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

Bruce Kennedy, RAL PPD 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 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 Symmetries Quantum Field Theory Symmetry group Particles And Forces Standard Model SU(3) x SU(2) x U(1)SO(10) ?? Grand Unification

Bruce Kennedy, RAL PPD Where did the antimatter go ? … so it should all annihilate Z0Z0 -- ++ -- ++  Matter and antimatter created equally  e.g.  … but there is some matter left over

Bruce Kennedy, RAL PPD u_su_s Matter-antimatter symmetry 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_su_s _us_us K+K+ K+K+ K-K-

Bruce Kennedy, RAL PPD Symmetry breaking Decays of K 0 and B 0 are slightly different from anti-K 0 and anti-B 0  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 The BaBar experiment Based at SLAC, Ca Studies B mesons  >10 8 B-meson decays recorded  High-precision results  CP violation confirmed Non-zero value  CP violation

Bruce Kennedy, RAL PPD 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 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 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” What is SUSY ? SUSY

Bruce Kennedy, RAL PPD … 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 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 collider Built in old LEP tunnel Beam energy 7 TeV, or 7000 GeV Due to start in 2007 Accelerator and detectors now being built. The Large Hadron Collider

Bruce Kennedy, RAL PPD LHC trivia 40 million collisions/sec 1000 million pp interactions/sec  … but almost all of them are background Raw data rate is bytes/sec  equivalent to >1 million CD-roms/sec Only % recorded for analysis  experimental “trigger” rejects the rest

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

Bruce Kennedy, RAL PPD 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 massmass  LHC produces 10 9 p-p interactions/sec  … but only a few thousand Higgs/year  LHC is a proton-proton collider  So not a clean environment like LEPnot a clean environment

Bruce Kennedy, RAL PPD Finding SUSY particles at LHC 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.

Bruce Kennedy, RAL PPD 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 What do we do next ? LHC good for “discovery”  Need a more precise tool for detailed understanding Muon collider ?  Exciting prospect, but very difficult Exciting prospect e+e- linear collider ?  Europe, USA, Japan all have plans Europe

Bruce Kennedy, RAL PPD 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

The CMS detector

Bruce Kennedy, RAL PPD The ATLAS detector

Bruce Kennedy, RAL PPD The LHCb detector

Bruce Kennedy, RAL PPD The ALICE detector

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

Bruce Kennedy, RAL PPD LHC Detectors ATLASLHCb ALICE CMS

Bruce Kennedy, RAL PPD 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 Underlying events Simulated data

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

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

Bruce Kennedy, RAL PPD 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 Symmetries Quantum Field Theory Symmetry group Standard Model Particles And Forces SU(3) x SU(2) x U(1)SO(10) ??