Form Factors for semi-leptonic $B$ decays

Abstract

Semi-leptonic B decays provide promising channels to test the Standard Model, search for signs of new physics, or determine fundamental parameters like CKM matrix elements. We present an update on our calculation of short distance contributions to GIM suppressed rare B decays focusing in particular on B s → φ + − decays. Furthermore we show first results for our calculation ofν semi-leptonic decays involving b → c transitions. Our calculations are based on RBC-UKQCD's 2+1 flavor domain-wall fermion and Iwasaki gauge field configurations featuring three lattice spacings in the range 1.73 GeV ≤ a −1 ≤ 2.77 GeV and pion masses down to the physical value. We calculate the form factors by simulating b-quarks using the relativistic heavy quark action, create light u/d and s quarks with standard domain-wall kernel, and use optimised Möbius domain-wall fermions for charm quarks.

Semileptonic $B\to\pi\ell\nu$, $B\to D\ell\nu$, $B_s\to K\ell\nu$, and $B_s\to D_s\ell\nu$ decays

“…Here we presented the status of our analysis for B → π ν, B → D ν, B s → K ν, and B s → D s ν. In addition to the charged current decays with pseudoscalar final state, our framework also includes operators to determine W ± mediated decays to vector final states as well as Glashow-Iliopoulos-Maiani (GIM) suppressed neutral current decays [66,67].…”

B Discrepancies Hold Their Ground

“…A more standard approach is to adopt the so-called narrow-width approximation, e.g., [67]. Interestingly, for the cases B → K * and B s → φ, of special interest in the context of B discrepancies, all local form factors are available, both from lattice QCD [46,48,[68][69][70][71] and with light cone sum rules [45, 65,72]. Similarly as in the case M = a pseudoscalar, the two approaches hold for large and respectively small q 2 -the region in between being narrow charmonium.…”

Lattice $B \to D^{(*)}$ form factors, $R(D^{(*)})$, and $|V_{cb}|$

“…There was a n f = 2 determination by the ETMC collaboration [48] in which they also determined the ratio of the tensor form factor to f + near zero recoil. The RBC/UKQCD collaboration presented preliminary results in [49,50] and these were updated at this conference [44]. The preliminary results for their form factors are shown in Fig.…”