Particle Physics 2

1. Particle Physics 2 Bruce Kennedy RAL PPD Bruce Kennedy, RAL PPD

2. 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 PPD

3. Symmetries • Central idea in physics • A physical theory is defined by its symmetries • Simple eg: cos(x) = cos(-x) • More complex example: • QCD (theory of strong interaction) • Invariant under “rotation” of quarks in “colour space” • Symmetry described mathematically by Group Theory Particles And Forces Quantum Field Theory SO(10) ?? SU(3) x SU(2) x U(1) Symmetry group Standard Model Bruce Kennedy, RAL PPD

4. Where did the antimatter go ? • Matter and antimatter created equally • e.g. • … so it should all annihilate - Z0 + -  + • … but there is some matter left over Bruce Kennedy, RAL PPD

5. Matter-antimatter symmetry K+ K- K+ • Symmetry operation “CP” • P – parity – mirror reflection • (x,y,z)  (-x,-y,-z) • C – charge conjugation • particle  antiparticle • CP is an exact symmetry in physics • e.g. rate for K++0 = K--0 • … except for neutral K & B mesons… _u s u _s u _s Bruce Kennedy, RAL PPD

6. Symmetry breaking • Decays of K0 and B0 are slightly different from anti-K0 and anti-B0 • ONLY known matter-antimatter difference • Requires 3 quark-lepton generations • Known as “CP-violation” • Effect is very small • Experimental study is difficult Bruce Kennedy, RAL PPD

7. 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 PPD

8. 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 1 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 PPD

9. 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 PPD

10. What is SUSY ? • Particles exist as • Fermions (eg e, , q) – matter particles • Bosons (eg , Z, W) – force carriers • In SUSY, fermions get boson partners (and vice versa) • electron e  ”selectron” • photon   “photino” SUSY Bruce Kennedy, RAL PPD

11. … so where are the SUSY particles ? • Must be heavy • … otherwise we would have found them •  SUSY is a “broken” symmetry • How heavy ? • No solid prediction from theory • Probably not more than 1 TeV • Lightest SUSY particle should be stable • (possible connection to Dark Matter) Bruce Kennedy, RAL PPD

12. The Large Hadron Collider • To study Higgs & supersymmetry • Need high energy beams • (particle masses up to 1000 GeV) • … and very intense beams • (because interesting processes are very rare) • New accelerator • The Large Hadron Collider proton-proton colliderBuilt in old LEP tunnelBeam energy 7 TeV, or 7000 GeVDue to start in 2007Accelerator and detectors now being built. Bruce Kennedy, RAL PPD

13. 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 0.00025% recorded for analysis • experimental “trigger” rejects the rest Bruce Kennedy, RAL PPD

14. Inside an LHC detector HCAL Muon chambers Tracker ECAL Magnet Bruce Kennedy, RAL PPD

15. Finding the Higgs particle at LHC • A few difficulties • We don’t know the mass of the Higgs • Anywhere from 114 GeV to 1000 GeV • Detection technique depends on mass • LHC produces 109 p-p 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 PPD

16. Lightest SUSY particle leaves detector Detection relies on study of “missing” energy and momentum Seen in detector: 2 jets of “hadrons” (mainly  mesons) 2 muons 1 electron Missing energy and momentum deduced from conservation laws. Finding SUSY particles at LHC Bruce Kennedy, RAL PPD

17. 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 PPD

18. What do we do 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 PPD

19. 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 PPD

20. Bruce Kennedy, RAL PPD

21. The CMS detector Bruce Kennedy, RAL PPD

22. The ATLAS detector Bruce Kennedy, RAL PPD

23. The LHCb detector Bruce Kennedy, RAL PPD

24. The ALICE detector Bruce Kennedy, RAL PPD

25. Example of a detector - CMS ECAL Bruce Kennedy, RAL PPD

26. LHC Detectors ATLAS LHCb ALICE CMS Bruce Kennedy, RAL PPD

27. 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 PPD

28. Underlying events Simulated data Bruce Kennedy, RAL PPD

29. Brookhaven (USA) muon collider • Muon lifetime is 2s • Need to • collect • accelerate • collide • beams before they decay Bruce Kennedy, RAL PPD

30. TESLA linear collider (Germany) • e+e- collider • Linear – avoids radiation losses • 33 km long • Energy up to 800 GeV Bruce Kennedy, RAL PPD