REVIEW 3 major objections 5 minor 5 cited by
NRQCD Re-Confronts LHCb Data on Quarkonium Production within Jets
T0 review · 3 major / 5 minor · reviewed 2026-08-15 · deepseek-v4-flash
Pith's one-line read The paper shows that LHCb's psi(2S) momentum-fraction distributions inside jets, binned in both jet and quarkonium transverse momentum, can discriminate between NRQCD production mechanisms, and that threshold-resummed fragmenting jet…
desk verdict Solid incremental step—threshold resummation in semi-inclusive FJFs applied to LHCb psi(2S) data—but the LDME-discrimination claim outruns the omitted scale uncertainties. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The carrying object is the semi-inclusive fragmenting jet function (FJF), which factorizes the cross section into a convolution $G_i^H(z,z_H,p_TR,\mu)=\sum_j J_{ij}(z,z_H,\mu)\otimes D_j^H(z_H,\mu)$, where $J_{ij}$ describes a mother parton splitting into a daughter parton inside the jet and $D_j^H$ is the quarkonium fragmentation function. The hierarchy $m_H \ll p_TR \ll p_T$ produces large logarithms $\ln(p_TR/m_H)$ and $\ln R$; the paper resums them by DGLAP evolution of the fragmentation function from $2m_c$ to the jet scale $p_TR$, then FJF evolution from $p_TR$ to the hard scale $p_T$, all at LL, reaching LLR + LL_threshold + NLO. Threshold resummation of the double logarithms $\log(1-z_H)/(1-z_H)$ is what makes the $z_H \to 1$ predictions finite and positive-definite. The experimental acceptance is implemented by modeling quarkonium decays as unpolarized and isotropic in the rest frame, boosting the muons to the lab frame, and applying the LHCb muon cuts, which produces the $z_H$-dependent acceptance that shapes the predictions.
What would settle it
Measure the polarization of prompt psi(2S) inside jets from the angular distribution of the two muons in the quarkonium rest frame and recompute the acceptance-corrected z_H predictions with that polarization; if the three LDME sets no longer separate in the binned distributions, or if the shape agreement changes materially, the discrimination claim fails. Alternatively, add the double-parton fragmentation contribution and test whether the z_H = 1 peaks in the LHCb data are reproduced; if they persist unexplained, the framework is missing another ingredient.
Extended reading notes
Core claim
The central claim is that the LHCb psi(2S) z_H distribution, measured separately in bins of jet pT and of psi(2S) pT, has enough discriminating power to tell apart competing sets of NRQCD long-distance matrix elements, something inclusive quarkonium pT spectra have failed to do. The paper reaches this by computing the distribution with semi-inclusive fragmenting jet functions at LL+NLO accuracy, including DGLAP evolution and, for the first time in this framework, threshold resummation of the double logarithms log(1-z_H)/(1-z_H). The threshold resummation cures the divergent growth toward z_H = 1 that plagued earlier FJF predictions. Comparing three representative LDME sets, the paper finds that none reproduces the full LHCb psi(2S) spectrum: one set does better at low z_H, a second at high z_H, and the third is less constraining because of its large uncertainties and negative direct-production predictions. The peaks the data show at z_H = 1, which the leading-power calculation cannot produce, are attributed to power-suppressed double-parton fragmentation, while low-z_H deviations in fixed jet-pT bins signal kinematical mass corrections of order (m_H/p_H^T)^2. The conclusion is that quarkonium production within jets is a critical probe of the NRQCD production mechanism, and that the psi(2S) dual-binning measurement is a sharper version of that probe than the pT-integrated J/psi measurement.
Load-bearing premise
The calculation assumes the quarkonia decay unpolarized and isotropically in their rest frame when modeling the LHCb muon acceptance; if prompt J/psi or psi(2S) are strongly polarized, the z-dependent acceptance corrections change and the comparison between LDME sets could shift.
Editorial extensions
If this is right
- The psi(2S) dual-binning strategy can separate LDME sets that inclusive pT spectra cannot, making it a practical discriminator for the quarkonium production mechanism.
- Threshold resummation turns the previously divergent z_H -> 1 predictions into finite, positive-definite distributions, so high-z_H bins become usable for comparisons.
- The z_H = 1 excess seen in the LHCb psi(2S) data, which grows at lower pT, indicates that power-suppressed double-parton fragmentation must be included for a complete description.
- For J/psi, the current pT-integrated data are less discriminating; analogous J/psi measurements binned in both pT variables would be needed to resolve LDME tensions in that channel.
- The calculation validates the semi-inclusive FJF framework against high-pT bins where mass corrections are small, supporting the use of this formalism for future quarkonium-in-jet analyses.
Reading between the lines
- A natural next step, not performed here, is a global fit that treats NRQCD LDMEs and the double-parton fragmentation strength as free parameters against the binned psi(2S) data; the current paper stops at comparing three fixed LDME sets.
- The same dual-binning logic could be applied to other identified hadrons inside jets, such as B mesons or charmed baryons, to test whether their fragmentation functions also separate competing nonperturbative matrix elements.
- The unpolarized-decay acceptance model could be checked by computing polarization-dependent dimuon distributions from the same NRQCD channels; if the z-dependent acceptance is sensitive, the discrimination statement would need to be made polarization-dependent.
- Because the paper normalizes predictions to the mid-z_H region, a next test is to insist on absolute normalization, which would turn the overall yield into an additional constraint on the LDME sets rather than just the shape.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This letter compares LHCb measurements of J/psi and psi(2S) transverse-momentum-fraction (z_H) distributions within jets with NRQCD predictions based on the semi-inclusive fragmenting jet function (FJF) formalism. The calculation uses NLO partonic cross sections, DGLAP evolution of fragmentation functions, threshold resummation in the z_H -> 1 limit, and a model of the LHCb muon acceptance. Three representative color-octet LDME sets are taken from the literature and compared visually with the data. The paper claims that the psi(2S) data, binned in both jet pT and quarkonium pT, have the potential to discriminate between NRQCD production mechanisms.
Significance. If the discrimination claim is quantitatively established, this would be a valuable step: it would show that quarkonium-in-jet distributions provide sharper constraints on NRQCD production mechanisms than inclusive cross sections, and it would validate the threshold-resummed, semi-inclusive FJF framework against new LHCb data. The technical advance over Ref. [10] is real, including the use of semi-inclusive FJFs matched to LHCb kinematics, threshold resummation that cures the earlier z_H -> 1 divergence, and the first comparison to the binned psi(2S) data. The paper also avoids circularity by using independent LDME sets rather than fitting new ones. However, the central claim is not yet demonstrated because perturbative scale uncertainties are omitted, the comparisons are normalized to the data in a mid-z_H window and judged visually, and no goodness-of-fit statistic is reported. These are fixable within a revision, so I do not regard the current form as ready for publication.
major comments (3)
- [Numerical calculation] The statement that "we intentionally exclude perturbative uncertainties from scale variations" directly undermines the discrimination claim. Because the B&K LDME uncertainties in Table I are very small, the apparent separation between the B&K band and the Brambilla/Bodwin bands in Fig. 1 could be inflated by the missing scale uncertainty. The authors should estimate scale uncertainties, for example by varying the fragmentation scale, the FJF scale, and the renormalization scale in the NLO cross section and in the resummation, and show that the three LDME sets remain visually and statistically separated after adding the scale uncertainty in quadrature.
- [Prompt-psi(2S) results] The claim that "the Brambilla set provides a better description at low zH and the B&K set performs better at high zH" is based only on visual inspection after normalizing the theory to the data area in 0.5 < zH < 0.8, and no chi-square, likelihood, or other goodness-of-fit statistic is reported. The choice of normalization window can itself trade against shape differences, so the current evidence does not quantitatively support the abstract's conclusion that the psi(2S) data can discriminate between production mechanisms. The authors should provide a quantitative comparison, ideally a chi-square or likelihood per LDME set using the experimental covariance matrix, or explicitly weaken the conclusion to an illustrative comparison.
- [Numerical calculation (acceptance model)] The acceptance model assumes "unpolarized quarkonium decays with isotropic mu+mu- angular distributions in the quarkonium rest frame." Since NRQCD allows significant quarkonium polarization and the z_H-dependent acceptance of the LHCb muon cuts is polarization-dependent, this assumption could change the predicted shapes and hence the discrimination conclusions. The authors should quantify the sensitivity by repeating the acceptance computation with maximally longitudinal and maximally transverse polarization scenarios, or by using measured polarizations where available, and state whether the discrimination conclusions survive.
minor comments (5)
- [Fig. 1 caption] The caption refers to "the factor sigma" but does not define it; please define it explicitly or point to the corresponding equation in the text.
- [Supplementary material] Figs. 3 and 4 are not referenced in the main text; add explicit references when describing the lower-pT bins in the supplementary material.
- [Prompt-psi(2S) results] In the sentence "This complimentary dual binning", "complimentary" should be "complementary".
- [Table I] In the psi(2S) row for Bodwin et al., the color-singlet LDME is listed as 0.76[16] with no uncertainty; please state whether this value is held fixed when propagating LDME uncertainties.
- [Abstract] The abstract's phrase "has the potential to discriminate" is weaker than the conclusions' phrasing that the data "enable discrimination"; please harmonize these statements with the level of quantitative support provided in the paper.
Circularity Check
No circularity: the LDME sets and perturbative FJF inputs are independent, and the psi(2S) comparison is a genuine forward prediction.
full rationale
The paper does not fit any LDME to the data it compares against. The three LDME sets in Table I are taken from independent global fits (Brambilla et al. [13], Bodwin et al. [14], Butenschoen and Kniehl [15,17]), and the LHCb psi(2S) data [9] postdates the fits used, so the z_H distributions are genuine predictions rather than refits. The FJF formalism and threshold resummation are independent perturbative ingredients: the cited threshold resummation formula [12] shares an author with this paper but is a parameter-free result whose stated assumptions do not include the LHCb quarkonium-in-jet distributions, so citing it is not a circular load-bearing step. The only data-dependent step is the common area normalization over the mid-z_H region (0.5 < z_H < 0.8), which rescales all predictions by the same overall factor and therefore cannot manufacture the shape differences among the three LDME sets; it also does not enter the LDME parameters themselves. The decision to omit perturbative scale uncertainties and the absence of a quantitative chi-square comparison are accuracy and evidentiary concerns, not circularity. Relative to the external LHCb benchmark, the derivation is self-contained and its central discriminator claim rests on independent model inputs, so no circular step is present.
Assumptions & free parameters
free parameters (3)
- J/psi color-octet LDMEs (3S1[8], 1S0[8], 3PJ[8]) from Refs. [13-15] =
Three sets, see Table I: Brambilla 1.40, -0.63, 2.33; Bodwin -0.71, 11.0, -0.31; B&K 0.22, 4.97, -0.72 (times 10^-2…
- psi(2S) color-octet LDMEs from Refs. [13,14,17] =
Table I: Brambilla 0.84, -0.37, 1.55; Bodwin -0.16, 3.14, -0.12; B&K 0.054, 1.00, -0.217 (times 10^-2 GeV^3)
- Mid-zH normalization factor for each comparison =
Not quoted; chosen so the theory area matches the data area in 0.5 < zH < 0.8
assumptions (5)
- domain assumption NRQCD factorization with the four channels 3S1[1], 3S1[8], 1S0[8], and 3PJ[8] describes J/psi and psi(2S) production at LHCb pT.
- domain assumption Semi-inclusive FJF factorization, G_i^H = sum_j J_ij tensor D_j^H, holds for m_H << pT R << pT with the coefficients J_ij from Ref. [11].
- domain assumption The threshold resummation formula of Ref. [12] can be embedded in the FJF framework and removes the zH to 1 divergence without double counting DGLAP logarithms.
- domain assumption Unpolarized isotropic decays for J/psi and psi(2S) in the acceptance modeling.
- domain assumption The three chosen LDME sets are representative of all published sets, with similar predictions within each category.
Cite this review
Pith. "Pith review of NRQCD Re-Confronts LHCb Data on Quarkonium Production within Jets." pith.science (2026). https://pith.science/paper/M6KLEZ24
@misc{pith2026250719022,
author = {Pith},
title = {Pith review of: NRQCD Re-Confronts LHCb Data on Quarkonium Production within Jets},
year = {2026},
howpublished = {\url{https://pith.science/paper/M6KLEZ24}},
note = {Machine review of arXiv:2507.19022}
}
abstract
We compare LHCb measurements of $J/\psi$ and $\psi(2S)$ transverse momentum distributions within jets with QCD calculations, which may be crucial in understanding the quarkonium production mechanism. Our theoretical calculations are based on the fragmenting jet function formalism, while the nonperturbative formation of quarkonia is described by the nonrelativistic QCD factorization formalism. We include the newest refinements in the perturbative calculation including resummation of threshold and DGLAP logarithms. We find that the $\psi(2S)$ data has the potential to discriminate between the different production mechanisms proposed in the literature.
Figures
Forward citations
Cited by 5 Pith papers
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Measurement of the fragmentation properties of jets containing $\Upsilon$(nS) mesons in proton-proton collisions at $\sqrt{s}$ = 13 TeV
First measurement of Upsilon(nS) jet-fragmentation profiles shows data have lower z and higher p_rel^T than PYTHIA 8.240/8.310 with CP1/CP5 tunes.
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Impact of relativistic corrections to high-pT prompt-psi(2S) production at hadron colliders
Relativistic O(v^2) corrections to color-singlet fragmentation functions, especially for gluons, bring leading-power NRQCD predictions for prompt psi(2S) at high pT into agreement with LHC data without color-octet mat...
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The role of the soft scale for $J/\psi$ production in the transverse momentum dependent framework
The paper derives new TMD soft transition functions and shows they dominate J/psi production at small transverse momentum by a factor of 1/v over previously used shape functions.
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Heavy Quark Pair Energy Correlators: From Profiling Partonic Splittings to Probing Heavy-Flavor Fragmentation
Heavy-flavor energy-energy correlators isolate the gluon to heavy quark-antiquark splitting and are predicted to be sensitive to medium modifications and anisotropic quark-gluon plasma structure.
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$\psi(2S)$ production in jets using NRQCD
Applying NRQCD fragmenting jet functions and gluon-fragmentation-improved Pythia to psi(2S) in jets, the authors find that the LHCb data favor the Bodwin et al. LDME set and expose large tensions with other extractions.
Reference graph
Works this paper leans on
-
[10]
R. Bain, L. Dai, A. Leibovich, Y. Makris, and T. Mehen, Phys. Rev. Lett. 119, 032002 (2017), arXiv:1702.05525 [hep-ph]
arXiv 2017
-
[1]
H. S. Chung, PoS Confinement2018, 007 (2018), arXiv:1811.12098 [hep-ph]
arXiv 2018
-
[2]
H. S. Chung, EPJ Web Conf. 274, 01011 (2022), arXiv:2211.10201 [hep-ph]
arXiv 2022
-
[3]
M. Baumgart, A. K. Leibovich, T. Mehen, and I. Z. Rothstein, JHEP 11, 003 (2014), arXiv:1406.2295 [hep- ph]
arXiv 2014
-
[4]
R. Bain, Y. Makris, and T. Mehen, JHEP 11, 144 (2016), arXiv:1610.06508 [hep-ph]
arXiv 2016
-
[5]
Z.-B. Kang, J.-W. Qiu, F. Ringer, H. Xing, and H. Zhang, Phys. Rev. Lett. 119, 032001 (2017), arXiv:1702.03287 [hep-ph]
arXiv 2017
-
[6]
R. Aaij et al. (LHCb), Phys. Rev. Lett. 118, 192001 (2017), arXiv:1701.05116 [hep-ex]
arXiv 2017
-
[7]
A. Tumasyan et al. (CMS), Phys. Lett. B 825, 136842 (2022), arXiv:2106.13235 [hep-ex]
arXiv 2022
Show all 47 references
-
[8]
Yang (STAR), PoS HardProbes2020, 072 (2021)
Q. Yang (STAR), PoS HardProbes2020, 072 (2021)
2021
-
[9]
Aaij et al
R. Aaij et al. (LHCb), (2024), arXiv:2410.18018 [hep-ex]
2024
-
[11]
Z.-B. Kang, F. Ringer, and I. Vitev, JHEP 11, 155 (2016), arXiv:1606.07063 [hep-ph]
2016 arXiv
-
[12]
H. S. Chung, U.-R. Kim, and J. Lee, Phys. Rev. Lett. 134, 071902 (2025), arXiv:2408.04255 [hep-ph]
2025 arXiv
-
[13]
Brambilla, H
N. Brambilla, H. S. Chung, A. Vairo, and X.-P. Wang, JHEP 03, 242 (2023), arXiv:2210.17345 [hep-ph]
2023 arXiv
-
[14]
G. T. Bodwin, K.-T. Chao, H. S. Chung, U.-R. Kim, J. Lee, and Y.-Q. Ma, Phys. Rev. D 93, 034041 (2016), arXiv:1509.07904 [hep-ph]
2016 arXiv
-
[15]
Butenschoen and B
M. Butenschoen and B. A. Kniehl, Phys. Rev. D84, 051501 (2011), arXiv:1105.0820 [hep-ph]
2011 arXiv
-
[16]
E. J. Eichten and C. Quigg, Phys. Rev. D 52, 1726 (1995), arXiv:hep-ph/9503356
1995 arXiv
-
[17]
Butenschoen and B
M. Butenschoen and B. A. Kniehl, Phys. Rev. D 107, 034003 (2023), arXiv:2207.09346 [hep-ph]
2023 arXiv
-
[18]
Brambilla, H
N. Brambilla, H. S. Chung, and A. Vairo, JHEP 09, 032 (2021), arXiv:2106.09417 [hep-ph]
2021 arXiv
-
[19]
Han, Y.-Q
H. Han, Y.-Q. Ma, C. Meng, H.-S. Shao, and K.-T. Chao, Phys. Rev. Lett. 114, 092005 (2015), arXiv:1411.7350 [hep-ph]
2015 arXiv
-
[20]
Zhang, Z
H.-F. Zhang, Z. Sun, W.-L. Sang, and R. Li, Phys. Rev. Lett. 114, 092006 (2015), arXiv:1412.0508 [hep-ph]
2015 arXiv
-
[21]
H. S. Shao, H. Han, Y. Q. Ma, C. Meng, Y. J. Zhang, and K. T. Chao, JHEP 05, 103 (2015), arXiv:1411.3300 [hep-ph]
2015 arXiv
-
[22]
Gong, L.-P
B. Gong, L.-P. Wan, J.-X. Wang, and H.-F. Zhang, Phys. Rev. Lett. 110, 042002 (2013), arXiv:1205.6682 [hep-ph]
2013 arXiv
-
[23]
Y. Feng, B. Gong, C.-H. Chang, and J.-X. Wang, Phys. Rev. D 99, 014044 (2019), arXiv:1810.08989 [hep-ph]
2019 arXiv
-
[24]
Procura and I
M. Procura and I. W. Stewart, Phys. Rev. D 81, 074009 (2010), [Erratum: Phys.Rev.D 83, 039902 (2011)], arXiv:0911.4980 [hep-ph]
2010 arXiv
- [25]
-
[26]
Procura and W
M. Procura and W. J. Waalewijn, Phys. Rev. D 85, 114041 (2012), arXiv:1111.6605 [hep-ph]
2012 arXiv
-
[27]
A. Jain, M. Procura, and W. J. Waalewijn, JHEP 04, 132 (2012), arXiv:1110.0839 [hep-ph]
2012 arXiv
-
[28]
A. Jain, M. Procura, B. Shotwell, and W. J. Waalewijn, Phys. Rev. D87, 074013 (2013), arXiv:1207.4788 [hep- ph]
2013 arXiv
-
[29]
C. W. Bauer and E. Mereghetti, JHEP 04, 051 (2014), arXiv:1312.5605 [hep-ph]
2014 arXiv
-
[30]
Ritzmann and W
M. Ritzmann and W. J. Waalewijn, Phys.Rev. D90, 6 054029 (2014), arXiv:1407.3272 [hep-ph]
2014 arXiv
-
[31]
Kaufmann, A
T. Kaufmann, A. Mukherjee, and W. Vogelsang, Phys. Rev. D92, 054015 (2015), arXiv:1506.01415 [hep-ph]
2015 arXiv
-
[32]
Z.-B. Kang, F. Ringer, and I. Vitev, JHEP 10, 125 (2016), arXiv:1606.06732 [hep-ph]
2016 arXiv
-
[33]
L. Dai, C. Kim, and A. K. Leibovich, Phys. Rev. D94, 114023 (2016), arXiv:1606.07411 [hep-ph]
2016 arXiv
-
[34]
L. Dai, C. Kim, and A. K. Leibovich, Phys. Rev. D 95, 074003 (2017), arXiv:1701.05660 [hep-ph]
2017 arXiv
-
[35]
Braaten and T
E. Braaten and T. C. Yuan, Phys. Rev. Lett. 71, 1673 (1993), arXiv:hep-ph/9303205 [hep-ph]
1993 arXiv
-
[36]
Braaten and S
E. Braaten and S. Fleming, Phys. Rev. Lett. 74, 3327 (1995), arXiv:hep-ph/9411365 [hep-ph]
1995 arXiv
-
[37]
Braaten, K.-m
E. Braaten, K.-m. Cheung, and T. C. Yuan, Phys. Rev. D48, 4230 (1993), arXiv:hep-ph/9302307 [hep-ph]
1993 arXiv
-
[38]
K. Lee, I. Moult, and X. Zhang, (2024), arXiv:2410.01902 [hep-ph]
2024 arXiv
-
[39]
K. Lee, I. Moult, and X. Zhang, (2024), arXiv:2409.19045 [hep-ph]
2024 arXiv
-
[40]
Jager, A
B. Jager, A. Schafer, M. Stratmann, and W. Vogelsang, Phys. Rev. D 67, 054005 (2003), arXiv:hep-ph/0211007
2003 arXiv
-
[41]
Ma, J.-W
Y.-Q. Ma, J.-W. Qiu, and H. Zhang, Phys. Rev. D89, 094029 (2014), arXiv:1311.7078 [hep-ph]
2014 arXiv
-
[42]
Fleming, A
S. Fleming, A. K. Leibovich, T. Mehen, and I. Z. Roth- stein, Phys. Rev. D86, 094012 (2012), arXiv:1207.2578 [hep-ph]
2012 arXiv
-
[43]
Fleming, A
S. Fleming, A. K. Leibovich, T. Mehen, and I. Z. Roth- stein, Phys. Rev. D87, 074022 (2013), arXiv:1301.3822 [hep-ph]
2013 arXiv
-
[44]
Kang, Y.-Q
Z.-B. Kang, Y.-Q. Ma, J.-W. Qiu, and G. Sterman, Phys. Rev. D 90, 034006 (2014), arXiv:1401.0923 [hep-ph]
2014 arXiv
-
[45]
Ma, J.-W
Y.-Q. Ma, J.-W. Qiu, and H. Zhang, Phys. Rev. D89, 094030 (2014), arXiv:1401.0524 [hep-ph]
2014 arXiv
-
[46]
Kang, Y.-Q
Z.-B. Kang, Y.-Q. Ma, J.-W. Qiu, and G. Sterman, Phys. Rev. D 91, 014030 (2015), arXiv:1411.2456 [hep-ph]
2015 arXiv
-
[47]
Zhang and H
S.-L. Zhang and H. Xing, Phys. Lett. B 863, 139382 (2025), arXiv:2403.12704 [hep-ph]. 7 SUPPLEMENTARY 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.0 0.1 0.2 0.3 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.0 0.1 0.2 0.3 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.0 0.1 0.2 0.3 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0...
2025 arXiv
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