Search for long-lived particles decaying into muons in proton-proton collisions at sqrt{s} = 13.6 TeV using data scouting
Pith reviewed 2026-06-25 19:34 UTC · model grok-4.3
The pith
No significant excess of displaced dimuon events is found in 13.6 TeV data, yielding new upper limits on branching fractions for long-lived particles in several beyond-standard-model scenarios.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Using proton-proton collisions at 13.6 TeV collected with low-threshold dimuon scouting triggers, corresponding to 62.4 fb inverse, no significant excess of events with displaced dimuons above the standard model prediction is observed. Upper limits at 95 percent confidence level are therefore placed on branching fractions in models where the Higgs boson decays to long-lived dark photons or to dark partons yielding showers of long-lived particles, and where a long-lived scalar resonance arises from b-hadron decay.
What carries the argument
The dimuon data scouting trigger stream, which records reduced event information at the high-level trigger to access low multimuon invariant mass and nonzero displacement from the primary vertex.
If this is right
- Branching fraction limits on Higgs decays to long-lived dark photons are strengthened in multiple mass and lifetime regions.
- Constraints apply to models in which the Higgs decays to dark partons that produce showers containing long-lived particles.
- Upper limits are set on the production rate of long-lived scalar resonances from b-hadron decays.
- The scouting approach extends experimental reach to lower masses and shorter lifetimes than conventional triggers.
Where Pith is reading between the lines
- If these particles exist at all, their couplings or lifetimes must lie below the excluded values in the tested models.
- Additional integrated luminosity in future LHC runs would allow the same method to probe smaller branching fractions.
- The scouting technique could be adapted to search for long-lived particles decaying to other final states at hadron colliders.
Load-bearing premise
The standard model background prediction for displaced dimuons in the scouting stream is accurate and the trigger plus reconstruction efficiencies for low-pT displaced vertices are correctly modeled without large unaccounted systematics.
What would settle it
A statistically significant excess of events above background in the displaced dimuon sample, with mass and lifetime distributions matching one of the tested signal hypotheses, would indicate the presence of long-lived particles.
Figures
read the original abstract
A search for long-lived particles decaying into muons is performed using proton-proton collisions at $\sqrt{s}$ = 13.6 TeV, collected by the CMS experiment at the LHC in 2022 and 2023, corresponding to an integrated luminosity of 62.4 fb$^{-1}$. The data were collected using dedicated dimuon triggers with low transverse momentum thresholds, recorded with a high-rate data scouting trigger stream. This data stream retains a reduced amount of information at the high-level trigger, to explore otherwise inaccessible phase space at low multimuon invariant mass and nonzero displacement from the primary interaction vertex. No significant excess of events above the standard model prediction is found. Upper limits on branching fractions at 95% confidence level are set for a wide range of mass and lifetime hypotheses in several beyond the standard model frameworks, where the Higgs boson decays into long-lived dark photons or into dark partons that produce showers containing long-lived particles, or where a long-lived scalar resonance is produced from the decay of a b hadron. The resulting constraints improve and extend existing ones in large regions of the parameter space.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript reports a search for long-lived particles decaying to muons in 13.6 TeV pp collisions with the CMS experiment, using 62.4 fb^{-1} of 2022-2023 data collected via dedicated low-pT dimuon triggers in the data scouting stream. This enables access to low multimuon invariant mass and nonzero displacement from the primary vertex. No significant excess above the SM prediction is observed, and 95% CL upper limits on branching fractions are set for BSM scenarios including Higgs decays to long-lived dark photons or dark partons, and long-lived scalars from b-hadron decays, improving existing constraints over wide regions of mass-lifetime parameter space.
Significance. The data scouting approach is a clear strength, allowing exploration of otherwise inaccessible low-pT displaced dimuon phase space. If the background modeling and efficiencies are robust, the resulting limits meaningfully extend constraints on LLP models in the low-mass regime.
major comments (1)
- [Background estimation and efficiency modeling (inferred from abstract and search description)] The null-result claim and derived 95% CL limits rest on the accuracy of the SM background prediction for displaced dimuons in the scouting stream (abstract and search description). The manuscript must provide quantitative validation of the data-driven background method, including closure tests or control-region comparisons specifically in the low-pT, low-mass, nonzero-displacement regime, to demonstrate control over potential systematics from material interactions or fake vertices.
Simulated Author's Rebuttal
We thank the referee for their positive assessment of the data scouting approach and for the constructive comment on background validation. We address the major comment below and will strengthen the manuscript accordingly.
read point-by-point responses
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Referee: [Background estimation and efficiency modeling (inferred from abstract and search description)] The null-result claim and derived 95% CL limits rest on the accuracy of the SM background prediction for displaced dimuons in the scouting stream (abstract and search description). The manuscript must provide quantitative validation of the data-driven background method, including closure tests or control-region comparisons specifically in the low-pT, low-mass, nonzero-displacement regime, to demonstrate control over potential systematics from material interactions or fake vertices.
Authors: We agree that quantitative validation of the data-driven background method is essential to support the null result and the 95% CL limits. The manuscript describes the background estimation procedure and includes validation in control regions. To directly address the referee's request for explicit tests in the low-pT, low-mass, nonzero-displacement regime and to demonstrate control over material interactions and fake vertices, we will expand the relevant section with additional closure tests, control-region comparisons, and quantitative metrics in the revised manuscript. revision: yes
Circularity Check
No circularity: experimental search is data-driven comparison with no self-referential derivation
full rationale
The paper performs a direct experimental search comparing observed dimuon events in the scouting stream to standard model background predictions, finding no excess and setting limits. No step in the analysis chain (trigger, reconstruction, background estimation, efficiency modeling, or limit setting) reduces by the paper's own equations or self-citation to a fitted input renamed as a prediction. Background estimation and efficiencies are external to the target BSM signals; the null result and limits are falsifiable against independent data. This matches the default expectation for non-circular experimental papers.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption Standard model processes accurately predict the background rate of displaced dimuon events in the scouting stream.
- domain assumption Trigger and reconstruction efficiencies for low-pT displaced muons are correctly modeled by simulation and data-driven methods.
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