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Top quark mass measurements at and above threshold at CLIC

High Energy Physics - Experiment · Submitted 15 Mar 2013 · 45 references

Pith's verdict: A careful full-simulation CLIC study whose above-threshold result holds up; the 34 MeV threshold number is a toy closure resting on a flat efficiency measured at one energy, and that gap is the one the authors don't flag.

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arXiv ID1303.3758 (version 3)
Pith IDH7BOLO6R, Pith's permanent record of this paper and its review
CitationFrank Simon, Katja Seidel, Michal Tesar, Stephane Poss. "Top quark mass measurements at and above threshold at CLIC." arXiv:1303.3758 (2013). https://pith.science/paper/H7BOLO6R
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Referee report
The paper

The paper claims

A simulated 500 GeV CLIC stage could pin the top quark mass to roughly 100 MeV, and the threshold scan does it in a mass scheme that theory can actually interpret.

The reading

The paper asks how precisely the top quark mass could be measured at a first-stage linear electron-positron collider built on CLIC technology, running at 500 GeV and around the top-pair threshold near 350 GeV, with 100 inverse femtobarns of data. Two routes are simulated in full: reconstructing the invariant mass of the top decay products above threshold, and scanning the rise of the top-pair cross section across the threshold. The direct reconstruction reaches a combined statistical precision of 80 MeV, but that number is a parameter of the PYTHIA event generator, and the authors say plainly that the theoretical bridge from a generator mass to a well-defined mass scheme is not yet built to match it. The threshold scan reaches 34 MeV statistical on the mass, simultaneously with the strong coupling at 0.0009, and because the cross-section shape is computed in the 1S mass scheme with next-to-next-to-leading-order QCD, the result lands in a scheme that can be translated into other conventions. The paper's real message is thus a comparison of two kinds of precision: experimental precision that theory cannot yet absorb, and a slower measurement whose precision theory can absorb.

What carries the argument

Two pieces of machinery carry the argument. The first is the kinematic fit: it enforces three-dimensional energy and momentum conservation including the beam crossing angle, fixes both $W$ masses to 80.4 GeV, and forces the top and anti-top masses to be equal, varying jet and lepton four-momenta within their measured resolutions; this both sharpens the mass distribution and rejects more than 97 percent of the $qbar{q}$ background. The second is the threshold template fit: the top-pair cross section near threshold is computed with the TOPPIK code at next-to-next-to-leading order in the 1S mass scheme, folded with initial-state radiation and with the machine's luminosity spectrum, and the simulated data points are compared against a grid of templates in mass and $alpha_{s}$ spaced by 50 MeV and 0.0007 respectively. The luminosity spectrum is the pivot of the comparison with ILC: beamstrahlung smears the threshold rise, so the shape of that spectrum is itself a systematic input to the mass.

Extended reading notes

Core claim

The central claim is that a 500 GeV CLIC stage with 100 inverse femtobarns delivers a top quark mass with a total uncertainty around or below 100 MeV by two independent routes, and that the threshold route is the one with a defensible theoretical interpretation. Above threshold, a kinematic fit imposing energy-momentum conservation, the nominal $W$ mass of 80.4 GeV, and equal masses for top and anti-top, followed by a binned-likelihood background rejection, yields clean fully-hadronic and semi-leptonic samples; an unbinned fit of a Breit-Wigner convolved with a three-Gaussian resolution function and a background tail gives $m_{t} = 174.133$ GeV with a combined statistical error of 80 MeV and a width of $1.55$ GeV with an error of 220 MeV. At threshold, ten energy points spaced by 1 GeV from 344 to 353 GeV, 10 inverse femtobarns each, are fitted against NNLO cross-section templates in the 1S scheme, giving a statistical mass error of 34 MeV and a strong coupling error of 0.0009, with a theory normalization uncertainty worth only 5 to 8 MeV on the mass. Repeating the threshold analysis with the ILC luminosity spectrum, which has a sharper main peak, tightens the statistical error to 27 MeV, a difference far below the systematic uncertainties.

Load-bearing premise

The threshold-scan precision rests on the assumption that the signal selection efficiency of 70.2 percent and the residual background cross section of 73 femtobarns, both measured from fully simulated events at a single energy of 352 GeV, stay constant across the entire 344 to 353 GeV scan range, even though near threshold the event kinematics and the kinematic-fit success rate change quickly with energy.

Editorial extensions

If this is right

  • A threshold scan at a linear collider would deliver the top mass in the 1S scheme, which can be converted into other mass conventions, unlike the generator mass extracted from invariant-mass reconstruction.
  • The same scan determines the strong coupling to about 0.0009, comparable to the current world-average uncertainty, so $alpha_{s}$ need not be taken as an external input.
  • Because the direct-reconstruction and threshold masses would be measured at the same machine, their difference becomes a handle on non-perturbative and colour-reconnection effects in the invariant-mass interpretation.
  • The comparison of CLIC and ILC luminosity spectra shows the sharper ILC peak buys only about 20 percent in statistical precision, so the choice between technologies is not decided by the threshold-scan mass error.
  • A ten-point scan of 100 inverse femtobarns total would already be limited by systematics rather than statistics, with the luminosity-spectrum shape the largest single worry.
  • A six-point scan from 344 to 349 GeV, 60 inverse femtobarns, degrades the mass error to 40 MeV and the coupling error to 0.0013, showing the region above threshold matters mainly for $alpha_{s}$.

Reading between the lines

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

  • The paper's two numbers point in opposite directions for strategy: the 80 MeV invariant-mass result is cheaper in luminosity but currently unusable for precision physics, while the 34 MeV threshold result is only meaningful if the machine's luminosity spectrum is known to better than roughly 20 percent in RMS width, so accelerator diagnostics become a physics deliverable.
  • If the flat-efficiency assumption across the scan range fails, the distortion enters as a shape change in the cross-section rise, which is degenerate with a mass shift; a single additional simulated point at 344 GeV would test this cheaply.
  • The 350 MeV shift from a 2 percent b-jet energy scale error, versus under 100 MeV from light jets, suggests the b-jet calibration programme (using $Z \to b\bar{b}$ in di-boson and radiative-return events) is the binding experimental systematic for the above-threshold measurement.
  • A future comparison of a threshold-scan 1S mass with a hadron-collider Monte Carlo mass would test the size of the non-perturbative correction directly, rather than inferring it from generator comparisons.
Original abstract

We present a study of the expected precision of the top quark mass determination, measured at a linear e+ e- collider based on CLIC technology. GEANT4-based detector simulation and full event reconstruction including realistic physics and beam-induced background levels are used. Two different techniques to measure the top mass are studied: The direct reconstruction of the invariant mass of the top quark decay products and the measurement of the mass together with the strong coupling constant in a threshold scan, in both cases including first studies of expected systematic uncertainties. For the direct reconstruction, experimental uncertainties around 100 MeV are achieved, which are at present not matched by a theoretical understanding on a similar level. With a threshold scan, total uncertainties of around 100 MeV are achieved, including theoretical uncertainties in a well-defined top mass scheme. For the threshold scan, the precision at ILC is also studied to provide a comparison of the two linear collider technologies.

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, 4,942 input tokens, $0.0002 reported.

What the abstract itself states, as probabilities: claims first 0.04 · states limitation 0.84 · human participants 0.02 · controlled comparison 0.13 · randomized assignment 0.01 · states quantitative result 0.97 · compares with prior results 0.83 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v3. Results and the main claim are underlined; .

We present a study of the expected precision of the top quark mass determination, measured at a linear e+ e- collider based on CLIC technology. GEANT4-based detector simulation and full event reconstruction including realistic physics and beam-induced background levels are used. Two different techniques to measure the top mass are studied: The direct reconstruction of the invariant mass of the top quark decay products and the measurement of the mass together with the strong coupling constant in a threshold scan, in both cases including first studies of expected systematic uncertainties. For the direct reconstruction, experimental uncertainties around 100 MeV are achieved, which are at present not matched by a theoretical understanding on a similar level. With a threshold scan, total uncertainties of around 100 MeV are achieved, including theoretical uncertainties in a well-defined top mass scheme. For the threshold scan, the precision at ILC is also studied to provide a comparison of the two linear collider technologies.

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 present a study of the expected precision of the top quark mass determination, measured at a linear e+ e- collider based on CLIC technology. contribution 1.00 0.81 0.06 asserted 0.91
s1 GEANT4-based detector simulation and full event reconstruction including realistic physics and beam-induced background levels are used. method 1.00 0.79 0.02 asserted 0.99
s2 Two different techniques to measure the top mass are studied: The direct reconstruction of the invariant mass of the top quark decay products and the measurement of the mass together with the strong coupling constant in a threshold scan, in both cases including first studies of expected systematic uncertainties. method 0.65 0.80 0.08 asserted 0.96
s3 For the direct reconstruction, experimental uncertainties around 100 MeV are achieved, which are at present not matched by a theoretical understanding on a similar level. result 0.93 0.76 0.18 asserted 1.00
s4 With a threshold scan, total uncertainties of around 100 MeV are achieved, including theoretical uncertainties in a well-defined top mass scheme. result 1.00 0.82 0.34 asserted 1.00
s5 For the threshold scan, the precision at ILC is also studied to provide a comparison of the two linear collider technologies. contribution 0.90 0.78 0.04 asserted 0.92

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 v3
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. Distribution of the reconstructed mass of the W bosons for a signal-only sample after the classification into fully-hadronic and semi￾leptonic candidates before further event selection for collisions at 500 GeV. The distributions are normalized to allow a shape comparison. 4.4 Jet pairing For both analysis branches (6-jet fully-hadronic and 4-jet semi-leptonic candidates), the two jets with the highest b￾tag values are classified as jets created by a b-quark (b-jets). All other jets in the event are classified as light jets (created by u, d, s or c-quarks) originating from the W…
Figure 2. Reconstructed top mass for signal-only events selected in the fully hadronic branch with and without kinematic fit for collisions at 500 GeV. For both distributions only events with a successful kinematic fit are shown. the jet pairing into W candidates and the kinematic fit are re￾peated for unsuccessful kinematic fits after exchanging the b-jet with the lower b-tag value and the light jet with the highest b-tag value. This procedure increases the number of successful kinematic fits by approximately 20%. Overall, 37% of the signal events classified as fully-ha￾dronic candidates and…
Figure 3. Distribution of reconstructed top mass for events classified as fully-hadronic (left) and semi-leptonic (right). The data points include signal and background for an integrated luminosity of 100 fb−1 . The pure background contribution contained in the global distribution is shown by the green solid histogram. The top mass is determined with an unbinned likelihood fit of this distribution, which is shown by the solid line. 5.1 Determination of top quark mass and width In this analysis, the distribution of the reconstructed invari￾ant mass for signal and background events after…
Figure 4. Top pair production cross section from theory calculations, with the luminosity spectrum (LS) of CLIC at 350 GeV and ISR as well as for all effects combined. with an integrated luminosity of 10 fb−1 each, resulting in a total integrated luminosity of 100 fb−1 . 6.1 The tt¯ threshold at CLIC The top-pair signal cross section is determined using full NNLO calculations provided by the code TOPPIK [8, 38]. The top mass input is set to 174 GeV in the 1S mass scheme [8]. The strong coupling constant αs is taken to be 0.118. Since TOPPIK provides the cross section in units of R, the ratio…
Figure 5. Background-subtracted simulated cross section measurements for 10 fb−1 per data point, together with the cross section for the gen￾erator mass of 174 GeV as well as for a shift in mass of ±200 MeV. 6.2 Generation of data points The signal and background efficiencies are determined using fully simulated events as outlined in Section 3. The kine￾matic fit and the likelihood-based background rejection are used to eliminate the majority of the non-tt¯ background. Overall, a signal selection efficiency of 70.2%, including the branching fractions of the considered fully-hadronic and…
Figure 7. Background-subtracted simulated cross section measurements with the ILC luminosity spectrum for 10 fb−1 per data point, together with the cross section for the generator mass of 174 GeV as well as for a shift in mass of ±200 MeV. 1S top mass and αs combined 2D fit mt stat. error 27 MeV mt theory syst. (1%/3%) 5 MeV / 9 MeV αs stat. error 0.0008 αs theory syst. (1%/3%) 0.0007 / 0.0022

Showing 6 of the paper's 7 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:1303.3758 by the authors.

References
How later papers used it

56 later papers cite it

Evidence: substantial. 48 of the citing papers share no author with it, and 10 of those carry a confident label from Pith's citation classifier.

Pith read 24 of the 101 citing sentences, choosing only those whose citation markers point at this paper alone, and wrote the paraphrases from them. The summary, the counts, the evidence level, the links and the quotes come from code; the summary counts the papers listed below. A later paper is listed under a label when Pith's citation classifier gives one of its sentences that label at probability 0.8 or more (0.95 for support), Pith's reading finds that the citing paper itself did it, and a second check confirms the paraphrase against the sentence. This section lists uses only. It does not list criticism or disagreement, so their absence here says nothing about how the paper has been received. Papers that share an author with this one are listed apart, under "By the same authors". A quote is the citing authors' own sentence, shown when their paper's licence is CC BY, CC BY-SA or CC0. JSON

Builds on it 1 of 2 papers with this label · 1 by the same authors

By the same authors

Uses its method or tool 4 of 7 papers with this label · 3 by the same authors

By the same authors

  • Combined the results of NNNLO QCD calculations with the experimental techniques developed in this paper to perform a first preliminary analysis of the impact of scale uncertainties on the top mass extraction.

    A First Look at the Impact of NNNLO Theory Uncertainties on Top Mass Measurements at the ILC (2016) (same authors) · 0.86 · paraphrased: the licence does not allow quoting

  • Corrected its theory cross section for initial state radiation and for the luminosity spectrum of the collider as described in this paper.

    Scanning Strategies at the Top Threshold at ILC (2019) (same authors) · 0.99 · paraphrased: the licence does not allow quoting

  • Used the methodology described in this paper with state-of-the-art NNNLO QCD calculations of ttbar production as input to account for the ILC luminosity spectrum, initial state radiation, signal efficiencies and background contributions.

    The Potential of the ILC for Discovering New Particles (2017) (same authors) · 0.99 · paraphrased: the licence does not allow quoting

Uses its data or values 3 of 10 papers with this label · 1 by the same authors

By the same authors

  • Assumed a signal efficiency of 70.2% for the cross section measurement, with an effective background level after all selection cuts of 73 fb, following this paper.

    Scanning Strategies at the Top Threshold at ILC (2019) (same authors) · 0.98 · paraphrased: the licence does not allow quoting

How the literature uses it

56 arXiv papers cite this in 101 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 whose main result relates to this one's

Found among the papers closest to this one by title and main claim. Pith's classifier compared each pair's main results and a second model family confirmed the relation; checked against two further families, shown conflicts agreed 118 times in 120 and shown same results 218 times in 239. The quoted sentence is the other paper's main claim.

States the same result 1 paper

Papers citing it · 70 sentences without a confident label

Builds on it 2 papers
Uses its method or tool 7 papers
Uses its data or values 10 papers
  • Following [ref] , a signal efficiency of 70.2% is assumed for the cross section measurement, with an effective background level after all selection cuts of 73 fb.

    Scanning Strategies at the Top Threshold at ILC · The simulation study · 0.98

  • When generating simulated measurements (pseudo-data), the overall top-pair event reconstruction efficiency of 70.2% (including the relevant branching fractions) was assumed, and the background contribution remaining after the event selection procedure corresponding to the cross section of 73 fb [ref] .

    Optimising top-quark threshold scan at CLIC using genetic algorithm · Reference scenario · 1.00

  • In summary, for a 300 fb$^-1$ threshold scan, the total expected uncertainty on the top quark mass is $∼100$ MeV, resulting from the sum in quadrature of the following contributions: a statistical uncertainty of order 30 MeV (from Ref. [ref] , confirmed to be possible also with 100 fb$^-1$ from a 2-parameter fit in a recent study in Ref. [ref] ), 35 MeV (beam energy), 50 MeV (luminosity spectrum) and 80 MeV (from the conversion of $s_res$ into $m_t$ according Eq. [ref]).

    Determination of the top quark mass circa 2013: methods, subtleties, perspectives · Threshold $tt̅$ production at $e^+e^-$ colliders: experimental simulations · 0.87

Compares with it 2 papers
Cites it as support 1 paper
  • In the context of Higgs boson and top quark physics, this is for example beneficial for the rejection of physics background in hadronic and semi-leptonic final states, for the kinematic reconstruction of particle masses and for the constraints on the jet energy scales, as shown for top quark pair events in [ref] .

    Higgs and top physics reconstruction challenges and opportunities at FCC-ee · Particle flow and beyond : reconstructing individual particles, jets, and global event kinematics · 1.00

Cites it as background 4 papers

What it cites · 6 sentences without a confident label

Uses the method or tool of 1 paper
Uses data or values from 1 paper
  • However, an additional systematic uncertainty of 20 MeV on the mass arises from the precision of $α_s$, when assuming the current uncertainty of the world average of 0.0007 [ref] .

    World Summary of $\alpha_s$ (2012) · Alternative scenarios · 1.00

Cites as background 2 papers

Discussion

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