the importance of knowing the primary mass – and how little we really know

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The importance of knowing the primary mass – and how little we really know. Alan Watson University of Leeds Pylos: 7 September 2004. Key Questions about UHECR. Energy Spectrum above 10 19 eV? Arrival Direction distribution? Mass Composition? - PowerPoint PPT Presentation


  • The importance of knowing the primary mass and how little we really knowAlan WatsonUniversity of 7 September 2004

  • Key Questions about UHECR Energy Spectrum above 1019 eV?

    Arrival Direction distribution?

    Mass Composition?

    Aim of talk is to show where I think that we have got to in trying to answer the fundamental question of what is the mass at the highest energies.

    Life may be less simple than some theorists seem to think!

  • We remain with the dilemma: protons versus heavy nuclei. A clear cut decision cannot be reached yet. I believe that up to the highest energies the protons are the most abundant in the primary cosmic rays. However, I must confess that a leak proof test of the protonic nature of the primaries at the highest energies does not exist. This is a very important problem. Experimentally it is quite a difficult problem. G Cocconi: Fifth International Cosmic Ray Conference, Guanajuato, Mexico, 1955Question of Mass CompositionFere libenter homines id, quod volunt, credunt!Men wish to believe only what they prefer Thanks to Francesco Ronga

  • ~ 5%Song et al Astroparticle Physics 2000The energy estimates are HIGHER if Fe is assumedCorrections necessary to determine energy from fluorescence

  • From Takeda et al Astroparticle Physics 20031. S(600), the energy estimates are LOWER if iron is assumedS0 = 50 vem

  • Mass Composition (i): Xmax with energyElongation Rate (Linsley 1977, Linsley and Watson 1981)

    dXmax/ dlog E < 2.3X0 g cm-2/decade

    from Heitler model Xmax = ln (Eo/c)/ ln 2 extended to baryonic primaries:

    dXmax/ dlog E = 2.3X0 (1 - Bn - B)

    where Bn = d ln(n)/ d ln E

    and B = (-N/X0)(d ln N/d ln E)

  • Composition from depth of maximum (i)Model dependent AND < 1019.25 eVAbbasi et al: astro-ph/0407622

  • Some personal comments on the recent HiRes Composition PaperAbbasi et al (astro-ph/0407622)

    Selection of events:

    2 per dof < 20

    2 measures of Xmax within 500 g cm-2

    Measurements within 400 g cm-2 for global fit to 2 eyes

    But resolution of Xmax claimed as 30 g cm-2 from Monte CarloBUT surely the resolution will depend on the distance from the Eyes (apparently not considered)

    Periods of calibrated and uncalibrated atmosphere (419 and 134 events) put together- would have been interesting to have seen these groups apart

  • HiRes Composition from Xmax fluctuations (ii)pFeSolid lines: data

    Models are Sibyll and QGSjetBUT diurnal and seasonal atmospheric changeslikely to be very important

  • Astroparticle Physics in press; also data shown at ICRC2003

  • M. Risse et al ICRC03Standard Atmospheres can bias composition inferences

  • From L Perrone (Auger group): Catania CRIS meeting

  • Mass Composition (iii): muonsMuon Content of Showers:-

    N (>1 GeV) = AB(E/A)p (depends on mass/nucleon)

    N(>1 GeV) = 2.8A(E/A)0.86 ~ A0.14

    So, more muons in Fe showers

    Muons are about 10% of total number of particles

    Used successfully at lower energies (KASCADE)

    VERY expensive - especially at high energies - conclusions derived are rather model dependent

  • Claim: Consistent with proton dominant component 1919.52020.5Log(Energy [eV])2101Log(Muon density@1000m[m2])Results from the AGASA arrayKenji Shinosaki: 129 events > 1019 eV

  • Model dependence of muon signals Sibyll 1.7: Sibyll 2.1: QGSjet98

    1: 1.17:1:45

    Important to recall that we do not know the correct model to use.

    LHC CMS energy corresponds to ~ 1017 eV

  • From Ralph Engelspresentation in Leeds,July 2004

  • Plots by Maria MarchesiniAGASA data: a second lookQGSjet(i)(i)(ii)(ii)

  • Mass Composition (iv): Using the lateral distribution(r)~ r ( + r/4000)

    circa 1978:Feynman ScalingPrimary Uranium?!

  • Sample LDF compared with new model: QGSjet98

  • Distribution of lateral distributionHaverah Park data: Ave et al. 2003

  • Estimate of Mass CompositionThe fraction of protons (Fp) as a function of energy for two QGSjet models (98, dotted line and 01, solid line). The three low energy points correspond to a range in which there is a well-understood trigger bias that favours steep showers [24]. QGSjet models (98, dotted line and 01, solid line).First 3 points: trigger bias

  • Lateral distribution data from Volcano Ranch interpreted by Dova et al (2004)Astropart Phys (in press)

  • Comparisons from Dova et al (2004) Astropart Phys

  • Are results consistent between different methods applied by same experimental group? An extreme situationHiRes/MIA data:Abu-Zayyad et al: PRL 84 4276 2000

  • Ideas to explain the Enigma Decay of super heavy relics from early Universe (or top down mechanisms) Wimpzillas/Cryptons/Vortons

    New properties of old particles? Breakdown of Lorentz Invariance? or is it simple? Are the UHE cosmic rays iron nuclei? Are magnetic field strengths really well known?

  • Potential of the Auger Observatory Directions Energy Mass- photons- neutrinos K-H Kamperts talk- protons or iron? HARDER: will useXmax , LDF, FADC traces,Radius of curvature

  • Mass information from study of Inclined Showers

  • M. Ave: 80, proton at 1019 eVDetails in Ave, Vazquez and Zas, Astroparticle Physics

  • Ave et al. PRL 85 2244 2000

  • Haverah Park:Photon limit at 1019 eV < 40% (@95% CL)AGASA: muon poor eventsGamma-ray fraction upper limits (@90%CL)34% (>1019eV) (g/p1019.5eV) (g/p
  • An Elegant Mass Determination MethodZatsepin EffectZatsepin 1951Zatsepin and Gerasimova 1960Solar Magnetic Field ImportantMedina Tanco and Watson (1998) from this very beautiful idea are too infrequent to be of use in any real experiment

  • Typical scale is ~ 1000 km

  • ConclusionsBeware: the experimentalists are still some way from AGREED statements about the mass composition above 1017 eV- after one studies the differences between different experiments - and even the different conclusions from within the same experiment.From Auger, we will get neutrino and photon limits (signals?) more readily than baryonic masses - but we have many tools in our armoury and should succeed in getting the latter, when we fully understand the showers and our hybrid detector. (Recall: ground breaking was only 5 years ago).Personal view: assume 100% protons above 1019 eV at your own risk!

    Ideas to explain the enigma


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