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arxiv: 2606.27165 · v1 · pith:BKA4ROUSnew · submitted 2026-06-25 · ✦ hep-ex

High Multiplicity Trigger for Long-Lived Particles in CMS detector

M. Abbott , D. Acosta , D. Aebi , M. Ahmad , A. Albert , A. Apresyan , C. Arbour , C. Aruta
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K. Banicz V. Barashko E. Barberis L. Benato A. Bolshov J. Bonilla R. Breedon K. Bunkowski H. Cai C. Campagnari J. Carlson V. Cherepanov M. Chen R. Clare R. Clark P.T. Cox R. De Los Santos S. Dildick M. Dittrich X. Dong L.S. Durkin R. Erbacher P. Fern\'andez Manteca P. Flanagan E. Fontanesi C. Galloni Y. Gao J. Gilmore A. Greshilov Y. Haddad Y. Han Z. Hao J. Hauser E. Hazen H. He J. Heikkilae M. Herndon C. Hill T. Huang M. Ignatenko M.A. Iqbal I. Israr M. Jeitler S. Jindariani E. Juska T. Kamon V. Karjavine H. Kim J. Kim A. Korytov O. Kukral K.H.M. Kwok E. Kuznetsova J. Liu W. Liu C. Lo A. Madorsky N. Manganelli M. Matveev H. Mei N. Menendez G. Mitselmakher G. Mocellin S. Mondal D.M. Morse M. Mulhearn B.P. Padley V. Palichik A. Peck C. Pena V. Perelygin D. Rabady N. Rawal J. Richman A. Safonov P. Siddireddy M. Spiropulu I. Suarez N. Terentyev M. Tripathi N. Turner V. Valuev C. Wang J. Wang Y. Wang Z. Wang D. Wenzl D. Wood S. Xie X. Yang E. Yigitbasi H. Zhang Y. Zhang J. Zheng X. Zuo
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Pith reviewed 2026-06-26 01:41 UTC · model grok-4.3

classification ✦ hep-ex
keywords long-lived particlesCMS triggerhigh multiplicitycathode strip chambersLHC Run 3displaced decaystrigger systembeyond Standard Model
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The pith

The CMS detector now uses a High Multiplicity Trigger that selects events with unusually large numbers of hits in its cathode strip chambers to capture long-lived particle decays.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper describes the development and deployment of a dedicated trigger in the CMS experiment at the LHC for Run 3. The trigger identifies events with high hit counts in the cathode strip chamber muon detectors, a pattern expected when long-lived particles decay after traveling some distance inside the detector. Optimized multiplicity thresholds keep the trigger rate acceptable even with high pileup while retaining efficiency for a wide range of particle lifetimes and momenta. Performance was checked with both simulated samples and real proton-proton collision data. The result is a new way to select non-standard event topologies that standard triggers often miss.

Core claim

The High Multiplicity Trigger (HMT) targets events containing unusually large numbers of hits in the CMS cathode strip chamber (CSC) muon detectors, a characteristic signature of several LLP scenarios involving displaced decays in the muon system. Optimized hit multiplicity thresholds are used to maintain acceptable trigger rates under high-luminosity and high-pileup conditions while preserving high efficiency across a broad range of LLP lifetimes and kinematic regimes. The trigger performance is evaluated using both simulated event samples and proton-proton collision data collected during Run 3 of the LHC.

What carries the argument

The High Multiplicity Trigger (HMT), which applies adjustable multiplicity thresholds on hits recorded in the cathode strip chambers to select candidate events for long-lived particle searches.

If this is right

  • The HMT substantially extends the CMS sensitivity to non-standard signatures associated with LLP decays.
  • It provides a flexible platform for future searches for physics beyond the Standard Model.
  • The trigger maintains acceptable rates under high-luminosity and high-pileup conditions while preserving high efficiency across a broad range of LLP lifetimes.
  • Operational stability has been demonstrated with both simulation and Run 3 collision data.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same multiplicity-selection logic could be adapted to other subdetectors or future collider runs to target decays in different detector volumes.
  • Data collected by this trigger can be combined with offline selections to set limits on specific long-lived particle models that predict muon-system decays.
  • The approach may allow searches for particles with lifetimes that place their decays precisely in the muon chambers, a region previously hard to trigger on efficiently.

Load-bearing premise

Large numbers of hits in the cathode strip chambers reliably mark long-lived particle decays and remain sufficiently free of ordinary background processes even at high pileup.

What would settle it

A direct measurement in collision data showing either that the trigger rate exceeds the allowed bandwidth at nominal pileup levels or that the efficiency measured for simulated long-lived particle signals deviates significantly from the rate observed in data.

read the original abstract

Searches for long-lived particles (LLPs) at the CMS experiment often involve unconventional event topologies that are difficult to efficiently select using standard trigger strategies. To improve sensitivity to such signatures during LHC Run~3 operation, a dedicated High Multiplicity Trigger (HMT) has been developed and deployed in the CMS trigger system. The trigger targets events containing unusually large numbers of hits in the CMS cathode strip chamber (CSC) muon detectors, a characteristic signature of several LLP scenarios involving displaced decays in the muon system. The HMT implementation, trigger logic, rate dependence with pileup, and operational stability are described. Optimized hit multiplicity thresholds are used to maintain acceptable trigger rates under high-luminosity and high-pileup conditions while preserving high efficiency across a broad range of LLP lifetimes and kinematic regimes. The trigger performance is evaluated using both simulated event samples and proton-proton collision data collected during Run~3 of the LHC. The HMT substantially extends the CMS sensitivity to non-standard signatures associated with LLP decays and provides a flexible platform for future searches for physics beyond the Standard Model.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 0 minor

Summary. The manuscript describes the development and deployment of a dedicated High Multiplicity Trigger (HMT) in the CMS experiment for LHC Run 3. The trigger targets events with unusually large numbers of hits in the cathode strip chamber (CSC) muon detectors, a signature for long-lived particle (LLP) decays. It covers the trigger logic, rate dependence on pileup, threshold optimization to maintain acceptable rates, and performance evaluation using simulated samples and Run 3 collision data. The work claims that the HMT extends CMS sensitivity to non-standard LLP signatures and provides a flexible platform for BSM searches.

Significance. If the performance claims hold, this represents a significant technical advancement in trigger strategies for LLP searches at CMS. By exploiting CSC hit multiplicity, it addresses a gap in standard trigger menus for displaced decays, potentially enabling new physics analyses in Run 3 data. The use of both simulation and real data for validation adds credibility to its operational readiness.

major comments (1)
  1. [Abstract] Abstract: The abstract states that performance was evaluated with simulated samples and Run 3 collision data and that thresholds maintain acceptable rates, but provides no quantitative results, error bars, or specific efficiency values; without these, the claim that the HMT substantially extends sensitivity cannot be assessed.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the detailed review and constructive comment on the abstract. We agree that the absence of quantitative metrics limits the ability to assess the performance claims and will revise the abstract to include key results from the manuscript.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The abstract states that performance was evaluated with simulated samples and Run 3 collision data and that thresholds maintain acceptable rates, but provides no quantitative results, error bars, or specific efficiency values; without these, the claim that the HMT substantially extends sensitivity cannot be assessed.

    Authors: We acknowledge the validity of this observation. The current abstract prioritizes brevity but omits specific numbers that appear in the body of the paper (rate vs. pileup curves in Section 3, efficiency tables for benchmark LLP models in Section 5, and data-MC comparisons in Section 6). To address the concern, we will expand the abstract with concise quantitative statements, for example noting the achieved rate at nominal thresholds and the efficiency range for displaced decays in the CSC system. These additions will be drawn directly from the existing results without altering the manuscript's conclusions. The revised abstract will be provided in the next version of the manuscript. revision: yes

Circularity Check

0 steps flagged

No significant circularity; experimental trigger implementation paper

full rationale

The paper is a purely experimental description of trigger hardware logic, threshold settings, rate measurements versus pileup, and efficiency checks on simulation plus Run-3 data. No derivation chain, equations, fitted parameters renamed as predictions, or load-bearing self-citations exist. All performance claims rest on direct measurements and standard CMS simulation, which are externally falsifiable. This matches the default case of a self-contained experimental methods paper.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No mathematical model, free parameters, axioms, or invented entities are present; the paper is an instrumentation and operations report.

pith-pipeline@v0.9.1-grok · 6225 in / 1066 out tokens · 31831 ms · 2026-06-26T01:41:43.759414+00:00 · methodology

discussion (0)

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Reference graph

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