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DOE OSTI2026

Measurement of the Zγ production cross section and search for anomalous neutral triple gauge couplings in pp collisions at $ \sqrt{s}=13 $ TeV

A measurement of the fiducial cross section of the associated production of a Z boson and a high-p$_{T}$ photon, where the Z decays to two neutrinos, and a search for anomalous triple gauge couplings are reported. The results are based on data collected by the CMS experiment at the LHC in proton-proton collisions at $ \sqrt{s}=13 $ TeV during 2016-2018, corresponding to an integrated luminosity of 138 fb$^{−1}$. The fiducial Zγ cross section, where a photon with a p$_{T}$ greater than 225 GeV is produced in association with a Z, and the Z decays to a $ \upnu \overline{\upnu} $ pair $ \left(\mathrm{Z}\left(\upnu \overline{\upnu}\right)\upgamma \right) $, is measured to be $ {23.3}_{-1.3}^{+1.4} $ fb, in agreement, within uncertainties, with the standard model prediction. The differential cross section as a function of the photon p$_{T}$ has been measured and compared with standard model predictions computed at next-to-leading and at next-to-next-to-leading order in perturbative quantum chromodynamics. Constraints have been placed on the presence of anomalous couplings that affect the ZZγ and Zγγ vertex using the p$_{T}$ spectrum of the photons. The observed 95% confidence level intervals for CP-conserving $ {h}_3^{\upgamma} $ and $ {h}_4^{\upgamma} $ are determined to be (−3.4, 3.5)×10$^{−4}$ and (−6.8, 6.8)×10$^{−7}$, and for $ {h}_3^{\mathrm{Z}} $ and $ {h}_4^{\mathrm{Z}} $ they are (−2.2, 2.2)×10$^{−4}$ and (−4.1, 4.2)×10$^{−7}$, respectively. These are the strictest limits to date on $ {h}_3^{\upgamma} $, $ {h}_3^{\mathrm{Z}} $ and $ {h}_4^{\mathrm{Z}} $.[graphic not available: see fulltext]

Hayrapetyan, Aram [Yerevan Phys. Inst.]↗

DOE OSTI2026

Search for heavy scalar resonances decaying to Lorentz-boosted Higgs and Higgs-like bosons in the $\mathrm{b}\overline{\mathrm{b}}4\mathrm{q}$ final state at $\sqrt{s}=13$ TeV

A search is performed for a heavy scalar resonance X decaying to a Higgs boson (H) and a Higgs-like scalar boson (Y) in the two bottom quark (H → $b\bar{b}$) and four quark (Y → VV → 4q) final state, where V denotes a W or Z boson. Masses of the X between 900 and 4000 GeV and the Y between 60 and 2800 GeV are considered. The search is performed in data collected by the CMS experiment at the CERN LHC from proton-proton collisions at 13 TeV center-of-mass energy, with a data set corresponding to a total integrated luminosity of 138 fb −1 . It targets the Lorentz-boosted regime, in which the products of the H → $b\bar{b}$ decay can be reconstructed as a single large-area jet, and those from the Y → VV → 4q decay as either one Y → 4q or two jets V → H → $q\bar{q}$. Jet identification and mass reconstruction exploit machine-learning tools, including a novel attention-based “particle transformer” for Y → 4q identification. No significant excess is observed in the data above the standard model background expectation. Upper limits on the product of production cross section and branching fraction as low as 0.2 fb are derived at 95% confidence level for various mass hypotheses. This is the first search at the LHC for scalar resonances in the all-hadronic H → $b\bar{b}$VV decay channel.

Beyond Standard Model↗

DOE OSTI2026

Search for a Higgs boson produced in association with a charm quark and decaying to a W boson pair in proton-proton collisions at $ \sqrt{s}=13 $ TeV

This paper presents a search for a Higgs boson produced in association with a charm quark (cH) which allows to probe the Higgs-charm Yukawa coupling strength modifier κ$_{c}$. Higgs boson decays to a pair of W bosons are considered, where one W boson decays to an electron and a neutrino, and the other W boson decays to a muon and a neutrino. The data, corresponding to an integrated luminosity of 138 fb$^{−1}$, were collected between 2016 and 2018 with the CMS detector at the LHC at a center-of-mass energy of $ \sqrt{s}=13 $ TeV. Upper limits at the 95% confidence level (CL) are set on the ratio of the measured yield to the standard model expectation for cH production. The observed (expected) upper limit is 1065 (506), corresponding to an observed (expected) constraint of |κ$_{c}$| < 211 (95). When combined with the previous search for cH in the diphoton decay channel of the Higgs boson, the limits are interpreted as observed (expected) constraints at 95% CL on the value of κ$_{c}$, |κ$_{c}$| < 47 (51).[graphic not available: see fulltext]

Hayrapetyan, Aram [Yerevan Phys. Inst.]↗

DOE OSTI2020

Search for supersymmetry in proton-proton collisions at $\sqrt{s} =$ 13 TeV in events with high-momentum Z bosons and missing transverse momentum

A search for new physics in events with two highly Lorentz-boosted Z bosons and large missing transverse momentum is presented. The analyzed proton-proton collision data, corresponding to an integrated luminosity of 137 fb$^{−1}$, were recorded at $ \sqrt{s} $ = 13 TeV by the CMS experiment at the CERN LHC. The search utilizes the substructure of jets with large radius to identify quark pairs from Z boson decays. Backgrounds from standard model processes are suppressed by requirements on the jet mass and the missing transverse momentum. No significant excess in the event yield is observed beyond the number of background events expected from the standard model. For a simplified supersymmetric model in which the Z bosons arise from the decay of gluinos, an exclusion limit of 1920 GeV on the gluino mass is set at 95% confidence level. This is the first search for beyond-standard-model production of pairs of boosted Z bosons plus large missing transverse momentum.[graphic not available: see fulltext]

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2022

Search for a W' boson decaying to a vector-like quark and a top or bottom quark in the all-jets final state at $\sqrt{\mathrm{s}}$ = 13 TeV

A search is presented for a heavy W' boson resonance decaying to a B or T vector-like quark and a t or a b quark, respectively. The analysis is performed using proton-proton collisions collected with the CMS detector at the LHC. The data correspond to an integrated luminosity of 138 fb -1 at a center-of-mass energy of 13 TeV. Both decay channels result in a signature with a t quark, a Higgs or Z boson, and a b quark, each produced with a significant Lorentz boost. The all-hadronic decays of the Higgs or Z boson and of the t quark are selected using jet substructure techniques to reduce standard model backgrounds, resulting in a distinct three-jet W' boson decay signature. No significant deviation in data with respect to the standard model background prediction is observed. Upper limits are set at 95% confidence level on the product of the W' boson cross section and the final state branching fraction. A W' boson with a mass below 3.1 TeV is excluded, given the benchmark model assumption of democratic branching fractions. In addition, limits are set based on generalizations of these assumptions. These are the most sensitive limits to date for this final state.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2022

Observation of the doubly Cabibbo-suppressed decays $D^+ → K^+π^0π^0$ and $D^+ → K^+π^0η$

By analyzing e + e - annihilation data corresponding to an integrated luminosity of 2.93 fb -1 collected at the center-of-mass energy of 3.773 GeV with the BESIII detector, we report the first observations of the doubly Cabibbo-suppressed decays D + → K + π 0 π 0 and D + → K + π 0 η. The branching fractions of D + → K + π 0 π 0 and D + → K + π 0 η are measured to be (2.1 ± 0.4 stat ± 0.1 syst ) x 10 -4 and (2.1 ± 0.5 stat ± 0.1 syst ) x 10 -4 with statistical significances of 8.8σ and 5.5σ, respectively. In addition, we search for the subprocesses D + → K * (892) + π 0 and D + → K * (892)+η with K * (892) + → K + π 0 . The branching fraction of D + → K * (892) + η is determined to be (4.4$^{+1.8}_{-1.5stat}$ ± 0.2 syst ) x 10 -4 , with a statistical significance of 3.2σ. No significant signal for D + → K * (892) + π 0 is found and we set an upper limit on the branching fraction of this decay at the 90% confidence level to be 5.4 x 10 -4 .

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2023

Search for a light charged Higgs boson in t → H±b decays, with H± → cb, in the lepton+jets final state in proton-proton collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A search for a charged Higgs boson, H ± , produced in top-quark decays, t → H ± b, is presented. The search targets H ± decays into a bottom and a charm quark, H ± → cb. The analysis focuses on a selection enriched in top-quark pair production, where one top quark decays into a leptonically decaying W boson and a bottom quark, and the other top quark decays into a charged Higgs boson and a bottom quark. This topology leads to a lepton-plus-jets final state, characterised by an isolated electron or muon and at least four jets. The search exploits the high multiplicity of jets containing b-hadrons, and deploys a neural network classifier that uses the kinematic differences between the signal and the background. The search uses a dataset of proton-proton collisions collected at a centre-of-mass energy $\sqrt{s}$ = 13 TeV between 2015 and 2018 with the ATLAS detector at CERN’s Large Hadron Collider, amounting to an integrated luminosity of 139 fb -1 . Observed (expected) 95% confidence-level upper limits between 0.15% (0.09%) and 0.42% (0.25%) are derived for the product of branching fractions $\mathscr{B}$ (t → H ± b) × $\mathscr{B}$(H ± → cb) for charged Higgs boson masses between 60 and 160 GeV, assuming the SM production of the top-quark pairs.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Search for a charged Higgs boson decaying into a heavy neutral Higgs boson and a W boson in proton-proton collisions at $ \sqrt{s}$ = 13 TeV

A search for a charged Higgs boson H ± decaying into a heavy neutral Higgs boson H and a W boson is presented. The analysis targets the H decay into a pair of tau leptons with at least one of them decaying hadronically and with an additional electron or muon present in the event. The search is based on proton-proton collision data recorded by the CMS experiment during 2016–2018 at $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 138 fb –1 . The data are consistent with standard model background expectations. Upper limits at 95% confidence level are set on the product of the cross section and branching fraction for an H ± in the mass range of 300–700 GeV, assuming an H with a mass of 200 GeV. The observed limits range from 0.085 pb for an H ± mass of 300 Ge V to 0.019 pb for a mass of 700 GeV. These are the first limits on H ± production in the H ± → HW ± decay channel at the LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Search for a vector-like quark T' → tH via the diphoton decay mode of the Higgs boson in proton-proton collisions at $ \sqrt{s}$ = 13 TeV

A search for the electroweak production of a vector-like quark T', decaying to a top quark and a Higgs boson is presented. The search is based on a sample of proton-proton collision events recorded at the LHC at $ \sqrt{s} $ = 13 TeV, corresponding to an integrated luminosity of 138 fb$^{–1}$. This is the first T' search that exploits the Higgs boson decay to a pair of photons. For narrow isospin singlet T' states with masses up to 1.1 TeV, the excellent diphoton invariant mass resolution of 1–2% results in an increased sensitivity compared to previous searches based on the same production mechanism. The electroweak production of a T' quark with mass up to 960 GeV is excluded at 95% confidence level, assuming a coupling strength κ$_{T}$ = 0.25 and a relative decay width Γ/M$_{T'}$< 5%.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Measurement of branching fractions of ${\Lambda}_{\textrm{c}}^{+}$ decays to Σ⁺K⁺K⁻, Σ⁺Φ and Σ⁺K⁺π⁻(π 0 )

Based on 4.5 fb - 1 data taken at seven center-of-mass energies ranging from 4.600 to 4.699 GeV with the BESIII detector at the BEPCII collider, we measure the branching fractions of $ {\Lambda}_c^{+} $ → Σ + + hadrons relative to $ {\Lambda}_c^{+} $ → Σ + π + π - . Combining with the world average branching fraction of $ {\Lambda}_c^{+} $ → Σ + π + π - , their branching fractions are measured to be (0 . 377 ± 0 . 042 ± 0 . 020 ± 0 . 021)% for $ {\Lambda}_c^{+} $ → Σ + K + K - , (0 . 200 ± 0 . 023 ± 0 . 011 ± 0 . 011)% for $ {\Lambda}_c^{+} $ → Σ + K + π - , (0 . 414 ± 0 . 080 ± 0 . 030 ± 0 . 023)% for $ {\Lambda}_c^{+} $ → Σ + Φ and (0 . 197 ± 0 . 036 ± 0 . 009 ± 0 . 011)% for $ {\Lambda}_c^{+} $ → Σ + K + K - (non- Φ ). In all the above results, the first uncertainties are statistical, the second are systematic and the third are from external input of the branching fraction of $ {\Lambda}_c^{+} $ → Σ + π + π - . Since no signal for $ {\Lambda}_c^{+} $ → Σ + K + π - π 0 is observed, the upper limit of its branching fraction is determined to be 0.13% at the 90% confidence level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Search for supersymmetry in final states with a single electron or muon using angular correlations and heavy-object identification in proton-proton collisions at $ \sqrt{s} $ = 13 TeV

A search for supersymmetry is presented in events with a single charged lepton, electron or muon, and multiple hadronic jets. The data correspond to an integrated luminosity of 138 fb –1 of proton-proton collisions at a center-of-mass energy of 13 TeV, recorded by the CMS experiment at the CERN LHC. The search targets gluino pair production, where the gluinos decay into final states with the lightest supersymmetric particle (LSP) and either a top quark-antiquark ($\text{t}\bar{\text{t}}$ pair, or a light-flavor quark-antiquark ($\text{q}\bar{\text{q}}$ pair and a virtual or on-shell W boson. The main backgrounds, $\text{t}\bar{\text{t}}$ pair and W+jets production, are suppressed by requirements on the azimuthal angle between the momenta of the lepton and of its reconstructed parent W boson candidate, and by top quark and W boson identification based on a machine-learning technique. The number of observed events is consistent with the expectations from standard model processes. Limits are evaluated on supersymmetric particle masses in the context of two simplified models of gluino pair production. Exclusions for gluino masses reach up to 2120 (2050) GeV at 95% confidence level for a model with gluino decay to a $\text{t}\bar{\text{t}}$ pair (a $\text{q}\bar{\text{q}}$ pair and a W boson) and the LSP. For the same models, limits on the mass of the LSP reach up to 1250 (1070) GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Search for dark matter produced in association with a Higgs boson decaying to tau leptons at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A search for dark matter produced in association with a Higgs boson in final states with two hadronically decaying τ-leptons and missing transverse momentum is presented. The analysis uses 139 fb -1 of proton-proton collision data at $\sqrt{s}$ = 13 TeV collected by the ATLAS experiment at the Large Hadron Collider between 2015 and 2018. No evidence of physics beyond the Standard Model is found. The results are interpreted in terms of a 2HDM+a model featuring two scalar Higgs doublets and a pseudoscalar singlet field. Exclusion limits on the parameters of the model in selected benchmark scenarios are derived at 95% confidence level. Model-independent limits are also set on the visible cross-section for processes beyond the Standard Model producing missing transverse momentum in association with a Higgs boson decaying into τ-leptons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Search for lepton-flavor-violating τ – → μ – μ + μ – decays at Belle II

We present the result of a search for the charged-lepton-flavor violating decay τ – → μ – μ + μ – using a 424 fb –1 sample of data recorded by the Belle II experiment at the SuperKEKB e + e – collider. The selection of e + e – → τ + τ – events is based on an inclusive reconstruction of the non-signal tau decay, and on a boosted decision tree to suppress background. We observe one signal candidate, which is compatible with the expectation from background processes. We set a 90% confidence level upper limit of 1.9 × 10 –8 on the branching fraction of the τ – → μ – μ + μ – decay, which is the most stringent bound to date.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

No ν s is Good News

The baryon acoustic oscillation (BAO) analysis from the first year of data from the Dark Energy Spectroscopic Instrument (DESI), when combined with data from the cosmic microwave background (CMB), has placed an upper-limit on the sum of neutrino masses, ∑m ν < 70 meV (95%). In addition to excluding the minimum sum associated with the inverted hierarchy, the posterior is peaked at ∑m ν = 0 and is close to excluding even the minumum sum, 58 meV at 2σ. In this paper, we explore the implications of this data for cosmology and particle physics. The sum of neutrino mass is determined in cosmology from the suppression of clustering in the late universe. Allowing the clustering to be enhanced, we extended the DESI analysis to ∑m ν < 0 and find ∑m ν =160 ± 90 meV (68%), and that the suppression of power from the minimum sum of neutrino masses is excluded at 99% confidence. We show this preference for negative masses makes it challenging to explain the result by a shift of cosmic parameters, such as the optical depth or matter density. We then show how a result of ∑m ν = 0 could arise from new physics in the neutrino sector, including decay, cooling, and/or time-dependent masses. These models are consistent with current observations but imply new physics that is accessible in a wide range of experiments. In addition, we discuss how an apparent signal with ∑m ν < 0 can arise from new long range forces in the dark sector or from a primordial trispectrum that resembles the signal of CMB lensing.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

Search for dark matter production in association with a single top quark in proton-proton collisions at $\sqrt{s} = 13$ TeV

A search for the production of a single top quark in association with invisible particles is performed using proton-proton collision data collected with the CMS detector at the LHC at $\sqrt{s}=13$ TeV, corresponding to an integrated luminosity of 138 fb −1 . In this search, a flavor-changing neutral current produces a single top quark or antiquark and an invisible state nonresonantly. The invisible state consists of a hypothetical spin-1 particle acting as a new mediator and decaying to two spin-1/2 dark matter candidates. The analysis searches for events in which the top quark or antiquark decays hadronically. No significant excess of events compatible with that signature is observed. Exclusion limits at 95% confidence level are placed on the masses of the spin-1 mediator and the dark matter candidates, and are compared to constraints from the dark matter relic density measurements. In a vector (axial-vector) coupling scenario, masses of the spin-1 mediator are excluded up to 1.85 (1.85) TeV with an expectation of 2.0 (2.0) TeV, whereas masses of the dark matter candidates are excluded up to 0.75 (0.55) TeV with an expectation of 0.85 (0.65) TeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Search for $t\overline{t}$ resonances in fully hadronic final states in $pp$ collisions at $ \sqrt{s} $ = 13 TeV with the ATLAS detector

This paper presents a search for new heavy particles decaying into a pair of top quarks using 139 fb -1 of proton-proton collision data recorded at a centre-of-mass energy of √s = 13 TeV with the ATLAS detector at the Large Hadron Collider. The search is performed using events consistent with pair production of high-transverse-momentum top quarks and their subsequent decays into the fully hadronic final states. The analysis is optimized for resonances decaying into a $t\overline{t}$ pair with mass above 1.4 TeV, exploiting a dedicated multivariate technique with jet substructure to identify hadronically decaying top quarks using large-radius jets and evaluating the background expectation from data. No significant deviation from the background prediction is observed. Limits are set on the production cross-section times branching fraction for the new Z' boson in a topcolor-assisted-technicolor model. The Z' boson masses below 3.9 and 4.7 TeV are excluded at 95% confidence level for the decay widths of 1% and 3%, respectively.

Heavy quark production↗

DOE OSTI2020

Searches for low-mass dimuon resonances

Searches are performed for a low-mass dimuon resonance, X, produced in proton-proton collisions at a center-of-mass energy of 13 TeV, using a data sample corresponding to an integrated luminosity of 5.1 fb -1 and collected with the LHCb detector. The X bosons can either decay promptly or displaced from the proton-proton collision, where in both cases the requirements placed on the event and the assumptions made about the production mechanisms are kept as minimal as possible. The searches for promptly decaying X bosons explore the mass range from near the dimuon threshold up to 60 GeV, with nonnegligible X widths considered above 20 GeV. The searches for displaced $X → µ^+µ^-$ decays consider masses up to 3 GeV. None of the searches finds evidence for a signal and 90% confidence-level exclusion limits are placed on the $X → µ^+µ^-$ cross sections, each with minimal model dependence. In addition, these results are used to place world-leading constraints on GeV-scale bosons in the two-Higgs-doublet and hidden-valley scenarios.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

Search for lepton-flavor-violating tau-lepton decays to ℓγ at Belle

Charged lepton flavor violation is forbidden in the Standard Model but possible in several new physics scenarios. In many of these models, the radiative decays τ ± → ℓ ± γ (ℓ = e, μ) are predicted to have a sizeable probability, making them particularly interesting channels to search at various experiments. An updated search via τ ± → ℓ ± γ using full data of the Belle experiment, corresponding to an integrated luminosity of 988 fb –1 , is reported for charged lepton flavor violation. No significant excess over background predictions from the Standard Model is observed, and the upper limits on the branching fractions, B(τ ± → μ ± γ) ≤ 4.2 × 10 –8 and B(τ ± → e ± γ) ≤ 5.6 × 10 –8 , are set at 90% confidence level.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗