Friday, November 21, 2008

QCD - The Source of Everyday Mass

Reported in this week's issue of Science, a new ab initio theoretical calculation using lattice QCD has produced a good agreement between the mass of various nucleons and other hadrons. This work was done by Durr et al.[1]

As reviewed in the Perspective by Andreas S. Kronfeld in the same issue of Science, this means that the source of our everyday mass lies in QCD.

Almost all of the mass (or weight) of the world we live in comes from atomic nuclei, which are composed of neutrons and protons (collectively called "nucleons"). Nucleons, in turn, are composed of particles called quarks and gluons, and physicists have long believed that the nucleon's mass comes from the complicated way in which gluons bind the quarks to each other, according to the laws of quantum chromodynamics (QCD). A challenge since the introduction of QCD has been to carry out an ab initio calculation of the nucleon's mass. On page 1224 of this issue, Dürr et al. (4) report the first such calculation that incorporates all of the needed physics, controls the numerical approximations, and presents a thorough error budget. Because these accurate calculations agree with laboratory measurements, we now know, rather than just believe, that the source of mass of everyday matter is QCD.


It is now up to the LHC to show that this premise is correct.

Dürr et al. start with QCD's defining equations and present a persuasive, complete, and direct demonstration that QCD generates the mass of the nucleon and of several other hadrons. These calculations teach us that even if the quark masses vanished, the nucleon mass would not change much, a phenomenon sometimes called "mass without mass" (19, 20). It then raises the question of the origin of the tiny up and down quark masses. The way nature generates these masses, and the even tinier electron mass, is the subject of the LHC, where physicists will explore whether the responsible mechanism is the Higgs boson or something more spectacular.


Edit: there's a coverage of this on Nature's daily news. {the link is open for free only for a limited time}

Zz.

[1] S. Dürr et al., Science v.322, p.1224 (2008).

1 comment:

budakfisika said...

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thanks