arXiv subjects

Philipp Böer

Publications and source records attributed to Philipp Böer.

22 records · Page 2Linked to original sources

arXiv2019

Angular Analysis of \boldmath $Λ_b\to Λ_c (\to Λπ)\ell\barν$

We revisit the decay $Λ_b^0\to Λ_c^+ \ell^-\barν$ ($\ell = e,μ,τ$) with a subsequent two-body decay $Λ_c^+ \to Λ^0 π^+$ in the Standard Model and in generic New Physics models. The decay's joint four-differential angular distribution can be expressed in terms of ten angular observables, assuming negligible polarization of the initial $Λ_b$ state. We present compact analytical results for all angular observables, which enables us to discuss their possible New Physics reach. We find that the decay at hand probes more and complementary independent combinations of Wilson coefficients compared to its mesonic counter parts $\bar{B}\to D^{(*)}\ell^-\barν$. Our result for the angular distribution is at variance with some of the results on scalar-vector interference terms in the literature. We provide numerical estimates for all angular observables based on lattice-QCD results for the $Λ_b \to Λ_c$ form factors and account for a recent measurement of the parity-violating parameter in $Λ_c^+\to Λ^0π^+$ decays by BESIII. A numerical implementation of our results is made publicly available as part of the EOS software.

hep-ph↗

arXiv2018

Testing lepton flavour universality in semileptonic $Λ_b \to Λ_c^*$ decays

Lepton Flavour Universality tests with semileptonic $Λ_b\toΛ_c^*$ decays are important to corroborate the present anomalies in the similar ratios $R_{D^{(*)}}$, and can provide complementary constraints on possible origins of these anomalies beyond the Standard Model. In this paper we provide - for the first time - all the necessary theoretical ingredients to perform and interpret measurements of $R_{Λ_c^*}$ at the LHCb experiment. For this, we revisit the heavy-quark expansion of the relevant hadronic matrix elements, and provide their expressions to order $α_s$ and $1/m$ accuracy. Moreover, we study the sensitivity to the form factor parameters given the projected size and purity of upcoming and future LHCb datasets of $Λ_b\to Λ_c^*μ\barν$ decays. We demonstrate explicitly the need to perform a simultaneous fit to both $Λ_c^*$ final states. Finally, we provide projections for the uncertainty of $R_{Λ_c^*}$ based on the form factor analysis from semimuonic decays and theoretical relations based on the heavy-quark expansion.

hep-ph↗

arXiv2017

QCD Factorization for $B \to ππ\ellν$ Decays at Large Dipion Masses

We introduce a factorization formula for semi-leptonic $b \to u$ transitions in the exclusive decay mode $B^- \to π^+π^-\ell^-\barν_\ell$ in the limit of large pion energies and large dipion invariant mass. One contribution can be described in terms of a universal $B \to π$ form factor and the convolution of a short-distance kernel $T^{\rm I}$ with the respective light-cone distribution amplitudes (LCDAs) of the positively charged pion. The second contribution, at leading power, completely factorizes, with a short-distance kernel $T^{\rm II}$ convoluted with the leading-twist LCDAs for both pions and the $B$-meson. We calculate the leading contributions to the short-distance kernels $T^{\rm I}$ and $T^{\rm II}$ in fixed-order perturbation theory, and discuss the approximate relations among the resulting $B \to ππ$ partial-wave form factors. Our results provide useful theoretical constraints for phenomenological models that aim to analyze the complete $B \to ππ\ellν$ phase space.

hep-ph↗

arXiv2016

Angular Analysis of the Decay $Λ_b \to Λ(\to N π) \ell^+\ell^-$

We study the differential decay rate for the rare $Λ_b \to Λ(\to N π)\ell^+\ell^-$ transition, including a determination of the complete angular distribution, assuming unpolarized $Λ_b$ baryons. On the basis of a properly chosen parametrization of the various helicity amplitudes, we provide expressions for the angular observables within the Standard Model and a subset of new physics models with chirality-flipped operators. Hadronic effects at low recoil are estimated by combining information from lattice QCD with (improved) form-factor relations in Heavy Quark Effective Theory. Our estimates for large hadronic recoil -- at this stage -- are still rather uncertain because the baryonic input functions are not so well known, and non-factorizable spectator effects have not been worked out systematically so far. Still, our phenomenological analysis of decay asymmetries and angular observables for $Λ_b \to Λ(\to N π)\ell^+\ell^-$ reveals that this decay mode can provide new and complementary constraints on the Wilson coefficients in radiative and semileptonic $b \to s$ transitions compared to the corresponding mesonic modes.

hep-ph↗