REVIEW
High precision fundamental constants at the TeV scale
High Energy Physics - Phenomenology · Submitted 19 May 2014 · 263 references
Pith's verdict: A candid 2014 status report on α_s and m_t whose diagnosis is solid and whose proposed fix is demonstrated on the wrong data.
T0 · AI review
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Referee report
The paper
The paper claims
The two most precisely quoted numbers in particle physics do not agree with themselves, and the report argues the quoted errors are too small.
The reading
What carries the argument
Two pieces of machinery carry the argument. The first is the renormalization-group evolution of $alpha_s$: because a fixed-order extraction freezes the scale near the process, while a resummed extraction already runs the coupling inside the prediction, combining results quoted at $M_Z$ mixes measurements that used different couplings to get there. The report proposes replacing weighted averaging of evolved values with a global fit directly to the running, and demonstrates it on three jet data sets, obtaining $alpha_s(M_Z) = 0.1153 pm 0.0029$ with $chi^2/text{ndof} = 1.27$. The second is the scheme-translation chain for the top mass, running from the Monte Carlo parameter through the MSR mass $m_t^{MSR}(R)$ at a low scale $R$ to the pole mass or to $m_t(m_t)$, with the scale $R$ in the range 3 to 9 GeV spanning the conceptual uncertainty. The report tabulates this conversion at $O(alpha_s^3)$ and shows that the pole mass obtained depends strongly both on the order of perturbation theory and on the scale at which the conversion is performed.
Extended reading notes
Core claim
The report's load-bearing assertion is that the precision frontier on $alpha_s$ and $m_t$ has moved past the point where the quoted uncertainties are honest. For $alpha_s$, the evidence is a table of determinations that cluster into two groups: deep-inelastic and thrust analyses near $0.113$-$0.114$, and $Z$-decay, three-jet-rate, $tau$-decay and some lattice analyses near $0.118$-$0.121$. The report states the situation directly: individual determinations quote rather small errors, yet different determinations are at best marginally compatible within those errors. It identifies candidate sources, including uncalculated NNLO corrections to jet production in PDF fits (estimated at about $0.0015$ in $alpha_s(M_Z)$), heavy-flavour scheme ambiguities of about $0.001$, and power corrections at low $Q^2$. For the top mass, the report corrects a misreading it found circulating in experimental combinations: the statement that the Monte Carlo mass may differ from the pole mass by up to 1 GeV is a mistranslation of a claim about the translation to a low-scale short-distance mass, not the pole mass. It endorses the relation $m_t^{MC} = m_t^{MSR}(3^{+6}_{-2}~text{GeV})$, under which the Tevatron average corresponds to $m_t(m_t) = 163.0 pm 1.3$ GeV in the $overline{text{MS}}$ scheme.
Load-bearing premise
The top-mass interpretation rests on identifying the Monte Carlo mass parameter with the MSR short-distance mass at a scale in the range 3 to 9 GeV, a relation the report itself calls an estimate of conceptual uncertainty that is likely not calculable, because analytic control of the generator's shower and hadronization is out of reach.
Editorial extensions
If this is right
- If the spread in $alpha_s$ reflects unquantified systematics rather than statistics, then the 2012 world average of $0.1184 pm 0.0007$ understates the true uncertainty, and every prediction that inherits that number inherits the understatement.
- The combined Tevatron and LHC value $m_t = 173.34 pm 0.76$ GeV should be read as a Monte Carlo mass parameter, corresponding to $m_t(m_t) = 163.0 pm 1.3$ GeV in the $overline{text{MS}}$ scheme under the MSR relation.
- On that reading, the measured top mass lies above the NNLO stability bound $M_t < 171.36 pm 0.46$ GeV, so the electroweak vacuum is metastable rather than absolutely stable up to the Planck scale.
- A future $e^+e^-$ threshold scan could reach an uncertainty below 100 MeV on a threshold mass, an order of magnitude better than current direct measurements, provided the NNNLO threshold calculation now in progress is brought under control.
- Measuring the ratio $R(rho_s)$ in $tbar{t}$ plus one jet, where a one percent change in $m_t$ produces a seventeen percent change in the observable near $rho_s approx 0.8$, offers a mass extraction that does not rely on the Monte Carlo mass identification.
Reading between the lines
- The $alpha_s$ and $m_t$ problems are not independent: PDF fits and the $tbar{t}$ total cross section both consume $alpha_s(M_Z)$, so a shift of $0.001$ in the coupling propagates into the extracted pole mass at the few-hundred-MeV level, which is comparable to the translation uncertainty the report is worried about.
- If the discrepancy is genuinely an observable-dependent effect rather than a statistical fluctuation, then a global fit directly to measured observables with one consistent running should return $chi^2/text{ndof}$ near one; the combined value of 1.27 quoted for the three jet data sets is a hint that the residual spread is not yet modelled rather than that the data are wrong.
- The report's own recommended remedy, a standing working group that cross-checks competing analyses, is itself testable: if the spread shrinks after such comparisons, range averaging was over-conservative; if it persists, the individual errors were underestimated.
- Since the low-scale MSR mass and the jet mass of the factorized invariant-mass distribution are conceptually the same object, a hadron-level comparison of a Monte Carlo generator against a resummed NLO+NLL calculation in the peak region would convert the 1 GeV conceptual uncertainty into a measured number.
Original abstract
This report summarizes the proceedings of the 2014 Mainz Institute for Theoretical Physics (MITP) scientific program on "High precision fundamental constants at the TeV scale". The two outstanding parameters in the Standard Model dealt with during the MITP scientific program are the strong coupling constant $\alpha_s$ and the top-quark mass $m_t$. Lacking knowledge on the value of those fundamental constants is often the limiting factor in the accuracy of theoretical predictions. The current status on $\alpha_s$ and $m_t$ has been reviewed and directions for future research have been identified.
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.
The abstract, sentence by sentence
This report summarizes the proceedings of the 2014 Mainz Institute for Theoretical Physics (MITP) scientific program on "High precision fundamental constants at the TeV scale". The two outstanding parameters in the Standard Model dealt with during the MITP scientific program are the strong coupling constant $\alpha_s$ and the top-quark mass $m_t$. Lacking knowledge on the value of those fundamental constants is often the limiting factor in the accuracy of theoretical predictions. The current status on $\alpha_s$ and $m_t$ has been reviewed and directions for future research have been identified.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | This report summarizes the proceedings of the 2014 Mainz Institute for Theoretical Physics (MITP) scientific program on "High precision fundamental constants at the TeV scale". | background 0.64 | 0.21 | 0.03 | asserted 0.97 |
| s1 | The two outstanding parameters in the Standard Model dealt with during the MITP scientific program are the strong coupling constant $\alpha_s$ and the top-quark mass $m_t$. | background 0.67 | 0.09 | 0.09 | asserted 1.00 |
| s2 | Lacking knowledge on the value of those fundamental constants is often the limiting factor in the accuracy of theoretical predictions. | background 0.79 | 0.06 | 0.09 | asserted 0.86 |
| s3 | The current status on $\alpha_s$ and $m_t$ has been reviewed and directions for future research have been identified. | contribution 0.79 | 0.37 | 0.37 | asserted 1.00 |
What was examined, and what was not
- arXiv listing abstract v1
- full text
- figures and tables
- references and citing sentences
- relations to other papers
- P abstract
- S sections
- T body sentences
- C citations
- R cross-paper relations
Figures
Figures reproduced from arXiv:1405.4781 by the authors.
References
How later papers used it
70 later papers cite it
3 later papers by other authors are listed below: 3 used its data or values.
Uses its data or values 3 of 7 papers with this label
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Derived its top quark mass value at m_h from the present world average obtained in another work using the conversion tables provided in this paper.
Exclusive Radiative Higgs Decays as Probes of Light-Quark Yukawa Couplings (2015) · 0.85 · paraphrased: the licence does not allow quoting
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Used this paper's value of M_t=171.2±2.4GeV for the 1σ level.
Multiple Point Principle of the Standard Model with Scalar Singlet Dark Matter and Right Handed Neutrinos (2014) · 1.00 · paraphrased: the licence does not allow quoting
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Used this paper's M_t=171.2±4.82GeV (95% CL) as the basis for the 2σ deviation bands.
Vanishing Higgs Potential in Minimal Dark Matter Models (2015) · 0.96 · paraphrased: the licence does not allow quoting
How the literature uses it
70 arXiv papers cite this in 89 sentences
Papers citing it · 59 sentences without a confident label
Uses its data or values 7 papers
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We refer the interested reader to [ref] and [ref] for more details; here we just mention our reference values: * for the strong coupling constant at $m_Z$, $α_s^(5)$: we take the present [ref] world average experimental value of the strong coupling constant at $m_Z$, $α_s^(5,exp)=0.1181$, and its associated $1 σ$ error, $Δα_s^(5,exp)=0.0013$; * for the Higgs mass, $m_H$: we take the combined ATLAS and CMS result (after Run1) at $1 σ$, $m_H^exp=125.09$ GeV and $Δm_H^exp =0.24$ GeV [ref] ; * for the top pole mass, $m_t$: we take the present combined Tevatron and LHC value of the MC top mass, $m_t^MC=(173.34 ±0.76$) GeV [ref] ; the uncertainty in the identification between the pole and MC top mass is currently estimated to be of order $200$ MeV [ref] (or even $1$ GeV for the most conservative groups [ref] ).
Ruling out Critical Higgs Inflation? · Matching and running · 0.87
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For the top quark we obtain $m_t(m_h)=(166.8±0.7)$ GeV starting from $m_t(m_t)=(163.4±0.7)$ GeV, which we have derived from the present world average obtained in [ref] using the conversion tables provided in [ref] .
Exclusive Radiative Higgs Decays as Probes of Light-Quark Yukawa Couplings · Effective Higgs couplings · 0.85
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For the 1$σ$ level, this is given by [ref] M_t=171.2±2.4GeV.If we assume that all the other parameters of the SM except for $M_t$ are fixed, we can find the scale $Λ_β$ where $β_λ_eff$ becomes zero as a function of $M_t$.
Multiple Point Principle of the Standard Model with Scalar Singlet Dark Matter and Right Handed Neutrinos · Preliminary - Multiple Point Principle of SM - · 1.00
Compares with it 1 paper
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In Table [ref] we compare the masses at the reference scale $μ_ref ≡m (μ_ref)$, i.e. , for charm-, bottom- and top-quarks [ For the top-quark masses, such comparisons have already been presented in Ref. [ref] .]
Heavy-flavor hadro-production with heavy-quark masses renormalized in the ${\overline{\rm MS}}$, MSR and on-shell schemes · Implementation of heavy-quark mass renormalization schemes · 0.86
Cites it as support 1 paper
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Nonetheless, the MC mass definition can be translated to a theoretically well-defined short-distance mass definition at a low scale with an uncertainty currently estimated to be of the order of 1 GeV, see [ref] .
Precision determination of the top-quark mass · Monte Carlo mass · 0.96
Cites it as background 18 papers
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While initially only qualitative arguments for the interpretation problem for $m_t^MC$ were available [ref] , recently some quantitative studies appeared, which have shed some light on the numerical aspect of the issue.
What is the Top Quark Mass? · Numerical Size of the Interpretation Problem · 0.85
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The different mass definition can be related to each other in perturbation theory, see, e.g., Ref. [ref] and Ref. [ref] for a review of relations between these and other renormalization schemes such as the so-called MSR mass.
Top-Quark Physics at the LHC · Top-quark mass determination · 0.92
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Explicitly, the running top-quark mass is determined in the SM with the highest available precision from the experimentally measured pole mass [For a detailed discussion about the distinction between the pole and the measured top-quark mass we refer to [ref] .].
O(\alpha_s^2) corrections to the running top-Yukawa coupling and the mass of the lightest Higgs boson in the MSSM · Introduction · 0.85
Discussion
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