{"id":"40ec60e9-fe8e-4ccd-8fe1-d5c3e1b0ffda","arxiv_id":"2605.02622","paper_version":2,"verdict":"UNVERDICTED","confidence":"LOW","novelty_score":5.0,"correctness_risk":"unknown","formal_verification":"none","parameter_count":1,"one_line_summary":"Implementation of two NLL-accurate dipole showers in Herwig shows that differences in infrared cutoffs produce noticeable effects at the hadron level and affect model tunability.","lead":"The paper implements two recently proposed dipole parton shower algorithms with next-to-leading-logarithmic accuracy in the Herwig event generator and compares their infrared behavior to existing showers. A smart generalist might read it to see how choices in the low-energy cutoff of these simulations affect the input to hadronization models used in collider physics.","discovery_kind":"extension","skeptic_critique":{"model":"grok-4.3","headline":"Attribution of hadron-level differences to IR cutoff lacks isolation from other algorithmic variations","rationale":"The reader's weakest_assumption directly identifies the same attribution gap. Because the review was performed on the abstract, the full text might contain an internal cross-check that was not visible; absent such a check the concern stands and the UNVERDICTED status is appropriate.","tokens_in":1675,"tokens_out":288,"duration_ms":13469,"concrete_test":"Within one fixed shower (e.g., the new dipole algorithm), implement both the original and the alternative IR cutoff prescription while keeping the NLO matching and cluster hadronization parameters identical; recompute the hadron-level observables shown in the paper and check whether the size of the differences matches those reported between distinct showers.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim is that precise IR cutoff definitions drive important hadron-level consequences and should be studied as the interface to cluster hadronization. However, the compared showers (new dipole vs. existing dipole vs. angular-ordered) differ simultaneously in hard-regime extrapolation, NLO matching procedure, and logarithmic accuracy implementation. The manuscript does not report a controlled test in which only the cutoff scale or definition is varied inside a single shower framework while holding matching and hadronization fixed; therefore the observed differences cannot be unambiguously assigned to the cutoff rather than to the other implementation distinctions.","agreement_with_reader":"agree"},"referee_report":{"model":"grok-4.3","summary":"The manuscript implements two recently proposed dipole parton shower algorithms with next-to-leading-logarithmic accuracy at leading colour inside the Herwig event generator. These are compared to Herwig's existing dipole and angular-ordered showers, with emphasis on their extrapolations into the hard regime (where NLO matching is performed) and the infrared regime (where the infrared cutoff serves as input to the cluster hadronization model). The authors report that differences in the precise definition of this infrared cutoff produce important consequences at the hadron level and propose the cutoff as a starting point for further study of shower-hadronization interplay; they conclude with a tunability study that identifies best-fit parameters for each model.","tokens_in":1806,"tokens_out":433,"duration_ms":28042,"significance":"If the reported hadron-level consequences of the infrared cutoff definitions are robust, the work is significant for clarifying the interface between perturbative showers and non-perturbative hadronization in general-purpose event generators. The explicit implementation of improved-logarithmic-accuracy showers and the concrete tuning exercise to data constitute practical strengths that can guide users of Herwig.","major_comments":[{"comment":"§4 (hadron-level results): the attribution of observed differences at the hadron level to the distinct infrared cutoff definitions is not supported by a controlled test in which only the cutoff scale or definition is varied inside a single shower framework while holding the NLO matching procedure, hard-regime extrapolation, and cluster hadronization model fixed. Because the compared showers differ simultaneously in multiple algorithmic aspects, the central claim that the cutoff is the dominant driver cannot be isolated from other implementation distinctions.","section":"§4 (hadron-level results)"}],"minor_comments":[{"comment":"Ensure that all tables reporting best-fit parameters explicitly list the observables and data sets used in the tuning procedure.","section":"tunability section"},{"comment":"Figure captions should state the precise infrared cutoff values employed by each shower variant.","section":null}],"recommendation":"major_revision","confidential_remarks":null},"author_rebuttal":{"model":"grok-4.3","summary":"We thank the referee for their careful reading of the manuscript and for highlighting the need for greater clarity on the origin of the observed hadron-level differences. We address the major comment below.","responses":[{"response":"We agree that a fully controlled test, in which only the infrared cutoff definition is varied inside one fixed shower framework while keeping NLO matching, hard-regime behaviour and the hadronization model identical, would strengthen the attribution. Such a test is not performed in the present work because the two NLL-accurate dipole showers are distinct algorithmic proposals; implementing a hybrid version that isolates only the cutoff would require substantial additional development beyond the scope of the paper. The manuscript instead compares complete, self-consistent implementations as they would be used in practice. We have revised §4 to state explicitly that the showers differ in several respects and that, while the infrared cutoff is expected to be an important driver of the hadron-level differences (because it directly sets the input to cluster hadronization), other algorithmic distinctions may also contribute. The text now frames the cutoff as a promising starting point for future dedicated studies rather than as the sole proven cause.","revision_made":"partial","referee_comment":"§4 (hadron-level results): the attribution of observed differences at the hadron level to the distinct infrared cutoff definitions is not supported by a controlled test in which only the cutoff scale or definition is varied inside a single shower framework while holding the NLO matching procedure, hard-regime extrapolation, and cluster hadronization model fixed. Because the compared showers differ simultaneously in multiple algorithmic aspects, the central claim that the cutoff is the dominant driver cannot be isolated from other implementation distinctions."}],"tokens_in":1302,"tokens_out":358,"duration_ms":16609,"standing_objections":[]},"desk_editor":{"model":"grok-4.3","letter":"The paper's main contribution is the implementation of two recently proposed dipole showers inside Herwig, followed by a direct comparison to the generator's existing angular-ordered and dipole options. They run the new showers through NLO matching and cluster hadronization, then examine how the infrared cutoff definitions feed into the hadronization model.\n\nThey do the implementation cleanly and report tunability studies that identify best-fit parameters for each shower. That part is practical and will be of immediate use to people who actually run Herwig.\n\nThe softer part is the emphasis on the infrared cutoff as the key driver of hadron-level differences. The showers vary simultaneously in their hard-regime behavior, matching procedure, and logarithmic accuracy, so the observed effects at hadron level cannot be cleanly attributed to the cutoff alone. No controlled test that holds everything else fixed and varies only the cutoff scale or definition is described.\n\nThis is a standard generator-implementation paper aimed at the small group of people who develop or tune parton showers inside Herwig. It does not reorganize the field, but the numerical comparisons are worth having in the literature.\n\nI would send it to referees. The work is honest, the code changes are real, and the community that maintains these tools needs this kind of documentation even if the interpretation of the cutoff effects needs more isolation.","headline":"They ported two recent NLL dipole showers into Herwig and show that the infrared cutoff choice affects hadron-level results, but the differences are not isolated from other shower variations.","tokens_in":2307,"tokens_out":347,"would_cite":false,"duration_ms":18627,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"grok-4.3","headline":"The precise infrared cutoff definition in parton showers drives observable differences at the hadron level in Herwig.","keywords":["parton showers","infrared cutoff","hadronization","Herwig","dipole showers","NLO matching","logarithmic accuracy","cluster hadronization"],"falsifier":"Re-running the hadron-level comparisons after forcing every shower to adopt an identical infrared cutoff value would show whether the reported differences disappear.","tokens_in":2578,"feed_emoji":"","tokens_out":487,"duration_ms":24184,"temperature":0.7,"pith_summary":"The paper implements two dipole parton shower algorithms with next-to-leading-logarithmic accuracy at leading colour inside the Herwig event generator. It compares their performance to Herwig's existing dipole and angular-ordered showers, paying special attention to how each algorithm behaves when extrapolated into the infrared regime. The central result is that the exact choice of infrared cutoff, which supplies the starting configuration for Herwig's cluster hadronization model, produces clear differences once hadron-level observables are examined. A sympathetic reader cares because this cutoff choice directly influences the reliability of collider predictions that rely on the transition from perturbative showers to non-perturbative hadronization. The authors also extract best-fit parameters for each shower after tuning.","feed_headline":"Shower infrared cutoffs shape hadron predictions in Herwig","feed_subtitle":"The exact definition of the infrared regime passed to cluster hadronization produces distinct results for different dipole and angular-order","key_machinery":"The infrared cutoff chosen by each shower algorithm, which supplies the initial configuration for the cluster hadronization model.","core_discovery":"The authors implemented two recently proposed dipole shower algorithms with NLL accuracy at leading colour in Herwig. While these algorithms improve properties in the logarithmic regime, their extrapolations into the infrared regime matter because the precise infrared cutoff each shower uses becomes the initial state passed to Herwig's cluster hadronization model. At the hadron level this cutoff difference produces important consequences, which the authors propose as a starting point for further study of the interplay between parton showers and hadronization models.","pith_inferences":[],"forward_implications":[],"fun_headline_variants":["Infrared cutoffs shape Herwig shower hadronization outcomes","Herwig dipole showers depend on infrared cutoff for hadron results","Dipole shower infrared regimes affect Herwig cluster hadronization","Parton shower infrared behaviour key in Herwig hadron predictions"],"cache_read_input_tokens":2112,"weakest_assumption_plain":"Observed differences at the hadron level arise primarily from the distinct infrared cutoff definitions rather than from other implementation details of the showers, the NLO matching, or the hadronization model itself.","fun_headline_variants_meta":{"raw":{"variants":["Infrared cutoffs shape Herwig shower hadronization outcomes","Herwig dipole showers depend on infrared cutoff for hadron results","Dipole shower infrared regimes affect Herwig cluster hadronization","Parton shower infrared behaviour key in Herwig hadron predictions"]},"model":"grok-4.3","cost_usd":0.003545,"raw_usage":{"total_tokens":1839,"prompt_tokens":627,"num_sources_used":0,"completion_tokens":65,"cost_in_usd_ticks":35449500,"prompt_tokens_details":{"text_tokens":627,"audio_tokens":0,"image_tokens":0,"cached_tokens":256},"completion_tokens_details":{"audio_tokens":0,"reasoning_tokens":1147,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}},"tokens_in":627,"tokens_out":65,"duration_ms":15043,"temperature":1.0,"reasoning_tokens":1147,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-07-01T00:13:43.823643+00:00","model_set":{"reader":"grok-4.3"},"falsifier":"Re-running the hadron-level comparisons after forcing every shower to adopt an identical infrared cutoff value would show whether the reported differences disappear.","supporting_citations":[],"review_version":2}