Transcript Results from LHC and CMS at 0.9 and 2.36 TeV

269B class
organizational
meeting
LHC and Geneva
Main CERN
Campus;
ATLAS
CMS
ASDF
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Today (good timing )
• 7 TeV collisions, but
miniscule luminosity (50 Hz
of proton-proton collisions)
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Tomorrow:
Classes of Topics
• Fundamental physics
– E.g. Higgs, Supersymmetry, large extra dimensions
• “Phenomenology” – the interplay between theory and experiment
– E.g. partons in protons, hard scattering, “ordinary” particles, jets
• General experimental issues
– E.g. accelerators, measuring momentum and energy
• Specific experimental issues
– E.g. pixel detectors, CMS versus ATLAS
• The future of physics at the energy frontier
– E.g. muon colliders, plasma wakefield acceleration
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More detailed list of topics
•Fundamental physics
•General experimental issues
–Higgs
–Accelerators
–Supersymmetry (several types)
–Luminosity
–Z’ and W’ particles
–Measuring momentum(tracking)
–Techniparticles
–Measuring energy (sampling calorimeters)
–Large extra dimensions, Kaluza-Klein particles,
–-Muon systems
black holes
–“Particle flow”
–Compositeness
–Magnetic monopoles
•Specific experimental issues
–b’ and t’ quarks
–Pixel, Si strip tracking detectors
–Massive charged stable particles
–CMS versus ATLAS
–Data analysis techniques
•“Phenomenology” – the interplay between
–Examine past discoveries, measurements
theory and experiment
–Partons in protons
–Elastic and diffractive scattering
–Hard scattering
–“ordinary” particles
–Heavy quarks (b and t)
–jets
•The future of physics at the energy frontier
–Upgrades to LHC
–ILC and CLIC electron positron colliders
–muon colliders
–plasma wakefield acceleration
–Laser acceleration
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Organizational issues:
• What is expected?
– Kind of apprenticeship experience, tailored to individual
– Grading scheme (attendance, participation, talk or paper)
• Who is enrolled?
• When to meet?
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A Superficial Introduction
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Known Particle Physics
• Assume relativistic quantum mechanics
(field theory)
• The Standard Model (1974) has two
basic principles:
1. Symmetry at every point in
space-time
2. Symmetry breaking
• Only the 1st principle is beautiful…
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Symmetry
–
aka SU3xSU2xU1: a rotation symmetry at every point in spacetime:
–
–
Explains the Strong (SU3) and weak (SU2) nuclear forces
Explains Electromagnetism (U1)
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Symmetry breaking
–
Simple classical example: vertical pencil
–
Introducing the Higgs mechanism:
–
A special particle that has a strange potential energy function
in the vacuum:
Massive electrons, quarks,
neutrinos, W and Z, and
other particles
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Standard Model: (too much) Success!
1974 Standard Model emerged with the “November revolution”
1979 I became a grad student
For 34 years no discrepancy has been found 
All of the known fundamental particles are listed below.
The Higgs is the fundamental particle that allows Electroweak unification. The
only missing piece. The only scalar (Spin 0) particle.
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Tevatron vs. LHC: Higgs
• Low-mass (<130 GeV):
LEP-TeV working group fit:
mH< 157 GeV (95% CL)
– Favored by precision data fits
– Experimentally very difficult
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Here’s what a Higgs particle might look like (H ZZ4)
• A simulation
• Muons in
green.
• The “golden”
discovery
mode for H
mass >135
GeV
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Technicolor
Theories beyond the Standard Model (sometimes, but not always, GUTs) which
do not have a scalar Higgs field.
Details (see Wikipedia):
Instead, they have a larger number of fermion fields than the Standard
Model and involve a larger gauge group.
This larger gauge group is spontaneously broken down to the Standard
Model group as fermion condensates form.
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GUTs and the Higgs particle
GUTs=Grand Unified Theories
Einstein tried but failed…
?
The SU3xSU2xU1 symmetries come from
one big symmetry
A beautiful idea
Forces of nature merge into one force
eventually (at high energy)
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GUTs seem incompatible with Higgs…
“Fine corrections” to the Higgs mass tend to become huge (~1015 GeV/c2 or more),
this cannot be
Known as the hierarchy problem
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Supersymmetry (SUSY)
g
G
~
G
SM particles have supersymmetric partners:
Differ by 1/2 unit in spin
Sfermions (squarks, selectron, smuon, ...): spin 0
Gauginos (chargino, neutralino, gluino,…): spin 1/2
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Supersymmetry:
• A symmetry that relates spins (fermions to bosons):
– One new superpartner for every known elementary particle.
– The superpartner differs only by half a unit of spin, and its mass.
• The lightest supersymmetric particle is the best candidate for Dark Matter
• If supersymmetry exists close to the TeV energy scale, it
– Solves the hierarchy problem
– The early universe should have produced just about the right amount of
Dark Matter
• Supersymmetry is also a consequence of most versions of string theory
– though it can exist in nature even if string theory is wrong.
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Mass [GeV]
Supersymmetry=Particles Galore
Example: a whole new spectrum waiting at a few hundred GeV mass?
2020
SUSY also fixes GUTs details
Standard Model only

A simple SUSY model
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Large extra dimensions, R-S:
Large extra dimensions (1998):
To explain the weakness of gravity relative to the other forces.
Fields of the Standard Model are confined to a four-dimensional
membrane, while gravity propagates in several additional
spatial dimensions that are large compared to the Planck
scale
Production of black holes at the LHC??
Randall-Sundrum models (1999):
our Universe is a five-dimensional anti de Sitter space and the
elementary particles except for the graviton are localized on a
(3+1)-dimensional brane or branes
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Modern Particle Accelerators
The particles are guided around a
ring by strong magnets so they
can gain energy over many cycles
and then remain stored for hours
or days
The particles gain energy by
surfing on the electric fields of
well-timed radio oscillations (in
a cavity like a microwave oven)
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CERN Accelerator Complex
LHC is designed for 14 TeV
energy (7 TeV per proton in
each beam)
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Add >1500 dipole and quadrupole magnets,
liquid helium services …
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..and Two Large Detectors
CMS
ATLAS
• Beams collide 40 million times
producing 1 billion proton-proton
collisions every second
• Typical data run will last 9
months
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Context
• See http://www.nature.com/nature/journal/v448/n7151/full/nature06076.html
• 1987 (Reagan) the U.S. proposed to build a 40 TeV
collider (the SSC) in Texas.
• 1991 CERN proposed to re-use an existing
accelerator tunnel to build a “wimpy” 14 TeV
collider.
– UCLA Prof. Dave Cline was one of a handful of
(unfunded) U.S. physicists involved in LHC.
• 1993 the SSC was killed by Congress (Clinton)
• 1994 UCLA and other U.S. institutions joined the
LHC effort
– Then >14 years of planning, prototyping, and
construction…
• Dec. 2009 collisions at 0.9 & 2.36 TeV
• Mar. 2010 collisions at 7 TeV (Fermilab 1.96 TeV)