Lecture 13: Detectors Visual Track DetectorsElectronic Ionization DevicesCerenkov DetectorsCalorimetersPhototubes & ScintillatorsTricks With TimingGeneric Collider DetectorSections 4.3, 4.4, 4.5Useful Sections in Martin & Shaw:

Consider a massless qq pair linked by a rotating string with ends moving at the speed of light. At rest, the string stores energy per unit length and we assume no transverse oscillations on the string. This configuration has the maximum angular momentum for a given mass and all of both reside in the string - the quarks have none. Consider one little bit of string at a distance r from the middle, with the quarks located at fixed distances R. Accounting for the varying velocity as a function of radial position, calculate both the mass, M, and angular momentum, J, as a function of and R.3sheet 4At rest: dM/dr = kIn motion: dM/dr = gkg = (1-b2)-= [1-(r/R)2]-= kRp

but M = kRpIn natural units v = b = (r/R)= kR2p/2thus, J = M2/(2pk)From experimental measurements of J versus M (Regge trajectories) it is found that 0.18GeV2 when expressed in natural units. Convert this to an equivalent number of tonnes.~15

Now consider the colour charge contained within a Gaussian surface centred around a quarks and cutting through a flux tube of cross sectional area A . By computing an effective field strength (in analogy to electromagnetism), derive an expression for the energy density of the string (i.e. ) in terms of the colour charge and the area A .Ec A = qc/ecEc = qc/(Aec)Assume A ~ 1 fm2k = energy/length = (energy density) x A = ec Ec2 A= qc2/(2Aec)

Lecture 13: Detectors Visual Track DetectorsElectronic Ionization DevicesCerenkov DetectorsCalorimetersPhototubes & ScintillatorsTricks With TimingGeneric Collider DetectorSection 3.3, Section 3.4Useful Sections in Martin & Shaw:

Wilson Cloud Chamber:Wilson Cloud Chamber

AntimatterAntimatterAnderson 1933

Evaporation-type Cloud Chamber:Evaporation Cloud Chamber

Photographic EmulsionsDiscovery of the Pion (Powell et al., 1947)Photographic Emulsions

DONUT (Direct Observation of NU Tau)July, 2000Emulsions & the Nu-tau

Donald Glazer (1952)Bubbles form at nucleation sites in regions of higher electric fields ionization tracksBubble ChamberBubble Chamber Idea

Donald Glazer (1952)Bubbles form at nucleation sites in regions of higher electric fields ionization tracksBubble ChamberBubble Chamber & Beer

Steves Tips for Becoming a Particle Physicist2) Start LyingTips 33) Sweat Freely4) Drink Plenty of Beer1) Be Lazy

Liquid superheated by sudden expansionBubbles allowed togrow over 10msthen collapsed during compression strokehydrogen,deuterium,propaneFreonBubble Chamber

High beam intensitiesswamp filmActs as bothtarget & detectorSlow repetition rateSpatial resolution100200 mTrack digitization cumbersomeDifficult to triggerMechanically ComplexBubble Chamber Pros & Cons

Electric field imposed to prevent recombinationMedium must be chemically inactive (so as not to gobble-up drifting electrons)and have a low ionization threshold(noble gases often work pretty well)Ionization DetectorsBasics of Ionization Detector

minimumionizingparticleheavilyionizingparticleIonization Regimes

Typical Parametersrin = 10-50 mE = 104 VAmplification = 105Proportional CounterMultiwire Proportional Counter (MWPC)Typical wire spacing ~ 2mmGeorge CharpakProportional Counters

Drift ChamberField-shaping wires provide~constant electric field socharges drift to anode wires with~constant velocity (~50mm/s)Timing measurement comparedwith prompt external trigger canthus yield an accurate position determination (~200m)use of MWPC indetermination of particle momentaDrift Chamber

Time Projection Chamber (TPC)TPC

but sometimes... occurs as a single quantum event within a nucleus''double decay"(Majorana particle)then the following would be possible:''neutrinoless double decay"One Application of a TPC:TPC & double-beta decay

Example of a radial drift chamber (''Jet Chamber")Angular segment ofJADE Jet ChamberJet Chamber

Spark ChamberSpark Chamber

Silicon Strip Detectorelectron-hole pairs instead of electron-ion pairs3.6 eV required to form electron-hole pair thin wafers still give reasonable signals and good timing (10ns) Spatial resolution 10mSilicon Strip Detector

CDF Silicon Tracking DetectorCDF Silicon Strips

CerenkovRadiationCerenkov Radiation

(c/n)tvt# photons dE d/2 blue lightCerenkovRadiationCerenkov Angle & Photon Yield

Threshold Cerenkov Counter:discriminates between particles of similar momentum but different mass(provided things arent too relativistic!)= (22 )/222 = 1 1/2 = 1 m2/E2= (m12 m22)/p2Threshold Cerenkov Counter

helium 3.3x105 123CO2 4.3x104 34pentane 1.7x103 17.2aerogel 0.0750.025 2.74.5H2O 0.33 1.52glass 0.750.46 1.221.37Medium n1 (thresh)Muon RingsliquidradiatorgaseousradiatorRing Imaging CHrenkov detectorRICH Detectors

Above some ''critical" energy, bremsstrahlung and pair production dominate over ionizationEC ~ (600 MeV)/ZMaximum development will occur when E(t) = EC :# after t radiation lengths = 2tAvg energy/particle:E(t) = E0/2tCalorimetersNmax = E0/ECEM Calorimeters

Depth of maximum increases logarithmically with primary energy Number of particles at maximum is proportional to primary energy Total track length of particle is proportional to primary energy Fluctuations vary as 1/N 1/E0 Typically, for an electromagnetic calorimeter:For hadronic calorimeter, scale set by nuclear absorption lengthScale is set by radiation length: X0 37 gm/cm2iron nuc = 130 gm/cm2lead nuc = 210 gm/cm2~ 30% of incident energy is lost by nuclear excitations and theproduction of ''invisible" particlesHadronic vs EM Calorimeters

Examples of Calorimeter Construction:Calorimeter Construction

Photomultiplier Tubes (PMTs)Photomultiplier Tubes A Typical ''Good" PMT: quantum efficiency30%collection efficiency80%signal risetime2ns

ScintillatorInorganicUsually grown with small admixture of impurity centres.Electrons created by ionization drift through lattice,are captured by these centres and form an excited state.Light is then emitted on return to the ground state.Most important example NaI (doped with thallium)Pros: large light outputCons: relatively slow time response (largely due to electron migration)OrganicExcitation of molecular energy levels.Medium is transparent to produced light.Why isnt light self-absorbed??Pros: very fastCons: smaller light outputScintillator

NaI (Tl) 2.2 250 410 3.7CsI (Tl) 2.4 900 550 4.5BGO 0.5 300 480 7.1 (Bi4Ge3O12)anthacene 1.0 25 450 1.25toluene 0.7 3 430 0.9polystyrene 0.3 3 350 0.9+ p-terphenylScintillator Relative Decay max Density light yield time (ns) (nm) (gm/cm3)Some Commonly Used Scintillators:some ways of coupling plasticscintillator to phototubes toprovide fast timing signal :Scintillator Charasteristics

t = Lc/ = ( 1 1/2 )1/2 = 1 1/2 1 1/(22)t Lc/2 (1/2)= Lc/2 ( m22/E22 m12/E12 ) Lc/2 ( m22 m12 )/E2Time Of Flight (TOF): An Application of Promt Timing(used to discriminate particle masses)Time Of Flight

High Energy Particle Detectors in a Nutshell:Collider Detector Configuration