{"id":"21e50037-b163-4ac0-b5af-693bea607e91","arxiv_id":"2506.02163","paper_version":1,"verdict":"ACCEPT","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"CMS reports a 95% CL upper limit of 7.8 times the SM rate for ttH with H->cc, and a combined constraint |kappa_c| < 3.5, the most stringent to date.","lead":"CMS searched for the Higgs boson decaying to charm quarks when produced with a top quark pair. The result places the strongest constraint yet on the Higgs to charm quark coupling, limiting it to less than 3.5 times the standard model value.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 'most stringent constraint on kappa_c' claim is sensitive to whether kappa_b is fixed or profiled; the paper's own ttH-only observed bound (|kappa_c|<3.0) is tighter than the combined limit (|kappa_c|<3.5).","rationale":"The reader's accepted verdict focuses on charm-tagging and tt+jets background modeling as the weakest assumption. That is a legitimate systematic concern, but the paper itself states that the leading uncertainty for mu_ttH(H->cc) is statistical (about 74%), which reduces the leverage of those systematics on the central limit. The more direct risk to the central claim is the internal comparison of kappa_c limits: the paper advertises the combined result as 'the most stringent constraint on kappa_c to date' while also reporting a numerically tighter observed bound from ttH alone under a different (fixed-kappa_b) assumption. Because the paper does not explain that the difference is due to marginalizing over kappa_b and including the upward-fluctuating VH data, a reader cannot tell whether the headline interval is indeed the strongest obtainable constraint. This is a load-bearing issue for the strongest_claim, but it is resolvable by a straightforward check of the PAS. The verdict should therefore be conditional: accept the paper if the profiled ttH-only limit confirms that the combined result is appropriate for the claim, or amend the claim if it does not.","tokens_in":4165,"tokens_out":9121,"duration_ms":83109,"concrete_test":"From CMS-PAS-HIG-24-018, extract the observed and expected 95% CL upper limit on |kappa_c| from the ttH-only fit with kappa_b profiled (not fixed to 1). Also check whether the combined 95% interval has a lower bound; if so, the quoted |kappa_c| < 3.5 is an incomplete representation. If the profiled ttH-only observed limit is less than 3.5 (or the expected limit less than 2.7), the paper should state that the strongest constraint comes from the ttH-only analysis, not the combination.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The headline claim is the statement that the combined ttH+VH result gives the most stringent constraint on kappa_c, with observed (expected) |kappa_c| < 3.5 (2.7). However, the same paper reports a ttH-only observed interval |kappa_c| < 3.0 obtained while fixing kappa_b to the SM value. These two numbers are not directly comparable: the combined result profiles over kappa_b and includes the VH search, whose data show an upward fluctuation (observed VH limit on mu_H->cc is 14, expected 7.6). This upward fluctuation plausibly explains why the combined observed upper bound is worse than the ttH-only bound. If the ttH-only fit with kappa_b profiled instead of fixed yields an observed upper limit below 3.5, then the combined result is not the most stringent observed constraint and the paper's central claim is incorrect as stated. The proceedings text does not provide enough detail to determine which interval should be quoted, so the claim rests on an unverified statistical treatment.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"These conference proceedings report a CMS search for the standard model Higgs boson decay H→cc in association with a top quark-antiquark pair (ttH), using 138 fb^-1 of 13 TeV proton-proton collisions. The analysis measures the ttH(H→bb) rate simultaneously, validates the method by measuring ttZ production, and sets an observed (expected) 95% CL upper limit on mu_ttH(H→cc) of 7.8 (8.7). The result is interpreted in the kappa framework and combined with an earlier VH search, yielding observed (expected) |kappa_c| < 3.5 (< 2.7), which the paper describes as the most stringent constraint on kappa_c to date.","tokens_in":4422,"tokens_out":5587,"duration_ms":51563,"significance":"If the quoted result is correct, it would provide the tightest direct constraint on the Higgs-charm Yukawa coupling, a key test of the standard model's second-generation fermion couplings. The analysis is technically sophisticated, using a ParticleNet-based flavor tagger and a ParT multiclass event classifier, and it simultaneously measures ttH(H→bb) and validates the approach with ttZ. The proceedings is concise and relies on the companion CMS-PAS-HIG-24-018 for systematic and technical details; this is appropriate for a conference summary. The central physics result is plausible and consistent with the numbers shown, but the headline claim of being the 'most stringent constraint' is not fully supported by the numbers as presented.","major_comments":[{"comment":"The statement 'This represents the most stringent constraint on kappa_c to date' is difficult to reconcile with the same section's earlier quoted result, obtained in the ttH-only analysis with kappa_b fixed to unity, of observed (expected) |kappa_c| < 3.0 (3.3). The combined observed limit is |kappa_c| < 3.5, which is numerically looser than the ttH-only fixed-kappa_b limit. The text does not specify the statistical treatment used for the combined result (e.g., whether kappa_b is profiled rather than fixed) nor why the two numbers are not directly comparable. If the ttH-only result with kappa_b profiled yields an observed upper bound below 3.5, then the combined result is not the most stringent observed constraint. I request that the authors clarify this point, either by providing the profiled ttH-only value or by qualifying the claim to refer to a specific statistical framework (e.g., 'in a combined fit with kappa_b allowed to float'). Without this clarification, the central claim of the paper is ambiguous.","section":"Section 3"}],"minor_comments":[{"comment":"The notation 'kappa_c < 3.5' and 'kappa_c < 2.7' should be '|kappa_c| < 3.5' and '|kappa_c| < 2.7' to match the body text and the convention for a two-sided parameter.","section":"Abstract"},{"comment":"The phrase 'observed (expected) 95% CL interval is |kappa_c| < 3.0 (3.3)' is unconventional because an upper limit is a one-sided interval; consider using 'upper limit' for clarity.","section":"Section 3"},{"comment":"In the sentence describing the floating tt+jets normalizations, the list 'tt+c, tt+≥2c, tt+b, tt+≥2b, and tt+light' would be clearer if set off with semicolons or presented as a parenthetical list.","section":"Section 2"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is a concise conference proceedings that appropriately refers to the detailed CMS physics analysis summary for systematics and likelihood construction. The main issue is the unqualified claim that the combined result gives the most stringent constraint on kappa_c, despite the ttH-only fixed-kappa_b limit being numerically tighter. This needs to be resolved either by providing the profiled ttH-only value or by explicitly stating the assumptions under which the combined limit is the most stringent. The underlying analysis appears sound based on the numbers reported, so I do not recommend rejection; however, the ambiguity is load-bearing for the paper's headline and should be addressed before publication."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Bottom line: this is a solid, incremental result from CMS. The genuinely new piece is the ttH-production search for H->cc; previous CMS and ATLAS limits came from VH only. The analysis is standard but well executed: ParticleNet for jet flavor, ParT as event classifier, a simultaneous fit of ttH(H->bb), ttH(H->cc), ttZ(Z->bb), and ttZ(Z->cc), with five floating tt+jets backgrounds. The ttZ validation (1.02 +0.79/-0.84 for Z->cc, 1.47 +0.45/-0.41 for Z->bb) is a genuine check and gives confidence that charm-tagging and background modeling are in the right ballpark.\n\nThe headline result, combined observed (expected) |kappa_c| < 3.5 (2.7), is plausible and more stringent than the ATLAS 4.2 and previous CMS 5.5 values. The stress-test note raises an apparent tension: the paper also quotes |kappa_c| < 3.0 for ttH-only when fixing kappa_b to unity. That number is tighter but comes from a more restrictive assumption; the combined bound profiles over kappa_b, so the two are not directly comparable. The loosening from 3.0 to 3.5 in the observed combined limit is likely due to the upward fluctuation in the VH channel (observed limit 14 vs expected 7.6). This does not invalidate the \"most stringent\" claim, but the paper should say explicitly that 3.0 is conditional on kappa_b = 1 and 3.5 is the profiled result. Without that caveat, a careful reader could fairly call the abstract misleading.\n\nThe main limitation is that this is a short proceedings: key systematic details, the likelihood, and the charm-tagging calibration live in CMS-PAS-HIG-24-018. That is normal for conference write-ups, but independent verification has to wait for the PAS or the journal paper. The citation pattern is clean; the one self-reference to the PAS is appropriate.\n\nNo serious flaws in the math or logic that I can see. The five float tt+jets normalizations are reasonable and constrained by control regions, and the quoted uncertainties are internally consistent.\n\nWho is this for? Higgs physicists and flavor physicists tracking Yukawa couplings. It is not a methodological breakthrough; it is a careful, incremental measurement. It deserves a serious referee if submitted to a journal; as a proceedings, it is fine once the kappa_b assumption is clarified. I would cite it in any review of Higgs couplings.","headline":"Solid incremental CMS result giving the tightest kappa_c bound to date; the headline claim needs a sharper caveat about fixed vs profiled kappa_b.","tokens_in":4910,"tokens_out":3802,"would_cite":true,"duration_ms":34114,"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":"A search for Higgs boson decays to charm quarks in $t\\bar{t}H$ production, combined with earlier $VH$ data, sets the most stringent limit on the charm Yukawa coupling: observed $|\\kappa_c|<3.5$ at 95% confidence.","keywords":["Higgs boson","charm Yukawa coupling","H to cc","ttH production","CMS","kappa_c","jet tagging","ParticleNet"],"falsifier":"Rerun the profile likelihood with the five $t\\bar{t}+$jets background components normalized freely in the signal regions instead of being tied to the control regions; if the resulting 95% interval on $\\kappa_c$ no longer respects $|\\kappa_c| < 3.5$, the headline bound depends on the control-region transfer assumption rather than being robustly determined by the data.","tokens_in":3985,"feed_emoji":"🔬","tokens_out":11504,"duration_ms":109411,"temperature":0.7,"pith_summary":"This paper reports a direct search for the Higgs boson decaying to a charm quark-antiquark pair, a process the standard model predicts at a small rate and that has not yet been observed. Using 138 fb$^{-1}$ of 13 TeV proton-proton collisions in the $t\\bar{t}H$ production mode, it sets an observed (expected) upper limit of 7.8 (8.7) times the standard model rate for $t\\bar{t}H(H\\to c\\bar{c})$. Combined with the earlier $VH$ search, the observed (expected) interval on the charm Yukawa coupling modifier is $|\\kappa_c| < 3.5$ ($|\\kappa_c| < 2.7$), which the paper identifies as the most stringent constraint on $\\kappa_c$ to date. The same analysis measures $t\\bar{t}H(H\\to b\\bar{b})$ relative to the standard model at $0.91^{+0.26}_{-0.22}$, a 4.4-standard-deviation observation, and validates the search strategy by measuring $t\\bar{t}Z$ decays to charm and bottom quark pairs. If correct, this result tightens the experimental picture of how the Higgs boson couples to second-generation quarks and sharpens the target for future searches.","feed_headline":"New search caps Higgs-charm coupling at 3.5","feed_subtitle":"Combining ttH and VH data gives the tightest limit yet on the Higgs boson's coupling to charm quarks.","key_machinery":"The argument is carried by a binned profile likelihood fit to event counts in signal and control regions defined by a transformer-based event classifier (ParT) and by two ParticleNet jet-tagging discriminants, $p_{B+C}$ and $p_{B\\rm vs C}$, which separate heavy-flavor from light-flavor jets and b jets from c jets. The fit treats the five $t\\bar{t}+$jets background components as independently floating normalizations constrained in dedicated control regions, and extracts signal strength modifiers for $t\\bar{t}H(H\\to c\\bar{c})$, $t\\bar{t}H(H\\to b\\bar{b})$, $t\\bar{t}Z(Z\\to c\\bar{c})$, and $t\\bar{t}Z(Z\\to b\\bar{b})$. The $\\kappa_c$ interpretation uses the kappa-framework, which expresses the $H\\to c\\bar{c}$ and $H\\to b\\bar{b}$ branching fractions as functions of the Yukawa coupling modifiers $\\kappa_c$ and $\\kappa_b$, and combines the $t\\bar{t}H$ likelihood with the previous $VH$ result.","core_discovery":"The paper's central claim is that a direct $t\\bar{t}H$-associated search for $H\\to c\\bar{c}$, combined with the earlier $VH$ search, yields the tightest bound yet on the Higgs-charm Yukawa coupling: observed $|\\kappa_c| < 3.5$ at 95% confidence, with an expected bound of $|\\kappa_c| < 2.7$. In the $t\\bar{t}H$ channel alone, no signal is established and the observed (expected) 95% CL upper limit on the $t\\bar{t}H(H\\to c\\bar{c})$ rate is 7.8 (8.7) times the standard model prediction. The companion $H\\to b\\bar{b}$ measurement returns a signal strength of $0.91^{+0.26}_{-0.22}$, a 4.4-standard-deviation effect, while the two $t\\bar{t}Z$ validation modes ($Z\\to c\\bar{c}$ and $Z\\to b\\bar{b}$) agree with the SM within one and two standard deviations, respectively. The $\\kappa_c$ interval is obtained by profiling $\\kappa_c$ and $\\kappa_b$ in the kappa-framework and then combining the $t\\bar{t}H$ likelihood with the $VH$ result, giving the paper's headline result.","pith_inferences":["Because the leading uncertainty on the $H\\to c\\bar{c}$ signal strength is statistical (roughly 74%), the same analysis at a higher-luminosity LHC should tighten the $\\kappa_c$ bound roughly as the square root of the accumulated luminosity before systematic uncertainties dominate.","The observed limit on $\\kappa_c$ being less stringent than expected (3.5 observed versus 2.7 expected) is consistent with a small upward fluctuation in the charm-like signal categories; the current evidence is far from conclusive, but a future run could test whether any hint of an enhanced charm coupling persists.","The combination logic used here could be extended to include gluon-fusion and vector-boson-fusion production of the Higgs boson, which would further constrain $\\kappa_c$ if charm-tagging performance at lower Higgs transverse momenta can be controlled."],"forward_implications":["The observed $|\\kappa_c| < 3.5$ is the most stringent experimental limit on the charm Yukawa coupling, improving on the previous $VH$-only bounds reported by both major Higgs experiments.","The $t\\bar{t}H(H\\to b\\bar{b})$ signal strength of $0.91^{+0.26}_{-0.22}$ and its 4.4-standard-deviation significance support the $t\\bar{t}H$ event-selection and background-modeling chain used for the charm search.","The $t\\bar{t}Z(Z\\to c\\bar{c})$ and $t\\bar{t}Z(Z\\to b\\bar{b})$ measurements, which agree with the standard model, validate that charm-jet tagging and the background estimation method perform as expected in this final state.","If the true charm Yukawa coupling is close to its standard model value, the expected bound of $|\\kappa_c| < 2.7$ implies that substantially more integrated luminosity will be required before a $H\\to c\\bar{c}$ signal can be established.","The simultaneous measurement of $H\\to b\\bar{b}$ and $H\\to c\\bar{c}$ in the same production mode offers a direct experimental handle on the ratio $\\kappa_c/\\kappa_b$, with production-side uncertainties suppressed."],"supporting_citations":[{"why":"Supplies the previous ATLAS $VH$ limit that this result's 'most stringent' claim is compared against.","marker":"9"},{"why":"The CMS $VH$ search whose likelihood is combined with the $t\\bar{t}H$ search to derive the combined $\\kappa_c$ interval.","marker":"10"},{"why":"Provides the ParticleNet jet-tagging algorithm whose $p_{B+C}$ and $p_{BvsC}$ discriminants define the heavy-flavor tagging categories.","marker":"11"},{"why":"The CMS physics analysis summary containing the full $t\\bar{t}H(H\\to c\\bar{c})$ analysis and the results quoted in these proceedings.","marker":"13"},{"why":"Provides the ParT transformer classifier used to separate the $t\\bar{t}H$, $t\\bar{t}Z$, and $t\\bar{t}+$jets event classes.","marker":"14"},{"why":"Defines the kappa-framework that parameterizes $H\\to c\\bar{c}$ and $H\\to b\\bar{b}$ branching fractions in terms of $\\kappa_c$ and $\\kappa_b$ for the combined interpretation.","marker":"17"}],"fun_headline_variants":["Higgs-charm coupling capped at 3.5","Best limit yet on Higgs-charm coupling","CMS caps Higgs-charm coupling at 3.5","Higgs-charm Yukawa capped at 3.5","New bound on Higgs-charm coupling: <3.5"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The result assumes that, after calibration, the simulation correctly predicts how often charm-quark jets are tagged and how much background from top-quark pairs with extra jets contaminates each region; if either prediction is wrong, the extracted signal strengths and the quoted $\\kappa_c$ limits are biased.","fun_headline_variants_meta":{"raw":{"variants":["Higgs-charm coupling capped at 3.5","Best limit yet on Higgs-charm coupling","CMS caps Higgs-charm coupling at 3.5","Higgs-charm Yukawa capped at 3.5","New bound on Higgs-charm coupling: <3.5"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000866,"raw_usage":{"total_tokens":3813,"prompt_tokens":1061,"completion_tokens":2752,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":677,"completion_tokens_details":{"reasoning_tokens":2672}},"tokens_in":677,"tokens_out":2752,"duration_ms":20506,"temperature":1.0,"reasoning_tokens":2672,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T11:28:55.748710+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Rerun the profile likelihood with the five $t\\bar{t}+$jets background components normalized freely in the signal regions instead of being tied to the control regions; if the resulting 95% interval on $\\kappa_c$ no longer respects $|\\kappa_c| < 3.5$, the headline bound depends on the control-region transfer assumption rather than being robustly determined by the data.","supporting_citations":[{"cited_title":"Measurements of WH and ZH production with Higgs boson decays into bottom quarks and direct constraints on the charm Yukawa coupling in 13 TeV pp collisions with the ATLAS detector","cited_arxiv_id":null,"evidence_quote":"Supplies the previous ATLAS $VH$ limit that this result's 'most stringent' claim is compared against."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"The CMS $VH$ search whose likelihood is combined with the $t\\bar{t}H$ search to derive the combined $\\kappa_c$ interval."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the ParticleNet jet-tagging algorithm whose $p_{B+C}$ and $p_{BvsC}$ discriminants define the heavy-flavor tagging categories."},{"cited_title":"Search for Higgs boson decay to a charm quark-antiquark pair via t¯tH production, 2023","cited_arxiv_id":null,"evidence_quote":"The CMS physics analysis summary containing the full $t\\bar{t}H(H\\to c\\bar{c})$ analysis and the results quoted in these proceedings."},{"cited_title":"Particle Transformer for jet tagging","cited_arxiv_id":null,"evidence_quote":"Provides the ParT transformer classifier used to separate the $t\\bar{t}H$, $t\\bar{t}Z$, and $t\\bar{t}+$jets event classes."},{"cited_title":"Handbook of LHC Higgs cross sections: 4","cited_arxiv_id":null,"evidence_quote":"Defines the kappa-framework that parameterizes $H\\to c\\bar{c}$ and $H\\to b\\bar{b}$ branching fractions in terms of $\\kappa_c$ and $\\kappa_b$ for the combined interpretation."}],"review_version":1}