Abstract
In the framework of the soft-collinear effective theory, we demonstrate that the leading-power heavy-to-light baryonic form factors at large recoil obey the heavy quark and large energy symmetries. Symmetry breaking effects are suppressed by Λ/mb or Λ/E, where Λ is the hadronic scale, mb is the b quark mass and E∼mb is the energy of light baryon in the final state. At leading order, the leading power baryonic form factor ξΛ,p(E), in which two hard-collinear gluons are exchanged in the baryon constituents, can factorize into the soft and collinear matrix elements convoluted with a hard-kernel of order αs2. Including the energy release dependence, we derive the scaling law ξΛ,p(E)∼Λ2/E2. We also find that this form factor ξΛ(E) is numerically smaller than the form factor governed by soft processes, although the latter is formally power-suppressed.
Highlights
Precision test of the unitarity of the CKM matrix, allowing us to explore the SM description of the CP violation and reveal any physics beyond the SM, greatly depends on our knowledge of the nonperturbative matrix elements
Apart from the theoretical analysis based on the heavy quark effective theory [2,3,4], the simplification of baryonic form factors in the large energy limit is exploited [5, 6], applying the method developed in the mesonic case [9, 10]
Weak decays of heavy baryons provide an ideal ground for the extraction of the helicity structure of the electroweak interaction, thanks to the spin correlation and polarization embedded in decay amplitudes
Summary
Precision test of the unitarity of the CKM matrix, allowing us to explore the SM description of the CP violation and reveal any physics beyond the SM, greatly depends on our knowledge of the nonperturbative matrix elements. In the Λb → Λ transition, only one soft form factor is nonzero after the reduction and this universal function is calculated within the light-cone QCD sum rules in conjunction with the effective field theory [5]. The function Ξπ breaks the large energy symmetry but it can factorize into a convolution of a hard kernel and process-independent quantities namely light-cone distribution amplitudes. The leading-power symmetry-breaking effects in B → π come from the small component of the energetic quark field, while the dominant corrections in baryonic transition have several origins: they may be generated from the small component of the heavy quark, the small component of the collinear quark, or the small component of the hard-collinear gluon emitted from the heavy quark. The baryonic form factors have additional contributions from the SCET operator which consists of two transverse hard-collinear gluons but this term obeys the large recoil symmetries.
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