arXiv subjects

Robert Fleischer

Publications and source records attributed to Robert Fleischer.

At least 91 records · Page 5Linked to original sources

arXiv2007

CP Violation and B Physics at the LHC

In this decade, there are huge efforts to explore B-meson decays, which provide an interesting playground for stringent tests of the Standard-Model description of the quark-flavour sector and the CP violation residing there. Thanks to the $e^+e^-$ B factories at KEK and SLAC, CP violation is now a well-established phenomenon in the B-meson system, and recently, also $B^0_s$--$\bar B^0_s$ mixing could be measured at the Tevatron. The decays of $B^0_s$ mesons are the key target of the B-physics programme at the LHC, and will be the focus of this presentation, discussing the theoretical aspects of various benchmark channels and the question of how much space for new-physics effects in their observables is left by the recent experimental results.

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arXiv2007

On Puzzles and Non-Puzzles in B -> pi pi, pi K Decays

Recently, we have seen interesting progress in the exploration of CP violation in B^0_d -> pi^+ pi^-: the measurements of mixing-induced CP violation by the BaBar and Belle collaborations are now in good agreement with each other, whereas the picture of direct CP violation is still unclear. Using the branching ratio and direct CP asymmetry of B^0_d -> pi^- K^+, this situation can be clarified. We predict A_CP^dir(B_d -> pi^+ pi^-) = -0.24+-0.04, which favours the BaBar result, and extract gamma=(70.0^{+3.8}_{-4.3})deg, which agrees with the unitarity triangle fits. Extending our analysis to other B -> pi K modes and B^0_s -> K^+ K^- with the help of the SU(3) flavour symmetry and plausible dynamical assumptions, we find that all observables with colour-suppressed electroweak penguin contributions are measured in excellent agreement with the Standard Model. As far as the ratios R_{c,n} of the charged and neutral B -> pi K branching ratios are concerned, which are sizeably affected by electroweak penguin contributions, our Standard-Model predictions have almost unchanged central values, but significantly reduced errors. Since the new data have moved quite a bit towards these results, the "B -> pi K puzzle" for the CP-conserving quantities has been significantly reduced. However, the mixing-induced CP violation of B^0_d -> pi^0 K_S does look puzzling; if confirmed by future measurements, this effect could be accommodated through a modified electroweak penguin sector with a large CP-violating new-physics phase. Finally, we point out that the established difference between the direct CP asymmetries of B^+- -> pi^0 K^+- and B_d -> pi^-+ K^+- appears to be generated by hadronic and not by new physics.

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arXiv2007

The B -> pi K Puzzle: A Status Report

We discuss the theoretical interpretation of the $B\toπK$ system in the light of new data. Using the branching ratio and direct CP asymmetry of $B^0_d\toπ^-K^+$, the picture of the direct CP violation in $B_d^0\toπ^+π^-$ could be clarified: we predict $A_{CP}^{dir}(B_d\toπ^+π^-)=-0.24\pm0.04$, which favours the BaBar measurement, and extract $γ=(70.0^{+3.8}_{-4.3})^\circ$, in agreement with the Standard-Model fits of the unitarity triangle. All $B\toπK$ modes with colour-suppressed electroweak penguin contributions are found in excellent agreement with the Standard Model. The data for the ratios $R_{c,n}$ of the charged and neutral $B\toπK$ branching ratios, which are sizeably affected by electroweak penguin contributions, have moved quite a bit towards the Standard-Model predictions, which are almost unchanged, thereby reducing the "$B\toπK$ puzzle". On the other hand, the mixing-induced CP violation of $B^0_d\toπ^0 K_S$ still looks puzzling and could be accommodated through a modified electroweak penguin sector with a large CP-violating new-physics phase, while the observed non-vanishing difference between the direct CP asymmetries of $B^\pm\toπ^0K^\pm$ and $B_d\toπ^\mp K^\pm$ seems to be caused by hadronic and not by new physics.

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arXiv2007

Theoretical Review of $γ/ϕ_3$ Measurements with $B_s$ Decays to Charm

We give an overview of various determinations of $γ/ϕ_3$ with the help of $B_s$ decays into charmed final states, distinguishing between transitions with tree and penguin contributions and pure tree decays. In the corresponding strategies, the $U$-spin flavour symmetry of strong interactions provides a very useful tool, and offers interesting "by-producs" for the $B$-physics programme at the LHC, including the control of the penguin uncertainties in the determinations of the $B^0_d$-$\bar B^0_d$ and $B^0_s$--$\bar B^0_s$ mixing phases $ϕ_d$ and $ϕ_s$ from $B_d\to J/ψK_S$ and $B_s\to J/ψϕ$, respectively, and an alternative extraction of the latter phase through $B_s\to D_s^+D_s^-$. Finally, we point out that the cleanest determinations of the mixing phases $ϕ_s$ and $ϕ_d$ are offered by the pure tree decays $B_s\to D_\pm K_{S(L)}$ and $B_d\to D_\pmπ^0, D_\pmρ^0, ...$, respectively, which are very interesting for the searches of new physics.

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arXiv2006

Flavour Physics and CP Violation

The starting point of these lectures is an introduction to the weak interactions of quarks and the Standard-Model description of CP violation, where the central role is played by the Cabibbo-Kobayashi-Maskawa matrix and the corresponding unitarity triangles. Since the B-meson system will govern the stage of (quark) flavour physics and CP violation in this decade, it will be our main focus. We shall classify B-meson decays, introduce the theoretical tools to deal with them, investigate the requirements for non-vanishing CP-violating asymmetries, and discuss the main strategies to explore CP violation and the preferred avenues for physics beyond the Standard Model to enter. This formalism is then applied to discuss the status of important B-factory benchmark modes, where we focus on puzzling patterns in the data that may indicate new-physics effects, as well as the prospects for B-decay studies at the LHC.

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arXiv2006

In Pursuit of New Physics in the B System

The B-meson system offers interesting probes for the search of physics beyond the Standard Model. After addressing possible signals of new-physics contributions to the B -> phi K and B -> pi K decay amplitudes, we focus on the data for B^0_q-\bar B^0_q mixing (q = d, s), giving a critical discussion of their interpretation in terms of model-independent new-physics parameters. We address, in particular, the impact of the uncertainties of the relevant input parameters, discuss benchmarks for future precision measurements at the LHC, and explore the prospects for new CP-violating effects in the B_s-meson system, which could be detected at the LHC.

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arXiv2006

Probing New Physics through B Mixing: Status, Benchmarks and Prospects

As is well known, $B^0_{d,s}$--$\bar B^0_{d,s}$ mixing offers a profound probe into the effects of physics beyond the Standard Model. The data obtained at the $e^+e^-$ $B$ factories have already provided valuable insights into the $B_d$-meson system, and very recently also the $B^0_s$--$\bar B^0_s$ oscillation frequency $ΔM_s$ has been measured at the Tevatron. We give a critical discussion of the interpretation of these data in terms of model-independent new-physics parameters. We address in particular the impact of the uncertainties of the relevant input parameters, set benchmarks for their accuracies as required by future precision measurements at the LHC, and explore the prospects for new CP-violating effects in the $B_s$ system. To complement our model-independent analysis, we also discuss the constraints imposed by the CDF measurement of $ΔM_s$ on popular models of new physics, namely scenarios with an extra $Z'$ boson and supersymmetry. We find that the new data still leave sizeable room for new-physics contributions to $B^0_{s}$--$\bar B^0_{s}$ mixing, which could be detected at the LHC.

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arXiv2005

CP Violation in the B System: Status and Perspectives

In this decade, the exploration of CP violation is governed by the B-meson system, where non-leptonic decays play an outstanding role. To set the stage, we have first a look at the main strategies to circumvent the calculation of the relevant hadronic matrix elements in these studies, and discuss popular avenues for physics beyond the Standard Model to enter the roadmap of quark-flavour physics. We are then well prepared to analyze puzzles in the data for B -> phi K and B -> pi K decays, and to discuss b -> d penguin processes, which represent a new territory for the B-factory studies. Finally, we turn to the physics potential of the Bs-meson system, which can be fully exploited at the LHC.

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arXiv2005

Highlights of the B-Physics Landscape

The exploration of the quark-flavour sector of the Standard Model is one of the hot topics in particle physics of this decade. In these studies, which show a fruitful interplay between theory and experiment, the B-meson system offers a particularly interesting laboratory. After giving an introduction to quark-flavour mixing and CP violation as well as to the theoretical tools to deal with non-leptonic B decays, we discuss popular avenues for new physics to enter the roadmap of quark-flavour physics. This allows us to have a detailed look at the B-factory benchmark modes $B^0_d\to J/ψK_S$, $B^0_d\to ϕK_S$ and $B^0_d\toπ^+π^-$, with a particular emphasis of the impact of new physics. We then perform an analysis of the $B\toπK$ puzzle, which may indicate new sources of CP violation in the electroweak penguin sector, and discuss its implications for rare B and K decays. The next topic is given by $b\to d$ penguin processes, which are now starting to become accessible at the B factories, thereby representing a new territory of the B-physics landscape. Finally, we discuss the prospects for B-decay studies at the Large Hadron Collider, where the $B^0_s$-meson system plays an outstanding role.

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arXiv2005

New Aspects of B -> pi pi, pi K and their Implications for Rare Decays

We analyse the B -> pi pi, pi K modes in the light of the most recent B-factory data, and obtain the following new results: (i) the B0 -> pi+ pi-, pi- K+ modes prefer gamma=(74+-6)deg, which - together with |V_ub/V_cb| - allows us to determine the ``true'' unitarity triangle and to search for CP-violating new-physics contributions to B0_d-\bar B0_d mixing; (ii) the B -> pi K puzzle reflected in particular by the low experimental value of the ratio R_n of the neutral B -> pi K rates persists and still favours new physics in the electroweak penguin sector with a new CP-violating phase phi ~ -90deg, although now also phi ~ +90deg can bring us rather close to the data; (iii) the mixing-induced B0 -> pi0 K_S CP asymmetry is a sensitive probe of the sign of this phase, and would currently favour phi ~ +90deg, as well as the direct CP asymmetry of B+- -> pi0 K+-, which suffers, however, from large hadronic uncertainties; (iv) we investigate the sensitivity of our B -> pi K analysis to large non-factorizable SU(3)-breaking effects and find that their impact is surprisingly small so that it is indeed exciting to speculate on new physics; (v) assuming that new physics enters through Z0 penguins, we study the interplay between B -> pi K and rare B, K decays and point out that the most recent B-factory constraints for the latter have interesting implications, bringing us to a few scenarios for the future evolution of the data, where also the mixing-induced CP violation in B0 -> pi0 K_S plays a prominent role.

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arXiv2005

Electroweak Penguin Hunting Through B -> pi pi, pi K and Rare K and B Decays

The $B\toπK$ decays with significant electroweak penguin contributions show a puzzling pattern. We explore this "$B\toπK$ puzzle" through a systematic strategy. The starting point, which is essentially unaffected by electroweak penguins, is the determination of the angle $γ$ of the unitarity triangle through the CP-violating $B^0_d\toπ^+π^-$, $B^0_d\toπ^-K^+$ asymmetries, yielding $γ=(73.9^{+5.8}_{-6.5})^\circ$, and the extraction of hadronic parameters through the measured $B\toππ$ branching ratios. Using arguments related to the SU(3) flavour symmetry, we convert the hadronic $B\toππ$ parameters into their $B\toπK$ counterparts, allowing us to predict the $B\toπK$ observables in the Standard Model. We find agreement with the data for those quantities that are only marginally affected by electroweak penguins, while this is not the case for the observables with sizeable electroweak penguin contributions. Since we may also perform a couple of internal consistency checks of our working assumptions, which are nicely satisfied for the current data, and find a small sensitivity of our results to large non-factorizable SU(3)-breaking corrections, the "$B\toπK$" puzzle may be due to new physics in the electroweak penguin sector. We show that it can indeed be resolved through such a kind of new physics with a large CP-violating phase. Further insights into the electroweak penguins are provided by the $B^+\toπ^0K^+$ and $B_d^0\toπ^0K_{\rm S}$ CP asymmetries, and in particular through correlations with various rare $K$ and B decays.

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arXiv2005

b -> d Penguins: CP Violation, General Lower Bounds on the Branching Ratios and Standard Model Tests

With the wealth of new data from the B-factories, b -> d penguin decays become available for study, in addition to their b -> s counterparts that have proven an indespensable tool for the exploration of new-physics effects in flavour physics. A prominent example of the b -> d penguin transitions is $\bar B^0_d \to K^0 \bar K^0$. We show that this decay can be charaterized in the Standard Model by a surface in the observable space of the direct and mixing-induced CP asymmetries and the branching ratio. The form of this surface, which is theoretically clean, implies a lower bound for the branching ratio that has recently been confirmed experimentally. If future measurements of the CP asymmetries yield a point away from the SM surface, this would be an interesting signal of new physics. We point out that the hadronic parameters in $\bar B^0_d \to K^0 \bar K^0$ that parameterize the position on the SM surface are related to hadronic parameters in the B -> pi K system. The fact that the branching ratio of $\bar B^0_d \to K^0 \bar K^0$ is very close to its lower bound yields interesting implications for B -> pi K even without knowledge of the CP asymmetries of $\bar B^0_d \to K^0 \bar K^0$. The mechanism that produces the lower bound for $\bar B^0_d \to K^0 \bar K^0$ is actually much more general; we derive lower bounds for various other b -> d penguin-induced processes, including B -> rho gamma and $B^\pm \to K^{(\ast)\pm} K^{(\ast)}$. Some of these theoretical lower bounds are very close to the current experimental upper bounds.

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arXiv2005

The B -> pi pi, pi K Puzzles: Implications for Hadron Physics, New Physics and Rare Decays

The B-meson system is an interesting probe for the exploration of strong interactions, the quark-flavour sector of the Standard Model, and the search for new physics. In this programme, non-leptonic B decays, which are particularly challenging from the point of view of QCD, play a key role. After discussing strategies to deal with the corresponding hadronic matrix elements of four-quark operators and popular avenues for new physics to manifest itself in B decays, we focus on puzzling patterns in the B-factory data for B -> pi pi, pi K decays; we explore their implications for hadron physics, new physics and rare K and B decays.

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arXiv2005

New Physics in B and K Decays

Flavour physics offers interesting probes for the exploration of the Standard Model and the search for new physics. In these lectures, we focus on B- and K-meson decays, introduce the concept of low-energy effective Hamiltonians to describe them theoretically, and discuss how physics beyond the Standard Model may generically affect the roadmap of quark-flavour physics. We address then both the implications of the B-factory data for the B_d -> J/psi K_S channel and the prospects of B_s -> J/psi phi modes for hadron colliders, and discuss how the Standard Model may be challenged through B_d -> phi K_S. Finally, as an example of a systematic flavour strategy to search for new physics, we analyze puzzling patterns in the B -> pi pi, pi K data and study their interplay with rare K and B decays.

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arXiv2005

General Lower Bounds for b -> d Penguin Processes

For the exploration of flavour physics, b -> d penguin processes are an important aspect, with the prominent example of \bar B^0_d -> K^0 \bar K^0. We recently derived lower bounds for the CP-averaged branching ratio of this channel in the Standard Model; they were found to be very close to the corresponding experimental upper limits, thereby suggesting that \bar B^0_d -> K^0 \bar K^0 should soon be observed. In fact, the BaBar collaboration subsequently announced the first signals of this transition. Here we point out that it is also possible to derive lower bounds for \bar B -> ργdecays, which are again surprisingly close to the current experimental upper limits. We show that these bounds are realizations of a general bound that holds within the Standard Model for b -> d penguin processes, allowing further applications to decays of the kind B^\pm -> K^{(\ast)\pm} K^{(\ast)} and B^\pm -> π^\pm \ell^+ \ell^-, ρ^\pm \ell^+ \ell^-.

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arXiv2004

B -> pi pi, New Physics in B -> pi K and Rare K and B Decays

We summarize a recent strategy for a global analysis of the B -> pi pi, pi K systems and rare decays. We find that the present B -> pi pi and B -> pi K data cannot be simultaneously described in the Standard Model. In a simple extension in which new physics enters dominantly through Z^0 penguins with a CP-violating phase, only certain B -> pi K modes are affected by new physics. The B -> pi pi data can then be described entirely within the Standard Model but with values of hadronic parameters that reflect large non-factorizable contributions. Using the SU(3) flavour symmetry and plausible dynamical assumptions, we can then use the B -> pi pi decays to fix the hadronic part of the B -> pi K system and make predictions for various observables in the B_d -> pi^-+ K^+- and B^+- -> pi^+- K decays that are practically unaffected by electroweak penguins. The data on the B^+- -> pi^0 K^+- and B_d -> pi^0 K modes allow us then to determine the electroweak penguin component which differs from the Standard Model one, in particular through a large additional CP-violating phase. The implications for rare K and B decays are spectacular. In particular, the rate for K_L -> pi^0 nu \bar nu is enhanced by one order of magnitude, the branching ratios for B_{d,s} -> mu^+ mu^- by a factor of five, and BR(K_L -> pi^0 e^+ e^-, pi^0 mu^+ mu^-) by factors of three.

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arXiv2004

The B -> pi pi,pi K Puzzles in the Light of New Data: Implications for the Standard Model, New Physics and Rare Decays

Recently, we developed a strategy to analyse the B -> pi pi,pi K data. We found that the B -> pi pi measurements can be accommodated in the Standard Model (SM) through large non-factorizable effects. On the other hand, our analysis of the ratios R_c and R_n of the CP-averaged branching ratios of the charged and neutral B -> pi K modes, respectively, suggested new physics (NP) in the electroweak penguin sector, which may have a powerful interplay with rare decays. In this paper, we confront our strategy with recent experimental developments, addressing also the direct CP violation in B_d -> pi^-+ K^+-, which is now an established effect, the relation to its counterpart in B^+- -> pi^0 K^+-, and the first results for the direct CP asymmetry of B_d -> pi^0 pi^0 that turn out to be in agreement with our prediction. We obtain hadronic B -> pi pi,pi K parameters which are almost unchanged and arrive at an allowed region for the unitarity triangle in perfect accordance with the SM. The ``B -> pi K puzzle'' persists, and can still be explained through NP, as in our previous analysis. In fact, the recently observed shifts in the experimental values of R_c and R_n have been predicted in our framework on the basis of constraints from rare decays. Conversely, we obtain a moderate deviation of the ratio R of the CP-averaged B_d -> pi^-+ K^+- and B^+- -> pi^+- K rates from the current experimental value. However, using the emerging signals for B^+- -> K^+- K modes, this effect can be attributed to certain hadronic effects, which have a minor impact on R_c and do not at all affect R_n. Our results for rare decays remain unchanged.

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arXiv2004

Waiting for the Discovery of B^0_d -> K^0 \bar K^0

The CP asymmetries of the decay B_d^0 -> K^0 \bar K^0, which originates from \bar b -> \bar d s \bar s flavour-changing neutral-current processes, and its CP-averaged branching ratio BR(B_d -> K^0 \bar K^0) offer interesting avenues to explore flavour physics. We show that we may characterize this channel, within the Standard Model, in a theoretically clean manner through a surface in observable space. In order to extract the relevant information from BR(B_d -> K^0 \bar K^0), further information is required, which is provided by the B -> pi pi system and the SU(3) flavour symmetry, where we include the leading factorizable SU(3)-breaking corrections and discuss how experimental insights into non-factorizable effects can be obtained. We point out that the Standard Model implies a lower bound for BR(B_d -> K^0 \bar K^0), which is very close to its current experimental upper bound, thereby suggesting that this decay should soon be observed. Moreover, we explore the implications for ``colour suppression'' in the B -> pi pi system, and convert the data for these modes into a peculiar Standard-Model pattern for the CP-violating B_d^0 -> K^0 \bar K^0 observables.

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