arXiv subjects

Robert Fleischer

Publications and source records attributed to Robert Fleischer.

At least 145 records · Page 8Linked to original sources

arXiv1999

Extracting $γ$ from $B_{s(d)}\to J/ψK_S$ and $B_{d(s)}\to D^{+}_{d(s)} D^{-}_{d(s)}$

A completely general parametrization of the time-dependent decay rates of the modes $B_s\to J/ψK_S$ and $B_d\to J/ψK_S$ is given, which are related to each other through the $U$-spin flavour symmetry of strong interactions. Owing to the interference of current--current and penguin processes, the $B_s\to J/ψK_S$ observables probe the angle $γ$ of the unitarity triangle. Using the $U$-spin symmetry, the overall normalization of the $B_s\to J/ψK_S$ rate can be fixed with the help of the CP-averaged $B_d\to J/ψK_{\rm S}$ rate, providing a new strategy to determine $γ$. This extraction of $γ$ is not affected by any final-state-interaction effects, and its theoretical accuracy is only limited by $U$-spin-breaking corrections. As a by-product, this strategy allows us to take into account also the penguin effects in the determination of $β$ from $B_d\to J/ψK_S$, which are presumably very small, and to predict the direct CP asymmetry arising in this mode. An analogous strategy is provided by the time-dependent $B_d\to D^+ D^-$ rate, if its overall normalization is fixed through the CP-averaged $B_s\to D^+_s D^-_s$ rate.

hep-ph↗

arXiv1999

New Strategies to Extract $β$ and $γ$ from $B_d\to π^+ π^-$ and $B_s\to K^+ K^-$

The decays $B_d\to π^+ π^-$ and $B_s\to K^+ K^-$ are related to each other by interchanging all down and strange quarks, i.e. through the $U$-spin flavour symmetry of strong interactions. A completely general parametrization of the CP-violating observables of these modes is presented within the framework of the Standard Model, allowing the determination of the angles $β$ and $γ$ of the unitarity triangle. This strategy is affected neither by penguin contributions nor by any final-state-interaction effects, and its theoretical accuracy is only limited by $U$-spin-breaking corrections. If the $B^0_d - \bar{B^0_d}$ mixing phase $2β$ is determined separately, for example with the help of $B_d\to J/ψK_S$, $γ$ can be extracted with a reduced $U$-spin flavour symmetry input. A variant of this strategy to determine $γ$, which uses $B_d\toπ^\mp K^\pm$ instead of $B_s\to K^+ K^-$ and relies -- in addition to the SU(3) flavour symmetry -- on a certain dynamical assumption, is also briefly discussed.

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arXiv1998

A General Analysis of $γ$ Determinations from $B\toπK$ Decays

We present a general parametrization of $B^\pm\toπ^\pm K, π^0K^\pm$ and $B_d\toπ^0 K, π^\mp K^\pm$ decays, taking into account both electroweak penguin and rescattering effects. This formalism allows -- among other things -- an improved implementation of the strategies that were recently proposed by Neubert and Rosner to probe the CKM angle $γ$ with the help of $B^\pm\toπ^\pm K, π^0K^\pm$ decays. In particular, it allows us to investigate the sensitivity of the extracted value of $γ$ to the basic assumptions of their approach. We find that certain SU(3)-breaking effects may have an important impact and emphasize that additional hadronic uncertainties are due to rescattering processes. The latter can be controlled by using SU(3) flavour symmetry arguments and additional experimental information provided by $B^\pm\to K^\pm K$ modes. We propose a new strategy to probe the angle $γ$ with the help of the neutral decays $B_d\toπ^0 K, π^\mp K^\pm$, which is theoretically cleaner than the $B^\pm\toπ^\pm K, π^0K^\pm$ approach. Here rescattering processes can be taken into account by just measuring the CP-violating observables of the decay $B_d\toπ^0K_{\rm S}$. Finally, we point out that an experimental analysis of $B_s\to K^+K^-$ modes would also be very useful to probe the CKM angle $γ$, as well as electroweak penguins, and we critically compare the virtues and weaknesses of the various approaches discussed in this paper. As a by-product, we point out a strategy to include the electroweak penguins in the determination of the CKM angle $α$ from $B\toππ$ decays.

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arXiv1998

Towards the Extraction of the CKM Angle $γ$

The determination of the angle $γ$ of the unitarity triangle of the CKM matrix is regarded as a challenge for future $B$-physics experiments. In this context, the decays $B^\pm\to π^\pm K$ and $B_d\toπ^\mp K^\pm$, which were observed by the CLEO collaboration last year, received a lot of interest in the literature. After a general parametrization of their decay amplitudes, strategies to constrain and determine the CKM angle $γ$ with the help of the corresponding observables are reviewed. The theoretical accuracy of these methods is limited by certain rescattering and electroweak penguin effects. It is emphasized that the rescattering processes can be included in the bounds on $γ$ by using additional experimental information on $B^\pm\to K^\pm K$ decays, and steps towards the control of electroweak penguins are pointed out. Moreover, strategies to probe the CKM angle $γ$ with the help of $B_s\to K\bar{K}$ decays are briefly discussed.

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arXiv1998

CP Violation in B Decays and Strategies for Extracting CKM Phases

A brief review of CP violation in the $B$-meson system and of strategies to determine the angles $α$, $β$ and $γ$ of the unitarity triangle of the CKM matrix is given. Both general aspects and some recent developments are discussed, including a critical look at the ``benchmark'' modes, CP violation in penguin decays, $B_s$ decays in the light of the width difference $ΔΓ_s$, charged $B$ decays, and strategies to probe the CKM angle $γ$ with $B\toπK$ modes.

hep-ph↗

arXiv1998

Probing the CKM Angle $γ$ with $B\toπK$ Decays

The decays $B^\pm\to π^\pm K$ and $B_d\to π^\mp K^\pm$ were observed by the CLEO collaboration last year; they may play an important role to probe the angle $γ$ of the unitarity triangle of the CKM matrix. After a general parametrization of their decay amplitudes within the Standard Model, strategies to constrain and determine the CKM angle $γ$ with the help of the corresponding CP-conserving and CP-violating observables are briefly reviewed. The theoretical accuracy of these methods is limited by certain rescattering and electroweak penguin effects. It is emphasized that the rescattering processes can be included in the bounds on $γ$ by using additional experimental information on $B^\pm\to K^\pm K$ decays, and steps towards the control of electroweak penguins are pointed out.

hep-ph↗

arXiv1998

Penguin Topologies, Rescattering Effects and Penguin Hunting with $B_{u,d}\to K\bar{K}$ and $B^\pm\toπ^\pm K$

In the recent literature, constraints on the CKM angle $γ$ arising from the branching ratios for $B^\pm\toπ^\pm K$ and $B_d\toπ^\mp K^\pm$ decays received a lot of attention. An important theoretical limitation of the accuracy of these bounds is due to rescattering effects, such as $B^+\to\{π^0K^+\}\toπ^+K^0$. We point out that these processes are related to penguin topologies with internal up quark exchanges and derive SU(2) isospin relations among the $B^+\toπ^+K^0$ and $B_d^0\toπ^-K^+$ decay amplitudes by defining ``tree'' and ``penguin'' amplitudes in a proper way, allowing the derivation of generalized bounds on the CKM angle $γ$. We propose strategies to obtain insights into the dynamics of penguin processes with the help of the decays $B_{u,d}\to K\bar{K}$ and $B^\pm\toπ^\pm K$, derive a relation among the direct CP-violating asymmetries arising in these modes, and emphasize that rescattering effects can be included in the generalized bounds on $γ$ completely this way. Moreover, we have a brief look at the impact of new physics.

hep-ph↗

arXiv1998

Towards Extractions of the CKM Angle $γ$ from $B_{u,d}\toπK$ and Untagged $B_s\to K\bar{K}$ Decays

The decays $B_d\toπ^\mp K^\pm$ and $B^\pm\toπ^\pm K$ provide interesting constraints on the angle $γ$ of the unitarity triangle of the CKM matrix. It is shown that bounds on $γ$ can also be obtained from the time evolution of untagged $B_s\to K^+K^-$ and $B_s\to K^0\bar{K^0}$ decays, provided the $B_s$ system exhibits a sizeable width difference $ΔΓ_s$. A detailed discussion of rescattering processes and electroweak penguin effects, which limit the theoretical accuracy of these constraints, and of methods to control them through experimental data is given. Moreover, strategies are pointed out to go beyond these bounds by relating the $B_{u,d}\toπK$ and untagged $B_s\to K\bar{K}$ decays through the SU(3) flavour symmetry of strong interactions. If a tagged, time-dependent measurement of the $B_s\to K^+K^-$ and $B_s\to K^0\bar{K^0}$ modes should become possible, $γ$ could be determined from the corresponding observables in a way that makes use of only the SU(2) isospin symmetry and takes into account rescattering effects ``automatically''. The impact of new-physics contributions to $B^0_s - \bar{B^0_s}$ mixing is also analysed, and interesting features arising in such a scenario of physics beyond the Standard Model are pointed out.

hep-ph↗

arXiv1998

Controlling Rescattering Effects in Constraints on the CKM Angle $γ$ arising from $B\toπK$ Decays

It has recently been pointed out that the observables of the decay $B^+\to K^+\bar{K^0}$ and its charge conjugate allow us to take into account rescattering effects in constraints on the CKM angle $γ$ arising from $B^\pm\toπ^\pm K$ and $B_d\toπ^\pm K^\pm$ modes, and that they play an important role to obtain insights into final-state interactions. In this paper, the formalism needed to accomplish this task is discussed in detail. Furthermore, using a transparent model to describe the rescattering processes, as well as electroweak penguins, we calculate the quantities parametrizing the $B^+\toπ^+ K^0$ and $B_d^0\toπ^- K^+$ decay amplitudes for specific examples, and illustrate the constraints on $γ$ arising from the corresponding observables. Although this model is very crude, it shows nicely the power of $B^\pm\to K^\pm K$ both to include the rescattering effects in the bounds on $γ$ and to obtain insights into final-state interactions. Moreover this model exhibits the interesting feature that the combined branching ratio BR$(B^\pm\to K^\pm K)$ may be considerably enhanced through rescattering processes, as was recently pointed out within a general framework.

hep-ph↗

arXiv1998

Extracting CKM Phases and $B_s - \bar{B}_s$ Mixing Parameters from Angular Distributions of Non-Leptonic B Decays

Suggestions for efficiently determining the lifetimes and mass difference of the light and heavy $B_s$ mesons ($B_s^L, B_s^H$) from $B_s \to J/ ψϕ, D_s^{*+}D_s^{*-}$ decays are given. Using appropriate weighting functions for the angular distributions of the decay products (moment analysis), one can extract $(Γ_H, Γ_L, Δm)_{B_s}$. Such a moment analysis allows the determination of the relative magnitudes and phases of the CP-odd and CP-even decay amplitudes. Efficient determinations of CP-violating effects occuring in $B_s \to J/ψϕ, D_s^{*+} D_s^{*-}$ are discussed in the light of a possible width difference $(ΔΓ)_{B_s}$, and the utility of this method for $B \to J/ψK^*, D^{\ast +}_s \bar D^{\ast}$ decays is noted. Since our approach is very general, it can in principle be applied to all kinds of angular distributions and allows the determination of all relevant observables, including fundamental CKM (Cabibbo-Kobayashi-Maskawa) parameters, as well as tests of various aspects of the factorization hypothesis. Explicit angular distributions and weighting functions are given, and the general method that can be used for any angular distribution is indicated.

hep-ph↗

arXiv1998

Resolving a Discrete Ambiguity in the CKM Angle $β$ through $B_{u,d} \to J/ψK^\ast$ and $B_s \to J/ψϕ$ Decays

It is well known that $\sin(2β)$, where $β$ is one of the angles of the unitarity triangle of the CKM matrix, can be determined in a theoretically clean way by measuring mixing-induced CP violation in the decay $B_d \to J/ψK_S$. Another clean extraction of this CKM angle is provided by the time-dependent angular distribution for the decay products of $B_d \to J/ψ(\to l^+l^-) K^{\ast0}(\to π^0 K_S)$, where we have more observables at our disposal than in the case of $B_d \to J/ψK_S$, so that in addition to $\sin(2β)$ also $\cos(2β)$ can be probed in a direct way. Unfortunately a sign ambiguity remains in $\cos(2β)$. If it could be resolved, a discrete ambiguity in the extraction of the CKM angle $β$ could be resolved as well, which would allow a more incisive test of the CKM model of CP violation. This note shows that detailed time-dependent studies of $B_{u,d} \to J/ψK^{\ast}$ and $B_s \to J/ψϕ$ decay processes can determine the sign of $\cos(2β)$, thereby removing the corresponding ambiguity in the extraction of the CKM angle $β$.

hep-ph↗

arXiv1998

Rescattering and Electroweak Penguin Effects in Strategies to Constrain and Determine the CKM Angle $γ$ from $B\toπK$ Decays

A general parametrization of the $B^+\toπ^+ K^0$ and $B_d^0\toπ^- K^+$ decay amplitudes is presented. It relies only on the isospin symmetry of strong interactions and the phase structure of the Standard Model and involves no approximations. In particular, this parametrization takes into account both rescattering and electroweak penguin effects, which limit the theoretical accuracy of bounds on $γ$ arising from the combined $B^\pm\toπ^\pm K$, $B_d\toπ^\mp K^\pm$ branching ratios. Generalized bounds making also use of the CP asymmetry in the latter decay are derived, and their sensitivity to possible rescattering and electroweak penguin effects is investigated. It is pointed out that experimental data on $B^\pm\to K^\pm K$ allow us to include rescattering processes in these bounds completely, and an improved theoretical treatment of electroweak penguins is presented. It is argued that rescattering effects may enhance the combined $B^\pm\to K^\pm K$ branching ratio by a factor of ${\cal O}(10)$ to the $10^{-5}$ level, and that they may be responsible for the small present central value of the ratio of the combined $B_d\toπ^\mp K^\pm$ and $B^\pm\toπ^\pm K$ branching ratios, which has recently been reported by the CLEO collaboration and, if confirmed, would exclude values of $γ$ within a large region around $90^\circ$.

hep-ph↗

arXiv1997

CP Violation and Strategies for Extracting CKM Phases

The phenomenon of CP violation and strategies for extracting the angles of the unitarity triangle are reviewed. Special emphasis is given to the B-meson system, as it plays an outstanding role to test the Standard Model description of CP violation at future experimental B-physics facilities. Both general aspects and recent developments are discussed. It is pointed out that combined branching ratios for $B_{u,d}\toπK$ modes, which have been observed recently by the CLEO collaboration, and untagged $B_s\to K\bar{K}$ decays may allow us to derive interesting constraints on the CKM angle $γ$ and may eventually lead to a solid determination of this angle.

hep-ph↗

arXiv1997

CP Violation Beyond the Standard Model

Recent developments concerning CP violation beyond the Standard Model are reviewed. The central target of this presentation is the $B$ system, as it plays an outstanding role in the extraction of CKM phases. Besides a general discussion of the appearance of new physics in the corresponding CP-violating asymmetries through $B^0_q$--$\bar{B^0_q}$ mixing $(q\in\{d,s\})$, it is emphasized that CP violation in non-leptonic penguin modes, e.g. in $B_d\toϕK_{S}$, offers a powerful tool to probe physics beyond the Standard Model. In this respect $B\toπK$ modes, which have been observed recently by the CLEO collaboration, may also turn out to be very useful. Their combined branching ratios allow us to constrain the CKM angle $γ$ and may indicate the presence of physics beyond the Standard Model.

hep-ph↗

arXiv1997

Current Issues in CP Violation

A brief review of CP violation in $K$ and $B$ decays is given. While the observables $\varepsilon$ and Re$(\varepsilon'/\varepsilon)$ describing CP violation in neutral $K$ decays do not allow a powerful test of the CKM mechanism of CP violation, rare $K\toπν\overlineν$ decays and in particular the $B$-meson system are much more promising in this respect. After a brief look at the $K$ system, selected aspects of CP-violating effects in $B$ decays are discussed. It is pointed out that combined branching ratios for $B\toπK$ modes, which have been observed recently by the CLEO collaboration, may allow to derive stringent constraints on the CKM angle $γ$ that could open a window to new physics.

hep-ph↗

arXiv1997

New physics in penguin dominated $B \to πK$ decays

Measurements of the combined branching ratios for $B^\pm \to π^\pm K$ and $B_d \to π^\mp K^\pm$ allow interesting constraints on the CKM angle $γ$, the ratio $r \equiv |T'|/|P'|$ of the current-current and penguin operator contributions to $B_d \to π^\mp K^\pm$, and the CP asymmetry in that decay. Present CLEO results for these branching ratios indicate where problems with consistency of the Standard Model may arise in the future. In this paper we discuss scenarios of new physics in these decays and investigate their implications for the above constraints.

hep-ph↗

arXiv1997

CP Violation in $B_s$ Decays

CP-violating effects in non-leptonic $B_s$-meson decays are reviewed. Special emphasis is given to implications arising from the width difference $ΔΓ_s$ between the $B_s$ mass eigenstates. If $ΔΓ_s$ is found to be sizable, certain untagged $B_s$-meson decays may allow interesting probes of CP violation, extractions of the CKM angle $γ$ and the Wolfenstein parameter $η$, and may indicate physics beyond the Standard Model.

hep-ph↗

arXiv1997

Constraining the CKM angle $γ$ and penguin contributions through combined $B \to πK$ branching ratios

Motivated by recent CLEO measurements of $B\toπK$ modes, we investigate their implications for the CKM angle $γ$ and a consistent description of these decays within the Standard Model. Interestingly it turns out that already the measurement of the combined branching ratios $B^\pm\toπ^\pm K$ and $B_d\toπ^\mp K^\pm$ allows to derive stringent constraints on $γ$ which are complementary to the presently allowed range for that angle. This range, arising from the usual fits of the unitarity triangle, is typically symmetric around $γ= 90^\circ$, while our method can in principle exclude a range of this kind. Consistency within the Standard Model implies furthermore bounds on the ratio $r\equiv|T'|/|\tilde P|$ of the current-current and penguin operator contributions to $B_d\toπ^\mp K^\pm$, and upper limits for the CP-violating asymmetry arising in that decay. Commonly accepted means to estimate $r$ yield values at the edge of compatibility with the present CLEO measurements.

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