Why Large Hadron Collider?

ROY, D. (2011). Why Large Hadron Collider?. Pramana: Journal Of Physics, 76(5), 741-756.

doi:10.1007/s12043-011-0083-6

High Energy collidersUsually accelerate particle and an

antiparticle beams .They have identical orbits in in same vacuum

pipe on top of one another.Made to collide with a magnetic switchDetector observes the particles coming out of

the collision

Electron-antielectron – more precisionProton-antiproton – less expensive

Large Hadron ColliderProton-proton collider

Gives high luminosity than proton-antiproton

Allows production of collision with energy greater than the current limit ~2Tev

Why do we want to do this? Stay tuned!

THE FERMIONS:•Three pairs of leptons(electron, muon, tau, plus their neutrinos) These vary in mass, electric charge, and color charge.

•Three pairs of quarks (up, down, strange, charm, bottom, top)

Quarks make up the proton and neutron, so together with the electron, they make up all visible matter in the universe!

The Standard Model

Bosons: Force carrier particlesFour Gauge Bosons:

γ (photon) – electromagnetic force g (gluon) – strong force Z – weak force W± - weak force

H0 Higgs Boson – responsible for Higgs fieldWhen particles interact with Higgs field, they acquire

mass. Existance needs to be confirmed.

Note: The gravitron is purely hypothetical and could be a gauge boson. It is not currently incorporated.

Lagrangian – summarizes the dynamics of a system

L = T – V (kinetic energy – minus potential energy)

Leads to conservation lawsNot taught in high school because 3D calculus is

usedUsually the time integral is used:S = ∫L dt

A couple of background concepts

Gauge SymmetryResults from conservation of a quantityGauge transformation = transformation of a

field from one configuration to anotherObservable quantities (mass, charge, energy,

velocity etc.) do not change even when the field they are derived form does change (invariance)

Back to Bosons and LHC

The problemIf a gauge boson mass term is added to the

Lagrangian, the invariance is broken. Somehow, the weak gauge boson must have

mass without breaking the gauge symmetry of the Lagrangian.

Note: Everything here (As well as in the “solution”) is proven mathematically, and no simple way to explain here.

The SolutionHiggs Mechanism of spontaneous

symmetry breaking provides the answer by giving mass through a “back door”

The math demonstrates that Higgs Boson (responsible for the mechanism) has mass.

This leads to a minimal supersymmetric extension of the Standard Model (MSSM)

Solution continuedSpontaneous symmetry breaking – symmetry broken at ground state of a system, but otherwise kept by Lagrangian.

Two Higgs doublets give mass to the upper and lower fermions

But. . .The Higgs Boson can also interact with other particles, which produces divergences. (Other interactions “work” that should not.)

Supersymmetry (symmetry between fermions and bosons) causes these unwanted effects to cancel out.

Fermions have bosionic super partners and vice versa.•Quark-squark, lepton-slepton, photino, gluino, wino, zino, Higgsino• I am not making this up, honestly!

The Large Hadron collider will allow us to investigate this.

What is Dark Matter? Dark matter is a type of matter that scientists

believe to make up a large part of the total mass (84 %) in the universe.

Dark matter does not emit or absorb Electromagnetic radiation (including light). So it cannot be “seen”.

We believe it exists because of its gravitational effects on visible matter and radiation.

What dark matter is NOT:AntimatterDark EnergyDark FluidDark FlowNegative matter

These are all completely different things.

Possible explanation for Dark MatterThe lightest Superparticle (LSP) is stable and

an admixture of photino and zino.

LSP is the leading candidate for cosmic matter(Better referred to as invisible matter)

The large Hadron Collider would help us to find these particles.

When the universe formed, super particles decayed into LSP’s until the dark matter density reached a critical level.

Hubble expansion caused them to not collide - the freeze-out point

Dark Matter content of the universe has remain frozen since this point.

Dark Matter particles started clumping due to gravity, (EM had no effect on them) – protogalaxies

After separating from EM radiation, “ordinary” matter was attracted to these.

Some Universe History

In ConclusionThe Large Hadron Collider will allow us to

search for the Higgs Boson and superparticles by producing collisions of 2 -3 Tev.

They will either be discovered or we will have clues for an alternative model. (There are some other models out there, and their predicted particles could also be found by the LHC)

The discovery of superparticles, and therefore SUSY, will help us understand dark matter better.