arXiv subjects

Michael Gronau

Publications and source records attributed to Michael Gronau.

At least 37 records · Page 2Linked to original sources

arXiv2012

Rescattering Contributions to rare B-Meson Decays

Several $B$ and $B_s$ decays have been observed which have been cited as evidence for exchange ($E$), penguin annihilation ($PA$) and annihilation ($A$) processes, such as $\bar b d \to \bar u u$, $\bar b s \to \bar u u$ and $\bar b u \to W^* \to \bar c s$, respectively. These amplitudes are normally thought to be suppressed, as they involve the spectator quark in the weak interaction and thus should be proportional to the $B$-meson decay constant $f_B$. However, as pointed out a number of years ago, they can also be generated by rescattering from processes whose amplitudes do not involve $f_B$, such as color-favored tree amplitudes. In this paper we investigate a number of processes such as $B^0 \to K^+ K^-$, $B_s \to π^+ π^-$, and $B^+ \to D_s^+ ϕ$, and identify promising states from which they can be generated by rescattering. We find that $E$ and $PA$-type processes are characterized respectively by amplitudes ranging from 5% to 10% and from 15% to 20% with respect to the largest amplitude from which they can rescatter. Based on this regularity, using approximate flavor SU(3) symmetry in some cases and time-reversal invariance in others, we predict the branching fractions for a large number of as-yet-unseen $B$ and $B_s$ decays in an extensive range from order $10^{-9}$ to $10^{-4}$.

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arXiv2012

Revisiting D0-D0bar mixing using U-spin

We prove that $D^0$-$\bar D^0$ mixing in the standard model occurs only at second order in U-spin breaking. The U-spin subgroup of SU(3) is found to be a powerful tool for analyzing the cancellation of intermediate-state contributions to the $D^0$--$\od^0$ mixing parameter $y = ΔΓ/(2 Γ)$. Cancellations due to states {\it within a single U-spin triplet} are shown to be valid to first order in U-spin breaking. Illustrations are given for triplets consisting of (a) pairs of charged pions and kaons; (b) pairs of neutral pseudoscalar members of the meson octet; (c) charged vector-pseudoscalar pairs, and (d) states of four charged kaons and pions.

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arXiv2012

Nonleptonic Charm Decays and CP Violation

In this talk we briefly present a flavor-SU(3) technique to study branching ratios and direct CP asymmetries $D$-meson decays. The first part of the talk is meant to set up a foundation, based on previous work, to deal with flavor-SU(3) amplitudes and relative strong phases. In addition, we present a model for dealing with SU(3)-breaking in branching ratio measurements of SCS $D^0$ decays. In the second part of the talk we make use of a proposal for an enhanced CP-violating penguin in the SM, to explain the recent LHCb and CDF observations of CP violation in SCS $D^0$ decays. Furthermore, we use our model to predict CP violation in $π^0π^0$ and $K^+\bar{K}^0$ final states. Large experimental bounds on individual CP asymmetries give rise to a large allowed range of $δ$, the strong phase of the CP-violating penguin. We also briefly discuss future prospects.

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arXiv2012

Direct CP Violation in D Decays in view of LHCb and CDF Results

The LHCb and CDF Collaborations have recently reported evidence for a CP asymmetry around -0.7% in $ΔA_{CP}$, the difference between $A_{CP}(D^0 \to K^+ K^-)$ and $A_{CP}(D^0 \to π^+π^-)$. In the Standard Model this effect may be accounted for by enhanced $1/m_c$ corrections in a CP-violating penguin amplitude governed by a Cabibbo-Kobayashi-Maskawa (CKM) factor $V^*_{cb}V_{ub}$. A consistent scheme based on broken flavor SU(3) is presented relating Cabibbo-favored (CF) and singly-Cabibbo-suppressed (SCS) $D$ meson decay rates into two pseudoscalars. Two important ingredients supporting the above interpretation for $ΔA_{CP}$ are a large exchange amplitude in CF decays which is formally $1/m_c$-suppressed, and a pure $ΔU=0$ U-spin breaking CP-conserving penguin amplitude involving $V^*_{cs}V_{us}$ and $V^*_{cd}V_{ud}$ which accounts for the difference between the $D^0\to K^+K^-$ and $D^0\to π^+π^-$ decay rates. The magnitudes of the CP conserving and CP violating penguin amplitudes, where the former involves U-spin breaking at a level of 10%, are shown to be related to each other by the magnitudes of corresponding CKM factors. This simple scheme leads to preferable sign predictions for CP asymmetries in charmed meson decays into two pseudoscalars and to correlations between asymmetries in two pairs of these processes.

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arXiv2012

CP asymmetries in singly-Cabibbo-suppressed $D$ decays to two pseudoscalar mesons

The LHCb Collaboration has recently reported evidence for a CP asymmetry approaching the percent level in the difference between $D^0 \to π^+ π^-$ and $D^0 \to K^+ K^-$. We analyze this effect as if it is due to a penguin amplitude with the weak phase of the standard model $c \to b \to u$ loop diagram, but with a CP-conserving enhancement as if due to the strong interactions. In such a case the magnitude and strong phase of this amplitude $P_b$ are correlated in order to fit the observed CP asymmetry, and one may predict CP asymmetries for a number of other singly-Cabibbo-suppressed decays of charmed mesons to a pair of pseudoscalar mesons. Non-zero CP asymmetries are expected for $D^+ \to K^+ \ok$ (the most promising channel for which a non-zero CP asymmetry has not yet been reported), as well as $D^0 \to π^0 π^0$, $D_s^+ \to π^+ \ko$, and $D_s \to π^0 K^+$. No CP asymmetry is predicted for $D^+ \to π^+ π^0$ or $D^0 \to \ko \ok$ in this framework.

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arXiv2012

Background dependence of dimuon asymmetry in $\bar p p$ interactions at $\sqrt{s} = 1.96$ TeV

The D0 Collaboration has reported an anomalous charge asymmetry in the production of same-sign muon pairs at the Fermilab Tevatron. The magnitude of this effect depends on the subtraction of several backgrounds, the most notable of which is due to kaons being misidentified as muons either through decays in flight or punch-through. The present authors suggested a check on such backgrounds consisting of a tight restriction on the muon impact parameter $b$, to confirm that this excess was indeed due to $B_{(s)}$ meson decays. The D0 Collaboration has performed a related check applying transverse impact parameter (IP) restrictions, whose implications are discussed. We study background asymmetry predictions for events involving two muons with IP bounds which are complementary to each other. These predictions may be used in future measurements of the net charge asymmetry from $B_{(s)}$ decays.

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arXiv2011

Triple product asymmetries in K, D_(s) and B_(s) decays

One distinguishes between "true" CP violating triple product (TP) asymmetries which require no strong phases and "fake" asymmetries which are due to strong phases but require no CP violation. So far a single true TP asymmetry has been measured in $K_L\to π^+π^- e^+e^-$. A general discussion is presented for T-odd TP asymmetries in four-body decays. It is shown that TP asymmetries vanish for two identical and kinematically indistinguishable particles in the final state. Two examples are $D^0\to K^-π^+π^-π^+$ and $D^+\to K^-π^+π^+π^0$. A non-zero TP asymmetry can be expected when non-trivial kinematic correlations exist, as in the decay $K_L \to e^+ e^- e^+ e^-$. Triple product asymmetries measured in charmed particle decays indicate an interesting pattern of final-state interactions. We reiterate a discussion of TP asymmetries in $B$ meson decays to two vector mesons each decaying to a pseudoscalar pair, extending results to decays where one vector meson decays into a lepton pair. We derive expressions for time-dependent TP asymmetries for neutral B decays to flavorless states in terms of the neutral $B$ mass difference $Δm$ and the width-difference $ΔΓ$. Time-integrated true CP violating asymmetries, measurable for untagged $B_s$ decays, are shown to be suppressed by neither $Γ_s/Δm_s$ nor $ΔΓ_s/Γ_s$ if transversity amplitudes for CP-even and CP-odd states involve different weak phases. In contrast, fake asymmetries require flavor tagging and are suppressed by the former ratio when time-integrated. We apply our results to $B\to K^*ϕ$ and $B_s\toϕϕ$ data and suggest an application for $B_s\to J/ψϕ$.

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arXiv2011

$B_s$ Decays and Mixing

Theoretical remarks are offered regarding recent hadron collider results on the mixing and decays of $B_s$ mesons. Topics covered include: (1) CP-violating mixing in $B_s(\ob_s) \to J/ψϕ$, (2) the D0 dimuon charge asymmetry, (3) information from triple products, (4) $B_s \to J/ψf_0$, (5) new physics constraints, (6) some illustrative new physics scenarios.

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arXiv2010

Ratios of heavy hadron semileptonic decay rates

Ratios of charmed meson and baryon semileptonic decay rates appear to be satisfactorily described by considering only the lowest-lying (S-wave) hadronic final states and assuming the kinematic factor describing phase space suppression is the same as that for free quarks. For example, the rate for $D_s$ semileptonic decay is known to be $(17.0 \pm 5.3)%$ lower than those for $D^0$ or $D^+$, and the model accounts for this difference. When applied to hadrons containing $b$ quarks, this method implies that the $B_s$ semileptonic decay rate is about 1% higher than that of the nonstrange $B$ mesons. This small difference thus suggests surprisingly good local quark-hadron duality for $B$ semileptonic decays, complementing the expectation based on inclusive quark-hadron duality that these differences in rates should not exceed a few tenths of a percent. For $Λ_b$ semileptonic decay, however, the inclusive rate is predicted to be about 13% greater than that of the nonstrange $B$ mesons. This value, representing a considerable departure from a calculation using a heavy quark expansion, is close to the corresponding experimental ratio $Γ(Λ_b)/ \bar Γ(B) = 1.13 \pm 0.03$ of total decay rates.

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arXiv2010

Second order direct CP asymmetry in B_(s) -> X l nu

A direct CP asymmetry in inclusive semileptonic B_(s) decays vanishes by CPT to lowest order in weak interactions. Calculating the asymmetry at second order weak interactions in the Cabibbo-Kobayashi-Maskawa framework we find A_{sl} = (-3.2 \pm 0.9) x 10^{-9}. A maximal asymmetry which is two orders of magnitude larger is estimated in a left-right symmetric model. This quite generic upper bound implies negligible effects on wrong-sign lepton asymmetries in B^0 and B_s decays.

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arXiv2010

Background check for anomalous like-sign dimuon charge asymmetry

The D0 Collaboration has reported an excess of roughly one percent of $μ^- μ^-$ pairs over $μ^+ μ^+$ pairs in $\bar p p$ collisions at a center-of-mass energy $\sqrt{s} = 1.96$ GeV at the Fermilab Tevatron, when known backgrounds are subtracted. This excess, if ascribed to CP violation in meson-antimeson mixing of non-strange or strange neutral $B$ mesons, is about 40 times that expected in the Standard Model (SM). We propose a null test, based on a tight restriction on the muon impact parameter $b$, to confirm that this excess is indeed due to $B$ mesons. If the asymmetry is due to anomalous CP violation in $B_s$-$\bar B_s$ mixing then a tight restriction on $b$ would increase by a factor two the net asymmetry from neutral $B$ mixing, while the sample of dimuons from neutral $B$ decays will be reduced significantly relative to background events.

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arXiv2010

Calculating Phases Between B => K* pi Amplitudes

A phase $ΔΦ$ between amplitudes for $B^0 \to K^{*0} π^0$ and $B^0 \to K^{*+} π^-$ plays a crucial role in a method for constraining Cabibbo-Kobayashi-Maskawa (CKM) parameters. We present a general argument for destructive interference between amplitudes for $B^0 \to K^{*+} π^-$ and $B^0 \to K^{*0} π^0$ forming together a smaller $I(K^* π) = 3/2$ amplitude. Applying flavor SU(3) and allowing for conservative theoretical uncertainties, we obtain lower limits on $|ΔΦ|$ and its charge-conjugate. Values of these two phases favored by the BaBar Collaboration are in good agreement with our bounds.

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arXiv2010

CP Asymmetries in B->K pi, K*pi, rho K Decays

We show that ratios of tree and penguin amplitudes in B-> K*pi and B->rho K are two to three times larger than in B-> K pi. This allows for considerably larger CP asymmetries in the former processes than the 10% asymmetry measured in B0 -> K+pi-. We study isospin sum rules for rate asymmetries in B-> K pi, K*pi, rho K, estimating small violation from interference of tree and electroweak penguin amplitudes. The breaking of the K pi asymmetry sum rule is estimated to be one to two percent and negative. Violation of K*pi and rho K sum rules can be estimated from B->rho pi amplitudes using flavor SU(3), while breaking of a sum rule combining K*pi and rho K asymmetries can be measured directly in a Dalitz analysis of B0-> K+pi-pi0. The three sum rules can be tested at the LHCb and at a future Super Flavor Factory, providing precision searches for new Delta S =Delta I=1 operators in the low energy effective Hamiltonian.

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arXiv2009

Diagnostic for new physics in $B \to πK$ decays

A recent analysis of $B \to πK$ decays concludes that present data do not clearly indicate whether (i) the standard model (or $ΔI=0$ new physics) is sufficient, or (ii) $ΔI=1$ new physics is needed. We show that these two possibilities can be distinguished by whether a sum rule relating the CP asymmetries of the four $B \to πK$ decays is valid. If case (i) is favored, the sum rule holds, and one predicts $A_{CP}(π^0 K^0) = -0.15$, while in case (ii) fits to new physics involving large values of a color-suppressed tree amplitude entail $A_{CP}(π^0 K^0) = -0.03$. The current experimental average $A_{CP}(π^0 K^0) = -0.01 \pm 0.10$ must be measured a factor of at least three times more precisely in order to distinguish between the two cases.

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arXiv2009

$D_s$ Inclusive Decays

The availability of branching fractions for a large majority of $D_s$ decays permits the prediction of inclusive branching fractions. This is achieved with the help of a modest amount of input from an isospin statistical model applied to non-resonant multibody $D_s$ decays. A systematic uncertainty in these mostly small branching ratios is estimated by comparing predictions of this model with those of a model involving quark-antiquark pair production. The calculated inclusive branching fractions can be compared with data (for example, from a large sample of $D_s^+ D_s^{*-} + D_s^{*+} D_s^-$ obtained by the CLEO Collaboration) and examined for specific final states which can shed light on strong and weak decay mechanisms.

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arXiv2009

$ω$-$ϕ$ mixing and weak annihilation in $D_s$ decays

The mixing between nonstrange and strange quark wavefunctions in the $ω$ and $ϕ$ mesons leads to a small predicted branching ratio $\b(D_s^+ \to ωe^+ ν_e) = {\cal O}(10^{-4})(δ/3.34^\circ)^2$, where $δ$ is the mixing angle. The value $δ= -3.34^\circ$ is obtained in a mass-independent analysis, while a mass-dependent analysis gives $δ= -0.45^\circ$ at $m(ω)$ and $-4.64^\circ$ at $m(ϕ)$. Measurement of this branching ratio thus can tell whether the decay is dominated by $ϕ$--$ω$ mixing, or additional nonperturbative processes commonly known as "weak annihilation" (WA) contribute. The role of WA in the decay $D_s^+ \to ωπ^+$ and its possible use in estimating WA effects in $D_s^+ \to ωe^+ ν_e$ are also discussed. Assuming that the dynamics of WA in $D_s^+ \to ωπ^+$ is similar in $D_s^+ \to ωe^+ ν_e$ we estimate $\b(D_s^+ \to ωe^+ ν_e) = (1.3 \pm 0.5)\times 10^{-3}$.

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arXiv2009

Doubly CKM-suppressed corrections to CP asymmetries in $B^0 \to J/ψK^0$

A doubly CKM-suppressed amplitude in $B^0\to J/ψK_S$ leads to corrections in CP asymmetries $S = \sin 2β, C=0$, which may be enhanced by long-distance rescattering. It has been suggested that this enhancement may lead to several percent corrections. We calculate an upper bound of order $10^{-3}$ on rescattering corrections using measured branching ratios for charmless $|ΔS|=1$ $B^0$ decays.

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arXiv2008

Flavor symmetry for strong phases and determination of $β_s, ΔΓ$ in $B_s \to J/ψϕ$

Studies of angular and time distributions and CP-violating observables in $B_s\to J/ψϕ$ decays yield a space of parameters which can be considerably reduced if relative strong phases among different amplitudes are specified. We show that the relations between $B_s \to J/ψϕ$ and $B^0 \to J/ψK^{*0}$ amplitudes given by flavor symmetry [actually U(3) rather than SU(3)] are likely to be quite reliable, and hence the use of strong phases from $B^0 \to J/ψK^{*0}$ in the analysis of $B_s \to J/ψϕ$ is justified. We point out the potential advantage of using helicity angles over transversity angles, and comment on a way to measure a sizable CP-violating phase independent of strong phases.

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