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  1. Overview • Ultra High Energy Cosmic Rays and their connection to neutrinos • The GZK Mechanism and the GZK neutrinos • The IceCube detector • Using IceCube to search for GZK neutrinos Sean Grullon

  2. Ultra High Energy Cosmic Rays • The most energetic radiation in the universe… Highest energy events around 1020 eV! • Interesting from an astrophysics perspective • Why do they have so much energy? (bottom-up models) • Interesting from a particle physics perspective • Grand Unified Theories and the so called “top-down” models • Low statistics (1 particle per km2 per century above 1020 eV!) • Thought to be extragalactic (Isotropic distribution of UHECRs) Sean Grullon

  3. The Cosmic Ray Spectrum ~ E-2.7 ~ E-3.1 Reference: Swordy – University of Chicago Sean Grullon

  4. The Neutrino Connection • Ultra high energy astrophysical neutrinos are intimately connected with UHECRs • Involved in UHECR propagation (The GZK mechanism) • Involved in UHECR production (Bottom Up vs. Top Down models) • One can study the UHECR problem from a neutrino perspective Sean Grullon

  5. Sean Grullon

  6. 2.725 K 411 photons / cm3 π ν + + γ μ + ν e p γ p n E = 10 20 eV E’=.3E The GZK Mechanism Sean Grullon

  7. Products of the GZK mechanism: Pions • Photopion production produces Gamma Rays and neutrinos. Sean Grullon

  8. Photopion production Cross Sections Solid line – protons Dashed line - neutrons 1st peak, single pions Higher peaks, multiple pions Bhattacharjee, Sigl astro-ph/9811011 Sean Grullon

  9. UHECR sources are constrained due to GZK suppression • UHECRs lose 30% of energy on average in a GZK interaction • Photodisintegration important at higher energies… UHECRs not as heavy nuclei rich as they should be Reference: Yoshida Sean Grullon

  10. How to calculate GZK neutrino Flux? • Pick a UHECR source distribution (eg. Cosmologically Isotropic) • From an initial Power Law spectrum, propagate UHECRs to Earth. • Take propagated UHECR spectrum and integrate (weighted by the neutrino yield) over proton energy and redshift to get neutrino luminosity. Sean Grullon

  11. The UHECR Transport Equation # of collisions per UHECR per recoil energy and time via GZK mechanism… given in next slide Mean free path of UHECRs Adiabatic Energy loss due to the Expansion of the Universe Sean Grullon

  12. Power Law UHECR spectrum from a single UHECR source • What is the observed flux at Earth for different cosmic ray accelerator distances? Reference – Yoshida & Teshima Sean Grullon

  13. Source Evolution Function • Source Evolution Function tells you how the number of UHECR sources increases with redshift. For an isotropic distribution it is given by: • Parametrized by two parameters, zmax and m. Zmax tells you how far out in space to look, m is how quickly the number of sources increases. Typical values range from (m,zmax)=(0,2) to (4,4). Sean Grullon

  14. Power law UHECR spectrum at Earth Source Evolution Varied: 1 – (m,zmax)=(0,2) 2 – (m,zmax)=(2,2) 3 – (m,zmax)=(2,4) 4 – (m,zmax)=(4,2) 5 – (m,zmax)=(4,4) Reference: Dai, Yoshida, et all. Sean Grullon

  15. Finally, the GZK Neutrino Flux! • We know the existing UHECR flux • Need the neutrino yield from the observed UHECR flux, number of neutrinos per proton per unit Energy • Get neutrino yield from the decay rates of pions and muons in the Nucleon Rest Frame. You then Lorentz transform the result to the UHECR lab frame to get the Neutrino Yield • Integrate over source evolution function, since interactions can take place over wide range of distances from Earth • Integrate over UHECR primary energy and redshift to get the final neutrino flux. Neutrino flux Source Evolution UHECR Flux Neutrino Yield Sean Grullon

  16. The GZK Neutrino Flux Features in Extragalactic UHECR spectrum washed out by galactic CRs! Engel, Stanev & Seckel – astro-ph/0101216 Sean Grullon

  17. The GZK neutrinos – a great tool to study UHECRs! • GZK neutrino flux very sensitive to the UHECR source evolution • Can infer the source evolution function for UHECRs • Observed UHECRs must come from our local neighborhood. EHE Neutrinos come from cosmological sources • Put constraints on EHE particle emission in the universe • Observation of GZK suppression by Auger would benefit from independent confirmation Sean Grullon

  18. Neutrino Flux as a Function of Source Evolution Flux changes by over 4 orders of magnitude! 1 -(m,zmax)=(0,2) 2 - (m,zmax)=(2,2) 3- (m,zmax)=(2,4) 4 – (m,zmax)=(4,4) Reference: Yoshida & Teshima Sean Grullon

  19. The GZK “crisis” • AGASA and Hi-Res disagree about the cutoff • AGASA observed 10 events above the GZK cutoff in 10 years of operation • AUGER in Argentina will study the nature and structure of the GZK cutoff Sean Grullon

  20. HiRes vs. AGASA Sean Grullon Reference: Takeda, et all 2003 astro-ph/0209422

  21. The Auger Surface Array Sean Grullon

  22. Preliminary Auger Results – Inconclusive! Reference: Matthews for Auger Collaboration Sean Grullon

  23. The IceCube Detector Sean Grullon

  24. South Pole Dark sector Skiway AMANDA Dome IceCube Sean Grullon

  25. A neutrino telescope: How we ‘see’ neutrinos Cherenkov light cone Cos(θ)=1/nβ muon or tau interaction Detector • Water/Ice used As: • Shield to filter out atmospheric muon background • A target in which neutrinos interact • A detection medium where Cherenkov Light is emitted. neutrino Sean Grullon

  26. IceTop AMANDA South Pole Skiway 1400 m 2400 m IceCube • 80 Strings by ~2010 • 4800 PMTs • Instrumented volume: 1 km3 (1 Gt) • IceCube is designed to detect neutrinos of all flavors at energies from 107 eV (SN) to 1020 eV Sean Grullon

  27. νµ IceCube event signatures: Eµ= 6 PeV Eµ= 10 TeV Sample IceCube Events Sean Grullon

  28. Sample ντ • “Double Bang” signature – Tau neutrino interacts inside detector volume, creating hadronic cascade and a Tau. • Subsequent Tau decays inside volume, creating another cascade. Sean Grullon

  29. Sample (375TeV) νe • Spherical, pointlike because extent of electromagnetic cascade small compared to DOM spacing. Sean Grullon

  30. Event Reconstruction Muon, with a Cherenkov cone Electromagnetic cascade, with spherical Cherenkov front. • Muons & Cascades reconstructed with a maximum log-likelihood technique: Sean Grullon

  31. m p e+e- photo-nuclear g pair-creation bremsstrahlung What do Extremely High Energy (EHE) Muons Really look like? • High Energy Muons Experience Significant Energy Losses: dE/dX~bE • The Series of Cascades dominates the “bare muon” cherenkov cone, forming approximately a continuous cylinder of light. (so called “lightsaber” event.) • Reliable reconstruction needed! Sean Grullon

  32. Event reconstruction in IceCube • The IceCube DAQ records the full waveform • Current reconstruction algorithms ported from AMANDA, which do not use full waveform information. (Use leading edge times) • Full waveform important to reconstruct EHE muon direction & energy… (EHE muon waveforms are wide with a lot of features) Sean Grullon

  33. Waveform Profile • Event generated by Nitrogen laser located at a depth of 1850 m in AMANDA Array. Pulse Shapes recorded at 3 distances from laser. (45m, 115m, and 167m) • The point? Width of waveform scales with distance! Sean Grullon

  34. Sample EHE Muon: ~10EeV Wide, Complex waveform ~3000 out of 4800 OMs hit! Sean Grullon

  35. Show Uncontained Event Display, possibly more sample WFs Sean Grullon

  36. Waveform-based Reconstruction • Generalize Maximum Likelihood Technique to Use Waveforms • Given a particle (the “hypothesis”) what is the probability of observing a given waveform f(t)? Observed Waveform “Expected” Waveform Probability of seeing observed waveform, given expected waveform Total number expected PEs time Sean Grullon

  37. Comments on Waveform-based Reconstruction • Algorithm works! Implemented in IceCube software framework • Full maximum log likelihood technique using the whole waveform • Factors in properly Antarctic ice model in the probability density function • Using the full waveform and the Anarctic ice model is all the information • What next? Gear reconstruction to EHE muons. Update PDF to model EHE muons properly Sean Grullon

  38. Reconstructing Muon Energy • Energy Loss scales with energy, dE/dX~bE • Reconstruct Energy Loss! (Difference just scale factor) • Pair creation dominates other channels. • Strategy? Convert what we measure (Photoelectrons) to Energy loss. Model this properly for an EHE muon. • With b nearly independent of energy, superimpose single cascade Probability Density Functions (PDFs) to model the energy loss more realistically Sean Grullon

  39. Sample Reconstruction Result - Muons Waveform Reconstruction has angular resolution of .9 degrees! An improvement (after cuts) over older algorithms with a resolution of 1.8 degrees. Sean Grullon

  40. Sample Cascade results, X Vertex resolution Black – waveform Red – classic reconstruction Distribution narrower! Reco – True (m) Sean Grullon

  41. Sample Cascade Results, Y resolution Reco – True (m) Sean Grullon

  42. Sample Cascade Results, Z resolution Reco – True (m) Sean Grullon

  43. Sample Cascade Results, Energy Resolution 5 percent in log(E) resolution! Even narrower energy resolution, ~2 percent Tails and smaller bump due to dust peak. Effect understood. Sean Grullon

  44. Digital Optical Module (DOM) HV Base “Flasher Board” Main Board (DOM-MB) 10” PMT 13” Glass (hemi)sphere Sean Grullon

  45. Detecting GZK neutrinos • Main channels of GZK neutrino searches – muons and taus. • EHE neutrinos are involved in a number of reactions, resulting in a number of particles of varying energies and types • Most events horizontal. (EHE neutrino mean free path ~ 100 km in rock due to higher cross sections in this energy range) • Major background: Atmospheric Muons Sean Grullon

  46. The GZK Neutrinos at IceCube depth Upward-going Downward going Atmospheric Muons, our main background! Sean Grullon

  47. 2800 m 1400 m GZK and Muon Flux vs. Angle Up Down heavily attenuated torwards horizon Sean Grullon

  48. Preliminary GZK Study • Preliminary MC Data Study of EHE muons and taus done by Aya Ishihara at UW-Madison and Shigeru Yoshida at Chiba University. • Initial Analysis done taking Detector Response into account, For the 80 string detector and different configurations. • Analysis done with simple variables only: NPE and MC truth information. • GZK flux taken to be strong source evolution case (m=4, zmax=4) Sean Grullon

  49. GZK flux distribution Strong enhancement at the horizon – Reliable zenith reconstruction crucial! Sean Grullon