1. Fluorescence and Cerenkov photons from air shower 1/9-10/2003 VHENTW-3 Palermo, Italy Ming-Huey A. Huang 黃明輝 Department of Physics, National Taiwan University

2. 1/9/2003M.A. Huang Contents Air shower longitudinal profile Fluorescence photon flux simulation Cerenkov photons Arrival time of photons Conclusion

3. 1/9/2003M.A. Huang Why need fluorescence and Cerenkov photons ? Previous simulation require trigger at distance up to 5~7 km from shower core. –Cerenkov photons density decrease exponentially outside Cerenkov ring. –Fluorescence photons distribution is more isotropic Optical detection can not distinguish fluorescence or Cerenkov photons –Trigger time may different ? –How to use trigger time?

4. 1/9/2003M.A. Huang Longitudinal profile Tau exit mountain, decay, then initiate air shower –decay length ~ d =50 (E/PeV) m –Assume tau decay to electron –Gaisser-Hillas formula d =50 km d =5 km

5. 1/9/2003M.A. Huang Common environment Pressure, density of atmosphere taken from typical value at altitude 2.5 km, Hualalai mountain top. Density is assumed as constant, valid for near horizontal events.

6. 1/9/2003M.A. Huang Parameters of G-H formula N max = E/(1.35  10 9 ) X max = 550 + 80  log(E/10 15 ) X 0 is insensitive and have large fluctuation, use 5 gm/cm 2

7. 1/9/2003M.A. Huang Simulation Detection by fluorescence light offers larger solid angle than by Cerenkov lights. For trial runs: simulate neutrinos from a typical configuration.

8. 1/9/2003M.A. Huang Simulation N ph =N e  gf Mirror size 1m 2 Angular size for each pixel 0.5º Simplify geometry to 1-D track on shower- detector plane. 1-D detector, cover  from -80º to +80º –Just to cover whole track, not the finial design Emission angle   =90º

9. 1/9/2003M.A. Huang Fluorescence yield Y: fluorescence yield N e : # of secondary particles  : fluorescence eff. = #/cm/e q: mean ionization energy 2.2 MeV/(g/cm 2 )  : density P: pressure T: temperature R i : Reflectance/transmittance at wavelength I E i : intensity P eff : effective pressure T 0 : Temperature at STP

10. 1/9/2003M.A. Huang Fluorescence efficiency Top : From P. Sokolsky book and many references Bottom: Data from Bunner’s thesis, used in this simulation. Quite similar, but small differences

11. 1/9/2003M.A. Huang Geometry factor R p  : distance covered in each pixel  : emission angle, between line of sight and shower axis r: distance from detector to shower track in FOV A: mirror/lens area : scattering length ~ 20km

12. 1/9/2003M.A. Huang Detail of geometric factor

13. 1/9/2003M.A. Huang Photon number per pixel Threshold = 3 photon per pixel Even electronics sensitive to single photo- electron, threshold energy is still high ~ 10 16.5 eV

14. 1/9/2003M.A. Huang Difficulty in telescope orientation Different distribution of shower maximum, a small coverage in azimuth angle could only see a fraction of total energy range.

15. 1/9/2003M.A. Huang Difference between results from Giancarlo’s and Alfred’s Fluorescence efficiency: –G: 4.5 photons/m/e & A: 2.3 photons/m/e Shower profile: –G: GIL formula –A: N max =E/1.35 (E in GeV) –At above 10 19 eV, difference ~  2% –At 10 15 eV, G is 38% higher Mirror size –G: 2 meter radius, A: 1m 2

16. 1/9/2003M.A. Huang Comparison: Giancarlo’s results is higher by –Mirror : 12 times larger –Efficiency: 2 times larger –Shower size: 38% larger at 10 15 eV Adapting Giancarlo’s number, the minimum threshold is around 10 15 eV –Geometric factor seems OK ! Questions remains!

17. 1/9/2003M.A. Huang Nighttime airglow Much complex than previous measurements Contamination? Johnston and Broadfoot, 1993, JGR, 98, 21593

18. 1/9/2003M.A. Huang Question: fluorescence efficiency Wavelength seems O.K. Absolute intensity is different in Bunner (Alfred’s and Chen’s) and Kakimoton’s P. Chen’ talk in Workshop of Laboratory Astrophysics, Taipei, 2002.

19. 1/9/2003M.A. Huang Cerenkov light simulation Study photon density and arrival time Use ground array to sample Cerenkov photons Cerenkov photons are integrated over whole shower track –Longitudinal profile similar to fluorescence mode. –Shower start at different altitude, 20, 30, and 40 km. –Shower energy 10 14, 10 16, 10 18 eV

20. 1/9/2003M.A. Huang Simulation of photon arrive time T=0 at injection point, where  e Calculate shower longitudinal profile, produce Cerenkov photons c/n  electrons have angular spread according to multiple scattering Cerenkov photons emit from electrons directions Calculate photons propagation time and hit positions at ground. C

21. 1/9/2003M.A. Huang Fluorescence photon arrival time Cerenkov photon time + decay time of fluorescence photons (10ns ~ 50ns, depends on wavelength)

22. 1/9/2003M.A. Huang Cerenkov longitudinal profile N ph =N e  exp(-r/ ) –  is Cerenkov efficiency Depend on mean energy and index of refraction ~ 203 photons/(g/cm 2 )/e –  length in FOV – : scattering length ~ 20km 10 18 eV

23. 1/9/2003M.A. Huang Arrival time Similar to simulation by Corsika 500ns CORSIKA Fast simulation

24. 1/9/2003M.A. Huang Mean arrival time Depends mainly on shower position

25. 1/9/2003M.A. Huang Cerenkov photons Arrival time T=0 when first photon hit detector Time gate for coincidence between two detectors –in the order of  sec. –depends on distance between detectors and Rp –important tools to reconstruct event arrival direction and Rp Photon wave front Rp

26. 1/9/2003M.A. Huang RMS of arrival time Depend mainly on shower position

27. 1/9/2003M.A. Huang RMS of arrival time Photons from different part of showers arrive same detector at different time. c c/n If electronics can measure the spread of arrival time, pulse width, it can be correlated to Rp! Time gate for individual detector –Depend on Rp –Could be as large as 200 ns (Rp<5km).

28. 1/9/2003M.A. Huang Conclusion on arrival time Arrival time is critical for : –requirement for electronics design –event reconstruction Still need more works in reconstruction programs For two detectors separated by 1km –Gate time for one detector: RMS of arrival time ~ 200ns at Rp = 3km –Coincidence time between detectors: ~ 1  s

29. 1/9/2003M.A. Huang Fluorescence + Cerenkov For events near shower core, small Rp, detected photons are combination of Cerenkov photons and fluorescence photons –Need to combined two simulation –Need to separate two photons in reconstruction. For events with large Rp and large energy, fluorescence photons is as important as Cerenkov photons.

30. 1/9/2003M.A. Huang Conclusion Photons are photons, no need to exclude fluorescence or Cerenkov photons. –Near PeV, Cerenkov photons flux is higher –Near EeV, both signals are strong, fluorescence mode have larger acceptance. Dream detector: –Detect both Cerenkov and fluorescence photons Best way to take advantage of all signals. Difficult to design electronics and trigger.

31. 1/9/2003M.A. Huang On-going and future projects Simulation: –Fluorescence + Cerenkov photons –Reconstruction –Parameters form stereo observation by two detectors Theoretical side: – e &  via W resonance –Energy resolution

32. Detector Design Concept 1/10/2003 Ming-Huey A. Huang 黃明輝 Department of Physics, National Taiwan University

33. 1/9/2003M.A. Huang Contents Sensitivity and Event rate Requirements on detector design Multi-mirrors approach Site issues

34. 1/9/2003M.A. Huang Expected performance Target volume: better than the design goal of IceCube ~ 1 km 3 at E > 10 15 eV

35. 1/9/2003M.A. Huang New flux sensitivity 0.3event/year/half decade of energy –Similar to single event sensitivity (SES) Great chance to see AGN and TD

36. 1/9/2003M.A. Huang Sensitivity and Event Rate Sensitivity : 1 event/yr/half decade of energy  A=R  R 2 =(  2 /  1 )R 1 Total Rate in 10 14 ~ 10 18 = 12.2 events/yr (include 10% duty time) Assuming detection efficiency 0.3-0.7, R~ 4-8 events/year

37. 1/9/2003M.A. Huang Requirements on detector Field of view 12º  135º 30 photons in 1 m 2 mirror/lens pixel size ~ 0.5º Trigger condition –2 pixels triggered with 2 photo-electrons combined efficiency (reflectance/transmission/quantum efficiency) ~ 4/30 ~ 0.13

38. 1/9/2003M.A. Huang Lateral profile of Cerenkov photons Similar profile for showers produced by e – and   Cerenkov ring distance ~ (L-R max )  Tan  c Outside ring, photon density ~ exponential decay Detector can trigger far away from Cerenkov ring 10 18 eV 10 16 eV 10 14 eV

39. 1/9/2003M.A. Huang Optical system Technical difficulty: –Odd shape field of view 12º  135º, difficult to covered by a single mirror or lens –F value! Constraints: –Palermo: 290 8x8 MAPMT –Budget –Construction time/complexity

40. 1/9/2003M.A. Huang Solution: multiple telescopes Connecting several small telescopes to cover full FOV Each unit can be modified from existing models and available technologies. Options: –4 Fresnel lens telescopes, each cover 12º  36º Similar to Shimizu’s EUSO prototype –11 Reflective telescopes, each cover 12º  12º Similar to HiRes (16º  16º) Divide and Conquer

41. 1/9/2003M.A. Huang Advantages and Disadvantages The good All technologies available! Modularized design –easy construction schedule –operation start from first module, early start! Chance to learn from first module, easy to modify. The bad Complexities in calibration and installation –Can not be avoid and can be done! The Ugly Environmental impact –larger building

42. 1/9/2003M.A. Huang Example: 11 modules Top view Side view

43. 1/9/2003M.A. Huang F problem Large FOV and small pixel size  F < 1 –Very difficult in optical design –loss effective collection area at large off axis angle. Can be manipulated by light guide –Also kill the dead-space problem –Light guide can match curved focal surface. MAPMT array Light guide Lens/Mirror

44. 1/9/2003M.A. Huang Site requirements Detector housing –Two 48 feet container for 11 reflective mirrors one for telescopes and one for electronics and others –One 48 feet container for 3-4 Fresnel lens Power –Solar and wind Communication

45. 1/9/2003M.A. Huang Some issues related to site Is Hawaii the only site available? –Worry about inversion layer of Hualalai site –Site survey of White mountain, CA? Need long term weather information –Pressure, temperature, wind speed, humidity,... –Cloud height, visibility (aerosol contents …) On-site background measurement