Tuesday, October 14, 2014

The Latest Lattice QCD Quark and Meson Mass Conclusions

Using the physical masses of Ds, Ds and J/ψ as inputs, Sommer's scale parameter r0 ... the masses of charm quark and strange quark in the MS scheme are determined to be r0=0.458(11)(8) fm, mMSc(2GeV)=1.111(12)(22) GeV (or mMSc(mc) = 1.291(10)(18) GeV), and mMSs(2GeV)=0.103(6)(8)GeV, respectively. Furthermore, we observe that the mass difference of the vector meson and the pseudoscalar meson with the same valence quark contents is proportional to the reciprocal of the square root of the valence quark masses.
From here.

These results are consistent with (at a 1 sigma level), but at the high end of, existing global average experimental values, and other recent lattice QCD calculations, although neither of the new estimates is record setting in its precision.

The pole mass of the charm quark is 1.291(21) GeV, compared to the value of PDG 1.275(25) GeV. Another recent lattice QCD analysis claimed that the charm quark mass was 1.273(6) GeV.

The strange quark mass (for which the pole mass is ill defined) is 0.103(10) GeV, compared to the PDG value of 0.095(5) GeV. Most strange quark mass estimates are below the mass of the muon, which is 0.1056583715(35) GeV, but it is not entirely certain that the mass of the muon is greater than (or different from) the appropriately defined mass of the strange quark. Two other recent lattice QCD determinations of the strange quark mass came up with 0.094(9) GeV and 0.992(39) GeV, respectively.

The relationship discussed between vector meson (i.e. spin-1 odd parity mesons) masses and pseudoscalar meson (i.e. spin-0 odd parity) masses in bold in the quoted material above appears to be a novel observation. I will have to read the paper more closely to clarify if this is merely an empirical observation or exists for some deeper reason.

There are two other grounds states of mesons - pseudovector aka axial vector mesons (i.e. spin-1 even parity), and scalar mesons (i.e. spin-0 even parity) that do not readily fit simple quark models of mesons.

Meanwhile, the final combined top quark mass measurement from Fermilab including all data through its shutdown from both experiments is 174.34(64) GeV.

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