arXiv subjects

Michael Gronau

Publications and source records attributed to Michael Gronau.

At least 127 records · Page 7Linked to original sources

arXiv1997

CP Violation in the B Meson System

CP violation in $B$ decays is reviewed in the Standard Model (SM) and beyond the SM. The present explanation of CP violation in terms of a phase in the Cabibbo-Kobayashi-Maskawa (CKM) matrix can be tested through a variety of CP asymmetries in neutral and charged $B$ decays. Usually, new mechanisms of CP nonconservation enter via $B-\bar{B}$ mixing and violate SM constraints on the CKM parameters in a few characteristic ways. Different models can be partially distinguished by penguin-dominated $B$ decay rate measurements. In radiative decays, large mixing-induced asymmetries may occur due to new contributions to the decay amplitude.

hep-ph↗

arXiv1997

Mixing-induced CP Asymmetries in Radiative B Decays in and beyond the Standard Model

In the Standard Model (SM) the photon in radiative $\bar B^0$ and $\bar B_s$ decays is predominantly left-handed. Thus, mixing induced CP asymmetries in $b\to sγ$ and $b\to dγ$ are suppressed by $m_s/m_b$ and $m_d/m_b$, respectively, and are very small. In many extensions of the SM, such as the left-right symmetric model (LRSM), SU(2)xU(1) models with exotic fermions and SUSY, the amplitude of right-handed photons grows proportional to the virtual heavy fermion mass, which can lead to large asymmetries. As an example, in the LRSM, asymmetries larger than 50% are possible even when radiative decay rate measurements agree with SM predictions.

hep-ph↗

arXiv1996

Weak Phases From B Decays to Kaons and Charged Pions

Phases of elements of the Cabibbo-Kobayashi-Maskawa (CKM) matrix can be obtained using decays of $B$ mesons to $π^+ π^-$, $π^\pm K^\mp$, and $π^+ K^0$ or $π^- \overline{K}^0$. For $B^0~{\rm or}~ \overline{B}^0 \to π^+ π^-$, one identifies the flavor of the neutral $B$ meson at time of production and studies the time-dependence of the decay rate. The other processes are self-tagging and only their rates need be measured. By assuming flavor SU(3) symmetry and first-order SU(3) breaking, one can separately determine the phases $γ\equiv {\rm Arg}~V_{ub}^*$ and $α= π- β- γ$, where $β\equiv {\rm Arg}~V_{td}^*$. Special cases include the vanishing of strong interaction phase differences between amplitudes, the possibility of recovering partial information when $π^+ π^-$ and $π^\pm K^\mp$ decays cannot be distinguished from one another, and the use of a correlation between $γ$ and $α$ in the region of allowed parameters.

hep-ph↗

arXiv1996

$V_{td}$ from Hadronic Two-Body $B$ Decays

Certain hadronic two-body decays of $B$ mesons are dominated by penguin diagrams. The ratios of rates for several such decays, including $Γ(B^0 \to \overline{K}^{*0} K^0)/Γ(B^0 \to ϕK^0)$, $Γ(B^0 \to \overline{K}^{*0} K^{*0})/Γ(B^0 \to ϕK^{*0})$, $Γ(B^+ \to \overline{K}^{*0} K^+)$ $/Γ(B^+ \to ϕK^+)$, and $Γ(B^+ \to \overline{K}^{*0} K^{*+})/Γ(B^+ \to ϕK^{*+})$, can provide information on the ratio of Cabibbo-Kobayashi-Maskawa (CKM) elements $|V_{td}/V_{ts}|$ in a manner complementary to other proposed determinations. SU(3) breaking effects cancel in some ratios. The cases of neutral $B$ decays are free of corrections from small annihilation terms.

hep-ph↗

arXiv1995

Determining the CKM Unitarity Triangle From $B$ Decays to Charged Pions and Kaons

Decay rates of $B^0(t)\toπ^+π^-,~B^0\toπ^- K^+,~B^+\toπ^+ K^0~ (K_S\toπ^+π^-$) and of charge-conjugate processes are studied within flavor SU(3) symmetry and first-order SU(3) breaking. We show that these measurements can determine with a reasonable accuracy the two angles, $α$ and $γ$, of the Cabibbo-Kobayashi-Maskawa unitarity triangle.

hep-ph↗

arXiv1995

Amplitude relations for $B$ decays involving $η$ and $η'$

A class of amplitude relations for decays of $B$ mesons is discussed. Processes involving $η$ and $η'$ in the final state are shown to provide useful information about weak phases in some cases even in the presence of octet-singlet mixing in these states. Some of the relations are unaffected by first-order SU(3) breaking.

hep-ph↗

arXiv1995

Determining the Weak Phase $γ$ From Charged $B$ Decays

A quadrangle relation is shown to be satisfied by the amplitudes for $B^+ \to π^0 K^+,~π^+ K^0,~ηK^+$, and $η' K^+$. By comparison with the corresponding relation satisfied by $B^-$ decay amplitudes, it is shown that the relative phases of all the amplitudes can be determined up to discrete ambiguities. Making use of an SU(3) relation between amplitudes contributing to the above decays and those contributing to $B^{\pm} \to π^{\pm} π^0$, it is then shown that one can determine the weak phase $γ\equiv {\rm Arg} (V_{ub}^* V_{cb}/V_{us}^* V_{cs})$, where $V$ is the Cabibbo-Kobayashi-Maskawa matrix describing the charge-changing weak interactions between the quarks $(u,c,t)$ and $(d,s,b)$.

hep-ph↗

arXiv1995

A variety of CP violating B decays

A variety of CP violating asymmetries in $B^0$ decays is predicted in the Standard Model in terms of CKM (Cabibbo-Kobayashi-Maskawa) complex phases. These phases can also be determined from rate measurements of certain $B^+$ and $B^-$ decays. We focus on the following processes: $B^0\toψK_S,~π^+π^-,~π^0π^0, ~ρ^{\pm}π^{\mp},~B_s\to D^+_s K^-,~π^0η, ~B^+\to D^0(\Dbar)K^+,~π^+π^0,~π^0 K^+,~ π^+ K^0,~ηK^+$ and their charge-conjugates. Complications due to gluonic-penguin and electroweak-penguin amplitudes are dealt with and are resolved. The importance of final state interaction phases in charged $B$ decay asymmetries is demonstrated in $B^+\toχ_{c0}π^+,~~χ_{c0}\toπ^+π^-$ through the effect of the $χ_{c0}$ width.

hep-ph↗

arXiv1995

Broken SU(3) Symmetry in Two-Body B Decays

The decays of $B$ mesons to two-body hadronic final states are analyzed within the context of broken flavor SU(3) symmetry, extending a previous analysis involving pairs of light pseudoscalars to decays involving one or two charmed quarks in the final state. A systematic program is described for learning information {}from decay rates regarding (i) SU(3)-violating contributions, (ii) the magnitude of exchange and annihilation diagrams (effects involving the spectator quark), and (iii) strong final-state interactions. The implication of SU(3)-breaking effects for the extraction of weak phases is also examined. The present status of data on these questions is reviewed and suggestions for further experimental study are made.

hep-ph↗

arXiv1995

ELECTROWEAK PENGUINS AND TWO-BODY B DECAYS

We discuss the role of electroweak penguins in $B$ decays to two light pseudoscalar mesons. We confirm that the extraction of the weak phase $α$ through the isospin analysis involving $B\toππ$ decays is largely unaffected by such operators. However, the methods proposed to obtain weak and strong phases by relating $B\toππ$, $B\toπK$ and $B\to KK$ decays through flavor SU(3) will be invalidated if electroweak penguins are large. We show that, although the introduction of electroweak penguin contributions introduces no new amplitudes of flavor SU(3), there are a number of ways to experimentally measure the size of such effects. Finally, using SU(3) amplitude relations we present a new way of measuring the weak angle $γ$ which holds even in the presence of electroweak penguins.

hep-ph↗

arXiv1995

Large CP Asymmetries in $B^{\pm}\toη_c(χ_{c0})π^{\pm}$ from $η_c(χ_{c0})$ Width

We study CP asymmetries in $B^{\pm}\to hπ^{\pm}$ decays, where the hadronic states $h=ρρ, K\Kbarπ$, $π^+π^-K^+K^-$, etc., and $h=π^+π^-, K^+K^-, 2(π^+π^-)$, etc., are taken on the resonances $η_c$ and $χ_{c0}$, respectively. The relatively large $η_c$ and $χ_{c0}$ decay widths, of about 10$-$15 MeV, provide the necessary absorptive phase in the interference between the resonance (going through $b\to c\cbar d$) and the background (through $b\to u\ubar d$) contributions to the amplitude. Large asymmetries of order 10$\%$ or more are likely in some modes.

hep-ph↗

arXiv1994

Testing the Standard Model of CP Violation in the B System

We review the subject of CP violation in the $B$ meson system within the Standard Model of CP violation, which is based on a complex phase in the Cabibbo-Kobayashi-Maskawa (CKM) matrix. Three kinds of CP nonconservation are studied: In $B^0-\Bbar$ mixing, in mixed neutral $B$ decays to states which are common decay products of $B^0$ and $\Bbar$ and in direct decays of charged $B$ mesons. Measurements of certain CP asymmetries are shown to determine the three angles of the CKM unitarity triangle. $β$ is measured cleanly in $B^0\toψK_S$. Uncertainties due to penguin amplitudes in the determination of $α$ using the asymmetry in $B^0\to π^+π^-$ (or $B^0 \to ρ^+π^-$) can be eliminated (or in the worst case only estimated) by relating the rate of this process to decay rates involving other two light pseudoscalars. The angle $γ$ can be measured in charged $B$ decays, provided that color suppression in $B\to DK$ (or $B\to DK_i(1400)$) is not too strong and/or that certain rescattering effects in $B$ decays to two light pseudoscalars are not too large.

hep-ph↗

arXiv1994

CP Violation

We review the present status of the Standard Model of CP violation, which is based on a complex phase in the Cabibbo-Kobayashi- Maskawa (CKM) matrix. So far CP violation has been observed only in $K^0-\Kbar$ mixing, consistent with a sizable phase. The implications of future CP nonconserving measurements in $K$ and $B$ decays are discussed within the model. Direct CP violation in $K\to 2π$ may be observed in the near future, however this would not be a powerful test of the model. $B$ decays provide a wide variety of CP asymmetry measurements, which can serve as precise tests of the Standard Model in cases where the asymmetry is cleanly related to phases of CKM matrix elements. Some of the most promising cases are discussed.

hep-ph↗

arXiv1994

Enhancement of CP Violation in B^+- to K_i^+- D^0 By Resonant Effects

Resonance width effects in charged $B$ decays to neutral $D$ mesons and excited kaon states $K_i$ around 1400 MeV are shown to lead to large calculable final state phases. $CP$ asymmetries are defined for any charged $B$ decay to three pseudoscalar mesons involving intermediate overlapping resonance states. Asymmetries up to about 10$\%$ are found in $B^+\to K^+_i D^0\to (Kπ)^+ D^0$. Decay distributions can be used to determine the weak phase $γ$ of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. No separation of the contributions from individual resonances is required.

hep-ph↗

arXiv1994

Measuring Strong and Weak Phases in Time-Independent B Decays

Flavor SU(3) symmetry implies certain relations among $B$-decay amplitudes to $ππ$, $πK$ and $K {\bar K}$ final states, when annihilation-like diagrams are neglected. Using three triangle relations, we show how to measure the weak CKM phases $α$ and $γ$ using time-independent rate measurements only. In addition, one obtains all the strong final-state phases and the magnitudes of individual terms describing tree (spectator), color-suppressed and penguin diagrams. Many independent measurements of these quantities can be made with this method, which helps to eliminate possible discrete ambiguities and to estimate the size of SU(3)-breaking effects.

hep-ph↗

arXiv1994

Decays of $B$ Mesons to Two Light Pseudoscalars

The decays $B \to PP$, where $P$ denotes a pseudoscalar meson, are analyzed, with emphasis on charmless final states. Numerous triangle relations for amplitudes hold within SU(3) symmetry, relating (for example) the decays $B^+ \to π^+ π^0,~ π^0 K^+$, and $π^+ K^0$. Such relations can improve the possibilities for early detection of $CP$-violating asymmetries. Within the context of a graphical analysis of decays, relations are analyzed among SU(3) amplitudes which hold if some graphs are neglected. One application is that measurements of the rates for the above three $B^+$ decays and their charge-conjugates can be used to determine a weak CKM phase. With measurements of the remaining rates for $B$ decays to $ππ,~πK$, and $K \bar K$, one can obtain two CKM phases and several differences of strong phase shifts.

hep-ph↗

arXiv1994

Weak Coupling Phase from Decays of Charged B Mesons to $πK$ and $ππ$

The theory of $CP$ violation based on phases in weak couplings in the Cabibbo-Kobayashi-Maskawa (CKM) matrix requires the phase $γ\equiv {\rm Arg~} V^*_{ub}$ (in a standard convention) to be nonzero. A measurement of $γ$ is proposed based on charged $B$ meson decay rates to $π^+ K^0$, $π^0 K^+$, $π^+ π^0$, and the charge-conjugate states. The corresponding branching ratios are expected to be of the order of $10^{-5}$. (submitted to Physical Review Letters)

hep-ph↗

arXiv1994

The Chirality of $b$ Quark Couplings

This review addresses the question of the chirality of $b$ quark weak couplings from a theoretical and from a purely phenomenological point of view. Due to their small magnitude $b$ decay couplings are subject to possible large corrections from right-handed terms, on the one hand, and do not affect the weak interactions of the first two quark families in any observable manner, on the other hand. This motivated an $SU(2)_L\times SU(2)_R\times U(1)$ model with purely right-handed $b$-decay couplings. The model is consistent with experiments, including recent measurements of a lepton forward-backward asymmetry in $B\to D^*\ellν$ and of radiative $B$ decays. Parity violating asymmetries in semileptonic decays of polarized $Λ_b$ baryons produced in $Z^0$ decays provide a promising way of measuring the chirality of the $b$ to $c$ current.

hep-lat↗