arXiv subjects

Michael Gronau

Publications and source records attributed to Michael Gronau.

At least 55 records · Page 3Linked to original sources

arXiv2008

Implications for CP asymmetries of improved data on $B \to K^0 π^0$

The decay $B^0 \to K^0 π^0$, dominated by a $b \to s$ penguin amplitude, holds the potential for exhibiting new physics in this amplitude. In the pure QCD penguin limit one expects $\ckp = 0$ and $\skp = \sin 2 β$ for the coefficients of $\cos Δm t$ and $\sin Δm t$ in the time-dependent CP asymmetry. Small non-penguin contributions lead to corrections to these expressions which are calculated in terms of isospin-related $B\to Kπ$ rates and asymmetries, using information about strong phases from experiment. We study the prospects for incisive tests of the Standard Model through examination of these corrections. We update a prediction $\ckp=0.15\pm 0.04$, pointing out the sensitivity of a prediction $\skp\approx 1$ to the measured branching ratio for $B^0\to K^0π^0$ and to other observables.

hep-ph↗

arXiv2008

Small amplitude effects in $B^0\to D^+D^-$ and related decays

Intrigued by a recent Belle result for a large direct CP asymmetry in $B^0\to D^+D^-$, we study the effects of a $\bar b\to \bar uu\bar d$ quark transition by combining the asymmetry information with rates and asymmetries in isospin-related decays. Arguing for a hierarchy among several contributions to these decays, including an exchange amplitude which we estimate, we present tests for factorization of the leading terms, and obtain an upper bound on the ratio of $\bar b\to \bar uu\bar d$ and $\bar b\to \bar cc\bar d$ amplitudes. We prove an approximate $ΔI=1/2$ amplitude relation for $B\to D\bar D$, and an approximate equality between CP asymmetries in $B^0\to D^+D^-$ and $B^+\to D^+\bar D^0$. Violations of these relations by Belle measurements, at $1.8σ$ and $3.6σ$ respectively, if confirmed, would indicate a possible New Physics contribution in $\bar b\to \bar uu\bar d$. Applying flavor SU(3), we extend this study to a total of ten processes including $ΔS=0$ decays involving final $D_s$ and initial $B_s$ mesons, and $ΔS=1$ decays of $B$ and $B_s$ mesons into pairs of charmed pseudoscalar mesons. The decays $B_s\to D\bar D$ provide useful information about a small exchange amplitude, responsible for a decay rate difference between $B^+\to D^+\bar D^0$ and $B^0\to D^+D^-$. A method for determining the weak phase $γ$, based on CP asymmetries in $B^0(t)\to D^+D^-$ and the decay rate for $B_s\to D^+_sD^-_s$ or $B^{+(0)}\to D^+_s\bar D^0 (D^-)$, is shown to involve high sensitivity to SU(3) breaking.

hep-ph↗

arXiv2008

B decays dominated by omega-phi mixing

Recently Belle has established the 90% confidence level (CL) upper limit $\b < 9.4 \times 10^{-7}$ for the branching ratio for $B^0\to J/ψϕ$, a process expected to be suppressed by the Okubo-Zweig-Iizuka (OZI) rule disfavoring disconnected quark diagrams. We use information on $ω$--$ϕ$ mixing to establish likely lower bounds on this and related processes. We find that the Belle result is about a factor of five above our limit, while other decays such as $B^0 \to \bar D^0 ϕ$ and $B^+ \to π^+ ϕ$, for which upper limits have been obtained by BaBar, could be observable with similar improvements in data. We argue that a significant enhancement of our predicted decay rates by rescattering is unlikely.

hep-ph↗

arXiv2008

Constraint on rho-bar, eta-bar from B to K*pi

A linear CKM relation, $\barη= \tanΦ_{3/2}(\barρ-0.24\pm 0.03)$, involving a $1σ$ range for $Φ_{3/2}$, $20^\circ < Φ_{3/2} < 115^\circ$, is obtained from $B^0\to K^*π$ amplitudes measured recently in Dalitz plot analyses of $B^0\to K^+π^-π^0$ and $B^0(t)\to K_Sπ^+π^-$. This relation is consistent within the large error on $Φ_{3/2}$ with other CKM constraints which are unaffected by new $b\to s\bar q q$ operators. Sensitivity of the method to a new physics contribution in the $ΔS=ΔI=1$ amplitude is discussed.

hep-ph↗

arXiv2008

Examination of Flavor Symmetry in $B, B_s \to K π$ Decays

We study a relation between the weak phase $γ$ and the rates and CP asymmetries of several $K π$ decays of $B^+$, $B^0$, and $B_s$, emphasizing the impact of the latter measurements. Current data indicate large SU(3) breaking in the strong phases or failure of factorization (including its application to penguin amplitudes) in $K π$ modes of $B^0$ and $B_s$. SU(3) and factorization only remain approximately valid if the branching ratio for $B_s \to K^- π^+$ exceeds its current value of $(5.27 \pm 1.17) \times 10^{-6}$ by at least 42%, or if a parameter $ξ$ describing ratios of form factors and decay constants is shifted from its nominal value by more than twice its estimated error.

hep-ph↗

arXiv2007

Studying New Physics Amplitudes in Charmless B_s Decays

A method based on flavour SU(3) is proposed for identifying and extracting New Physics (NP) amplitudes in charmless $ΔS=1$ $B_s$ decays using time-dependent CP asymmetries in these decays and in flavour SU(3) related $ΔS=0$ decays. For illustration, we assume a hierarchy, $\sim 1: λ: λ^2$ ($λ=0.2$), between a dominant $ΔS=1$ penguin amplitude, a NP amplitude and a Standard Model amplitude with weak phase $γ$. An uncertainty from SU(3) breaking corrections, reduced by using ratios of hadronic amplitudes, is further suppressed by a factor $λ$. We discuss examples for pairs of decays into two neutral vector mesons, $B_s\toϕϕ, B_s\toϕ\bar K^{*0}$ and $B_s\to K^{*0}\bar K^{*0}, B^0\to K^{*0}\bar K^{*0}$, where the magnitude of the NP amplitude, its weak and strong phases can be determined.

hep-ph↗

arXiv2007

Direct CP Violation in B Decays

We discuss several aspects of direct CP asymmetries in B decays, which are very useful in spite of hadronic uncertainties in asymmetry calculations. 1) Asymmetries in decays to $D^{(*)}K^{(*)}$, $π^+π^-, ρ^+ρ^-$, providing precision tests for the CKM phase $γ$. 2) Null tests in $B^+\to J/ψK^+, π^+π^0$, where a nonzero asymmetry provides evidence for New Physics. 3) Isospin and broken flavor SU(3) relations among CP asymmetries in $B\to Kπ, ππ$ predicting $A_{CP}(B^0\to K^0π^0)$ and $A_{CP}(B^0\to π^0π^0)$. 4) The significance of $A_{CP}(B^0\to K^+π^-)\ne A_{CP}(B^+\to K^+π^0)$. 5) A potentially stringent constraint on $γ$ from $A_{CP}(B^+\to K^+π^0)$ and $R_c\equiv 2Γ(B^+\to K^+π^0)/Γ(B^+\to K^0π^+)$. 6) The role of direct CP asymmetries in $b\to s\bar qq$ decays for studying the origin of potential New Physics.

hep-ph↗

arXiv2007

Systematic Error on Weak Phase $γ$ from $B \to π^+ π^-$ and $B \to K π$

When CP asymmetries in $B^0(t)\to π^+ π^-$ are combined using broken flavor SU(3) with decay rates for $B^+\to K^0π^+$ and/or $B^0\to K^+π^-$, one can obtain stringent limits on the weak phase $γ$ which are consistent with those obtained from other CKM constraints. Experimental data in the past few years have improved to the extent that systematic errors associated with uncertainty in SU(3) symmetry breaking dominate the determination of $γ$. We obtain a value $γ=(73 \pm 4^{+10}_{-8})^\circ$, where the first error is statistical while the second one is systematic.

hep-ph↗

arXiv2007

CP violation in beauty decays

Precision tests of the Kobayashi-Maskawa model of CP violation are discussed, pointing out possible signatures for other sources of CP violation and for new flavor-changing operators. The current status of the most accurate tests is summarized.

hep-ph↗

arXiv2007

Isospin of new physics in $|ΔS|=1$ charmless B decays

New physics (NP) in charmless strangeness-changing $B$ and $B_s$ decays, which are dominated by the $b \to s$ penguin amplitudes, can either preserve isospin or change it by one unit. A general formalism is presented studying pairs of processes related to each other by isospin reflection. We discuss information on $ΔI$ in NP amplitudes, provided by time-integrated CP-violating rate asymmetries in $B^+$ and $B^0$ decays (or in $B_s$ decays), differences between rates for isospin-reflected processes, and coefficients $S$ of $\sin Δm t$ in time-dependent CP asymmetries. These four asymmetries in $B^+$ and $B^0$ decays (or five asymmetries in $B_s$ decays) are shown to determine the magnitude and CP-violating phase of a potential isovector NP amplitude, and the imaginary part of an isoscalar amplitude, assuming that strong phases in NP amplitudes are negligible. This information may be compared with predictions of specific models, for which we discuss a few examples.

hep-ph↗

arXiv2007

Enhanced effects on extracting γfrom untagged B^0 and B_s decays

The weak phase γcan be determined using untagged B^0\to DK_S or B_s\to Dϕ, Dη^{(')} decays. In the past, the small lifetime difference y\equiv ΔΓ/(2Γ) has been neglected in B^0, while the CP violating parameter ε\equiv 1-|q/p|^2 has been neglected in both B^0-\bar B^0 and B_s-\bar B_s mixing. We estimate the effect of neglecting y and ε. We find that in D decays to flavor states this introduces a systematic error, which is enhanced by a large ratio of Cabibbo-allowed to doubly Cabibbo-suppressed D decay amplitudes.

hep-ph↗

arXiv2006

Sum rule for rate and CP asymmetry in $B^+\to K^+π^0$

A sum rule relating the ratio $R_c = 2 Γ(B^+ \to K^+ π^0)/Γ(B^+ \to K^0 π^+)$ and the CP asymmetry $A_{CP}(B^+ \to K^+π^0)$ is proved to first order in the ratio of tree to penguin amplitudes. The sum rule explains why it is possible to have $R_c$ consistent with 1 together with a small CP asymmetry in $B^+ \to K^+ π^0$. The measured ratio $A_{CP}(B^+\to K^+π^0)/A_{CP}(B^0\to K^+π^-)$ rules out a small strong phase difference between a color-suppressed and a color-favored tree amplitude contributing to $B^+\to K^+π^0$ as favored by QCD factorization.

hep-ph↗

arXiv2006

Improved method for CKM constraints in charmless three-body B and B_s decays

Recently Ciuchini, Pierini and Silvestrini proposed a method for constraining CKM parameters in B->K pi pi and B_s-> K pi pi through phase measurements of amplitudes involving I=3/2 K*pi final states. We show that complementary information on CKM parameters may be obtained by studying the phases of Delta I=1 B->(K*pi)_{I=1/2}, B_s->(K*\bar K)_{I=1} and B_s->(\bar K* K)_{I=1} amplitudes. Hadronic uncertainties in these constraints from electroweak penguin operators O_9 and O_10, studied using flavor SU(3), are shown to be very small in B->K pi pi and B_s->K pi pi and somewhat larger in B_s-> K\bar K pi. The first processes imply a precise linear relation between \bar rho and \bar eta, with a measurable slope and an intercept at \bar eta=0 involving a theoretical error of 0.03. The decays B_s-> K pi pi permit a measurement of gamma involving a theoretical error below a degree. We note that while time-dependence is required when studying B^0 decays at the Upsilon(4S), it may not be needed when studying B_s decays at hadronic colliders.

hep-ph↗

arXiv2006

Updated bounds on CP asymmetries in $B^0 \to η' K_S$ and $B^0 \to π^0 K_S$

New rate measurements of $B^0$ decays into $π^0π^0, π^0η, π^0η', ηη, ηη', η'η'$ and $K^+ K^-$ are used in conjunction with flavor SU(3) to constrain the coefficients $S$ and $C$ of $\sinΔmt$ and $\cosΔmt$ in the time-dependent CP asymmetries of $B^0 \to η' K_S$ and $B^0 \to π^0 K_S$. Experimental values of $S_{η' K}$ are now seen to be closer to the Standard Model expectations, fully consistent with the new improved bounds.

hep-ph↗

arXiv2006

Rate and CP-asymmetry sum rules in $B \to K π$

The observed violation of $A_{CP}(B^0 \to K^+ π^-) = A_{CP}(B^+ \to K^+ π^0)$ has been recently mentioned as a puzzle for the standard model. We point out that while this violation may be accounted for by a large color-suppressed tree amplitude, a sum rule involving three or four $B\to Kπ$ CP asymmetries should hold. The current experimental status of these sum rules and of a sum rule for $B\to Kπ$ decay rates is presented.

hep-ph↗

arXiv2006

Precision Tests of Flavor and CP violation in B Decays

Isospin and flavor SU(3) set stringent bounds on penguin pollution in $B^0(t)\to ρ^+ρ^-$, providing a theoretically precise determination of $α\equiv ϕ_2 $, $α= (91\pm 7_{\rm exp}\pm 3_{\rm th})^\circ$. Isospin breaking in a sum rule for $B\to Kπ$ rates is shown to be suppressed. A similar sum rule holds for CP asymmetries in $B\to Kπ$. Violation of these sum rules would be evidence for an anomalous $ΔI=1$ piece in ${\cal H}_{\rm eff}$.

hep-ph↗

arXiv2006

A precise determination of $α$ using $B^0\toρ^+ρ^-$ and $B^+\to K^{*0}ρ^+$

The effect of the penguin amplitude on extracting $α$ from CP asymmetries in $B^0\to ρ^+ρ^-$ decays is studied using information on the SU(3)-related penguin amplitude in $B^+\to K^{*0}ρ^+$. Conservative bounds on non-factorizable SU(3) breaking, small amplitudes, and the strong phase difference between tree and penguin amplitudes, are shown to reduce the error in $α$ in comparison with the one obtained using isospin symmetry in $B\toρρ$. Current measurements imply $α= [90 \pm 7 f{\rm exp})^{+2}_{-5} ({\rm th})]^\circ$.

hep-ph↗

arXiv2006

Isospin in $B$ Decays and the $(B^0 \bar B^0)/(B^+ B^-)$ Production Ratio

Methods are proposed for measuring the ratio $R^{+/0} = Γ(Υ(4S) \to B^+ B^-)/$ $Γ(Υ(4S) \to \bo \ob)$ without assuming isospin invariance in exclusive hadronic decays such as $B \to J/ψK$. The validity of isospin invariance in various B decays is discussed. Isospin violations are expected to be especially small in inclusive semileptonic decays, so that $Γ(B^+ \to X_c^0 \ell^+ ν_\ell) = Γ(B^0 \to X_c^- \ell^+ ν_\ell)$ is expected to hold at the sub-percent level. Suggestions are made for utilizing this relation. The accuracy of a ``double-tag'' method for obtaining $R^{+/0}$, such as that used for measuring the $D^+ D^-/D^0 \od$ ratio at the $ψ'' \equiv ψ(3770)$, is also estimated.

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