PHYS 3446 – Lecture #11Project: SubjectsProject DetailsSlide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Application of Photoelectric EffectWednesday, Oct. 13, 2010 PHYS 3446, Fall 2010 Andrew Brandt 1PHYS 3446 – Lecture #11Wednesday, Oct. 13, 2010Dr. Andrew Brandt•Energy Deposition in Media- Charged Particle Detection- Ionization Process- Photon Energy LossHW5 due 10/18; Review 10/18; Test will be Weds 10/20 on Ch 1-4;Project: Subjects•Quark-Gluon Plasma (RHIC)•Higgs Boson Theory•Higgs Boson Searches at LEP•Higgs Boson Searches at DZero•Higgs Boson Searches at CMS•Beyond the Standard Model Higgs rumors and CDF search•Supersymmetry or Blackhole Searches at ATLAS•Solar Neutrino Deficit•Long baseline neutrino experiments (neutrino mass)•G-2 experiments•HERA experiments: diffraction/large rapidity gapsWednesday, Oct. 13, 2010 PHYS 3446, Fall 2010 Andrew Brandt 2Project Details•16 minute presentation (preferably powerpoint) will be done on Dec. 1 and Dec. 3. You should provide me with a draft by Nov. 15 in order to get feedback in time to make modifications It is important to get an early start in case you have some questions about the project as it will be a significant part of your grade. At least 3 sources including original paper and not including wikipedia. Should answer most if not all of these questions as applicable. Suggested split: intro/detector results/data analysis1) what is signature involved, are there other signatures not used, why?2) was experiment designed to find this particle3) what detector was/will be used, describe detector’s and sub-detectors4) what was/will be importance of discovery5) who was involved names if small, institutions if large, ~how many people6) what was major source of uncertainty, statistical or systematic7) what were two most important systematic errors8) what was largest background9) etc.Wednesday, Oct. 13, 2010 PHYS 3446, Fall 2010 Andrew Brandt 3Wednesday, Oct. 13, 2010 PHYS 3446, Fall 2010 Andrew Brandt 4•Stopping power decreases with increasing particle velocity independent of incident particle mass–Minimum occurs when ~3 •Particle is minimum ionizing when v~0.96c•For massive particles the minimum occurs at higher momenta–This is followed by a ln() relativistic rise (see Beth-Bloch formula)–Energy loss plateaus at high due to long range inter-atomic screening effect which is ignored in Beth-Bloch–In non-gaseous media stopping power can be approximated by MIP valueProperties of Ionization ProcessPlateau due to inter-atomic screening MIP( Minimum Ionizing Particle)Relativistic rise ~ln ()Wednesday, Oct. 13, 2010 PHYS 3446, Fall 2010 Andrew Brandt 5•Once the stopping power is known, we can compute the expected range of any particle in the medium–The distance the incident particle can travel in the medium before its kinetic energy runs out•At low E, two particles with same KE but different mass can have very different ranges–This is why and radiation have quite different stopping requirementsRanges of Ionization ProcessR =0Rdx =�0TdxdTdT=�0( )TdTS T�Wednesday, Oct. 13, 2010 PHYS 3446, Fall 2010 Andrew Brandt 6•What would be the sensible unit for energy loss?–MeV/cm–Equivalent thickness of g/cm2: MeV/(g/cm2)•Range is expressed in–cm or g/cm2 (units related through density)•Minimum value of S(T) for z=1 at =3 is •Using <Z>=20 we can approximateUnits of Energy Loss and Rangemin( )S T �min( )S T �( )42 2 202 242lne A Z AmcIm cp rg bb� �- �� �� �( )75.2 10 13.7 ln erg/cmZ Z Ar-� -( )23.5 MeV/ g/cmZAEx. 1+2Wednesday, Oct. 13, 2010 PHYS 3446, Fall 2010 Andrew Brandt 7•Phenomenological calculations can describe average behavior, but large fluctuations are observed on an event-by-event bases–This is due to the statistical nature of scattering process•Statistical effect of angular deviation experienced in Rutherford scattering off atomic electrons in the medium–Consecutive collisions add up in a random fashion and provide net deflection of any incident particles from its original path–Called “Multiple Coulomb Scattering” Increases as a function of path length •z:particle charge L: material thickness, X0: radiation length of the medium(distance electron travels before T’=T/e)Multiple Scattering rmsq �020MeV Lzpc XbWednesday, Oct. 13, 2010 PHYS 3446, Fall 2010 Andrew Brandt 8•Energy loss of incident electrons–Bethe-Bloch formula works well (up to above 1 MeV for electrons)–But due to the small mass, electron’s energy loss gets complicated•Relativistic corrections have large effect even down to a few keV level•Electron projectiles can transfer large fractions of energies to the atomic electrons they collide with–Produce -rays (ejected electrons) Which have the same properties as the incident electrons–Electrons are accelerated as a result of interaction with electric field by nucleus. What do this do?–Causes electrons to radiate or emit photons•Bremsstrahlung Braking radiation (as electron decelerates) an important mechanism of relativistic electron energy lossEnergy Loss Through BremsstrahlungWednesday, Oct. 13, 2010 PHYS 3446, Fall 2010 Andrew Brandt 9•The electron energy loss can be written•Relative magnitude between Bremsstrahlung and ionization is•Z: Atomic number of the medium, me: rest mass of the electron, T: Kinetic energy of the electron in MeV•At high energies, ionization loss is constant–Radiation dominates the energy loss–The energy loss is directly proportional to incident energy– T=T0 e-x/X0 (electrons radiate most of energy within a few radiation lengths)Total Electron Energy LosstotdTdx� �- =� �� �brem iondT dTdx dx� � � �- - �� � � �� � � �iondTdx� �-� �� �bremdTdx� �+ -� �� �21200eTZm cWednesday, Oct. 13, 2010 PHYS 3446, Fall 2010 Andrew Brandt 10•Above the critical energy (Tc) the brem process dominatesTotal Electron Energy LossbremdTdx� �=� �� �iondTdx� �=� �� �0cTX-202170 ( / )AX g cmZ�radiation length=distance electron travels before its energy drops to T/eWednesday, Oct. 13, 2010 PHYS 3446, Fall 2010 Andrew Brandt 11•Photons are electrically neutral–They do not feel Coulomb force–They cannot directly ionize atoms•Photons are EM force carriers–Can interact with matter resulting in
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