HA HA It felt like weeks and years

HA HA! It felt like weeks and years and days and surely hours before we could get on with the detectors. At long last we can finally start !!!!! ‘Please read all the included instruction manuals. ’ Ch Co ere un nko te v rs Tran s Rad ition iatio n Silic Pro p on D ortio n al C h amb etec ers tors Scintillators !

20, 000 Calorimeters in Experiments

Excited States Meta stable States Life in an Excited States Excitation of other Molecules Radiation Positive Ions + Free Electron Negative Ion Recombination Neutral State at Cathode Radiation Collected at Anode Excited States Dissociation Recombination Radiation Electron Emission Ionization by Collision

Approximate computed curves showing the percentage of electron energy going to various actions at a given X/p (V/cm/mm. Hg) Elastic: loss to elastic impact Excitation: excitation of electron levels, leading to light emission and metastable states Ionization: ionization by direct impact Kinetic: average kinetic energy divided by their “temperature” Vibration: energy going to excitation of vibrational levels L. B. Loeb, Basic Processes of Gaseous Electronics

Experimental results. Rare gases. Experimental results. Diatomic molecules. D. Rapp et al. , Journal of Chemical Physics, 43, 5 (1965) 1464

Ionization Potential: The work required to remove a given electron from its orbit and place it at rest at an infinite distance. Only first spectrum plotted. CRC Handbook 63 ed.

q Gedanken experiment. (this time leave the cat outside the box !) Let a charged particle pass through a gas volume. Primary and secondary ion pair production given at atmospheric pressure and for minimum ionizing particles C 4 H 10 Xe Ne CH 4 N 2

Cathode A metallic cylinder of radius R Anode A gold plated tungsten wire of radius r 0 = 10 -5 m R/r 0 = 1000 sio niza tion Gas Amplification process Let a-1 be the mean free path between each ionization a=a(E) and E=E(r) The gas amplification is then given by Korff’s approximation Where A and B are gas dependent constants and p is the pressure.

For the straw-tube, this gives for a gas mixture of (about) Ar/CO 2 : 80/20

Drift of electrons under the action of the electric field. The drift velocity of the positive ions under the action of the electric field is linear with the reduced electric field up to very high fields. v +ions = m +ions * E where + 1/p and diffusion D +ions T * m +ions in CO 2 with E=104 V/cm At NTP

Cathode Anode Cathode Signal induced by (mainly) the positive ions moving a high electric field. Assume that all charges are created a distance l from the anode. (l. C is the total capacitance) l is of the order of a few µm v electron = v ion /100

More or less any gas can be used. The Penning effect. The action of excited states in ionizing atoms of lower ionizing potentials is an example of inelastic impacts of second class. The metastable states are responsible for the effect. Kruithoff and Penning’s data for Ne/Ar mixtures. (Scale as above. ) The endless futile controversies of the counter ‘gadgeteers’, who can not spend the time to take basic data, will bedevil the literature indefinitely. L. B. Loeb; Basic Processes of Gaseous Electronics (1955)

Approximate computed curves showing the percentage of electron energy going to various actions at a given X/p (V/cm/mm. Hg) Add a sprinkling of argon L. B. Loeb, Basic Processes of Gaseous Electronics

Nearly all gasses can be used. Noble gases. Energy dissipation mainly via ionization. Hydrogen atom De-excitation of a noble gas is only possible via the emission of a photon. If the photon energy is above the ionization threshold for other molecules in the set-up, new avalanches will be created. Permanent discharges Add poly-atomic gases as quenchers. What the water molecule can do. 5 e. V

There will also be effects due to the way the electrons are collected at the anode. The electric field of the chamber will be screened by the positive ions. The gas amplification will therefore change as the angle between the electric field and the ionizing particle changes. Other effects. Drift velocity and diffusion of the electrons changes with the gas mixture. A magnetic field will change the drift path of the electrons as well as the diffusion.

Still possible to calculate by hand Classic multi-wire proportional chamber Typical parameters l : 5 mm s : 2 - 4 mm d : 20 m and Vs(z) x (mm) y (mm) The positive pulses induced by the positive ions onto the neighboring wires is much greater than the negative pulses induced electrostatically. The net effect is thereby positive. Advanced calculations of electric field, drift, diffusion and signal formation can be done with Garfield Version 6. 19. (Try first Ohm’s Law. )

With these tools, we can now make Time Expansion Chambers Time Projection Chambers Proportional Chambers Thin Gap Chambers Drift Chambers Jet Chambers Straw Tubs (and some I have forgotten. ) Large fluctuations and Landau tails limits the resolution. Many samples and truncated mean. Yeah, just gloat about your tail. It is still a Vavilov to me!

Let us have a closer look at some of the gas based tracking detectors Start with Drift Chambers Measure the arrival time on wire

Electric Field Electron Swarm Drift s Ds, Dt Drift velocity: Space diffusion rms: Drift velocity and diffusion are gas and field dependent: P : pressure

Anode Wire Drift s. L Single electron Several electrons Many electrons Detection threshold Error on first electron: N=100 s 1~ 0. 4 s. L

E and B fields ^ r B r E v. B q. B : mean collision time Larmor frequency s. T s. L r B v. B

Some planar drift chamber designs Optimize geometry constant E-field Choose drift gases with little dependence v. D(E) linear space - time relation r(t)

MAGNETIC FIELD EFFECTS: DISTORSIONS IN DRIFT CHAMBERS W. de Boer et al, Nucl. Instr. and Meth. 156(1978)249

Time Projection Chambers Large volume active detector. full 3 -D track reconstruction x-y from wires and segmented cathode of MWPC z from drift time d. E/dx Usually B || E improvement of diffusion Drift length up to > 1 m Rather stringent requirement on homogeneity of E and B field Space charge by ions “Slow” detector t. D ~ 10. . 100 s 420 cm

Space charge problem from positive ions, drifting back to medial membrane gating Gate open Gate closed DVg = 150 V

MICRO-STRIP GAS CHAMBER (MSGC) THIN ANODE AND CATHODE STRIPS ON AN INSULATING SUPPORT Drift electrode Anode strip Glass support Back plane Cathode strips

Gas Electron Multiplier - GEM Thin metal-coated polymer foil chemically pierced by a high density of holes. On application of a voltage gradient, electrons released on the top side drift into the hole, multiply in avalanche and transfer the other side. Proportional gains above 103 are obtained in most common gases. F. Sauli, Nucl. Instrum. Methods A 386(1997)531

Typical geometry: 5 µm Cu on 50 µm Kapton 70 µm holes at 140 mm pitch Multiple GEM Structures Cascaded GEMs permit to obtain larger gains

MICROMEGAS: Thin-gap parallel plate chamber 3ème Atelier Micromégas IPHE, Univ. Lausanne, March 9 -10, 2000 by Peter Cwetanski

An example on the software tools available in the understanding of the detectors: Micromegas 3 D Simulations • Computation of field maps using 3 D Finite Element Method. Software: Maxwell 3 D Field Simulator ® (Ansoft Corp. ) • Obtain gas transport parameters for operating gas with Monte Carlo simulation using imonte 4. 5 (author: Steve Biagi). • Input of field maps and gas parameters in detector simulation software Garfield (author: Rob Veenhof).

The DELPHI Time Projection Chamber http: //pubxx. home. cern. ch/pubxx/tasks/hadident/www/dedx/#A 1. 5. 1

Just some words about Attachment in Gases by Electron Impact. D. Rapp et al. , Journal of Chemical Physics, 43, 5 (1965)

Water Allowed and forbidden energy bands. In metal one band is only partially filed. In a semiconductor, the valence band is (nearly) filled and the conduction band is (nearly) empty.

Excitation of electrons in a semiconductor due to passage of a charged particle Residual Hole. Electron excitation Auger effect: an electron from a higher shell to a vacant electronic state and ejecting an electron from the same higher shell. WF = Fermi Level = the Energy where P(W)=1/2 Electron Configuration for Si: K 2 L 8 M 4 + 4 by bonding 8 group E g 1 e. V http: //phys. educ. ksu. edu/ for Visual Quantum Mechanics

Doping of semiconductors. N-Type P, As, Sb 5 electrons in the M-shell 1 electron with binding energy 10 -50 me. V P-Type B, Al, Ga 3 electrons in the M-shell 1 electron missing P-doped Equilibrium N-doped Depletion Layer Capacitance Forward Bias X i Reverse Bias X i N: #Donors X: Thickness of depletion Area

Mobility , conductivity s, majority [donors (e) acceptors (holes)] and minority [donors (holes) acceptors (e)] carrier concentration as function of temperature. ni is the intrinsic carrier density. Ge Si volume resistivity 0. 49 m at 300 K some 100 m due to impurities Take a Si crystal of 10 x 0. 3 mm 3 ~4 -5 108 free carriers A minimum ionizing particle would produce ~3 -4 104 e-h pairs Reduce the number of free carriers by either Depleting or Freeze out D. A. Fraser, The Physics of Semiconductor devices, ISBN 0 19 851859 5 A. Peisert, Silicon Microstrip Detectors, Instrumentation in High Energy Physics

Partial die shot of the Intel i 960 Cobra microprocessor showing the hundreds of bus connections on the chip All of the photographs in the Molecular Expressions collection are jointly owned by Michael W. Davidson and The Florida State University. As copyright holders in the interest of these photographs, we reserve all of our rights granted by the United States copyright law. We also reserve the right to regulate the use of these photographs, and we strictly forbid any unlicensed or otherwise unauthorized use of any kind, including production of derivative works, without permission. The only use permitted without our written approval is "personal use" that does not involve publication, distribution, or any commercial applications.

Silicon Detectors. p+ implant Si (n type) n+ implant H. Pernegger - CERN G. Bagliesi - INFN Pisa

The DELPHI Vertex Detector Reconstructed B decays K 0 and Lambda reconstruction

Scintillators Inorganic Crystalline Scintillators The most common inorganic scintillator is sodium iodide activated with a trace amount of thallium [Na. I(Tl)], Energy bands in impurity activated crystal Strong dependence of the light output and the decay time with temperature. http: //www. bicron. com.

Organic Scintillators Benzene C 6 H 6 Single Bond = sigma Bond Pi Bond Double Bond = one sigma + one pi Bond If we have atoms with parallel p atomic orbitals, we get more kinds of pi modes by adding and subtracting them. There are 6 pi electrons in benzene. These electrons fill 3 bonding pi molecular orbitals In addition, combining the carbon p orbitals, gives 3 antibonding molecular orbitals. The pi electrons form the basis for the scintillation mechanism. They are quantized in a series of singlets Sij and triplets Tij http: //bouman. chem. georgetown. edu/genchem. html http: //library. thinkquest. org/10429/low/geometry/geobody. htm

Pi electron energy levels 10 -11 sec non-radiative transition ~ 10 -6 sec Fluorescence 10 -8 - 10 -9 sec peak ~ 320 nm Practical organic scintillators uses a solvent + large concentration of primary fluor + smaller concentration of secondary fluor +. . . Phosphorescence 10 -4 sec

Photo Multiplier Tube Typical gain 106 Transient time spread 200 ps Anode Photon-to-Electron Converting Photo-Cathode http: //www. hamamatsu. com/ Dynodes with secondary electron emission

The energy resolution is determined mainly by the fluctuation of the number of secondary electrons emitted at each dynode. Poisson distribution where = mean number = the variance r = 1, 2 , 3. . . Fluctuations mainly induced at the first dynode where the number of primary electrons are small

Physical principles of Hybrid Photo Diodes Take one Photo Multiplier Tube Remove dynodes and anode Add Silicon Sensor inside tube Electron-hole pairs: Kinetic energy of the impinging electron - work to overcome the surface / Silicon ionization energy Hybrid Photo Diode ~ 4 - 5000 electron-hole pairs Good energy resolution

Hybrid Photo Diode Q. E. Bialkali Sb. K 2 Cs Multialkali Sb. Na 2 KCs (S 20) Solar blind Cs. Te photocathode (Philips Photonic) Transmission of various windows materials (Philips Photonic) not shown: Mg. F 2: cut @115 nm Li. F: cut @105 nm

But… • Electronic noise, typically of the order of 500 e • Back scattering of electrons from Si surface back scattering probability at E 20 k. V 20% of the electrons deposit only a fraction o <1 of their initial energy in the Si sensor. continuous background (low energy side) 3 parameters: - - <npe> - Si C. D’Ambrosio et al. NIM A 338 (1994) p. 396.

Current and Charges in an Ionization Chamber i V/d=E 1/td Single deposit Q (d-x)/d Ionizing track i=Ne. E[1 -t/td] Q=½ Ne W. J. Willis, V. Radeka; NIM 120(1974)221

And we should now be ready to look at Cherenkov radiation and transition radiation