What is the Standard Model

From: Patrick Reany (reany_at_asu.edu)
Date: 06/12/04 

Date: 12 Jun 2004 10:07:36 -0700

Recently, Bilge and I had a disagreement about what is meant by the
so-called Standard Model of particle physics. What I'm interested in
is the opinions of the readership about what they feel it means.
Please choose from the choices below:

1) The Standard Model refers to the consensus of the best estimate at
any given moment of the behavior of particles from a quantum
mechanical viewpoint which includes electroweak and stong force
particles; this consensus includes specifying particles mass of all
"known" particles. Thus the Standard Model is a theory, not just a
framework.

2) The Standard Model refers to the consensus of the best fixed
framework to theorize about the behavior of particles from a quantum
mechanical viewpoint which includes electroweak and stong force
particles; this consensus does NOT include specifying all particles
mass. In other words, the Standard Model is a research program's
formal point of view (a framework only, not a theory), which is itself
incapable of making predictions until the masses are set independently
of the framework.

3) Other. Please explain in detail.

**********************************************

Now, for some on-line references:

http://www2.slac.stanford.edu/vvc/theory/model.html

The Standard Model
The Standard Model is the name given to the current theory of
fundamental particles and how they interact. This theory includes:

Strong interactions due to the color charges of quarks and gluons.
A combined theory of weak and electromagnetic interaction, known as
electroweak theory, that introduces W and Z bosons as the carrier
particles of weak processes, and photons as mediators to
electromagnetic interactions.
The theory does not include the effects of gravitational interactions.
These effects are tiny under high-energy Physics situations, and can
be neglected in describing the experiments. Eventually, we seek a
theory that also includes a correct quantum version of gravitational
interactions, but this is not yet achieved.

The Standard Model was the triumph of particle physics of the 1970's
. It incorporated all that was known at that time and has since then
successfully predicted the outcome of a large variety of experiments.
Today, the Standard Model is a well established theory applicable over
a wide range of conditions.

-----------------------------------------------------

http://particleadventure.org/particleadventure/frameless/standard_model.html

Physicists have developed a theory called The Standard Model that
explains what the world is and what holds it together. It is a simple
and comprehensive theory that explains all the hundreds of particles
and complex interactions with only:

6 quarks.
6 leptons. The best-known lepton is the electron. We will talk about
leptons in just a few pages.
Force carrier particles, like the photon. We will talk about these
particles later.

-----------------------------------------------------
http://en.wikipedia.org/wiki/Standard_Model

The Standard Model of particle physics is a theory which describes the
strong, weak, and electromagnetic fundamental forces, as well as the
fundamental particles that make up all matter. It is a quantum field
theory, and consistent with both quantum mechanics and special
relativity. To date, almost all experimental tests of the three forces
described by the Standard Model have agreed with its predictions.
However, the Standard Model is not a complete theory of fundamental
interactions, primarily because it does not describe gravity..........

Although the Standard Model has had great success in explaining
experimental results, it has never been accepted as a complete theory
of fundamental physics. This is because it has two important defects:

The model contains 19 free parameters, such as particle masses, which
must be determined experimentally (plus another 10 for neutrino
masses). These parameters cannot be independently calculated.

[My comment: I doubt that the particle masses are uniquely determined
by experiment.]

-----------------------------------------------------
http://www.lns.cornell.edu/public/lab-info/quark.html ******

In recent years, high energy physicists have arrived at a picture of
the microscopic physical universe, called "The Standard Model", which
unifies the nuclear, electromagnetic, and weak forces and enumerates
the fundamental building blocks of the universe:

6 leptons:
electron, electron neutrino
muon, muon neutrino
tau, tau neutrino
6 quarks:
d (down), u (up)
s (strange), c (charm)
b (bottom), t (top)
Ordinary matter is made of protons (each a u-u-d quark triplet),
neutrons (each a u-d-d quark triplet), and electrons. Quarks cannot
exist singly (or so it appears), so the particles created in
accelerator collisions include mesons (combinations of a quark and an
anti-quark), baryons (combinations of three quarks), and leptons. All
but the proton, electron and neutrinos are unstable and decay to the
stable particles. In the Standard Model the forces are communicated
between particles by the exchange of quanta which behave like
particles:

4 intermediate vector bosons:
gluon (nuclear force)
photon (electromagnetic force)
W and Z bosons (weak force)
In principle, the model can predict the outcome of any experiment (or
the probabilities of the various possible outcomes), but in most cases
of interest the theoretical calculations are too complicated to be
carried out with current techniques.

[My comment: If the model can predict the outcome of any experiment,
it must contain a commitment to particle masses! There seems to be
some confusion about what the "Model" really is, and it has affected
more than just me.]
-----------------------------------------------------

http://superstringtheory.com/experm/exper2.html
   
 Through a combination of theory and experiment, a mathematical model
that describes or explains all particle physics observed so far by
physicists has been worked out. This model is called the Standard
Model. From the experimental point of view, the Standard Model is
studied and confirmed so well that things are, well, almost boring.
 
[My comment: Same as last.]
-----------------------------------------------------
http://zebu.uoregon.edu/~js/glossary/standard_model.html

The Standard Model is the combination of two theories of particle
physics into a single framework to describe all interactions of
subatomic particles, except those due to gravity. The two components
of the standard model are electroweak theory, which describes
interactions via the electromagnetic and weak forces, and quantum
chromodynamics, the theory of the strong nuclear force. Both these
theories are gauge field theories, which describe the interactions
between particles in terms of the exchange of intermediary "messenger"
particles that have one unit of intrinsic angular momentum, or spin.

[My comment: framework is not a theory.]
-----------------------------------------------------

So, is the Standard Model a framework or a theory? I really don't care
which it is. I just want to know. But I will propose this: The
Standard Model ought to be considered an evolving theory which is
accountable for all experimental tests brought against it. That is, it
is capable of being formally "falsified," in which case it has to
evolve into a new "version" of the Model. But all I require is that
people not confuse a "framework for building a theory" and a theory.

Patrick

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  • Re: What is the Standard Model
    ... Let's look at what the standard model is and is not - and how it got ... Here physics takes a course that seems to be foreign to a certain ... Anyway, what we have now, is the electroweak theory as first proposed ... extension to the electroweak that includes the u and d quark along ...
    (sci.physics.relativity)
  • Re: What is the Standard Model
    ... > so-called Standard Model of particle physics. ... The Standard Model is that which is given by the Standard Model ... > mechanical viewpoint which includes electroweak and stong force ... > particles; this consensus includes specifying particles mass of all ...
    (sci.physics)
  • What is the Standard Model
    ... The Standard Model refers to the consensus of the best estimate at ... mechanical viewpoint which includes electroweak and stong force ... particles; this consensus includes specifying particles mass of all ... These effects are tiny under high-energy Physics situations, ...
    (sci.physics.relativity)