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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Search for B 0 → K *0 𝜏 + ⁢𝜏 − Decays at the Belle II Experiment

We present a search for the rare flavor-changing neutral-current decay 𝐵 0 →𝐾 *0 ⁢𝜏 + ⁢𝜏 − with data collected by the Belle II experiment at the SuperKEKB electron-positron collider. The analysis uses a 365 fb −1 data sample recorded at the center-of-mass energy of the ϒ⁡(4⁢𝑆) resonance. One of the 𝐵 mesons produced in the ϒ⁡(4⁢𝑆)→𝐵 0 $⁢\overline{𝐵}$ 0 process is fully reconstructed in a hadronic decay mode, while its companion 𝐵 meson is required to decay into a 𝐾 *0 and two 𝜏 leptons of opposite charge. The 𝜏 leptons are reconstructed in final states with a single electron, muon, charged pion or charged 𝜌 meson, and additional neutrinos. We set an upper limit on the branching fraction of ℬ⁡(𝐵 0 →𝐾 *0 ⁢𝜏 + ⁢𝜏 − )<1.8×10 −3 at the 90% confidence level, which is the most stringent constraint reported to date.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Search for Higgs boson production at high transverse momentum in the WW decay channel in proton-proton collisions at $\sqrt{s}=13$ TeV

A search for Higgs boson (H) production at high transverse momentum (p T ) in the WW decay channel is presented. The analysis uses proton-proton collisions at $\sqrt{s}=13$ TeV recorded by the CMS experiment in 2016–2018, corresponding to an integrated luminosity of 138 fb −1 . The visible decay products of the Higgs boson are reconstructed as a single large-radius jet with one isolated lepton or none (1ℓ and 0ℓ, respectively; ℓ = e, μ). The H-candidate jets are identified using an advanced transformer-based algorithm and are calibrated with the Lund jet plane reweighting technique. The 1ℓ channel is further split into gluon fusion, vector boson fusion, and associated production with hadronically decaying vector boson categories, while the 0ℓ channel considers all production processes inclusively. The measured cross section times the H → WW branching fraction relative to the standard model expectation is $\mu =-{0.19}_{-0.46}^{+0.48}$, indicating no evidence of a signal above the background. This measurement represents the first dedicated study of highly Lorentz-boosted H → WW decays, complementing earlier searches for high-p T Higgs boson in other decay channels.

Hadron-Hadron Scattering↗
DOE OSTI2026

Machine-learning techniques for model-independent searches in dijet final states

Anomaly detection methods used in a recent search for new phenomena by CMS at the CERN LHC are presented. The methods use machine learning to detect anomalous jets produced in the decay of new massive particles without depending on a specific theory model. The effectiveness of these approaches in enhancing sensitivity to various simulated signal samples is studied and compared using data collected in proton–proton collisions at a center-of-mass energy of 13 TeV. In an example analysis, the capabilities of anomaly detection methods are further demonstrated by identifying large-radius jets consistent with Lorentz-boosted hadronically decaying top quarks in a model-agnostic framework.

CMS↗
DOE OSTI2024

Search for a resonance decaying to a W boson and a photon in proton-proton collisions at $\sqrt{s}$ = 13 TeV using leptonic W boson decays

A search for a new charged particle X with mass between 0.3 and 2.0 TeV decaying to a W boson and a photon is presented, using proton-proton collision data at a center-of-mass energy of 13 TeV, collected by the CMS experiment and corresponding to an integrated luminosity of 138 fb$^{-1}$. Particle X has electric charge $\pm$ 1 and is assumed to have spin 0. The search is performed using the electron and muon decays of the W boson. No significant excess above the predicted background is observed. The upper limit at 95% confidence level on the product of the production cross section of the X and its branching fraction to a W boson and a photon is found to be 94 (137) fb for a 0.3 TeV resonance and 0.75 (0.81) fb for a 2.0 TeV resonance, for an X width-to-mass ratio of 0.01% (5%). This search presents the most stringent constraints to date on the existence of such resonances across the probed mass range. A statistical combination with an earlier study based on the hadronic decay mode of the W boson is also performed, and the upper limit at 95% confidence level for a 2.0 TeV resonance is reduced to 0.50 (0.63) fb for an X width-to-mass ratio of 0.01% (5%).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Measurement of beauty production via non-prompt charm hadrons in p–Pb collisions at $\sqrt{s_{\textrm{NN}}}$ = 5.02 TeV

The production cross sections of D 0 , D + , and Λ$^{+}_{c}$ hadrons originating from beauty-hadron decays (i.e. non-prompt) were measured for the first time at midrapidity in proton–lead (p–Pb) collisions at the center-of-mass energy per nucleon pair of $\sqrt{s_{\textrm{NN}}}$ = 5.02 TeV. Nuclear modification factors (R pPb ) of non-prompt D 0 , D + , and Λ$^{+}_{c}$ are calculated as a function of the transverse momentum (p T ) to investigate the modification of the momentum spectra measured in p–Pb collisions with respect to those measured in proton–proton (pp) collisions at the same energy. The R pPb measurements are compatible with unity and with the measurements in the prompt charm sector, and do not show a significant p T dependence. The p T -integrated cross sections and p T -integrated R pPb of non-prompt D 0 and D + mesons are also computed by extrapolating the visible cross sections down to p T = 0. The non-prompt D-meson R pPb integrated over p T is compatible with unity and with model calculations implementing modification of the parton distribution functions of nucleons bound in nuclei with respect to free nucleons. The non-prompt Λ$^{+}_{c}$/D 0 and D + /D 0 production ratios are computed to investigate hadronisation mechanisms of beauty quarks into mesons and baryons. The measured ratios as a function of p T display a similar trend to that measured for charm hadrons in the same collision system.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Measurement of the branching fraction of Λ + 𝑐 →𝑝⁢𝐾 0 𝑆⁢ 𝜋 0 at Belle

We report a precise measurement of the ratio of branching fractions ℬ⁡(Λ$^+_𝑐$ → 𝑝⁢𝐾$^0_𝑆$⁢𝜋 0 )/ℬ⁡(Λ$^+_𝑐$ → 𝑝⁢𝐾 − ⁢𝜋 + ) using 980 fb −1 of 𝑒 + ⁢𝑒 − data from the Belle experiment. We obtain a value of ℬ⁡(Λ$^+_𝑐$ → 𝑝⁢𝐾$^0_𝑆$⁢𝜋 0 )/ℬ⁡(Λ$^+_𝑐$ → 𝑝⁢𝐾 − ⁢𝜋 + ) =0.339 ±0.002 ±0.009, where the first and second uncertainties are statistical and systematic, respectively. This Belle result is consistent with the previous measurement from the CLEO experiment but has a fivefold improvement in precision. By combining our result with the world average ℬ⁡(Λ$^+_𝑐$ → 𝑝⁢𝐾 − ⁢𝜋 + ), we obtain the absolute branching fraction ℬ⁡(Λ$^+_𝑐$ → 𝑝⁢𝐾$^0_𝑆$⁢𝜋 0 ) =(2.12 ± 0.01 ±0.05 ±0.10)%, where the uncertainties are statistical, systematic, and the uncertainty in the absolute branching fraction scale ℬ⁡(Λ$^+_𝑐$ → 𝑝⁢𝐾 − ⁢𝜋 + ), respectively. This measurement can shed light on hadronic decay mechanisms in charmed baryon decays.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Measurements of W + W − production cross-sections in pp collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Measurements of W + W − → e ± νμ ∓ ν production cross-sections are presented, providing a test of the predictions of perturbative quantum chromodynamics and the electroweak theory. The measurements are based on data from pp collisions at $\sqrt{s}$ = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider in 2015–2018, corresponding to an integrated luminosity of 140 fb −1 . The number of events due to top-quark pair production, the largest background, is reduced by rejecting events containing jets with b-hadron decays. An improved methodology for estimating the remaining top-quark background enables a precise measurement of W + W − cross-sections with no additional requirements on jets. The fiducial W + W − cross-section is determined in a maximum-likelihood fit with an uncertainty of 3.1%. The measurement is extrapolated to the full phase space, resulting in a total W + W − cross-section of 127 ± 4 pb. Differential cross-sections are measured as a function of twelve observables that comprehensively describe the kinematics of W + W − events. The measurements are compared with state-of-the-art theory calculations and excellent agreement with predictions is observed. A charge asymmetry in the lepton rapidity is observed as a function of the dilepton invariant mass, in agreement with the Standard Model expectation. A CP-odd observable is measured to be consistent with no CP violation. Limits on Standard Model effective field theory Wilson coefficients in the Warsaw basis are obtained from the differential cross-sections.

Accelerator Physics↗
DOE OSTI2025

Heavy flavour jet substructure

We present a comprehensive study of energy correlation functions and jet angularities for heavy-flavour QCD jets. In particular, we discuss the possibility of using these observables to expose the dead cone effect, i.e. the suppression of collinear QCD radiation around massive quarks, and to investigate the sensitivity of different observable definitions to the presence of quark masses. Our calculations are presented as all-order resummed predictions at next-to-leading-logarithmic accuracy, matched to (partial) fixed-order results to obtain a better description of the transition around the dead cone threshold. We also compare our analytic results with Pythia, Herwig and Sherpa Monte Carlo predictions to estimate the impact of non-perturbative contributions such as hadronisation, underlying events and B-hadron decays.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Indirect constraints on third generation baryon number violation

Abstract The non-observation of baryon number violation suggests that the scale of baryon-number violating interactions at zero temperature is comparable to the GUT scale. However, the pertinent measurements involve hadrons made of the first-generation quarks, such as protons and neutrons. One may therefore entertain the idea that new flavour physics breaks baryon number at a much lower scale, but only in the coupling to a third generation quark, leading to observable baryon-number violatingb-hadron decay rates. In this paper we show that indirect constraints on the new physics scale Λ BNV from the existing bounds on the proton lifetime do not allow for this possibility. For this purpose we consider the three dominant proton decay channelsp→$$ {\ell}^{+}{\nu}_{\ell}\overline{\nu} $$ ℓ + ν ℓ ν ¯ ,p→$$ {\pi}^{+}\overline{\nu} $$ π + ν ¯ andp→π 0 ℓ + mediated by a virtual bottom quark.

Physics↗
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 OSTI2026

Investigating charm quark energy loss in medium with the nuclear modification factor of D 0 -tagged jets

The nuclear modification factor R AA of charm jets, identified by the presence of a D 0 meson among the jet constituents, has been measured for the first time in Pb–Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{NN}} = 5.02$ TeV with the ALICE detector at the LHC. The D 0 mesons and their charge conjugates are reconstructed from the hadronic decay D 0 → K – π + . Jets are reconstructed from D 0 -meson candidates and charged particles using the anti-k T algorithm with jet resolution parameter R = 0.3, in the jet transverse momentum (p T ) range 5 < $p^{ch}_{T}$$^{jet}$ < 50 GeV/c and pseudorapidity |η ch jet| < 0.6. A hint of reduced suppression in the charm-jet R AA is observed in comparison to inclusive jets in central Pb–Pb collisions with a significance of about 2σ in 20 < $p^{ch}_{T}$$^{jet}$ < 50 GeV/c, suggesting the in-medium energy loss to depend on both the difference between quark and gluon coupling strength (Casimir colour-charge effect) and quark mass (dead-cone effect). The data are compared with model calculations that include mass effects in the in-medium energy loss. Several state-of-the-art models are consistent with the data, with the LIDO model providing the best description of the data in the common kinematic range of inclusive and D 0 -tagged jets, highlighting the role of mass effects in interpreting the results.

Acharya, S. (ORCID:0000000292135329)↗
DOE OSTI2024

Observation of $\gamma\gamma\to\tau\tau$ in proton-proton collisions and limits on the anomalous electromagnetic moments of the $\tau$ lepton

The production of a pair of τ leptons via photon–photon fusion, ${{\unicode{x03B3}\unicode{x03B3}\to\unicode{x03C4}\unicode{x03C4}}}$, is observed for the first time in proton–proton collisions, with a significance of 5.3 standard deviations. This observation is based on a data set recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb$^{−1}$. Events with a pair of τ leptons produced via photon–photon fusion are selected by requiring them to be back-to-back in the azimuthal direction and to have a minimum number of charged hadrons associated with their production vertex. The τ leptons are reconstructed in their leptonic and hadronic decay modes. The measured fiducial cross section of ${{\unicode{x03B3}\unicode{x03B3}\to\unicode{x03C4}\unicode{x03C4}}}$ is $\sigma^\text{fid}_\text{obs} = 12.4 ^{+3.8}_{-3.1}\,\textrm{fb}$. Constraints are set on the contributions to the anomalous magnetic moment (${a_{\unicode{x03C4}}}$) and electric dipole moments (${d_{\unicode{x03C4}}}$) of the τ lepton originating from potential effects of new physics on the $\unicode{x03B3}\unicode{x03C4}\unicode{x03C4}$ vertex: ${a_{\unicode{x03C4}}} = 0.0009_{-0.0031}^{+0.0032}$ and $|{d_{\unicode{x03C4}}}| \lt 2.9\times 10^{-17}\,{e}\,\textrm{cm}$ (95% confidence level), consistent with the standard model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Performance of the CMS high-level trigger during LHC Run 2

The CERN LHC provided proton and heavy ion collisions during its Run 2 operation period from 2015 to 2018. Proton-proton collisions reached a peak instantaneous luminosity of 2.1× 10 34 cm -2 s -1 , twice the initial design value, at √(s)=13 TeV. The CMS experiment records a subset of the collisions for further processing as part of its online selection of data for physics analyses, using a two-level trigger system: the Level-1 trigger, implemented in custom-designed electronics, and the high-level trigger, a streamlined version of the offline reconstruction software running on a large computer farm. This paper presents the performance of the CMS high-level trigger system during LHC Run 2 for physics objects, such as leptons, jets, and missing transverse momentum, which meet the broad needs of the CMS physics program and the challenge of the evolving LHC and detector conditions. Sophisticated algorithms that were originally used in offline reconstruction were deployed online. Highlights include a machine-learning b tagging algorithm and a reconstruction algorithm for tau leptons that decay hadronically.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Configuration, Performance, and Commissioning of the ATLAS b-jet Triggers for the 2022 and 2023 LHC data-taking periods

In 2022 and 2023, the Large Hadron Collider produced approximately two billion hadronic interactions each second from bunches of protons that collide at a rate of 40 MHz. The ATLAS trigger system is used to reduce this rate to a few kHz for recording. Selections based on hadronic jets, their energy, and event topology reduce the rate to 𝒪(10) kHz while maintaining high efficiencies for important signatures resulting in b-quarks, but to reach the desired recording rate of hundreds of Hz, additional real-time selections based on the identification of jets containing b-hadrons (b-jets) are employed to achieve low thresholds on the jet transverse momentum at the High-Level Trigger. The configuration, commissioning, and performance of the real-time ATLAS b-jet identification algorithms for the early LHC Run 3 collision data are presented. These recent developments provide substantial gains in signal efficiency for critical signatures; for the Standard Model production of Higgs boson pairs, a 50% improvement in selection efficiency is observed in final states with four b-quarks or two b-quarks and two hadronically decaying τ-leptons.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Identification of tau leptons using a convolutional neural network with domain adaptation

A tau lepton identification algorithm,DeepTau, based on convolutional neural network techniques, has been developed in the CMS experiment to discriminate reconstructed hadronic decays of tau leptons (τ h ) from quark or gluon jets and electrons and muons that are misreconstructed as τ h candidates. The latest version of this algorithm, v2.5, includes domain adaptation by backpropagation, a technique that reduces discrepancies between collision data and simulation in the region with the highest purity of genuine τh candidates. Additionally, a refined training workflow improves classification performance with respect to the previous version of the algorithm, with a reduction of 30–50% in the probability for quark and gluon jets to be misidentified as τ h candidates for given reconstruction and identification efficiencies. This paper presents the novel improvements introduced in theDeepTau algorithm and evaluates its performance in LHC proton-proton collision data at √(s) = 13 and 13.6 TeV collected in 2018 and 2022 with integrated luminosities of 60 and 35 fb -1 , respectively. Techniques to calibrate the performance of the τ h identification algorithm in simulation with respect to its measured performance in real data are presented, together with a subset of results among those measured for use in CMS physics analyses.

Large detector-systems performance↗
DOE OSTI2025

Kinematically enhanced interpolating operators for boosted hadrons

We propose to use interpolating operators for lattice quantum chromodynamics calculations of highly boosted pions and nucleons with kinematically enhanced ground-state overlap factors at large momentum. Because this kinematic enhancement applies to the signal but not the variance of the correlation function, these interpolating operators can achieve better signal-to-noise ratios at large momentum. We perform proof-of-principle calculations with boosted pions and nucleons using close-to-physical and larger quark masses to explore the utility of our proposal. Results for effective energies and matrix elements, as well as Lanczos ground-state energy estimators, are consistent with theoretical expectations for signal-to-noise improvement at large momenta.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Measurements of the branching fractions of the P -wave charmonium spin-singlet state h c ( P 1 1 ) → h + h − π 0 / η

Based on ( 2712.4 ± 14.3 ) × 10 6 ψ ( 3686 ) events, we investigate four hadronic decay modes of the P -wave charmonium spin-singlet state h c ( 1 P 1 ) → h + h − π 0 / η ( h = π or K ) via the process ψ ( 3686 ) → π 0 h c at BESIII. The h c → π + π − π 0 decay is observed with a significance of 9.6 σ after taking into account systematic uncertainties. Evidences for h c → K + K − π 0 and h c → K + K − η are found with significances of 3.5 σ and 3.3 σ , respectively, after considering the systematic uncertainties. The branching fractions of these decays are measured to be B ( h c → π + π − π 0 ) = ( 1.36 ± 0.16 ± 0.14 ) × 10 − 3 , B ( h c → K + K − π 0 ) = ( 3.26 ± 0.84 ± 0.36 ) × 10 − 4 , and B ( h c → K + K − η ) = ( 3.13 ± 1.08 ± 0.38 ) × 10 − 4 , where the first uncertainties are statistical and the second are systematic. No significant signal of h c → π + π − η is found, and the upper limit of its decay branching fraction is determined to be B ( h c → π + π − η ) < 4.0 × 10 − 4 at the 90% confidence level. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2024

Search for η c ( 2 S ) → 2 ( π + π − ) and improved measurement of χ c J → 2 ( π + π − )

We search for the hadronic decay η c ( 2 S ) → 2 ( π + π − ) in the ψ ( 3686 ) → γ η c ( 2 S ) radiative decay using ( 27.12 ± 0.14 ) × 10 8 ψ ( 3686 ) events collected by the BESIII detector at the BEPCII collider. No significant signal is found, and the upper limit of B [ ψ ( 3686 ) → γ η c ( 2 S ) ] B [ η c ( 2 S ) → 2 ( π + π − ) ] is determined to be 1.43 × 10 − 6 at the 90% confidence level. Using ψ ( 3686 ) → γ χ c J transitions, we also measure the branching fractions of B [ χ c J ( J = 0 , 1 , 2 ) → 2 ( π + π − ) ] , which are B [ χ c 0 → 2 ( π + π − ) ] = ( 2.127 ± 0.002 ( stat ) ± 0.101 ( syst ) ) % , B [ χ c 1 → 2 ( π + π − ) ] = ( 0.685 ± 0.001 ( stat ) ± 0.031 ( syst ) ) % , and B [ χ c 2 → 2 ( π + π − ) ] = ( 1.153 ± 0.001 ( stat ) ± 0.063 ( syst ) ) % . Published by the American Physical Society 2024

Ablikim, M.↗