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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

2 νββ spectrum in chiral effective field theory

We investigate two-neutrino double beta decay (2νββ) in chiral effective field theory. We find contributions from weak magnetism and double-weak pion-exchange at next-to-leading-order in the chiral power counting. We discuss the impact of the chiral corrections on the electron spectra and find that they should be included in analyses of 2νββ decay that aim to uncover new physics signatures in the electron spectrum. We illustrate this point by revisiting the effect of sterile neutrinos and non-standard charged interactions. We also find that the pion-exchange contributions involve nuclear matrix elements that are related to those appearing in neutrinoless double beta decay (0νββ). We investigate whether the 0νββ nuclear matrix elements can be obtained from detailed measurements of the energy spectrum of the outgoing electrons in 2νββ transitions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Implications of the Upper Bound on h → μ + μ - on the Baryon Asymmetry of the Universe

The upper bounds from the ATLAS and CMS experiments on the decay rate of the Higgs boson to two muons provide the strongest constraint on an imaginary part of the muon Yukawa coupling. This bound is more than an order of magnitude stronger than bounds from $\mathcal{CP}$-violating observables, specifically the electric dipole moment of the electron. It excludes a scenario $-$ which had been viable prior to these measurements $-$ that a complex muon Yukawa coupling is the dominant source of the baryon asymmetry. Even with this bound, the muon source can still contribute ${\cal O}(16\%)$ of the asymmetry.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Revisiting 𝐶 and 𝐶⁢𝑃 violation in 𝜂 → 𝜋 + 𝜋 - ⁢𝜋 0 decay

The decay 𝜂 → 𝜋 + ⁢𝜋 − ⁢𝜋 0 is an ideal process in which to study flavor-conserving 𝐶 and 𝐶⁢𝑃 violation beyond the Standard Model. We deduce the 𝐶- and 𝐶⁢𝑃-odd quark operators that contribute to 𝜂 → 𝜋 + ⁢𝜋 − ⁢𝜋 0 originating from the mass-dimension-six Standard Model effective field theory. The corresponding hadron-level operators that generate a nonvanishing 𝐼 = 0 amplitude at order 𝑝 6 in the chiral effective theory are presented for the first time, to the best of our knowledge, in addition to the leading-order operators ascribed to the 𝐼 = 2 final state. By fitting the KLOE-2 and the most recent BESIII experimental data, we determine the coefficients of the lowest-order 𝐼 = 0 and 𝐼 = 2 amplitudes and estimate the potential new physics energy scale. We also perform an impact study of the future 𝜂 → 𝜋 + ⁢𝜋 − ⁢𝜋 0 experiments.

CP violation↗
DOE OSTI2021

Towards a New μ→eγ Search with the MEG II Experiment: From Design to Commissioning

The MEG experiment represents the state of the art in the search for the Charged Lepton Flavour Violating μ + →e + γ decay. With its first phase of operations at the Paul Scherrer Institut (PSI), MEG set the most stringent upper limit on the BR (μ + →e + γ) ≤ 4.2×10 –13 at 90% confidence level, imposing one of the tightest constraints on models predicting LFV-enhancements through new physics beyond the Standard Model. An upgrade of the MEG experiment, MEG II, was designed and it is presently in the commissioning phase, aiming at a sensitivity level of 6×10 –14 . The MEG II experiment relies on a series of upgrades, which include an improvement of the photon detector resolutions, brand new detectors on the positron side with better acceptance, efficiency and performances and new and optimized trigger and DAQ electronics to exploit a muon beam intensity twice as high as that of MEG (7×10 7 μ + /s). This paper presents a complete overview of the MEG II experimental apparatus and the current status of the detector commissioning in view of the physics data taking in the upcoming three years.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Test of lepton universality with $ {\Lambda}_b^0\to {pK}^{-}{\mathrm{\ell}}^{+}{\mathrm{\ell}}^{-}$ decays

The ratio of branching fractions of the decays \( {\Lambda}_b^0 \) → pK - e + e - and \( {\Lambda}_b^0 \) → pK - μ + μ - , \( {R}_{pK}^{-1} \) , is measured for the first time using proton-proton collision data corresponding to an integrated luminosity of 4 . 7 fb - 1 recorded with the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV. In the dilepton mass-squared range 0 . 1 < q 2 < 6 . 0 GeV 2 /c 4 and the pK - mass range m ( pK - ) < 2600 MeV /c 2 , the ratio of branching fractions is measured to be \( {R}_{pK}^{-1}={1.17}_{-0.16}^{+0.18}\pm 0.07 \) , where the first uncertainty is statistical and the second systematic. This is the first test of lepton universality with b baryons and the first observation of the decay \( {\Lambda}_b^0 \) → pK - e + e - .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

A measurement of the K + → π + μ + μ – decay

A sample of 2.8 × 10 4 K + → π + μ + μ – candidates with negligible background was collected by the NA62 experiment at the CERN SPS in 2017–2018. The model-independent branching fraction is measured to be (9.15 ± 0.08) × 10 –8 , a factor three more precise than previous measurements. The decay form factor is presented as a function of the squared dimuon mass. A measurement of the form factor parameters and their uncertainties is performed using a description based on Chiral Perturbation Theory at O(p 6 ).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Search for the lepton-flavour violating decays B0 → K *0 μ ± e ∓ and ${B}_s^0$ → Φμ ± e ∓

A search for the lepton-flavour violating decays B 0 → K *0 μ ± e ∓ and \( {B}_s^0 \) → Φμ ± e ∓ is presented, using proton-proton collision data collected by the LHCb detector at the LHC, corresponding to an integrated luminosity of 9 fb - 1 . No significant signals are observed and upper limits of $$ {\displaystyle \begin{array}{c}\mathcal{B}\left({B}^0\to {K}^{\ast 0}{\mu}^{+}{e}^{-}\right)<5.7\times {10}^{-9}\left(6.9\times {10}^{-9}\right),\\ {}\mathcal{B}\left({B}^0\to {K}^{\ast 0}{\mu}^{-}{e}^{+}\right)<6.8\times {10}^{-9}\left(7.9\times {10}^{-9}\right),\\ {}\mathcal{B}\left({B}^0\to {K}^{\ast 0}{\mu}^{\pm }{e}^{\mp}\right)<10.1\times {10}^{-9}\left(11.7\times {10}^{-9}\right),\\ {}\mathcal{B}\left({B}_s^0\to \phi {\mu}^{\pm }{e}^{\mp}\right)<16.0\times {10}^{-9}\left(19.8\times {10}^{-9}\right)\end{array}} $$ are set at 90% (95%) confidence level. These results constitute the world’s most stringent limits to date, with the limit on the decay \( {B}_s^0 \) → Φμ ± e ∓ the first being set. In addition, limits are reported for scalar and left-handed lepton-flavour violating New Physics scenarios.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Search for π 0 decays to invisible particles

The NA62 experiment at the CERN SPS reports a study of a sample of 4 × 10 9 tagged π0 mesons from K + → π + π 0 (γ), searching for the decay of the π 0 to invisible particles. No signal is observed in excess of the expected background fluctuations. An upper limit of 4.4 × 10 –9 is set on the branching ratio at 90% confidence level, improving on previous results by a factor of 60. This result can also be interpreted as a model- independent upper limit on the branching ratio for the decay K + → π + X, where X is a particle escaping detection with mass in the range 0.110–0.155 GeV/c 2 and rest lifetime greater than 100 ps. Model-dependent upper limits are obtained assuming X to be an axion-like particle with dominant fermion couplings or a dark scalar mixing with the Standard Model Higgs boson.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

First observation and study of the $K^± → π^0π^0μ^±ν$ decay

The NA48/2 experiment at CERN reports the first observation of the $K^± → π^0π^0μ^±$ν decay based on a sample of 2437 candidates with 15% background contamination collected in 2003–2004. The decay branching ratio in the kinematic region of the squared dilepton mass above 0.03 GeV 2 /c 4 is measured to be (0.65 ± 0.03) × 10 –6 . The extrapolation to the full kinematic space, using a specific model, is found to be (3.45 ± 0.16) × 10 –6 , in agreement with chiral perturbation theory predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Search for the decay $B^0$ → $\phiμ^+μ^–$

A search for the decay $B^0$ → $\phiμ^+μ^–$ is performed using proton-proton collisions at centre-of-mass energies of 7, 8, and 13 TeV collected by the LHCb experiment and corresponding to an integrated luminosity of 9 fb –1 . No evidence for the $B^0$ → $\phiμ^+μ^–$ decay is found and an upper limit on the branching fraction, excluding the $\phi$ and charmonium regions in the dimuon spectrum, of 4.4 × 10 –3 at a 90% credibility level, relative to that of the $B^0_s$ → $\phiμ^+μ^–$ branching fraction and assuming a phase-space model, the absolute branching fraction of the $B^0$ → $\phiμ^+μ^–$ in the full q 2 range is determined to be less than 3.2 x 10 –9 at a 90% credibility level.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Measurement of the B s 0 → μ + μ - decay properties and search for the B 0 → μ + μ - and B s 0 → μ + μ - γ decays

An improved measurement of the decay $B^0_S$ → $μ^+μ^-$ and searches for the decays $B^0$ → $μ^+μ^+$ and $B^0_S$ → $μ^+μ^-γ$ are performed at the LHCb experiment using data collected in proton-proton collisions at $\sqrt{s}$ = 7, 8 and 13 TeV. corresponding to integrated luminosities of 1, 2 and 6 fb -1 , respectively. The $B^0_S$ → $μ^+μ^-$ branching fraction and effective lifetime are measured to be $\mathscr{B}$($B^0_S$ → $μ^+μ^-$) = (3.09$^{(+0.46+0.15)}_{(-0.43-0.11)}$) x 10 -9 and $τ(B^0_s →μ^+μ^-)$ = (2.07 ± 0.29 ± 0.03) ps, respectively, where the uncertainties include both statistical and systematic contributions. No significant signal for $B^0$ → $μ^+μ^-$ and $B^0_S$ → $μ^+μ^-γ$ decays is found and the upper limits $\mathscr{B}$($B^0$ → $μ^+μ^-$) < 2.6 x 10 -10 and $B^0_S$ → $μ^+μ^-γ$ < 2.0 x 10 -9 at 95% confidence level are determined, where the latter is limited to the range $m_{μμ}$ > 4.9 GeV/c 2 . Additionally, the ratio between the $B^0$ → $μ^+μ^-$ and $B^0_S$ → $μ^+μ^-$ branching fractions is measured to be $\mathscr{R}_{μ+μ-}$ < 0.095 at 95% confidence level. The results are in agreement with the Standard Model predictions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Search for the dark photon in B 0 → A'A', A' → e + e – , μ + μ – , and π + π – decays at Belle

We present a search for the dark photon A' in the B 0 → A'A' decays, where A' subsequently decays to e + e – , μ + μ – , and π + π – . The search is performed by analyzing 772 × 10 6 $B$$\overline{B}$ events collected by the Belle detector at the KEKB e + e – energy-asymmetric collider at the Υ(4S) resonance. No signal is found in the dark photon mass range 0.01 GeV/c 2 ≤ m A' ≤ 2.62 GeV/c 2 , and we set upper limits of the branching fraction of B0 → A'A' at the 90% confidence level. The products of branching fractions, B(B 0 →A'A')×B(A'→e + e – ) 2 and B(B 0 →A'A')×B(A'→μ + μ – ) 2 , have limits of the order of 10 –8 depending on the A' mass. Furthermore, considering A' decay rate to each pair of charged particles, the upper limits of B(B 0 →A'A') are of the order of 10 –8 –10 –5 . From the upper limits of B(B 0 →A'A'), we obtain the Higgs portal coupling for each assumed dark photon and dark Higgs mass. The Higgs portal couplings are of the order of 10 –2 –10 –1 at m h' ≃m B 0 ± 40 MeV/c 2 and 10 –1 –1 at m h' ≃m B 0 ± 3 GeV/c 2 .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Search for the lepton-flavour violating decays B 0 → K *0 τ ± μ ∓

A first search for the lepton-flavour violating decays B 0 → K*0 τ ± μ ∓ is presented. The analysis is performed using a sample of proton-proton collision data, collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 TeV between 2011 and 2018, corresponding to an integrated luminosity of 9 fb –1 . No significant signal is observed, and upper limits on the branching fractions are determined to be B (B 0 → K* 0 τ + μ – ) < 1.0(1.2) x 10 –5 and B(B 0 → K* 0 τ – μ + ) < 8.2(9.8) x 10 –6 at the 90% (95%) confidence level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Search for the baryon- and lepton-number violating decays B 0 → pμ⁻ and $B^0_s$ → pμ⁻

A search for the baryon- and lepton-number violating decays and $B$$^{0}_{s}$ →pμ – is performed at the LHCb experiment using data collected in proton-proton collisions at √s =7, 8 and 13 TeV, corresponding to integrated luminosities of 1, 2, and 6 fb –1 , respectively. No significant signal for B 0 → p⁢μ – and $B$$^{0}_{s}$ → p⁢μ – decays is found and the upper limits on the branching fractions are determined to be Β⁡(B 0 → pμ – ) < 2.6⁢(3.1) ×10 –9 and Β($B$$^{0}_{s}$ → pμ – ) < 12.1⁢(14.0) ×10 –9 , respectively, at 90% (95%) confidence level. These are the first limits on these decays to date.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗