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					                           A review on mass
  The highest energy cosmic rays above the GZK cut off are a mystery
  both in terms of their origin and their mass composition. Conventional
  acceleration mechanisms, so called `bottom up' scenarios, predict an
  extragalactic origin with mainly proton composition as, although nuclei of
  higher charge are more easily accelerated, they are fragile to
  photonuclear processes in the strong photon fields to be expected in
  likely source regions. “Top down" models explain the highest energy
  cosmic rays as arising from the decay of some sufficiently massive “X-
  particles". These models predict particles such as nucleons, photons and
  even possibly neutrinos as the high energy cosmic rays, but not heavy
  nuclei. There is however some partial evidence against the photon
  hypothesis. Shower development of the highest energy event, is
  inconsistent with a photon initiated shower while AGASA measurements
  of the muon lateral distribution of the highest energy events are
  compatible with a proton origin.

Valencia meeting – 20 Ottobre 2003                               Carla Aramo
Lo spettro dei raggi cosmici

           The CR energy spectrum above 109
           eV can be described by a series of
           power laws, with the fux falling
           about 3 orders of magnitude for
           each decade increase in energy. In
           the decade centered at 5x1015 eV
           (the knee) the spectrum steepens
           from E-2.7 a E-3.0 .
           This feature, discovered around 40
           years ago is still not consistently
           The spectrum steepens further to
           E-3.3 above 7x1017 eV eV and then
           flattens to E-2.7 at 5x1018 eV (the ankle).
Parametri misurati


Profili longitudinali per differenti primari
Analisi in Ne- Nm (1)

          E = 1018 eV, q = 0o
Analisi in Ne- Nm (2)
Analisi in Xmax – Nmax (1)
Analisi in Xmax – Nmax (2)
                        Elongation rate
The rate of change of Xmax with the log of the energy of the primary,
dXmax/dlog(E), is known as the elongation rate
                                                                Gap – 2003-029

          Parametri misurati:
   • Componente elettromagnetica (Ne)
       • Componente muonica (Nm )
       • Componente adronica (Nh)
Analisi in composizione
Confronto tra modelli di interazioni adroniche
Confronto in log(A)
Haverah Park

        The HP extensive air shower array
        was situated near Leeds, UK, at an
        altitude of 220 m asl.
        Particles were detected with water
        Cherenkov counters of approximately
        2.29 m2 area 1.2 m depth, viewed by a
        Photomultiplier tube (PMT).
        The number of Cherenkov photons
        released in a water tank is proportional
        to the energy deposit of the shower
        particles in the water.
                            Sviluppo laterale

La distribuzione di densità laterale del segnale Cherenkov in funzione della distanza dall’asse
  dello sciame è parametrizzata dalla “funzione di distribuzione laterale”:
                                                    h  f ( r )
                                    (r )  k  r
dove f e k dipendono dal rivelatore e h dall’angolo di incidenza e dall’energia del primario.
Per r> 800 m questa formula empirica deve essere modificata introducendo il fattore (r/800)1.03
Nuova analisi dei dati di Haverah Park

      This array is called the Akeno
 Giant Air Shower Array (AGASA) .
 AGASA covers an area of about 100
 km2 and consists of 111 detectors on
 the ground (surface detectors) and
 27 detectors under absorbers (muon
 detectors). Each surface detector is
 placed with a nearest-neighbor
 separation of about 1 km and the
 detectors are sequentially connected
 with a pair of optical fibers. All
 detectors    are    controlled   and
 operated by a set of commands
 transmitted    from      a    central
Sviluppo laterale in AGASA

               dove: rM raggio di Molière
               (91.6 m per Akeno)
               C fattore di normalizzazione
               a = 1.2, d = 0.6
               S0 (600) è la densiyà di
               Particelle cariche in 1/m2 a
               600 m dal core per sciami
   Sciame da     2x1020   eV rivelato da AGASA

                             I cerchi sono le densità delle
                             particelle rivelate, il cui raggio
                             corrisponde al logaritmo
Distribuzione laterale       della densità
Mass composition from AGASA
            Data from the AGASA array (muon
            threshold of 0.5GeV) .
            Sold lines and triangles show
            simulations from MOCCA+SIBYLL
            for iron (top) and proton (bottom)
            primary particles.
Fly’s eye
       Number of mirrors
                                        1.575 m
       Diameter of mirrors
                                        1.500 m
       Focal Length
       Number of PMT
       Mirror Obscuration by PMT        13%
       Mirror-cone efficiency product
       PMT type
                                      9861 B
       Peak PMT quantum efficiency at 0.21
       360 nm
                                      91.5 mr
       Angular Aperture per PMT
                                      6.57 msr
       Solid Angle per PMT
       Number of electronic channels
                                      105 linear
       Charge dynamic range
                                      25 ns
       Time Resolution
Sviluppo longitudinale (Fly’s eye)

                      Profilo longitudinale
                          di uno sciame
                         innescato da un
                      particella primaria di
        It uses 14 spherical
        telescopes of d= 2.0m to
        collect the light from a
        0.95 sr portion of the
        sky. The image plane of
        each telescope is
        populated with an array
        of 256 hexagonal PMTs,
        yielding pixel of 1o. In
        monocular mode, the
        effective acceptance of
        this instrument is 350
        (1000) km2 sr at 1019
        (1020) eV, on average
        about 6 times the Fly's
        Eye acceptance, and the
        threshold energy is 1017
Reconstructed event with Hires
                 Display of an Event with
                 reconstructed energy of 52 EeV.
                 The upper left part of this figure
                 shows the four mirrors that
                 triggered for this event.
                 The upper right panel shows the
                 azimuthal vs. elevation angles of
                 triggered tubes, with a fit
                 superimposed. The lower left panel
                 shows the time of the tube hits in
                 FADC time slices vs. the angle of
                 the tube measured along the track,
                 with two ts superimposed: a straight
                 line and the result of the time t.
                 The lower right quarter shows the
                 number of charged particles in the
                 shower as a function of slant depth
                 (in g/cm2), with the fit to the
                 Gaisser-Hillas formula superimposed.
             Confronto sullo spettro


The result is consistent with the flux measured by the Fly's Eye experiment using
the stereo reconstruction technique. Above 1020eV the Hires data is significantly
different from that of the AGASA experiment. The data are fitted with a model
incorporating both galactic and extragalactic sources of cosmic rays, which
includes the GZK cutoff, and find a good agreement.
Xmax vs Energy
            Energy spectrum

               A composite energy spectrum
               including recently reanalysed
               Haverah Park data assuming
               proton and iron primaries
               (the parameter measures the
               Attenuation length of the
               density of charged particles
               at 600 m from the shower
               core), stereo Fly's Eye data,
               Monocular HiRes data from
               both eyes up to 60, and
               Hybrid HiRes MIA data.

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