Transcript Compelling Questions of High Energy Physics?

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
Quarks
Leptons
u(p)
c(charm)
t(top)
d(down)
s(strange) b(bottom)
e


e


Forces and Force Carriers
Gravity
Gravitino
Electromagnetic
Photon
Weak
W+,W-,Z0
Strong
Gluon
The decay of the muon via
the weak interactions

e-
W-
-

e
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
Weak
EM
Strong
Gravity
• 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
d
s
=
Vud Vus Vub
d
Vcd Vc sVcb
s
• Leaves us with lots of Vunanswered
questions!
td Vts Vtb
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)
d
s
=
Vud Vus Vub
d
Vcd Vc sVcb
s
Vtd Vts Vtb
b weak of flavor mixing
• Phenomenology
b
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 Density Frontier(Nucleon+Nucleon)
BNL
-High Precision Frontier-
• Rare K and B decays
• Masses and mixing of 
– Flavor oscillations
-Precision FrontierNeutrino 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
e

=
Lepton
Mixing
Matrix
e



mass simplest solution:weak
• Problem with
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
-Precision FrontierCP Violation
• What happened to the anti-matter?
Big Bang
Matter=Antimatter
Now
Matter only
– 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.
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
Be Optimistic!