{"id":"eb2d12d5-6989-47a6-ba59-2d197e1a9362","arxiv_id":"2506.15205","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"PYTHIA 8.312 with the new quarkonia parton shower reproduces the LHCb and CMS prompt J/psi-in-jet data, and predicts that distinguishing the shower effect for Upsilon(1S) requires jet pT above 50 GeV/c at LHCb and 70 GeV/c at CMS.","lead":"This paper uses PYTHIA 8 simulations to test how well a new quarkonia parton shower reproduces LHC data on J/psi mesons produced inside jets. The simulations show the new shower fixes a known discrepancy and predicts that experiments need higher jet momentum cuts to see the effect with Upsilon(1S) mesons.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Central claim rests on visual agreement; no MC uncertainties or goodness-of-fit, so 'correctly describe' and the CR-discrimination claim are not quantitatively established.","rationale":"The reader's verdict is already CONDITIONAL, and the reader's rationale explicitly notes the absence of Monte Carlo uncertainty bands and any quantitative goodness-of-fit. My concern is consistent with that rationale, but it is not identical to the reader's stated weakest_assumption, which focuses on the omitted octet splitting kernels and the massive-gluon treatment of the color-octet state. I regard the lack of uncertainty quantification as more directly load-bearing: even if the implemented shower approximations are physically reasonable, the paper's central empirical claim is a comparison between simulated and measured normalized z distributions, and that comparison cannot be judged without statistical errors on the simulation and a quantitative measure of agreement. The text in Section 3 does provide an ordering argument for why the missing gluon- and heavy-quark-initiated octet kernels are subleading, but it gives no numerical impact estimate, so that approximation is a secondary risk rather than the primary defect. A concrete rerun with enough events and a chi2-based test would settle whether the apparent QCD-CR preference and the overall 'correctly describe' claim survive; until then CONDITIONAL is the appropriate verdict, so I recommend no change to the reader's decision.","tokens_in":10193,"tokens_out":6521,"duration_ms":77616,"concrete_test":"Generate at least 10 independent PYTHIA 8.312 samples of at least 10^7 minimum-bias events for each of the four setups (8.307 and 8.312, each with MPI-CR and QCD-CR), using the same LHCb and CMS selections as in the paper. Compute the normalized z distributions with per-bin statistical errors and run-to-run spread, then evaluate a binned chi2 or negative log-likelihood against the published data points, including published data uncertainties and, where possible, MC bin correlations. If the chi2 difference between QCD-CR and MPI-CR for CMS is not significant, or if the red and blue CMS curves agree within MC errors in the z bins that currently appear to discriminate, then the claims of correct description and CR discrimination are not established.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The load-bearing step is the comparison in Figs. 1-2 that converts simulation output into 'correctly describe' and 'data clearly favours QCD-CR'. The paper provides no statistical or systematic uncertainty bands for the PYTHIA histograms, no number of generated events, and no chi2 or likelihood value. The observable is a normalized z distribution, and the high-z bins that drive the CMS CR discrimination are narrow; for the data, statistical and systematic uncertainties are only added in quadrature in the published points. Without Monte Carlo error bars, the apparent flattening of the LHCb distribution in Fig. 2a and the difference between the red and blue CMS curves in Fig. 2b could be within Monte Carlo statistical fluctuations, especially since the MPI-CR curve's rise appears only near z approximately 1, where few events populate the bins. The statement 'correctly describe' is therefore an interpretation of overlaid histograms rather than a tested quantitative claim. This weakness is load-bearing because the Upsilon prediction and the proposed CR-discrimination test inherit their credibility from this comparison. The missing-octet-kernel approximation acknowledged in Section 3 is an additional reason to demand quantitative checks, but the first-order issue is that no uncertainty quantification is provided for the claimed agreement.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This manuscript compares PYTHIA 8.307 and 8.312 predictions for the normalized z distribution of prompt J/ψ mesons inside jets with LHCb (√s=13 TeV) and CMS (√s=5.02 TeV) data, for the MPI and QCD color reconnection schemes. It reports that PYTHIA 8.307 overshoots the data at z≈1 regardless of the CR model, while PYTHIA 8.312 with the new quarkonia parton shower improves the agreement, especially with QCD-CR. It then proposes higher jet pT selections (50 GeV/c for LHCb, 70 GeV/c for CMS) as a way to discriminate CR models for prompt J/ψ, and predicts Υ(1S) production in jets at the same LHCb/CMS kinematics, concluding that high jet pT cuts are needed to distinguish simulations with and without the quarkonia shower. The study uses publicly available generator versions with default tunes and LDMEs and performs no fits.","tokens_in":10436,"tokens_out":8686,"duration_ms":84555,"significance":"If the quantitative concerns below are addressed, this is a useful phenomenological result: it highlights a qualitatively new effect of the NRQCD parton shower on jet fragmentation into quarkonia, and it makes concrete, falsifiable predictions for Υ(1S) at high jet pT that LHC experiments can test. The paper is honest about the approximations in the new shower and does not introduce ad hoc parameters. Its current weakness is that the central claims—'correctly describe the experimental results' and 'the data clearly favours the QCD-CR model'—are supported only by visual comparison of normalized histograms, with no Monte Carlo uncertainty bands and no goodness-of-fit quantification.","major_comments":[{"comment":"The abstract and Section 3 state that PYTHIA 8.312 can 'correctly describe the experimental results' and that 'the data clearly favours the QCD-CR model' (Fig. 2b), but the manuscript provides no Monte Carlo uncertainty bands, no number of generated events, and no goodness-of-fit measure such as a chi-squared or Kolmogorov-Smirnov statistic. The observable is a normalized z distribution written as (1/N) dN/dz, and the discriminating bins at high z contain relatively few entries; without MC statistical uncertainties, the visible differences between the red and blue curves in Fig. 2b, and the apparent flattening in Fig. 2a, could be statistical fluctuations. Please add MC error bars and report a quantitative comparison metric for each data/MC panel.","section":"Abstract; Section 3, Figs. 1-2"},{"comment":"The new quarkonia parton shower is implemented with only three splitting kernels, with the color-octet state treated as a massive gluon, and with the gluon- and heavy-quark-initiated octet splittings omitted. The text acknowledges these approximations but does not quantify their effect on the z distribution. Because the claim is that the shower provides the 'correct amount of jet activity,' the agreement with data could depend on cancellations among the missing kernels. Please estimate the numerical impact of each omitted kernel (for example, by switching individual kernels on and off, or by comparing with a full NRQCD calculation) before concluding that the shower describes the data.","section":"Section 3, second paragraph"},{"comment":"The comparison between PYTHIA 8.307 and 8.312 attributes all differences to the new quarkonia parton shower, but PYTHIA 8.312 contains other changes relative to 8.307, and Fig. 1 already uses a 'new beam remnant model' in the QCD-CR simulation. To isolate the effect of the quarkonia shower, the authors should compare, within the same PYTHIA version, runs with the quarkonia shower enabled and disabled, or otherwise demonstrate that no other version change affects the z distribution.","section":"Figs. 1-2"},{"comment":"The Υ(1S) predictions and the proposed experimental discrimination inherit their credibility from the J/ψ validation, but they are also presented without uncertainty bands, and the manuscript does not state the number of generated events, the PDF set, the CR parameter values (e.g., Reconnection Range), or the exact PYTHIA run configuration. Please provide these technical details so that the results are reproducible, and include MC uncertainties in the prediction figures.","section":"Figs. 4-5; Section 3"}],"minor_comments":[{"comment":"There are numerous typographical errors: 'non of' should be 'none of'; 'chamonium' should be 'charmonium'; 'relavistically' should be 'relativistically'; 'octate' should be 'octet'; 'wether' should be 'whether'; 'taged' should be 'tagged'; 'topologycal' should be 'topological'; 'the later' should be 'the latter'; 'independently if' should be 'regardless of whether'.","section":"Throughout"},{"comment":"The text first lists the NRQCD matrix elements as 3S(1)_1, 1S(8)_0, 3S(8)_1 and 3P(8)_J, but later refers to 3P(8)_0; please make the notation consistent.","section":"Section 1"},{"comment":"Reference [15] contains the placeholder text 'Image 1' in the title and should be corrected.","section":"Reference [15]"},{"comment":"Please clarify how 'prompt J/ψ' is defined in the simulation, in particular whether feed-down from excited charmonia states (e.g., ψ(2S) or χ_c) is included; the experimental prompt distributions include such feed-down.","section":"Section 3"},{"comment":"The caption states that the green curve uses 8.307 with MPI-CR while the text says the 8.307 results are independent of the CR choice; this should be stated consistently, and the invisible CR dependence of 8.307 should be shown or explicitly demonstrated.","section":"Fig. 4 caption"}],"recommendation":"major_revision","confidential_remarks":"This is a short generator-based phenomenological study. The qualitative effect is interesting and the Υ(1S) prediction is testable, but the paper currently lacks the quantitative support (MC uncertainties, goodness-of-fit, and isolation of the quarkonia-shower effect) needed to justify the strong claims in the abstract. I would be willing to reconsider after a major revision; the scope is appropriate for a letter-style journal."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick read on arXiv:2506.15205. Short version: this is the first direct test, as far as I know, of the new quarkonia parton shower in PYTHIA 8.312 against the LHCb and CMS prompt J/psi-in-jet data, and it makes a concrete, testable Upsilon(1S) prediction. That is real value. The paper also correctly shows that PYTHIA 8.307 with either CR model fails the same way, so the problem is not the CR model alone.\n\nWhat it does well: the comparison logic is clear, the description of the new shower's approximations is honest (Section 3 lists the missing kernels and gives a scaling argument for why they should be small), and the Upsilon prediction is stated with the kinematic conditions that would actually separate the versions. If the prediction holds, it gives LHC experiments a concrete target.\n\nSoft spots, in order of importance. First, there are no MC statistical uncertainty bands and no goodness-of-fit. The claim that PYTHIA 8.312 'correctly describes' the data, and the stronger claim that CMS 'clearly favours' QCD-CR, rest on visual overlay. At high z, where the CMS discrimination is driven, the bins are narrow and MC statistics matter. Without error bars on the red and blue histograms, the difference could be within fluctuations. This is load-bearing, because the Upsilon prediction inherits its credibility from the J/psi validation. Second, the paper doesn't quantify the effect of the missing octet splitting kernels. The alpha_s and mass-suppression arguments are plausible, but a numerical test (varying the kernels or switching them off) would be more convincing. Third, the 'data clearly favours QCD-CR' phrasing is stronger than the plots support for LHCb—the improvement is most evident for CMS; for LHCb both CR variants seem acceptable. That should be softened.\n\nThe citation pattern looks fine; the input LDMEs and tunes are standard, and nothing is fitted here. The paper is honest about its limitations. It deserves a serious referee, but the revision should add uncertainty bands and a statistical comparison, and temper the language. I'd bring it to our reading group after that version exists.","headline":"First direct test of the PYTHIA 8.312 quarkonia parton shower against LHCb/CMS J/psi-in-jet data, with a testable Upsilon(1S) prediction, but the central 'correctly describes' claim rests on visual agreement pending MC uncertainties.","tokens_in":10996,"tokens_out":3213,"would_cite":true,"duration_ms":30938,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"The new quarkonia parton shower in PYTHIA 8.312 reproduces prompt $J/\\psi$ production in jets at LHCb and CMS, and the QCD-based color-reconnection model improves that agreement.","keywords":["hadron-hadron collisions","quarkonia production","parton shower","color reconnection","J/psi production in jets","Upsilon(1S)","NRQCD","PYTHIA 8.312"],"falsifier":"Measure the $\\Upsilon(1S)$ $z$ distribution in jets at LHCb with $p_T^{\\rm jet}>50$ GeV/c and at CMS with $p_T^{\\rm jet}>70$ GeV/c: the paper predicts that the old and new PYTHIA versions separate near $z\\approx1$; if no separation appears, the proposed mechanism and its claimed discriminating power fail.","tokens_in":9973,"feed_emoji":"⚛️","tokens_out":9953,"duration_ms":90477,"temperature":0.7,"pith_summary":"The paper addresses a long-standing discrepancy: PYTHIA 8.307 predicts too many prompt $J/\\psi$ mesons produced with little or no jet activity, while LHCb and CMS data show them embedded in jets. The paper shows that the new quarkonia parton shower in PYTHIA 8.312, which lets quarkonium states be produced during the shower itself, flattens the jet-momentum-fraction ($z$) distribution and brings the simulation into agreement with both experiments. Replacing the MPI-based color reconnection with the QCD-based model improves the description further and changes the predicted $z$ shape, so the observable can distinguish between the two color-reconnection implementations. For $\\Upsilon(1S)$, the paper predicts that distinguishing the old and new showers requires a higher jet transverse-momentum threshold than the one used for $J/\\psi$.","feed_headline":"New parton shower fixes J/psi-in-jet mismatch","feed_subtitle":"PYTHIA 8.312 with QCD color reconnection matches LHCb and CMS data; Upsilon needs higher jet pT.","key_machinery":"The central object is the quarkonia parton shower newly implemented in PYTHIA 8.312: the splitting kernels $Q \\to Q\\bar Q[{}^3S_1^{(1)}] Q$, $g \\to Q\\bar Q[{}^3S_1^{(1)}] g g$, and $g \\to Q\\bar Q[{}^3S_1^{(8)}]$, with the only implemented color-octet state treated as a massive gluon. The diagnostic observable is $z$, the fraction of the jet's transverse momentum carried by the quarkonium; the new kernels add surrounding radiation and thereby change the predicted $z$ distribution. The paper uses this observable to compare the MPI-based and QCD-based color-reconnection models against LHCb and CMS data.","core_discovery":"The central claim is that the PYTHIA 8.307 discrepancy was not evidence against NRQCD-based quarkonium production but a symptom of missing shower physics. The new quarkonia parton shower adds three splitting kernels for S-wave quarkonia, $Q \\to Q\\bar Q[{}^3S_1^{(1)}] Q$, $g \\to Q\\bar Q[{}^3S_1^{(1)}] g g$, and $g \\to Q\\bar Q[{}^3S_1^{(8)}]$, creating quarkonia during the parton shower rather than only in the hard scattering. With this shower active, the normalized $z$ distributions for prompt $J/\\psi$ at LHCb ($\\sqrt{s}=13$ TeV) and CMS ($\\sqrt{s}=5.02$ TeV) agree with data, and the QCD-based color reconnection describes the data better than the MPI-based one, especially for CMS. For $\\Upsilon(1S)$, the paper finds that the old and new showers give almost identical predictions at the jet $p_T$ thresholds used for $J/\\psi$, because the heavier quarkonium needs a more energetic parton to be created during the shower; raising the jet $p_T$ cut to 50 GeV/c for LHCb and 70 GeV/c for CMS should separate the predictions near $z\\approx1$.","pith_inferences":["A test not performed in the paper: switch each of the three quarkonia splitting kernels on and off separately in PYTHIA 8.312; if the $z$ distribution still matches data when the octet kernel is removed, that kernel is not the source of the improvement.","If the mechanism is genuine, the same shower treatment should also shape $\\psi(2S)$ and $\\Upsilon(2S,3S)$ fragmentation in jets, with the mass hierarchy dictating the jet $p_T$ values at which the effect appears.","The QCD-based color-reconnection preference implied by the data may also show up in other color-flow-sensitive observables, such as baryon production or the underlying event, which this paper does not address."],"forward_implications":["If the claim holds, the prompt $J/\\psi$ fragmentation function in jets becomes an observable that discriminates between MPI-based and QCD-based color reconnection, and the data favour the QCD-based model.","The long-standing excess of isolated $J/\\psi$ in PYTHIA 8 disappears once quarkonium production is included in the parton shower, shifting the interpretation from a failing production rate to missing shower radiation.","For $\\Upsilon(1S)$, measurements at the jet $p_T$ cuts used for $J/\\psi$ will not distinguish the old and new showers; LHCb needs $p_T^{\\rm jet}>50$ GeV/c and CMS $p_T^{\\rm jet}>70$ GeV/c, especially near $z\\approx1$.","The mass dependence implies that heavier quarkonium states require harder jets for the quarkonia parton shower to leave a visible imprint on the $z$ distribution."],"supporting_citations":[{"why":"Supplies the LHCb 13 TeV prompt $J/\\psi$ in jets $z$-distribution data that the paper must reproduce.","marker":"[20]"},{"why":"Supplies the CMS 5.02 TeV fragmentation data that show the same discrepancy and provide the second comparison.","marker":"[21]"},{"why":"Introduces the quarkonia parton shower implemented in PYTHIA 8.312, the central mechanism of the claim.","marker":"[29]"},{"why":"Provides the QCD-based color reconnection model that improves the agreement with data.","marker":"[23]"},{"why":"Documents PYTHIA 8.3 and the generator setup, including the versions compared.","marker":"[22]"},{"why":"The Monash tune used for the LHCb simulations that produce the quoted predictions.","marker":"[27]"},{"why":"The CP5 tune used for the CMS simulations, needed to reproduce the comparison.","marker":"[28]"}],"fun_headline_variants":["Quarkonia parton shower matches LHC J/psi jet data","New PYTHIA shower fixes J/psi jet puzzle, Upsilon needs higher pT","QCD color reconnection best with quarkonia shower for J/psi","Upsilon prediction: raise jet pT to see quarkonia shower","J/psi jets fixed by quarkonia parton shower"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The central premise is that the simplified quarkonium splitting rules in the new shower---only three kernels, with the lone color-octet state modeled as a massive gluon and the other octet splittings omitted---are accurate enough that the improved agreement with data is real rather than accidental.","fun_headline_variants_meta":{"raw":{"variants":["Quarkonia parton shower matches LHC J/psi jet data","New PYTHIA shower fixes J/psi jet puzzle, Upsilon needs higher pT","QCD color reconnection best with quarkonia shower for J/psi","Upsilon prediction: raise jet pT to see quarkonia shower","J/psi jets fixed by quarkonia parton shower"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000705,"raw_usage":{"total_tokens":3230,"prompt_tokens":1048,"completion_tokens":2182,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":664,"completion_tokens_details":{"reasoning_tokens":2086}},"tokens_in":664,"tokens_out":2182,"duration_ms":16221,"temperature":1.0,"reasoning_tokens":2086,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T19:40:27.025689+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the $\\Upsilon(1S)$ $z$ distribution in jets at LHCb with $p_T^{\\rm jet}>50$ GeV/c and at CMS with $p_T^{\\rm jet}>70$ GeV/c: the paper predicts that the old and new PYTHIA versions separate near $z\\approx1$; if no separation appears, the proposed mechanism and its claimed discriminating power fail.","supporting_citations":[],"review_version":2}