Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 298.882 LHC PhysicsExperimental Methods and MeasurementsParticle Detectors Overview[Lecture 3, February 11, 2009]‘09The Physics Colloquium SeriesThursday, February 12 at 4:15 pm in room 34-101 Jochen SchneiderLCLS Experimental Facilities Division, SLAC, CA and Center for Free-Electron Laser Science (CFEL), Germany "Science at SASE Free-Electron Lasers" SpringFor a full listing of this semester’s colloquia, please visit our website at web.mit.edu/physicsColloquium SeriesPhysicsC.Paus, LHC Physics: Particle Detectors Overview 3Organizational Issues•Accounts•please make sure you have one so we can get started•Teaching assistant•I will be the TA...•Recitation•Friday at 10:00pm in 24-507C.Paus, LHC Physics: Particle Detectors Overview 4Lecture Outline•Particle Detectors Overview•introduction and a bit of history•general organization of detectors•particle interactions with matter•tracking•calorimetry•modern integrated detectors•conclusions and next lectureC.Paus, LHC Physics: Particle Detectors Overview 5Motherhood and Apple Pie•The ultimate goal of particle detectors is to determine the particles creation/decay point, its momentum and its type (mass). •Detecting particles always implies to interact with them. Path is thus always affected by observation. If it's perfect it ain't real.•Particle detectors always rely on electromagnetic interaction (photons or charged particles).C.Paus, LHC Physics: Particle Detectors Overview 6Definitions and Units•Energy of a particle:•energy, E, measured in eV (= 1.6 · 10-19 J)•momentum, p, measured in eV/c•mass, m, measured in eV/c2•mbee = 1 g = 5.8· 1032 eV/c2•vbee = 1 m/s → Ebee = 10-3 J = 6.25 · 10-15 eV•Ep,LHC = 14· 1012 eV, but all protons 1014 → 108 J•From special relativitym = 100 Tv = 120 km/hC.Paus, LHC Physics: Particle Detectors Overview 7Definitions and Units•Cross Section, σ•cross section or differential cross section expresses probability of a process to occur•two colliding bunches: N1/t collides with N2/t•rate is•differential cross section:•fraction of cross section scattered in dΩ angular arealuminosity [cm-2 s-1]cross section is an area1 barn = 10-24 cm2C.Paus, LHC Physics: Particle Detectors Overview 8Natural Particle Detectors•A very common particle detectors: the eye•Properties of 'eye' detector•highly sensitive to photons•decent spatial resolution•excellent dynamic range 1-1014•automatic threshold adaptation•energy discrimination, though limited range: wavelength•modest speed: data taking at 10 Hz, inc. processing•excellent data processing connection (at times)C.Paus, LHC Physics: Particle Detectors Overview 9Extending the Eye•Photographic paper as detector•1895 W.C. Röntgen•detection of photons (x-rays) invisible to the eye•silver bromide or chlorides (emulsion)•AgBr + energy → silver (black)•Properties of 'paper' detector•very good spatial resolution•good dynamic range•no online recording•no time resolutionC.Paus, LHC Physics: Particle Detectors Overview 10The Cathode Ray•1897 J.J.Thomson discovers the electron•From his publication: Scintillation of glass caused the visible light patch•“Cathod Rays”: Philosophical Magazine, 44, 293 (1897)•… The rays from the cathode C pass through a slit in the anode A, which is a metal plug fitting tightly into the tube and connected with the earth; after passing through a second slit in another earth-connected metal plug B, they travel between two parallel aluminum plates about 5 cm. long by 2 broad and at a distance of 1.5 cm. apart; they then fall on the end of the tube and produce a narrow well-defined phosphorescent patch. A scale pasted on the outside of the tube serves to measure the deflection of this patch….C.Paus, LHC Physics: Particle Detectors Overview 11The First Electrical Signal•The Geiger counter•a gas volume•anode and cathode•passing charge particle ionizes the gas•ionization drifts:•ion – cathode•electron – anode•pulse can be used in various ways, for example as a 'click' on a little speaker•Counter gets improved and called Geiger-MüllerC.Paus, LHC Physics: Particle Detectors Overview 12The First Tracking Detector•The Cloud Chamber (C.T.R. Wilson)•an air volume saturated with water•lower pressure to generate a super-saturated air volume•charged particles cause condensation of vapour into small droplets•droplets form along particle trajectory and are observed•photographs allow longer inspectionsC.Paus, LHC Physics: Particle Detectors Overview 13Detectors and Particle PhysicsTheory and experiment share an intimate and fruitful connection:•detectors allow one to detect particles•experimenters study their behaviour •new particles are found by direct observation or by analyzing their decay products•theorists predicts behaviour of (new) particles•experimentalists design the particle detectors to detect them and collect the dataC.Paus, LHC Physics: Particle Detectors Overview 14Overview of Detectors•What do particle detectors measure?•spacial locations•momentum•energy•flight times•Modern detector types•tracking (gas, solids)•scintillation and light detectors•calorimeters•particle Id systems•Integral piece of detectors•trigger systems•data acquisition systems•offline systemC.Paus, LHC Physics: Particle Detectors Overview 15The Ideal Detector•Properties•cover the full solid angle•measurement of momentum and/or energy•detect, track and identify all particles•fast response, no dead time•Limitations•technology•space•budgetC.Paus, LHC Physics: Particle Detectors Overview 16Following a Particle•Scattering with the nucleus, charge Z (Rutherford)•Particles do not scatter or very little•if the material is thick they may scatter multiple times•Multiple scattering•particle scatters multiple times•the smaller the momentum the larger the effect•kind of Gaussian around original directionC.Paus, LHC Physics: Particle Detectors Overview 17Following the Particle•Energy loss in matter•multiple scattering? no! collision elastic (heavy nucleus)•scattering with electrons from the atoms•energy loss per length xelectron densitycross section