3/22/2002M.A. Huang George W.S. Hou & M.A. Huang Center for Cosmology and Particle Astrophysics Department of Physics, National Taiwan University

3/22/2002M.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

3/22/2002M.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.

3/22/2002M.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

3/22/2002M.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 ~ eV.

3/22/2002M.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 ~ eV.

3/22/2002M.A. Huang Window of opportunity Conventional  detector UHECR  detector ?

3/22/2002M.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

3/22/2002M.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.

3/22/2002M.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 ~ gm/cm 2, 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.

3/22/2002M.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

3/22/2002M.A. Huang 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.

3/22/2002M.A. Huang From  to detectable signal Efficiency of  convert to  in mountain, then  decay and being detected.  = P 1 × (  0 L P 2 (x) P 3 (L-x) dx/ ) × P d P 1 :  survive in atmosphere, P 1 = exp{-X atm / } P 2 :  survive in rock, P 2 = exp{-X rock / } dx/ : convert to  P 3 :  survive the rest of rock, P 3 = exp{-(L-X rock )/  } P d : detection probability

3/22/2002M.A. Huang P 1 : Survivor probability in atmosphere P 1 = exp{-X atm / } X atm : atmospheric depth –Linsley’s atmosphere model from Aires –Consider the curvature and ellipsoid shape of the Earth. Zenith angle changes with position 1/ = N A ×  N) Interaction probability = 1- P 1

3/22/2002M.A. Huang interaction cross-section 1/ = N A ×  ×  N) –   : neutrino current cross- section,  + N   + X –  : rock density = 2.65 g/cm 3  =  × c × T   (E  /10 15 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

3/22/2002M.A. Huang P  : Conversion efficiency in mountain When energy loss is ignored, P  can be calculated analytically.  »   P    / P   E 1.4

3/22/2002M.A. Huang Optimal thickness Most of the effective interaction occur several decay length inside mountain.

3/22/2002M.A. Huang Energy loss of tau High energy tau loss energy quickly, tau surviving probability decrease much quicker. Example of  of ¾  eV in rock.

3/22/2002M.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

3/22/2002M.A. Huang P d : Detection probability  = 0.83 : Branching ratio of  decay to detectable channels –  (     ) ~ 0.17, undetectable Decay probability of  in distance d, from mountain to detector.

3/22/2002M.A. Huang Acceptance and Event Rate R (E) = A  E)  (E) –R: event rate [s –1 ] –A: acceptance = area  solid angle [cm 2 sr ] –  E) : cosmic neutrino flux [cm –2 s –1 sr –1 ] –  (E) : neutrino conversion efficiency

3/22/2002M.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

3/22/2002M.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

3/22/2002M.A. Huang Acceptance Acceptance : Include Mauna Loa and Mauna Kea  km 2 sr (10 14 to eV) Consider: –  (     shower) conversion efficiency –Energy loss of 

3/22/2002M.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.

3/22/2002M.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

3/22/2002M.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!

3/22/2002M.A. Huang Conclusion - 1 The optimal range for detecting by conversion in mountain/Earth is to 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.

3/22/2002M.A. Huang Conclusion - 2 Hualalai on the Big Island of Hawaii is a great site. –Good weather –Large acceptance ~ 1 km 2 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.

3/22/2002M.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