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Introduction to CERN Activities

Introduction to CERN Activities. Intro to particle physics Accelerators – the LHC Detectors - CMS. From atoms to quarks I. Hadrons are made of quarks, e.g. p = uud L 0 = uds L 0 b = udb p + = ud Y = cc U = bb. Baryons. Mesons. From atoms to quarks II. Leptons are fundamental

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Introduction to CERN Activities

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  1. Introduction to CERN Activities Intro to particle physics Accelerators – the LHC Detectors - CMS David Barney, CERN

  2. From atoms to quarks I David Barney, CERN

  3. Hadrons are made of quarks, e.g. p = uud L0 = uds L0b = udb p+ = ud Y = cc U = bb Baryons Mesons From atoms to quarks II Leptons are fundamental e.g. electron muon neutrinos David Barney, CERN

  4. The structure of the Proton Proton is not, in fact, simply made from three quarks (uud) There are actually 3 “valence”quarks (uud) + a “sea” of gluonsand short-lived quark-antiquark pairs David Barney, CERN

  5. Leptons Strong Electromagnetic Electric Charge Gluons (8) Photon Tau Tau -1 0 Neutrino Muon Muon -1 0 Neutrino Quarks Atoms Light Electron Electron -1 0 Neutrino Chemistry Mesons Electronics Baryons Nuclei Quarks Weak Gravitational Electric Charge Bosons Graviton ? Bottom Top -1/3 2/3 (W,Z) Strange Charm -1/3 2/3 Neutron decay Down Solar system Up Beta radioactivity -1/3 2/3 Galaxies Neutrino interactions Black holes Burning of the sun each quark: R , B , G 3 colours The particle drawings are simple artistic representations Matter and Force Particles David Barney, CERN

  6. Interaction Exchanged Range Relative Examples quantum (m) Strength in nature (source ch) Strong gluon 10-15 1 proton (quarks) colour Electromagneticphoton <10-2atoms electric Weak W, Z <10-17 10-5 radioactivity hypercharge Gravity graviton ? 10-38 solar system mass Characteristics of the 4 forces What characterizes a force ? Strength, range and source charge of the field. Ratio of electrical to gravitational force between two protons is ~ 1038 !! Can such different forces have the same origin ?? David Barney, CERN

  7. Unification of fundamental forces David Barney, CERN

  8. Unanswered questions in Particle Physics a. Can gravity be included in a theory with the other three interactions ? b.What is the origin of mass? LHC c. How many space-time dimensions do we live in ? d. Are the particles fundamental or do they possess structure ? e. Why is the charge on the electron equal and opposite to that on the proton? f. Why are there three generations of quark and lepton ? g. Why is there overwhelmingly more matter than anti-matter in the Universe ? h. Are protons unstable ? i. What is the nature of the dark matter that pervades our galaxy ? j. Are there new states of matter at exceedingly high density and temperature? k. Do the neutrinos have mass, and if so why are they so light ? David Barney, CERN

  9. The Standard Model Me ~ 0.5 MeV Mn ~ 0 Mt ~ 175,000 MeV! Mg = 0 MZ ~ 100,000 MeV Why ? Where is Gravity? David Barney, CERN

  10. Mathematical consistency of the SM David Barney, CERN

  11. What is wrong with the SM? David Barney, CERN

  12. Origin of mass and the Higgs mechanism Simplest theory – all particles are massless !! A field pervades the universe Particles interacting with this field acquire mass – stronger the interaction larger the mass The field is a quantum field – the quantum is the Higgs boson Finding the Higgs establishes the presence of the field David Barney, CERN

  13. CERN Site LHC SPS CERN Site (Meyrin) David Barney, CERN

  14. CERN Member States David Barney, CERN

  15. CERN Users David Barney, CERN

  16. Particle Collider David Barney, CERN

  17. d d u u u u Types of Particle Collider Proton-Proton Collider (e.g. LHC) Electron-Positron Collider (e.g. LEP) e- e+ Eproton1 = Ed1 + Eu1 + Eu2 + Egluons1 Eproton2 = Ed2 + Eu3 + Eu4 + Egluons2 Collision could be between quarksor gluons, so 0 < Ecollision < (Eproton1 + Eproton2) Electrons are elementary particles, so Ecollision = Ee- + Ee+ = 2 Ebeam e.g. in LEP, Ecollision ~ 90 GeV = mZ i.e. can tune beam energy so thatyou always produce a desired particle! i.e. with a single beam energy you can “search” for particles of unknown mass! David Barney, CERN

  18. CERN Accelerator Complex David Barney, CERN

  19. Collisions at the Large Hadron Collider 7x1012 eV Beam Energy 1034 cm-2 s-1 Luminosity 2835 Bunches/Beam 1011 Protons/Bunch 7.5 m (25 ns) 7 TeV Proton Proton colliding beams Bunch Crossing 4x107 Hz Proton Collisions 109 Hz n - e e Parton Collisions q µ + - c 1 µ - ~ q q Z ~ p g H p New Particle Production 105 Hz p p ~ q (Higgs, SUSY, ....) Z + m µ + - q ~ m c 0 µ 2 - c ~ 0 1 David Barney, CERN

  20. LHC Detectors General-purpose Higgs SUSY ?? Heavy Ions Quark-gluon plasma General-purpose Higgs SUSY ?? B-physics CP Violation David Barney, CERN

  21. The two Giants! David Barney, CERN

  22. Particle Detectors I • Cannot directly “see” the collisions/decays • Interaction rate is too high • Lifetimes of particles of interest are too small • Even moving at the speed of light, some particles (e.g. Higgs) may only travel a few mm (or less) • Must infer what happened by observing long-lived particles • Need to identify the visible long-lived particles • Measure their momenta • Energy • (speed) • Infer the presence of neutrinos and other invisible particles • Conservation laws – measure missing energy David Barney, CERN

  23. Particle Momentum Measurement • Electrically charged particles moving in a magnetic field curve • Radius of curvature is related to the particle momentum • R = p/0.3B • Should not disturb the passage of the particles • Low-mass detectors sensitive to the passage of charged particles • Many layers – join the dots! • E.g. CMS silicon tracker Electron In CMS David Barney, CERN

  24. Idea is to “stop” the particles and measure energy deposit Particles stop via energy loss processes that produce a “shower” of many charged and neutral particles – pair-production, bremstrahlung etc. Detector can be to measure either hadrons or electrons/photons Two main types of calorimeter: Homogeneous: shower medium is also used to produce the “signal” that is measured – e.g. CMS electromagnetic calorimeter Sampling: the shower develops in one medium, whilst another is used to produce a signal proportional to the incident particle energy – e.g. CMS Hadron Calorimeter Energy Measurement - Calorimeters David Barney, CERN

  25. Particle interactions in detectors David Barney, CERN

  26. CMS – Compact Muon Solenoid David Barney, CERN

  27. CMS – Compact Muon Solenoid David Barney, CERN

  28. Puzzle David Barney, CERN

  29. Answer Make a “cut” on the Transverse momentum Of the tracks: pT>2 GeV David Barney, CERN

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