Compelling Questions of High Energy Physics? What does the future hold? Persis S. Drell Physics Department Cornell University
Physics: “The knife that cuts into the grain of nature” -Jacob Bronowski “The rules of the game are what we mean by fundamental physics…” -Richard Feynman
Fundamental Questions of Particle Physics • What are the fundamental constituents of matter? How many are there? Can we understand why they have the masses that they do? • What are the fundamental forces? Can we understand why some are weak and some are strong? Can they be unified? • What is the structure of spacetime? • How did the Universe evolve in the first seconds after the big bang?
Building Blocks Forces and Force Carriers
The decay of the muon via the weak interactions e - nm ne W- - m
Ingredients of the Standard Model • Local Gauge Invariance • Symmetries Generate Interactions • Spontaneous Symmetry Breaking • Gives mass to force carriers • Predicts a Higgs • Non-Abelian • The force carriers can have charge • Add in the matter fields of the quarks and leptons, lots of extra parameters, bake at 350 for 30 minutes • Correctly predict the results of every high energy physics experiment for the last 30 years.
Top Features of the Standard Model • Every experiment for last 30 years has either agreed with the model or the experiment is wrong. • Unification of 3 of 4 forces • Explains HEP to the TeV scale (10-18 m) • Predicted the existence and mass of the Z boson • Makes flavor mixing in the quark sector understandable to a 1st year physics grad • CKM • Leaves us with lots of unanswered questions! Weak EM Strong Gravity Vud Vus Vub Vcd Vc sVcb Vtd Vts Vtb d d = s s b b strong weak
Quark Flavor Mixing • Eigenstates of the strong interactions (states of quark flavor u,d,s,c,b,t) are not eigenstates of the weak interactions • Flavor a symmetry of the SI • Flavor not a symmetry of the WI • Weak Interaction diagonal on a different basis • WI basis and SI basis related by rotation matrix (CKM) • Phenomenology of flavor mixing Vud Vus Vub Vcd Vc sVcb Vtd Vts Vtb d d s = s b b weak strong
Worst “bugs” in the Standard Model • Too many free parameters • Different bases for strong and weak interactions • Where do the masses come from? • Parity violation of the weak interactions added by hand • Fundamental Scalar (spin 0) Higgs • Fine tuning problems • Only works to 1TeV • Doesn’t include gravity • Leaves us with lots of unanswered questions
Compelling Questions for the Next Decade-Going beyond the SM- • What is the right description of gravity? • Can all the forces be unified? • What is the origin of mass? • What is the new physics beyond the SM? • Can we understand flavor mixing and where does CP violation come from? • Can we explain the Universe?
Current Probes of SM-The high energy frontier- • LEP: MH > 100GeV • Possible signal at MH = 114GeV ?? • FNAL: May discover Higgs if light enough • LHC: Will discover the Higgs!
-High Precision Frontier- • Rare K and B decays • Masses and mixing of n • Flavor oscillations
-Precision Frontier-Neutrino Oscillations • Lepton Flavor Mixing • No neutrino mass => no lepton flavor mixing • Finite neutrino mass => expect lepton flavor mixing just like we have quark flavor mixing • Simplest solution: leptons mix just like quarks • Problem with simplest solution: very unnatural. • Once allow neutrino to have mass: • Dirac mass like quarks • Majorana mass (unique to particles without electric charge) • Rule of QFT: be as generic as possible ne ne Lepton Mixing Matrix = nm nm nt nt weak mass
-Precision Frontier-CP Violation • What happened to the anti-matter? • Studies of CP Violation in K and B decays • Studies of rare processes that are highly suppressed in the SM so new physics has a chance to compete favorably. Big Bang Matter=Antimatter Now Matter only
Be Broad Warning: focus on the problem at hand, but still be a student of problems in other fields
Be Critical Warning: Always temper your criticism with judgement
Three of these plots show statistical fluctuations. One shows a real signal. Can you pick out the real signal?
Be Bold ‘Truth emerges more readily from error than from confusion’ -Francis Bacon 1561-1626