dd q2q2  b

What about the ENERGY LOST in the collision? the recoiling target carries energy some of the projectile’s energy was surrendered if the target is heavy the recoil is small the energy loss is insignificant Reminder:  1/ (3672  Z)

mv 0 mv f  (mv) =  recoil momentum of target ( )  mv 0 mv f large impact parameter b and/or large projectile speed v 0 v f  v o For small scattering (  )

mv 0 mv f pp  /2 Together with: Recognizing that all charges are simple multiples of the fundamental unit of the electron charge e, we write q 1 = Z 1 e q 2 = Z 2 e

q1=Z1eq1=Z1e q2=Z2eq2=Z2e Z 2 ≡Atomic Number, the number of protons (or electrons)

Recalling that kinetic energy K = ½mv 2 = (mv) 2 /(2m) the transmitted kinetic energy (the energy lost in collision to the target) K = (  p) 2 /(2m target )

For nuclear collisions: m target  2Z 2 m proton

For collisions with atomic electrons: m target  m electron q 1 = e Z 2 times as many of these occur! Z2Z2

The energy loss due to collisions with electrons is GREATER by a factor of m proton = kg m electron = kg

Notice this simple approximation shows that Why are  -particles “more ionizing” than  -particles?

energy loss speed

We express the energy loss as But in practice the thickness, x, alone is not important. So we define an effective or relative length that incorporates the target material’s density: Notice this x does not carry “normal” length units!

the probability that a particle, entering a target volume with energy E “collides” within and loses an amount of energy between E' and E' + dE'  P (E, E' ) dE'  dx Or P (E, E' ) dE'  dx = P  1 / (E') 2 ( 2  b db )  (  dx N A Z/A )

P  1 / (E') 2 Charged particles passing through material undergo multiple collisions with atomic electrons shedding tiny fractions of their energy along the way. E' is a function of impact parameter b The (mean) energy loss involves logarithms of energy extremes

Need to average this over all possible values of b. Through any thickness, subsequent encounters are with progressively smaller values of E so need to integrate over E 0 to E f. The electrons involved were assumed FREE. Only energy in excess of the ionization energy I participates in this sort of momentum exchange. A single encounter! Actually should be redone relativistically!

E (MeV) Range of dE/dx for proton through various materials Pb target H 2 gas target dE/dx ~ 1/  2 Logarithmic rise dE/dx = (4  N o z 2 e 4 /m e v 2 )(Z/A)[ ln {2m e v 2 /I(1-  2 )}-  2 ] I = mean excitation (ionization) potential of atoms in target ~ Z10 GeV Felix Bloch Hans Bethe NOTE : a function of only incoming particle’s  (not mass!) so a fairly universal expression x  x dx  dx defines effective depth through material

E (MeV) Range of dE/dx for proton through various materials Pb target H 2 gas target dE/dx ~ 1/  ~constant for several decades of energy ~4.1 MeV/(g/cm 2 ) ~1 MeV/(g/cm 2 ) typically MeV(g/cm 2 ) for solid targets minimum at  ~0.96, E~1 GeV for protons

Particle Data Group, R.M. Barnett et al., Phys.Rev. D54 (1996) 1; Eur.Phys.J. C3 (1998) Muon momentum [GeV/c]  

D. R. Nygren, J. N. Marx, Physics Today 31 (1978) 46    p d e Momentum [GeV/c] dE/dx(keV/cm)

1911 Rutherford’s assistant Hans Geiger develops a device registering the passage of ionizing particles.

50  m 1937 Marietta Blau and Herta Wambacher report “stars” of tracks resulting from cosmic ray collisions with nuclei within the emulsion

C.F.Powell, P.H. Fowler, D.H.Perkins Nature 159, 694 (1947) Nature 163, 82 (1949)

Cloud chamber photographs by George Rochester and J.G. Wilson of Manchester University showed the large number of particles contained within cosmic ray showers.

3.7m diameter Big European Bubble Chamber CERN (Geneva, Switzerland) Side View Top View

CASA detectors’ new home at the University of Nebraska 2000 scintillator panels, 2000 PMTs, 500 low and power supplies at UNL

PMMA (polymethyl methacrylate) doped with a scintillating fluor Read out by 10 stage EMI 9256 photomultiplier tube 2 ft x 2 ft x ½ inch

Schematic drawing of a photomultiplier tube Photons eject electrons via photoelectric effect Photocathode (from scintillator) Each incident electron ejects about 4 new electrons at each dynode stage Vacuum inside tube “Multiplied” signal comes out here An applied voltage difference between dynodes makes electrons accelerate from stage to stage

PMT output viewed on an oscilloscope

Spark Chambers High Voltage across two metal plates, separated by a small (~cm) gap can break down. d

If an ionizing particle passes through the gap producing ion pairs, spark discharges will follow it’s track. In the absence of HV across the gap, the ion pairs usually recombine after a few msec, but this means you can apply the HV after the ion pairs have formed, and still produce sparks revealing any charged particle’s path! Spark chambers (& the cameras that record what they display) can be triggered by external electronics that “recognize” the event topology of interest.

HV pulse Logic Unit A B C Incoming particle Outgoing particles

M.Schwartz poses before the Brookhaven National Laboratory experiment which confirmed two distinct types of neutrinos.

Georges Charpak develops the multiwire proportional chamber 1992 Charpak receives the Nobel Prize in Physics for his invention

20  m dia 2 mm spacing argon-isobutane spatial resolutions < 1mm possible

100 MHz 50 MHz

DO

Experimental Objects muon chambers stee l HAD calorimeter EM calorimeter solenoid jet e  electrons & photons quarks & gluons neutrinos  K,  etc. tracking volume Quarks & gluons do not exist (for long) as free particles Due to hadronization we observe a collimated spray of particles (“jet”) Neutrinos escape without detection Electrons and photons deposit most of their energy in the EM calorimeter  muons

DØ 5500 tons 120,000 digitized readout channels

– 2T super conducting solenoid – disk/barrel silicon detector – 8 layers of scintillating fiber tracker – preshower detectors Shielding New Solenoid & Tracking: Silicon, SciFi, Preshowers + New Electronics, Trigger, DAQ Forward Scintillator Forward Mini- drift chambers

The Detector in various stages of assembly

Fermilab, Batavia, Illinois CERN, Geneva, Switzerland Protons Anti-protons