HiggsMaxwell Workshop Edinburgh 10 Feb 2010 Latest Results

Higgs-Maxwell Workshop: Edinburgh: 10 Feb 2010 Latest Results on the Highest Energy Cosmic Rays Alan Watson University of Leeds a. a. watson@leeds. ac. uk 1

OVERVIEW • Why there is interest in cosmic rays > 1019 e. V • The Auger Observatory • Description and discussion of measurements: Energy Spectrum Arrival Directions Primary Mass • Are there hints of new particle physics? 2

Flux of Cosmic Rays 1 particle m-2 s-1 Air-showers 25 decades in intensity S Swordy (Univ. Chicago) ‘Knee’ 1 particle m-2 per year Ankle 1 particle km-2 per year LHC 11 Decades 3 in Energy

Why the interest in studying very high energy CR? (i) Are there excesses from some regions of sky? – can there be a cosmic-ray astronomy? Deflections in magnetic fields: at ~ 1019 e. V: still ~ 10° in Galactic magnetic field - depending on the direction For interpretation, and to help deduce the B- fields, we really need to know Z (we try to infer A) 4

(ii) Can anything be learned from the shape of the spectrum? Steepening above 5 x 1019 e. V predicted Greisen-Zatsepin-Kuz’min – GZK effect (1966) γ 2. 7 K + p Δ+ n + π+ or p + πo (sources of photons and neutrinos) or These lead to +the γIR/2. 7 Kreactions + A (A – 1) n ONLY firm predictions in cosmic rays (IR background more uncertain) 5

Interaction Length of protons as function of energy Leads to attenuation on scale of ~ 100 Mpc Taylor and Aharonian 2008 6

(iii) How are the particles accelerated? • Synchrotron Acceleration (e. g. CERN) Emax = Ze. BR c • Diffusive Shock Acceleration Emax = k. Ze. BR c, with k<1 (e. g. Shocks in AGNs, near Black Holes……? ) Observed at interplanetary shocks……… 7

* Magnetar Emax = k. Ze. BRβc k<1 Hillas 1984 ARA&A B vs R Synchrotron Losses B Colliding Galaxies R 8

To summarise: • Particles of energy near predicted GZK-steepening could tell us about sources within 70 – 100 Mpc • IF particles are protons, the deflections are expected to be small enough above ~ 5 x 1019 e. V that point sources might be seen – provided there are not too many. • So, measure: - energy spectrum - to test prediction - arrival direction distribution - explore - mass composition – for interpretation 9

The Pierre Auger Collaboration *Croatia Czech Republic France Germany Italy Netherlands Poland Portugal Slovenia Spain United Kingdom Argentina Australia Brasil *Bolivia Mexico USA *Vietnam *Associate Countries ~330 Ph. D scientists from ~100 Institutions and 18 countries Aim: Find properties of UHECR with unprecedented precision 10 First discussions in 1991 (Jim Cronin and Alan Watson)

Auger Observatory is a HYBRID Detector Nitrogen fluorescence as at Fly’s Eye and Hi. Res Fluorescence → AND Arrays of water→ Cherenkov detectors 11 11

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Area of Lancashire West Yorkshire Inside M 25 30 x area of Paris Rhode Island, USA 1390 m above sea-level or ~ 875 g cm-2 13

GPS Receiver and radio transmission Fluorescence Detector site 14

Telecommunication system 15

Zenith Angle ~ 48º Energy ~ 7 x 1019 e. V 18 detectors triggered S Lateral density distribution km An example of an event recorded with the Cherenkov detectors 16

Fluorescence telescopes: Number of telescopes: 24 Mirrors: 3. 6 m x 3. 6 m with field of view 30º x 30º, each telescope is equipped with 440 photomultipliers. 17 May 3, 2009

FD reconstruction Signal and timing Direction & energy Pixel geometry shower-detector plane 18

A Hybrid Event Energy Estimate - from area under curve (2. 1 ± 0. 5) x 1019 e. V must account for ‘missing energy’ 19

f = Etot/Eem 1. 17 f 1. 07 Etot (log 10(e. V)) 20

Results from Pierre Auger Observatory Data-taking started on 1 January 2004 with 125 (of 1600) water-Cherenkov detectors 6 (of 24) fluorescence telescopes more or less continuous operation since then Exposure = 12, 790 km 2 sr yr > 1019 e. V: 4440 > 5 x 1019 e. V: 59 > 1020 e. V: 3 (Hi. Res stereo: 307 : 19 : 1) Hi. Res Aperture: x 4 at highest energies 21 x 10 AGASA

Auger Energy Calibration 785 EVENTS S(1000) log E FD(e. V) 22

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Energy Spectrum from Auger Observatory SD + FD Accepted Physics Letters B Schuessler 4 Feb 2010 HE 0114 fit: index, is breakpoint, index, critical 1% energy, normalization Above 3 x Five-parameter 1018 e. V, the exposure energy independent: corrections in overlap 24 region 24

Energy Estimates are model and mass dependent Takeda et al. Ap. P 2003 25

For the few events above 1020 e. V Auger (3) and Hi. Res stereo (1) Integral flux is (2. 36 ± 1. 9/1. 1) x 10 -4 km-2 sr-1 yr-1 11 AGASA events (6. 35 ± 1. 9) x 10 -3 km-2 sr-1 yr-1 a factor of more than 25 Even a factor of x 2 increase in Auger energies would not be enough to explain difference Consensus is that Auger and Hi. Res have got it right 26

Searching for Anisotropies 27

ANISOTROPY Situation as at November 2007: Science and Astroparticle Physics Correlation with VCV catalogue of AGN for < 3. 1°, <75 Mpc and E > 5. 5 x 1019 e. V Cen A 27 events 28 Now recognised as a non-optimum catalogue: event number has doubled

The Auger Sky above 60 Ee. V Comparison with Swift-BAT AGN density map 5° of smoothing Simulated data sets based on isotropy (I) and Swift-BAT model (II) compared to data (black line/point). 29 29

Indications on Mass Composition • Anisotropy surely suggests a large proton fraction • Most unexpected result from Pierre Auger Observatory so far points in another direction • Could be indicative of interesting new physics (? ? ) 30

How we try to infer the variation of mass with energy photons < 2% above 10 Ee. V Xmax protons Data? Fe Energy per nucleon is crucial Energy 31

Some Longitudinal Profiles measured with Auger 32

Xmax Resolution 33

Mean Xmax from 3754 events 138 71 34 685 34

Xmax rms for same events 685 138 71 34 35

Accepted by PRL: 29 Jan 2010 36

Some of the outstanding questions: - • Is the spectrum suppression the GZK effect? • Why does AGASA find such a different spectrum? • How can anisotropy and mass data be reconciled? • Could there be something wrong with particle physics at trans-LHC energies? 37

Need to reconcile: • Anisotropy - but Xmax suggests diminishing fraction of protons • AGASA result on spectrum Could cross-section (p-air) be high? Could leading particle take very little energy? Could the multiplicity be unexpectedly high? These features would give Xmax higher in atmosphere than current models Reduce fluctuations in Xmax 38 Flatten particle distribution close to shower axis (AGASA)

The p-p total cross-section LHC measurement of s. TOT expected to be at the 1% level – very useful in the extrapolation up to UHECR energies 10% difference in measurements of Tevatron Expts: (log s) 39 James L. Pinfold IVECHRI 2006 14

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 (IP 1 ATLAS) For low luminosity running 40

Prospects from LHCf 41

Some of the outstanding questions: Is the spectrum suppression the GZK effect? Why does AGASA find such a different spectrum? How can anisotropy and mass data be reconciled? Could there be something wrong with particle physics? OR: • Cosmic Rays are rather isotropic even above 5 x 1019 e. V • They are mainly Fe nuclei • The suppression marks an acceleration limit 42

Next steps: Run Auger South until at least 2015 Build Auger North (x 7 AS) in South East Colorado Go into space: JEM-EUSO on ISS and free-flyer in 2020 s? There are still lots of questions to answer 43

Back Up Slides 44

The essence of the hybrid approach Precise shower geometry from degeneracy given by SD timing Essential step towards high quality energy and Xmax resolution Times at angles, χ , are key to finding Rp 45

Angular Resolution from Central Laser Facility 355 nm, frequency tripled, YAG laser, giving < 7 m. J per pulse: GZK energy Mono/hybrid rms 1. 0°/0. 18° 46

12/15 events close to AGNs in Veron-Cetty Catalogue 47

Test Using Independent Data Set 8/13 events lined up as before: chance 1/600 48

Using Veron-Cetty AGN catalogue First scan gave ψ < 3. 1°, z < 0. 018 (75 Mpc) and E > 56 Ee. V Period total AGN hits 1 Jan 04 - 26 May 2006 27 May 06 – 31 August 2007 Chance Probability hits 15 12 3. 2 1 st Scan 13 8 2. 7 1. 7 x 10 -3 Each exposure was 4500 km 2 sr yr 6 of 8 ‘misses’ are with 12° of galactic plane 49

Nature has been unkind (? ) AND we chose a poor catalogue 50

A clear message from the Pierre Auger Observatory is that we made it too small Rate of events that seem to be anisotropically distributed 51 is only ~ 2 per month

Swift-Bat catalogue Top: Flux-Weighted Bottom: Unweighted Smearing takes account of angular resolution and deflections Maximum Likelihood fit 52