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The Upsilon spectrum and m_b from full lattice QCD

High Energy Physics - Lattice · Submitted 13 Jul 2005 · 54 references

Pith's verdict: First bottomonium spectrum and bottom mass from 2+1-flavor lattice QCD; the scale-consistency argument is the real result, and the m_b error bar is the part to argue about.

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arXiv IDhep-lat/0507013 (version 2)
Pith IDBW2Q3EFA, Pith's permanent record of this paper and its review
CitationA.Gray, C. T. H. Davies, E. Gulez, G. P. Lepage, I. Allison, J. Shigemitsu, M. Wingate. "The Upsilon spectrum and m_b from full lattice QCD." arXiv:hep-lat/0507013 (2005). https://pith.science/paper/BW2Q3EFA
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Referee report
The paper

The paper claims

With light and strange quark vacuum polarization included, two independent splittings in the Upsilon spectrum finally agree on a single lattice spacing, and the same bare bottom mass reproduces both the Upsilon and the B_s meson.

The reading

Lattice QCD has a long-standing embarrassment: different quantities used to fix the lattice spacing give different answers, so predictions cannot be made unambiguously. This paper argues that the fault lies with the sea-quark content of the simulation, not with the method. Using gluon configurations that include vacuum polarization from up, down and strange quarks, the authors compute the Upsilon spectrum with nonrelativistic bottom quarks and find that the orbital $1P-1S$ and radial $2S-1S$ splittings give the same lattice spacing, whereas the quenched approximation gives answers differing by about 9 percent. If that is right, the parameters of QCD can be fixed consistently for the first time, and the payoff is a bottom quark mass from full lattice QCD, $m_b^{MSbar}(m_b^{MSbar}) = 4.4(3)$ GeV, together with physical values for the heavy-quark potential scales $r_0 = 0.469(7)$ fm and $r_1 = 0.321(5)$ fm.

What carries the argument

The load-bearing device is a consistency test rather than a single number: two spin-independent splittings in the same meson family, one orbital and one radial, are each matched to experiment to give an inverse lattice spacing, and the ratio of the two answers is examined as a function of sea quark mass and lattice spacing. The bottom quarks are handled by lattice nonrelativistic QCD through next-to-leading order in $v^2$, with the relativistic, radiative and discretisation corrections estimated term by term and tabulated, so that the reader can see which uncertainty dominates at each lattice spacing. The same bare bottom mass then feeds the heavy-light sector, where the $B_s$ mass is extracted from a dispersion relation, making the Upsilon and B sectors a joint test rather than two separate calculations.

Extended reading notes

Core claim

The central claim is that a simulation with realistic sea quarks restores internal consistency to the bottomonium spectrum. On the coarse 2+1-flavor ensembles the ratio of the inverse lattice spacing from $2S-1S$ to that from $1P-1S$ is $0.984(20)(34)$; on the fine ensembles it is $1.021(23)(13)$; on quenched ensembles the same ratio is about $1.09$. Since the lattice spacing should be unique, the quenched disagreement was a symptom of missing quark vacuum polarization, and its disappearance is the paper's evidence that the 2+1-flavor configurations are close enough to the real world to fix QCD's parameters. The authors then show that the bare bottom mass tuned to reproduce the Upsilon mass also reproduces the $B_s$ mass to within the quoted errors, and convert the bare mass to the $MSbar$ scheme at one loop, obtaining $m_b^{MSbar}(m_b^{MSbar}) = 4.4(3)$ GeV. Along the way they quote predictions for states not yet measured: $M_ ext{Upsilon} - M_{eta_b} = 61(14)$ MeV, $M_{ ext{Upsilon}'} - M_{eta_b'} = 30(19)$ MeV, and a splitting between the $h_b$ and the spin average of the $chi_b$ states below 6 MeV.

Load-bearing premise

The step from the bare lattice bottom mass to the quoted $MSbar$ value rests on one-loop perturbative matching evaluated at a scale $mu = 2/a$ chosen by hand to make the first-order coefficient small, with the quoted error being an estimate of the uncomputed next-order terms rather than a calculated bound.

Editorial extensions

If this is right

  • The lattice spacing can be fixed from the Upsilon $2S-1S$ splitting without the ambiguity that plagued quenched calculations, so dimensionful predictions from these ensembles become well defined.
  • A bottom quark mass in the $MSbar$ scheme, $4.4(3)$ GeV, follows from one-loop matching of the bare lattice mass, removing the roughly 30 percent spread between bottom masses used in separate quenched Upsilon and B analyses.
  • The $B_s$ mass comes out about 4 percent high, within one standard deviation, when the bottom mass is fixed from the Upsilon, which is the check that the same parameters describe both sectors.
  • The heavy-quark potential scales come out as $r_0 = 0.469(7)$ fm and $r_1 = 0.321(5)$ fm, giving other lattice calculations a common ruler tied to an experimentally measured splitting.
  • The predicted $eta_b$ mass of 9.399(14) GeV and the near-degeneracy of the $h_b$ with the $chi_b$ spin average are concrete targets for experiment.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • If the consistency of the two splittings really is driven by sea-quark content rather than by the improved gluon action or the improved operators, then other quantities that disagreed in the quenched approximation, such as the charmonium spectrum and heavy-light decay constants, should show the same repair on these ensembles.
  • The prediction that the $h_b$ lies within 6 MeV of the $chi_b$ spin average is a sharp test that does not depend on the overall scale, so a future measurement of the $h_b$ mass would probe the spin-dependent part of the nonrelativistic action almost independently of the tuning.
  • Because the quoted $4.4(3)$ GeV error is an estimate of uncomputed higher-order matching terms rather than a derived bound, the same ensembles combined with a two-loop self-energy calculation would convert this result from a plausible central value into a controlled one.
  • The pattern here, where a long-standing discrepancy between two scale determinations dissolves once the sea-quark content is realistic, suggests that other reported tensions between lattice observables should first be checked against sea-quark content before being attributed to the discretisation or the effective theory.
Original abstract

We show results for the Upsilon spectrum calculated in lattice QCD including for the first time vacuum polarization effects for light u and d quarks as well as s quarks. We use gluon field configurations generated by the MILC collaboration. The calculations compare the results for a variety of u and d quark masses, as well as making a comparison to quenched results (in which quark vacuum polarisation is ignored) and results with only u and d quarks. The b quarks in the Upsilon are treated in lattice Nonrelativistic QCD through NLO in an expansion in the velocity of the b quark. We concentrate on accurate results for orbital and radial splittings where we see clear agreement with experiment once u, d and s quark vacuum polarisation effects are included. This now allows a consistent determination of the parameters of QCD. We demonstrate this consistency through the agreement of the Upsilon and B spectrum using the same lattice bare b quark mass. A one-loop matching to continuum QCD gives a value for the b quark mass in full lattice QCD for the first time. We obtain m_b^{\bar{MS}}(m_b^{\bar{MS}}) = 4.4(3) GeV. We are able to give physical results for the heavy quark potential parameters, r_0 = 0.469(7) fm and r_1 = 0.321(5) fm. Results for the fine structure in the spectrum and the Upsilon leptonic width are also presented. We predict the Upsilon - eta_b splitting to be 61(14) MeV, the Upsilon^{\prime} - eta_b^{\prime} splitting as 30(19) MeV and the splitting between the h_b and the spin-average of the chi_b states to be less than 6 MeV. Improvements to these calculations that will be made in the near future are discussed.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13-20260917 via OpenRouter, question bank abstract-p1-20260923, 2026-09-23: 1 request, 9,642 input tokens, $0.0004 reported.

What the abstract itself states, as probabilities: claims first 0.90 · states limitation 0.57 · human participants 0.01 · controlled comparison 0.83 · randomized assignment 0.01 · states quantitative result 0.99 · compares with prior results 0.97 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v2. Results and the main claim are underlined; .

We show results for the Upsilon spectrum calculated in lattice QCD including for the first time vacuum polarization effects for light u and d quarks as well as s quarks. We use gluon field configurations generated by the MILC collaboration. The calculations compare the results for a variety of u and d quark masses, as well as making a comparison to quenched results (in which quark vacuum polarisation is ignored) and results with only u and d quarks. The b quarks in the Upsilon are treated in lattice Nonrelativistic QCD through NLO in an expansion in the velocity of the b quark. We concentrate on accurate results for orbital and radial splittings where we see clear agreement with experiment once u, d and s quark vacuum polarisation effects are included. This now allows a consistent determination of the parameters of QCD. We demonstrate this consistency through the agreement of the Upsilon and B spectrum using the same lattice bare b quark mass. A one-loop matching to continuum QCD gives a value for the b quark mass in full lattice QCD for the first time. We obtain m_b^{\bar{MS}}(m_b^{\bar{MS}}) = 4.4(3) GeV. We are able to give physical results for the heavy quark potential parameters, r_0 = 0.469(7) fm and r_1 = 0.321(5) fm. Results for the fine structure in the spectrum and the Upsilon leptonic width are also presented. We predict the Upsilon - eta_b splitting to be 61(14) MeV, the Upsilon^{\prime} - eta_b^{\prime} splitting as 30(19) MeV and the splitting between the h_b and the spin-average of the chi_b states to be less than 6 MeV. Improvements to these calculations that will be made in the near future are discussed.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 We show results for the Upsilon spectrum calculated in lattice QCD including for the first time vacuum polarization effects for light u and d quarks as well as s quarks. contribution 0.99 0.96 0.17 asserted 1.00
s1 We use gluon field configurations generated by the MILC collaboration. method 1.00 0.34 0.01 asserted 1.00
s2 The calculations compare the results for a variety of u and d quark masses, as well as making a comparison to quenched results (in which quark vacuum polarisation is ignored) and results with only u and d quarks. method 0.86 0.89 0.05 asserted 0.96
s3 The b quarks in the Upsilon are treated in lattice Nonrelativistic QCD through NLO in an expansion in the velocity of the b quark. method 1.00 0.79 0.04 asserted 1.00
s4 We concentrate on accurate results for orbital and radial splittings where we see clear agreement with experiment once u, d and s quark vacuum polarisation effects are included. result 0.90 0.96 0.41 asserted 1.00
s5 This now allows a consistent determination of the parameters of QCD. interpretation 0.98 0.52 0.26 asserted 0.92
s6 We demonstrate this consistency through the agreement of the Upsilon and B spectrum using the same lattice bare b quark mass. result 0.64 0.94 0.15 asserted 1.00
s7 A one-loop matching to continuum QCD gives a value for the b quark mass in full lattice QCD for the first time. contribution 0.62 0.94 0.19 asserted 1.00
s8 We obtain m_b^{\bar{MS}}(m_b^{\bar{MS}}) = 4.4(3) GeV. result 1.00 0.97 0.30 asserted 1.00
s9 We are able to give physical results for the heavy quark potential parameters, r_0 = 0.469(7) fm and r_1 = 0.321(5) fm. result 1.00 0.96 0.08 asserted 1.00
s10 Results for the fine structure in the spectrum and the Upsilon leptonic width are also presented. result 0.76 0.91 0.03 asserted 0.99
s11 We predict the Upsilon - eta_b splitting to be 61(14) MeV, the Upsilon^{\prime} - eta_b^{\prime} splitting as 30(19) MeV and the splitting between the h_b and the spin-average of the chi_b states to be less than 6 MeV. result 1.00 0.94 0.08 asserted 0.93
s12 Improvements to these calculations that will be made in the near future are discussed. future work 1.00 0.24 0.02 asserted 0.55

What kind of paper the classifier reports this is: simulation study 1.00 · evidence from simulation or computation 1.00.

What was examined, and what was not

sources read
  • arXiv listing abstract v2
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. FIG. 1: Dependence of Υ energy splittings on change in
Figure 2. FIG. 2: Υ energies in lattice units as a function of number
Figure 3. FIG. 3: The ratio of lattice spacing values obtained from the
Figure 4. FIG. 4: The value of
Figure 6. FIG. 6: Spin-independent splittings in the Υ spectrum as a
Figure 8. FIG. 8: The value of the Υ mass in physical units plotted
Figure 10. FIG. 10: The perturbative estimate of the shift between mass
Figure 11. FIG. 11: The value of the
Figure 13. FIG. 13: The ratio of the splitting between the Υ
Figure 14. FIG. 14: The ground-state hyperfine splitting in the Υ system
Figure 15. FIG. 15: Hyperfine splittings in the Υ and
Figure 16. plots the lattice results for the ground state P-wave splittings, each relative to the spin average. We use the 2S−1S lattice spacing values to convert to physi￾cal units. The plot shows the coarse and fine unquenched and fine quenched results only since the results on the super-coarse ensemble have error bars which are too large to be useful, although they are consistent with the others. The Figure shows that the size of the quenched P-wave splittings are smaller than experiment. The results on the coarse 2+1 flavor configurations look consistent with -60 -40 -20 0 20 40 60 MeV…
Figure 17. FIG. 17: The ratio of leptonic width times mass squared for
Figure 18. FIG. 18: The dependence on
Figure 19. FIG. 19: The ratio of lattice results to experiment for var

Showing 15 of the paper's 19 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:hep-lat/0507013 by the authors.

References
How the literature uses it

49 arXiv papers cite this in 90 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers citing it · 36 sentences without a confident label

Builds on it 1 paper
Uses its method or tool 9 papers
Uses its data or values 13 papers
Compares with it 11 papers
Cites it as background 10 papers

Discussion

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