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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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