arXiv subjects

Jaehoon Leem

Publications and source records attributed to Jaehoon Leem.

At least 19 recordsLinked to original sources

arXiv2024

2024 Update on $\varepsilon_K$ with lattice QCD inputs

We report recent progress on $\varepsilon_K$ evaluated directly from the standard model (SM) with lattice QCD inputs such as $\hat{B}_K$, exclusive $|V_{cb}|$, $|V_{us}|$, $|V_{ud}|$, $\xi_0$, $\xi_2$, $\xi_\text{LD}$, $f_K$, and $m_c$. We find that the standard model with exclusive $|V_{cb}|$ and lattice QCD inputs describes only $2/3 \cong 65\%$ of the experimental value of $|\varepsilon_K|$ and does not explain its remaining 35\%, which represents a strong tension in $|\varepsilon_K|$ at the $5.1\sigma \sim 4.1\sigma$ level between the SM theory and experiment. We also find that this tension disappears when we use the inclusive value of $|V_{cb}|$ obtained using the heavy quark expansion based on the QCD sum rule approach. We also report results for $|\varepsilon_K|$ obtained using the Brod-Gorbahn-Stamou (BGS) method for $\eta_i$ of $u-t$ unitarity, which leads to even a stronger tension of $5.7\sigma \sim 4.2\sigma$ with lattice QCD inputs.

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arXiv2024

Progress report on testing robustness of the Newton method in data analysis on 2-point correlation function using a MILC HISQ ensemble

We report recent progress in data analysis on the two point correlation functions which will be prerequisite to obtain semileptonic form factors for the $B_{(s)} \to D_{(s)}\ell\nu$ decays. We use a MILC HISQ ensemble for the measurement. We use the HISQ action for light quarks, and the Oktay-Kronfeld (OK) action for the heavy quarks ($b$ and $c$). We used a sequential Bayesian method for the data analysis. Here we test the new fitting methodology of Benjamin J.~Choi in a completely independent manner.

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arXiv2024

Current progress on the semileptonic form factors for $\bar{B} \to D^{\ast} \ell \bar{\nu}$ decay using the Oktay-Kronfeld action

We present recent progress in calculating the semileptonic form factors $h_{A_1}(w)$ for the $\bar{B} \to D^{\ast} \ell \bar{\nu}$ decays. We use the Oktay-Kronfeld (OK) action for the charm and bottom valence quarks and the HISQ action for light quarks. We adopt the Newton method combined with the scanning method to find a good initial guess for the $\chi^2$ minimizer in the fitting of the 2pt correlation functions. The main advantage is that the Newton method lets us to consume all the time slices allowed by the physical positivity. We report the first, reliable, but preliminary results for $h_{A_1}(w)/\rho_{A_1}$ at zero recoil ($w=1$). Here we use a MILC HISQ ensemble ($a = 0.12$ fm, $M_{\pi}$ = 220 MeV, and $N_f = 2 + 1 + 1$ flavors).

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arXiv2023

2023 Update of $\varepsilon_K$ with lattice QCD inputs

We report recent progress on $\varepsilon_K$ evaluated directly from the standard model (SM) with lattice QCD inputs such as $\hat{B}_K$, $|V_{cb}|$, $|V_{us}|$, $|V_{ud}|$, $ξ_0$, $ξ_2$, $ξ_\text{LD}$, $f_K$, and $m_c$. We find that the standard model with exclusive $|V_{cb}|$ and lattice QCD inputs describes only 66\% of the experimental value of $|\varepsilon_K|$ and does not explain its remaining 34\%, which corresponds to a strong tension in $|\varepsilon_K|$ at the $4.9σ\sim 3.9σ$ level between the SM theory and experiment. We also find that this tension disappears when we use the inclusive value of $|V_{cb}|$ obtained using the heavy quark expansion based on the QCD sum rule approach.

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arXiv2023

2022 Update on $\varepsilon_K$ with lattice QCD inputs

We present recent updates for $\varepsilon_K$ determined directly from the standard model (SM) with lattice QCD inputs such as $\hat{B}_K$, $|V_{cb}|$, $|V_{us}|$, $ξ_0$, $ξ_2$, $ξ_\text{LD}$, $f_K$, and $m_c$. We find that the standard model with exclusive $|V_{cb}|$ and other lattice QCD inputs describes only 65% of the experimental value of $|\varepsilon_K|$ and does not explain its remaining 35%, which leads to a strong tension in $|\varepsilon_K|$ at the $5.1σ\sim 3.9σ$ level between the SM theory and experiment. We also find that this tension disappears when we use the inclusive value of $|V_{cb}|$ obtained using the heavy quark expansion based on the QCD sum rule approach, although this inclusive tension is small ($\approx 1.4σ$) but keeps increasing as time goes on.

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arXiv2022

Improved data analysis on two-point correlation function with sequential Bayesian method

We report our progress in data analysis on two-point correlation functions of the $B$ meson using sequential Bayesian method. The data set of measurement is obtained using the Oktay-Kronfeld (OK) action for the bottom quarks (valence quarks) and the HISQ action for the light quarks on the MILC HISQ lattices. We find that the old initial guess for the $\chi^2$ minimizer in the fitting code is poor enough to slow down the analysis somewhat. In order to find a better initial guess, we adopt the Newton method. We find that the Newton method provides a natural test to check whether the $\chi^2$ minimizer finds a local minimum or the global minimum, and it also reduces the number of iterations dramatically.

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arXiv2022

2021 Update on $\varepsilon_K$ with lattice QCD inputs

We present recent updates for $\varepsilon_K$ determined directly from the standard model (SM) with lattice QCD inputs such as $\hat{B}_K$, $|V_{cb}|$, $|V_{us}|$, $ξ_0$, $ξ_2$, $ξ_\text{LD}$, $f_K$, and $m_c$. We find that the standard model with exclusive $|V_{cb}|$ and other lattice QCD inputs describes only 66\% of the experimental value of $|\varepsilon_K|$ and does not explain its remaining 34\%, which leads to a strong tension in $|\varepsilon_K|$ at the $4.5σ\sim 3.7σ$ level between the SM theory and experiment. We also find that this tension disappears when we use the inclusive value of $|V_{cb}|$ obtained using the heavy quark expansion based on the QCD sum rule approach.

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arXiv2021

Improvement of heavy-heavy and heavy-light currents with the Oktay-Kronfeld action

The CKM matrix elements $V_{cb}$ and $V_{ub}$ can be obtained by combining data from the experiments with lattice QCD results for the semi-leptonic form factors for the $\bar{B} \to D^\ast \ell \barν$ and $\bar{B} \to π\ell \barν$ decays. It is highly desirable to use the Oktay-Kronfeld (OK) action for the form factor calculation on the lattice, since the OK action is designed to reduce the heavy quark discretization error down to the $\mathcal{O}(λ^4)$ level in the power counting rules of the heavy quark effective theory (HQET). Here, we present a matching calculation to improve heavy-heavy and heavy-light currents up to the $λ^3$ order in HQET, the same level of improvement as the OK action. Our final results for the improved currents are being used in a lattice QCD calculation of the semi-leptonic form factors for the $\bar{B} \to D^\ast \ell \barν$ and $\bar{B} \to D \ell \barν$ decays.

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arXiv2020

Semileptonic $B \to D^{(\ast)} \ell\nu$ Decay Form Factors using the Oktay-Kronfeld Action

We report recent progress in calculating semileptonic form factors for the $\bar{B} \to D^\ast \ell \bar{\nu}$ and $\bar{B} \to D \ell \bar{\nu}$ decays using the Oktay-Kronfeld (OK) action for bottom and charm quarks. We use the second order in heavy quark effective power counting $\mathcal{O}(\lambda^2)$ improved currents in this work. The HISQ action is used for the light spectator quarks. We analyzed four $2+1+1$-flavor MILC HISQ ensembles with $a\approx 0.09\,\mathrm{fm}$, $0.12\,\mathrm{fm}$ and $M_\pi \approx 220\,\mathrm{MeV}$, $310\,\mathrm{MeV}$: $a09m220$, $a09m310$, $a12m220$, $a12m310$. Preliminary results for $B\to D^\ast\ell\nu$ decays form factor $h_{A_1}(w)$ at zero recoil ($w=1$) are reported. Preliminary results for $B \to D\,\ell\nu$ decays form factors $h_\pm(w)$ over a kinematic range $1<w<1.3$ are reported as well.

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arXiv2020

Leptonic decays of $B_{(s)}$ and $D_{(s)}$ using the OK action

We present recent progress in the lattice calculation of leptonic decay constants for $B_{(s)}$ and $D_{(s)}$ mesons using the Oktay-Kronfeld (OK) action for charm and bottom valence quarks, whose masses are tuned non-perturbatively. The calculations are done on 6 HISQ ensembles generated by the MILC collaboration with $N_f=2+1+1$ flavors. We also use the HISQ action for the light spectator quarks. Results are presented for the ratios $f_{B_s}/f_B$ and $f_{D_s}/f_D$, which reflect $SU(3)$ flavor symmetry breaking, and are independent of the renormalization constants of the axial currents.

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arXiv2019

2019 Update on $\varepsilon_K$ with lattice QCD inputs

We present updated results for $\varepsilon_K$ determined directly from the standard model (SM) with lattice QCD inputs such as $\hat{B}_K$, $|V_{cb}|$, $|V_{us}|$, $ξ_0$, $ξ_2$, $ξ_\text{LD}$, $f_K$, and $m_c$. We find that the standard model with exclusive $|V_{cb}|$ and other lattice QCD inputs describes only 65\% of the experimental value of $|\varepsilon_K|$ and does not explain its remaining 35\%, which leads to a strong tension in $|\varepsilon_K|$ at the $4.6σ\sim 4.2σ$ level between the SM theory and experiment. We also find that this tension disappears when we use the inclusive value of $|V_{cb}|$ obtained using the heavy quark expansion based on QCD sum rules.

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arXiv2018

Update on $B\to D^\ast \ell \nu$ form factor at zero-recoil using the Oktay-Kronfeld action

We present an update on the calculation of $\bar{B}\to D^\ast \ell \bar{\nu}$ semileptonic form factor at zero recoil using the Oktay-Kronfeld bottom and charm quarks on $N_f=2+1+1$ flavor HISQ ensembles generated by the MILC collaboration. Preliminary results are given for two ensembles with $a\approx 0.12$ and $0.09$ fm and $M_\pi\approx 310$ MeV. Calculations have been done with a number of valence quark masses, and the dependence of the form factor on them is investigated on the $a\approx 0.12$ fm ensemble. The excited state is controlled by using multistate fits to the three-point correlators measured at 4--6 source-sink separations.

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arXiv2018

2018 Update on $\varepsilon_K$ with lattice QCD inputs

We present updated results for $\varepsilon_K$ determined directly from the standard model (SM) with lattice QCD inputs such as $\hat{B}_K$, $|V_{cb}|$, $|V_{us}|$, $ξ_0$, $ξ_2$, $ξ_\text{LD}$, $F_K$, and $m_c$. We find that the standard model with exclusive $|V_{cb}|$ and other lattice QCD inputs describes only 70% of the experimental value of $|\varepsilon_K|$ and does not explain its remaining 30%, which leads to a strong tension in $|\varepsilon_K|$ at the $4σ$ level between the SM theory and experiment. We also find that this tension disappears when we use the inclusive value of $|V_{cb}|$ obtained using the heavy quark expansion based on QCD sum rules.

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arXiv2018

Updated evaluation of $\varepsilon_K$ in the Standard Model with lattice QCD inputs

We report a strong tension in $\varepsilon_K$ at the $4σ$ level between the experimental value and the theoretical value calculated directly from the standard model using lattice QCD inputs such as $\hat{B}_K$, $|V_{cb}|$, $|V_{us}|$, $ξ_0$, $ξ_2$, $ξ_\text{LD}$, $F_K$, and $m_c$. The standard model with lattice QCD inputs describes only 70% of the experimental value of $\varepsilon_K$, and does not explain its remaining 30%. We also find that this tension disappears when we use the inclusive value of $|V_{cb}|$ (results of the heavy quark expansion based on QCD sum rules) to determine $\varepsilon_K$. This tension is highly correlated with the present discrepancy between the exclusive and inclusive values of $|V_{cb}|$. In order to resolve, in part, the issue with $|V_{cb}|$, it would be highly desirable to have a comprehensive re-analysis over the entire set of experimental data on the $\bar{B} \to D^* \ell \barν$ decays using an alternative parametrization of the form factors, such as the BGL parametrization, and a comparison with results of the CLN method.

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arXiv2017

Improvement of heavy-heavy current for calculation of $\bar{B}\to D^{(*)}\ell\barν$ form factors using Oktay-Kronfeld heavy quarks

The CKM matrix element $|V_{cb}|$ can be extracted by combining data from experiments with lattice QCD results for the semileptonic form factors for the $\bar{B}\to D^{(*)} \ell \barν$ decays. The Oktay-Kronfeld (OK) action was designed to reduce heavy-quark discretization errors to below $1\%$, or through $\mathcal{O}(λ^3)$ in HQET power counting. Here we describe recent progress on bottom-to-charm currents improved to the same order in HQET as the OK action, and correct formerly reported results of our matching calculations, in which the operator basis was incomplete.

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arXiv2017

Calculation of $\bar B \rightarrow D^\ast \ell \bar ν$ form factor at zero recoil using the Oktay-Kronfeld action

We present the first preliminary results for the semileptonic form factor $h_{A_1}(w=1)/ρ_{A_j}$ at zero recoil for the $\bar B \rightarrow D^\ast \ell \bar ν$ decay using lattice QCD with four flavors of sea quarks. We use the HISQ staggered action for the light valence and sea quarks (the MILC HISQ configurations), and the Oktay-Kronfeld (OK) action for the heavy valence quarks.

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arXiv2017

Update on $\varepsilon_K$ with lattice QCD inputs

We report updated results for $\varepsilon_K$, the indirect CP violation parameter in neutral kaons, which is evaluated directly from the standard model with lattice QCD inputs. We use lattice QCD inputs to fix $\bar{B}_K$, $|V_{cb}|$, $ξ_0$, $ξ_2$, $|V_{us}|$, and $m_c(m_c)$. Since Lattice 2016, the UTfit group has updated the Wolfenstein parameters in the angle-only-fit method, and the HFLAV group has also updated $|V_{cb}|$. Our results show that the evaluation of $\varepsilon_K$ with exclusive $|V_{cb}|$ (lattice QCD inputs) has $4.0σ$ tension with the experimental value, while that with inclusive $|V_{cb}|$ (heavy quark expansion based on OPE and QCD sum rules) shows no tension.

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arXiv2016

Heavy-heavy current improvement for calculation of $\bar{B}\rightarrow D^{(*)}\ell \barν$ semi-leptonic form factors using the Oktay-Kronfeld action

Lattice calculations of the form factors for $\bar{B}\to D^{(*)}\ell\barν$ decays can be used to extract the CKM matrix element $|V_{cb}|$. The Oktay-Kronfeld action is a highly improved version of the Fermilab action, which systematically reduces heavy quark discretization effects through $\mathcal{O}(λ^3)$ in HQET power counting, for heavy-light meson quantities. To calculate $\bar{B}\rightarrow D^{(*)}\ell \barν$ semi-leptonic form factors using Oktay-Kronfeld heavy quarks, we need to improve the heavy quark currents to the same level. We report our progress in calculating the improvement coefficients for currents composed of bottom and charm quarks. Our results presented in this paper are preliminary.

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