Very happy to start at @IPPP_Durham as an Assistant Professor in Particle Physics Phenomenology on August 1st! Looking forward to work with @martinmbauer, @spannowsky and all the other fine people at IPPP!.

We plan to expand this type of analysis to other measurements. So we already contacted @alexlenz42 and his team of #subatomicheroes to see if we can join efforts!.

The blue results are closer to the SM than the orange ones, but neither truly includes the SM point. The green ellipses arise from the usage of the inclusive nonleptonic decay width. As you can see, for some WET parameters the inclusive measurements are already very constraining!.

Armed with these results, Stefan fitted the WET coefficients from data. Unconventional use of measurements of the B-meson lifetime allowed him to fit the WET parameters from the existing decay measurements:

The 2-particle results were already known, and he finds agreement with the literature. But the full set of 3-particle results for arbitrary WET contributions is new!.

This does not change the overall picture, and the tensions persist. He expanded his calculation to also cover all possible contributions by heavy beyond the Standard Model (SM) physics (i.e., in the so-called Weak Effective Theory = WET).

As part of his PhD thesis. Stefan investigated this tension from two points of view. First, he repeated the calculation to NLO αₛ for 2-particle and LO for the 3-particle terms. He finds full agreement with the literature for the former, and a missing prefactor for the latter.

The tension in a nutshell: these clean predictions seem to work excellently for ratios of the decay frequencies, but not for the decay frequencies themselves. The experimental measurements are lower than the predictions by a whopping 20% to 30%.

Theory predictions for these decays, based on "collinear factorization", are expected to be very "clean", i.e., in a double expansion in terms of αₛ and the inverse b quark mass, the leading terms can be computed with controllable uncertainty.

Our analysis inputs, numerical results, and figures are available at .

We are already discussing how to drive this further, e.g. by studying both isospin projections of the electromagnetic pion form factor simultaneously, or by including higher resonances like the ρ(1450).

We also compare our postdiction for the phase shift with what other groups obtain. We find reasonable agreement. However, it is difficult to compare it accurately, since we account in principle also for "inelastic" contributions that are not present in the δ₁¹ phase shift.

The result looks stunning (we stop fitting at q² = 1 GeV²)

With only 2 pole parameters and 3 shape parameters, we obtain an excellent description of the data of the form factor magnitude. Contrary to other parametrisations, we do not require information about the phase shift of the form factor as an input!.

In our new paper, we explicitly account for such above-threshold resonances. Moreover, we demonstrate how well our proposal works at hand of the pion vector form factor. We chose the later because of the abundance of data and the dominant impact of the ρ(770) resonance.

The application of these parametrisations was limited to momentum transfer below the pair production threshold. Using D→π as an example, the semileptonic decay D→πℓ⁺ν can be described; however, the pair production ℓ⁺ν→Dπ cannot, due to the presence of the D* resonance.

Form factor parametrisations based on the z expansion have been around since the '90 thanks to seminal works by Boyd, Grinstein & Lebed, and many others later. Caprini's textbook provides an excellent overview:

Matthew Kirk, Bastian Kubis, Méril Reboud and I submitted a new paper to the arXiv that appeared today: . We propose a simple new parametrisation for hadronic form factors that works both below and above the pair production threshold. 🧵👇.

RT @JesseP4Florida: Elon Musk is LITERALLY going to cause another riot. This election will end up similar to 2020 where the popular vote is….

Very nice group in Maastricht. Can highly recommend applying to people working in flavour physics experiment or phenomenology!.

On my way to Manchester to examine a PhD candidate. Pretty excited!.