{"id":"904ec3bc-43bf-48ad-8813-d1e4a1aedfe4","arxiv_id":"2507.16900","paper_version":1,"verdict":"ACCEPT","confidence":"HIGH","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":7,"one_line_summary":"Adding a second fractionally charged particle can weaken existing LHC bounds on the heavy partner by factors of a few while boosting production of the light partner by up to three orders of magnitude, motivating new inclusive and missing-energy searches.","lead":"This paper studies models with two new 'fractionally charged' particles, whose electric charges are multiples of one sixth of the electron charge, and shows their predicted signals at the LHC are much richer than in models with just one such particle.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The quantitative exclusion contours rest on the assumption that Q/e ≤ 1/3 FCPs are invisible in the tracker; if track reconstruction is non-negligible, the quoted mass limits and cross-section boosts would shift. A full detector simulation is needed to settle whether this assumption holds.","rationale":"The reader's weakest assumption identifies exactly the same point: the reinterpreted limits assume low-charge FCPs are effectively invisible and contribute only to MET, while the CMS FCP search rejects events with more than two energetic tracks. My independent reading reaches the same conclusion, so agreement is 'agree.' I do not see an internal inconsistency in the cross-section calculations or in the model-building; the concern is about the mapping from the proposed signals to existing search acceptances. The authors are unusually transparent about this limitation in Secs. 1.3, 2.1, and 2.4, and they present the bounds as approximate rather than precise. The qualitative conclusion that two-FCP extensions can weaken constraints on colored FCPs and enhance production of low-charge states is robust to plausible variations in the invisible assumption, because even a modest track efficiency would not erase the existence of the new production/decay channels. However, the specific numerical limits—such as 600–900 GeV colored bounds and the ~10^3 boost factors—are sensitive to this assumption. A dedicated detector-level study would settle whether the quantitative contours survive, but the central physical message does not depend on the exact efficiency. For this reason the appropriate verdict remains unchanged: the paper should be accepted with its clearly stated caveats, and the proposed simulation is a worthwhile next step rather than a blocking requirement.","tokens_in":19571,"tokens_out":8850,"duration_ms":114812,"concrete_test":"Run a Geant4-based detector simulation for pair-produced Q/e = 1/6 and 1/3 scalars and fermions with pT between 20 and 200 GeV, measuring track reconstruction efficiency, dE/dx tag efficiency, and the resulting MET response; then re-evaluate the Sec. 2.3 and 2.4 exclusion contours using the measured efficiency. If the reconstruction efficiency is below ~1% for pT > 55 GeV, the paper's conclusions stand; if it is at the few-percent level or higher, the quoted mass limits and inclusive/exclusive boost claims require revision.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's headline quantitative results—colored-FCP limits weakening to roughly 600–900 GeV and inclusive-over-exclusive cross-section boosts up to ~10^3—are obtained by treating the lightest hypercharge-only FCP (Q/e = 1/6 or 1/3) as contributing only to missing transverse energy in every reinterpreted search. This is the load-bearing step: in the HX portal (Sec. 2.1), eR portal (Sec. 2.3), and uR portal (Sec. 2.4), existing bounds are ported by assuming the low-charge state leaves no reconstructable track and no ionization signature that would fail the search's track-quality or isolation cuts. The authors explicitly flag the need for full detector response and cite a thesis indicating that Q/e = 1/3 track reconstruction efficiency is nearly zero, but the Q/e = 1/6 case and the intermediate pT range are not quantified. If the track efficiency is non-negligible, the /ET-based limits are not directly applicable: signal events would contain charged tracks and reduced missing energy, changing both signal acceptance and the derived exclusion contours. Because the main new bounds are numerical, not merely existence statements, this assumption is load-bearing for the central claim.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper studies four minimal two-FCP extensions of the Standard Model, in which a pair of fractionally charged states couples to a single SM field through a Higgs, scalar, lepton, or quark portal. For each benchmark, the authors compute leading-order production cross sections at the 13 TeV LHC and reinterpret existing experimental searches: the CMS low-ionization FCP search, electroweakino and slepton searches with missing transverse energy, jets-plus-MET searches, disappearing-track searches, Higgs invisible-width bounds, and milliQan limits. The central claims are that (i) colored FCPs that can decay to a lighter hypercharge-only FCP are constrained much more weakly than stable colored FCPs, with lower bounds dropping from roughly 1.5 TeV to about 600-900 GeV, and (ii) the production rate of the least-visible, low-charge species can be enhanced by orders of magnitude when they are produced in association with leptons or jets, motivating FCP-plus-jet/lepton searches and reanalysis of existing missing-energy data for low-quality tracks.","tokens_in":20004,"tokens_out":7665,"duration_ms":89689,"significance":"If the results hold, they materially change the phenomenological case for FCP searches at the LHC: the most constrained single-particle representations can be destabilized by a second FCP, while the least constrained species become far more accessible through associated production. The paper is explicit about its main assumptions, particularly that Q/e <= 1/3 particles are effectively invisible in LHC trackers, and it repeatedly flags the absence of full detector simulation. This limitation is real and should be kept in mind when quoting the numerical contours, but it is not an unacknowledged flaw; the cited thesis evidence and the authors' own caveats in Sec. 1.3 and footnotes make the approximate nature of the bounds clear. The qualitative conclusions, especially the need for inclusive and associated-production searches, are robust to plausible variations in track-reconstruction efficiency. The paper is a well-scoped sequel to the authors' previous work, makes concrete use of public experimental data, and provides a clear set of falsifiable predictions, which are strengths for a phenomenological study.","major_comments":[],"minor_comments":[{"comment":"The numerical contours in Secs. 2.1-2.4 all rest on the statement that Q/e <= 1/3 FCPs are effectively invisible in the tracker, as is explicitly acknowledged; since this is the main source of systematic uncertainty in the quoted mass limits, I suggest collecting the evidence (the cited thesis benchmarks, the pT dependence, and the Q/e = 1/6 case) into a single short paragraph or table so readers can judge the robustness of the bounds at a glance.","section":"Sec. 1.3 and footnote 1"},{"comment":"The caption states that the top two panels and the bottom left panel show Y = 1, but the panel labels are not visible in the figure as typeset; please add explicit panel labels or state the layout more clearly.","section":"Fig. 2"},{"comment":"For the estimate of the branching ratio for t -> X Xbar b W, please state explicitly whether the W is on-shell or virtual and specify the phase-space approximation used in the four-body estimate, since the displayed formula does not show the W propagator dependence.","section":"Eq. (2.11)"},{"comment":"The stability argument based on separate Z2 and Z3 selection rules is terse; one additional sentence explaining why phi_2 decays are forbidden in the regime M_phi1 < M_phi2 < 2 M_phi1 would make the discussion self-contained.","section":"Sec. 2.2, footnote 5"},{"comment":"The contour labels in the right-hand panels appear garbled in the current typesetting (e.g., '10 2 5 100' and '2 5 10. 100 500'); please ensure the contour levels are legible and consistent with the factor-of-10^2 to 10^3 boost quoted in the abstract.","section":"Figs. 5 and 6"}],"recommendation":"accept","confidential_remarks":"The manuscript is a well-scoped sequel to the authors' previous paper, and the self-references are appropriate. The approximate reinterpretation of public experimental limits is within normal practice for JHEP phenomenology, and the explicit caveats should be retained in the published version. I see no grounds for concern about novelty or scope."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The real news here is that adding a second fractionally charged state opens decay channels and associated-production modes that flip which searches are powerful. The paper shows that colored FCPs, previously pinned above ~1.5 TeV, can evade the strong bounds once they decay to a lighter, hypercharge-only FCP; and that the least visible species (Q/e = 1/6, 1/3) can get a 10^2–10^3 boost in inclusive production. These are genuinely new benchmark models, not a repackaging of the authors' single-particle paper, and the four portals cover a sensible range of SM couplings. The qualitative conclusions follow from the LO cross sections and the stated approximations.\n\nWhat I like: the paper is upfront about its limitations. Section 1.3 and the benchmark sections explicitly flag the lack of full detector simulation and the assumption that low-charge FCPs are invisible. The CMS search reinterpretation is handled with both conservative and optimistic variants, which is the right way to show the uncertainty. There is no circular logic; the comparison to existing limits is straightforward. The 'free search' idea—reinterrogating /ET events for low-quality tracks—is a practical, cheap way to get discovery potential from data on tape.\n\nThe soft spot is the one the stress-test names: the invisibility assumption is load-bearing for the numerical contours. The paper cites a thesis showing Q/e = 1/3 track efficiency is nearly zero, but Q/e = 1/6 and intermediate pT are not quantified. If low-charge FCPs leave reconstructable tracks at non-negligible efficiency, the /ET-based limits and the quoted mass reach shift. But the authors say this themselves, and the central message—that two-particle extensions change the search strategy—does not depend on the precise mass limit. The milliQan reverse-engineering and the EWPO estimates are also approximate, but those are minor.\n\nThis paper is for collider phenomenologists and experimentalists designing FCP searches. It gives them concrete new benchmarks and shows where existing searches apply. It deserves a serious referee; the main request should be a fuller treatment of the track-efficiency assumption, ideally a detector-level study or at least a scan over track efficiencies. I would not desk-reject it.","headline":"Two-FCP portals genuinely change the search strategy landscape, and the paper is honest about where its numbers depend on the low-charge state being invisible—the qualitative point holds even if the exact contours shift.","tokens_in":20511,"tokens_out":1258,"would_cite":true,"duration_ms":16896,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Two fractionally charged particles can hide at the LHC or reveal themselves with a thousand-fold rate boost.","keywords":["fractionally charged particles","charge quantization","one-form global symmetry","grand unification","collider searches","missing transverse energy","LHC phenomenology","milliQan"],"falsifier":"A detector simulation or test-beam measurement showing that charge e/6 or e/3 particles are reconstructed as tracks with non-negligible efficiency, or a re-analysis of CMS FCP search events showing that events with three or more energetic tracks are retained, would invalidate the missing-energy reinterpretations and change the quoted mass bounds.","tokens_in":19335,"feed_emoji":"⚛️","tokens_out":5045,"duration_ms":53692,"temperature":0.7,"pith_summary":"This paper argues that adding two fractionally charged particles (FCPs) coupled to one Standard Model field, instead of just one, reshapes the collider search landscape in two opposite ways. Opening a decay portal lets a colored FCP decay to Standard Model particles plus a lighter, lower-charge FCP, so the colored particle's mass bound weakens from roughly 1.5 TeV down to about 600-900 GeV. Conversely, the nearly invisible low-charge partner inherits the larger production rate of its heavier partner, which can enlarge its cross section by up to roughly a factor of $10^{3}$. The paper shows, through four benchmark portal models, that the lightest FCP will usually appear together with extra jets or leptons, so exclusive searches miss most of the signal. It therefore motivates inclusive or associated-production searches, and points to the possibility of reanalyzing existing missing-energy datasets for subtle FCP tracks.","feed_headline":"Pairing fractionally charged particles reshapes LHC searches","feed_subtitle":"Decay channels relax colored-particle limits to ~600-900 GeV and lift invisible-species rates by ~10^3.","key_machinery":"The central objects are 'portal' interactions: single renormalizable operators coupling one Standard Model field to two FCPs, such as the Higgs-fermion coupling $\\lambda H \\bar{X}_1 X_2$, the Higgs-scalar coupling $\\lambda H \\phi_2 \\phi_1^2$, the lepton Yukawa $y \\bar{e}_R P_L X \\phi$, and the up-type quark Yukawa $y \\bar{u}_R P_L X \\phi$. These operators allow heavier FCPs to decay to Standard Model particles plus a lighter, lower-charge FCP, and the mixing angle $\\tan(2\\alpha) = \\sqrt{2}\\lambda v/(M_2 - M_1)$ controls which states are produced and how they decay. The machinery converts low-charge species that were only produced feebly through Drell-Yan into particles that inherit large cross sections from strongly or electroweakly produced partners, while destabilizing otherwise stable colored FCPs so their mass limits relax.","core_discovery":"The paper establishes that the phenomenology of fractionally charged particles changes qualitatively when a second FCP shares a renormalizable portal interaction with a Standard Model field. In the single-particle case, FCPs only couple to gauge bosons and are effectively stable, giving strong bounds on colored states and weak bounds on hypercharge-only states. With two FCPs, the heavier state can decay to the lighter one plus Standard Model particles, which weakens the constraints on strongly interacting FCPs by factors of a few, while the low-charge, nearly invisible state gains access to much larger production cross sections through its partner. The authors demonstrate this with four portals: a Higgs coupling to a fermion pair, a Higgs coupling to two scalars, a Yukawa coupling to right-handed leptons, and a Yukawa coupling to right-handed up-type quarks. Across these benchmarks, the least visible species (charges e/6 or e/3) can have their discovery potential enhanced by orders of magnitude, and the lightest FCP frequently appears with associated jets or leptons, making inclusive searches essential.","pith_inferences":["If the track reconstruction efficiency for charge e/6 or e/3 particles turns out to be higher than assumed, the missing-energy bounds presented here would be replaced by direct track-based limits, which could strengthen rather than weaken the constraints.","The same portal logic likely applies to other Standard Model fields, such as left-handed quarks or leptons, down-type quarks, or three-scalar couplings, and may produce a similar pattern of weakened colored bounds and boosted low-charge cross sections.","A dedicated detector-level study of low-charge track reconstruction, including hadronization of colored FCPs, would sharpen every bound in the paper and could reveal signatures not captured by simplified assumptions.","The 'free' reanalysis strategy of scanning existing missing-energy events for anomalous tracks is a near-term, low-cost experiment that could find FCPs before any new collider search is built."],"forward_implications":["Colored FCP mass bounds can drop from about 1.5 TeV to roughly 600-900 GeV when the colored state can decay to Standard Model particles plus a low-charge FCP.","The least visible species, such as charge e/6 particles, can have their inclusive production cross sections boosted by up to about 10^3 through associated production with dileptons or jets.","Searches should target FCPs produced together with extra leptons or jets, since the exclusive one- or two-track signature excludes most signal events in these models.","Existing missing-energy datasets at the LHC could be re-examined for low-quality tracks with anomalous energy loss, providing discovery potential without new data taking.","A discovery of a charge e/6 particle would pin down the global structure of the Standard Model gauge group and its one-form symmetry, ruling out the simplest grand unified theories that predict a smaller quotient."],"supporting_citations":[{"why":"Supplies the single-particle FCP framework, the gauge-group global-structure formalism, and the baseline mass bounds that the two-particle models are compared against.","marker":"[1]"},{"why":"The CMS search for fractionally charged particles provides the leading LHC constraint for charges e/3 and above, and its one-or-two-track selection motivates the inclusive-search arguments.","marker":"[24]"},{"why":"The milliQan sensitivity study provides current and projected cross-section limits used to bound low-charge species such as e/6.","marker":"[27]"},{"why":"The CMS combined electroweakino search is reinterpreted to place dilepton-plus-missing-energy and W/Z-plus-missing-energy bounds on the Higgs and lepton portal scenarios.","marker":"[51]"},{"why":"The ATLAS combination of chargino and neutralino searches provides an independent electroweakino bound applied in the same way as [51].","marker":"[52]"},{"why":"The CMS disappearing-track search supplies the bound on long-lived components of scalar FCPs in the H phi2 phi1^2 portal.","marker":"[53]"},{"why":"The ATLAS slepton search in the two-lepton-plus-missing-energy final state is reinterpreted for the right-handed lepton portal where heavy FCPs decay to leptons plus low-charge particles.","marker":"[54]"},{"why":"The CMS jets-plus-missing-energy supersymmetry search is used to bound the up-type quark portal scenario where a colored FCP decays to a jet plus a low-charge particle.","marker":"[57]"}],"fun_headline_variants":["Two fractionally charged particles transform collider search outlook","Paired FCPs weaken limits and boost discovery odds","FCP pairs unlock hidden discovery channels at LHC","Double FCPs ease constraints and amplify signals by 1000x"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that low-charge FCPs (charge e/6 or e/3, especially e/6) are effectively invisible in LHC detectors, contributing only to missing transverse energy, and that the CMS FCP search rejects events with more than two energetic tracks.","fun_headline_variants_meta":{"raw":{"variants":["Two fractionally charged particles transform collider search outlook","Paired FCPs weaken limits and boost discovery odds","FCP pairs unlock hidden discovery channels at LHC","Double FCPs ease constraints and amplify signals by 1000x"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000217,"raw_usage":{"total_tokens":1433,"prompt_tokens":939,"completion_tokens":494,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":555,"completion_tokens_details":{"reasoning_tokens":426}},"tokens_in":555,"tokens_out":494,"duration_ms":5310,"temperature":1.0,"reasoning_tokens":426,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T15:00:57.653192+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A detector simulation or test-beam measurement showing that charge e/6 or e/3 particles are reconstructed as tracks with non-negligible efficiency, or a re-analysis of CMS FCP search events showing that events with three or more energetic tracks are retained, would invalidate the missing-energy reinterpretations and change the quoted mass bounds.","supporting_citations":[{"cited_title":"Sensitivity to millicharged particles in future proton-proton collisions at the LHC","cited_arxiv_id":"2104.07151","evidence_quote":"The milliQan sensitivity study provides current and projected cross-section limits used to bound low-charge species such as e/6."},{"cited_title":"Combined search for electroweak production of winos, binos, higgsinos, and sleptons in proton-proton collisions at $\\sqrt{s}$ = 13 TeV","cited_arxiv_id":"2402.01888","evidence_quote":"The CMS combined electroweakino search is reinterpreted to place dilepton-plus-missing-energy and W/Z-plus-missing-energy bounds on the Higgs and lepton portal scenarios."},{"cited_title":"A statistical combination of ATLAS Run 2 searches for charginos and neutralinos at the LHC","cited_arxiv_id":"2402.08347","evidence_quote":"The ATLAS combination of chargino and neutralino searches provides an independent electroweakino bound applied in the same way as [51]."}],"review_version":1}