PH2520 Particle Detectors and Accelerators ========================================== 2007/08 - Autumn term --------------------- Lecture 1 - 01/10/07 -------------------- Introduction. Revision of Particle Physics (PH1530). The fundamental matter fermions: quarks and leptons. The four basic interactions in Nature, and their associated gauge bosons. The Higgs boson. Supersymmetry: motivation and the particles it predicts. Lecture 2 - 01/10/07 -------------------- Overview of modern accelerators & colliders. Justification for the need for high energy beams. Demonstration of operation of LEP collider (java applet). Basic components of a circular accelerator: dipole magnets, quadrupole magnets and RF accelerating cavities. The LEP collider. Energy loss from synchrotron radiation. How to overcome the beam-energy limitation imposed by synchrotron energy loss. Lecture 3 - 05/10/07 -------------------- Hadron colliders, linear colliders; advantages and disadvantages of each type of collider. The TeVatron. The Large Hadron Collider (LHC). Detector systems for Particle Physics: quick overview. Description of a few typical events, with a view to establishing requirement for an adequate detector system. Some requirements for a detector system: hermeticity; granularity; fast response time; E, p, charge measurement. [PS1 e-mailed to students; due 18/10/07] [Chapter 1 of Lecture Notes handed out] Lecture 4 - 08/10/07 -------------------- Layout of a typical detector system at a collider: tracking chambers, electromagnetic calorimeter, hadronic calorimeter, muon detectors. Tracking chambers: measurement of p and sign(Q); need for strong axial magnetic field, superconducting solenoid. Function of the electromagnetic and hadronic calorimeters. Muon detector function. Response of the main detector types to the main types of particles produced in events. Discussion of several examples of actual events recorded with the ALEPH detector system at the LEP collider. Lecture 5 - 08/10/07 -------------------- Organization of field trip: possible location and date; travel and insurance issues. Interaction of Radiation with Matter. Interaction of heavy charged particles in matter. Elastic and inelastic processes. Coulomb deflection from nucleus; ionization/excitation of atoms; nuclear interaction (e.g. absorption by nucleus). Inelastic collisions with atomic electrons: soft, hard; knock-on electrons. Ionization energy loss of heavy charged particles: Bohr's classical calculation. Recall Gauss' Law. Lecture 6 - 12/10/07 -------------------- Bohr's derivation of specific energy loss (conclusion). Dependence of specific energy loss on z, Z and relativistic beta. Main features of dE/dx curves: minimum ionization point, relativistic rise, Fermi plateau. -dE/dx expressed as a function of momentum of the heavy charged particle: use in charged particle identification. Bragg curve, energy deposition in an absorber as a function of penetration depth; medical application. Lecture 7 - 15/10/07 -------------------- Interactions of electrons and positrons in matter. Bremsstrahlung. Critical Energy. Radiation Length. Interactions of high-energy photons (x-rays, gamma-rays) in matter. Lecture 8 - 15/10/07 -------------------- Penetration and attenuation of high-energy photons in matter, compared to charged particles. Occurrence of photoelectric effect, Compton scattering, pair-production, and their probabilistic nature. [no lecture 19/10/07] Lecture 9 - 22/10/07 -------------------- Linear attenuation of a beam of monoenergetic photons in an absorber; linear attenuation coefficient. Probabilistic nature of photon interactions; results from numerical simulation: look at history of individual photons in an absorber. Electron-photon showers. Lecture 10 - 22/10/07 --------------------- The Simple Shower model and its predictions for shower development, depth of shower maximum, number of particles at shower maximum. Summary of the predictions of the Simple Sower model. Interactions of neutrons in matter. Hadronic showers. Electron-photon shower component in hadronic showers. Energy leakage in hadronic showers, due to e.g., charged pion decay, nuclear excitation and breakup. Lecture 11 - 26/10/07 --------------------- Solution to problems 1, 2, 3 and 4 of Problem Sheet 1. [PS2 handed out to students; due 5/11/07] Lecture 12 - 29/10/07 --------------------- Charged particle detectors based on the measurement of ionization. The ionization chamber. The proportional counter; derivation of electric field strength in a proportional counter. The Townsend avalanche charge multiplication process. Lecture 13 - 29/10/07 --------------------- Output signal of proportional counter as a function of the applied voltage: the ionization chamber, proportional counter and Geiger-Muller regimes. Ionization measurement detectors for position measurement. Multi-Wire Proportional Chambers (MWPC): position measurement along one (x) and two (x&y) coordinates; segmented cathodes: cathode strips, cathode pads; resolving x&y measurement ambiguities. Lecture 14 - 02/11/07 --------------------- Drift chambers: principle of drift time measurement. Drift chambers. Planar drift chambers; cylindrical drift chambers. Measurement of the momentum of charged particles in cylindrical tracking devices; solenoids; uniformity of magnetic field. Lecture 15 - 05/11/07 --------------------- Calculation of magnetic field strength in a solenoid by integration of Ampere's Law. Superconducting solenoids. Time Projection Chambers: operation principle, performance, advantages (high-precision 3D position measurement) and disadvantages (slow read-out time). Time Projection Chambers (cont'd); Typical example: the ALEPH TPC, example of two-jet event recorded in the TPC; dE/dx measurement with ALEPH TPC and particle separation based on dE/dx. Lecture 16 - 05/11/07 --------------------- Semiconductor detectors; electron-hole pair creation and their contribution to the current in a semiconductor. Basic operating principle of semiconductor detectors. Pitch and spatial resolution; thickness; fast charge collection time and ability for operating detector at high rate (eg at LHC). ALEPH semiconductor vertex detector; example of secondary vertex reconstruction. ATLAS semiconductor tracker (SCT; strip segmentation) and pixel detectors (pad segmentation); barrel and forward disks. CMS Si tracker; geometry; single- and double-sided wafers. Lecture 17 - 09/11/07 --------------------- Calorimetry. Basic principle of calorimetric energy measurement in high-energy experiments. Recall Simple Shower Model predictions for electromagnetic (EM) showers. Longitudinal EM shower development as a function of absorber depth, in radiation lengths. General rule for longitudinal containment (95%) of an EM shower, t_95. Proportionality between total number of particles in electromagnetic shower, Ntotal, and incident particle energy, E0. Sampling calorimeter design. Lecture 18 - 12/11/07 --------------------- The ALEPH electromagnetic calorimeter: lead absorber interleaved with proportional wire chambers. Statistical fluctuations affecting Ntotal, and relative energy resolution of EM calorimeter. Basic pinciple of operation of an hadronic calorimeter; recall hadronic shower development, EM component, energy leakage. Longitudinal hadron shower development and nuclear interaction length. Impact of hadron shower characteristics on hadronic calorimeter design. Sampling hadronic calorimeters; comparison with electromagnetic calorimeters. Examples of actual electromagnetic and hadronic sampling calorimeters and their resolutions. Lecture 19 - 12/11/07 --------------------- Multicomponent detector systems. Layout of a typical detector (tracking devices, solenoid, calorimeters, etc): function of the main detector components, examples of types of detector technology for each component and their basic principle of operation. Requirements for a multi-component system. Discussion of the measurement of missing energy and momentum and its usefulness. Discussion of the Compact Muon Solenoid (CMS) detector at the LHC; response of the various CMS detectors to the main different types of particle. The search for the Higgs particle; dependence of Higgs decay mode on the Higgs particle mass; role played by different sub-detectors for different decay modes: H-->gamma gamma; H-->ZZ --> 4electrons, 4 muons, 2e+2jets. Lecture 20 - 16/11/07 --------------------- (cont. from previous lecture) Importance of stand-alone muon spectrometer. ATLAS detector overview. ATLAS stand-alone muon spectrometer and its toroidal magnetic field. Problem solving: dE/dx scaling law (Q1 PS2). Lecture 21 - 19/11/07 --------------------- Solutions to problems in Problem Sheet 2 (Q2, Q3 and Q5) related to electromagnetic shower development, the Simple Shower Model and calorimetry. Lecture 22 - 19/11/07 --------------------- Accelerators -- The electrostatic accelerator; HV generators (Cockroft-alton; Marx); electrostatic accelerator limitation from corona formation. The linear accelerator; principle of operation; advantages and disadvantages. The cyclotron; the cyclotron principle for non-relativistic particles; mode of operation of a cyclotron; advantages and disadvantages. Relativistic limitation to cyclotron operation. Lecture 23 --------------------- [Detailed information regarding the preparation & details of the visit to CERN.] The Synchrotron and its mode of operation. Synchrotron components: pre-accelerator, injection "kicker" magnet, bending magnets (dipoles), accelerating RF voltage (accelerating cavities), focussing (quadrupole) magnets. Lecture 24 --------------------- Phase stability (a.k.a. phase focusing) in RF oscillating voltage accelerators. Synchronous particle. Synchrotron radiation. Emitted instantaneous power. Energy loss per particle in a complete turn in the synchrotron; dependency on energy and mass of beam particles, and on the radius of the collider. Lecture 25 --------------------- Synchrotron radiation (conclusion): Compare energy loss for electrons and protons. Calculate the typical energy loss per particle per turn at LEP1 (E_CM=~50 GeV) and at LEP2 (E_CM=~100 GeV). Calculate the synchrotron power radiated by the LEP beams, give the LEP current. Synchrotron radiation facilities (e.g., "Diamond" in the UK). Description of essay topics and assignment to students. Reminder of various Higgs particle search channels (namely H-->2 photons; Higgs --> 4 muons, Higgs --> 2muons + 2jets) and the relevance of the various detector components for the experimental detection of the Higgs particle. Lecture 26 --------------------- Storage rings (colliders). Recall advantage of symmetric collisions with respect to fixed-target. Storage rings with one set of bending dipole magnets common to both beams (eg LEP, TeVatron), and two opposite-polarity bending channels. Collision rate; definition of luminosity: dependency on relevant parameters. Typical values of these parameters at LEP and the LHC and corresponding luminosity values. Definition of cross-section for a given physics reaction. Calculation of the number of events produced at the LHC in one year of data-taking, for the pp->ttbar reaction. Lecture 27 --------------------- Transverse motion of beam particles in a storage ring. Betatron oscillations. The ideal orbit (a.k.a., central orbit, reference orbit). Co-moving coordinate system to describe deviations from ideal orbit. Displacement and divergence. Bending, dipole magnets and magnetic rigidity. Bending angle of beam in a dipole. Lecture 28 --------------------- Beam focusing with quadrupole magnets. Magnetic field of a quadrupole magnet. Characteristic strength of a quadrupole magnet. Change of particle's divergence in a quadrupole magnet. Infinitely long quadrupole (gutter analogy); phase space diagram. Alternating gradient focusing. F0D0 cell. Lecture 29 --------------------- Hill's equations of transverse motion; step-by-step solution of the equations for the case of a horizontally-focusing magnetic quadrupole (QF). Solutions for the case of a horizontally-defocusing (QD) quadrupole. Trajectory vector and transfer matrix notation.