arXiv subjects

Martin Beneke

Publications and source records attributed to Martin Beneke.

82 records · Page 5Linked to original sources

arXiv2007

Four-fermion production near the W pair production threshold

We perform a dedicated study of the four-fermion production process e- e+ -> mu- nubar_mu u dbar X near the W pair-production threshold in view of the importance of this process for a precise measurement of the W boson mass. Accurate theoretical predictions for this process require a systematic treatment of finite-width effects. We use unstable-particle effective field theory (EFT) to perform an expansion in the coupling constants, GammaW/MW, and the non-relativistic velocity v of the W boson up to next-to-leading order in GammaW/MW ~ alpha_ew ~ v^2. We find that the dominant theoretical uncertainty in MW is currently due to an incomplete treatment of initial-state radiation. The remaining uncertainty of the NLO EFT calculation translates into delta MW ~ 10-15 MeV, and to about 5 MeV with additional input from the NLO four-fermion calculation in the full theory.

hep-ph↗

arXiv2007

Branching fractions, polarisation and asymmetries of B -> VV decays

We calculate the hard-scattering kernels relevant to the negative-helicity decay amplitude in B decays to two vector mesons in the framework of QCD factorisation. We then perform a comprehensive analysis of the 34 B->VV decays, including B_s decays and the complete set of polarisation observables. We find considerable uncertainties from weak annihilation and the non-factorisation of spectator-scattering. Large longitudinal polarisation is expected with certainty only for a few tree-dominated colour-allowed modes, which receive small penguin and spectator-scattering contributions. This allows for an accurate determination of the CKM angle alpha (or gamma) from S_L(rhorho) resulting in alpha=(85.6^{+7.4}_{-7.3}) degrees. We also emphasize that the rho K* system is ideal for an investigation of electroweak penguin effects.

hep-ph↗

arXiv2007

Spectator scattering at NLO in non-leptonic B decays: Leading penguin amplitudes

We complete the computation of the 1-loop (alpha_s^2) corrections to hard spectator scattering in non-leptonic B decays at leading power in Lambda/m_b by evaluating the penguin amplitudes. This extends the knowledge of these next-to-next-to-leading-order contributions in the QCD factorization formula for B decays to a much wider class of final states, including all pseudoscalar-pseudoscalar, pseudoscalar-vector, and longitudinally polarized vector-vector final states, except final states with eta or eta' mesons. The new 1-loop correction is significant for the colour-suppressed amplitudes, but turns out to be strongly suppressed for the leading QCD penguin amplitude alpha_4^p. We provide numerical values of the phenomenological P/T and C/T amplitude ratios for the pi pi, pi rho and rho rho final states, and discuss corrections to several relations between electroweak penguin and tree amplitudes.

hep-ph↗

arXiv2006

A precise determination of $α$ using $B^0\toρ^+ρ^-$ and $B^+\to K^{*0}ρ^+$

The effect of the penguin amplitude on extracting $α$ from CP asymmetries in $B^0\to ρ^+ρ^-$ decays is studied using information on the SU(3)-related penguin amplitude in $B^+\to K^{*0}ρ^+$. Conservative bounds on non-factorizable SU(3) breaking, small amplitudes, and the strong phase difference between tree and penguin amplitudes, are shown to reduce the error in $α$ in comparison with the one obtained using isospin symmetry in $B\toρρ$. Current measurements imply $α= [90 \pm 7 f{\rm exp})^{+2}_{-5} ({\rm th})]^\circ$.

hep-ph↗

arXiv2005

Hard spectator-scattering in B -> pi pi decays at NNLO

We compute the 1-loop (NNLO) corrections to hard spectator-scattering in tree-dominated hadronic B decays. Depending on the values of hadronic input parameters the corrections are shown to have a significant impact on the B -> pi pi branching fractions.

hep-ph↗

arXiv2003

QCD factorization for B->PP and B->PV decays

A comprehensive study of exclusive hadronic B-meson decays into final states containing two pseudoscalar mesons (PP) or a pseudoscalar and a vector meson (PV) is presented. The decay amplitudes are calculated at leading power in Lambda_{QCD}/m_b and at next-to-leading order in alpha_s using the QCD factorization approach. The calculation of the relevant hard-scattering kernels is completed. Important classes of power corrections, including ``chirally-enhanced'' terms and weak annihilation contributions, are estimated and included in the phenomenological analysis. Predictions are presented for the branching ratios of the complete set of the 96 decays of B^-, B^0, and B_s mesons into PP and PV final states, and for most of the corresponding CP asymmetries. Several decays and observables of particular phenomenological interest are discussed in detail, including the magnitudes of the penguin amplitudes in PP and PV final states, an analysis of the pi-rho system, and the time-dependent CP asymmetry in the K phi and K eta' final states.

hep-ph↗

arXiv2002

Flavor-Singlet B-Decay Amplitudes in QCD Factorization

Exclusive hadronic B-meson decays into two-body final states consisting of a light pseudoscalar or vector meson along with an eta or eta' meson are of great phenomenological interest. Their theoretical analysis involves decay mechanisms that are unique to flavor-singlet states, such as their coupling to gluons or their ``intrinsic charm'' content. These issues are studied systematically in the context of QCD factorization and the heavy-quark expansion. Theory can account for the experimental data on the B->K^{(*)} eta^{(')} branching fractions, albeit within large uncertainties.

hep-ph↗

arXiv2001

Present and Future CP Measurements

We review theoretical and experimental results on CP violation summarizing the discussions in the working group on CP violation at the UK phenomenology workshop 2000 in Durham.

hep-ph↗

arXiv2000

Lifetime difference of $B_s$ mesons - Theory status

We give an update on the lifetime difference of $B_s$ mesons which accounts for recent lattice bag parameter results, and obtain $(ΔΓ/Γ)_{B_s}=(9.3^{+3.4}_{-4.6})%$. We then review the current theoretical uncertainties and conclude with a pessimistic perspective on further improvements.

hep-ph↗

arXiv1996

Mixing-induced CP Asymmetries in Inclusive $B$ Decays

We consider CP violating asymmetries that are induced by particle-antiparticle mixing in inclusive channels of neutral $B$ meson decay. Not only are the branching ratios sizable, at the 1% to 50% level, but some of those asymmetries are expected to be large because of substantial CKM phases. The inclusive sum partially dilutes the asymmetries, but the dilution factor is calculable, assuming local quark-hadron duality, and CKM parameters can be reliably extracted. We discuss in detail the determination of $sin 2α$ from charmless final states in decays of $B_d$ mesons and survey the asymmetries for other inclusive final states. While probably not yet sensitive to standard model predictions, meaningful CP violation studies can be conducted with existing data samples of inclusive neutral $B$ decays.

hep-ph↗