* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download hdwsmp2011 - FSU High Energy Physics
Theory of everything wikipedia , lookup
Canonical quantization wikipedia , lookup
Quantum electrodynamics wikipedia , lookup
Peter Kalmus wikipedia , lookup
Technicolor (physics) wikipedia , lookup
History of quantum field theory wikipedia , lookup
Higgs mechanism wikipedia , lookup
Search for the Higgs boson wikipedia , lookup
Quantum chromodynamics wikipedia , lookup
Introduction to quantum mechanics wikipedia , lookup
Renormalization wikipedia , lookup
Strangeness production wikipedia , lookup
Relativistic quantum mechanics wikipedia , lookup
Large Hadron Collider wikipedia , lookup
Minimal Supersymmetric Standard Model wikipedia , lookup
Nuclear structure wikipedia , lookup
Double-slit experiment wikipedia , lookup
Weakly-interacting massive particles wikipedia , lookup
Atomic nucleus wikipedia , lookup
Mathematical formulation of the Standard Model wikipedia , lookup
Identical particles wikipedia , lookup
ALICE experiment wikipedia , lookup
Theoretical and experimental justification for the Schrödinger equation wikipedia , lookup
Grand Unified Theory wikipedia , lookup
Future Circular Collider wikipedia , lookup
Particle accelerator wikipedia , lookup
Electron scattering wikipedia , lookup
ATLAS experiment wikipedia , lookup
Compact Muon Solenoid wikipedia , lookup
Overview of Particle Physics -- the path to the Standard Model 1 Topics “Prehistory” (A.A.) o “prehistory” -- 19th century o electron, radioactivity, nucleus historical flashback over development of the field o cosmic rays o spectroscopy era, particle zoo o collider era standard model of particle physics 2 Atoms, Nucleus electron: first hint that atom not indivisible natural radioactivity understanding of composition of atom, nucleus atom = nucleus surrounded by electrons (Geiger, Marsden, Rutherford, 1906 -1911) hydrogen nucleus = proton, is component of all nuclei (1920) neutron (Bothe, Becker, Joliot-Curie, Chadwick, 1930 – 1932) Neutrino predicted by Pauli 1930 to solve puzzle in some nuclear decays (“beta decays”) 3 Status of satisfaction Atoms are made of electrons and nucleus Nuclei are made of protons and neutrons everything looks simple and tidy But…. 4 Cosmic rays Charged particles coming from the sky discovered by Victor Hess (1912) Observed on mountains and from balloons intensity increases with height above Earth o must come from “outer space” Lots come from the Sun Mostly low energy protons and nuclei Very high energy cosmic rays are from outside the Solar System, but probably from within the galaxy 5 6 Cosmic rays new “elementary” particles new detectors (cloud chambers, emulsions) exposed to cosmic rays discovery of many new particles positron (anti-electron) : predicted by Dirac (1928), discovered by Anderson 1932 muon (μ): 1937 Nedermeyer, Anderson, Street, Stevenson pion (π) predicted by Yukawa (1935), observed 1947 (Lattes, Occhialini, Powell) strange particles (K, Λ, Σ,….. 7 Cloud chamber Container filled with gas (e.g. air), plus vapor close to its dew point (saturated) Passage of charged particle ionization; Ions form seeds for condensation condensation along path of particle path of particle becomes visible as chain of droplets 8 Positron discovery Positron (anti-electron) predicted by Dirac (1928) -- needed for relativistic quantum mechanics existence of antiparticles doubled the number of known particles!! Cloud chamber with lead sheet in middle Particle loses energy going through lead Track going downward (has lower energy after lead – more curved) Positron made by “pair production” 9 Anderson and his cloud chamber 10 Muon discovery Nedermeyer, Anderson, Street, Stevenson 1936-1937, using cloud chambers Found mass to be between that of electron and proton --called “mesotron” Later other particles with intermediate mass found – called “mesons” Mesotron renamed “muon” μ -- very different from mesons (no strong interaction, spin ½) -- was like an electron, but heavier I. Rabi: “who ordered that?” 11 “Strange particles” Kaon: discovered 1947; first called “V” particles, later “strange” because they did not decay as expected K0 production and decay in a bubble chamber 12 Towards the “Particle Zoo” Accelerators, beam lines increase energy of particles and steer them where you want them become independent of cosmic rays can make new particles and use them as projectiles can do planned experiments with probes of your choice new detectors: bubble chamber, wire chamber, …. 13 Bubble chamber Operating principle: Vessel, filled with (e.g.) liquid hydrogen at a temperature above the normal boiling point but held under a pressure of about 10 atmospheres by a large piston to prevent boiling. After passage of particles, move piston to reduce pressure boiling point lowered boiling starts along particle tracks bubbles develop. Let bubbles grow (about 3 milliseconds), then tracks are photographed (flash); provide stereo views of tracks by use of several cameras . Then move piston back recompress the liquid collapse bubbles before boiling all over. Invented by Glaser in 1952 (when he was drinking beer) 14 -- _ p p _ p n K0 K- + - 0 _ n + p 3 pions 0 , e+ e K0 + - 15 Particle Zoo 1940’s to 1960’s : Plethora of new particles discovered (mainly in cosmic rays): o μ-, π±, π0, K, Λ0, Σ+ , Σ0 , Ξ,…. Accelerators, better detectors: o Yet more “stable particles, Plus many (100’s) particles decaying very fast (“resonances”) (decay after 10-21 sec) 16 The Particle Zoo! e, ± 0 , , ± 0 0 K , K S, K L, 0 + , p, n, , 0 , , , … ρ, ω, φ, f, Δ, N, …… ± e, ± , 17 Too many particles, chaos question: Can nature be so messy? are all these particles really intrinsically different? or can we recognize patterns or symmetries in their nature (charge, mass, flavor) or the way they behave (decays)? 18 Symmetry to the rescue – Periodic table of particles 1962: “eightfold way”, “flavor SU(3)” symmetry (Gell-Mann, Ne’eman) allows classification of particles into “multiplets” Mass formula relating masses of particles in same multiplet Symmetry can be explained by quark hypothesis quark model (Gell-Mann, Zweig 1964) : three different kinds of quarks (u, d, s) Explains grouping of all strongly interacting particles Allows prediction of new particle Ω- , with all of its properties (mass, spin, expected decay modes,..) subsequent observation of Ω- with expected properties at BNL (1964) 19 ΩBNL 1964 http://www.bnl.gov/bnlweb/history/Omega-minus.asp eight-fold way quark model – particles made up of three different “quarks” – u, d, s p = uud, n = udd,… Ω- = sss 20 Quark discovery Deep inelastic scattering (1968, Kendall, Taylor) Shoot electrons of high energy on protons proton u electron d u sometimes electron can penetrate deep into proton: “deep” => probe inside structure (like Rutherford scattering probed inside of nucleus) 21 22 “Standard Model” refinement of these ideas, more quarks, “color”, gauge field theory Standard Model matter particles – quarks and leptons force carriers – “gauge bosons” 23 Contemporary Physics Education Project24 “every-day” matter Proton Neutron d u u u d Photon d Electron e Electron Neutrino e 25 No isolated quarks _ q’ q _ q’ q q q q q _ _ q’ _ q’ q q’ _ _ q’ q _ q’ q two separating quarks q’ _ q’ _ q’ q q q q _ _ q’ q q’ _ _ q’ q _ q’ q q’ _ q’ jets 26 Forces (interactions) Strong interaction 1 Binds protons and neutrons to form nuclei Electromagnetic interaction 10-2 Binds electrons and nuclei to form atoms Binds atoms to form molecules etc. Weak interaction 10-10 changes “flavors” (e.g. decay) important in stars’ energy “production” Gravitational interaction 10-39 Binds matter on large scales 27 Particles of Standard Model Leptons -1/3 -1 0 u u u d d d e e c c c s s s t t t b b b t t g g g g g g g g I II III Z W± Bosons Fermions +2/3 Quarks 28 Electromagnetic interaction Proton exchange of photons q1 Photon q1q2 F k 2 r Electron q2 29 The Strong Force d u g u Strong force caused by the exchange of gluons d 30 Weak interaction Beta decay Neutron u d Mean lifetime of a free neutron ~ 10.3 minutes Proton d u d Mean lifetime of a free proton > 1031 years! u WElectron e Exchange of W± e Anti-electron Neutrino 31 Testing the Standard Model The Standard Model works very well, but we want to want to make sure want to probe small structures, create massive particles need more powerful accelerators – big colliders more sophisticated and big detectors many people necessary => big collaborations resources concentrated in large laboratories, effort international in scope 32 The Colliders Tevatron collider Colliding bunches of protons and anti protons; bunches meet each other every _ detectors (DØ 396 ns in the center of two and CDF) (steered apart at other places) particle has ~ 980 GeV of energy, soEach the total energy in the center of mass is 1960 GeV = 1.96 TeV About 10M collisions per second LHC Colliding bunches of protons; bunches meet each other every 25ns in the center of 4 detectors particle has ~ 3.5TeV of energy, Each so the total energy in the center of mass is 7 (=> 14) TeV Susan Blessing About 400M collisions per second 33 Fermi National Accelerator Laboratory 34 peak luminosity 4X1032 cm-1s-1 ) energy in c.m.s. 1.9 TeV, bunch crossing time 396 ns total integrated luminosity 10fb-1 35 Modern particle physics detectors today’s particle physics detectors: combine many detection techniques “Russian doll” like structure -- many layers surrounding interaction region “general purpose detectors” – detect, identify and measure as many different kinds of particles as possible, (nearly) complete coverage of interaction region (“hermetic”) 36 Identifying particles 37 DØ Detector Central Tracking 38 Artist’s impression of a top event 39 Double b-tagged +jets event B decay Primary vertex b jet MTC Primary vertex IP B decay b jet 40 Standard Model A theoretical model of interactions of elementary particles, based on quantum field theory “Matter particles” Quarks: up, down, charm,strange, top, bottom Leptons: electron, muon, tau, neutrinos “Force particles” Gauge Bosons o (electromagnetic force) o W, Z (weak, electromagnetic) o g gluons (strong force) Higgs boson (not yet observed) Mass But note: gravity not part of SM 41 Summary we’ve come a long way …… technical breakthroughs in accelerators and detectors allowed new discoveries New theoretical ideas provided new understanding Standard Model (theory of particle interactions) works embarrassingly well! Has been tested by many hundreds of precision measurements over last four decades – very few measurements differ by more than 1 or 2 standard deviations Even some amount of frustration – always hope to see experimental result in disagreement with theory But there are some open questions ………………… 42 The End 43 44 Testing the Standard Model want to probe small structures, create massive particles need more powerful accelerators – big colliders more sophisticated and big detectors many people necessary => big collaborations resources concentrated in large laboratories, effort international in scope 45 The TeVatron Collider Tevatron collider Colliding bunches of protons and anti-protons; bunches meet each other every 396 ns in the center of two detectors (DØ and CDF) (steered apart at other places) Each particle has ~ 980 GeV of energy, so the total energy in the center of mass is 1960 GeV = 1.96 TeV About 2,500,000 collisions per second 46 Fermilab aerial view 47 Fermilab TeVatron tunnel 48 the new DØ detector 49 DØ Detector in hall January 2001 50 The Discovery of Top Quark 1977 – 1992 Many null results 1992 – 1993 A few interesting events show up 1994, CDF First evidence mt ~ 170 GeV/c2 1995 – CDF, DØ Discovery! 1994, DØ mt > 131 GeV/c2 51 Creating Top Anti-Top Quark pairs b P t + t b e t uc + -1/ 3 +2 / 3 W + + + e t d s P -2 / 3 +1/ 3 e t uc - W - - - e t d s 52 - What do we actually “see” _ t t e+ jets Muon Jet-1 Jet-2 Missing energy Electron 53 “event display” of a DØ top event t t e + jets 54 Ωb (http://www.fnal.gov/pub/presspass/images/DZero-Omega-discovery.html 2008 DØ experiment at Fermilab: discover brother of Ω- , the Ωb Ω- = sss, Ωb = ssb, theory predicts properties, decay modes, .. confirmed by experiment 55 Summary we’ve come a long way …… technical breakthroughs in accelerators and detectors allowed new discoveries and new understanding Standard Model (theory of particle interactions) works embarrassingly well! Has been tested by many hundreds of precision measurements over last three decades – very few measurements differ by more than 1 or 2 standard deviations Even some amount of frustration – always hope to see experimental result in disagreement with theory But there are some open questions ………………… 56 Higgs search – status 2011 combination of over 40 analyses by 100 physicists in two experiments 57 Higgs decay Branching Fraction Decay modes depend on mass A low-mass Higgs will decay primarily to bb high-mass Higgs will decay primarily to W+W A low-mass Higgs (below 130 GeV) is favored by supersymmetric models There were “hints” of Higgs production at >≈115 GeV, just before LEP was turned off. Higgs Mass (GeV/c2) 58 Future of DØ The Tevatron stopped running at the end of September with 10 fb-1 of data recorded per experiment. So there’s plenty of data analysis for the next few years. 59 Higgs Decay Modes Decay modes depend on Higgs mass A low-mass Higgs will _ decay primarily to bb Branching Fraction A high-mass Higgs will decay primarily to W+W- A low-mass Higgs (below 130 GeV/c2) is favored by supersymmetric models. And, those “hints” of Higgs production at 115 GeV/c2, just before LEP was turned off. Higgs Mass (GeV/c2) 60 Summary many different types of accelerators have been developed for nuclear and particle physics research different techniques suitable for different particles and energy regimes most accelerators in large research laboratories use several of these techniques in a chain of accelerators active research going on to develop new accelerating techniques for future applications many types of accelerators have found applications in fields other than nuclear and particle physics (e.g. medicine, ion implantation for electronics chips, condensed matter research, biology,….) 61 Summary Particle detection is based on interaction of particles with material in the detector; detectors usually have some “amplification” mechanism to render result of this interaction observable Many detection techniques have been developed over the last century breakthrough in detection techniques often led to breakthrough discoveries many of the detectors and/or techniques that were originally developed for basic research in nuclear or particle physics are now used in other fields; they often have led to advances in medical diagnosis (e.g. MRI, PET,….) 62 63 A Century of Particle Physics J.J Thomson Top quark 1995 Electron – 1897 64 Sizes and distance scales visible light: wavelength ≈5∙10-7m virus 10-7m molecule 10-9m atom 10-10m nucleus 10-14m nucleon 10-15m quark <10-18m 65 The Building Blocks of a Dew Drop dew drop: 1021 molecules of water. Each molecule = one oxygen atom and two hydrogen atoms (H2O). Atom: nucleus surrounded by electrons. Electrons bound to the nucleus by photons nucleus of a hydrogen atom = single proton. Proton: three quarks, held together by gluons just as photons hold the electron to the nucleus in the atom 66 Very early era (19th century) chemistry, electromagnetism discharge tubes, “canal rays”, “cathode rays” photoelectric effect (Hertz, 1887) radioactivity (Becquerel, 1895) X-rays (Röntgen, 1895) 67 68 What holds the world together? interaction strong electromagnetic weak gravity participants quarks charged particles all particles all particles 1 10-2 10-10 10-39 g gluon relative strength field quantum (boson) photon W± Z0 G graviton 69 The CMS Detector HF HE HB HO 70 DØ detector Muon System 1.9T magnetized Fe, Prop. drift tubes 40,000 channels Central Tracking Calorimeter Uranium-liquid Argon 60,000 channels 71 Transverse slice through CMS detector 72 Seeing = photon scattering experiment our eye is a photon detector; (photons = light “quanta” = packets of light -- see “photoelectric effect”) “seeing” is performing a photon scattering experiment: o light source provides photons o photons “interact” with object of our interest -- some absorbed, some scattered, reflected o some of scattered/reflected photons make it into eye; focused onto retina; o photons detected by sensors in retina (photoreceptors -- rods and cones) o transduced into electrical signal (nerve pulse) o amplified when needed o transmitted to brain for processing and interpretation 73 HOW TO SEE SMALL THINGS “seeing an object” = detecting light that has been reflected off the object's surface “visible light”= those electromagnetic waves that our eyes can detect “wavelength” of e.m. wave (distance between two successive crests) determines “color” of light if size of object is much smaller than wavelength, then wave is hardly influenced by object wavelength of visible light: between 410-7 m (violet) and 7 10-7 m (red); diameter of atoms: 10-10 m can’t see them with “ordinary” (visible) light generalize meaning of seeing: seeing is to detect effect due to the presence of an object quantum theory “particle waves”, with wavelength 1/(m v) use accelerated (charged) particles as probe, can “tune” wavelength by choosing mass m and changing velocity v this method is used in electron microscope, as well as in “scattering experiments” in nuclear and particle physics 74 Particle physics experiments Particle physics experiments: collide particles to o produce new particles o reveal their internal structure and laws of their interactions by observing regularities, measuring cross sections,... colliding particles need to have high energy o to make objects of large mass o to resolve structure at small distances to study structure of small objects: o need probe with short wavelength: use particles with high momentum to get short wavelength o Particles behave as if they had a wavelength = h/p mass-energy equivalence (E = mc2) plays an important role; in collisions, kinetic energy converted into mass energy; 75 ACCELERATORS are devices to increase the energy of charged particles; magnetic fields to shape (focus and bend) the trajectory of the particles; electric fields for acceleration. types of accelerators: electrostatic (DC) accelerators o Cockcroft-Walton accelerator (protons up to 2 MeV) o Van de Graaff accelerator (protons up to 10 MeV) o Tandem Van de Graaff accelerator (protons up to 20 MeV) resonance accelerators o cyclotron (protons up to 25 MeV) o linear accelerators electron linac: 100 MeV to 50 GeV proton linac: up to 70 MeV synchronous accelerators o synchrocyclotron (protons up to 750 MeV) o proton synchrotron (protons up to TeV) o electron synchrotron (electrons from 50 MeV to 90 GeV) storage ring accelerators (colliders) 76 Van de Graaff accelerator use powersupply to deposit charges on belt; pick charges off at other end of belt and deposit on “terminal” now rubber belt replaced by “pellet” chain – “pelletron” 77 Cyclotron two hollow metal chambers (“dees”) with “gap” between them dees connected to AC voltage source - one dee positive when other negative electric field in gap between dees, but no electric field inside the dees; source of protons in center, everything in vacuum chamber; whole apparatus in magnetic field perpendicular to plane of dees; frequency of AC voltage such that particles always accelerated when reaching the gap between the dees; in magnetic field, particles are deflected: p = qBR p = momentum, q = charge, B = magnetic field strength, R = radius of curvature radius of path increases as momentum of proton increases time for passage always the same as long as momentum proportional to velocity; this is not true when velocity becomes too big (relativistic effects) 78 Synchrotron synchrotron Magnetic field B (to keep particles on circle) synchronized with electric field (for acceleration); magnetic field increases during acceleration, radius of orbit fixed. synchrotron is most common accelerator used in particle physics first synchrotrons: Cosmotron (Brookhaven), 3.3 GeV, 1953 Bevatron (Berkeley): 6.2 GeV, 1954 PS (CERN) 26 -> 28 GeV, 1959 AGS (Brookhaven) 30 -> 33 GeV, 1960 79 80 81 Particle physics experiments Particle physics experiments: collide particles to o produce new particles o reveal their internal structure and laws of their interactions by observing regularities, measuring cross sections,... colliding particles need to have high energy o to make objects of large mass o to resolve structure at small distances to study structure of small objects: o need probe with short wavelength: use particles with high momentum to get short wavelength o Particles behave as if they had a wavelength = h/p mass-energy equivalence (E = mc2) plays an important role; in collisions, kinetic energy converted into mass energy; 82 Standard Model A theoretical model of interactions of elementary particles, based on quantum field theory Symmetry: SU(3) x SU(2) x U(1) “Matter particles” Quarks: up, down, charm,strange, top, bottom Leptons: electron, muon, tau, neutrinos “Force particles” Gauge Bosons o (electromagnetic force) o W, Z (weak, electromagnetic) o g gluons (strong force) Higgs boson spontaneous symmetry breaking of SU(2) mass 83 Detector Cartoon Measure transverse momentum/energy ** * Tracking chamber Toroidal magnet ** * Tracking chamber Calorimeter (dense material) Solenoidal magnet * * * * Electron * * ** Muon ** * ** * **** ** Jet Tracking chamber Neutrino (missing energy) 84 Detector Cartoon ** * Measure transverse momentum/energy Tracking chamber Toroidal magnet ** * Tracking chamber Calorimeter (dense material) Solenoidal magnet * * * * * * * * Electron Muon ** ** ** ** Jet * * * * Tracking chamber Neutrino (missing energy) Susan Blessing 85