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Auger at 10 18 eV

Auger at 10 18 eV. Bruce Dawson University of Adelaide, Australia. Introduction. Auger was primarily designed for energies beyond 10 19 eV but significant aperture at lower energies interesting physics around 10 18 eV

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Auger at 10 18 eV

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  1. Auger at 1018eV Bruce DawsonUniversity of Adelaide, Australia

  2. Introduction • Auger was primarily designed for energies beyond 1019eV • but significant aperture at lower energies • interesting physics around 1018eV • existing observatory is making measurements, and some longer-term plans for enhancements to study in more detail • sorry, no new results!

  3. The Observatory Surface Array 1600 detector stations 1.5 km spacing 3000 km2 Fluorescence Detectors 4 Telescope enclosures 6 Telescopes per enclosure 24 Telescopes total ~2/3 tanks in field, completed in early 2007. Routine data taking since Jan. 2004.

  4. The Surface ArrayDetector Station Water Cherenkov detector, depth 1.2m, area 10 m2

  5. Fluorescence Detector (24 like this) 3.4 metre diameter segmented mirror Aperture stop and optical filter 440 pixel camera

  6. Physics Motivation around 1018eV • knee region increasingly well studied e.g. KASCADE results imply rigidity-dependent escape from galactic sources (SNRs?) or galaxy itself. • at highest energies, no galactic anisotropy is evident, and search continues for a definite extragalactic signature (e.g. GZK suppression) • region below and around 1018eV may be the transition between galactic and extragalactic sources. (from T. Gaisser in Hillas astro-ph/0607109)

  7. Some possible models (Hillas astro-ph/0607109) suppressione+e- on CMBR? Hatched region: possible galactic fall-off if KASCADE rigidity dependent turn-overs extend to the Si-Fe mass components. Many extragalactic scenarios: depends on source spectrum, source composition, evolution of sources, distribution of sources etc etc 3 possible extragalactic models:EGAL p Jsource=kE-2.4 exp(-E/Emax) (similar to Berezinsky et al.), EGAL H+He (Hillas JPhysG 2005), EGAL mixed (Allard et al. 2005).

  8. Some possible models (Hillas astro-ph/0607109) Transition region (galactic to extragalactic) depends on model. In some models (eg EGAL p or EGAL p+He) there would be rapid change in mass composition below and around 1018eV.e.g. EGAL p model: Extragalactic flux 50% at 1017.3eV, 80% at 1017.7eV

  9. Some evidence for transitions, but energy of transition not clear

  10. “Low” energy capabilities of Auger • Fluorescence detector (FD), surface detector (SD) and hybrid apertures • detector resolution (directions, energy…) • physics topics

  11. FD-only apertures for completed Auger.Trigger aperture.Significant aperture at lower energies. Mono aperture:TriggerGeometry fitProfile fit (Xmax viewed) Bellido et al. (Auger Collab) 29th ICRC HE15 (2005)

  12. SD Trigger Each tankhas 3 PMTs(summed here)40 MHz (25ns) digitization. E ~ 5 EeV Two types of tank trigger: “threshold” or “time over threshold” (TOT) (100Hz, noisy) (1.6 Hz, very clean)“Threshold trigger”: 3-fold coincidence of signal above 1.75 V.E.M. (needed for fast signals from horizontal showers). TOT trigger is most relevant to low energy aperture:- requires 13 bins in a 120 bin (3us) window above threshold of 0.2 V.E.M. in 2 PMTs

  13. Protons, log E = 17.8 Protons, q=25 deg log E= Allard et al. (Auger Collab) 29th ICRC HE14 (2005) TOT (pink)dominates over thethreshold (blue) trigger To calculate SD aperture-Lateral Trigger Probability (LTP) functions - for TOT trigger Allard et al. (Auger Collab) 29th ICRC HE14 (2005)

  14. Allard et al. (Auger Collab) 29th ICRC HE14 (2005)3 tanks with TOT = 3TOT (fully efficient at ~ 3 EeV)4 tanks with TOT = 4TOT (fully efficient at ~ 7 EeV) mass-dependent aperture in the dip region - maybe we can exploit this real data from 0.4 - 0.9 EeVsignal rise-time - potential for mass composition study hereP. Ghia, 28th ICRC p337 (2003)

  15. FD Aperture…SD Aperture…Hybrid aperture: single-tank TOT Hybrid aperture is determined by FD since SD single-tankTOT trigger has low threshold. (Observatory trigger (T3) for hybrids is initiated by the FD and tank triggers are collected) (aperture as of October, 2004) Bellido et al. (Auger Collab) 29th ICRC HE15 (2005)

  16. (statistical errors only) Dawson et al. (Auger Collab) 27th ICRC, 714 (2001) Hybrid Resolution ~3 EeV

  17. SD Angular resolution From time-variancemodel (using data from dual stations). Allowscalculation of space angleerror for each event.“Angular resolution” is the space angle containing 68% of the 3D probability distribution. Roughly,3 stations: E < 4 EeV4 stations: 3 < E < 10 EeV 5 or more: E > 8 EeV Bonifazi et al. (Auger Collab) 29th ICRC HE14 (2005)

  18. SD Angular resolution from hybrid Bonifazi et al. (Auger Collab) 29th ICRC HE14 (2005) From hybrid/SD comparisons on same showers.To get SD resolution subtract hybrid resolution (0.4 deg) in quadrature.Angular resolution=1.5 sigma Results approx.consistent with time variance method. Thus, SD angular resolution is better than 2.2 deg for 3 stations (E< 4 EeV)(and better than 1.7 deg for 4-folds (3-10 EeV), better than 1.4 deg for >8 EeV)

  19. Physics studies so far: search for anisotropies in arrival directions towards the Galactic Centre around 1018eV

  20. Hints from earlier experiments … AGASA experimentHayashida et al. 1999 re-analysis of SUGAR experimentBellido et al. 2001 GC

  21. Letessier-Selvon et al. (Auger Collab) 29th ICRC HE14 (2005) no statistically significant excesses or deficits - with 4x more data than AGASA

  22. Energy spectrum - extension to lower energies anticipated (hybrid) but priority on the high energies! Auger energy calibration provided by fluorescence detectors 1) M. Takeda et al. Astroparticle Physics 19, 447 (2003) 2) R.U. Abbasi et al. Phys Lett B (to be published) Sommers et al. (Auger Collab) 29th ICRC HE14 (2005)

  23. Hybrid Mass Composition Studies First hybrid elongation rate (Xmax) study in final stages. Expect measurementsdown to around 1017.8 eV or lower (Michael Unger, Karlsruhe) Auger telescopes view elevations up to 30 degrees.Care must be taken to avoid biases in Xmax studies, particularly for low energy (close-by) events.(solution - geometrical cuts to avoid FOV problem - core distance cuts to avoid SD bias at low E)

  24. An example of a possible enhancement for Auger South- at one FD site, 3 extra telescopes A proposal by European Auger colleagues, under active study.Aim is to enhance useful low energy aperture.

  25. 1017.25 eV, 1.2km 1018 eV, 5km

  26. Conclusions • Auger was designed for E>1019eV, and this is the main focus of our endeavour • But some lower-energy aperture came for free, and we are exploiting it • some low energy enhancements possible, but only when construction is complete on the main observatory

  27. (Hillas astro-ph/0607109)

  28. FD aperture with energy

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