Wednesday, Oct. 27, 2010 PHYS 3446, Fall 2010 Andrew Brandt 1PHYS 3446 – Lecture #14Wednesday, Oct. 27, 2010Dr. Andrew Brandt• Test Review• Particle Detection• Ionization detectorsHW6• CH 6 problems 1,2,3,4,7,9• Due Monday 11/1Wednesday, Oct. 27, 2010 PHYS 3446, Fall 2010 Andrew Brandt 2Project: Subjects• Quark-Gluon Plasma (RHIC)• Higgs Boson Theory• Higgs Boson Searches at LEP• Higgs Boson Searches at DZero• Higgs Boson Searches at CMS• Beyond the Standard Model Higgs rumors and CDF search• Supersymmetry or Blackhole Searches at ATLAS• Solar Neutrino Deficit• Long baseline neutrino experiments (neutrino mass)• G-2 experiments• HERA experiments: diffraction/large rapidity gapsWednesday, Oct. 27, 2010 PHYS 3446, Fall 2010 Andrew Brandt 3Particle DetectionInteractionPointelectronphotonjetmuonneutrino -- or any non-interacting particle missing transverse momentumÄBScintillating FiberSilicon TrackingCharged Particle TracksCalorimeter (dense)EM hadronicEnergyWire ChambersMagnetMuon TracksWe know x,y starting momenta is zero, butalong the z axis it is not, so many of our measurements are in the xy plane, or transverseWednesday, Oct. 27, 2010 PHYS 3446, Fall 2010 Andrew Brandt 4• Measure the ionization produced when particles traverse a medium• Can be used to– Track charged particles path through the medium– Measure the energy loss (dE/dx) of the incident particle• Must prevent re-combination of an ion and electron pair into an atom after the ionization• Apply high electric field across medium– Separates charges and accelerates electronsIonization DetectorsWednesday, Oct. 27, 2010 PHYS 3446, Fall 2010 Andrew Brandt 5• Basic ionization detector consist of – A chamber with an easily ionizable medium• The medium must be chemically stable and should not absorb ionization electrons• Should have low ionization potential ( I ) To maximize the amount of ionization produced per given energy– A cathode and an anode held at some large potential difference– The device is characterized by a capacitance determined by its geometryIonization Detectors – Chamber StructureWednesday, Oct. 27, 2010 PHYS 3446, Fall 2010 Andrew Brandt 6• The ionization electrons and ions drift to their corresponding electrodes, the anode and the cathode– Provide small currents that flow through the resistor– The current causes voltage drop that can be sensed by the amplifier– Amplifier signal can be analyzed to obtain pulse height that is related to the total amount of ionizationIonization Detectors – Chamber StructureCathode: NegativeAnode: PositiveWednesday, Oct. 27, 2010 PHYS 3446, Fall 2010 Andrew Brandt 7Wednesday, Oct. 27, 2010 8 PHYS 3446, Fall 2010 Andrew Brandt• Depending on the magnitude of the electric field across the medium different behaviors are expected– Recombination region: Low electric field– Ionization region: Medium voltage that prevents recombination– Proportional region: large enough HV to cause acceleration of ionization electrons and additional ionization of atoms– Geiger-operating region: Sufficiently high voltage that can cause large avalanche if electron and ion pair production that leads to a discharge– Discharge region: HV beyond Geiger operating region, no longer usableIonization Detectors – HVFlat!!!Flat!!!• Operate at relatively low voltage (in ionization region of HV)• Generate no amplification of the original signal• Output pulses for minimum ionizing particle is small• Insensitive to voltage variation• Have short recovery time Used in high interaction rate environment• Linear response to input signal • Excellent energy resolution• Liquid argon ionization chambers used for sampling calorimeters• Gaseous ionization chambers are useful for monitoring high level of radiation, such as alpha decayIonization CountersWednesday, Oct. 27, 2010 PHYS 3446, Fall 2010 Andrew Brandt
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