HiRes Composition. John Belz, University of Utah Nuclear Interactions Workshop University of Washington 20 February 2008

Transcription

1 HiRes Composition John Belz, University of Utah Nuclear Interactions Workshop University of Washington 20 February 2008

2 Search for AGN Correlations... 2

3 ...using PAO criteria Match energy scales: lower HiRes energies by 10%. Use PAO optimal criteria: E > 56 EeV θ < 3.1 z < HiRes has 13 events (same as PAO) 2 are correlated, where 3 are expected by chance. no effect. 3

4 ...scanning HiRes Stereo Data Use method of Finley and Westerhoff APP 21 (2004): Scan to determine E,, z bin with lowest chance probability in data, Examine MC isotropic data sets, counting ones with equal or lower chance probability. This takes statistical penalty into account. At 15.8 EeV, 2.0, there were 36/198 correlated, chance probability =.0018 MC data sets had lower chance probabilities 24% of the time. No effect. 4

5 Composition via Xmax 5

6 Stereo measurement of Xmax First HiRes published result on elongation rate and Xmax distribution in Ap. J. 622 (2005). Complete HiRes stereo has ~4x statistics. Completely new stereo reconstruction program. Includes hourly atmospheric corrections and cloud detection database. 6

7 Data Quality Cuts Tuned on Fe/P CORSIKA/QGSJET01 Cuts intended to make sure Xmax is visible < Xmax< 1300 g/cm2 FOV > 250 g/cm2 Rp(2) > 5 km, Rp(1) > 2 km... and good Xmax resolution is obtained Gaussian in age width 0.11 < σs < 0.29 Stereo Opening angle > 3.6º 7

8 Xmax Resolution for p and Fe 8

9 Data Quality Cuts Cuts to insure Fe/p reconstruction ratio is flat over the entire energy range Particularly important at low energies 9

10 Predicted Proton and Fe Xmax Distribution 10

11 HiRes Data 11

12 Effect of Atmospheric Cuts 12

13 HiRes Stereo <Xmax> Favors Break 13

14 Comparison w/ Previous HiRes 14

15 Comparison w/ PAO 15

16 Breakpoint Location? 16

17 Breakpoint Location? ~3 from any fit. Ignore? 17

18 HiRes/PA0 Structure Similar 18

19 In Progress: Fit Data to Sum of P+ Fe Make use of full Xmax distribution. Here, just below break in elongation rate (bin centered at log(e) = 18.25). 19

20 Xmax distributions black Data, red Proton MC 14

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24 HiRes Composition: Conclusion With 4x larger data set: Elongation rate and <Xmax> distribution consistent with a light composition Good agreement with previous HiRes measurements above 1018 ev Good agreement with Auger Studies in progress utilizing full Xmax shape to extract Fe fraction. 24

25 Telescope Array Low Energy Extension (TALE) 25

26 TALE Detectors: the Tower Detector Tower detector: Mirrors 3x larger than HiRes Observes from 31 to 72 degrees in elevation Designed for hybrid observation with infill array from to 1018 ev No transverse or longitudinal biases in this energy range 26

27 Another Composition Window: Muons 1017 ev showers, 30 zenith at TA ground, 100 meters from core of shower (CORSIKA/EPOS) 27

28 TALE: Underground Muon Detectors Preferred design, if BLM permits Reduced cost Simpler Reclamation, reseeding required 28

29 TALE Prototype Sand Box muon detectors Shield 12 m2 scintillator from electrons, gammas Sandbags 12 m2 scintillator Scintillator 20' shipping containers 29

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31 TALE Summary Composition studies are vital to TALE nd objectives of understanding 2 knee and ankle. Tower Detector, surface infill array will perform Xmax studies down to 2nd knee. Muon detectors provide complementary 16.5 measurements to 10 ev. 31