The Mudcat Café TM
Thread #59418   Message #1483753
Posted By: Amos
12-May-05 - 08:45 PM
Thread Name: BS: The Mother of all BS threads
Subject: RE: BS: The Mother of all BS threads
Looks like Gluon has gone and gotten a job!

theoretical physicists have produced the best prediction of a
particle's mass. And within days of their paper being submitted to
Physical Review Letters, that very particle's mass was accurately
measured at Fermilab, providing striking confirmation of the
predicted value. How do the known particles acquire the mass they
have? The answer might come from lattice QCD, the name for a
computational approach to understanding how quarks interact.
Imagine quarks placed at the interstices of a crystal-like
structure. Then let the quarks interact with each other via the
exchange of gluons along the links between the quarks. The gluons
are the designated carriers of the strong nuclear force under the
general auspices of the theory called quantum chromodynamics (QCD).
From this sort of framework the mass of the known hadrons
(quark-containing composite particles such as mesons and baryons)
can be calculated. Until recently, however, the calculations were
marred by a crude approximation. A big improvement came only in
2003, when uncertainties in mass predictions went from the 10% level
to the 2% level (see Davies et al., Physical Review Letters, 16
January 2004). The mass of the proton, for example, could be
calculated within a few percent of the actual value. Progress has
come from a better treatment of the light quarks and from greater
computer power. Together the improvements provide the researchers
with a realistic treatment of the "sea quarks," the virtual
quarks whose ephemeral presence has a noticeable influence over the
"valence" quarks that are considered the nominal constituents of a
hadron. A proton, for example, is said to consist of three valence
quarks---two up quarks and one down quark---plus a myriad of sea
quarks that momentarily pop into existence in pairs. Now, for the
first time, the mass of a hadron has been predicted with lattice
QCD. Andreas Kronfeld (, 630-840-3753) and his
colleagues at Fermilab, Glasgow University, and Ohio State report a
mass calculation for the charmed B meson (Bc, for short, consisting
of an anti-bottom quark and a charmed quark). The value they
predict is 6304 +/- 20 MeV---the remarkable precision stems not only
from the improvements discussed above, but also from the
researchers' methods for treating heavy quarks. A few days after
they submitted their Letter for publication, the first good
experimental measurement of the same particle was announced 6287 +/-
5 MeV. This successful confirmation is exciting, because it
bolsters confidence that lattice QCD can be used to calculate many
other properties of hadrons. (Allison et al., Physical Review
Letters,6 May 2005, Lattice QCD website at )