Peter Paul 04/21/05PHY313-CEI544 Spring-051 PHY313 - CEI544 The Mystery of Matter From Quarks to the...

Peter Paul 04/21/05 PHY313-CEI544 Spring-05 1

PHY313 - CEI544The Mystery of Matter

From Quarks to the CosmosSpring 2005

Peter Paul

Office Physics D-143

www.physics.sunysb.edu PHY313

mailto:[email protected]


Example: decay at rest

e

e

Note helicities of neutrinos

Note: helicity of e+ due

to neutrino helicities

ee

Note: μ spin aligned to theright

The spin & helicity of the electron neutrino takes away the spin & helicity of the . The spin & helicity of the positron cancels the spin & helicity of the anti-neutrino


Example: - decay at rest

e

e

Note helicities of neutrinos

Note: helicity of edue to neutrino helicities

ee

:Note μ spin aligned to the left

The fact that the neutrino always spins

with a left hand screw allows to

differentiate between the real world and .the mirror world


Proof of direct CP violation in B-decay

• The difference between the lifetimes of the B0 and its antiparticle, the B0-bar, is clearly visible. If the symmetry between particle and antiparticle were complete, these lifetimes would be identical.

• The observed CP violation is in agreement with the Standard Model.


How many building blocks are there ?

• There are 6 quarks and 6 antiquarks• Each quark occurs in 3 colors.• The antiquarks have the opposite charge

of the related quarks.For example the u quark has q = +2/3x eThe u-bar quark has q = -2/3 x e

• So there are 36 different quarks.

• There are 6 leptons and 6 antileptons.• The antileptons have the opposite charge

of the related leptons.– For example the muon has q = - e– The antimuon has q = +e

• There are NO colors in the lepton sector.• So there are 12 different leptons

: Reminder this is thebasic box


Gauge Symmetry

• Physically relevant variables must be independent of the choice of the local frames of measurement.

• The principal answer of a calculation should not depend on whether a length is measured in inches here and in cm there (even if the numerical value does). The description of a result should not depend on the measuring “gauge”.

• Gauge transformations transform a description of a solution at one point in space to another description in another point in space.

• “My work always tried to unite the truth with the beautiful, but when I had to choose one or the other, I usually chose the beautiful.”

•Herman Weyl;

the master of symmetries


Gauge Invariance

• Description A of the moving system must transform uniquely into Description B describing the same phenomenon in a different frame with a different “gauge”.

• This is a powerful requirement that underlies almost all basic physical theories. For example:

1. It requires that there should be force carrying Bosons for each gauge invariant interaction, such as the Photon, the W±, the Z0.

2. Therefore these Bosons are also called Gauge Bosons.

Moving system

Frame BFrame A

GaugeTransformatio

n

,x t

He usescentimeter

s

Sheuses

inches


Why are Symmetries important in Physics

• Symmetries that exist in Nature impose a general structure on the equations that describe Nature.

• Gauge Invariance alone completely determines e.g. the basic equations for the Electromagnetic Theory (Maxwell’s Equations) and the QCD equation.

• Often symmetries exist in an ideal world but then are broken in the real world. Such symmetries are called “Hidden Symmetries”.

• In mathematical terms the Standard Model has the symmetrySU(3) x SU(2) x U(1)

1. SU(3) is the Symmetric Unitary Group with 3 colors. As we know this requires 8 gluons (the gauge bosons of the strong interaction) to carry color between quarks.

2. S(2) x U(1) is the symmetry associated with the Electro-weak theory. It contains the gauge Bosons W, Z0 and . This symmetry is badly broken as can be seen form the fact that the Gauge Bosons have very different masses.


The Mystery of Matter: How much does the SM explain?

• Quarks and gluons well understood

• Particle and antiparticle concept well understood.

• The force carriers for Electro-weak and strong interaction are well understood, except for their masses.

• The symmetries of the Standard Model well understood: SU(3)x SU(2) U(1), but badly broken!

• We wished that all forces be unified with the same strength at a certain high energy to attain the ultimate symmetry.

And yet, they do not come together in the SM as we expect they should


EM and Weak Interaction coming together

The strengths of elastic scattering of positrons from protons through the EM interaction and the weak interaction are becoming more and more equal as the energy Q2 in the reaction increases.


Spontaneous Symmetry Breaking

• The Electro-weak force contains force carriers of very different mass:

• The photon has zero mass, the Z0 has ~ 90 GeV mass. Why is that?

• It is estimated that his mass breaking occurred at a time when the local energy in the universe was ~ 200 GeV (“the weak energy scale” ).

• Something must have given mass to the Z0 and the W±, but left the photon alone.

• The Higgs process was “invented” to produce this effect.


The Higgs Particle• In a perfectly symmetric world all

Gauge Bosons and all quarks and leptons would have zero mass.

• But the SU(2)U(1) symmetry is “hidden”: It reveals itself only at much higher energy of ~ 1016 GeV.

• Mr. Higgs in 1966 introduced a background “field”, a molasses condensate, that permeates space everywhere and puts a drag on the W and Z Bosons, and other particles, like the quarks.

• The Higgs particle (or particles) are the excitations, or wiggles, in that molasses. In the SM one Higgs can do the job.

• Peter Higgs from Edinburgh

A famous guest traveling

through a crowd is slowed down

by peopleaggregating

.around her


Where Does Mass Come From?

• We fill the vacuum with some sludge. A particle’s mass is then proportional to the amount each particle couples to this sludge.

• The sludge is the everywhere constant vacuum value of the neutral Higgs.

• Three extra Higgs fields, H+, H-, anti-H0 make up the extra component of the W and Z spins needed to make them massive.

• The W’s have a mass of 81 GeV, and the Z of 90 GeV.

• The H0 has a constant vacuum density, and can also make a physical particle

H

H

H

H 0

0,


How various particles get mass in SUSY

Each particle plotted at the energy of its current mass couples to the Higgs Boson which lies around 115 GeV.

Shown are the lepton (t), the charmed quark ©, the b-quark, the Gauge Bosons Z0 and W, and the heaviest particle, the top quark.


A problem with the Higgs field


The mass of the Higgs Particle

Particles can interact with heavy particles that are hidden in the vacuum. In tis example the 5-GeV B0 meson feels the presence of the 90 GeV W± particles. These virtual particles affect the energy of the real particle. In turn from the energy of the real particle we can deduce approximately the mass of the virtual particle.

!


Fermions and Bosons

• Nature seems to contain two distinct families of particles: Those with half-integer spin are called Fermions.

• Most of the fundamental Fermions have spin 1/2, such as electron and positron and all other leptons, all quarks and antiquarks.

• Fermions obey the Pauli principle: No two Fermions can have exactly the same quantum numbers in a quantum system.

• Examples are electrons in atomic orbits and nucleons in nuclear orbits.

• Further examples are the quark wave functions that build up the nucleons and other Baryons. Here color provides additional differentiation.


Bosons• Particles with integer spin, such as

0 or 1 are NOT subject to the Pauli principle: An infinite number can fit into any level, for instance the lowest level of a quantum system.

• They are called Bosons, after Mr. Bose

• The most widely known Boson system is the Laser: It traps photons between two mirrors, all with the exact same wavelength, i.e. the same energy, and the same spin.

http://www.colorado.edu/physics/2000/applets/laser2.html

LhcnhchE

nL

nL

2//

/2

2/




How a Laser puts many photons into the same state.


Can Fermions and Bosons be combined: Supersymmetry

• Why are there two separate families of particles, Fermions and Bosons? In a perfect world they should be related as part of one family.

• The symmetry of this complete family is called super symmetry.

• Supersymmetry emerges naturally from String Theory.

• It achieves perfect unification of the strong and electroweak forces at ~1016 GeV

• It also allows incorporation of the gravitational force with its gauge boson, the Gravitons\.


Sparticle Names

• Thus with quarks there would be spin 0 squarks

• Leptons would have spin 0 sleptons (selectron and sneutrino)

• The photon also would have a spin ½ photino

• The W’s and Z’s would have spin ½ Winos and Zinos (after Wess and Zumino)

• Spin 0 Higgs would have spin ½ Higgsinos

• In a supergravity theory, spin 2 gravitons have spin 3/2 gravitino look-alikes.


Evolution of Gauge Couplings (reciprocals)

Standard Model Supersymmetry


Running Couplings


A list of outstanding questions• Where is the Higgs, and is there

only one or are there more? This should become evident at energies between 100 and 1000 GeV.

• Is there evidence for new super-symmetric particles? These should become evident at energies below 1 GeV.

• The Minimal Standard model violates basic principles (Unitarity) at energies ~ 1 TeV.

• Is there a heavy Boson that produces CP violation?

More far ranging:

• What is the association of quarks with the lepton cousins? Which quark relates to which lepton?

• How come the proton, which is composed of 3 quarks, each with a fractional charge, adds up to precisely the positive equal to the negative electron charge: If not, atoms would not be neutral.

If this were not the case, atoms would not be neutral!


Proposed next generation facilities

• A number of new, powerful and expensive facilities are under construction or being proposed to address these and other issues.

• We will discuss here three or four of them:

• The Large Hadron Collider under construction at CERN.

It is under construction.

• The International Linear Collider.It is in a discussion and design phase as a World Facility

• Long Baseline neutrino experiments.It is in the planning stage.

• Large underground detectors for proton decay and neutrino-less double beta decay.


History: The SSC Debacle of the 1990’s I• Already in 1978 a 20 TeV proton-proton

Collider was discussed to explore the energy and mass region near 1 TeV. This was the ill-fated Superconducting Supercollider (SSC).

• By 1984 technical design studies by ~ 150 scientists and engineers were completed.

• The basis for the collider ring were single-bore 6 Tesla superconducting high-field magnets.

• By 1986 ~ 250 scientist and engineers had prepared a Conceptual Design Report.

• The collider had a circumference of 54 miles (about the distance of the Beltway around Washington, DC)

•The costs were increasing:

In 1988 $5.3 Billion as spent;

In 1990 $5.9 Billion

In 1991 $ 8.25 Billion

Finally $ 11.8 Billion

.


The SSC Debacle II

• In 1987 President Reagan made the decision to proceed with construction of the SSC, funded as a national US project.

• A site selection process produced 35 viable proposals.

• A site 16,000 acre site in Waxahachie, TX, was chosen in March 1990. The State of Texas contributed as much as ~$1 Billion toward the facility. A magnet facility of 200,000 sqft area was set up to produce 25 magnets/day. The tunnel was being bored

• In 1990 several specifications were changed to a more conservative design: Doubling the injection energy from 1 TeV to 2 TeV, and increasing the aperture from 4cm to 5cm. This increased the cost.

• On Oct. 28 1993. President Clinton cancelled the project


The Large Hadron Collider

• The LHC is a 14 TeV proton on proton collider, build at CERN near Geneva, Switzerland.

• Each proton consists of 3 quarks, so that only 1/9th of energy is available in quark on quark collisions.

• The heaviest mass that can be produced in collision is ~ 3 TeV. This is sufficient to find Higgs, supersymmetric particles, such as squarks and gluinos.

The LHC runs deep underneath the city of

Geneva and its.suburbs


Proton beams are really quark beams


The LHC deep underground

• The LHC uses the available smaller accelerators as injectors.

• It serves three detectors; ATLAS, CVMS and Alice.

• The U.S> has contributed about $ 800 Million to ATLAS and CMS.

• The accelerator is under intense construction and scheduled to start operation in June 22007.

• http://www.CERN.ch

http://www.cern.c/

http://www.cern.c/


The superconducting magnets, the tunnel


The ATLAS Detector


ATLAS being assembled


The decay of the Higgs


Eleventh Homework Set, due April 28, 2005

1. Describe briefly the differences between Fermions and Bosons.

2. Explain what Gauge symmetry stipulates.

3. By whom, when and where was the mechanism invented that can give mass to the elementary particles?

4. What particles does the Large Hadron Collider (LHC) accelerate and to what energy. Where is it being built?

5. Give at least one scientific goal for the LHC.

6. What are the supersymmetric partners of quarks and gluons?

Peter Paul 04/21/05PHY313-CEI544 Spring-051 PHY313 - CEI544 The Mystery of Matter From Quarks to the...

Documents

Transcript of Peter Paul 04/21/05PHY313-CEI544 Spring-051 PHY313 - CEI544 The Mystery of Matter From Quarks to the...