arXiv subjects

Robert Fleischer

Publications and source records attributed to Robert Fleischer.

154 records · Page 9Linked to original sources

arXiv1997

Quark mixing, CP violation and rare decays after the top quark discovery

We review the highlights of quark mixing, particle-antiparticle mixing, CP violation and rare K- and B-decays in the Standard Model. The top quark discovery, the precise measurement of its mass, the improved knowledge of the couplings $V_{cb}$ and $V_{ub}$, and the calculations of NLO short distance QCD corrections improved considerably the predictions for various decay rates, the determination of the couplings $V_{td}$ and $V_{ts}$ and of the complex phase in the Cabibbo-Kobayashi-Maskawa matrix. After presenting the general theoretical framework for weak decays, we discuss the following topics in detail: i) the CKM matrix, its most convenient parametrizations and the unitarity triangle, ii) the CP-violating parameter $ε_K$ and $B^0_{d,s}-\bar B^0_{d,s}$ mixings, iii) the ratio $ε'/ε$, iv) the rare K-decays $K_L\toπ^0e^+e^-$, $K^+\toπ^+ν\barν$, $K_L\toπ^0ν\barν$ and $K_L\toμ^+μ^-$, v) the radiative decays $B\to X_sγ$ and $B\to X_s l^+l^-$, vi) the rare B-decays $B\to X_{s,d}ν\barν$ and $B_{d,s}\to l^+l^-$, vii) CP violation in neutral and charged B-decays putting emphasis on clean determinations of the angles of the unitarity triangle, and viii) the role of electroweak penguins in B-decays. We present several future visions demonstrating very clearly the great potential of CP asymmetries in B-decays and of clean K-decays such as $K^+\toπ^+ν\barν$ and $K_L\toπ^0ν\barν$ in the determination of the CKM parameters and in decisive testing of the Standard Model. An outlook for the coming years ends our review.

hep-ph↗

arXiv1996

CP Violation and the Role of Electroweak Penguins in Non-leptonic B Decays

The phenomenon of CP violation in the B system and strategies for extracting CKM phases are reviewed. We focus both on general aspects and on some recent developments including CP-violating asymmetries in B_d decays, the B_s system in light of a possible width difference $ΔΓ_s$, charged B decays, and SU(3) relations among certain transition amplitudes. In order to describe the relevant non-leptonic B decays, low energy effective Hamiltonians calculated beyond the leading logarithmic approximation are used. Special emphasis is given to the role of electroweak penguin operators in such transitions. These effects are analyzed both within a general framework and more specifically in view of the theoretical cleanliness of methods to determine CKM phases. Strategies for obtaining insights into the world of electroweak penguins are discussed.

hep-ph↗

arXiv1996

Penguin Zoology in $B\toππ$ and the Extraction of the CKM Angle $α$

We reanalyze the decay $B_d\toπ^+π^-$ without assuming dominance of QCD penguins with internal top-quark exchanges. In that case the weak phase of the $\bar b \to\bar d$ QCD penguin amplitude is not related in a simple way to the CKM angle $β$. Nevertheless it is still possible to extract the CKM angle $α$ in a transparent and almost model-independent way from the time-dependent CP-violating asymmetry of the transition $B_d\toπ^+π^-$. Aside from that CP asymmetry this approach needs as an input only amplitudes of decays with branching ratios of order $10^{-5}$ and will thus be well within reach at future $B$-factories.

hep-ph↗

arXiv1996

CP Violation and CKM Phases from Time-dependences of Untagged $B_s$ Decays

The $B_s$ system is analyzed in light of a possible width difference $ΔΓ_s$ between its mass eigenstates. If $ΔΓ_s$ is sizable, untagged $B_s$-meson decays may allow a probe of CP violation and moreover the extraction both of the Wolfenstein parameter $η$ and of the notoriously difficult to measure angle $γ$ of the unitarity triangle. To accomplish this ambitious task, time-dependent angular distributions for untagged $B_s$ decays into admixtures of CP eigenstates and channels that are caused by $\bar b\to\bar c u\bar s$ quark-level transitions play a key role. The work described here was done in collaboration with Isard Dunietz.

hep-ph↗

arXiv1996

CP Violation in the B System

Strategies for extracting CKM phases from non-leptonic $B$ decays are reviewed briefly. Both general aspects and some recent developments including CP-violating asymmetries, the $B_s$ system in light of a possible width difference $ΔΓ_s$, and triangle relations among $B$ decay amplitudes are discussed. The role of electroweak penguins in these strategies is illustrated briefly.

hep-ph↗

arXiv1996

CP violation and the CKM angle $γ$ from angular distributions of untagged $B_s$ decays governed by $\bar b\to\bar c u\bar s$

We demonstrate that time-dependent studies of angular distributions for $B_s$ decays caused by $\bar b\to\bar cu\bar s$ quark-level transitions extract cleanly and model-independently the CKM angle $γ$. This CKM angle could be cleanly determined from untagged $B_s$ decays alone, if the lifetime difference between the $B_s$ mass eigenstates $B_s^L$ and $B_s^H$ is sizable. The time-dependences for the relevant tagged and untagged observables are given both in a general notation and in terms of linear polarization states and should exhibit large CP-violating effects. These observables may furthermore provide insights into the hadronization dynamics of the corresponding exclusive $B_s$ decays thereby allowing tests of the factorization hypothesis.

hep-ph↗

arXiv1996

CP violation and CKM phases from angular distributions for $B_s$ decays into admixtures of CP eigenstates

We investigate the time-evolutions of angular distributions for $B_s$ decays into final states that are admixtures of CP-even and CP-odd configurations. A sizable lifetime difference between the $B_s$ mass eigenstates allows a probe of CP violation in time-dependent untagged angular distributions. Interference effects between different final state configurations of $B_s\to D^{*+}_s D^{*-}_s$, $J/ψϕ$ determine the Wolfenstein parameter $η$ from untagged data samples, or -- if one uses $|V_{ub}|/|V_{cb}|$ as an additional input -- the notoriously difficult to measure CKM angle $γ$. Another determination of $γ$ is possible by using isospin symmetry of strong interactions to relate untagged data samples of $B_s\to K^{\ast+} K^{\ast-}$ and $B_s\to K^{\ast0} \overline{K^{\ast0}}$. We note that the untagged angular distribution for $B_s\toρ^0 ϕ$ provides interesting information about electroweak penguins.

hep-ph↗

arXiv1995

Strategies for Fixing the CKM-angle $γ$ and Obtaining Experimental Insights into the World of Electroweak Penguins

Using the $SU(3)$ flavour symmetry of strong interactions, we propose strategies for extracting both the CKM-angle $γ$ and the $\bar b\to\bar uu\bar s$ tree-level amplitude $T'$. We present also an approximate approach using the branching ratios for the modes $B^+\toπ^+ K^0$, $B^0_d\toπ^- K^+$, $\bar B^0_d\toπ^+ K^-$ and $B^+\toπ^+π^0$ which should be rather promising from the experimental point of view. The quantities $γ$ and $T'$ determined this way may well be used as an input to control electroweak penguins in nonleptonic $B$-decays as has been discussed in previous work. Following these lines, we propose strategies for obtaining quantitative insights into the physics of the electroweak penguin operators and performing some consistency checks. As a by-product, we derive an upper bound of $6^\circ$ for the uncertainty originating from electroweak penguins in the $α$-determination by means of $B\toππ$ decays.

hep-ph↗

arXiv1995

A Determination of the CKM-angle $α$ using Mixing-induced CP Violation in the Decays $B_d\toπ^+π^-$ and $B_d\to K^0 \bar K^0$

We present a method of determining the CKM-angle $α$ by performing simultaneous measurements of the mixing-induced CP asymmetries of the decays $B_d\toπ^+π^-$ and $B_d\to K^0\bar K^0$. The accuracy of our approach is limited by $SU(3)$-breaking effects originating from $\bar b\to \bar ds\bar s$ QCD-penguin diagrams. Using plausible power-counting arguments we show that these uncertainties are expected to be of the same order as those arising through electroweak penguins in the standard Gronau-London-method in which $α$ is extracted by means of isospin relations among $B\toππ$ decay amplitudes. Therefore our approach, which does not involve the experimentally difficult mode $B_d\toπ^0π^0$ and is essentially unaffected by electroweak penguins, may be an interesting alternative to determine $α$.

hep-ph↗

arXiv1995

Towards the Control over Electroweak Penguins in Nonleptonic B-Decays

We present strategies for determining electroweak penguins from experimental data. Using the CKM-angle $γ$ as one of our central inputs and making some reasonable approximations, we show that the $\bar b\to\bar s$ electroweak penguin amplitude can be determined in a two-step procedure involving i) BR$(B^+\toπ^0K^+)$, BR$(B^-\toπ^0K^-)$, BR$(B^+\toπ^+K^0)$ and ii) either BR$(B^0_d\toπ^-K^+)$, BR$(\bar B^0_d\toπ^+K^-)$ or $\acp(t)$ of the mode $B_s\to K^+K^-$. The determination employing the $B\toπK$ transitions is not affected by $SU(3)$-breaking effects. Relating the $\bar b\to\bar s$ electroweak penguin amplitude to the $\bar b\to\bar d$ case through $SU(3)$ symmetry arguments, we are in a position to estimate the electroweak penguin uncertainty affecting the extraction of the CKM-angle $α$ by using isospin relations among $B\toππ$ decays. Our results allow in principle the determination of CKM-phases in a variety of $B$-decays.

hep-ph↗