Search for events with a pair of displaced vertices from long-lived neutral particles decaying into hadronic jets in the ATLAS muon spectrometer in $pp$ collisions at $\sqrt{s}=13\text{ }\text{ }\mathrm{TeV}$

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Search for events with a pair of displaced vertices from long-lived neutral particles decaying into hadronic jets in the ATLAS muon spectrometer in $p p$ collisions at $\sqrt{s} = 13 TeV$

G. Aad et al. (ATLAS Collaboration)

Phys. Rev. D 106, 032005 – Published 9 August 2022

Abstract

A search for events with two displaced vertices from long-lived particle (LLP) pairs using data collected by the ATLAS detector at the LHC is presented. This analysis uses $139 {fb}^{- 1}$ of proton-proton collision data at $\sqrt{s} = 13 TeV$ recorded in 2015–2018. The search employs techniques for reconstructing vertices of LLPs decaying to jets in the muon spectrometer displaced between 3 and 14 m with respect to the primary interaction vertex. The observed numbers of events are consistent with the expected background and limits for several benchmark signals are determined. For the Higgs boson with a mass of 125 GeV, the paper reports the first exclusion limits for branching fractions into neutral long-lived particles below 0.1%, while branching fractions above 10% are excluded at 95% confidence level for LLP proper lifetimes ranging from 4 cm to 72.4 m. In addition, the paper present the first results for the decay of LLPs into $t \bar{t}$ in the ATLAS muon spectrometer.

Received 4 March 2022
Accepted 13 May 2022

DOI:https://doi.org/10.1103/PhysRevD.106.032005

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Physics Subject Headings (PhySH)

Extensions of Higgs sector Extensions of gauge sector Hierarchy problem

Hypothetical gauge bosons Hypothetical scalars

Hadron colliders

Particles & Fields

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Vol. 106, Iss. 3 — 1 August 2022

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Figure 1
Diagram of the scalar portal model studied in this paper. The LLPs are represented by double lines and labeled $s$ , and the final-state SM fermions are labeled as $f$ [13].
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Figure 2
Efficiency for the muon ROI cluster trigger as a function of the decay position of the LLP for some scalar portal samples in the (a) MS barrel and (b) MS end caps for events passing the data quality requirements and having a reconstructed primary vertex. These efficiency distributions are based solely on MC simulation, without any corrections applied for the mismodeling described in Sec. 6a. The vertical lines show the relevant detector boundaries, where “HCAL end” is the outer limit of the hadronic calorimeter, “RPC $1 / 2$ ” represent the first/second stations of RPC chambers, “TGC 1” represents the first stations of TGC chambers, and “L/S” indicate whether they are in the large or small sectors.
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Figure 3
Cumulative efficiency of vertices in the barrel where the vertex is required to be isolated from (a) jets and (b) high- $p_{T}$ tracks, as a function of the selected $Δ R$ , when the sum of low- $p_{T}$ tracks in a $Δ R = 0.2$ cone around the vertex direction is required to be less than a specified cut in $p_{T}$ (c), and when the sum of low- $p_{T}$ tracks in a $Δ R$ cone around the vertex is required to be less than 10 GeV, as a function of the $Δ R$ value (d). The vertical lines show the selected $Δ R$ value that is used in analysis. The differences between pythia multijet and data distributions are attributable to the noncollision background, which is not present in MC simulations.
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Figure 4
Efficiency to reconstruct a MS DV for scalar portal samples with $m_{φ} = 125 GeV$ for vertices that pass the baseline event selection and satisfy the vertex isolation criteria. (a) Barrel MS DV reconstruction efficiency as a function of the transverse decay position of the LLP. (b) End cap MS DV reconstruction efficiency as a function of the longitudinal decay position of the LLP relative to the center of the detector. The efficiency distributions are corrected for the mismodeling described in Sec. 7c. The vertical lines show the relevant detector boundaries, where “HCAL end” is the outer limit of the hadronic calorimeter, “MDT $1 / 2$ ” represent the first/second stations of MDT chambers and “ $L / S$ ” indicate whether they are in large or small sectors.
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Figure 5
Comparison between observed and expected 95% C.L. limits (a) on $(σ / σ_{SM}) \times B$ for $m_{Φ} = 125$ and $m_{s} = 35 GeV$ . Observed 95% C.L. limits (b) on $(σ / σ_{SM}) \times B$ for $m_{Φ} = 125 GeV$ and (c)–(f) on $σ \times B$ for $m_{Φ} \neq 125 GeV$ .
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Physical Review D

covering particles, fields, gravitation, and cosmology

Search for events with a pair of displaced vertices from long-lived neutral particles decaying into hadronic jets in the ATLAS muon spectrometer in $p p$ collisions at $\sqrt{s} = 13 TeV$

G. Aad et al. (ATLAS Collaboration)

Phys. Rev. D 106, 032005 – Published 9 August 2022

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Physical Review D

covering particles, fields, gravitation, and cosmology

Search for events with a pair of displaced vertices from long-lived neutral particles decaying into hadronic jets in the ATLAS muon spectrometer in pp collisions at s=13 TeV

G. Aad et al. (ATLAS Collaboration)

Phys. Rev. D 106, 032005 – Published 9 August 2022

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Search for events with a pair of displaced vertices from long-lived neutral particles decaying into hadronic jets in the ATLAS muon spectrometer in $p p$ collisions at $\sqrt{s} = 13 TeV$