1 Is the Search for the Origin of the Highest-Energy Cosmic Rays Over? Alan Watson School of Physics and Astronomy University of Leeds, UK

2 OVERVIEW Why there is interest in cosmic rays > eV The Auger Observatory Description and discussion of measurements:- Energy Spectrum Arrival Directions Primary Mass (not photons or neutrinos) Prospects for the future

3 Knee >10 19 eV 1 km -2 sr -1 year -1 air-showers after Gaisser Ankle

4 Four Questions: (i) Can there be a cosmic ray astronomy? Searches for Anisotropy (find the origin) Deflections in magnetic fields: at ~ eV: ~ 10° in Galactic magnetic field for protons - depending on the direction For interpretation, and to deduce B-fields, ideally we need to know Z - hard enough to find A! History of withdrawn or disproved claims

5 (ii) Can anything be learned from the spectrum shape? ‘ankle’ at ~ 3x10 18 eV - galactic/extra-galactic transition? Steepening above 5 x eV because of energy losses? Greisen-Zatsepin-Kuz’min – GZK effect (1966) γ 2.7 K + p  Δ +  n + π + or p + π o (sources of photons and neutrinos) or γ IR/2.7 K + A  (A – 1) + n (IR background more uncertain)

6 (iii) How are the particles accelerated? Synchrotron Acceleration E max = ZeBR  c Single Shot Acceleration E max = ZeBR  c Diffusive Shock Acceleration E max = kZeBR  c, with k<1 Shocks in AGNs, near Black Holes……?

7 Hillas 1984 ARA&A B vs R Magnetars? GRBs?

8 (iv) Could we learn anything about high-energy interactions? Cross-sections for any effects would need to be quite large Neutrino behaviour? p-air cross-section as function of energy? I will say very little about this topic

9 Existence of particles above GZK-steepening would imply that sources are nearby, 70 – 100 Mpc, depending on energy Essentially the CMB acts as a shield against cosmic rays from distant sources reaching earth IF particles are protons, the deflections could be small enough above ~ 5 x eV so that point sources might be seen So, measure: - energy spectrum - arrival direction distribution - mass composition But rate at eV is < 1 per km 2 per century

10 Shower initiated by proton in lead plates of cloud chamber 1.3 cm Pb Fretter: Echo Lake, 1949

11 LHC measurement of  TOT expected to be at the 1% level – very useful in the extrapolation up to UHECR energies The p-p total cross-section 10% difference in measurements of Tevatron Expts: James L. Pinfold IVECHRI (log s) 

12 Models describe Tevatron data well - but LHC model predictions reveal large discrepancies in extrapolation. LHC Forward Physics & Cosmic Rays James L. Pinfold IVECHRI E T (LHC) E(LHC)

13 LHCf: an LHC Experiment for Astroparticle Physics LHCf: measurement of photons and neutral pions and neutrons in the very forward region of LHC Add an EM calorimeter at 140 m from the Interaction Point (IP1 ATLAS) For low luminosity running From Kasahara

14 Prospects from LHCf

15 Czech Republic France Germany Italy Netherlands Poland Portugal Slovenia Spain United Kingdom Argentina Australia Brasil Bolivia* Mexico USA Vietnam* *Associate Countries ~330 PhD scientists from ~100 Institutions and 17 countries The Pierre Auger Collaboration Aim: To measure properties of UHECR with unprecedented precision – first discussions in 1991 (Cronin and Watson)

16 Arrays of water- → Cherenkov detectors Fluorescence → The design of the Pierre Auger Observatory marries the two well-established techniques  the ‘HYBRID’ technique 11 ANDOR Nitrogen fluorescence as at Fly’s Eye and HiRes Shower Detection Methods or Scintillation Counters

17 Surface Array (29 Sept 2008) 1660 surface detector assemblies deployed 1637 surface detectors filled with water 1627 surface detectors with electronics 1390 m above sea-level or ~ 875 g cm -2 ~ 10 times land area of Stockholm

18 GPS Receiver and radio transmission Antenna Tower

19 Telecommunication system

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21 θ~ 48º, ~ 70 EeV or 7 x eV Flash ADC traces Lateral density distribution Typical flash ADC trace at about 2 km Detector signal (VEM) vs time (µs) PMT 1 PMT 2 PMT µs 18 detectors triggered

22 UV optical filter (also: provide protection from outside dust) Camera with 440 PMTs (Photonis XP 3062) Schmidt Telescope using 11 m 2 mirrors

23 Pixel geometry shower-detector plane Signal and timing Direction & energy FD reconstruction

24 20 May 2007 E ~ eV

25 The essence of the hybrid approach Precise shower geometry from degeneracy given by SD timing Essential step towards high quality energy and X max resolution Times and angles, χ, are key to finding R p

26 Angular Resolution from Central Laser Facility Mono/hybrid rms 1.0°/0.18° 355 nm, frequency tripled, YAG laser, giving < 7 mJ per pulse: GZK energy

27 Time, t Χ°Χ° R p km 7 tank event

28 A Hybrid Event

30 Results from Pierre Auger Observatory Data-taking started on 1 January 2004 with 125 (of 1600) water tanks 6 (of 24) fluorescence detectors more or less continuous since then ~ 1.3 Auger years to 31 Aug 2007 for anisotropy ~ 1 Auger year for spectrum analysis

31 Energy Determination with Auger The detector signal at 1000 m from the shower core – S(1000) - determined for each surface detector event S(1000) is proportional to the primary energy The energy scale is determined from the data and does not depend on a knowledge of interaction models or of the primary composition – except at level of few %. Zenith angle ~ 48º Energy ~ 70 EeV

32 S 38 (1000) vs. E(FD) 661 Hybrid Events 5.6 x eV Energy from Fluorescence Detector

33 Summary of systematic uncertainties Note: Activity on several fronts to reduce these uncertainties Fluorescence Detector Uncertainties Dominate

34 Slope = ± 0.02 ± 0.06 Calibration unc. 19% FD system. 22% 7000 km 2 sr yr ~ 1 Auger year ~ 20,000 events Exp Obs > 4 x eV 179 ± 9 75 > eV 38 ± 3 1 Energy Spectrum from Surface Detectors θ < 60° ± 0.4 Could we be missing events?

35  = 79 ° Inclined Events offer additional aperture of ~ 29% to 80° Evidence that we do not miss events with high multiplicity

36 Zenith angle < 60°

37 Energy Estimates are model and mass dependent Takeda et al. ApP 2003 AGASA: Surface Detectors: Scintillators over 100 km 2 Recent reanalysis has reduced number > eV to 6 events

38 Summary of Inferences on Spectrum Clear Evidence of Suppression of Flux > 4 x eV Rough agreement with HiRes at highest energies Auger statistics are superior - but is it the GZK-effect (mass, distance scale)? AGASA result not confirmed Excess over GZK above eV not found` AGASA flux higher by about 2.5 at eV Some events (~1 with Auger) above eV Only a few per millenium per km 2 above eV

39 Spectrum shape does not give insights into mass

40 Searching for Anisotropies We have made targeted searches of claims by others - no confirmations (Galactic Centre, BL Lacs) There are no strong predictions of sources (though there have been very many) So:- Take given set of data and search exhaustively Seal the ‘prescription’ and look with new data At the highest energies we think we have observed a significant signal

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42 Test Using Independent Data Set 8/13 events lined up as before: chance 1/600

43 PeriodtotalAGN hits Chance hits Probability 1 Jan May st Scan 27 May 06 – 31 August x First scan gave ψ 56 EeV Using Veron-Cetty AGN catalogue 6 of 8 ‘misses’ are with 12° of galactic plane Each exposure was 4500 km 2 sr yr

44 Science: 9 November 2007 First scan gave ψ 56 EeV

45 Official First Day Stamp

46 Angular scan with E > 57 EeV and z < g)g)

47 Distribution of angular separations to closest AGN within 71 Mpc Isotropy IbI < 12°

isotropic protons 27 events with E > 57 EeV B-SSS model of Galactic Field: some support from Han, Manchester and Lyne - but see arXiv: (22 May 2008)

49 SGP correlation? Pre-View of the Future

50 HiRes Search for AGN correlation: arXiv: vr1 Stereo data only Claim angular accuracy of 0.8° 13 events > 56 EeV (‘after energy decreased by about 10%’) Only 2 of these 13 events are within 3.1° of AGN Possible that angular accuracy is poorer and/or that energy alignment is not correct. There are some puzzling features about the stereo aperture Follow-up work by others

51 [Diego Harari] Red dots: 13 HiRes events Black dots: 27 Auger events Why are so many (9/13) in ‘our’ bit of the sky?

52 Ghisellini et al June 2008 Catalogue of HI Galaxies

53 HI Galaxies contain lots of hydrogen AND Magnetars Ghisellini et al (June 2008) suggested association with HI galaxies iM104

54 H I galaxies contain MAGNETARS 10 9 to T Neutron Star Magnetars may be able to accelerate particles to above eV!

55 Hillas 1984 ARA&A B vs R Magnetars? GRBs? Magnetar * *

56 Conclusions from ~ 1 year of data (as if full instrument) 1.There is a suppression of the CR flux above 4 x eV 2.The 27 events above 57 EeV are not uniformly distributed 3.Events are associated with AGNs, from the Veron-Cetty catalogue, within 3.1° and 75 Mpc. This association has been demonstrated using an independent set of data with a probability of ~1.7 x that it arises by chance ( ~1/600) Interpretation: The highest energy cosmic rays are extra-galactic The GZK-effect has probably been demonstrated The primaries are possibly proton-dominated with energies ~ 30 CMS-energy at LHC. BUT

57 photons protons Fe Data Energy X max How we try to infer the variation of mass with energy Energy per nucleon is crucial < 2% above 10 EeV

58 X up – X down chosen large enough to detect most of distribution

59 Elongation Rate measured over two decades of energy Fluctuations in X max are being exploited Partilce Physics Correct?

60 What new astrophysics and physics could be learned? Magnetic field models can be tested Source spectra will come – rather slowly Map sources such as Cen A – if it is a source Deducing the MASS is crucial: mixed at highest energy? Fluctuation studies key and independent analysis using SD variables Certainly not expected – do hadronic models need modification? - Larger cross-section? Higher multiplicities? LHC results will be very important Particle Physics at extreme energies?

61 What next? Work hard on analysis of data from Auger-South Build Auger-North to give all-sky coverage: plan is for ~ 2 x 10 4 km 2 in South-East Colorado Fluorescence Detector in Space: - JEM-EUSO (2013) - LoI to ESA in response to Cosmic Vision - SSAC ‘support technology’ for S-EUSO ~€100M

62 Is the search for the origin of the highest energy cosmic rays over? No - certainly not yet! Indeed we are only at ‘the end of the beginning’. There is much still to be done. We need Exposure, Exposure, Exposure to exploit several exciting opportunities in astrophysics and particle physics

63 Carlo Crivelli (1430 – 1490): ‘The Annuciation with St Edimus’

64 Back-up slides

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66 Confirmation of claim using a Complete Catalogue George, Fabian, Baumgartner, Mushotsky and Tueller MNRAS submitted (April 2008) Swift BAT (14 – 195 keV) catalogue of AGNs First 22 months: 254 objects have known red-shifts and 138 AGNs are in the field of view of Auger (> few x erg cm -2 s -1 ) - with 19 Auger events in BAT field of view 1. When weighted by hard X-ray flux, AGNs within 100 Mpc are correlated at 98% significance level (2-D KS) 2. Correlation decreases sharply beyond ~ 100 Mpc, suggesting GZK suppression

67 Auger: open red, BAT AGN within 100 Mpc: filled blue, scaled by X-ray flux and Auger Exposure. 6 AGN within 20 Mpc and 6° marked with x. Super-galactic coordinates George et al 2008

68 Correlation dependence with distance Light (dark) blue for unweighted (weighted) flux values George et al 2008

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70 Large number of events allows good control and understanding of systematic uncertainties

71 We were careful NOT to say (at least we thought we were) that AGNs are the sources of UHECR that Cen A is a particularly favoured source Gorbunov et al and Wibig and Wolfendale have developed discussions of the anisotropy result on the assumption that the sources are AGNs – the latter suggesting that the mass of the primaries is mixed. Cuoco and Hannestad assume that there are 2 events from Cen A and deduce a rate of 100 TeV neutrinos of about 0.5 yr -1 in IceCube De Angelis et al derived an Intergalactic Magnetic Field of nG Follow up comments:-

72 (iii) How are the particles accelerated? Synchrotron Acceleration (as at CERN) E max = ZeBR  c Single Shot Acceleration (possibly in pulsars) E max = ZeBR  c Diffusive Shock Acceleration at shocks E max = kZeBR  c, with k<1 Shocks in AGNs, near Black Holes, Colliding Galaxies ……

73 Hillas 1984 ARA&A B vs R Magnetars? GRBs?

74 Summary of Inferences on Mass Nuclear Masses: After getting lighter, it looks – on the basis of present models of hadronic interactions – that the mean mass becomes heavier at the highest energies Interpretation If the highest energy events are really protons then the extrapolations of Tevatron physics are not correct. The p-air cross-section must increase quite rapidly above a few times eV. The multiplicity may be larger than expected or in early collisions little energy is transferred to the leading nucleon

75 From cover of Science, 9 November equi-exposure plot

76 Super Galactic Plane Galactic Plane

77 Auger Events > 57 EeV 27 events Galactic Plane

78 θ = 40° θ = 80° Principles of Neutrino Detection

79 Picture by J Alvarez-Muñiz

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81 Hillas 1984 ARA&A B vs R Magnetars? GRBs?

82

83 Time, t Χ°Χ° R p km 7 tank times used in fit

84 Stecker et al. 1976

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86 The Hybrid Era Angular Resolution Aperture Energy Hybrid SD-only FD-only mono (stereo – low N) ~ 0.2° ~ 1 - 2° ~ 3 - 5° Flat with energy AND E, A, spectral mass and model (M) free slope and M dependent A and M free A and M A and M free dependent

87 Lateral density distribution θ~ 60º, ~ 86 EeV Flash ADC traces Flash ADC Trace for detector late in the shower PMT 1 PMT 2 PMT µs 35 detectors triggered Much sharper signals than in more vertical events leads to ν - signature

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/- 0.4 (~ one quarter)

90 X up – X down chosen large enough to detect most of distribution

91 Large number of events allows good control and understanding of systematics

92 Comparison with different predictions Low energy

93 SD DEPLOYMENT

94 10 EeV S(1000) Precision of S(1000) improves as energy increases σ(S(1000))/S(1000)

95 Event  = 87.6°  = ° E = 49.2 EeV R= 19 km  /dof =1.7 N Tanks = 37  km  Understanding inclined events gives more aperture AND perhaps insights into hadronic interactions

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97 Fluorescence Detectors The HiRes group have yet to release a stereo spectrum. Recent paper: astro-ph/ Not yet accepted

98 Solar Panel Electronics enclosure 40 MHz FADC, local triggers, 10 Watts Communication antenna GPS antenna Battery box Plastic tank with 12 tons of water three 9” PMTs (XP1805)

99 Carmen and Miranda

100 Time difference (ns)

101 Summary of Results from Auger Observatory Spectrum: suppression of highest energy flux seen - with model independent measurements and analyses at ~ 3.55 x eV Arrival Directions: At highest energies there is an anisotropy associated with nearby objects (< 75 Mpc) Mass Composition: Getting heavier as energy increases – if extrapolations of particle physics are correct The statistics and precision that are being achieved with will improve our understanding of UHECR dramatically.