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Expected Sensitivity of a Neutrino Telescope at Hawaii. Neutrino Telescope Project. George W.S. Hou & M.A. Huang Center for Cosmology and Particle Astrophysics Department of Physics, National Taiwan University. Contents. A new type of detector for Neutrino - PowerPoint PPT Presentation
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3/22/2002 M.A. Huang
George W.S. Hou & M.A. Huang
Center for Cosmology and Particle AstrophysicsDepartment of Physics, National Taiwan University
3/22/2002 M.A. Huang
Contents
• A new type of detector for Neutrino • Neutrino conversion inside mountain• Potential site at Hawaii, Big Island• Acceptance and flux sensitivity• Sky coverage
3/22/2002 M.A. Huang
Why neutrino telescope?• JLC schedule delay
– 1997 proposed to build in 2001– 2nd ACFA statement 2001, expected
construction time as early as 2005, finish time ~ 2009, well beyond CosPA schedule!
– No need to continue original plan “BPC prototype”.
• Dark matter detector prototype: Finished!
• Great potential for neutrino astrophysics.
3/22/2002 M.A. Huang
Neutrinos from Universe CR interact with matter or
photons and produce neutrino through pions decay.– CR + X e 2 e
• Cosmological sources: WB and MPR limit
• Galactic CR + ISM galactic
– UHECR + CMB p + GZK
3/22/2002 M.A. Huang
Conventional detectors
• Shield from CR and atmospheric muons.– Underground, under-sea, or under-ice.
• Very large target volume = detection volume
• Difficult to expand target volume, maximum energy ~ 1015 eV.
3/22/2002 M.A. Huang
UHECR detectors
• UHECR detector such as Auger array could also detect neutrino induced air showers
• Conversion efficiency in atmosphere is small and the energy threshold is high ~ 1018 eV.
3/22/2002 M.A. Huang
Window of opportunityConventional detector UHECR detector?
3/22/2002 M.A. Huang
Alternative approach• Use mountain as target and shield.
• Use atmosphere as calorimeter, measured air shower initiated by the decay/interaction of .
• Advantage– Lower cost
– Larger acceptance
• Disadvantage– Limited by site, same problem
as any experiment.
– Limited field of view
3/22/2002 M.A. Huang
Detection mechanism
• High energy interact inside mountain, produce lepton via charge current interaction. + X e/ + X’– e will shower in very short distance, will pass through valley without interaction could decay in the valley, produce shower and being detected.
• Detector similar to -ray imaging Chrenkov telescope.
3/22/2002 M.A. Huang
Site selection• The cross-section of target mountain should be as large as
possible
• The valley should be as wide as few 10s km.– Shower maximum ~ 500 -700 gm/cm2, for atmosphere at 1-3 km
altitude, this corresponds to 4.5km to 7.8 km.
– Proper distance for to decay.
• Because of optical detection, the atmosphere should be dry and less cloudy.
• Night sky should be dark and free from artificial lights.
• It is preferred if the galactic center is visible.
3/22/2002 M.A. Huang
Hawaii big island• Astronomer’s dream site
– Good weather
– Less artificial light
• Mt. Hualalai provide a good view of Mt. Loa and situated in the dryer west side of island.
• Mt. Loa provide long base line, ~ 90 km wide and 4 km high.
Mauna Loa
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Field of view of telescope• Azimuth angle: from
south to east.• Zenith angle: from
86.9º to 91.5º min=86.9º: from
detector to top of
Mauna Loa, < min sky is visible.
max=91.5º: line of sight tangent to Earth,
> max skimming through Earth first.
3/22/2002 M.A. Huang
From to detectable signal
Efficiency of convert to in mountain, then decay and being detected.
= P1× ( 0L P2(x) P3(L-x) dx/ ) × Pd
P1: survive in atmosphere, P1 = exp{-Xatm/ }
P2: survive in rock, P2 = exp{-Xrock/ }
dx/ : convert to
P3: survive the rest of rock, P3 = exp{-(L-Xrock)/ }
Pd: detection probability
3/22/2002 M.A. Huang
P1: Survivor probability in atmosphere
P1 = exp{-Xatm/ }• Xatm : atmospheric depth
– Linsley’s atmosphere model from Aires
– Consider the curvature and ellipsoid shape of the Earth.
• Zenith angle changes with position
• 1/ = NA ×N)
• Interaction probability = 1- P1
3/22/2002 M.A. Huang
interaction cross-section• 1/ = NA × ×N)
: neutrino current cross-
section,
+ N + X : rock density = 2.65 g/cm3
= × c × T
(E /1015 eV) ×48.92 m
• E = (1-y) E where y is fraction of energy carry out by interacting nucleon, y=¼, So E = ¾ E
3/22/2002 M.A. Huang
P : Conversion efficiency in mountain
• When energy loss is ignored, P can be calculated analytically.
//
0
11/
0
/)(/
LL
L xL
L xLx
ee
dxee
dxeeP
»
P /P E1.4
3/22/2002 M.A. Huang
Optimal thickness
• Most of the effective interaction occur several decay length inside mountain.
log
0/
m
LL
LL
L
ee
L
P m
m
3/22/2002 M.A. Huang
Energy loss of tau High energy tau loss
energy quickly, tau surviving probability decrease much quicker.
βxeExE
Edx
dE
0
0
)(
xExexP /)(
Example of of ¾1018 eV in rock.
3/22/2002 M.A. Huang
Effect of energy loss• Reduce range of tau,
increase acceptance• Increase fluctuation of
tau energy, energy resolution become worse.
Blue : No dE/dX Red: dE/dX
3/22/2002 M.A. Huang
Pd: Detection probability
= 0.83 : Branching ratio of decay to detectable channels ( ) ~ 0.17,
undetectable
• Decay probability of in distance d, from mountain to detector.
Edd eP /
3/22/2002 M.A. Huang
Acceptance and Event Rate
R (E) = A E) (E)– R: event rate [s–1 ]
– A: acceptance = area solid angle [cm2 sr ]
E) : cosmic neutrino flux [cm –2 s –1 sr –1 ] (E) : neutrino conversion efficiency
3/22/2002 M.A. Huang
Effective solid angle• Effective solid angle is
Cerenkov light cone• Because lateral
distribution, air shower light cone is extended to c ~ 5 º
sr 0.0239
cos12
sin0
2
0
c
c
dd
3/22/2002 M.A. Huang
Effective area• Effective area: area
where tau decay and initiate shower.– On average, tau decay at
one decay length ( ) pass
mountain. : solid angle of each pixel
– D: distance from detector to
mountain surface
dEDEaFOV
2)()(
3/22/2002 M.A. Huang
Acceptance• Acceptance : Include
Mauna Loa and Mauna Kea 1.72 - 0.3 km2 sr
(1014 to 1018 eV)
• Consider: ( shower)
conversion efficiency
– Energy loss of
3/22/2002 M.A. Huang
Sensitivity • Assuming sensitivity
is the flux which produce 0.3 events/year per half decade of energy.
• Chance to explore MPR limits and set similar upper limit as AMANDA-B10 at higher energy.
• Nearby point source could be detected.
3/22/2002 M.A. Huang
Run time• Optical detector operate in
moonless and cloudless night.
• The moonless nights from 12/2003 to 12/2007 are shown, ~5200 hours, ~20%.– In realistic case, the run time
should be deducted by some fraction when weather is cloudy or foggy.
– Normally, use 10% as duty time.
Source code come from HiRes group
3/22/2002 M.A. Huang
Sky coverage :
• Consider:– FOV of Hualalai site (looking at Mauna Kea and Mauna Loa)– Run time 12/2003 to 12/2007; 20% duty time
Galactic center is visible!
3/22/2002 M.A. Huang
Conclusion - 1• The optimal range for detecting by conversion in
mountain/Earth is 1015 to 1018 eV, – Conversion efficiencies are high and energy resolutions
are reasonable.
– Gap between conventional detectors and UHECR detectors.
– This uniqueness make this project attractive!
• Great chance to initiate the first experiment of this technique.
3/22/2002 M.A. Huang
Conclusion - 2• Hualalai on the Big Island of Hawaii is a great site.
– Good weather
– Large acceptance ~ 1 km2 sr
– Reach similar sensitivity as AMANDA-B10.
– Galactic center is visible
• Potential increase of acceptance– Add Earth skimming events below horizon (>91.5º)
– Add fluorescent mode
– Add sea-skimming events• Looking at the west of Hualalai• Could be more noisy due to reflection from waves.
3/22/2002 M.A. Huang
Technical challenges
• Acceptance is limited by the site!
• A compact detector would need low-noisy and high gain electronics.
• Short signal pulse (~ ns), extremely low event rate (~1/year)– Potentially many background signals – Need multiple coincidence trigger
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