Basic Measurements: What do we want to measure What Makes Particle Detection Possible

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Basic Measurements: What do we want to measure What Makes Particle Detection Possible

Farber, Stephen, Film Critic has reference to this Academic Journal, PHwiki organized this Journal Basic Measurements: What do we want to measure Prof. Robin D. Erbacher University of Cali as long as nia, Davis References: R. Fernow, Introduction to Experimental Particle Physics, Ch. 15 D. Green, The Physics of Particle Detectors, Ch. 13 http://pdg.lbl.gov/2004/reviews/pardetrpp.pdf Fundamental Measurements: From Quarks to Lifetimes Fundamental Particle Properties Charge: Charge of a particle can be determined two ways Sign of charge: Direction of deflection in a magnetic field Magnitude of charge: Infer from knowledge of momentum in addition to B-field strength Charge-dependent quantity, such as ionization energy loss, or Ruther as long as d scattering cross section Direction: tracking detectors, B-field Momentum: tracking detectors, B-field Ionization energy loss: sampling w/ scintillation, TOF ( as long as ) (Example: combine from time of flight (TOF) with dE/dx in addition to use Bethe Bloch equation to get charge) Fundamental Particle Properties Mass: Complicated: mainly specialized techniques One Example: Measure two independent mass-dependent quantities: Momentum often one; ionization, range, or velocity Momentum/range: tracking detectors, B-field Ionization/velocity: scintillation, TOF/ dE/dx, C, TOF Example: (Fernow) Use conservation of energy in addition to momentum to measure mass of muon neutrino Use knowledge of mass of pion in addition to muon, in addition to measure momentum in addition to B-field strength accurately Scintillator stops s, magnets guide s, silicon gives momentum v

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Fundamental Particle Properties Mass: Complicated: mainly specialized techniques Second Example: Measure most quantities in an event, reconstruct mass: Jet energies, lepton momenta, missing ET as long as examples Jet energies: em in addition to hadron calorimeters (fragmentation, etc) Momenta: tracking detectors, B-field Missing ET: all of the above, plus missing info & corrections Example: Measure top quark mass from tt pair production events Use best combination (2) of partons to reconstruct top mass to best resolution possible. – Fundamental Particle Properties Spin: Spins complicated as long as decaying particles Ground state particles, electrons in addition to nucleons: Hyperfine structure in optical spectroscopy, atomic/molecular beam experiments, bulk matter measurements using NMR. Other low energy particles: Various techniques eg: charged pions determined by relating the cross section as long as reaction to the cross section as long as the inverse reaction. High energy interactions: Spins can be found from the decay angular distributions, in addition to from the production angular distributions as long as particle interactions. Example: Measure top quark pair spin correlations using angles of decay products. Fundamental Particle Properties Magnetic Moment: Closely related to spin Ground state particles, electrons in addition to nucleons: Again use optical spectroscopy, atomic/molecular beam experiments, bulk matter measurements using NMR. Muons: Original measurement of g-factor done at CERN storage rings including a precise demonstration of relativistic time dilation. Details of these, in addition to current g-2 experiments (BNL) leave as long as homework. Measuring the hyperon: Fermilab protons on beryllium target, s 8% polarized, sent through magnet in addition to spin precession measured, giving , in addition to hence . Keys to measurement: s produced inclusively w/ large cross section, large detector acceptance, high energy long decay length

Fundamental Particle Properties Lifetime: Time dilation, lab distance: Distribution of decays at distance x is exponential: Slope depends on D, hence on c , measure slope/D to get lifetime . Example: Lifetime fraction of the new particle X(3872) Not quite a lifetime measurement, since need to know branching ratios in addition to production. Measure fraction of X that are long-lived (from B meson decays) versus prompt. Measuring muon lifetime: Senior lab course: measure the muon lifetime in the lab. Leave setup in addition to procedures as long as homework exercise. Fundamental Particle Properties Total Cross Section (prod rate): Two main methods 1) Measure every event (4 colliders & bubble chambers): Often called a “counting experiment” : Example: Top Pair Production Rate of production of tt pairs one of first things to measure upon discovery 2) Transmission Experiment: Measure particle intensity be as long as e in addition to After target in addition to extract cross section. Used at fixed target experiments, most often. Fundamental Measurements New Particle Searches: Many categories/methods -Counting excess events over St in addition to ard Model background -Fits kinematic distributions to expected shapes 1) Expected Particles: Searching as long as particles that are predicted by theory, or expected by data. May or may not know mass or other properties. (W, Z, J/psi, top, Higgs ) Example: Single Top Production Never yet observed, but expected by electroweak production, Vtb

Fundamental Measurements New Particle Searches: Many categories/methods (Counting excess events, or fits to distributions) 2) Completely New Phenomena: Beyond St in addition to ard Model, unexpected. Some- times theories exist, sometimes not. Difficult: little in as long as mation to optimize the search. Carefully control background don’t want false positive! Example: Search as long as Z’: “bump hunts” Look as long as excess, usually in tails of distributions. Statistics of small numbers. Problem: optimize differently as long as discovery than as long as searches (setting limits). What Makes Particle Detection Possible Next time- Passage of particles through matter: How we “see” particles

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