The Auger Observatory and UHE neutrinos

1. The Auger Observatory and UHE neutrinos • Why UHE neutrinos ? • What is the Auger Observatory ? • How can it see UHE neutrinos ? • How to discriminate them ? • What sensitivity ? • Systematic errors NOW 2006 Pierre Billoir LPNHE Paris, CNRS/univ. Paris 6 and 7 Auger Collaboration P. Billoir, Auger Collab., NOW2006

2. UHE neutrinos • expected from interaction of accelerated particles with photons in the source region or with the CMBR (GZK effect): • relatively soft spectrum • decay of ultra massive objects: harder spectrum expected: • UHE photons and neutrinos are a signature of top-down scenarii • propagation in straight line: point to the source • differences with photons : • propagation over cosmological distances • low probability to produce an observable atmospheric shower Photons and neutrinos: possible interesting byproducts of the Auger Observatory P. Billoir, Auger Collab., NOW2006

3. general framework • noscillations:~ equal fluxes of the 3 flavours • assume neutrinos weakly interacting, even at UHE • probability of interaction in atmosphere <~ 10-4 • better sensitivity to nt t in earth skimming scenario • (t emerging within a few degrees from horizontal) This study: based on Astrop. Phys. 17 (2002) 183 (X. Bertou, P.B., O. Deligny, C. Lachaud, A. Letessier-Selvon) + work on first Auger Surface Detector data (2004-06) (special contribution of Oscar Blanch Bigas) Studies on Fluorescence Detector exist also P. Billoir, Auger Collab., NOW2006

4. GPS antenna Communications antenna Solar panels Battery box Electronics enclosure Plastic tank with 12 tons of water 3 nine inch photomultiplier tubes Water Cherenkov tanks P. Billoir, Auger Collab., NOW2006

5. Optical system (fluorescence telescopes) corrector lens (aperture x2) 440 PMT camera 1.5° per pixel segmented spherical mirror aperture box shutter filter UV pass safety curtain P. Billoir, Auger Collab., NOW2006

6. Present status (beg. Sept.2006) (Loma Amarilla) Coihueco Los Morados central buildings Los Leones P. Billoir, Auger Collab., NOW2006

7. First results: spectrum (from ICHEP06) Error bars at 1018 at 1020 Caveat: energy scale still uncertain !!! P. Billoir, Auger Collab., NOW2006

8. First results: anisotropy (from ICRC05) SUGAR region AGASA region GC Anisotropy around Galactic Center not confirmed (AGASA and SUGAR results excluded) global distribution compatible with isotropy – no clusters P. Billoir, Auger Collab., NOW2006

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11. 1 atmospere P. Billoir, Auger Collab., NOW2006

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14. 2 atmospheres P. Billoir, Auger Collab., NOW2006

15. Hybrid detection P. Billoir, Auger Collab., NOW2006

16. “normal” (nucleic) showers almost vertical: thick curved front muons + electromagnetic earth atmosphere very inclined: thin flat front High energy muons P. Billoir, Auger Collab., NOW2006

17. a real vertical event (20 deg) Noise ! doublet P. Billoir, Auger Collab., NOW2006

18. a real horizontal event (80 deg) “single” peaks : fast rise + exp. light decay (t ~ 70 ns) accidental background signals are similar P. Billoir, Auger Collab., NOW2006

19. a real “monster” (lightning event) 15 km ! Many stations triggered with abnormal signal (e.g. quasi-periodic oscillations) easily rejected (even if pattern is not well understood !) P. Billoir, Auger Collab., NOW2006

20. neutrino showers (distinguishable if almost horizontal) downgoing (direct n interaction in atmosphere) upgoing (nt in earth t decay in flight ) P. Billoir, Auger Collab., NOW2006

21. Simulation chain • inject nt at 0.1, 0.3, 1, 3, …, 100 EeV into earth crust • generate c.c. and n.c interactions (CTEQ4-DIS) , t decay and energy loss • if a t emerges: generate decay in atmosphere • (modes e, p, pp0, ppp0 , pp0p0, ppp , pppp0 , pp0p0p0 + neutrinos) • inject the products of decay into AIRES (shower simulation package) • regenerate particles entering the tank from the “ground” output file • simulate the Cherenkov response and FADC traces • apply a specific analysis (trigger + selection) P. Billoir, Auger Collab., NOW2006

22. ground spot decay of an horizontal t of 1 EeV enn (almost pure e.m. cascade) pn (hadronic+e.m. cascade) injected t average level of trigger P. Billoir, Auger Collab., NOW2006

23. Simulated t • p+ (0.27 EeV) n • 400 m above ground P. Billoir, Auger Collab., NOW2006

24. Simulated t • p+ (5.1) p0(16.1)n • 1800 m above ground P. Billoir, Auger Collab., NOW2006

25. candidate selection 1.“young” showers • online local triggers (one tank): • threshold: one slot above Th • (detection of peaks) • time over threshold: N slots within 3 ms above th • (detection of long signals) Global condition: at least 3 t.o.th. stations satisfying area/peak > 1.4 * “single” one “central” + one within 1500 m + one within 3000 m P. Billoir, Auger Collab., NOW2006

26. Trigger efficiency Fraction of decaying t (excludingmnnchannel) giving a trigger En = 0.1 EeV En = 1 EeV En = 100 EeV En = 10 EeV 1 km 2 km P. Billoir, Auger Collab., NOW2006

27. footprint analysis • Variables defined from the footprint • (in any configuration, even aligned) • lengthL and width W • (major and minor axis of the ellipsoid of inertia) • “speed” for each pair of stations • (distance/difference of time) tj ti dij major axis P. Billoir, Auger Collab., NOW2006

28. candidate selection 2. Discriminating variables Search for long shaped configurations, compatible with a front moving horizontally at speed c, well contained inside the array (background: vertical or inclined showers, d/Dt > c ) cuts: L/W > 5 0.29 < av. Speed < 0.31 r.m.s. < 0.08 from years 2004-2006: no real event survived… P. Billoir, Auger Collab., NOW2006

29. Possible additional criterion: front curvature Quasi-horizontal real events Fitted from arrival times in stations: radius of curvature “center” q > 70 deg q > 80 deg Shower axis a Peak around 10 km (lower values expected for neutrinos) P. Billoir, Auger Collab., NOW2006

30. A nearly candidate event (rejected for shape) trom times: “trans-horizontal” event (L/Dt = 0.294 m/ns for all pairs) rare coincidence small shower (right side) + a double accidental (left) ? P. Billoir, Auger Collab., NOW2006

31. What can be measured ? • direction: precision better than 2 deg • (improving with Nstat) • difficult to distinguish up-going/down-going • (narrow distribution around 90 deg ?) • energy: possible lower bound for a given event • - unknown energy losses in interaction/decay chain • - estimation of Eshower depends on altitude • (possible evaluation from signal shapes, with large Nstat ?) possible strategy in a first step: inject in the simulation chain a spectrum with a given shape deduce from the selected data a level (or an upper bound) model dependent result P. Billoir, Auger Collab., NOW2006

32. systematic errors (1) • detection: triggering/selection efficiency, effective integrated aperture: to be evaluated (not dominant) • topography (Andes, Pacific Ocean): not crucial • cross section of neutrinos • modelling of UHE hadronic interactions • (not dominant, but maybe not well known…) t of 3 EeV (all channels except m) AIRES/QGSJET AIRES/SIBYLL P. Billoir, Auger Collab., NOW2006

33. systematic errors (2) • t polarization (depends on parton distribution) • using TAUOLA • here: extreme cases (very unlikely !): difference ~ 30 % h = -1 h = +1 h = +1 h = -1 P. Billoir, Auger Collab., NOW2006

34. systematic errors (3) energy loss of t in earth: big uncertainty ! -dE/dx = a + b(E) E - bremsstrahlung + pair production: well defined - deep inelastic scattering in photonuclear process: “pessimistic” hypothesis from Dutta et al, Phys.Rev. D63 (2001) Contrib. of dE/dx factor ~5 between low and high estimations of the acceptance dominant at high E total P. Billoir, Auger Collab., NOW2006

35. Auger sensitivity uncertainty range “pessimistic” t energy loss TD preliminary GRB GZK AGN Points: 1 event / year / decade of energy P. Billoir, Auger Collab., NOW2006

36. upper bounds for 1 year of full Auger(if no candidate) (“pessimistic” hypothesis for t energy loss) Solid: various models from Protheroe (astro-ph/9809144) Dashed: upper bounds at 95 % C.L. for each shape if no candidate preliminary uncertainty range P. Billoir, Auger Collab., NOW2006

37. Detection with fluorescence telescope ? Can see showers well above the ground, but: - duty cycle ~ 10 % of the time - limited range at low energy Potential advantages: - can distinguish up-going showers - direct evaluation of altitude and energy (if large angle of view) • Acceptance studied in • C. Aramo et al., Astrop. Phys. 23 (2005) 65 • G. Miele et al., Phys. Lett. B634 (2006) 137 P. Billoir, Auger Collab., NOW2006

38. summary and perspectives • the Pierre Auger Observatory is sensitive to UHE neutrinos • most promising: earth skimming (decay of t in air) • real data are clean • simple criteria allow to reject the background • still room for refinement … • constraining upper bounds expected within a few years • Ongoing studies: • other criteria to select neutrino candidates • specific trigger to enhance sensitivity at low energy • acceptance calculations • shower energy evaluation • observation with the fluorescence detector • atmospheric n interactions (down-going, less horizontal) P. Billoir, Auger Collab., NOW2006