PHYS 3446 – Lecture #20Example: Hadronic Shower (20GeV)Run II DØ DetectorThe DØ Upgrade Tracking SystemDØ DetectorSlide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19HW8 (due 11/12)Wednesday Nov. 5, 2008 PHYS 3446, Fall 2008Andrew Brandt1PHYS 3446 – Lecture #20Wednesday, Nov. 5, 2008Dr. Andrew Brandt1. Particle Detection•Dzero Detector2. Particle Accelerators•Electrostatic Accelerators•Accelerators•Synchrotron AcceleratorsWednesday Nov. 5, 2008 PHYS 3446, Fall 2008 Andrew Brandt 2Example: Hadronic Shower (20GeV)Wednesday Nov. 5, 2008 PHYS 3446, Fall 2008 Andrew Brandt 3Run II DØ DetectorWednesday Nov. 5, 2008 PHYS 3446, Fall 2008 Andrew Brandt 4The DØ Upgrade Tracking SystemCharged Particle Momentum ResolutionpT/pT ~ 5% @ pT = 10 GeV/cWednesday Nov. 5, 2008 PHYS 3446, Fall 2008 Andrew Brandt 5DØ Detectormuon systemshieldingelectronicsWednesday Nov. 5, 2008 PHYS 3446, Fall 2008 Andrew Brandt 6DØ DetectorCentral CalorimeterSolenoidFiber TrackerSiliconPHYS 3446, Fall 2008 Andrew Brandt 7New forward components of the D0 detectorIntercryostat detectorForward pre-showerWednesday Nov. 5, 2008Wednesday Nov. 5, 2008 PHYS 3446, Fall 2008 Andrew Brandt 8•How can one obtain high energy particles?–Cosmic ray Sometimes we observe 1000 TeV cosmic rays•Low flux and cannot control energies too well•To probe the fundamental constituents with full control of particle energies and fluxes–Particle accelerators•Accelerators need not only to accelerate particles but also to–Maneuver them–Constrain their motions to the order of 1m–Must correct particle paths and momenta to increase fluxes and control momentaParticle AcceleratorsWednesday Nov. 5, 2008 PHYS 3446, Fall 2008 Andrew Brandt 9•Fixed target experiments: Probe the nature of the nucleons Structure functions–Results also can be used for producing secondary particles for further accelerations Tevatron anti-proton production•Colliders: Probes the interactions between fundamental constituents–Hadron colliders: Wide kinematic ranges and high discovery potential•Proton-anti-proton: TeVatron at Fermilab, SppS at CERN•Proton-Proton: Large Hadron Collider at CERN–Lepton colliders: Very narrow kinematic range, typically used for precision measurements•Electron-positron: LEP at CERN, Petra at DESY, PEP at SLAC, Tristan at KEK, ILC in the med-range future•Muon-anti-muon: Conceptual accelerator in the far future–Lepton-hadron colliders: HERA at DESY (ep)Particle AcceleratorsWednesday Nov. 5, 2008 PHYS 3446, Fall 2008 Andrew Brandt 10•Cockcroft-Walton Accelerator–Pass ions through sets of aligned DC electrodes at successively increasing fixed potentials–Consists of ion source (hydrogen gas) and a target with the electrodes arranged in between–Acceleration Procedure•Electrons are either added or striped off of an atom•Ions of charge q then get accelerated through series of electrodes, gaining kinetic energy of T=qV through every set of electrodesElectrostatic Accelerators: Cockcroft-Walton•Limited to about 1MeV acceleration due to voltage breakdown and discharge•Available commercially and also used as the first step high current injector (to ~1mA).Wednesday Nov. 5, 2008 PHYS 3446, Fall 2008 Andrew Brandt 11•Energies of particles through DC accelerators are proportional to the applied voltage•Robert Van de Graaff developed a clever mechanism to increase HV–The charge on any conductor resides on its outermost surface–If a conductor carrying additional charge touches another conductor that surrounds it, all of its charges will transfer to the outer conductor increasing the charge on the outer conductor, increasing HVElectrostatic Accelerators: Van de GraaffWednesday Nov. 5, 2008 PHYS 3446, Fall 2008 Andrew Brandt 12•Sprayer adds positive charge to the conveyor belt at corona points •Charge is carried on an insulating conveyor belt•The charges get transferred to the dome via the collector•The ions in the source then get accelerated to about 12MeV•Tandem Van de Graff can accelerate particles up to 25 MeV•This acceleration normally occurs in high pressure gas that has very high breakdown voltage Electrostatic Accelerators: Van de GraaffWednesday Nov. 5, 2008 PHYS 3446, Fall 2008 Andrew Brandt 13•Fixed voltage machines have intrinsic limitations in their energy due to breakdown•Machines using resonance principles can accelerate particles to higher energies•Cyclotron developed by E. Lawrence is the simplest one•Accelerator consists of–Two hollow D shaped metal chambers connected to alternating HV source–The entire system is placed under a strong magnetic fieldResonance Accelerators: CyclotronWednesday Nov. 5, 2008 PHYS 3446, Fall 2008 Andrew Brandt 14•Because of shielding of the metal D’s, there is no electric field inside them•Strong electric field exists only in the gap between the D’s•An ion source is placed in the gap•The path is circular due to the perpendicular magnetic field•Ion does not feel any acceleration inside a D but gets bent due to magnetic field•When the particle exits a D, the direction of voltage can be changed and the ion gets accelerated before entering into the D on the other side•If the frequency of the alternating voltage is just right, the charged particle gets accelerated continuously until it is extractedResonance Accelerators: CyclotronWednesday Nov. 5, 2008 PHYS 3446, Fall 2008 Andrew Brandt 15•For non-relativistic motion, the frequency appropriate for alternating voltage can be calculated from the fact that the magnetic force provides centripetal acceleration for a circular orbit•In a constant angular speed, =v/r. The frequency of the motion is•Thus, to continue accelerate the particle the electric field should alternate in this frequency, cyclotron resonance frequency•The maximum kinetic energy achievable for an cyclotron with radius R is Resonance Accelerators: Cyclotron2vmr=v qBr mc=2fvp= =( )22 2 2max max21 12 2qBRT mv m Rmcv= = =vBqcw=2qBmcp=12q Bm cp� �� �� �Wednesday Nov. 5, 2008 PHYS 3446, Fall 2008 Andrew Brandt 16•Accelerates particles along a linear path using resonance principle•A series of metal tubes are located in a vacuum vessel and connected successively to alternating terminals of radio frequency oscillator•The directions of the electric fields changes before the particles exits
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