269B class organizational meeting

LHC and GenevaLHC and Geneva

CMS

Main CERNCampus;ATLAS

2ASDF

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Today (good timing )

• 7 TeV collisions, but miniscule luminosity (50 Hz of proton-proton collisions)

Tomorrow:

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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

–Higgs–Supersymmetry (several types)–Z’ and W’ particles–Techniparticles–Large extra dimensions, Kaluza-Klein particles, black holes–Compositeness–Magnetic monopoles–b’ and t’ quarks–Massive charged stable particles

•“Phenomenology” – the interplay between theory and experiment

–Partons in protons–Elastic and diffractive scattering–Hard scattering–“ordinary” particles–Heavy quarks (b and t)–jets

•General experimental issues–Accelerators–Luminosity–Measuring momentum(tracking)–Measuring energy (sampling calorimeters)–-Muon systems–“Particle flow”

•Specific experimental issues–Pixel, Si strip tracking detectors–CMS versus ATLAS–Data analysis techniques–Examine past discoveries, measurements

•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 PhysicsKnown Particle Physics

• Assume Assume relativisticrelativistic quantumquantum mechanics (field theory)mechanics (field theory)

• The Standard Model (1974) has The Standard Model (1974) has two basic principles:two basic principles:

1. Symmetry at every point in space-time

2. Symmetry breaking

• Only the 1Only the 1stst principle is principle is beautiful…beautiful…

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SymmetrySymmetry– aka SU3xSU2xU1: a rotation symmetry at every

point in space-time:– Explains the Strong (SU3) and weak (SU2)

nuclear forces– Explains Electromagnetism (U1)

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Symmetry breakingSymmetry 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) Standard Model: (too much) Success!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):

– Favored by precision data fits– Experimentally very difficult

LEP-TeV working group fit:mH< 157 GeV (95% CL)

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Here’s what a Higgs particle might look Here’s what a Higgs particle might look like (H like (H ZZZZ44))

• A simulation

• Muons in green.

• The “golden” discovery mode for H mass >135 GeV

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TechnicolorTechnicolorTheories beyond the Standard Model (sometimes, but not always, Theories beyond the Standard Model (sometimes, but not always,

GUTs) which GUTs) which do not have a scalar Higgs field. do not have a scalar Higgs field.

Details (see Wikipedia):Details (see Wikipedia):

Instead, they have a larger number of fermion fields than the Instead, they have a larger number of fermion fields than the Standard Model and involve a larger gauge group. Standard Model and involve a larger gauge group.

This larger gauge group is spontaneously broken down to the This larger gauge group is spontaneously broken down to the Standard Model group as fermion condensates form.Standard Model group as fermion condensates form.

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GUTs and the Higgs particleGUTs and the Higgs particle

?

GUTs=Grand Unified TheoriesGUTs=Grand Unified Theories

Einstein tried but failed…Einstein tried but failed…

The The SU3xSU2xU1 symmetries symmetries

come from one big symmetrycome from one big symmetry

A beautiful ideaA beautiful idea

Forces of nature merge into Forces of nature merge into one force eventually (at high one force eventually (at high energy)energy)

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GUTs seem incompatible with Higgs…““Fine corrections” to the Higgs mass tend to become huge (~10Fine corrections” to the Higgs mass tend to become huge (~101515 GeV/c GeV/c22 or more), this cannot be or more), this cannot be

Known as the Known as the hierarchy problemhierarchy problem

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Supersymmetry (SUSY)Supersymmetry (SUSY)

SM particles have supersymmetric partners:SM particles have supersymmetric partners:

Differ by 1/2 unit in spinDiffer by 1/2 unit in spinSfermions (squarks, selectron, smuon, ...): spin 0 (squarks, selectron, smuon, ...): spin 0Gauginos (chargino, neutralino, gluino,…): spin 1/2 (chargino, neutralino, gluino,…): spin 1/2

G~G

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Supersymmetry:Supersymmetry:• A symmetry that relates spins (fermions to bosons):A symmetry that relates spins (fermions to bosons):

– One new superpartner for every known elementary particle.One new superpartner for every known elementary particle.

– The superpartner differs only by half a unit of spin, and its mass.The superpartner differs only by half a unit of spin, and its mass.

• The lightest supersymmetric particle is the best candidate for Dark MatterThe lightest supersymmetric particle is the best candidate for Dark Matter

• If supersymmetry exists close to the TeV energy scale, itIf supersymmetry exists close to the TeV energy scale, it

– Solves the hierarchy problemSolves the hierarchy problem

– The early universe should have produced just about the right amount of The early universe should have produced just about the right amount of Dark MatterDark Matter

• Supersymmetry is also a consequence of most versions of string theorySupersymmetry is also a consequence of most versions of string theory

– though it can exist in nature even if string theory is wrong.though it can exist in nature even if string theory is wrong.

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Supersymmetry=Particles Supersymmetry=Particles GaloreGalore

Example: a whole new spectrum waiting at a few hundred GeV mass?

Mas

s [G

eV]

2020

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SUSY also fixes GUTs details

Standard Model onlyStandard Model only A simple SUSY A simple SUSY modelmodel

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Large extra dimensions, R-Large extra dimensions, R-S:S:

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Large extra dimensions (1998):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):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 Modern Particle AcceleratorsAccelerators

The particles gain energy by surfing on the electric fields of well-timed radio oscillations (in a cavity like a microwave oven)

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

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CERN Accelerator ComplexCERN Accelerator Complex

LHC is designed for 14 LHC is designed for 14 TeV energy (7 TeV per TeV energy (7 TeV per proton in each beam)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..and Two Large Detectors

ATLASCMS

• Beams collide 40 million times Beams collide 40 million times producing 1 billion proton-proton producing 1 billion proton-proton collisions every secondcollisions every second

• Typical data run will last 9 monthsTypical data run will last 9 months

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)