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G. Buchalla

Publications and source records attributed to G. Buchalla.

At least 37 records · Page 2Linked to original sources
arXiv2008

B, D and K decays

With the advent of the LHC, we will be able to probe New Physics (NP) up to energy scales almost one order of magnitude larger than it has been possible with present accelerator facilities. While direct detection of new particles will be the main avenue to establish the presence of NP at the LHC, indirect searches will provide precious complementary information, since most probably it will not be possible to measure the full spectrum of new particles and their couplings through direct production. In particular, precision measurements and computations in the realm of flavour physics are expected to play a key role in constraining the unknown parameters of the Lagrangian of any NP model emerging from direct searches at the LHC. The aim of Working Group 2 was twofold: on one hand, to provide a coherent, up-to-date picture of the status of flavour physics before the start of the LHC; on the other hand, to initiate activities on the path towards integrating information on NP from high-pT and flavour data.

hep-ph↗
arXiv2004

Comment on ``B->M_1 M_2: Factorization, charming penguins, strong phases, and polarization''

We show that the factorization formula for non-leptonic B decays to two light flavor non-singlet mesons derived by Bauer et al. in the context of soft-collinear effective theory is equivalent to the corresponding formula in the QCD factorization approach. The apparent numerical differences in the analysis of B->pi+pi data performed by these authors, as compared to previous QCD factorization analyses, can largely be attributed to the neglect of known perturbative and power corrections.

hep-ph↗
arXiv2003

The CKM Matrix and the Unitarity Triangle

This report contains the results of the Workshop on the CKM Unitarity Triangle, held at CERN on 13-16 February 2002 to study the determination of the CKM matrix from the available data of K, D, and B physics. This is a coherent document with chapters covering the determination of CKM elements from tree level decays and K and B meson mixing and the global fits of the unitarity triangle parameters. The impact of future measurements is also discussed.

hep-ph↗
arXiv2003

CP asymmetry in flavour-specific B decays beyond leading logarithms

We compute next-to-leading order QCD corrections to the CP asymmetry a_{fs} = Im(Gamma_{12}/M_{12}) in flavour-specific B_{d,s} decays such as B_d->X l nu or B_s->D^-_s pi^+. The corrections reduce the uncertainties associated with the choice of the renormalization scheme for the quark masses significantly. In the Standard Model we predict a^d_{fs} = -(5.0 +- 1.1)*10^{-4}. As a by-product we also obtain the width difference in the B_d system at next-to-leading order in QCD.

hep-ph↗
arXiv2002

The B^+ B_d^0 Lifetime Difference Beyond Leading Logarithms

We compute perturbative QCD corrections to the lifetime splitting between the charged and neutral $B$ meson in the framework of the heavy quark expansion. These next-to-leading logarithmic corrections are necessary for a meaningful use of hadronic matrix elements of local operators from lattice gauge theory. We find the uncertainties associated with the choices of renormalization scale and scheme significantly reduced compared to the leading-order result. We include the full dependence on the charm-quark mass $m_c$ without any approximations. Using hadronic matrix elements estimated in the literature with lattice QCD we obtain $τ(B^+)/τ(B^0_d)=1.053\pm 0.027\pm 0.017$, where the effects of unquenching and $1/m_b$ corrections are not yet included. The lifetime difference of heavy baryons $Ξ^0_b$ and $Ξ^-_b$ is also briefly discussed.

hep-ph↗
arXiv2001

Kaon physics with a high-intensity proton driver

We study opportunities for future high-precision experiments in kaon physics using a high-intensity proton driver, which could be part of the front-end of a muon storage ring complex. We discuss in particular the rare decays $K_L\toπ^0ν\barν$, $K^+\toπ^+ν\barν$, $K_L\toπ^0e^+e^-$, and lepton-flavour violating modes such as $K_L\toμe$ and $K\toπμe$. The outstanding physics potential and long-term interest of these modes is emphasized. We review status and prospects of current and planned experiments for the processes under consideration, and indicate possible improvements and strategies towards achieving the necessary higher sensitivity. Finally, we outline the machine requirements needed to perform these high-precision kaon experiments in the context of a muon storage ring facility.

hep-ph↗
arXiv2001

QCD Factorization in B -> pi K, pi pi Decays and Extraction of Wolfenstein Parameters

In the heavy-quark limit, the hadronic matrix elements entering nonleptonic $B$-meson decays into two light mesons can be calculated from first principles including ``nonfactorizable'' strong-interaction corrections. The $B\toπK,ππ$ decay amplitudes are computed including electroweak penguin contributions, SU(3) violation in the light-cone distribution amplitudes, and an estimate of power corrections from chirally-enhanced terms and annihilation graphs. The results are then used to reduce the theoretical uncertainties in determinations of the weak phases $γ$ and $α$. In that way, new constraints in the $(\barρ,\barη)$ plane are derived. Predictions for the $B\toπK, ππ$ branching ratios and CP asymmetries are also presented. A good global fit to the (in part preliminary) experimental data on the branching fractions is obtained without taking recourse to phenomenological models.

hep-ph↗
arXiv2000

Phenomenology of non-standard Z couplings in exclusive semileptonic b -> s transitions

The rare decays $B\to K^{(*)}\ell^+\ell^-$, $B\to K^{(*)}ν\barν$ and $B_s\toμ^+μ^-$ are analyzed in a generic scenario where New Physics effects enter predominantly via $Z$ penguin contributions. We show that this possibility is well motivated on theoretical grounds, as the $\bar sbZ$ vertex is particularly susceptible to non-standard dynamics. In addition, such a framework is also interesting phenomenologically since the $\bar sbZ$ coupling is rather poorly constrained by present data. The characteristic features of this scenario for the relevant decay rates and distributions are investigated. We emphasize that both sign and magnitude of the forward-backward asymmetry of the decay leptons in $\bar B\to \bar K^*\ell^+\ell^-$, ${\cal A}^{(\bar B)}_{FB}$, carry sensitive information on New Physics. The observable ${\cal A}^{(\bar B)}_{FB}+{\cal A}^{(B)}_{FB}$ is proposed as a useful probe of non-standard CP violation in $\bar sbZ$ couplings.

hep-ph↗
arXiv2000

QCD factorization for $B\toπK$ decays

We examine some consequences of the QCD factorization approach to non-leptonic B decays into $πK$ and $ππ$ final states, including a set of enhanced power corrections. Among the robust predictions of the approach we find small strong-interaction phases (with one notable exception) and a pattern of CP-averaged branching fractions, which in some cases differ significantly from the current central values reported by the CLEO Collaboration.

hep-ph↗
arXiv2000

QCD factorization for exclusive, non-leptonic B meson decays: General arguments and the case of heavy-light final states

We provide a rigorous basis for factorization for a large class of non-leptonic two-body $B$-meson decays in the heavy-quark limit. The factorization formula incorporates elements of the naive factorization approach and the hard-scattering approach, but allows us to compute systematically radiative (``non-factorizable'') corrections to naive factorization for decays such as $B\to Dπ$ and $B\to ππ$. We discuss the factorization formula for a general final state from a general point of view. We then consider factorization for decays into heavy-light final states (such as $B\to Dπ$) in more detail, including a proof of the factorization formula at two-loop order. Explicit results for the leading QCD corrections to factorization are presented and compared to existing measurements of branching fractions and final-state interaction phases.

hep-ph↗
arXiv1999

Next-to-Leading Order QCD Corrections to the Lifetime Difference of $B_s$ Mesons

We compute the QCD corrections to the decay rate difference in the $B_s-\bar B_s$ system, $ΔΓ_{B_s}$, in the next-to-leading logarithmic approximation using the heavy quark expansion approach. Going beyond leading order in QCD is essential to obtain a proper matching of the Wilson coefficients to the matrix elements of local operators from lattice gauge theory. The lifetime difference is reduced considerably at next-to-leading order. We find $(ΔΓ/Γ)_{B_s}=(f_{B_s}/210 MeV)^2 [0.006 B(m_b)+0.150 B_S(m_b)-0.063]$ in terms of the bag parameters $B, B_S$ in the NDR scheme. As a further application of our analysis we also derive the next-to-leading order result for the mixing-induced CP asymmetry in inclusive $b\to u\bar ud$ decays, which measures $\sin 2α$.

hep-ph↗
arXiv1999

QCD Factorization for $B\toππ$ Decays: Strong Phases and CP Violation in the Heavy Quark Limit

We show that, in the heavy quark limit, the hadronic matrix elements that enter $B$ meson decays into two light mesons can be computed from first principles, including `non-factorizable' strong interaction corrections, and expressed in terms of form factors and meson light-cone distribution amplitudes. The conventional factorization result follows in the limit when both power corrections in $1/m_b$ and radiative corrections in $α_s$ are neglected. We compute the order-$α_s$ corrections to the decays $B_d\toπ^+π^-$, $B_d\toπ^0π^0$ and $B^+\toπ^+π^0$ in the heavy quark limit and briefly discuss the phenomenological implications for the branching ratios, strong phases and CP violation.

hep-ph↗
arXiv1997

CP Violation in Neutral Kaon Decays

A brief review of the theoretical status of CP violation in decays of neutral kaons is presented. We focus on three important topics: $\varepsilon$, $\varepsilon'/\varepsilon$ and $K_L\toπ^0ν\barν$.

hep-ph↗
arXiv1997

Corrections of Order $Λ^2_{QCD}/m^2_c$ to Inclusive Rare B Decays

We calculate nonperturbative ${\cal O}(Λ^2_{QCD}/m^2_c)$ corrections to the dilepton invariant mass spectrum and the forward-backward charge asymmetry in $B\to X_se^+e^-$ decay using a heavy quark expansion approach. The method has recently been used to estimate long-distance effects in $B\to X_sγ$. We generalize this analysis to the case of nonvanishing photon invariant mass, $q^2\not= 0$, relevant for the rare decay mode $B\to X_se^+e^-$. In the phenomenologically interesting $q^2$ region away from the $c\bar c$ resonances, the heavy quark expansion approach should provide a reasonable description of possible nonperturbative corrections. In particular this picture is preferable to the model-dependent approach relying on the tails of Breit-Wigner resonances, which has been employed so far in the literature to account for these effects. We find that the ${\cal O}(Λ^2_{QCD}/m^2_c)$ corrections to the dilepton invariant mass spectrum and to the forward-backward asymmetry in $B\to X_se^+e^-$ amount to several percent at most for $q^2/m^2_b < 0.3$ and $q^2/m^2_b > 0.6$. The ${\cal O}(Λ^2_{QCD}/m^2_c)$ correction to the $B\to X_sγ$ decay rate is also computed and found to be +3%, which agrees in magnitude with previous calculations. Finally, we comment on long-distance effects in $B\to X_sν\barν$, which in this case are extremely suppressed due to the absence of virtual photon contributions.

hep-ph↗
arXiv1996

Width Difference in the $B_s-\bar{B_s}$ System

We use the heavy quark expansion to investigate the width difference $ΔΓ_{B_s}$ between the $B_s$ mass eigenstates. The corrections of ${\cal O}(Λ_{QCD}/m_b)$ and ${\cal O}(m_s/m_b)$ to the leading order expression in the operator product expansion are derived and estimated to yield a sizable reduction of the leading result for $ΔΓ_{B_s}$ by typically $30\%$. For completeness we also quantify small effects due to penguin operators and CKM suppressed contributions. Based on our results we discuss the prediction for $(ΔΓ/Γ)_{B_s}$ with particular emphasis on theoretical uncertainties. We find $(ΔΓ/Γ)_{B_s}=0.16^{+0.11}_{-0.09}$, where the large error is dominated by the uncertainty in hadronic matrix elements. An accuracy of about $10\%$ in $(ΔΓ/Γ)_{B_s}$ should be within reach, assuming continuing progress in lattice calculations. In addition we address phenomenological issues and implications of a $ΔΓ_{B_s}$ measurement for constraints on $ΔM_{B_s}$ and CKM parameters. We further consider in some detail the lifetime ratio $τ(B_s)/τ(B_d)$ and estimate that, most likely, $|τ(B_s)/τ(B_d)-1|<1\%$.

hep-ph↗
arXiv1996

The $B_c$ Meson Lifetime

We investigate the total inclusive decay rate of the (ground state) $B_c$ meson within the framework of an operator product expansion in inverse powers of the heavy quark masses and subsequent matching onto nonrelativistic QCD. The expansion is organized as a series in the strong coupling and in powers of the heavy quark velocities in the $B_c$, reflecting the nonrelativistic nature of a heavy-heavy bound state. In this aspect the character of the expansion differs from the more familiar case of heavy-light mesons. The framework incorporates systematically corrections to the leading $b$- and $c$-quark decays due to binding effects, as well as contributions from weak annihilation and Pauli interference. Based on this approach we find for the $B_c$ meson lifetime $τ_{B_c}=(0.4 - 0.7)\,$ps, the dominant mechanism being the decay of the charm constituent.

hep-ph↗
arXiv1995

GIM Violation and New Dynamics of the Third Generation

In strong dynamical schemes for electroweak symmetry breaking the third generation must be treated in a special manner, owing to the heavy top quark. This potentially leads to new flavor physics involving the members of the third generation in concert with the adjoining generations, with potential novel effects in beauty and charm physics. We give a general discussion and formulation of this kind of physics, abstracted largely from Topcolor models which we elaborate in detail. We identify sensitive channels for such new physics accessible to current and future experiments.

hep-ph↗