Transcript PHY313 - CEI544 The Mystery of Matter From Quarks to the

PHY313 - CEI544
The Mystery of Matter
From Quarks to the Cosmos
Spring 2005
Peter Paul
Office Physics D-143
www.physics.sunysb.edu PHY313
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Example:  decay at rest
  e  e  


Note: μ spin aligned to the right

e
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

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



e
Note helicities
of neutrinos
Note: helicity of e+ due
to neutrino helicities
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Example: - decay at rest
   e  e  
Note: μ spin aligned to the left



e
The fact that the neutrino
always spins with a left
hand screw allows to
differentiate between the
real world and the mirror
world.

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

e

Note helicities
of neutrinos
Note: helicity of e due
to neutrino helicities
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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.
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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 e
The 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
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Reminder: this is the basic
box
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Gauge Symmetry
• Physically relevant variables must
• “My work always tried to unite the
be independent of the choice of the
truth with the beautiful, but when I
local frames of measurement.
had to choose one or the other, I
usually chose the beautiful.”
• The principal answer of a
calculation should not depend on
•
Herman Weyl;
whether a length is measured in
inches here and in cm there (even if
the master of symmetries
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.
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Gauge Invariance
• Description A of the moving system
x, t
must transform uniquely into
Description B describing the same
phenomenon in a different frame with a
Moving system
different “gauge”.
• This is a powerful requirement that
Frame A
Frame B
underlies almost all basic physical
theories. For example:
1. It requires that there should be force
Gauge
carrying Bosons for each gauge
Transformation
invariant interaction, such as the Photon,
the W±, the Z0.
2. Therefore these Bosons are also called
He uses
She uses
Gauge Bosons.
centimeters
inches
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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”.
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•
In mathematical terms the
Standard Model has the symmetry
SU(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.
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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.
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And yet, they do not come together
in the SM as we expect they should
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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.
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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.
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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.
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• Peter Higgs
from Edinburgh
A famous guest
traveling through
a crowd is slowed
down by people
aggregating
around her.
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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-
•
•
H  H 

, 

H0  H 




0
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
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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.
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A problem with the Higgs field
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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.
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Fermions and Bosons
• Examples are electrons in atomic orbits
• Nature seems to contain two
and nucleons in nuclear orbits.
distinct families of particles:
• Further examples are the quark wave
Those with half-integer spin are
functions that build up the nucleons and
called Fermions.
other Baryons. Here color provides
• Most of the fundamental Fermions
additional differentiation.
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.
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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.
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http://www.colorado.edu/physics/2000/a
pplets/laser2.html
L  n / 2
  2L / n
E  h  hc /   hcn / 2 L
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How a Laser puts many photons into the same state.
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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\.
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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 lookalikes.
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Evolution of Gauge Couplings (reciprocals)
Standard Model
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Supersymmetry
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Running Couplings
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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 supersymmetric 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?
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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!
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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.
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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 singlebore 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)
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•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
.
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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
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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.
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Proton beams are really quark beams
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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
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The superconducting magnets, the tunnel
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The ATLAS Detector
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ATLAS being assembled
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The decay of the Higgs
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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?
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