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?

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Building Blocks Forces and Force Carriers

The decay of the muon via the weak interactions   e e   W-W-

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 ( 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 V ud V us V ub V cd V c s V cb V td V ts V tb d s b d s 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 V ud V us V ub V cd V c s V cb V td V ts V tb d s b d s b = strong weak

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: M H > 100GeV – Possible signal at M H = 114GeV ?? FNAL: May discover Higgs if light enough LHC: Will discover the Higgs!

-High Density Frontier- (Nucleon+Nucleon) BNL

-High Precision Frontier- Rare K and B decays Masses and mixing of –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 = e   e   Lepton Mixing Matrix 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

Warning: focus on the problem at hand, but still be a student of problems in other fields Be Broad

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

Be Optimistic!