ICECUBE Design, Performance, Experimental requirements

1
ICECUBEDesign, Performance, Experimental
requirements
Internal Review, Madison, August 2001

• Albrecht Karle
• University of Wisconsin-Madison
• karle_at_alizarin.physics.wisc.edu

2
Outline of Talk

• Overview
• Muon neutrinos from
• a) diffuse sources
• b) point sources
• c) Gamma Ray Bursts
• Electron Neutrinos Cascades
• Tau Neutrinos
• Detector, optical sensor
• Construction

3
IceCube
IceTop
AMANDA
South Pole
Skiway
80 Strings 4800 PMT
1400 m
2400 m
4
IceCube has been designed as a discovery
instrument with improved

• telescope area
• detection volume
• energy measurement of secondary muons and
  electromagnetic showers
• identification of neutrino flavor
• angular resolution
• wide energy range

5
??- flavours and energy ranges
Overview

• Filled area particle id, angle, energy
• Shaded area energy only

6
Signals and Background rejection
Backgrounds Atmospheric neutrinos Cosmic ray
muons (misreconstructed downgoing)
At extremely high energies, the downgoing
signals can be accepted
7
µ-event in Ice3
Low Noise 10 random pe / 4 µsec
1 km
8
Search for diffuse n-fluxes

• Method
• Assume a diffuse neutrino flux (Hypothesis), e.g.
  the current AMANDA limit
• dN/dE 10-6E-2/(cm2 sec GeV sr)
• --gt 11.500 events /year
• The background is the atmospheric neutrino flux
  (after quality cuts) 130.000 events / year
• Apply energy cut.

Atmospheric n
E-2 flux
9
Muon events
Eµ10 TeV
Eµ6 PeV
Measure energy by counting the number of fired
PMT. (This is a very simple but robust method)
10
Diffuse flux, 3 years of IceCube

• Optimize model rejection of nch (no. of fired
  PMT) cut.
• Sensitivity of IceCube after 3 years of operation
  (90 c.l.)
• dN/dEn 4.8 x 10-9 E-2/(cm2 sec GeV)

11
Sensitivity to diffuse fluxes
Using simple energy estimator
12
Sensitivity to point sources

• Reject background
• Angular resolution
• Energy cut

Search bin radius 1.0 Solid angle 2p/6500
0
1
2
4
3
6
Angular error (degrees)
13
Angular resolution for muonsversus energy

• Resolution 0.8 deg (median)
• Improves slightly with energy
• Reconstruction methods for high energies still in
  development

14
Angular resolution versus cos(?)

• Better near horizon 0.7

15
Sensitivity to Neutrinos from astrophysical point
sources

• Reject background by
• Energy (fired PMT 43, case of 3 years)
• Angle (circular bin of 1º radius)

A 10-7E-2 flux would yield 138 events above an
expected background of 0.8 events). Sensitivity
of IceCube after 3 years of operation (90 c.l.,
average for zenith angles gt 90º) dN/dEn 2.3 x
10-9 E-2/(cm2 sec GeV)
16
Point sources events rates
dN/dE 10-6E-2/(cm2 sec GeV)
17
Sensitivity to point sources

• Atmospheric Neutrinos, 2x2 deg. (vertical)
• Atmospheric Neutrino, 2x2 deg. (horizontal)
• AMANDA preliminary limit
• AGN Core (Nellen et al.)
• Crab Nebula (Bednarek Protheroe model I)
• Coma Cluster (Colafrancesco Blasi)
• P-gamma neutrinos(Stecker Salamon)
• 8. SNR IC444 (Gaissser et al)\

E2 (dN/dE)n / (GeV cm-2 s-1)
dN/dEn 2.3 x 10-9 E-2/(cm2 sec GeV) (3 years,
90 c.l.)
18
Neutrinos from Gamma Ray Bursts

• Reject background by
• Energy (number of fired PMT)
• Angle (circular bin of 1º radius)
• Time ( 10 sec/ GRB, coincident to known GRB)

19
Neutrinos from Gamma Ray Bursts

• Test signal 1000 GRB Waxman/Bahcall 1999
• Expected no. of events 11 upgoing muon events
• Expected background 0.05 events
• Sensitivity (1000 bursts) 0.2 x dN/dE
  (Waxman/Bahcall 99)

• IceCube is extremely sensitive to GRB neutrinos
  neutrino observation essentially without
  background.
• Only 200 GRB needed to detect/rule out WB99 flux

20
Cascade event
E 375 TeV
ne N --gt e- X

• The length of the actual cascade, 10 m, is
  small compared to the spacing of sensors
• gt roughly spherical density distribution of
  light
• 1 PeV 500 m diameter
• Local energy deposition good energy resolution
  of neutrino energy

21
Effective volume for cascades

• Trigger volume grows with size of event.
• Effective volume with background rejection and
  containement requirement saturates 1 km3

22
Size of cascades in ice

• Volume illuminated by 1 photoelectron by a
  cascade is well correlated with primary energy.

Photoelectrons / OM / PeV
23
Event rates of cascades (ne)
Assumed flux dN/dE 10-7E-2/(cm2 sec GeV sr)
24
????????gtDouble Bang
?t N --gt t- X
?t X (82)
E ltlt 1PeV Single cascade (2
cascades coincide) E 1PeV Double bang Egtgt 1
PeV Partially contained
25
Density profile of double bang eventE 10 PeV
photoelectrons
26
Capture Waveform information
E10 PeV

• Complex waveforms provide additional information

27
?? at EgtPeV Partially contained

• The incoming tau radiates little light.
• The energy of the second bang can be measured
  with high precision.
• Clear signature
• Muon Brem would be much brighter than the tau
  (compare to the PeV muon event shown before)

Photoelectron density
Timing, realistic spacing
Result high eff. Volume Only second bang needs
to be seen in Ice3
28
OM design DOM

• Design parameters
• Time resolution 5 nsec (system level)
• Dynamic range 200 photoelectrons/10 nsec
• Dynode tap under investigation.
• (Integrated dyn. range gt 2000 photoelectrons)
• Digitization depth 4 µsec.
• Noise rate in situ 500 Hz

DOM
33 cm
29
Observed waveforms in Ice
N2-Laser event generated by in situ
laser Amplitude 1010 photons, Wavelength
335 nm Pulse width 10 nsec- comparable to
300 TeV cascade
Distance of OM
Simulation
Data
45 m

115 m
167 m
2 µsec
HV of this PMT was lowered
30
Photomultiplier

• Best candidate Hamamatsu R7081
• Diameter 25 cm
• Gain 107
• Noise lt 300 Hz _at_ -30 C
• (Lab measurement)
• Number of Dynodes 10 or 12 (final decision after
  test measurements)
• Use µ-metal shielding against Earths magnetic
  field.
• This PMT is designed very similar to the R5912-2,
  which has been tested successfully in AMANDA
  (670 PMT).
• Other PMT
• Photonis, 11 inch ruled out (noise rate 200 Hz)
• Electron Tubes, 11 inch theoretically still an
  option.

31
Glass instrument housing

• Glass transmission matches PMT sensitivity and
  absorption minimum of ice.
• Low potassium glass allows low noise rates
  lt 500 Hz/OM

32
Glass instrument housing

• Improved Glass transmission lower UV cutoff.
• Measurements of candidates Benthos, Nautilus.
• K40 content 0.05 (AMANDA0.7)

33
IceCube String
1400 m
OM Spacing 17 m
2400 m
34
Breakouts

• One twisted quad
• 2 twisted pairs
• 4 Optical Modules
• 15 breakouts for 60 OMs

35
String design Surface cable and In-ice cable
36
(No Transcript)
37
South Pole
38
South Pole
Dark sector
Skiway
AMANDA
Dome
IceCube
39
Top View
40
Construction 11/03-1/09