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Tag: Particle, Atomic & Nuclear Physics

  • LHCb measures B+ decay angular coefficients in agreement with expectations

    What the study found

    The measured angular distribution of B+ → J/ψK+ decays agrees with expectations. The study also indicates that the LHCb Upgrade I detector response is understood to the precision needed to extract angular coefficients in related rare decays.

    Why the authors say this matters

    The authors conclude that these measurements show the detector response is understood well enough to reliably extract angular coefficients linked to rare b → sμ+μ− and b → dμ+μ− transitions, which the abstract says are particularly sensitive to physics beyond the Standard Model.

    What the researchers tested

    The researchers measured the normalised decay rate of B+ → J/ψ(→ μ+μ−)K+ as a function of the lepton helicity angle, which describes the angle of the emitted lepton in the decay. They used 1.1 fb−1 of data collected in October 2024 with the upgraded LHCb detector and parameterised the angular distribution with the forward-backward asymmetry, AFB, and the flatness parameter, FH.

    What worked and what didn't

    The coefficients were measured both overall and across several kinematic and detector-response variables, and the results were found to be in good agreement with expectations. The abstract does not report any major discrepancy or failed measurement.

    What to keep in mind

    The summary does not describe detailed uncertainties, numerical values, or specific limitations beyond the scope of the reported measurements. It also only states that the results agree with expectations; it does not provide a broader interpretation beyond detector-response validation.

    • The normalised decay rate of B+ → J/ψ(→ μ+μ−)K+ was measured as a function of lepton helicity angle.
    • The analysis used 1.1 fb−1 of data collected in October 2024 with the upgraded LHCb detector.
    • The angular distribution was described using forward-backward asymmetry (AFB) and flatness parameter (FH).
    • The measurements were made both integrated and differentially across kinematic and detector-response variables.
    • The results were found to be in good agreement with expectations.
    • The authors say the detector response is understood well enough for related rare b decays.

  • Toponium masses estimated with QCD sum rules

    What the study found

    The study reports estimates for pseudoscalar toponium, vector toponium, and the triply-top baryon. The pseudoscalar toponium estimate is said to be consistent with near-threshold events reported by CMS and ATLAS.

    Why the authors say this matters

    The authors conclude that the results can provide a precise theoretical guide for future experimental investigations of purely top-quark states at the LHC and future facilities such as the FCC. They also suggest the calculations help interpret the recent near-threshold pseudoscalar enhancement as a possible toponium signal.

    What the researchers tested

    They examined the masses and binding energies of these purely top-quark states.

    What worked and what didn't

    For the triply-top baryon, the central mass was found to be slightly above the sum of the constituent top-quark masses.

    What to keep in mind

    The summary does not describe detailed numerical values beyond the qualitative mass and binding-energy statements. It also does not provide experimental confirmation of the triply-top baryon or a direct proof that the near-threshold events are toponium.

    • The paper estimates masses for pseudoscalar toponium, vector toponium, and the triply-top baryon.
    • The pseudoscalar toponium result is described as consistent with CMS and ATLAS near-threshold events.
    • Both toponium states were found to have negative binding energy in the authors' calculations.
    • The triply-top baryon mass was reported to be slightly above the sum of three top-quark masses.
    • The authors say the results may guide future experiments at the LHC and FCC.

  • Modified PYTHIA mPDFs better satisfy symmetry and sum rules

    What the study found

    The study found that an updated PYTHIA-based construction for equal-scale multi-parton distribution functions can give symmetric functions and improve agreement with the required number and momentum sum rules. For double and triple parton distribution functions, the sum rules were obeyed to within 10% over most of the tested phase space.

    Why the authors say this matters

    The authors say multi-parton distribution functions are important for predicting multiple scattering rates at hadron colliders. They suggest their improved construction matters because the earlier PYTHIA model could not satisfy both symmetry and the sum rules at the same time.

    What the researchers tested

    The researchers introduced an algorithm for equal-scale multi-parton distribution functions based on the PYTHIA procedure, with three additional modifications. They tested it on double parton distribution functions (dPDFs) and triple parton distribution functions (tPDFs), and also used the dPDFs to compute rapidity asymmetries for same-sign WW and ZZ production via double parton scattering.

    What worked and what didn't

    The modified construction produced symmetric dPDFs and tPDFs that met the sum rules to within about 10% for most of the phase space and scales tested, with deviations only mildly above that level. The study also compared the rapidity-asymmetry predictions with results from PYTHIA and the GS09 dPDFs, but the abstract does not state a clear winner among those comparisons.

    What to keep in mind

    The summary only reports results for the equal-scale case, where all partons share the same scale. The abstract does not describe detailed limitations beyond the noted deviations from the sum rules, and it does not provide the full comparison outcomes for the collider predictions.

    • The paper addresses equal-scale multi-parton distribution functions, which are used in predictions for multiple scattering at hadron colliders.
    • An updated PYTHIA-based algorithm was built with three extra modifications.
    • The new construction aims to produce symmetric mPDFs that better satisfy number and momentum sum rules.
    • For dPDFs and tPDFs, the sum rules were obeyed to within 10% over most of the tested phase space.
    • The dPDFs were used to compute rapidity asymmetries for same-sign WW and ZZ production via double parton scattering.

  • Hydration redirects electron-induced chemistry in uracil

    What the study found

    The study found that microsolvation, meaning the presence of just a few water molecules, can fundamentally change how electron-attached uracil behaves. Even one water molecule was enough to suppress covalent bond rupture and shift the system toward water evaporation.

    Why the authors say this matters

    The authors conclude that immediate hydration qualitatively redirects the relaxation pathways of electron-attached nucleobases. They say this has important implications for understanding electron-driven chemistry in aqueous biological environments.

    What the researchers tested

    The researchers studied mass-selected hydrated uracil anions after photoexcitation across a wide energy range from 0.5 to 5.5 eV. They used photofragment excitation spectroscopy to examine the electronic structures of individual hydrated uracil anions and compared the solvent-loss patterns with a stochastic evaporation model.

    What worked and what didn't

    Instead of bond cleavage, electronically excited clusters relaxed through rapid internal conversion to a vibrationally hot ground state, followed by sequential loss of water molecules. The observed solvent-loss patterns were quantitatively described by a stochastic evaporation model, with an average water binding energy of about 0.4 eV that did not depend on cluster size.

    What to keep in mind

    The summary provided here is limited to hydrated uracil anions studied under the reported photoexcitation conditions. The abstract does not describe broader tests on other nucleobases, nor does it provide additional limitations.

    • A single water molecule suppressed covalent bond rupture in electron-attached uracil.
    • Excited hydrated uracil clusters mainly lost water rather than breaking covalent bonds.
    • Rapid internal conversion led to a vibrationally hot ground state before sequential water evaporation.
    • Photofragment excitation spectroscopy was used to probe individual hydrated uracil anions.
    • The average water binding energy was about 0.4 eV and was independent of cluster size.

  • ANATAR integrates tools for multi-loop amplitude generation

    What the study found

    The study presents ANATAR, a Mathematica package for multi-loop computations, which are calculations involving more than one loop in a particle-physics process. The package integrates existing tools to generate and manipulate amplitudes and to support higher-order calculations.

    Why the authors say this matters

    The authors say ANATAR is efficient without compromising user-friendliness and flexibility. They also conclude that it is optimized for computations in effective field theories and supports large classes of BSM (beyond the Standard Model) models with the same gauge group as the SM (Standard Model).

    What the researchers tested

    The researchers introduced and reviewed the main functionalities of ANATAR. According to the abstract, the package uses QGRAF to generate Feynman diagrams, FORM to perform Dirac and color algebra, and interfaces to codes for integration-by-parts reduction to reduce expressions to master integrals.

    What worked and what didn't

    The abstract says ANATAR can manipulate generated amplitudes, extract scalar form factors, and map expressions to integral families for later reduction. It also states that the package integrates several existing tools and is equipped for phenomenological applications.

    What to keep in mind

    The abstract does not describe numerical benchmarks, comparisons with other software, or specific performance limits. It also does not provide detailed results from the phenomenological applications beyond stating that they are illustrated.

    • ANATAR is a new Mathematica package for multi-loop computations.
    • It integrates QGRAF for Feynman diagram generation and FORM for Dirac and color algebra.
    • The package can manipulate amplitudes, extract scalar form factors, and map expressions to integral families.
    • ANATAR interfaces with integration-by-parts reduction codes to reach master integrals.
    • The abstract says it is optimized for effective field theory calculations and supports many BSM models.
  • LHCb could improve Lambda mass precision with lower tracking uncertainty

    LHCb could improve Lambda mass precision with lower tracking uncertainty

    What the study found

    The study found that detector-related uncertainties in precision two-body mass measurements can be studied by looking at how observed mass shifts depend on the sum and difference of the daughter particle momenta. Using the Lambda hyperon mass as an example, the authors show that the LHCb experiment could control tracking-system systematics to 0.7 keV/c^2 and reach a total precision of 2.2 keV/c^2.

    Why the authors say this matters

    The authors say this matters because the method provides a more rigorous way to identify the physical causes of bias than ad hoc rules often used in these measurements. They also note that the result could improve current knowledge of the Lambda hyperon mass by a factor of three.

    What the researchers tested

    The researchers investigated how detector effects influence the determination of a parent particle mass in two-body decays. They developed an approach based on the dependence of mass shifts on the sum and difference of daughter particle momenta, and illustrated it with a case study of measuring the Lambda hyperon mass.

    What worked and what didn't

    The approach was shown to connect observed mass shifts with the physical causes of bias more rigorously than common ad hoc rules. In the Lambda mass example, the tracking-system uncertainty could be controlled to 0.7 keV/c^2, while the total precision was limited mainly by the knowledge of the K-short mass used for calibration.

    What to keep in mind

    The abstract does not describe experimental limitations beyond noting that the total precision is dominated by the K-short mass used for calibration. The results are presented as an illustration of the method using the Lambda hyperon mass case.

    • Detector effects are critical in precision two-body mass measurements in charged spectrometers.
    • Mass shifts can be analyzed using the sum and difference of daughter particle momenta.
    • The method is illustrated with a Lambda hyperon mass measurement.
    • The LHCb experiment could control tracking-system systematics to 0.7 keV/c^2.
    • The paper reports a total precision of 2.2 keV/c^2, mainly limited by K-short mass calibration knowledge.

  • Bell nonlocality observed in tau pairs at the LHC

    What the study found

    The study reports a clear observation of Bell nonlocality in tau-plus tau-minus pairs, which are a two-qubit quantum state. The authors also state that they measured quantum entanglement and the full spin density matrix with high precision.

    Why the authors say this matters

    The authors conclude that tau-plus tau-minus should be regarded as a new benchmark system for quantum information studies at the Large Hadron Collider. They say it can complement and extend insights previously gained from the top-antitop system.

    What the researchers tested

    The researchers carried out detailed simulations of proton-proton collisions producing tau-plus tau-minus pairs, written as pp → tau-plus tau-minus X. They used machine learning techniques to reconstruct neutrino momentum, and they included both statistical and systematic uncertainties while performing quantum tomography, which is a way to reconstruct the quantum state.

    What worked and what didn't

    The machine-learning-based neutrino reconstruction enabled precise measurements of the full spin density matrix, which the abstract describes as a critical advantage over earlier studies limited by missing-momentum reconstruction. The analysis found Bell nonlocality at more than 5 sigma significance and reports precise measurements of entanglement.

    What to keep in mind

    The abstract describes simulations rather than a direct experimental measurement, so the summary here is limited to what was tested in those detailed simulations. It does not provide additional caveats beyond noting statistical and systematic uncertainties.

    • The study reports Bell nonlocality in tau-plus tau-minus pairs at more than 5 sigma significance.
    • Machine learning was used for neutrino momentum reconstruction.
    • The authors say they measured the full spin density matrix with high precision.
    • The analysis included statistical and systematic uncertainties.
    • The authors propose tau-plus tau-minus as a new benchmark system for quantum information studies at the LHC.

  • Next-to-leading power terms are significant in slepton pair production

    What the study found

    The study finds that next-to-leading power contributions in the threshold variable can be significant for inclusive slepton pair production. It also reports that existing calculations may underestimate the scale error for large slepton masses.

    Why the authors say this matters

    The authors note that cross sections near threshold are sensitive to large logarithmic terms that must be resummed to all orders in perturbation theory. The study suggests that including next-to-leading power effects is important for assessing the reliability of predictions, especially for large slepton masses.

    What the researchers tested

    The researchers evaluated the next-to-leading power contribution in the threshold variable to leading logarithmic accuracy for inclusive slepton pair production at hadron colliders. They also included results for a potential future FCC-hh machine at 85 TeV.

    What worked and what didn't

    The next-to-leading power contributions were found to be significant compared with the next-to-leading logarithmic terms at leading power. The abstract also states that existing calculations underestimate the scale error for large slepton masses.

    What to keep in mind

    The available summary does not describe detailed numerical values, experimental data, or a full comparison across all parameter ranges. It also does not provide additional limitations beyond the focus on leading logarithmic accuracy and the specific collider scenarios studied.

    • Next-to-leading power contributions in the threshold variable can be significant.
    • These contributions were evaluated for inclusive slepton pair production at hadron colliders.
    • Existing calculations may underestimate the scale error for large slepton masses.
    • The study includes results for a future FCC-hh machine at 85 TeV.
    • The work focuses on leading logarithmic accuracy near threshold.

  • Neutral-kaon decays can show CP violation through detector-dependent effects

    What the study found

    The study found that CP violation in decays to final states containing neutral kaons is governed by an efficiency function. That function can be split into two parts: the kaon energy spectrum and a detector-dependent factor that does not depend on the decay process.

    Why the authors say this matters

    The authors conclude that matter effects on kaon oscillations can have a significant effect on CP asymmetries, which are measures of differences between matter and antimatter behavior. They also provide theoretical estimates for some of these asymmetries for a Belle II-type experiment.

    What the researchers tested

    The researchers examined CP violation in the kaon system, focusing on decays into final states that contain neutral kaons. They analyzed how the relevant efficiency function behaves in a specific experimental setup and considered matter effects on kaon oscillations.

    What worked and what didn't

    The efficiency function was shown to factorize into a kaon energy spectrum and a detector-dependent factor independent of the decay process. The abstract states that matter effects can significantly affect CP asymmetries, and that the authors estimated theoretical predictions for some asymmetries in a Belle II-type experiment.

    What to keep in mind

    The abstract does not give numerical results in the text provided here. It also does not describe detailed limitations, so only the scope mentioned in the abstract can be summarized.

    • CP violation in the kaon system can appear in decays with neutral kaons in the final state.
    • The relevant efficiency function splits into a kaon energy spectrum and a detector-dependent factor.
    • The detector-dependent factor is described as independent of the decay process.
    • Matter effects on kaon oscillations can significantly affect CP asymmetries.
    • The authors provide theoretical estimates for some CP asymmetries for a Belle II-type experiment.

  • Semi-visible jets may probe Higgs-linked dark sectors at FCC-ee

    What the study found

    The study found that Higgs boson-mediated interactions in the Future Circular Collider's electron-positron mode could produce semi-visible jets, meaning jet-like particle sprays containing both visible and invisible particles. The authors report that these signals can be used to probe a wide range of the dark-sector models they considered.

    Why the authors say this matters

    The authors conclude that their strategy could improve sensitivity to Higgs boson-induced semi-visible jets and enhance discovery prospects at the Future Circular Collider. They also say it can constrain Higgs boson exotic branching ratios, meaning the fraction of Higgs decays into nonstandard final states, into dark quarks at the permille level.

    What the researchers tested

    The researchers studied exotic signatures from confining dark sectors in electron-positron collisions at the Future Circular Collider. They assumed the Higgs boson mediates between the Standard Model and the dark sector, then examined semi-visible jets with different invisible fractions, including versions enriched in leptons and photons. They used kinematic selections such as missing energy and a graph neural network jet tagger, a machine learning tool that analyzes relationships inside jets through their substructure.

    What worked and what didn't

    When the invisible component was large, selections based on kinematic features like missing energy already gave good signal-to-background discrimination. When the invisible fraction was smaller, the signals looked more like Standard Model events, and the graph neural network jet tagger improved sensitivity by using jet substructure differences. The abstract states that the proposed strategy can effectively probe a wide parameter space for the models considered and a variety of signatures.

    What to keep in mind

    The summary describes only the models and signatures considered in this study, so the results apply to that scope. The abstract does not provide detailed numerical performance measures beyond the stated permille-level constraint on exotic branching ratios.

    • The study examines semi-visible jets from confining dark sectors at the Future Circular Collider.
    • The Higgs boson is assumed to mediate interactions between the Standard Model and the dark sector.
    • Large missing-energy signals are easier to separate from background than cases with smaller invisible fractions.
    • A graph neural network jet tagger improved sensitivity when the signals resembled Standard Model events more closely.
    • The authors say the approach can constrain Higgs exotic branching ratios into dark quarks at the permille level.