Characterization of Orbiting Wide-angle Light-collectors ( OWL )

1. Characterization of Orbiting Wide-angle Light-collectors (OWL) By: Rasha Usama Abbasi

2. OUTLINE • Motivation • Shower Generation and Reconstruction • OWL Simulation Study • Quality cuts • Energy and Angular resolution • Aperture calculations • OWL optical simulation and design • Conclusion

3. Unsolved problems in Ultra-High Energy Cosmic Rays. • Motivation • Origin of these rays. • Acceleration mechanism. • Determine Energies, chemical composition, arriving direction . • Discovering cosmic rays > Greisen-Zatsepin-Kuzmin (GZK) cut off 6×1019 eV. • Propagation through CMBR ?

4. Comparison of UHECR Experiments

5. OWL Inclined air shower • Two satellites • 1000 km height and 500 km separation • View common volume of the atmosphere • Tilted near the nadir point • Obtain a large field of view FOV with ~106 pixels, ~106 km2 sr

6. Shower Generation Geometry generation • Shower core : randomly simulated location could lie outside the Field Of View (FOV) of the detector. • Shower direction: randomly simulated isotropic direction Energy generation • Energy is generated with several set of fixed energies.

7. Shower generation Profile generation • Profile simulation is based on Gaisser-Hillas (G-H) parameterization.

8. Xo :the point of the first interaction (g/cm2) simulated with an exponential function. • Xmax : the point of the maximum development of the shower (g/cm2) sampled from a Gaussian function. • l: constant 70 g/cm2 . • : shower size at maximum.

9. Simulated event Y-axis angular position vs. X-axis angular position Pixel size is 0.07o, FOV on ground is 1km2/pixel

10. OWL Simulation Study • Goals of my study • Aperture of the detector • Number of events collected each year • Energy and Angular resolution

11. Reconstruction • Plane Reconstruction • Determines the Shower Detector (SD) plane that contains the detector and the shower track which depends on the triggered pixel direction.

12. Plane Reconstruction Minimizing : normal to the plane. :direction of the pixel :number of photoelectrons triggering the pixel . :angular error of the pixel ~ 0.07 0 .

13. Track Reconstruction • Track reconstruction • SD’s depends on triggered tube direction • Intersection between the SD planes of the orbiting detectors.

14. Track Reconstruction fit for the 1st and 2nd eye . Time (micro seconds) vs. Θ (in degrees)

15. Profile Reconstruction Profile reconstruction • Minimizing between the signal that is produced by the shower and detected in the pixels.

16. Profile Reconstruction :number of photoelectrons detected per each pixel :number of photoelectrons predicted by trial simulated event. :error by adding Poisson fluctuation and ground light noise.

17. Observed shower profiles Pe/ 1deg / m2 vs. Xmax (gm/cm2)

18. Reconstruction of the simulated event • Energy • Direction • Composition (Xmax)

19. Quality cuts • Optimization between best fractional energy, and angular error while maximizing a usable reconstructible aperture. • Energy and angular resolution

20. Quality cuts • Zenith angle of the shower > 930 • Opening angle between the reconstructed SD’s planes >100

21. Quality cuts • Track length > 0.70 • Geometry of the track • Photoelectron per good tube > 5.2 • Low energy events and noise sources

22. Quality cut Energy resolution vs. track length for a simulated shower

23. Energy resolution histogram 3×1019 eV • Number of events vs. Fractional energy error 14% shift in the mean

24. Energy resolution histogram 1×1020 eV • Number of events vs. Fractional energy error -2% shift in the mean

25. Energy resolution histogram 3×1020 eV • Number of events vs. Fractional energy error -3% shift in the mean • Energy resolution gets better with higher energies

26. Angular resolution histogram 3×1019 eV • Number of events vs. Angular error (deg) • Half of the events are better than 0.9o

27. Angular resolution histogram 1×1020 eV • Number of events vs. Angular error (deg) • Half of the events are better than 0.6o

28. Angular resolution histogram 3×1020 eV • Number of events vs. Angular error (deg) • Half of the events are better than 0.3o • Angular resolution also gets better with higher energies

29. Aperture calculation To calculate the aperture we need to find. • First the Generation aperture

30. Find the triggered aperture (Monte Carlo integration) Find the reconstructed aperture Aperture calculation

31. Trigger Aperture Aperture (×106 km2 sr) vs. Log(E(EeV)) Note: that it saturate at 2.4×106 km2 sr

32. Reconstruction Aperture Aperture (106 km2 sr) vs. Log(E(EeV))

33. Large drop between the trigger and the reconstruction aperture at 3×1019eV because there is not enough photoelectrons to fit it to the G-H function (can not find minimum because of insufficient SNR).

34. Number of events per energy bin. Knowing that The assumed flux j(E) is taken from Fly’s Eye spectrum, extrapolated to beyond 1020 eV.

35. Fly’s Eye stereo spectrum

36. Number of events per energy bin. • The number of events collected by the detector in a year duration (10% duty cycle) of time that holds energies between Ei = 5 × 1019eVand Ef = 3 × 1020 eV is equal to 2376 events.

37. Number of events per energy bin.

38. From the simulation results • Angular resolution ( 0.3o 0.9o ) . • The directional accuracy of OWL is comparable to HiRes. • OWL does not provide us with an astronomical quality accuracy. i.e. important for ID n and g sources.

39. From the simulation results • Although the threshold of the trigger aperture is ~ 1×1019 eV, the threshold of the reconstructed aperture is much higher ~ 4×1019 eV • High threshold is problematic: not knowing how the detector acts in low energies will compromise the accuracy of our experiment.

40. OWL optical simulation • Construct a photon-by-photon ray tracing simulation. • Use the ray tracing simulation to characterize the proposed system. • Without a Schmidt corrector plate. • With a Schmidt corrector plate. • Comparison.

41. OWL optics • Wide angle viewing camera (400 FOV) • Pixel size is 0.070, 4.4mm on the focal plane with FOV of (1km2/pixel) on the ground.

42. OWL optics • Spherical mirror (7.1 m diameter , 6.0 m radius of curvature). • Spherical focal plane surface ( 3.0 m radius of curvature, 3.15 m focal length and 2.3 m diameter) • 3.0 m corrector plate with an aspherical front and a planer back surface .

43. Schmidt camera geometry

44. Lego plot (m) without the corrector, angle of incidence =00 ~18 pixels across each side Note: coma

45. Lego plot (m) without the corrector, angle of incidence =100 ~18 pixels across each side Note: coma

46. Corrector plate • The profile of the corrector plate is T(r) : thickness of the corrector plate at a radial distance r from the center f: focal length of the mirror n: the refractive index of the plate Rd: the radius of the entrance from center

47. Lego plot (m) with the corrector plate, angle of incidence =00 The size of the center is comparable to a pixel

48. Lego plot (m) with the corrector plate, angle of incidence =100 The size of the center is comparable to a pixel

49. Entrance aperture Number of particles/radial position vs. Radial position (without the corrector plate)

50. Number of particles/radial position vs. Radial position (with the corrector plate)