arXiv subjects

Gerhard Buchalla

Publications and source records attributed to Gerhard Buchalla.

42 records · Page 3Linked to original sources

arXiv1996

Renormalization of $ΔB=2$ Transitions in the Static Limit Beyond Leading Logarithms

The renormalization group evolution of $ΔB=2$ transition operators is studied at leading order in heavy quark effective theory and at next-to-leading order in QCD. We calculate new contributions that were not taken into account in previous work and obtain the complete result to next-to-leading logarithmic accuracy. The various scheme and scale dependences and their cancellation in physical quantities are discussed explicitly.

hep-ph↗

arXiv1996

$K\toπν\barν$ and High Precision Determinations of the CKM Matrix

We investigate the future determination of the CKM matrix using theoretically clean quantities, like $B(K^+\toπ^+ν\barν)$, $B(K_L\toπ^0ν\barν)$ or $\sin 2β$, $\sin 2α$ as extracted from CP violation studies in $B$ physics. The theoretical status of $K\toπν\barν$ is briefly reviewed and their phenomenological potential is compared with that of CP asymmetries in $B$ decays. We stress the unique opportunities provided by measuring the CP violating rare decay $K_L\toπ^0ν\barν$. It is pointed out that this mode is likely to offer the most precise determination of ${\rm Im}V^*_{ts}V_{td}$ and the Jarlskog parameter $J_{CP}$, the invariant measure of CP violation in the Standard Model.

hep-ph↗

arXiv1995

Weak Decays Beyond Leading Logarithms

We review the present status of QCD corrections to weak decays beyond the leading logarithmic approximation including particle-antiparticle mixing and rare and CP violating decays. After presenting the basic formalism for these calculations we discuss in detail the effective hamiltonians for all decays for which the next-to-leading corrections are known. Subsequently, we present the phenomenological implications of these calculations. In particular we update the values of various parameters and we incorporate new information on m_t in view of the recent top quark discovery. One of the central issues in our review are the theoretical uncertainties related to renormalization scale ambiguities which are substantially reduced by including next-to-leading order corrections. The impact of this theoretical improvement on the determination of the Cabibbo-Kobayashi-Maskawa matrix is then illustrated in various cases.

hep-ph↗

arXiv1995

Hadronization of $b\to c\bar cs$

The b -> c cbar s transition is usually believed to hadronize predominantly in Bbar -> X_c Ds(*)- with the Ds(*)- originating from the virtual W. We demonstrate in a variety of independent ways that other hadronization processes cannot be neglected. The invariant mass of cbar s has sizable phase-space beyond m_D+m_K. The rate for Bbar -> D Dbar Kbar X could be significant and should not be ignored as was done in previous experimental analyses. We estimate the number of charmed hadrons per B-decay, n_c, to be about 1.3 to higher accuracy than obtained in previous investigations. Even though n_c is currently measured to be about 1.1, observing a significant Bbar -> D Dbar Kbar X would support n_c of about 1.3. Many testable consequences result, some of which we discuss.

hep-ph↗

arXiv1994

$\sin 2β$ from $K\toπν\barν$

We point out that the measurement of just the two branching fractions \linebreak $B(K^+\toπ^+ν\barν)$ and $B(K_L\toπ^0ν\barν)$ can in a theoretically clean manner determine $\sin 2β$ almost independently of $m_t$ and $V_{cb}$. This allows to obtain an interesting relation between the CP asymmetry $A_{CP}(ψK_S)$ in B physics and the branching ratios for these two rare K decays. The recently calculated next-to-leading order QCD corrections improve the accuracy of this analysis. We find typically $Δ\sin 2β=\pm 0.11$ provided $B(\kpn)$ and $B(\klpn)$ are measured within $\pm 10\%$ accuracy. With decreasing uncertainty in $Λ_{\overline{MS}}$ and $m_c$ this error could be reduced to $Δ\sin 2β< \pm 0.10$. The determination of $\sin 2α$ and $\sin 2γ$ on the other hand is rather poor. However respectable determinations of the Wolfenstein parameter $η$ and of $\mid V_{td}\mid$ can be obtained.

hep-ph↗

arXiv1994

$K^+\toπ^+ν\barν$ Beyond Leading Logs and $V_{td}$

The calculation of QCD corrections beyond the leading logarithmic approximation for the short-distance dominated rare decay $K^+\toπ^+ν\barν$ is summarized. This analysis requires the complete ${\cal O}(α_s)$ corrections to the top contribution to all orders in the top-quark mass and a two-loop renormalization group (RG) calculation for the charm contribution. The inclusion of these QCD corrections reduces considerably the theoretical uncertainty in calculating $B(K^+\toπ^+ν\barν)$. Implications for the determination of $V_{td}$ from this decay are discussed.

hep-ph↗