Chiral corrections to hyperon vector form factors

Abstract

We show that the leading chiral corrections to the AS= 1 f, vector form factors of hyperons are 0 (m, ) and O(mj'*), and are expected to be -20-30 % by dimensional analysis. This is consistent with the Ademollo-Gatto theorem. We compute the O(m,) corrections and a subset of the O(mg") corrections using an effective Lagrangian in which the baryons are treated as heavy particles. All of these corrections are surprisingly small, -5%; combining them, we obtain -5-10 7% corrections. The pattern of corrections is very different from that predicted by quark models.PACS number(s1: 13.30. Ce, 11.30.Rd, 14.20.Gk, 14.20.Jn I. INTRODUCTIONIn this paper we consider the application of chiral perturbation theory to the f vector form factor of octet baryon states. The form factors of the vector current are conventionally defined by where q ~p , -p , . Our interest in the form factor f is due to the fact that it is important for semileptonic hyperon decays, which in turn are used to determine Vu, [I].It is often assumed that SU(3bbreaking corrections to f, are ~( m ? ) and small due to the Ademollo-Gatto (AG) theorem [2]. Indeed, nonrelativistic quark model and bag model calculations of SU(3)-breaking corrections to f , typically give corrections of order 1 % [3]. In the SU(3) limit mu = m d = m , , the vector form factors at zero-momentum transfer are simply Clebsch-Gordan coefficients, while the axial form factors are simple linear combinations of two parameters D and F. (Be-

Baryon vector current in the chiral and1/Ncexpansions

“…[12,13,15]. When the decuplet fields are retained, there is a full agreement with the ones presented in Ref.…”

“…However, the numerical values have significant discrepancies between the calculation in HBChPT and the one in covariant BChPT. The calculations without the decuplet [13,15] give O (p 2 ) results which are very different with each other and the ones with the decuplet included. In particular some of the signs of the corrections are different.…”

“…The earliest computations in baryon chiral perturbation theory (BChPT) of the vector form factors for HSD were performed in the works by Krause [12] and by Anderson and Luty [13]. In both works the baryonic degrees of freedom involve only the spin 1/2 octet.…”

“…In both works the baryonic degrees of freedom involve only the spin 1/2 octet. Reference [12] presents the calculation in relativistic BChPT to O(p 2 ), while [13] works in HBChPT and performs a (partially complete) O(p 3 ) computation 2 . An analysis which is closest to the one in the present work is the one by Villadoro [14], where HBChPT including both octet and decuplet baryon degrees of freedom is used.…”

Measurement of the branching ratio of the decay Ξ0→Σ+μ−νBatley1, Kalmus2, Lazzeroni3 et al. 2013Physics Letters B5030View full textAdd to dashboardCite

“…In this framework, measurements on Ξ 0 semileptonic decays and on the related parameters are fundamental to further increase our knowledge on the constituents of the baryon octet. In particular, a clear evidence for the decay Ξ 0 → Σ + µ − ν µ and a measurement of its branching ratio will add one more constraint to the theoretical frameworks [2,3,4,5,6] built to explain the behaviour of the baryon semileptonic decays.…”