Some Thoughts on Laboratory Astrophysics for UHE Cosmic Rays. Pierre Sokolsky University of Utah SABRE Workshop SLAC, March, 2006

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1 Some Thoughts on Laboratory Astrophysics for UHE Cosmic Rays Pierre Sokolsky University of Utah SABRE Workshop SLAC, March, 2006

2 UHE Cosmic Ray detection (N, gamma, neutrino) Indirect - Extensive Air Shower in atmosphere or solid/liquid. Energy not directly measured - surrogate such as air fluorescence, cherenkov radiation, radio emission, electron/muon density at surface is measured instead Depending on surrogate, calibration or validation of detailed modeling of EAS cascade is required.

3 Eamples from UHECR experiments HiRes Auger Telescope Array

4 Detector Design Each HiRes detector unit ( mirror ) consists of: spherical mirror w/ 3.72m 2 unobstructed collection area 16x16 array (hexagonally close-packed) of PMT pixels each viewing 1 cone of sky: giving 5 improvement in S:N over FE (5 pixels) UV-transmitting filter to reduce sky+ambient background light Steel housing (2 mirrors each) with motorized garage doors

5 HiRes Monocular & Prelim Stereo Spectra (Stereo Normalized to Monocular)

6 Pierre Auger Observatory Surface Array 1600 detector stations 1.5 km spacing 3000 km 2 Fluorescence Detectors 4 Telescope enclosures 6 Telescopes per enclosure 24 Telescopes total

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8 Principle of Hybrid Detection MC Simulation of ev Proton Shower 10km ~ 27X o ~ 11λ I e ± μ ± EM Only Air Fluorescence Detector EM + Muon Ground Array

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10 Auger Surface Array Detector Station Communications antenna GPS antenna Electronics enclosure Solar panels Battery box 3 nine inch photomultiplier tubes Plastic tank with 12 tons of water

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12 Shower Development 320 EeV event detected by monocular Fly s Eye Fly s Eye Big Event

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14 Example Hybrid Event Θ~ 30º, ~ 8 EeV elevation [deg] y [km] x [km] )] 2 de/dx [GeV/(g/cm azimuth [deg] slant depth [g/cm ]

15 Some Examples of Expts. Requiring Calibration Atmospheric Fluorescence - Fly s Eye, HiRes, Auger fluorescence detector, TA fluorescence detectors, OWL-like detectors Askarian effect - microwave Cherenkov emission in ice or salt - ANITA, Salsa Atmospheric radio emission by EAS

16 Comparison of HiRes, AGASA and Auger (prelim) Spectra - Is it the energy scale, stupid? Blue triangles AGASA Circles - HiRes Mono Purple triangles Auger (prelim)

17 Flourescence Yield, Al Bunner s Thesis - circa 1967

18 The E-165 Thin Target Experimental Setup: Spectral Shape of Fluorescence Use SLAC FFTB e - beam Bunch energy = ev. Measure total and spectral fluorescence yield.

19 FLASH Thin Target Results Photons per meter per electron

20 FLASH Thin Target Results Photons per meter per electron

21 Thin Target Summary The total and spectrally resolved air fluorescence yield has been measured using 28.5 GeV electrons The overall uncertainty of the total yield measurement is ~10% The preliminary E-165 total yield result agrees with the previous T-461 measurement: Results of T 461: astro-ph/ SLAC-PUB-11254

22 Thick Target Run Motivation Strategy: produce a shower with similar characteristics to electromagnetic airshower in the lab. Test observed yields against EGS and GEANT simulations, predicted energy loss curves.

23 Thick Target Fluorescence Vessel and Ion Chamber Goal: Sum fluorescence light produced in a slice of an EM shower. Reduce scattered and nonfluorescence (Cherenkov) contributions to collected light Reduce backgrounds from stray particles hitting light detectors Drop-in mechanical shutter, (background studies) and filter holder.

24 Direct Detection of Shower Particles: Ion Chamber Direct measurement of ionization produced by beam particles. Collected simultaneously with fluorescence data; important crosscheck of data and simulation.

25 Detailed shower simulation 2 radiation length block partially interacts with shower particles. Reduces particle/light yield at 4, 8, and 12 r.l. Well simulated (ion chamber). Second order effect in fluorescence vessel: Albedo produces optical background hard to simulate!

26 Signal vs Shower Depth Five series of runs overlaid on this plot Variations consistent with statistics Very stable method! ±0.8% at 6 r.l. ±7% at 14 r.l.

27 Comparison to GEANT 3.2 Check hypothesis that fluorescence yield is proportional to energy deposition. Plot fluorescence signal and GEANT energy deposition at 2, 6, 10, 14 radiation lengths. Excellent agreement: ±1%

28 Longitudinal Fluorescence Profile Corrections applied to light yields at 4, 8, 12 radiation lengths Fit de/dt shower max at 5.5 radiation lengths agrees well with critical energy model prediction. Curve:

29 Using band-pass filters, we can isolate the contributions of several different wavelength bands to the overall light yield. Shape of fluorescence profile unchanged Filter None OF2 KG3 U360 Band 310 < λ < 400 nm 370 < λ < 400 nm 330 < λ < 390 nm 330 < λ < 380 nm

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31 Conclusion It s NOT the Fluorescence energy scale, stupid! Excellent agreement with Nagano et al., Effect on CR of using new numbers is miniscule. Other experiments (McFly, AirLight) in progress.

32 Radio signal from Askarian Effect Askarian predicted development of coherent Cherenkov radiation in microwave region due to effective dipole produced by charge separation in EAS. First confirmation of effect at SLAC in sand and then salt - Peter Gorham, David Saltzberg et al.

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36 SLAC has been a leader in calibration experiments FFTB! LPM effect Askarian effect FLASH - air fluorescence

37 Are there other such? Follow-up on FLASH - increase precision, effects of impurities ANITA radio detection efficiency tests Validation of low energy electromagnetic shower codes at large Moliere radii. Atmospheric EAS radio detection - what is the balance of Askarian vs Earth s magnetic field effects? - Possible controlled experiment producing shower in dense material with B field?

38 FLASH Thin Target Results Red: humid air Photons per meter per electron

39 Radio signals from EAS in Air Mechanism is Askarian + curvature of charged particles in Earth s B field (coherent geosynchrotron radiation). Exact balance not well known First convincing demonstration by French and German groups (LOPES with Kascade-Grande, CODALEMA) - coincidence with particle ground arrays. May be the next big step??

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43 Some Examples of Experiments that require simulations Measurement of lateral distribution of electrons and muons in EAS - AGASA, Auger ground array, TA ground array. At lower energies near the knee of the CR spectrum, interpretation of Kaskade electron and muon data depends critically on hadronic models Validation that longitudinal EAS development can be accurately measured by fluorescence or radio. Understanding relation of energy measured by fluorescence vs electron/muon lateral distribution Atmospheric neutrino background for UHE neutrino experiments ( prompt particle production)

44 Issues, continued Low energy shower modeling validation - GEANT, FLUKA predictions for e, gamma and hadron subshowers - very significant for understanding muon content of EAS, even at EHE High energy interaction models - pp cross-section, p-air cross section - pion and kaon multiplicities, forward direction physics - important for Xmax composition measurement

45 Impact of other accelerator measurements Xmax fluorescence measurement measures composition of CR if hadronic model is reliable. Need better bounds on parameters in these models this is primarily a high-energy problem Problem of apparent excess of low-energy muons in EAS - pion physics not well modeled? Both a high energy and a low energy problem! UHE hadronic models - QGSJet, Sybill

46 Better understanding of: P-p cross section at highest energies P-Air and N-Air cross sections Secondary hadron inelasticity and multiplicity Very small x behavior of proton form factors Validation of models at LHC and at low energies

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54 HiRes Measurement σ p Air in = 456± 17( stat) + 39( sys) 11( sys) mb at ev HiRes: σ p Air in = 456± 17( stat) + 39( sys) 11( sys) mb 18.5 at 10 ev

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64 Muon multiplicity problem Ground arrays typically use density near 1 km to estimate energy - muons are significant here, particularly for water tanks. Muon multiplicity typically is larger experimentally than even Fe simulations would predict - more like Pb or U - makes composition measurement difficult What are inadequacies of hadronic models? Is the simulation technology itself flawed? Thinning etc.

65 Detector Response AGASA Auger-SD μ ± e ± γ μ ± e ± γ ~1GeV ~10MeV ~10MeV ~1GeV ~10MeV ~10MeV 5cm Plastic 1.2m Water 10MeV ~10MeV ~1MeV Energy Deposit 240MeV ~10MeV ~10MeV

66 Energy Spectrum (10EeV Vertical Proton, r=1km) Gammas Electrons Muons 1MeV 10MeV 100MeV

67 Water Tank: Aperture vs. Zenith EM Shower Dominant Muon Dominant Muon Only Neutrino

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73 New possibilities LHC forward experiments proposed -TOTEM,etc. Need significant interaction between Cosmic Ray community and particle physics community for these to be useful Major effort in this direction at ISVHECRI 2006 in Wuhei, China this summer - bring major players together. RHIC - RIKEN workshop at Brookhaven this fall on nuclear effects.

74 Conclusions Calibration experiments continue to be very important for UHECR -FFTB and now SABRE remain critical venues for such experiments. Collaboration with particle physicists on forward scattering physics at LHC is growing. Much remains to be done. BJ is no longer the lone voice in the wilderness! Collaboration with Nuclear community also growing in importance. Progress in UHECR REQUIRES Laboratory Astrophysics in the broadest sense.