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Expected Sensitivity of a Neutrino Telescope at Hawaii

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

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Expected Sensitivity of a Neutrino Telescope at Hawaii

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  1. 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 M.A. Huang

  2. Contents • A new type of detector for Neutrino • Neutrino conversion inside mountain • Potential site at Hawaii, Big Island • Acceptance and flux sensitivity • Sky coverage M.A. Huang

  3. 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. M.A. Huang

  4. 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  M.A. Huang

  5. 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. M.A. Huang

  6. 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. M.A. Huang

  7. Window of opportunity UHECR n detector Conventional n detector ? M.A. Huang

  8. 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 M.A. Huang

  9. 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. M.A. Huang

  10. 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. M.A. Huang

  11. 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 M.A. Huang

  12. 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. M.A. Huang

  13. From  to detectable signal Efficiency of  convert to  in mountain, then  decay and being detected.  = P1× ( 0LP2(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 M.A. Huang

  14. 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 M.A. Huang

  15.  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 M.A. Huang

  16. P : Conversion efficiency in mountain • When energy loss is ignored, P can be calculated analytically.  »  P / P  E1.4 M.A. Huang

  17. Optimal thickness • Most of the effective interaction occur several decay length inside mountain. M.A. Huang

  18. Energy loss of tau Example of  of ¾1018 eV in rock. High energy tau loss energy quickly, tau surviving probability decrease much quicker. M.A. Huang

  19. Effect of energy loss Blue : No dE/dX Red: dE/dX • Reduce range of tau, increase acceptance • Increase fluctuation of tau energy, energy resolution become worse. M.A. Huang

  20. 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. M.A. Huang

  21. 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 M.A. Huang

  22. Effective solid angle • Effective solid angle is Cerenkov light cone • Because lateral distribution, air shower light cone is extended to c ~ 5 º M.A. Huang

  23. 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 M.A. Huang

  24. 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  M.A. Huang

  25. 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. M.A. Huang

  26. 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 M.A. Huang

  27. 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! M.A. Huang

  28. 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. M.A. Huang

  29. 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. M.A. Huang

  30. 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 M.A. Huang

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