Model-independent description of 𝐵→𝐷𝜋ℓ𝜈 decays
Semileptonic B-meson decays involving multiple final-state hadrons play a crucial role as backgrounds to studies of lepton flavour universality such as R(D(*)) determinations, or searches for ultra-rare processes like B → Kνν.
Decays of this type generally constitute poorly understood orbitally excited states of the charmed meson, collectively referred to as D**, as well as non-resonant contributions of B → Xclν that remain largely unmeasured. Recent studies using data from the LHCb experiment at CERN provide strong evidence that the scalar member of the D** family, the D0*, is in fact an overlap of two resonances, which would suggest that the lineshape of this state needs a more complicated description than a simple Breit-Wigner distribution.
As a first step to improve understanding of these processes, a team of scientists from KIT, Fermilab and the University of Zurich developed a novel description of semileptonic decays with two final-state hadrons by using dispersive methods to derive stringent bounds on the kinematic properties of the decay products. This method treats the two-hadron lineshapes in a model-independent manner using Omnès functions, thus allowing model parameters to be directly determined from available experimental data.
Using this formalism, they studied the composition of B → Dπlν decays by fitting to the Dπ invariant-mass spectrum, recently measured by the Belle experiment, to investigate the plausibility of the two-pole structure of the D0* resonance. While obtaining intriguing results suggesting that the semileptonic data are indeed compatible with the presence of two poles, more experimental measurements from Belle II is required to ultimately determine the exact composition of the Dπ spectrum.
Raynette van Tonder, post doc at the ETP and one of the authors explains: “This paper provides the first step towards a model-independent study of semileptonic B-meson decays into higher resonances and non-resonant final states. Our framework does not include any assumptions about lineshapes of resonances and is extendable to other decay processes with charmed mesons in the final state such as Bs → DKℓν.”
The paper has been published in the peer-reviewed journal Phys. Rev. D 110, L091502 and is available as a preprint.
Contact: Dr. Raynette van Tonder