Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userPrecise determination of V_ud and V_us
100
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The actual limit of the unitarity condition of the first row of the CKM matrix |V_ud|^2+|V_us|^2+|V_ub|^2=1+Delta_CKM is Delta_CKM=-0.0001(6). In 2010 the same was Delta_CKM=+0.0001(6). Despite the only difference of a sign, and with an absolute change of the value of one third of the accuracy, a substantial amount of work has been done in the last two years to improve the knowledge of all the contributions to this stringent limit to CKM unitarity, and more is expected in the next years. In this paper we present an organized summary of all the important contributions presented during the WG1 sessions, referring as much as possible to the contribution papers prepared by the individual authors.
rate research
Read More
Recent sum rule determinations of |V_us|, employing flavor-breaking combinations of hadronic tau decay data, are significantly lower than either expectations based on 3-family unitarity or determinations from K_ell3 and Gamma[K_mu2]/Gamma[pi_mu2]. We use lattice data to investigate the accuracy/reliability of the OPE representation of the flavor-breaking correlator combination entering the tau decay analyses. The behavior of an alternate correlator combination, constructed to reduce problems associated with the slow convergence of the D = 2 OPE series, and entering an alternate sum rule requiring both electroproduction cross-section and hadronic tau decay data, is also investigated. Preliminary updates of both analyses, with the lessons learned from the lattice data in mind, are also presented.
We report a high-precision calculation of the Standard Model electroweak radiative corrections in the $Kto pi e^+ u(gamma)$ decay as a part of the combined theory effort to understand the existing anomaly in the determinations of $V_{us}$. Our new analysis features a chiral resummation of the large infrared-singular terms in the radiative corrections and a well-under-control strong interaction uncertainty based on the most recent lattice QCD inputs. While being consistent with the current state-of-the-art results obtained from chiral perturbation theory, we reduce the existing theory uncertainty from $10^{-3}$ to $10^{-4}$. Our result suggests that the Standard Model electroweak effects cannot account for the $V_{us}$ anomaly.
We reassess the $Btopiell u_{ell}$ differential branching ratio distribution experimental data released by the BaBar and Belle Collaborations supplemented with all lattice calculations of the $Btopi$ form factor shape available up to date obtained by the HPQCD, FNAL/MILC and RBC/UKQCD Collaborations. Our study is based on the method of Pad{e} approximants, and includes a detailed scrutiny of each individual data set that allow us to obtain $|V_{ub}|=3.53(8)_{rm{stat}}(6)_{rm{syst}}times10^{-3}$. The semileptonic $B^{+}toeta^{(prime)}ell^{+} u_{ell}$ decays are also addressed and the $eta$-$eta^{prime}$ mixing discussed.
The leading order hadronic contribution to the muon magnetic moment anomaly, $a^{HAD}_mu$, is determined entirely in the framework of QCD. The result in the light-quark sector, in units of $10^{-10}$, is $a^{HAD}_mu|_{uds} =686 pm 26$, and in the heavy-quark sector $a^{HAD}_mu|_{c} =14.4 pm 0.1$, and $a^{HAD}_mu|_{b} =0.29 pm 0.01$, resulting in $a^{HAD}_mu = 701 pm 26$. The main uncertainty is due to the current lattice QCD value of the first and second derivative of the electromagnetic current correlator at the origin. Expected improvement in the precision of these derivatives may render this approach the most accurate and trustworthy determination of the leading order $a^{HAD}_mu$.
We present a precise calculation of the dilepton invariant-mass spectrum and the decay rate for $B^pm to pi^pm ell^+ ell^-$ ($ell^pm = e^pm, mu^pm $) in the Standard Model (SM) based on the effective Hamiltonian approach for the $b to d ell^+ ell^-$ transitions. With the Wilson coefficients already known in the next-to-next-to-leading logarithmic (NNLL) accuracy, the remaining theoretical uncertainty in the short-distance contribution resides in the form factors $f_+ (q^2)$, $f_0 (q^2)$ and $f_T (q^2)$. Of these, $f_+ (q^2)$ is well measured in the charged-current semileptonic decays $B to pi ell u_ell$ and we use the $B$-factory data to parametrize it. The corresponding form factors for the $B to K$ transitions have been calculated in the Lattice-QCD approach for large-$q^2$ and extrapolated to the entire $q^2$-region using the so-called $z$-expansion. Using an $SU(3)_F$-breaking Ansatz, we calculate the $B to pi$ tensor form factor, which is consistent with the recently reported lattice $B to pi$ analysis obtained at large~$q^2$. The prediction for the total branching fraction ${cal B} (B^pm to pi^pm mu^+ mu^-) = (1.88 ^{+0.32}_{-0.21}) times 10^{-8}$ is in good agreement with the experimental value obtained by the LHCb Collaboration. In the low $q^2$-region, heavy-quark symmetry (HQS) relates the three form factors with each other. Accounting for the leading-order symmetry-breaking effects, and using data from the charged-current process $B to pi ell u_ell$ to determine $f_+ (q^2)$, we calculate the dilepton invariant-mass distribution in the low $q^2$-region in the $B^pm to pi^pm ell^+ ell^-$ decay. This provides a model-independent and precise calculation of the partial branching ratio for this decay.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
