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Universality of the Collins-Soper-Sterman nonperturbative function in gauge boson production

High Energy Physics - Phenomenology · Submitted 23 Jun 2005 · 15 references

Pith's verdict: A real, useful revision of the b_* model — the Z-mass nonperturbative correction drops to about a third of BLNY — but the abstract's 'closely agrees' is stated at a precision the quoted errors don't support.

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arXiv IDhep-ph/0506225 (version 3)
Pith IDXZLOM6GG, Pith's permanent record of this paper and its review
CitationAnton V. Konychev, Pavel M. Nadolsky. "Universality of the Collins-Soper-Sterman nonperturbative function in gauge boson production." arXiv:hep-ph/0506225 (2005). https://pith.science/paper/XZLOM6GG
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The paper

The paper claims

One nonperturbative function is enough to fit Drell-Yan and Z data

The reading

Transverse-momentum distributions of Drell-Yan pairs and $Z$ bosons are predicted by a resummation that splits into a computable short-distance part and a nonperturbative function $F_{NP}(b,Q)$ that has to be extracted from data. The authors argue that the standard $b_*$ prescription, which freezes the perturbative form factor at $b_{max}=0.5$ GeV$^{-1}$, cuts off the perturbative region too early, and that raising $b_{max}$ to $1$-$2$ GeV$^{-1}$ lets the known short-distance calculation carry more of the answer. With that single change, a global fit to 98 fixed-target Drell-Yan and Tevatron $Z$ data points returns a nonperturbative function whose coefficient of $b^2$ grows almost linearly with $a_2 = 0.184$ GeV$^2$ per unit $a_2 = 0.184$ GeV$^2$ per unit of $a_2 = 0.184$ GeV$^2$ per unit of $a_2 = 0.184$ GeV$^2$ per unit of $a_2 = 0.184$ GeV$^2$ per unit of $a_2 = 0.184$ GeV$^2$ per unit of $a_2 = 0.184$ GeV$^2$ per unit of $a_2 = 0.184$ GeV$^2$ per unit of $a_2 = 0.184$ GeV$^2$ per unit of $a_2 = 0.184$ GeV$^2$ per unit of $a_2$.

What carries the argument

The carrying device is the $b_*$ model with a raised cutoff: $b_* = b(1+b^2/b_{max}^2)^{-1/2}$, so that the leading-power form factor is the exact perturbative one, $W_{LP}(b) = W_{pert}(b_*)$, for $b$ up to roughly $b_{max}$ and only saturates beyond it. The full form factor is written $W(b) = W_{LP}(b)e^{-F_{NP}(b,Q)}$, which isolates the power-suppressed terms in the exponent while keeping the logarithmic terms in the perturbative piece. Because the choice of factorization scale $a_2 = 0.184$ GeV$^2$ is tied to $b_*$, the authors also prescribe $a_2 = C_3/b_*(b, b_0/Q_{ini})$ once $b_{max}$ exceeds $b_0/Q_{ini} = 0.86$ GeV$^{-1}$, so that the CTEQ6M densities are never evaluated below their starting scale.

Extended reading notes

Core claim

The paper's central claim is that the nonperturbative function of Collins-Soper-Sterman resummation, $F_{NP}(b,Q)$, is universal across Drell-Yan and $Z$ production and depends quasi-linearly on $a_2 = 0.184$ GeV$^2$ per unit of $a_2$.

Load-bearing premise

The functional form $F_{NP}=b^2(a_1+a_2a_2 = 0.184$ GeV$^2$.

Editorial extensions

If this is right

  • The same nonperturbative function, with its fitted $a_2 = 0.184\pm0.018$ GeV$^2$, describes fixed-target Drell-Yan data near $Q\approx5$-$10$ GeV and Tevatron $Z$ data at $Q=M_Z$ without retuning.
  • The nonperturbative correction at the $Z$ pole, $a(M_Z) = 0.85\pm0.10$ GeV$^2$, is about a third of the $2.7$ GeV$^2$ assumed in the earlier fit, which shrinks a leading theory uncertainty in the extraction of the $W$ mass.
  • The fitted slope agrees numerically with the infrared-renormalon estimate of $0.19^{+0.12}_{-0.09}$ GeV$^2$, giving the soft-gluon interpretation of the dominant nonperturbative term direct empirical support.
  • The coefficient $a_3$ that measures departure from pure $\ln Q$ dependence comes out below $0.05$ GeV$^2$, so the quasi-linear form is preferred by the data once the leading-power piece is modelled with a larger $b_{max}$.
  • The quality of the fit is flat for $b_{max}$ between $1$ and $2$ GeV$^{-1}$ and degrades outside that window, which localizes where the perturbative and nonperturbative regions may be joined.

Reading between the lines

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

  • If the slope really is the renormalon slope, then the same two-parameter description should carry over to $W$ production at the LHC without new fitting, which is a sharp test the paper does not perform here.
  • The dependence on the factorization-scale parameter $C_3$ (from $0.184$ to $0.158$ GeV$^2$) is comparable to the quoted statistical error, so an extraction with higher-order coefficient functions would be the natural way to tell whether the renormalon agreement is coincidence or content.
  • The paper notes that two E605 points contribute $15$-$25$ units of $\chi^2$ at any $b_{max}$ and that $\chi^2/\mathrm{d.o.f.}\approx1$ follows if they are dropped; a reader should treat the absolute fit quality as partly hostage to those two points rather than to the model.
  • Because the linear $\ln Q$ form is imposed by renormalization-group invariance rather than discovered, the genuinely empirical statements are the magnitude of $a_2$ and the smallness of $a_3$; a future fit that leaves the $Q$ dependence free would be the cleanest confirmation of universality.
Original abstract

We revise the $b_*$ model for the Collins-Soper-Sterman resummed form factor to improve description of the leading-power contribution at nearly nonperturbative impact parameters. This revision leads to excellent agreement of the transverse momentum resummation with the data in a global analysis of Drell-Yan lepton pair and Z boson production. The nonperturbative contributions are found to follow universal quasi-linear dependence on the logarithm of the heavy boson invariant mass, which closely agrees with an estimate from the infrared renormalon analysis.

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, 3,006 input tokens, $0.0001 reported.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.10 · human participants 0.02 · controlled comparison 0.06 · randomized assignment 0.01 · states quantitative result 0.12 · compares with prior results 0.70 · mentions code or data availability 0.02.

The abstract, sentence by sentence

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

We revise the $b_*$ model for the Collins-Soper-Sterman resummed form factor to improve description of the leading-power contribution at nearly nonperturbative impact parameters. This revision leads to excellent agreement of the transverse momentum resummation with the data in a global analysis of Drell-Yan lepton pair and Z boson production. The nonperturbative contributions are found to follow universal quasi-linear dependence on the logarithm of the heavy boson invariant mass, which closely agrees with an estimate from the infrared renormalon analysis.

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 revise the $b_*$ model for the Collins-Soper-Sterman resummed form factor to improve description of the leading-power contribution at nearly nonperturbative impact parameters. contribution 0.74 0.93 0.09 asserted 0.96
s1 This revision leads to excellent agreement of the transverse momentum resummation with the data in a global analysis of Drell-Yan lepton pair and Z boson production. result 0.99 0.87 0.28 asserted 1.00
s2 The nonperturbative contributions are found to follow universal quasi-linear dependence on the logarithm of the heavy boson invariant mass, which closely agrees with an estimate from the infrared renormalon analysis. result 0.97 0.93 0.64 asserted 1.00

What kind of paper the classifier reports this is: theoretical result 0.54 · evidence from analysis of existing data 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. The best-fit values of a(Q) obtained in independent scans of χ 2 for the contributing experiments. The vertical error bars correspond to the increase of χ 2 by unity above its minimum in each Q bin. The slope of the line is equal to the central-value prediction from the renormalon analysis [11]. exception of the CDF Run-1 normalization (rescaled down by 7%). To test the universality of FNP , we individually examine each bin of Q. We choose FNP = a(Q)b 2 and independently fit it to each of the 5 experimental data sets to determine the most plausible normalization in each experiment.…
Figure 2. The best-fit χ 2 and coefficients a1, a2, and a3 in FNP (b, Q) for different values of bmax, C3 = b0 (stars) and C3 = 2b0 (squares). The size of the symbols approximately corresponds to 1σ errors for the shown parameters. To further explore the issue, we simultaneously fit our model to all the data. We parametrize a(Q) as a(Q) ≡ a1+a2ln [Q/(3.2 GeV)]+a3ln [100x1x2] . This parametrization coincides with the BLNY form [9], if the parameters are re￾named as {g1, g2, g1g3}(BLNY) → {a1, a2, a3}(here). It agrees with the generic form of FNP (b, Q) in Eq. (5), if one identifies φ(x) =…
Figure 3. Differences between the measured (Data) and theoretic
Figure 4. The best-fit form factors bWf(b) in (a) Tevatron Run-2 Z boson production; (b) E605 experiment. In the E605 case, bWf(b) are divided by the best-fit normaliza￾tions Nf it for the E605 data, and the form factor in the Qiu-Zhang parametrization [12] for b QZ max = 0.3 GeV−1 is also shown. renormalon analysis estimate. The coefficient a3, which parametrizes devia￾tions from the linear ln Q dependence, is considerably smaller (< 0.05) than both a1 and a2 (∼ 0.2). A reasonable quality of the fit is retained if a3 is set to zero by hand: χ 2 increases by ≈ 5 in such a fit above its…

Figures reproduced from arXiv:hep-ph/0506225 by the authors.

References
How the literature uses it

44 arXiv papers cite this in 72 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 · 42 sentences without a confident label

Contests it 1 paper
Uses its method or tool 3 papers
Uses its data or values 5 papers
Compares with it 1 paper
Cites it as support 1 paper
  • Confirmations are given both at perturbative level (the coefficients of perturbative expansion are known up to four loops [ref] , and also in the non-perturbative regime, where both phenomenological extractions [ref] and lattice computations [ref] agree on considering $g_K$ as a positive-definite monotonically increasing function of $b_T$.

    Full treatment of the thrust distribution in single inclusive $e^+ e^- \to h \, X$ processes · Rapidity regulator as a function of thrust · 0.96

Cites it as background 15 papers
  • The original CSS formula [ref] , as used in the fits in [ref] , was obtained starting from a TMD factorization formula, using the specific definitions of TMD parton densities that had been given by Collins and Soper (CS) [ref] .

    Connecting Different TMD Factorization Formalisms in QCD · Original CSS formalism · 0.83

  • In previous work on CSS resummation, the $b_*$-prescription was introduced along with non-perturbative Sudakov factors, which were modeled through various functional forms and obtained by fitting to experimental data [ref] .

    QCD resummation of dijet azimuthal decorrelations in pp and pA collisions · Parameterization · 0.99

  • The presence, at low lepton-pair transverse momenta, of large logarithmically enhanced QCD corrections and the role, in the same kinematic region, of non-perturbative effects have been discussed in Refs. [ref] , but the dependence of the resulting model on the acceptance cuts has never been investigated in detail and will deserve a dedicated study.

    Prospects for improving the LHC W boson mass measurement with forward muons · Uncertainties stemming from the modelling · 0.94

Discussion

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