Nature s building blocks
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Nature’s building blocks. building blocks → matter. Baryons: qqq Examples: proton (p) = uud   charge: 1e=(2/3 e) + (2/3 e) + (-1/3 e) neutron (n) = udd  charge: 0 = (2/3 e) + (-1/3 e) + (-1/3 e) Mesons: q anti-q. Examples:  + = u anti-d   charge: 1e=(2/3 e) + (1/3 e)

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Building blocks matter l.jpg
building blocks → matter

  • Baryons: qqq

  • Examples:

  • proton (p) = uud  

  • charge: 1e=(2/3 e) + (2/3 e) + (-1/3 e)

  • neutron (n) = udd 

  • charge: 0 = (2/3 e) + (-1/3 e) + (-1/3 e)

  • Mesons: q anti-q.

  • Examples:

  • + = u anti-d   charge: 1e=(2/3 e) + (1/3 e)

  • - = d anti-u   charge: -1e=(-1/3 e) + (-2/3 e)

  • atoms: p+n+e; e.g. hydrogen: p + e


Cosmic rays l.jpg
Cosmic Rays

  • Outside earth’s atmosphere, these are charged particles, 86% protons

  • These primary cosmic ray particles interact with air high in the atmosphere (15 km), creating showers of secondary particles

  • By time the secondaries reach sea level, muons dominate the flux

  • The detectable (vertical) rate at sea level is 1/cm2/min (e.g. in CRDs)

  • Throughout our galaxy, CRs have an energy density of 1 eV/cm3

    • Starlight: 0.6 eV/cm3

    • CMB: 0.26 eV/cm3

  • 30% of natural radiation (sea level)

  • Provide charge and seeds for lightning

from QuarkNet CRD manual

QuarkNet Oregon 2008, R Frey


Energy and origin of primaries l.jpg
energy and origin of primaries

  • Steeply falling, power law energy spectrum

  • For E1014 eV, spectrum and flux are consistent with acceleration by shock waves from supernovae (“Fermi acceleration”)

  • For larger energy, mechanism is unknown (black hole at galactic center??)

  • For E1019 eV, protons would not be captured by galactic magnetic field (310-10 T)

    • pt [GeV] = (0.3q/e)B[T] R[m]

  • So higher energy CRs must be extra-galactic... but GZK cutoff...

QuarkNet Oregon 2008, R Frey


Auger cr observatory www auger org l.jpg
Auger CR observatorywww.auger.org

  • Sites in Mexico and Argentina

  • Array of detectors: (40x1.5 km)x(40x1.5 km)

  • GZK: extragalactic CRs attenuated:

    p +  (CMB)  +  p + , n + +

    • 411 CMB photons/ cm3 ; E=k2.7K=2.410-4 eV

    • No protons >1020 eV from further than 5 Mpc

  • Summer 2007: No excess above GZK cutoff

  • Fall 2007: UHE CRs associated with AGNs

QuarkNet Oregon 2008, R Frey


The cosmic ray showers l.jpg
The cosmic ray showers

  • Primaries interact in the atmosphere – the maximum production of pions and muons is at z15 km, making showers of (mostly) short-lived particles.(e.g. pion () lifetime is 2.610-8 s)

  • Characteristic shower angle:

      pt / pL  0.2 GeV/E

  • The long-lived secondaries are:

    • e, photons: mostly absorbed

    • neutrinos (): practically invisible

    • muons (): =lifetime is 2.210-6 s

  • Without time dilation, muons would travel dc=660 m, with a survival fraction

    e-0.66/15 10-10

  • Instead, for a 10 GeV muon, 10/0.1=100, then mean distance is 66 km. (OK)

QuarkNet Oregon 2008, R Frey


Cosmic rays at earth s surface l.jpg
cosmic rays at earth’s surface

  • Predominantly muons

  • Detectable (vertical) flux is 1/ cm2/ min

  • Mean energy  4 GeV

  • Originate at altitude of 15 km, on average

  • The very low energy muons (1-3 GeV) mostly decay

    • 15 km decay length corresponds to a 2.4 GeV muon

  • The higher energy muons lose about 2 GeV (on average) due to ionization in the atmosphere

    • and about 4 MeV / cm in concrete

QuarkNet Oregon 2008, R Frey




Quarknet cosmic ray detectors l.jpg
QuarkNet cosmic ray detectors

  • 4 scintillator paddles and photomultiplier tubes

  • requires only wall plug power

  • GPS receiver

  • electronics card and computer interface

  • measure cosmic ray rates in various configurations

  • datasets written to computer

  • combine with other setups

  • muon lifetime experiment

QuarkNet Oregon 2008, R Frey


Crd principle in a nutshell l.jpg
CRD principle in a nutshell

  • A “minimum ionizing particle” (MIP), e.g. a typical cosmic ray muon, passes through a plastic scintillator, depositing (on average) about 2 MeV / cm (ionization of the plastic)

  • Typically, the scintillation yield is 1 photon per 100 eV of ionization  2104 photons/ cm for each muon

  • Some fraction of the photons are collected at the photomultiplier tube (PMT) – depends on geometry and indices of refraction

  • The photocathode of the PMT converts a blue photon to an electron with efficiency of 10%

  • The PMT multiplies an electron by a factor 106

    • depends on high voltage setting, number of stages N (N=10 to 12 typically), and geometry

    • Gain  (few)N

QuarkNet Oregon 2008, R Frey


A community of cosmic experimenters l.jpg
a community of cosmic experimenters

QuarkNet Oregon 2008, R Frey


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