Modern Physics

The “Why,” “What,” and “How?”of the Higgs Boson

Sean YeagerUniversity of Portland

10 April 2015

Outline

Review of the Standard Model Review of Symmetries Symmetries in the Standard Model The Higgs Mechanism Electroweak Symmetry Breaking Searching for the Higgs The Compact Muon Solenoid The Future

The Standard Model

6 Quarks 6 Leptons 3 Forces 4 Mediators 1 Higgs...?

Symmetries and Conservation

Noether (1918) Conservation laws correspond

to symmetries

– Momentum : Translation

– Energy : Time

– Angular Momentum : Rotation

We have particle conservation laws as well

Review of Laws

Baryon number

– Quark number Lepton number Angular momentum Charge Flavor Energy (mass)

Practice Problems

According to the SM, which of these reactions are possible? If not, say what law is violated.

p+ + p- → π+ + π0

n → p+ + e-

p+ + p+ → p+ + p+ + p+ + p-

μ- → e- + νe + νμ

e- + e+ → μ+ + μ-

π0 → γ + γ

π0 → p+ + p-

Symmetries as Groups

Explore symmetry in greater detail Consider equilateral triangle

– What operations that leave it unchanged?

– 3 rotations

– 3 reflections Transformations form a group Combination of members is also a member

Symmetries in Fields

What can we vary without changing the Lagrangian?

Gauge invariance Static electricity:

V→V+C Generalize to EM

Symmetries and Forces

Yang and Mills (1954) Non-Abelian groups

to understand strong force

Can think of all 3 forces as arising from gauge symmetries

Successful, but big problem

Massless mediators

Aside into Solid State Physics

Nambu and Goldstone (1960)

Superconductors Look at chiral

symmetry in fermions Symmetry breaking Field self interacts Produces massive

particles

Higgs Mechanism

Suggested by Anderson (1962) PRL Symmetry Breaking Articles (1964)

– Higgs

– Brout and Englert

– Guralnik, Hagen, and Kibble Combine a gauge field with another field that

breaks the symmetry group Higgs bosons are excitations in field Gauge bosons interact with Higgs Bosons Gain mass based on strength of interaction

The Champagne Bottle Potential

Ground state is non-zero

Higher than surrounding area

Symmetric central position is spontaneously broken by perturbation

Analogies

Swimming Toddler vs. Shark Water : Higgs field Drag : coupling

Political gathering Obama vs. Bush People : Higgs field Popularity : coupling

Electroweak Breaking

Weinberg and Salam (1967) Assume a Higgs field Use it to break electroweak symmetry Predictions

Neutral weak current • Observed at Gargamelle (CERN, 1973)

Two charged weak mediators; mass of 82 ± 2 GeV

One neutral weak mediator; mass 92 ± 2 GeV• Observed at Super Proton Synchotron (CERN, 1983)

• Masses 80.4 and 91.2 GeV

Nobel Prize (1979)

Something is Missing

They also predicted the Higgs Boson Didn't see it for 40 years Several more generations of accelerators

– Large Electron Positron Collider (CERN, 1989-2000)

– Superconducting Supercollider (Texas, canceled 1993)• Would have been 20 TeV!

– Tevatron (Fermilab, 1989-2011)

– Relativistic Heavy Ion Collider (BNL, 2000-present)

– LHC (CERN 2009-present)

The Large Hadron Collider >10,000 scientists From >100 countries 27 km circumference 175 m underground Spans two countries

Proton-proton collisions Run 1 (2010-2012)

– 7 TeV → 8 TeV Run 2 (2015-?)

– 14 TeV

Compact Muon Solenoid

Interaction Point Proton beams collide Beam radius: 17μm

2808 bunches of protons 1.15 x 1011 protons each Cross every 25 ns 31.6 million collisions / sec

Silicon Tracker Charged particles Magnetic field 66 million sensors

Measures momentum by looking at position

Curvature and momentum inversely related

Accurate to 10 μm

ECAL Lead tungstate PbWO

4

Transparent

Measures energy Electrons and photons

cause scintillation >76,000 crystals

HCAL Layered heavy materials

and plastic scintillators Brass and steel

Measures energy of quark based particles

Endcaps old artillery shells

Magnet Superconducting Niobium titanium 100,000 Earth's field

Provides field for tracker 3.8 T; 18,160 A; 2.3 GJ About ½ tonne of TNT

Muon Detectors Drift tubes (barrel) Cathode strip chambers (caps) Gas and wire Muons ionize gas

Critical feature Muons penetrate Not stopped by cals

The Higgs of July

July 4 2012 ATLAS and CMS About 125 GeV 2 interaction channels

– 2 photon

– 4 lepton Both detectors saw

excess in channels About 5 sigma ~125 GeV

So What's Next?

“Real” world – not much

– ...for now? Validates Standard Model Scalar fields do exist in nature Cosmology

Inflation?

Fate of the universe?