arXiv subjects

M. Gronau

Publications and source records attributed to M. Gronau.

13 recordsLinked to original sources

arXiv2019

The Belle II Physics Book

We present the physics program of the Belle II experiment, located on the intensity frontier SuperKEKB $e^+e^-$ collider. Belle II collected its first collisions in 2018, and is expected to operate for the next decade. It is anticipated to collect 50/ab of collision data over its lifetime. This book is the outcome of a joint effort of Belle II collaborators and theorists through the Belle II theory interface platform (B2TiP), an effort that commenced in 2014. The aim of B2TiP was to elucidate the potential impacts of the Belle II program, which includes a wide scope of physics topics: B physics, charm, tau, quarkonium, electroweak precision measurements and dark sector searches. It is composed of nine working groups (WGs), which are coordinated by teams of theorist and experimentalists conveners: Semileptonic and leptonic B decays, Radiative and Electroweak penguins, phi_1 and phi_2 (time-dependent CP violation) measurements, phi_3 measurements, Charmless hadronic B decay, Charm, Quarkonium(like), tau and low-multiplicity processes, new physics and global fit analyses. This book highlights "golden- and silver-channels", i.e. those that would have the highest potential impact in the field. Theorists scrutinised the role of those measurements and estimated the respective theoretical uncertainties, achievable now as well as prospects for the future. Experimentalists investigated the expected improvements with the large dataset expected from Belle II, taking into account improved performance from the upgraded detector.

hep-ex↗

arXiv2006

Weak phase alpha from B^0-> a_1^{+-}(1260) pi^{-+}

Quasi two-body decays B^0(t)-> a_1^{+-}(1260) pi^{-+} identified by four charged pions determine a phase alpha_eff, which is equal to the weak phase alpha in the limit of vanishing penguin amplitudes. Applying flavor SU(3) to these decays and to B->a_1 K and B->K_1 pi, with K_1 an admixture of K_1(1270) and K_1(1400), we derive expressions providing bounds on alpha-alpha_{eff}. Higher precision in alpha may be achieved by an overall fit to a complete set of SU(3) related measurements. A method is sketched applying isospin symmetry to time-dependent invariant mass distributions in B->pi^+ pi^- pi^0 pi^0.

hep-ph↗

arXiv2005

The Discovery Potential of a Super B Factory

The Proceedings of the 2003 SLAC Workshops on flavor physics with a high luminosity asymmetric e+e- collider. The sensitivity of flavor physics to physics beyond the Standard Model is addressed in detail, in the context of the improvement of experimental measurements and theoretical calculations.

hep-ph↗

arXiv2005

Isospin-breaking effects on alpha extracted in B --> pi pi, rho rho, rho pi

Isospin-breaking in B --> pi pi caused by pi^0-eta-eta' mixing is studied in a model-independent way using flavor SU(3). Measured branching ratios for B^+ --> pi^+ pi^0, B^+ --> pi^+ eta^(') and B^0 --> pi^0 eta^(') imply an uncertainty in alpha smaller than 1.4 degree. We find a negligible effect of pi^0-eta-eta' mixing on alpha in B --> rho pi. Characterizing the effect of rho^0-omega mixing in B --> rho rho and in B --> rho pi by the two-pion invariant mass dependence, we point out a way of constraining this effect experimentally or eliminating it altogether. We show that a model-independent shift in alpha caused by electroweak penguin amplitudes in B --> pi pi and B --> rho rho, Δalpha_{EWP}=1.5+- 0.3 degree, may be slightly different in B --> rho pi. Other sources of isospin-breaking in these processes are briefly discussed.

hep-ph↗

arXiv2004

Reducing the Error on alpha in B-> pi pi, rho rho, rho pi

Theoretical errors in the extraction of alpha from B -> pi^+ pi^-, rho^+ rho^-, rho pi decays are usually given in terms of upper bounds on alpha_eff-alpha obtained from isospin or from SU(3) relations, where alpha_eff is measured through CP asymmetries. We show that mild assumptions about magnitudes and strong phases of penguin and tree amplitudes (|P/T| < 1 and |delta| < pi/2) in B -> pi pi and B -> rho rho, imply alpha_eff > alpha, thus reducing by a factor two the error in alpha. Similarly, the assumptions |p_+-/t_+-| < 1, |δ_-| < pi/2 <|δ_+| in B -> rho pi lead to a cancellation between two terms in alpha_eff-alpha. Current data support these conditions.

hep-ph↗

arXiv2004

On measuring alpha in B(t)-> rho^\pm pi^\mp

Defining a most economical parametrization of time-dependent B-> rho^\pm pi^\mp decays, including a measurable phase alpha_{eff} which equals the weak phase alpha in the limit of vanishing penguin amplitudes, we propose two ways for determining alpha in this processes. We explain the limitation of one method, assuming only that two relevant tree amplitudes factorize and that their relative strong phase, delta_t, is negligible. The other method, based on broken flavor SU(3), permits a determination of alpha in B^0-> rho^\pm pi^\mp in an overconstrained system using also rate measurements of B^{0,+}-> K^* pi and B^{0,+}->rho K. Current data are shown to restrict two ratios of penguin and tree amplitudes, r_\pm, to a narrow range around 0.2, and to imply an upper bound |alpha_{eff} - alpha| < 15 degrees. Assuming that delta_t is much smaller than 90 degrees, we find alpha =(93\pm 16) degrees and (102 \pm 20) degrees using BABAR and BELLE results for B(t)-> rho^\pm pi^mp. Avoiding this assumption for completeness, we demonstrate the reduction of discrete ambiguities in alpha with increased statistics, and show that SU(3) breaking effects are effectively second order in r_\pm.

hep-ph↗

arXiv2004

Using untagged B^0 -> D K_S to determine gamma

It is shown that the weak phase gamma=arg(-V_{ud}V^*_{ub}V_{cb}V_{cd}^*) can be determined using only untagged decays B/Bbar--> D K_S. In order to reduce the uncertainty in gamma, we suggest combining information from B^{+-}--> DK^{+-} and from untagged B^0 decays, where the D meson is observed in common decay modes. Theoretical assumptions, which may further reduce the statistical error, are also discussed.

hep-ph↗

arXiv1997

Annihilation, Rescattering, and CP Asymmetries in B Meson Decays

A number of $B$ meson decays may proceed only through participation of the spectator quark, whether through amplitudes proportional to $f_B/m_B$ or via rescattering from other less-suppressed amplitudes. An expected hierarchy of amplitudes in the absence of rescattering will be violated by rescattering corrections. Such violations could point the way toward channels in which final-state interactions could be important. Cases in which final state phases can lead to large CP asymmetries are pointed out.

hep-ph↗

arXiv1996

New Physics in CP Asymmetries and Rare B Decays

We review and update the effects of physics beyond the standard model on CP asymmetries in B decays. These asymmetries can be significantly altered if there are important new-physics contributions to \bqbqbar mixing. This same new physics will therefore also contribute to rare, flavor-changing B decays. Through a study of such decays, we show that it is possible to partially distinguish the different models of new physics.

hep-ph↗

arXiv1996

CP Violation: The Future of B Physics

The subject of 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 phases in the Cabibbo-Kobayashi-Maskawa (CKM) matrix can be tested through a variety of CP asymmtries in neutral and charged B decays. SM constraints on the CKM phases are violated by new mechanisms of CP nonconservation beyond CKM. Different mechanisms can be distinguished by combining measurements of CP asymmetries with rate measurements of so-called penguin B decays.

hep-ph↗

arXiv1996

CP Violation in B Decays: The Standard Model and Beyond

We review the subject of CP violation in $B$ decays in the Standard Model (SM) and beyond the SM. We describe some of the present most promising ways of testing the Cabibbo-Kobayashi-Maskawa (CKM) origin of CP violation through a determination of the three angles of the CKM matrix unitarity triangle. Other sources of CP nonconservation violate SM constraints on the unitarity triangle. We show that different models of physics beyond the SM can be distinguished by combining their effects in CP asymmetries and in rare flavor-changing $B$ decays.

hep-ph↗

arXiv1992

Large Penguin effects in the CP Asymmetry of B0d ->pi+pi-

Penguin effects in the CP asymmetries of $B^0_d\rightarrow π^+π^-$ , $\bd\rightarrowρ^{\pm}π^{\mp}$ and $\bd\rightarrow a^{\pm}_1 π^{\mp}$ are studied as function of the CKM unitarity triangle $α$. Despite a fairly small penguin amplitude, it leads to quite sizable uncertainties in the determination of $\sin(2α)$ from all but very large asymmetries. This effect is maximal for vanishing final state interaction phases, for which it can cause, for instance, an asymmetry of 40\%\ if $α=π/2$.

hep-ph↗

arXiv1992

On Testing V-A in Lambda_b Decays

We comment on a recent suggestion by Amundson, Rosner, Worah and Wise to test the chirality of the $b$-quark decay coupling via polarized $Λ_b$ baryons produced in $e^+e^-\rightarrow Z\rightarrow Λ_b +X$. We study the effect of contributions from an amplitude in which a right-handed $b$ to $c$ current couples to a V-A lepton current.

hep-ph↗