

Waveform

nt

t

m

nm

nt

Decreasing IceCube Acceptance Energy 

D. Cowen/Penn State


Lollipop
Lollipop

nt

t

D. Cowen/Penn State


Inverted lollipop
Inverted Lollipop

nt

t

D. Cowen/Penn State


Sugardaddy
Sugardaddy

nt

t

m

See talk by T. DeYoung

D. Cowen/Penn State


Double bang
Double Bang

nt

t

D. Cowen/Penn State


Double pulse
Double Pulse

nt

t

DOM

Waveform

D. Cowen/Penn State


Low e t m lollipop
Low Etm Lollipop

t

m

nm

nt

D. Cowen/Penn State


Tau channels in icecube
Tau Channels in IceCube

D. Cowen/Penn State


Toy mc studies of tau neutrinos in icecube
“Toy” MC Studies of Tau Neutrinos in IceCube

  • Many of the channels mentioned here are under active investigation

  • Using very simple MC at present

    • no actual tau decay—we fake it for now

    • no full detector simulation—but geometry and timing resolution are reasonably accurate

  • Initial goal is to do feasibility studies

    • if a signal is not detectable under these idealized circumstances, it will not be detectable under more realistic circumstances

D. Cowen/Penn State


Double pulse channel
Double Pulse Channel

nt

t

DOM

Waveform

  • Look at tagging efficiency using a toy simulation, full km3:

    • place first cascade randomly in box ±200m from detector center with E = 0.25 E(nt)

    • Tau travels in same direction as initial nt and then decays following the expected lifetime

    • Tau decays to an electron with E = 0.42 E(nt)

    • Look at variety of energies and zenith angles

    • Calculate time separation Dt detected at one (or more) DOMs purely geometrically(i.e. no scattering);

      • For this study, we require large enough Dt to consider a two-pulse waveform to be detectable and

      • we crudely simulate scattering by varying a cut on the shower-to-DOM distance

D. Cowen/Penn State


Double pulse channel1
Double Pulse Channel

  • Cuts (>=1 or >=2 DOMs):

    • cut1: r<70m && 30<Dt<300ns (~ignores scattering, optimistic Dt)

    • cut2: r<70m && 60<Dt<300ns (~ignores scattering, conservative Dt)

    • cut3: r<35m && 30<Dt<300ns (~no scattering, optimistic Dt)

    • cut4: r<35m && 60<Dt<300ns (~no scattering, conservative Dt)

Pat Toale, Penn State

  • (Efficiency is basically flat as a function of zenith angle to tau track)

D. Cowen/Penn State


Double pulse channel2
Double Pulse Channel

  • Here is what a fully simulated waveform looks like for a 75 TeV tau (~300 TeV nt)

    • designing a robust algorithm for identifying the two separate pulses is underway (and should not be terribly hard for cases like this)

cascade 1

cascade 2

sum

 MC truth

Light from two cascades from 75 TeV tau in a single DOM (5mV=1p.e.)

D. Cowen/Penn State


Lollipop channels
Lollipop Channels

nt

nt

t

t

50 TeV nt

  • The lollipop channels consist of a cascade and a track in the same event

  • For an initial feasibility study, we simulate a cascade followed by a muon, using the average Ec and Em energies expected for a tmnn decay

    • Investigate whether or not we can reconstruct such a “hybrid” event

      • reconstruct cascade and muon as distinct entities

    • Use full detector simulation

D. Cowen/Penn State


Lollipop channels1
Lollipop Channels

nt

t

  • In the topology under study

    • the early high- multiplicity- photon hits will come mainly from the cascade

    • the later low-multiplicity hits will come mainly from the muon

  • This is borne out by the MC:

multiplicity (p.e.)

time (ns)

D. Cowen/Penn State


Lollipop channels2
Lollipop Channels

  • Initial findings are that

    • the muon reconstructs well even if the fitter is given all hit DOMs (including those from the cascade)

      • here, “tagged” = space angle is within ~6o of true direction

    • the cascade reconstructs better if it is only given the earlier hits

      • here, “tagged” = vertex position within ~50 m of true vertex

D. Cowen/Penn State


Lollipop channels3
Lollipop Channels

  • Estimate of tagging efficiency vs. E

Seon-Hee Seo, Penn State

D. Cowen/Penn State


Sugardaddy channel
Sugardaddy Channel

  • This channel relies on seeing an increase in track brightness produced by tmnn

    • probably background-free signal

      • tracks from background processes should only decrease in brightness along their lengths

    • expect brightness increase of 3x to 7x

      • see Ty DeYoung’s talk for details

  • Toy simulation uses single muon track that is overlaid with 2 or 6 additional collinear muon tracks about halfway along its length

D. Cowen/Penn State


Sugardaddy channel1
Sugardaddy Channel

“decay”

at -100m

  • Toy simulation of 10 PeV tau lepton

    • use 1 PeV muon

    • overlay with additional 1PeV m tracks to mimic decay tmnn

  • Look at number of hit DOMs as a function of length along the track(s)

7x

number of DOMs hit

4x

Dawn Williams, Penn State

no “decay”

distance along track (m)

D. Cowen/Penn State


Conclusions
Conclusions

  • Many different tau decay channels are accessible to large-scale UHE neutrino detectors (not just IceCube)

    • tau neutrinos can be relatively background-free as a signal for cosmological neutrino detection

    • tagging efficiencies are reasonably high

    • different tau neutrino channels can be compared to one another as a valuable systematic check

  • Initial studies are encouraging

    • more detailed Monte Carlo studies are underway

  • Ultimately, expect to have sensitivity to tau neutrinos at energies 1-2 orders of magnitude below and many orders of magnitude above the better-known double bang channel

D. Cowen/Penn State


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