pphysics today 2

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Particle Physics Bruce Kennedy RAL PPD Bruce Kennedy, RAL Open questions • What happened to the antimatter ?  Why is there some matter left over • What is the origin of mass ?  Higgs mechanism (cf Bill Murray’s talk)  Can we find the Higgs particle ? • Where does gravity come in ?  “Theory of everything” Bruce Kennedy, RAL Symmetries • Central idea in physics • A physical theory is defined by its symmetries Quantum • Simple eg: cos(x) = cos(-x) Field SU(3) SO(10) x SU(2) ?? x U(1) Symmetry group • MoreTheory complex example:  QCD (theory of strong interaction) Particles And Forces  Invariant under “rotation” of quarks in “colour space” • Symmetry described mathematically by Grand Standard Unification Model Group Theory Bruce Kennedy, RAL Where did the antimatter go ? • Matter and antimatter created equally µ -  e.g Z0 µ+ • … so it should all annihilate µ- µ + … but there is some matter left over Bruce Kennedy, RAL γ Matter-antimatter symmetry • Symmetry operation “CP” P – parity – mirror reflection (x,y,z) ↔ (-x,-y,-z) C – charge conjugation K+ u _ s particle ↔ antiparticle • CP is an exact symmetry in physics  e.g rate for K+→π+π0 = K-→π-π0 • … except for neutral K & B mesons… Bruce Kennedy, RAL KK+ _ u u _ s s Symmetry breaking • Decays of K0 and B0 are slightly different from anti-K0 and anti-B0  ONLY known matter-antimatter difference  Requires quark-lepton generations • Known as “CP-violation” • Effect is very small  Experimental study is difficult Bruce Kennedy, RAL The BaBar experiment • Based at SLAC, Ca • Studies B mesons  >108 B-meson decays recorded  High-precision results  CP violation confirmed Non-zero value ⇒ CP violation Bruce Kennedy, RAL Where is the Higgs particle ? • Was it seen at LEP ?  (see Bill Murray’s talk) • How heavy is it ?  At least 114 GeV  No more than 1000 GeV (or TeV) • How can we find it (if it exists)  Collide intense high-energy particle beams (eg at LHC)  Search for Higgs signature (not so easy…) Bruce Kennedy, RAL What about gravity ? • Particle physics tries to unify forces  Electromagnetic+weak, strong • Why not gravity ? • Symmetries of particle physics (SM) and gravitation (GR) incompatible  Can be fixed by adding a new symmetry  “Supersymmetry” (SUSY) Bruce Kennedy, RAL What is SUSY ? • Particles exist as (eg e, µ, q) – matter particles  Bosons (eg γ, Z, W) – force carriers  Fermions SUSY • In SUSY, fermions get boson partners (and vice versa) e ↔ ”selectron”  photon γ ↔ “photino”  electron Bruce Kennedy, RAL What will we learn from LHC • Should find “the” Higgs particle  Or more than one ? • Should discover supersymmetry  (If it exists – no experimental evidence so far) • Better understanding of CP violation  (Matter-antimatter differences) • Maybe something unexpected ? Bruce Kennedy, RAL What we next ? • LHC good for “discovery”  Need a more precise tool for detailed understanding • Muon collider ?  Exciting prospect, but very difficult • e+e- linear collider ?  Europe, USA, Japan all have plans Bruce Kennedy, RAL Conclusion • Exciting times ahead for particle physics  Matter-antimatter Why is the universe made of matter ? Current experiments should give some answers  LHC should go beyond the Standard Model Higgs particle(s), SUSY, new questions  New colliders planned for next generation of experiments Bruce Kennedy, RAL Bruce Kennedy, RAL PPD The CMS detector Bruce Kennedy, RAL The ATLAS detector Bruce Kennedy, RAL The LHCb detector Bruce Kennedy, RAL The ALICE detector Bruce Kennedy, RAL Example of a detector - CMS ECAL Bruce Kennedy, RAL LHC Detectors ATLAS LHCb ALICE CMS Bruce Kennedy, RAL Where to look for the Higgs ? • Best method depends on its mass • If it is light, we can look for decay to two photons Bruce Kennedy, RAL Underlying events Simulated data Bruce Kennedy, RAL Brookhaven (USA) muon collider • Muon lifetime is 2µs  Need to collect accelerate collide  beams decay before they Bruce Kennedy, RAL TESLA linear collider (Germany) • e+e- collider  Linear – avoids radiation losses  33 km long  Energy up to 800 GeV Bruce Kennedy, RAL Symmetries • • • • Central idea in physics A physical theory is defined by its symmetries Simple eg: cos(x) = cos(-x) Particles Quantum MoreField complex example:  QCD (theory Theory SU(3) SO(10) x SU(2) ?? x U(1) Symmetry group of strong interaction) And  Invariant under “rotation” of quarks in “colour space” Forces • Symmetry described mathematically by Group Theory Standard Model Bruce Kennedy, RAL [...]... (because Due to startinteresting in 20 07 processes are very rare) and detectors now NewAccelerator accelerator being built  The Large Hadron Collider Bruce Kennedy, RAL LHC trivia • 40 million collisions/sec • 1000 million pp interactions/sec … but almost all of them are background • Raw data rate is 1015 bytes/sec  equivalent to >1 million CD-roms/sec • Only 0.00 025 % recorded for analysis  experimental... interactions/sec … but only a few thousand Higgs/year  LHC is a proton-proton collider So not a clean environment like LEP Bruce Kennedy, RAL Finding SUSY particles at LHC • Seen in detector: 2 jets of “hadrons” (mainly π mesons) 2 muons  1 electron  Missing energy and momentum deduced from conservation laws • Lightest SUSY particle leaves detector • Detection relies on study of “missing” energy and momentum... method depends on its mass • If it is light, we can look for decay to two photons Bruce Kennedy, RAL Underlying events Simulated data Bruce Kennedy, RAL Brookhaven (USA) muon collider • Muon lifetime is 2 s  Need to collect accelerate collide  beams decay before they Bruce Kennedy, RAL TESLA linear collider (Germany) • e+e- collider  Linear – avoids radiation losses  33 km long  Energy up to 800... Symmetries • • • • Central idea in physics A physical theory is defined by its symmetries Simple eg: cos(x) = cos(-x) Particles Quantum MoreField complex example:  QCD (theory Theory SU(3) SO(10) x SU (2) ?? x U(1) Symmetry group of strong interaction) And  Invariant under “rotation” of quarks in “colour space” Forces • Symmetry described mathematically by Group Theory Standard Model Bruce Kennedy,
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