1. HiRes Usage

2. Outline ● Shower energy ( Size, dE/dx ) ● Atmospheric profile ( stdz76, radiosonde) ● Rayleigh Scattering ● Aerosols Model ( density, variability ) ● Aerosols Scattering ● Detector Optical Efficiency.

3. Old HR1 Mono Shower Energy ● E tot = E em + E miss ● E em = Profile Integral x const. ● Profile Integral <== Nmax, x 0, x max ● const = 2.18 ( Average dE/dx ) ● N max = E tot / 1.3e9 ● E miss ~ 5-15 % ( Linsley )

4. New HR1 Mono Shower Energy ● E tot, N max,x max, x0 ( Based on Corsika ) ● N max /E tot =a0+a1*x+a2*x*x ● x== x max - x 0 ● N max / E tot ~ 0.65 or N max ~ E tot / 1.5e9 ● But ~ 11% shower particles below tracking threshold in Corsika, so put them back in: ● N max /E tot ~ 0.73 or N max ~ E tot / 1.4e9 ● No explicit missing energy correction

5. Proper Accounting ?! ● Old vs. New HR1 mono: ● Old Nmax > New Nmax by ~10% ● Old dE/dx < New dE/dx by ~ 10% ● A shower with a given energy will produce the roughly the same amount of light at the detector in old/new analysis ● An observed event will be reconstructed to the same nominal energy in old/new analysis. ● BUT for real showers, reconstructed N max will be 10% too high

6. Energy Reconstruction ● We use an “inverse Monte Carlo” technique for energy reconstruction. ● Calculate tube signals for a shower with “unit energy”, compare to measured tube signals and do fit to best match observed tube signals. ● The fit energy = scaling factor x “unit energy” ● So, the ratio of N max to E tot factors out and does not affect energy estimate.

7. Scintillation Yield ● dE/dx:  Old: Based on Hillas Calculations  New: Based on Corsika simulations ● Yield:  Old/New use Kakimoto et al. total yield ● Wavelength Dependence:  Old/New use Bunner Spectrum ● New Analysis may be updated to use newer measurements

8. Atmospheric Profile ● Old Analysis uses the 1976 U.S. Standard Atmosphere Model. ● New Analysis uses Radiosonde measured profiles IF available, reverts to standard atmosphere otherwise. ● Atmospheric ceiling at 70 km for old analysis, Radiosonde data available up to 30 km. ● We use linear interpolation of measured points, maybe can improve?

9. Rayleigh Scattering ● Depends on atmospheric density, so altitude. ● Well known physics... but ● Wavelength dependence of scattering length changed from 1/lambda 4 to 1/lambda 4.22 in MC and reconstruction codes!

10. Aerosols Scattering ● Mostly in the forward peak ( Longtin Phase function ) ● Weak wavelength dependence ( Etterman ) ● At Dugway Average attenuation length 25 km, average scale height 1 km. ( No mixing layer ) ● Data Base: fit for attenuation length and scale height; No mixing layer ( 2 parameter fit )

11. Detector Optical Efficiency ● Mirror Reflectivity  Nominal Value / Measured  Time Variability  Wavelength Dependence ● UV Filter Transmission ● PMT QE ● PMT Response profile