Pith. Sign in

REVIEW

Polarization of Prompt J/psi at the Tevatron

High Energy Physics - Phenomenology · Submitted 22 Nov 1999 · 19 references

Pith's verdict: The reference calculation for prompt J/psi polarization: the qualitative rise of alpha is solid, but the quoted 3-sigma significance leans on a quadrature band over a parameter that isn't Gaussian.

T0 · AI review

How this review was made: An AI referee (selfhosted/deepseek-v4.1-flash) read the paper on November 13, 2026 and answered a fixed list of questions about it. T0 is the starting level every paper gets. The levels describe how deeply Pith has checked the paper, never the authors.

  1. T0 AI review An AI read the paper and answered a fixed list of questions.
  2. T1 Audit Automatic checks that the references and files the paper relies on exist and match.
  3. T2 Compute The paper's code or calculations re-run with the same results.
  4. T3 Formal statement The claims written out in a formal math language a computer can read.
  5. T4 Proof Those claims proved, and the proof checked by computer.

How Pith checks papers →

· 3 major objections · 5 minor · Ask about this paper · The compiled record · Read the full review →
Challenge this review Comment (0) Read on arXiv ↗
Cite ▾
arXiv IDhep-ph/9911436 (version 3)
Pith ID5YJITQIX, Pith's permanent record of this paper and its review
CitationBernd A. Kniehl, Eric Braaten (Ohio State), Jungil Lee (Hamburg). "Polarization of Prompt J/psi at the Tevatron." arXiv:hep-ph/9911436 (1999). https://pith.science/paper/5YJITQIX
Cite this reviewBibTeX for Pith's review of this paper
Claim paper

Why Pith says this

Highlight any text to comment on it.

Referee report
The paper

The paper claims

Prompt $J/psi$ mesons should become transversely polarized as their transverse momentum grows, and the size of that polarization can now be predicted including feeddown from heavier charmonium states.

The reading

The paper asks a sharp question about a striking prediction of the nonrelativistic QCD factorization approach to quarkonium production: that vector quarkonium states made in hadron collisions should come out transversely polarized once transverse momentum $p_T$ is large enough. Earlier calculations of this effect were done for direct $psi'$ mesons, but the experimentally copious signal is the prompt $J/psi$, roughly a third of which arrives through decays of $chi_{c1}$, $chi_{c2}$, and $psi'$. The authors redo the bookkeeping for that mixed sample, fitting the color-octet matrix elements to CDF $p_T$ distributions and computing the polarization of each spin state of each parent, then propagating it through the radiative decay probabilities into a longitudinally polarized $J/psi$. The result is a predicted angular parameter $alpha$ that climbs from near zero at $p_T = 5$ GeV to about 0.5 at $p_T = 20$ GeV, matching CDF at intermediate $p_T$ and missing the highest measured bin by about three standard deviations. The point of the exercise is that feeddown softens but does not remove the transverse-polarization prediction, so the residual disagreement has to be explained by something other than forgotten decay chains.

What carries the argument

The machinery is the NRQCD factorization formula $d sigma_{H_lambda}(P) = d sigma_{c bar{c} n}(P) langle O_{H_lambda}(P)_n rangle$, in which the short-distance parton cross sections for each color and angular momentum state $n$ of the $c bar{c}$ pair are multiplied by nonperturbative matrix elements, and the spin dependence of the bound state enters only through the polarization tensor of $H_lambda$. The authors re-extract the color-octet parameters $langle O_8(^3S_1) rangle$, the combination $M_r = langle O_8(^1S_0) rangle + r langle O_8(^3P_0) rangle/m_c^2$, and $langle O_{chi_{c0}8}(^3S_1) rangle$ from CDF $p_T$ distributions for $J/psi$, $chi_c$, and $psi'$, add the gluon fragmentation contribution $g to c bar{c}_8(^3S_1)$ with its timelike evolution, and interpolate between the fusion and fragmentation regimes. New parton cross sections for the individual spin states of the $chi_{cJ}$ were required and are cited to a companion paper. The decay step then converts parent spin states into longitudinal $J/psi$ fractions, which is what turns a set of partonic polarization cross sections into a single measurable $alpha$ curve.

Extended reading notes

Core claim

The central claim is that within NRQCD factorization, the angular distribution parameter $alpha = (sigma_T - 2 sigma_L)/(sigma_T + 2 sigma_L)$ for leptons from prompt $J/psi$ at the Tevatron rises with transverse momentum, from near 0 at $p_T = 5$ GeV to roughly 0.5 at $p_T = 20$ GeV, once the $chi_{cJ}$ and $psi'$ feeddown contributions are computed spin state by spin state. Radiative $P$-wave decays reduce the transverse polarization relative to the direct-$J/psi$ case but do not eliminate it, because the decay probabilities into a longitudinal $J/psi$ are only $1/3$ for $chi_{c0}$, $1/2$ for the transverse $chi_{c1}$ and $chi_{c2}$ states, $2/3$ for $chi_{c2}(0)$, and zero for the rest. Comparing to the CDF measurement, the prediction agrees at intermediate $p_T$ but sits about three standard deviations high in the 15 to 20 GeV bin, where CDF finds $alpha = -0.29 plus or minus 0.23. The authors read that mismatch as a serious challenge to the formalism rather than a detail, since the qualitative rise is what the low-order spin dynamics of massless partons and heavy quarks requires.

Load-bearing premise

The longitudinal cross section for $psi(nS)$ depends on a combination of two color-octet matrix elements that the $p_T$-distribution fit does not determine, so the authors fix the mixing ratio $x = langle O_8(^1S_0) rangle / M_r$ at $1/2$ by hand and treat the whole range from 0 to 1 as an error bar; the polarization prediction therefore rests on a parameter no data constrains.

Editorial extensions

If this is right

  • If the calculation is right, any future measurement of prompt $J/psi$ polarization at the Tevatron or the LHC should show $alpha$ increasing with $p_T$ rather than falling, so a continued downward trend would falsify the low-order spin-dynamics picture rather than merely refine it.
  • The $psi'$ channel provides a cleaner test than the $J/psi$ channel, since no feeddown complicates it; a more precise direct-$psi'$ polarization measurement would discriminate between the present prediction and the earlier, higher curves.
  • Improved $J/psi$ and $psi'$ cross-section data would shrink the dominant ambiguities, which the authors trace to the fitted color-octet matrix elements, the parton distribution choice, and the unmeasured mixing parameter $x$.
  • Because the disagreement grows with $p_T$, a Run II sample extending the measurement beyond 20 GeV would decide whether the discrepancy is a statistical fluctuation in the top bin or a systematic failure of the factorization approach for charmonium.

Reading between the lines

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

  • The paper's logic suggests a useful diagnostic separation: measure $alpha$ for $psi'$ and for $chi_{cJ}$-tagged events independently, since the two feeddown streams partly cancel at high $p_T$ in the prompt sample and could mask a real discrepancy in either one.
  • The same spin-bookkeeping could be run in reverse, using measured polarization as an additional constraint that breaks the degeneracy between $langle O_8(^1S_0) rangle$ and $langle O_8(^3P_0) rangle$ that the $p_T$ distributions alone cannot resolve.
  • If the anomaly survives, the most economical reading is not that QCD is wrong but that $m_c$ is too light for the velocity expansion to control the spin-dependent channels, which would predict the discrepancy to shrink for bottomonium, where the same calculation is more trustworthy.
  • The three-sigma tension sits in a single bin with a large error bar, so a reanalysis combining bins or quoting a correlation-aware goodness of fit would be a cheap way to see how much of the tension is real.
Original abstract

The polarization of prompt J/psi at the Fermilab Tevatron is calculated within the nonrelativistic QCD factorization framework. The contribution from radiative decays of P-wave charmonium states decreases, but does not eliminate, the transverse polarization at large transverse momentum. The angular distribution parameter alpha for leptonic decays of the J/\psi is predicted to increase from near 0 at p_T = 5 GeV to about 0.5 at p_T = 20 GeV. The prediction is consistent with measurements by the CDF Collaboration at intermediate values of p_T, but disagrees by about 3 standard deviations at the largest values of p_T measured.

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, 3,665 input tokens, $0.0002 reported.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.86 · human participants 0.02 · controlled comparison 0.06 · randomized assignment 0.01 · states quantitative result 0.98 · compares with prior results 0.91 · mentions code or data availability 0.02.

The abstract, sentence by sentence

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

The polarization of prompt J/psi at the Fermilab Tevatron is calculated within the nonrelativistic QCD factorization framework. The contribution from radiative decays of P-wave charmonium states decreases, but does not eliminate, the transverse polarization at large transverse momentum. The angular distribution parameter alpha for leptonic decays of the J/\psi is predicted to increase from near 0 at p_T = 5 GeV to about 0.5 at p_T = 20 GeV. The prediction is consistent with measurements by the CDF Collaboration at intermediate values of p_T, but disagrees by about 3 standard deviations at the largest values of p_T measured.

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 The polarization of prompt J/psi at the Fermilab Tevatron is calculated within the nonrelativistic QCD factorization framework. contribution 0.69 0.90 0.08 asserted 1.00
s1 The contribution from radiative decays of P-wave charmonium states decreases, but does not eliminate, the transverse polarization at large transverse momentum. result 0.99 0.78 0.30 asserted 1.00
s2 The angular distribution parameter alpha for leptonic decays of the J/\psi is predicted to increase from near 0 at p_T = 5 GeV to about 0.5 at p_T = 20 GeV. result 1.00 0.88 0.27 asserted 0.98
s3 The prediction is consistent with measurements by the CDF Collaboration at intermediate values of p_T, but disagrees by about 3 standard deviations at the largest values of p_T measured. result 0.64 0.59 0.29 asserted 0.75

What kind of paper the classifier reports this is: theoretical result 0.99 · evidence from simulation or computation 0.58.

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. FIG. 1. Polarization variable

Figures reproduced from arXiv:hep-ph/9911436 by the authors.

References
How the literature uses it

33 arXiv papers cite this in 48 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 · 25 sentences without a confident label

Contests it 3 papers
Uses its method or tool 1 paper
Uses its data or values 8 papers
Compares with it 1 paper
Cites it as background 7 papers

Discussion

Disagree with the review, or know something it missed? Leave a comment, highlight any passage above to comment on it, or challenge this review formally.