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Mitglied der Helmholtz-Gemeinschaft Lecture 9 PARTICLE DETECTORS Detlev Gotta Institut fr Kernphysik, Forschungszentrum Jlich / Universitt zu Kln GGSWBS'12, Batumi, Georgia 5th Georgian German School and Workshop in Basic Science August 16, 2012

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Folie 2 EXAMPLES OF COMBINED DETECTION SYSTEMS HOW TO DETECT? INTERACTION OF CHARGED PARTICLES WITH MATTER MASSIVE NEUTRAL PARTICLES WITH MATTER RADIATION WITH MATTER DETECTOR PRINCIPLES WHAT TO DETECT ?

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Folie 3 WHAT TO DETECT ?

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Folie 4 PARTICLES Light Heavy particle detectorregistration

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Folie 5 PARTICLES What characterizes a particle? mass M charge Q Spin intrinsic angular momentumS life time shape (for extended particles)

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Folie 6 RADIATION fluid gas light fundamental constant: c = speed of light in vacuum ( 30 cm / ns)

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Folie 7 RADIATION What characterizes waves? wave propagation velocityc = wave length frequency particle physics usually electromagnetic radiation wave propagation velocity in vacuum c = in medium c = c index of refaction n = c / c

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Folie 8 CONSTITUENTS OF MATTER I atoms 10 -10 m atomic shells nucleus electron proton neutron e p n Q 1 + 1 0 M M p / 1836 M p M p size < 10 -18 m 0.8 10 -15 m life time 0 > 10 26 y > 10 29 y 886 s decay - - n p e

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Folie 9 CONSTITUENTS OF MATTER II pions kaons many more K Q 0, 1 2 0, 1 M M p / 7 M p / 2 size 0.6 10 -15 m 0.6 10 -15 m life time 0 26 10 -9 s K 12 10 -9 s 0 8 10 -17 s K 0 S,L 9 10 -10 / 5 10 -8 s decay new particles unstable being free

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Folie 10 PARAMETERS total energy rest massm 0 0 range in matter = 0 attenuation in matter chargeQ 0 deflection in el.-mag fields = 0 no deflection life time = 0 decay length l = v = relativistic factor massive particles el.-mag. radiation h Planck constant = minimal action

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Folie 11 HOW TO DETECT ?

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Folie 12 FORCES nuclear forcekeeps protons and neutrons together electromagnetic forcekeeps electrons around the nuclei weak force makes the (free) neutron to decay gravitationkeeps us on the ground strength Standard Model

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Folie 13 ELECTROMAGNETIC FORCE a force is mediated classical picture quantum world by field around a source field quanta = particles light particles = photons electromagnetic radiation = E and B fields interacts with electric charges

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Folie 14 DEFLECTION OF CHARGED PARTICLES IN EL.-MAG. FIELDS electric field magnetic field B = const. circular motion B plane of projection r

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Folie 15 SIGNAL CREATION via electric charges measure the electric current I or voltage U resistor R U I capacitor C U Q

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Folie 16 INTERACTION OF CHARGED PARTICLES WITH MATTER

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Folie 17 beforeafter collision 1.M particle 1 >> M particle 2 2.M particle 1 = M particle 2 CHARGED PARTICLES interaction happens by collisions of particles type 1 and 2

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Folie 18 CHARGED PARTICLES I: ENERY LOSS BY COLLISIONS 1.M particle >> M electron e.g. protons, deuterons, 2.M particle = M electron electrons or positrons collisions create electron ion pairs strongly ionising weakly ionising exponential attenuation with depth x : material dependent attenuation coefficient for all elements no defined range R! Bragg peak well defined range R!

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Folie 19 CHARGED PARTICLES II: ENERY LOSS BY RADIATION the charge polarizes the medium emission under specific angle C Radiation if v particle > c in medium Cerenkov 1930s C measures the velocity of the particle electrons radiate in the water above the core of a nuclear power plant cos C = 1 / n n = index of refraction (small) dispersion ! Cerenkov wave front acoustics analogue: Machs cone for supersonic source light blue!

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Folie 20 INTERACTION OF MASSIVE NEUTRAL PARTICLES WITH MATTER

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Folie 21 neutrons no defined range detection by recoil of protons (from hydrogen) M Proton M Neutron i.e. good shieldings are water concrete (15% water) paraffin ( (CH) n ) NEUTRONS collisions create recoil particles maximum energy transfer for M neutral = M recoil central collisionall energy is transferred non centralall energies according to scattering angle cloud chamber picture neutrons energy transfer E per collision EE probability

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Folie 22 INTERACTION OF RADIATION WITH MATTER

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Folie 23 RADIATION I : PHOTO EFFECT 1.photon disappears photo electronE e = E photon - E B 2.refilling of hole in electron shell by a) emission of photon or b) Auger electron emission of loosely bound outer electron E Auger E B detected energy E photo peak E = E photon = E e + E B escape peak E = E photon - E K example Argon E K = 2.95 keV photonE Photon = 6.41 keV photo peak escape peak requires particle nature of light Einstein 1905 Energy

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Folie 24 RADIATION II : COMPTON EFFECT photon does not disappear recoil electronE e = E photon E photon continuous spectrum detected energy E = E e we neglegt E B of the electron and E recoil of the nucleus because usually E B, E recoil

Folie 26 RADIATION IV : PAIR PRODUCTION +Ze E photon = h > 2 m electron in general > 2 m particles at very high energies el.-mag shower e + e - cascade pair production and Bremsstrahlung alternate shower may start with photon or electron radiation length x 0 characteristic material dependent constant depth, where about 2/3 of the incident energy is converted proof of mass-energy equivalence Blackett 1948 conversion of energy into matter magnetic field B a recoil partner (nucleus) is needed to fulfil energy and momentum conservation

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Folie 27 CHARGED PARTICLES : SUMMARY I Fractional energy loss. MIPs minimum ionsing particles 2 M 0 T < 2 M 0 stopping power

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Folie 28 CHARGED PARTICLES : SUMMARY II Fractional energy loss per radiation length in lead as a function of electron or positron energy.

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Folie 29 RADIATION: SUMMARY I cross section reaction probability

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Folie 30 RADIATION: SUMMARY II intensity after layer thickness x attenuation Lambert-Beer law IoIo I x dx transmission sum of linear attanuation coeff.

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Folie 31 DETECTOR PRINCIPLES

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Folie 32 (Wilson) cloud chamber typical Open Day presentations saturated alcohol vapor -particle emitting nuclide overheated LH 2 bubble chamber (D. Glaser noble prize 1960) + magnetic field "beer" inspired !!! among others discovery of the weak neutral current BEBC @ CERN 73 until 80ies 3.7 T, 35 m 3 LH 2 not only HISTORY

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Folie 33 CHARGE capacitor voltage generator ionising particle current or voltage detection charge created by charged particles or by light is collected by applying a voltage by means of a curent or voltage detection

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Folie 34 SCINTILLATORS produce LIGHT ionisation caused by charged particles or light excitation and delayed light emission usually in the UV range anorganic NaI(Tl), CSI, BaF 2, inorganic doped plastics UV light is converted to charge at a photo cathode and multiplied by a multi stage photo multiplier

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Folie 35 TIME 10 ns

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Folie 36 WIRE CHAMBERS I to control avalanche quench gases, e.g. CO 2, CH 4, C 2 H 6 multiplication avalanche gain 10 5 - 10 6 wire chambers tutorial: F. Sauli CERN yellow report 99-07 electron multiplication around anode (fast) drift of ions (slow) typical ion drift velocity: 1 - 10 cm/(s kV) Ar CH 4

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Folie 37 WIRE CHAMBERS II many wires: MWPC = multiwire proportional chamber position resolution wire distance typically 2 mm (x,y) - coordinate per pair of frames trajectory from MWPC stacks field configuration

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Folie 38 tracking: cut on fiducial target volume example: -3 He pnn or dn WIRE CHAMBERS III 3 He vesssel pion beam beam defining counters mainly carbon reactions protons deuterons MWPC 1 MWPC 2 target beam defining counters good bad event

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Folie 39 "simple" mechanics 10 MHz rate inside magnetic field ZEUS - DESY wedge Type-2 module (520 straws) ATLAS at the LHC individual counters, timing 20 ns HV: coat, ground: sense wire (~ kV) typical size: length 1 - 2 m, mm - cm resistive read out I left I right z z < 1 mm Monte Carlo simulation gas filling e.g., Ar/C 2 H 6 wall: aluminised mylar foils anode wire: 20 m STRAW TUBES

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Folie 40 time position external time reference, e.g., plastic scintillator trick: choose field configuration, which keeps the nonlinearity of time-to-position relation small position resolution DRIFT CHAMBERS I 20 m

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Folie 41 The wires are arranged in layers that pass through the cylinder at three different angles. The set of wires that give a signal can be used to allow computer reconstruction of the paths (or tracks) of all the charged particles through the chamber. The "drift" in the name of this chamber refers to the time it takes electrons to drift to the nearest sense wire from the place where the high-energy particle ionized an atom. Any three sense wires are only nearby in one place so a set of "hits" on these three fix a particle track in this region. By measuring the drift time, the location of the original track can be determined much more precisely than the actual spacing between the wires. improved position resolution by nearest 3 wires method inclined wires DRIFT CHAMBERS II

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Folie 42 properties: full 3-dimensional detector constant drift velocity due to the collisions in the gas mixture (typical a few cm/s). low occupancy even for high background (high rates) large dE/dx due to large gas thickness (particle identification) idea: avoid pile-up many MWPC planes (typical gas thickness of 1 cm) principle: electrons produced follow the constant electric field lines to a single MPWC plane located at one end of the volume ( x-y coordinates on this plane) Third coordinate, z, from the drift time of the electrons to the anode plane STAR TPC - RHIC, Brookhaven TPC - time projection chamber David Nygren, 1974

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Folie 43 Single Track Track Cluster Pixel Tracker Pixel Size Occupancy Charge Sharing S/N ExB Drift Radiation Damage LHC - 10 14 /cm 2 /yr vertex resolution (20-30) m IP & Trigger Charge Sharing charge center of gravity high position resolution

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Folie 44 + + charged particle principle pn diode as almost all semiconductor detectors miniaturisation Readout Chip Sensor arrays of soldering dots typical x-y (front-back) arrangements 200 m strips layer thickness 300 m SILICON MICRO - STRIP DETECTORS I

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Folie 45 CMS - LHC scheme silicon -strip module semiconductor telescope 65/300/300/5500 m thick double-sided Si-strip detectors ANKE - COSY inner tracker vertex detection recoils polarisation (left-right asymmetry) SILICON MICRO - STRIP DETECTORS II

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Folie 46 EXAMPLES OF COMBINED DETECTION SYSTEMS

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Folie 47 focal plane particle identification by dE/dx counter number 1 16 FOCAL PLANE SPECTROMETER for positively charged particles ANKE@COSY I: SET-UP aim: measure simultanuously positively and negatively charged particles e.g., pp pp K + K

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Folie 48 ANKE@COSY II: FOCAL PLANE DETECTOR

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Folie 49 WASA@COSY I: SET-UP aim: measure photons from neutral particle decay in coincidence with charged particles e.g., dd 4 He 0 photon detector: calorimetercharged particle detector: forward hodoscope

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Folie 50 WASA@COSY II: CALORIMETER

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Folie 51 WASA@COSY III: FORWARD HODOSCOPE

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Folie 52 Silicon Vertex Tracker (SVT) - precise position information on charged tracks Drift Chamber (DCH) - the main momentum measurements for charged particles and helps in particle identification through dE/dx measurements Detector of Internally Refected Cerenkov radiation (DIRC or DRC) - charged hadron identification Electromagnetic Calorimeter (EMC) - particle identification for electrons, neutral electromagnetic particles, and hadrons Solenoid (not a subdetector) high magnetic field for needed for charge and momentum measurements Instrumented Flux Return (IFR) - muon and neutral hadron identification and more Todays detectors comprise...

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Folie 53 EXERCISES LECTURE 9: PARTICLE DETECTORS 1.Derive the nonrelativistic relation between kinetic energy and momentum from the relativistic energy-momentum relation. 2.By which process charged particles loose kinetic energy in matter? 3.Which process dominates depending on the energy of the radiation the attenuation in matter? 4.Which processes are involved in an X-ray session at your medical doctor having an apparatus labeled 25 keV? 5.Which is the minimum velocity (in units of speed of light c) for particles in order to produce Cerenkov light in plastic material with index of refraction n = 1.5? 6.Which kind of detector should be used to detect neutral pion decays? 7.How many planes of MWPCs are needed to measure the trajectory of a charged particle with and without the presence of a magnetic field B.