QuarkNet Oregon 2012, R Frey 1pages.uoregon.edu/rayfrey/QuarkNet/Ray_detection_CR.pdfQuarkNet Oregon...
Transcript of QuarkNet Oregon 2012, R Frey 1pages.uoregon.edu/rayfrey/QuarkNet/Ray_detection_CR.pdfQuarkNet Oregon...
Nature’s building blocks
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building blocks → matter
Baryons: qqq• Baryons: qqq Examples: proton (p) = uud
charge: 1e=(2/3 e) + (2/3 e) + ( 1/3 e)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-qMesons: 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) = d anti-u charge: -1e=(-1/3 e) + (-2/3 e)
• atoms: p+n+e; e.g. hydrogen: p + e2QuarkNet Oregon 2012, R Frey
Cosmic Rays
• Outside earth’s atmosphere, these are charged particles, 86% protons
• These primary cosmic ray particles• These primary cosmic ray particles interact with air high in the atmosphere (15 km), creating h f d ti lshowers 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 Th h t l CR h• 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• Provide charge and seeds for
lightningfrom QuarkNet CRD manual
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energy and origin of primaries
• Steeply falling, power law energy spectrumF E 1014 V t d fl• For E1014 eV, spectrum and flux are consistent with acceleration by shock waves from supernovae (“Fermi acceleration”)
• For largest energies, mechanism is unknown (Gamma-rayis unknown (Gamma ray bursts??)
• For E1019 eV, protons would not b t d b l ti tibe captured by galactic magnetic field (310-10 T) pt [GeV] = (0.3q/e)B[T] R[m]pt [ ] ( q ) [ ] [ ]
• So higher energy CRs must be extra-galactic (but GZK cutoff)
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Auger CR observatorywww.auger.org
• Sites in Mexico and Argentina• Array of detectors: (40x1.5 km)x(40x1.5 km)• GZK: extragalactic CRs attenuated:• GZK: extragalactic CRs attenuated:
p + (CMB) + p + , n + +
411 CMB photons/ cm3 ; E=k2.7K=2.410-4 eV No protons >1020 eV from further than 5 Mpc
• Summer 2007: No excess above GZK cutoff• Fall 2007: UHE CRs associated with AGNs• Fall 2007: UHE CRs associated with AGNs
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The cosmic ray showers
• Primaries interact in the atmosphere the• Primaries interact in the atmosphere – the maximum production of pions and muons is at z15 km, making showers of (mostly) short-lived particles (e g pion () lifetime is 2 610-8 s)particles.(e.g. pion ( ) lifetime is 2.610 s)
• Characteristic shower angle: pt / pL 0.2 GeV/E
• The long-lived secondaries are: e, photons: mostly absorbed neutrinos (): practically invisibleneutrinos (): practically invisible muons (): =lifetime is 2.210-6 s
• Without time dilation, muons would travel dc=660 m with a survival fractiondc=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)
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cosmic rays at earth’s surface
• Predominantly muons
• Detectable (vertical) flux is 1/ cm2/ min• Detectable (vertical) flux is 1/ cm / min
• Mean energy 4 GeVgy
• 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 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
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Basic principle of particle detectors
• High-energy charged particles (e.g. cosmic rays, nuclear decays, LHC collisions x-rays, gamma rays, etc) ionize the medium they pass throughmedium they pass through.
• The ionization is detected directly or by separation (and amplification) of the charge pairs.
• Uncharged particles (e.g. x/gamma-rays) similar• That’s it (almost).
• Examples: Geiger and other gaseous countersg g Scintillator (e.g. quarknet CRDs) Smoke detectors Semiconductor detectors Bubble chambers Spark chambers Spark chambers Cloud chambers
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Cloud chambers
• A supersaturated vapor will preferentially condense along the ionization trail left by a passing particlepassing particle.
• Basic ingredients are: • A fluid with high vapor pressure
(alcohol)• A cold plate at temperature well below
boiling pointboiling point• Very still conditions• A strong light and black background• An electric field is sometimes applied
In ented b Wilson (1911)• Invented by Wilson (1911)• Used to discover positron (1932) by
Anderson• Replaced by other techniques for HEP
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Modern particle detectors
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What particles are actually detected?
( tl )(mostly)
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Detectors revealed
• Inner detectors: Low density ionization detectors to measure trajectory of chargeddetectors to measure trajectory of charged particles (gas, thin silicon) in a uniform magnetic field (p=qvB). [trackers]
• Outer detectors absorb and measure particle energies. [calorimeters]
• Muons (and neutrinos) surviveMuons (and neutrinos) survive.• Energy & Momentum conservation to
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pix (silicon detectors)
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e.g. e+e- → e+e- at E=91 GeV
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e+e- → q anti-q at E=91 GeV
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QuarkNet cosmic ray detectors
• 4 scintillator paddles and photomultiplier tubesphotomultiplier tubes• requires only wall plug power• GPS receiverGPS receiver• electronics card and computer interface
• measure cosmic ray rates in various configurationsvarious configurations• datasets written to computer• combine with other setups• muon lifetime experimentmuon lifetime experiment
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CRD principle in a nutshellA “minimum ionizing particle” (MIP) e g a typical cosmic ray muon• 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 2104 photons/ cm for each muon
• Some fraction of the photons are collected at the photomultiplier tubeSome 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 ith ffi i f 10%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 12depends on high voltage setting, number of stages N (N 10 to 12 typically), and geometry
Gain (few)N
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a community of cosmic experimenters
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