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Searches for heavy long-lived charged particles with the ATLAS detector in proton-proton collisions at $\sqrt{s}$ = 8 TeV

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ATLAS Collaboration

High Energy Physics - Experiment · Submitted 25 Nov 2014 · 78 references

Pith's verdict: A careful, well-documented 8 TeV LLP search whose exclusions are solid but whose trigger-efficiency extrapolation to slow particles deserves a referee question.

T0 · AI review

How this review was made: An AI referee (selfhosted/deepseek-v4.1-flash) read the paper on October 29, 2026 and answered a fixed list of questions about it. T0 is the starting level every paper gets. The levels describe how deeply Pith has checked the paper, never the authors.

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arXiv ID1411.6795 (version 2)
Pith IDOUGKJWC3, Pith's permanent record of this paper and its review
CitationATLAS Collaboration. "Searches for heavy long-lived charged particles with the ATLAS detector in proton-proton collisions at $\sqrt{s}$ = 8 TeV." arXiv:1411.6795 (2014). https://pith.science/paper/OUGKJWC3
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The paper

The paper claims

ATLAS finds no heavy long-lived charged particles at 8 TeV, and converts the null result into mass limits reaching 1.27 TeV.

The reading

The ATLAS collaboration asks whether heavy particles that live long enough to traverse the whole detector — stable staus, charginos, and composite 'R-hadrons' built from a gluino or a squark — are produced in 8 TeV proton–proton collisions. The strategy is to catch them by speed: a particle of a few hundred GeV moving measurably below the speed of light leaves a time-of-flight signature in the calorimeters and muon chambers and an anomalously large ionisation signal in the silicon pixel detector, and either measurement converts into a mass through $m = p/βγ$. No candidate survives in the cleanest signal regions, so the paper turns the null result into 95% confidence lower bounds on the mass of each hypothesised particle. The bounds are the deliverable: they close off substantial regions of gauge-mediated supersymmetry, simplified LeptoSUSY, nearly degenerate chargino–neutralino models, and R-hadron scenarios. One bookkeeping point worth flagging: the abstract quoted in the record states 19.8 fb$^{-1}$ of data while the manuscript's own abstract and body use 19.1 fb$^{-1}$, the larger figure belonging to a separate stream reserved for timing calibration.

What carries the argument

The load-bearing mechanism is a mass measurement from speed. Two independent observables give the velocity: time-of-flight to calorimeter cells and to RPC and MDT hits, combined in a weighted average with per-detector-element calibration from $Z → μμ$ events, and the specific ionisation $dE/dx$ in the pixel detector, whose most probable value is parameterised as a function of $βγ$ by a five-parameter curve. Either route yields $m = p/βγ$ for a track of measured momentum, and the searches select on the reconstructed mass $m_β$ (or $m_{βγ}$) because signal peaks there while background is continuous. The second piece of machinery is the background estimate: rather than simulating instrumental muon fakes, the paper builds the background mass spectrum by randomly re-pairing measured candidate momenta with $β$ values drawn from the muon $β$ probability density function measured in data, separately in eight $|η|$ regions, so that the estimate inherits the actual resolution of the detector.

Extended reading notes

Core claim

Using 19.1 fb$^{-1}$ of $√s = 8$ TeV data, ATLAS observes no excess over a data-driven background estimate in any of its long-lived-particle signal regions, and sets 95% CL lower mass limits: long-lived $˜τ_1$ sleptons in GMSB are excluded up to 440, 440, 430, 410 and 385 GeV for $tan β = 10, 20, 30, 40, 50$, with a 286–290 GeV limit when only direct $˜τ_1$ pair production is assumed; in simplified LeptoSUSY with stable 300 GeV sleptons, squarks and gluinos are excluded up to 1500 and 1360 GeV; directly produced charginos nearly degenerate with the lightest neutralino are excluded up to 620 GeV; and R-hadrons containing a gluino, sbottom or stop are excluded up to 1270, 845 and 900 GeV with the full detector, or 1260, 835 and 870 GeV when all muon-spectrometer information is discarded. The limits are strongest where the two-candidate signal regions are essentially empty: zero observed events against estimated backgrounds of $0.43 ± 0.05$ (GMSB stau), $1.36 ± 0.14$ (LeptoSUSY) and $0.010$–$0.73$ (R-hadrons).

Load-bearing premise

The whole background estimate rests on the claim that the measured muon speed distribution is pure detector resolution and therefore independent of the candidate's momentum within each of eight pseudorapidity bins, so that momenta and speeds can be re-paired at random to model the high-mass tail.

Editorial extensions

If this is right

  • Gauge-mediated supersymmetry with a long-lived stau NLSP is pushed out of the 385–440 GeV window for $tan β$ between 10 and 50, so any GMSB variant invoked to accommodate a 125 GeV Higgs must place its sparticle spectrum above that range or shorten the stau lifetime so it decays inside the detector.
  • Simplified LeptoSUSY with stable 300 GeV sleptons is excluded for squarks below 1500 GeV and gluinos below 1360 GeV, which removes a broad corner of the leptophilic-supersymmetry parameter space that prompt searches cannot reach.
  • Chargino–neutralino degeneracy at the 140 MeV level is excluded up to 620 GeV, constraining wino-like dark matter scenarios in which the charged and neutral states are nearly mass-degenerate.
  • The MS-agnostic R-hadron limits (1260, 835, 870 GeV) come within a few tens of GeV of the full-detector limits (1270, 845, 900 GeV), which says that the muon spectrometer adds little once the inner detector and calorimeter timing are available — an argument for the robustness of the calorimeter-only approach against modelling of R-hadron interactions with matter.
  • The same data and method extend the reach of earlier 7 TeV ATLAS long-lived searches and are complementary to prompt supersymmetry searches, since a particle that escapes the detector is invisible to the latter.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The MS-agnostic and full-detector R-hadron limits sitting so close together suggests the dominant systematic for coloured long-lived particles is no longer the modelling of charge exchange in the muon system but the signal cross-section uncertainty, quoted at 15–56% and growing with mass; a future analysis may gain more from better cross-section calculations than from better detectors.
  • Because the background estimate is built from the muon $β$ distribution itself, the same machinery could be inverted as a calibration tool: any excess in the high-mass tail of the re-paired distribution would be a direct signature of an unmodelled $β$–momentum correlation, so the method carries its own diagnostic.
  • The paper's null results are quoted at 95% CL against the lower edge of the $±1σ$ theoretical cross-section band; if the true cross-section sits at the upper edge of that band, the quoted mass limits are conservative by roughly the width of the band, which matters most for the R-hadron limits where the band is widest.
  • The single largest residual exposure is the assumption that $β$ resolution is momentum-independent within each $|η|$ bin; a dedicated study using $Z → μμ$ events binned simultaneously in momentum and $η$ would either close that gap or reveal it, and it costs no new data.
Original abstract

Searches for heavy long-lived charged particles are performed using a data sample of 19.8 fb$^{-1}$ from proton-proton collisions at a centre-of-mass energy of $\sqrt{s}$ = 8 TeV collected by the ATLAS detector at the Large Hadron Collider. No excess is observed above the estimated background and limits are placed on the mass of long-lived particles in various supersymmetric models. Long-lived tau sleptons in models with gauge-mediated symmetry breaking are excluded up to masses between 440 and 385 GeV for $\tan\beta$ between 10 and 50, with a 290 GeV limit in the case where only direct tau slepton production is considered. In the context of simplified LeptoSUSY models, where sleptons are stable and have a mass of 300 GeV, squark and gluino masses are excluded up to a mass of 1500 and 1360 GeV, respectively. Directly produced charginos, in simplified models where they are nearly degenerate to the lightest neutralino, are excluded up to a mass of 620 GeV. $R$-hadrons, composites containing a gluino, bottom squark or top squark, are excluded up to a mass of 1270, 845 and 900 GeV, respectively, using the full detector; and up to a mass of 1260, 835 and 870 GeV using an approach disregarding information from the muon spectrometer.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13-20260917 via OpenRouter, question bank abstract-p1-20260923, 2026-09-23: 1 request, 5,441 input tokens, $0.0002 reported.

What the abstract itself states, as probabilities: claims first 0.02 · states limitation 0.41 · human participants 0.01 · controlled comparison 0.21 · randomized assignment 0.01 · states quantitative result 0.99 · compares with prior results 0.39 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v2. Results and the main claim are underlined; .

Searches for heavy long-lived charged particles are performed using a data sample of 19.8 fb$^{-1}$ from proton-proton collisions at a centre-of-mass energy of $\sqrt{s}$ = 8 TeV collected by the ATLAS detector at the Large Hadron Collider. No excess is observed above the estimated background and limits are placed on the mass of long-lived particles in various supersymmetric models. Long-lived tau sleptons in models with gauge-mediated symmetry breaking are excluded up to masses between 440 and 385 GeV for $\tan\beta$ between 10 and 50, with a 290 GeV limit in the case where only direct tau slepton production is considered. In the context of simplified LeptoSUSY models, where sleptons are stable and have a mass of 300 GeV, squark and gluino masses are excluded up to a mass of 1500 and 1360 GeV, respectively. Directly produced charginos, in simplified models where they are nearly degenerate to the lightest neutralino, are excluded up to a mass of 620 GeV. $R$-hadrons, composites containing a gluino, bottom squark or top squark, are excluded up to a mass of 1270, 845 and 900 GeV, respectively, using the full detector; and up to a mass of 1260, 835 and 870 GeV using an approach disregarding information from the muon spectrometer.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 Searches for heavy long-lived charged particles are performed using a data sample of 19.8 fb$^{-1}$ from proton-proton collisions at a centre-of-mass energy of $\sqrt{s}$ = 8 TeV collected by the ATLAS detector at the Large Hadron Collider. method 0.89 0.95 0.03 asserted 0.98
s1 No excess is observed above the estimated background and limits are placed on the mass of long-lived particles in various supersymmetric models. result 1.00 0.95 0.89 asserted 1.00
s2 Long-lived tau sleptons in models with gauge-mediated symmetry breaking are excluded up to masses between 440 and 385 GeV for $\tan\beta$ between 10 and 50, with a 290 GeV limit in the case where only direct tau slepton production is considered. result 1.00 0.94 0.11 asserted 1.00
s3 In the context of simplified LeptoSUSY models, where sleptons are stable and have a mass of 300 GeV, squark and gluino masses are excluded up to a mass of 1500 and 1360 GeV, respectively. result 1.00 0.92 0.07 asserted 1.00
s4 Directly produced charginos, in simplified models where they are nearly degenerate to the lightest neutralino, are excluded up to a mass of 620 GeV. result 1.00 0.95 0.10 asserted 1.00
s5 $R$-hadrons, composites containing a gluino, bottom squark or top squark, are excluded up to a mass of 1270, 845 and 900 GeV, respectively, using the full detector; and up to a mass of 1260, 835 and 870 GeV using an approach disregarding information from the muon spectrometer. result 1.00 0.96 0.10 asserted 1.00

What kind of paper the classifier reports this is: empirical study 1.00 · evidence from observation or experiment 0.67.

What was examined, and what was not

sources read
  • arXiv listing abstract v2
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. Distribution of the muon speed, β, from the calorimeter (left) and combined measure￾ments of calorimeter and muon spectrometer (right) obtained for selected Z → µµ events in data (points) and smeared MC simulation (line). 3.3 Muon system The muon spectrometer forms the outer part of the ATLAS detector, detects charged particles exiting the calorimeters and measures their momenta in the pseudorapidity range |η| < 2.7. It is also designed to trigger on these particles in the region |η| < 2.4. In the barrel the chambers are arranged in three concentric cylindrical shells around the…
Figure 2. Reconstructed mass mβ of one candidate (m2) versus mβ of the other candidate (m1) for observed data and expected signal, in the GMSB slepton search in the two-candidate signal region (top-left). Observed data, background estimate and expected signal in the slepton search for the lower of the two masses (m) in the two-candidate signal region (GMSB ˜τ1 masses of 344.5 and 437 GeV; top-right) and for the one-candidate signal region (LeptoSUSY mq˜ = 2.0, 1.2 and 0.9 TeV with mg˜ = 1.2 TeV; bottom). – 23 –
Figure 3. Reconstructed mass mβ in observed data, background estimate and expected signal ( ˜χ ± 1 masses of 400 and 600 GeV) in the chargino search for the lower of the two masses (m) in the two-candidate signal region (top-left), for the one-loose-candidate signal region (top-right) and the one-candidate signal region (bottom). – 24 –
Figure 4. Data and background estimates for the reconstructed mass based on time-of-flight, mβ, (top-left) and based on specific energy loss, mβγ, (top-right) for combined candidates in the full-detector 500 GeV gluino R-hadron search (SR-RH-FD), as well as mβ (bottom-left) for the MS￾agnostic 500 GeV sbottom and mβγ (bottom-right) for the MS-agnostic 500 GeV stop R-hadron search (SR-RH-MA). – 25 –
Figure 5. Cross-section upper limits as a function of the mass of the lightest stau for the GMSB models organised by tan β: 10 and 20 first row, 30 and 40 second row and 50 last row. The expected limit is drawn as a dashed black line with ±1σ and ±2σ uncertainty bands drawn in green and yellow, respectively. The observed limit is shown as solid black line with markers. The theoretical cross-section prediction is shown as a solid blue line with a shaded ±1σ uncertainty band. – 26 –
Figure 6. 95% CL excluded regions for directly produced sleptons in the plane m( ˜`)–m(˜τ1) vs. m(˜τ1). The excluded region is is shown in blue. The expected limit is drawn as a solid black line with a ±1σ uncertainty band drawn as dashed black lines. The observed limit is shown as solid red line with a ±1σ uncertainty band drawn as dashed red lines. mass [GeV] 1τ∼ 250 300 350 400 450 500 Cross-section [fb] 1 theory prediction tanβ=10 expected limit ± 1σ ± 2σ observed limit tanβ=10 tanβ=30 tanβ=50 ATLAS -1 s = 8 TeV, 19.1 fb
Figure 7. Cross-section upper limits as a function of the ˜τ1 mass for direct ˜τ1 production and three values of tan β. The expected limit for tan β = 10 is drawn as a dashed black line with ±1σ and ±2σ uncertainty bands drawn in green and yellow, respectively. The observed limits for three values of tan β are shown as solid lines with markers. The theoretical cross-section prediction for tan β = 10 is shown as a coloured ±1σ band, and does not vary significantly for the other tan β values. – 27 –
Figure 8. Cross-section upper limits as a function of the ˜χ1 mass for ˜τ1 sleptons resulting from the decay of directly produced charginos and neutralinos in GMSB. Observed limits are given as a solid black line with markers. Expected limits for tan β = 10 are drawn as a dashed black line with ±1σ and ±2σ uncertainty bands drawn in green and yellow, respectively. The theoretical cross-section prediction (dominated by ˜χ 0 1χ˜ + 1 production) is shown as a coloured ±1σ band. Depending on the hypothesis and to a small extent on tan β, in these models, the chargino mass is 210 to 260 GeV higher…
Figure 9. 95% CL excluded regions of squark mass and gluino mass in the LeptoSUSY models. The excluded region is is shown in blue. The expected limit is drawn as a solid black line with a ±1σ uncertainty band drawn as dashed black lines. The observed limit is shown as solid red line with a ±1σ uncertainty band drawn as dashed red lines. – 28 –
Figure 10. Cross-section upper limits for various chargino masses in stable-chargino models. The expected limit is drawn as a dashed black line with ±1σ and ±2σ uncertainty bands drawn in green and yellow, respectively. The observed limit is shown as solid black line with markers. The theoretical cross-section prediction is shown as a solid blue line with a shaded ±1σ uncertainty band. – 29 –
Figure 11. Cross-section upper limits as a function of the LLP mass for the R-hadron models for the MS-agnostic (left) and full-detector search (right). The expected limit is drawn as a dashed black line with ±1σ and ±2σ uncertainty bands drawn in green and yellow, respectively. The observed limit is shown as solid black line with markers. The theoretical cross-section prediction is shown as a solid blue line with a shaded ±1σ uncertainty band. – 30 –

Figures reproduced from arXiv:1411.6795 by the authors.

References
How later papers used it

72 later papers cite it

Evidence: substantial. 69 of the citing papers share no author with it, and 27 of those carry a confident label from Pith's citation classifier.

Pith read 21 of the 105 citing sentences, choosing only those whose citation markers point at this paper alone, and wrote the paraphrases from them. The summary, the counts, the evidence level, the links and the quotes come from code; the summary counts the papers listed below. A later paper is listed under a label when Pith's citation classifier gives one of its sentences that label at probability 0.8 or more (0.95 for support), Pith's reading finds that the citing paper itself did it, and a second check confirms the paraphrase against the sentence. This section lists uses only. It does not list criticism or disagreement, so their absence here says nothing about how the paper has been received. Papers that share an author with this one are listed apart, under "By the same authors". A quote is the citing authors' own sentence, shown when their paper's licence is CC BY, CC BY-SA or CC0. JSON

Uses its method or tool 1 paper
Uses its data or values 3 of 22 papers with this label
How the literature uses it

71 arXiv papers cite this in 100 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers citing it · 59 sentences without a confident label

Uses its method or tool 1 paper
Uses its data or values 21 papers
  • In particular, model independent bounds on the mass come from LHC limits on electro-weak Drell-Yan production of pairs [ref] , yielding $m_⩾289$ GeV [ref] .

    Beyond standard model particles in the atmospheric flux: a long-lived stau example · SUSY models with long-lived staus · 0.88

  • We check our model against LHC bounds and constraints from the ATLAS and CMS collaborations [ref] , which in our case comprise of: a Higgs mass between $123 ≤m_H ≤127$ GeV (where we've assumed a 2GeV theoretical uncertainty arising from FlexibleSUSY) [ref] ; a gluino mass larger than $m_ g̃ ≥2$ TeV [ref] ; a neutralino mass larger than $m_ χ̃_1^0 ≥537$ for $tanβ∈[10, 50]$ [ref] ; a stop mass larger than $m_ t̃ ≥1TeV$ [ref] ; a chargino mass larger than $m_χ̃^±_1 ≥460$ GeV [ref] ; an extra $Z'$ gauge boson with a mass larger than $m_Z' ≥2.4$ TeV [ref] for the $U(1)$ extensions.

    Confronting Scherk-Schwarz orbifold models with LHC data · Methodology and Constraints · 0.88

  • At the ATLAS detector, the resolution of ToF is reported as $2.5%$ [ref] .

    Long-Lived Sleptons at the LHC and a 100 TeV Proton Collider · Monte Carlo Simulation · 1.00

Compares with it 2 papers
Cites it as support 2 papers
Cites it as background 10 papers

What it cites · 9 sentences without a confident label

Uses the method or tool of 18 papers
Uses data or values from 2 papers
Cites as support 2 papers
Cites as background 23 papers
  • Heavy long-lived particles (LLP) are predicted in a range of extensions of the Standard Model (SM) [ref] . $R$-parity-conserving supersymmetry (SUSY) [ref] models, such as split SUSY [ref] , gauge-mediated SUSY breaking (GMSB) [ref] and [ref] , as well as other scenarios such as universal extra dimensions [ref] and leptoquark extensions [ref] , allow for a variety of LLP states stable enough to be directly identified by the ATLAS detector.

    Low-scale gaugino mediation, lots of leptons at the LHC · Introduction · 0.92

  • Heavy long-lived particles (LLP) are predicted in a range of extensions of the Standard Model (SM) [ref] . $R$-parity-conserving supersymmetry (SUSY) [ref] models, such as split SUSY [ref] , gauge-mediated SUSY breaking (GMSB) [ref] and [ref] , as well as other scenarios such as universal extra dimensions [ref] and leptoquark extensions [ref] , allow for a variety of LLP states stable enough to be directly identified by the ATLAS detector.

    Bounds on Universal Extra Dimensions · Introduction · 0.92

  • Heavy long-lived particles (LLP) are predicted in a range of extensions of the Standard Model (SM) [ref] . $R$-parity-conserving supersymmetry (SUSY) [ref] models, such as split SUSY [ref] , gauge-mediated SUSY breaking (GMSB) [ref] and [ref] , as well as other scenarios such as universal extra dimensions [ref] and leptoquark extensions [ref] , allow for a variety of LLP states stable enough to be directly identified by the ATLAS detector.

    Aspects of Split Supersymmetry · Introduction · 0.92

Discussion

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