introduction to particle physics - wordpress.com · 27/4/2013 · internal symmetries internal...
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Introduction to Particle Physics
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The building blocks of the Universe
The Universe according to (ancient) Greeks
The Universe according to (modern) Geeks
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How did we get from here… And what does it have to do with particle physics?
… to here?
If Geeks are right, then…
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Scale separation in physics
Molecular physics, chemistry
Atomic physics
Nuclear Physics
Particle physics
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Symmetry as a guide to the Universe
Symmetry makes the world nice….
… it also explains conservation of energy, momentum, …, electrical charge, etc.
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Space-time symmetries
Shift car’s position from x0 to x0’
Moving car has momentum
Now moving car’s momentum … is the same!!! Both momentum and energy are not changed (conserved)!
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Internal symmetries
Internal symmetries do not involve transformations in space-time but change one type of particle into another.
Let’s make internal symmetry transformation…
But both momentum and energy are not changed (conserved)!
Apply this principle to elementary particles…
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Internal symmetries and interactions
SU(3)× SU(2)L× U(1) symmetry QCD electroweak
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The Standard Model
The Standard Model of particle physics is a remarkably simple and powerful construct…
One ingredient is missing…
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All particles in the Standard Model must have zero mass in order for it to be invariant under
all its symmetries!!!
We are missing the masses of all particles!!!
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+ Standard = Model
The Ultimate Equation?
Periodic table of matter Can Standard Model be the Ultimate Theory of the Universe?
Something is needed to give masses to all particles
The answer is, unfortunately, no…
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2. Problems, problems…
Gauge forces in SM do not distinguish between fermions of different generations: e, µ,t have same electrical charge quarks have same color charge
Why generations? Why 3? Why hierarchies of masses and
mixings? What stabilizes Higgs mass? What makes SM select left-handed
interactions?
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Even more problems…
Standard Model does not explain how the Universe was formed…
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A 10,000,000.00 Swedish Kronor question:
Where did all the antimatter go?
More baryons than antibaryons: baryonogenesis
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Conditions for the asymmetry
Matter-antimatter imbalance in the Universe
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2. What is CP(T)?
P: parity (inversion of space)
C: charge conjugation
T: time reversal
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Can Standard Model violate CP?
Strong and electromagnetic interactions conserve C, P and T
All interactions (local QFT) conserve combination CPT
Weak interactions violate P and C… what about CP?
But: if SM contains operators with complex phases then there just might be CP violation in the Standard Model!
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Need for New Physics…
It appears that the Standard Model does not have enough CP-violation to explain baryonogenesis
Thus, New Physics is needed
But of what kind? Multi-Higgs/LR models? Supersummetry (SUSY)? Little Higgs? Large extra dimensions? Technicolor? Compositeness? … other weird theory?
Ultimately: strings, M-theory? Only experiment will identify
The Correct Theory
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Aside: units used in particle physics
Energy: electron-volt: 1 eV = 1.6x10-19 J
(energy that an electron gains going through a potential difference of 1 Volt)
E = mc2, so set c=1! natural units
Mass: electron-volt
proton mass mp = 938.27 MeV
Momentum: electron-volt
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Experimental methods
Experimental methods of studies of “intrinsic properties” are well-known…
Several experimental facilities for direct and indirect searches for New Physics
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Direct vs. indirect signals of New Physics
Direct detection Indirect detection
Look for direct production of new particles
(big expensive machine)
Look for quantum effects due to new particles
(careful data analysis)
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Experimental Facilities
KEK (Japan) SLAC (Menlo Park, CA)
FNAL (Batavia, IL)
CERN (Geneva)
Indi
rect
sea
rche
s D
irec
t se
arch
es
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Experimental Facilities: accelerator
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Experimental Facilities: detectors
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Theoretical facilities
WSU, PRB, Room 358 (Detroit, MI)
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Theoretical facilities, cont.
WSU, PRB, Room 358 (Detroit, MI)
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Indirect methods
Indirect methods seek to understand effects of virtual New Physics particles
or
A Big Problem: no free quarks exist!
Strong interactions must be tamed!
Standard Model Supersymmetric SM
or ???
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Quantum Chromodynamics (QCD)
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Electromagnetic and color forces
γ
±1 charge
O(a) ~ 0.01
g
±3 “color” charges
O(as) ~ 1
QCD: a Yang-Mills theory based on SU(3) gauge group
Elec
trom
agne
tic
Stro
ng
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The toughness of soft QCD
QCD Lagrangian is written in terms of “wrong” degrees of freedom
QCD: quarks, gluons Experiment: mesons, baryons…
Bound states (mesons and baryons): no perturbative expansion in coupling constant
Numerical (lattice) QCD studies: flux tubes
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Open questions
Higgs particle is not (yet) discovered mechanism of electroweak symmetry breaking
Standard Model does not have ``enough’’ asymmetry between particles and antiparticles to create the Universe as we know it CP-violation and baryonogenesis
New Physics beyond the Standard Model? supersymmetry, strings, extra dimensions…
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5. Conclusions
New Physics might be just around the corner Various models can be tested with heavy quarks Results in charm and beauty sectors are complementary
QCD can be “tamed” in the decays of heavy hadrons this does not constitute “a solution of QCD” a $1M is still up for grabs…
LHC will bring new tasks and applications… stay tuned!