arXiv subjects

Robert Fleischer

Publications and source records attributed to Robert Fleischer.

At least 127 records · Page 7Linked to original sources

arXiv2002

CP Violation in the B System and Relations to $K\toπν\barν$ Decays

A review of CP violation in the $B$ system and strategies to determine the unitarity triangle of the CKM matrix is given. We begin with an introduction to the description of CP violation in the Standard Model of electroweak interactions, and discuss the basic features of the theoretical framework to deal with non-leptonic B decays, which play the main role in this review. After a brief look at CP violation in the kaon system and a discussion of the rare decays $K^+\toπ^+ν\barν$ and $K_L\toπ^0ν\barν$, we turn to the formalism of $B^0_{d,s}$--$\bar{B^0_{d,s}}$ mixing, allowing us to explore important $B$-factory benchmark modes and the $B_s$-meson system. We then focus on charged B decays, $B\toπK$ modes and the phenomenology of $U$-spin related B decays, including the $B_d\toπ^+π^-$, $B_s\to K^+K^-$ system. Finally, we discuss a particularly simple -- but very predictive -- scenario for new physics, which is provided by models with ``minimal flavour violation''. In this framework, various bounds can be derived and interesting connections between the $B$ system and the rare kaon decays $K^+\toπ^+ν\barν$ and $K_L\toπ^0ν\barν$ arise.

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arXiv2001

Extraction of gamma

After a brief look at the well-known standard approaches to determine the angle gamma of the unitarity triangle, we focus on two kinds of strategies, employing $B\toπK$ modes, and U-spin-related B decays. Interesting "puzzles", which may already be indicated by the present B-factory data, are pointed out, and the importance of the extraction of hadronic parameters, which are provided by these strategies as by-products, is emphasized.

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arXiv2001

Bounds on the Unitarity Triangle, $\sin 2β$ and $K\toπν\barν$ Decays in Models with Minimal Flavour Violation

We present a general discussion of the unitarity triangle from $ε_K$, $ΔM_{d,s}$ and $K \to πν\overlineν$ in models with minimal flavour violation (MFV), allowing for arbitrary signs of the generalized Inami--Lim functions $F_{tt}$ and $X$ relevant for $(ε_K,ΔM_{d,s})$ and $K \to πν\overlineν$, respectively. In the models in which $F_{tt}$ has a sign opposite to the one in the Standard Model, i.e. $F_{tt}<0$, the data for $(ε_K, ΔM_{d,s})$ imply an absolute lower bound on the $B_d\toψK_{S}$ CP asymmetry $a_{ψK_S}$ of 0.69, which is substantially stronger than 0.42 arising in the case of $F_{tt}>0$. An important finding of this paper is the observation that for given $Br(K^+\toπ^+ν\overlineν)$ and $a_{ψK_S}$ only two values for $Br(K_{L}\toπ^0ν\overlineν)$, corresponding to the two signs of $X$, are possible in the full class of MFV models, independently of any new parameters arising in these models. This provides a powerful test for this class of models. Moreover, we derive absolute lower and upper bounds on $Br(K_{L}\toπ^0ν\overlineν)$ as functions of $Br(K^+\toπ^+ν\overlineν)$. Using the present experimental upper bounds on $Br(K^+\toπ^+ν\overlineν)$ and $|V_{ub}/V_{cb}|$, we obtain the absolute upper bound $Br(K_{L}\toπ^0ν\overlineν)< 7.1 \cdot 10^{-10}$ (90% C.L.).

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arXiv2001

Exploring New Physics in the $B\to ϕK$ System

Employing the SU(2) isospin symmetry of strong interactions and estimates borrowed from effective field theory, we explore the impact of new physics on the decays $B^\pm\to ϕK^\pm$ and $B_d\to ϕK_S$ in a model-independent manner. To this end, we introduce - in addition to the usual mixing-induced CP asymmetry in $B_d\to ϕK_S$ - a set of three observables, which may not only provide smoking-gun signals for new-physics contributions to different isospin channels, but also valuable insights into hadron dynamics. Imposing dynamical hierarchies of amplitudes, we discuss various patterns of these observables, including also scenarios with small and large rescattering processes. Whereas the $B\toϕK$ system provides, in general, a powerful tool to search for indications of new physics, there is also an unfortunate case, where such effects cannot be distinguished from those of the Standard Model.

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arXiv2001

In Pursuit of New Physics with B_s Decays

The presence of a sizeable CP-violating phase in B_s^0-B_s^0-bar mixing would be an unambiguous signal of physics beyond the Standard Model. We analyse various possibilities to detect such a new phase considering both tagged and untagged decays. The effects of a sizeable width difference Delta Gamma between the B_s mass eigenstates, on which the untagged analyses rely, are included in all formulae. A novel method to find this phase from simple measurements of lifetimes and branching ratios in untagged decays is proposed. This method does not involve two-exponential fits, which require much larger statistics. For the tagged decays, an outstanding role is played by the observables of the time-dependent angular distribution of the B_s -> J/psi [-> l^+ l^-] ϕ[-> K^+K^-] decay products. We list the formulae needed for the angular analysis in the presence of both a new CP-violating phase and a sizeable Delta Gamma, and propose methods to remove a remaining discrete ambiguity in the new phase. This phase can therefore be determined in an unambiguous way.

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arXiv2001

General Analysis of New Physics in $B\to J/ψK$

We present a model-independent parametrization of the $B^\pm\to J/ψK^\pm$, $B_d\to J/ψK_S$ decay amplitudes by taking into account the constraints that are implied by the isospin symmetry of strong interactions. Employing estimates borrowed from effective field theory, we explore the impact of physics beyond the Standard Model and introduce -- in addition to the usual mixing-induced CP asymmetry $A_{CP}^{mix}$ in $B_d\to J/ψK_S$ -- a set of three observables, allowing a general analysis of possible new-physics effects in the $B\to J/ψK$ system. Imposing a dynamical hierarchy of amplitudes, we argue that one of these observables may already be accessible at the first-generation $B$-factories, whereas the remaining ones will probably be left for second-generation $B$ experiments. However, in the presence of large rescattering effects, all three new-physics observables may be sizeable. We also emphasize that a small value of $A_{CP}^{mix}$ could be due to new-physics effects arising at the $B\to J/ψK$ decay-amplitude level. In order to establish such a scenario, the observables introduced in this paper play a key role.

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arXiv2000

B Physics and CP Violation

After an introduction to the Standard-Model description of CP violation and a brief look at the present status of this phenomenon in the kaon system, a classification of non-leptonic B-decays is given and the formalism of $B^0_{d,s}$--$\bar{B^0_{d,s}}$ mixing is discussed. We then turn to the $B$-factory benchmark modes, CP violation in charged B decays, and the $B_s$-meson system. Finally, we focus both on $B\toπK$ decays, which play an important role to probe the CKM angle $γ$, and on the $B_d\toπ^+π^-$, $B_s\to K^+K^-$ system, which allows an interesting determination of $β$ and $γ$.

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arXiv2000

Constraints on $γ$ and Strong Phases from $B\toπK$ Decays

As we pointed out recently, the neutral decays $B_d\toπ^\mp K^\pm$ and $B_d\toπ^0K$ may provide non-trivial bounds on the CKM angle $γ$. Here we reconsider this approach in the light of recent CLEO data, which look very interesting. In particular, the results for the corresponding CP-averaged branching ratios are in favour of strong constraints on $γ$, where the second quadrant is preferred. Such a situation would be in conflict with the standard analysis of the unitarity triangle. Moreover, constraints on a CP-conserving strong phase $δ_n$ are in favour of a negative value of $\cosδ_n$, which would be in conflict with the factorization expectation. In addition, there seems to be an interesting discrepancy with the bounds that are implied by the charged $B\toπK$ system: whereas these decays favour a range for $γ$ that is similar to that of the neutral modes, they point towards a positive value of $\cosδ_c$, which would be in conflict with the expectation of equal signs for $\cosδ_n$ and $\cosδ_c$.

hep-ph↗

arXiv2000

Theoretical Overview of CP Violation in B-Meson Decay

After a brief look at CP violation in kaon decays, a short overview of CP violation in the $B$-meson system and of strategies to determine the angles of the unitarity triangles of the CKM matrix is given. Both general aspects and some recent developments are discussed, including $B_c^\pm\to D^\pm_s D$ and $B\toπK$ decays, as well as the $B_d\toπ^+π^-$, $B_s\to K^+K^-$ system.

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arXiv2000

Exploring CP Violation with $B_c$ Decays

We point out that the pure ``tree'' decays $B_c^\pm\to D^\pm_s D$ are particularly well suited to extract the CKM angle $γ$ through amplitude relations. In contrast to conceptually similar strategies using $B^\pm\to K^\pm D$ or $B_d\to K^{\ast0} D$ decays, the advantage of the $B_c$ approach is that the corresponding triangles have three sides of comparable length and do not involve small amplitudes. Decays of the type $B_c^\pm\to D^\pm D$ -- the $U$-spin counterparts of $B_c^\pm\to D^\pm_s D$ -- can be added to the analysis, as well as channels, where the $D^\pm_s$- and $D^\pm$-mesons are replaced by higher resonances.

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arXiv2000

Constraints on the CKM Angle $γ$ and Strong Phases from $B\toπK$ Decays

As we pointed out recently, the neutral decays $B_d\toπ^\mp K^\pm$ and $B_d\toπ^0K$ may provide non-trivial bounds on the CKM angle $γ$. In this paper, we reconsider this approach in the light of recent CLEO data, which look very interesting. In particular, the results for the corresponding CP-averaged branching ratios are in favour of strong constraints on $γ$, where the second quadrant is preferred. Such a situation would be in conflict with the standard analysis of the unitarity triangle. Moreover, constraints on a CP-conserving strong phase $δ_n$ are in favour of a negative value of $\cosδ_n$, which would be in conflict with the factorization expectation. In addition, there seems to be an interesting discrepancy with the bounds that are implied by the charged $B\toπK$ system: whereas these decays favour a range for $γ$ that is similar to that of the neutral modes, they point towards a positive value of $\cosδ_c$, which would be in conflict with the expectation of equal signs for $\cosδ_n$ and $\cosδ_c$. If future data should confirm this ``puzzle'', it may be an indication for new-physics contributions to the electroweak penguin sector, or a manifestation of large non-factorizable SU(3)-breaking effects.

hep-ph↗

arXiv2000

Constraining Penguin Contributions and the CKM Angle $γ$ through $B_d\toπ^+π^-$

The decays $B_d\toπ^+π^-$ and $B_s\to K^+K^-$ provide an interesting strategy to extract the CKM angle $γ$ at ``second-generation'' $B$-physics experiments of the LHC era. A variant for ``first-generation'' experiments can be obtained, if $B_s\to K^+K^-$ is replaced by $B_d\toπ^\mp K^\pm$. We show that the most recent experimental results for the CP-averaged $B_d\toπ^+π^-$ and $B_d\toπ^\mp K^\pm$ branching ratios imply a rather restricted range for the corresponding penguin parameters, and upper bounds on the direct CP asymmetries $A_{CP}^{dir}(B_d\toπ^+π^-)$ and $A_{CP}^{dir}(B_d\toπ^\mp K^\pm)$. Moreover, we point out that interesting constraints on $γ$ can be obtained from the CP-averaged $B_d\toπ^+π^-$ and $B_d\toπ^\mp K^\pm$ branching ratios, if in addition mixing-induced CP violation in the former decay is measured, and the $B^0_d$--$\bar{B^0_d}$ mixing phase is fixed through $B_d\to J/ψK_S$. An extraction of $γ$ becomes possible, if furthermore direct CP violation in $B_d\toπ^+π^-$ or $B_d\toπ^\mp K^\pm$ is observed.

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arXiv1999

An Analysis of B_s Decays in the Left-Right-Symmetric Model with Spontaneous CP Violation

Non-leptonic B_s decays into CP eigenstates that are caused by \bar b -> \bar cc\bar s quark-level transitions, such as B_s -> D_s^+D^-_s, J/psi eta^(') or J/psi phi, provide a powerful tool to search for ``new physics'', as the CP-violating effects in these modes are tiny in the Standard Model. We explore these effects for a particular scenario of new physics, the left-right-symmetric model with spontaneous CP violation. In our analysis, we take into account all presently available experimental constraints on the parameters of this model, i.e. those implied by K- and B-decay observables; we find that CP asymmetries as large as O(40%) may arise in the B_s channels, whereas the left-right-symmetric model favours a small CP asymmetry in the ``gold-plated'' mode B_d -> J/psi K_S. Such a pattern would be in favour of B-physics experiments at hadron machines, where the B_s modes are very accessible.

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arXiv1999

Searching for New Physics in Non-Leptonic B Decays

We present allowed regions in the space of observables of certain non-leptonic B-meson decays that characterize these modes within the Standard Model. A future measurement of observables lying significantly outside of these regions would indicate the presence of new physics. Making use of SU(3) arguments, we give the range for $B\toπK$ decays, and for the system of $B_d\toπ^+π^-$, $B_s\to K^+K^-$ modes.

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arXiv1999

New Strategies to Extract CKM Phases from Non-Leptonic B Decays

Several new strategies to extract CKM phases, including a determination of $γ$ from $B_{s(d)}\to J/ψK_S$ decays and a general approach, which makes use of the angular distributions of certain $B_{d,s}$ modes, such as $B_d\to J/ψρ^0$ and $B_s\to J/ψϕ$, are discussed. Special emphasis is put on a simultaneous determination of $β$ and $γ$ with the help of the decays $B_d\to π^+ π^-$ and $B_s\to K^+ K^-$, which relies only on the $U$-spin flavour symmetry of strong interactions and is not affected by any penguin or final-state-interaction effects.

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arXiv1999

Recent Theoretical Developments in CP Violation in the B System

After a brief review of the present status of the standard methods to extract CKM phases from CP-violating effects in non-leptonic B-decays, an overview of recent theoretical developments in this field is given, including extractions of $γ$ from $B\toπK$ and $B_{s(d)}\to J/ψK_S$ decays, a simultaneous determination of $β$ and $γ$, which is provided by the modes $B_d\to π^+ π^-$ and $B_s\to K^+ K^-$, and extractions of CKM phases from angular distributions of certain $B_{d,s}$ decays, such as $B_d\to J/ψρ^0$ and $B_s\to J/ψϕ$.

hep-ph↗

arXiv1999

Extracting CKM Phases from Angular Distributions of $B_{d,s}$ Decays into Admixtures of CP Eigenstates

The time-dependent angular distributions of certain $B_{d,s}$ decays into final states that are admixtures of CP-even and CP-odd configurations provide valuable information about CKM phases and hadronic parameters. We present the general formalism to accomplish this task, taking also into account penguin contributions, and illustrate it by considering a few specific decay modes. We give particular emphasis to the decay $B_d\to J/ψρ^0$, which can be combined with $B_s\to J/ψϕ$ to extract the $B^0_d - \bar{B^0_d}$ mixing phase and - if penguin effects in the former mode should be sizeable - also the angle $γ$ of the unitarity triangle. As an interesting by-product, this strategy allows us to take into account also the penguin effects in the extraction of the $B^0_s - \bar{B^0_s}$ mixing phase from $B_s\to J/ψϕ$. Moreover, a discrete ambiguity in the extraction of the CKM angle $β$ can be resolved, and valuable insights into SU(3)-breaking effects can be obtained. Other interesting applications of the general formalism presented in this paper, involving $B_d\toρρ$ and $B_{s,d}\to K^{\ast} \bar{K^\ast}$ decays, are also briefly noted.

hep-ph↗

arXiv1999

A Critical Look at $γ$ Determinations from $B\toπK$ Decays

The determination of the angle $γ$ of the unitarity triangle of the CKM matrix is a challenge for the $B$-factories. In this context, $B\toπK$ decays received a lot of attention, providing various interesting ways to constrain and determine $γ$. These strategies are briefly reviewed, and their virtues and weaknesses are compared with one another.

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