| Topic: |
Science > Physics |
| User: |
"Robert Karl Stonjek" |
| Date: |
06 Aug 2005 03:44:09 PM |
| Object: |
Article: Prediction of a Composite Particle Mass |
PREDICTION OF A COMPOSITE PARTICLE MASS
The following points are made by Ian Shipsey (Nature 2005 436:186):
1) The endeavor of particle physicists to understand the birth, evolution,
and ultimate fate of the Universe by studying its fundamental particles has
recently received a significant boost. The difficult equations of the strong
nuclear force have yielded to a 30-year effort to allow the first precise
prediction of a composite particle's mass[1], a prediction promptly
confirmed by experiment[2]. The computational technique responsible, lattice
quantum chromodynamics, could also be used to estimate quark masses better,
to shed light on the origin of mass, and to reveal how the Universe,
originally made of matter and antimatter in equal proportions, ended up
containing just matter.
2) The "standard model" of particle physics describes the interaction of
fundamental particles, such as quarks and electrons, as the exchange of
other particles that convey force. In an atom, for example, electrons bind
to protons by swapping massless photons -- the familiar electromagnetic
force encompassed by the theory of quantum electrodynamics (QED). Similarly,
inside the proton, "up" and "down" quarks bind by exchanging massless
particles called gluons -- an interaction described by the so-called strong
force and the theory of quantum chromodynamics (QCD). Without this strong
force, which not only binds quarks to form protons, but also keeps protons
together in the nucleus, matter would simply fall apart.
3) The fundamental particles possess a wide range of masses: an electron is
about 360,000 times lighter than the heaviest, or "top", quark. In the
standard model, the origin of the mass of fundamental particles is the
yet-to-be-discovered Higgs force field. The reason electrons and quarks have
the exact masses that they do must, however, come from a deeper theory of
nature. Physicists hope that gaining knowledge of the quark masses will
guide them to that theory.
4) As quarks are permanently bound into composite particles, it is not
possible to determine their masses directly. Theorists instead solve the
equations of QCD for a composite particle made up of quarks (protons and
neutrons are examples) with the quark masses and strength of the strong
force as unknowns. The most likely value of a quark mass is that which best
reproduces the measured mass of the composite particle. As energy is related
to mass through E=mc^(2), where m is the mass of the particle and c the
speed of light, this mass depends not only on the mass of the constituent
quarks, but also on the bonds between them (potential energy) and their
motion (kinetic energy).[3-5]
References (abridged):
1. Allison, I. et al. Phys. Rev. Lett. 94, 172001 (2005)
2. Acosta, D. et al. Phys. Rev. Lett. (submitted); preprint at
http://www.arxiv.org/hep-ex/0505076
3. Davies, C. T. H. et al. Phys. Rev. Lett. 92 022001 (2004)
4. Shipsey, I. et al. Nature 427 591-592 (2004)
5. Aubin, C. et al. Phys. Rev. Lett. (submitted); preprint at
http://www.arxiv.org/hep-lat/0506030 (2005)
Nature http://www.nature.com/nature
From ScienceWeek
http://scienceweek.com/2005/sw050812-1.htm
--
Posted by
Robert Karl Stonjek
.
|
|
| User: "Bjoern Feuerbacher" |
|
| Title: Re: Article: Prediction of a Composite Particle Mass |
08 Aug 2005 05:25:19 AM |
|
|
Robert Karl Stonjek wrote:
PREDICTION OF A COMPOSITE PARTICLE MASS
The following points are made by Ian Shipsey (Nature 2005 436:186):
1) The endeavor of particle physicists to understand the birth, evolution,
and ultimate fate of the Universe by studying its fundamental particles has
recently received a significant boost. The difficult equations of the strong
nuclear force have yielded to a 30-year effort to allow the first precise
prediction of a composite particle's mass[1], a prediction promptly
confirmed by experiment[2].
This was already reported by Sam Wormley, I think about two weeks ago.
The computational technique responsible, lattice
quantum chromodynamics, could also be used to estimate quark masses better,
Right.
to shed light on the origin of mass, and to reveal how the Universe,
originally made of matter and antimatter in equal proportions, ended up
containing just matter.
I don't see the relationship of lattice QCD to that... Does he perhaps
mean lattice QFT calculations in general?
[snip]
Bye,
Bjoern
.
|
|
|
|
|
Related Articles |
|
|
