We present an updated extraction of the transversity parton distribution based on the analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets in collinear factorization. Data for proton and deuteron targets make it possible to perform a flavor separation of the valence components of the transversity distribution, using di-hadron fragmentation functions taken from the semi-inclusive production of two pion pairs in back-to-back jets in e + e − annihilation. The e + e − data from Belle have been reanalyzed using the replica method and a more realistic estimate of the uncertainties on the chiral-odd interference fragmentation function has been obtained. Then, the transversity distribution has been extracted by using the most recent and more precise COMPASS data for deep-inelastic scattering off proton targets. Our results represent the most accurate estimate of the uncertainties on the valence components of the transversity distribution currently available.

We present an extraction of the valence transversity parton distributions based on an analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets. Recently released data for proton and deuteron targets at HERMES and COMPASS permit a flavor separation of valence transversities. The present extraction is performed in the framework of collinear factorization, where dihadron fragmentation functions are involved. The latter are taken from a previous analysis of electron-positron annihilation measurements.Comment: 23 pages, 4 (multiple) figures; JHEP styl

We report on the first extraction of interference fragmentation functions from the semi-inclusive production of two hadron pairs in back-to-back jets in e + e − annihilation. A nonzero asymmetry in the correlation of azimuthal orientations of opposite π + π − pairs is related to the transverse polarization of fragmenting quarks through a significant polarized dihadron fragmentation function. Extraction of the latter requires the knowledge of its unpolarized counterpart, the probability density for a quark to fragment in a π + π − pair. Since data for the unpolarized cross section are missing, we extract the unpolarized dihadron fragmentation function from a Monte Carlo simulation of the cross section.

We present first observations of the transversity parton distribution based on an analysis of pion-pair production in deep inelastic scattering off transversely polarized targets. The extraction of transversity relies on the knowledge of dihadron fragmentation functions, which we take from electron-positron annihilation measurements. This is the first attempt to determine the transversity distribution in the framework of collinear factorization.

We evaluate the impact of recent developments in hadron phenomenology on extracting possible fundamental tensor interactions beyond the standard model. We show that a novel class of observables, including the chiral-odd generalized parton distributions, and the transversity parton distribution function can contribute to the constraints on this quantity. Experimental extractions of the tensor hadronic matrix elements, if sufficiently precise, will provide a, so far, absent testing ground for lattice QCD calculations. DOI: 10.1103/PhysRevLett.115.162001 PACS numbers: 13.60.Hb, 13.40.Gp, 24.85.+p High precision measurements of beta decay observables play an important role in beyond the standard model (BSM) physics searches, as they allow us to probe couplings other than of the V − A type, which could appear at the low energy scale. Experiments using cold and ultracold neutrons [1][2][3][4], nuclei [5][6][7][8], and meson rare decays [9] are being performed, or have been planned, that can reach the per-mil level or even higher precision. Effective field theory (EFT) allows one to connect these measurements and BSM effects generated at TeV scales. In this approach that complements collider searches, the new interactions are introduced in an effective Lagrangian describing semileptonic transitions at the GeV scale including four-fermion terms, or operators up to dimension six for the scalar, tensor, pseudoscalar, and V þ A interactions (for a review of the various EFT approaches, see Ref.[10]). Because the strength of the new interactions is defined with respect to the strength of the known SM interaction, the coefficients of the various terms, ϵ i , (i ¼ S; T; P; L; R) depend on the ratio m 2 W =Λ 2 i , where Λ i is the new physics scale relevant for these nonstandard interactions, and mW Þ. Therefore, the precision with which ϵ i ∝ m 2 W =Λ 2 i , is known determines a lower limit for Λ i . The scalar (S) and tensor (T) operators, in particular, contribute linearly to the beta decay parameters through their interference with the SM amplitude, and they are, therefore, more easily detectable. The matrix elements or transition amplitudes between neutron and proton states of all quark bilinear Lorentz structures in the effective Lagrangian which are relevant for beta decay observables, involve products of the BSM couplings, ϵ i , and the corresponding hadronic charges, g i , i.e., considering only terms with left-handed neutrinos,whereSðTÞ , characterize nucleon structure; however, at variance with the electroweak currents, there exists no fundamental coupling to these charges in the standard model. Therefore, they cannot be measured directly in elastic scattering processes. This Letter is concerned with an alternative approach aimed at extracting the hadronic charges from experimental data obtained in electron scattering. In previous work, various approaches have been developed to calculate these quantities including lattice QCD [11][12][13][14][15], and most recently, Dyson-Schwinger equations [16,17]. Lattice QCD ...

We develop a formalism to evaluate the Sivers function. The approach is well suited for calculations which use constituent quark models to describe the structure of the nucleon. A nonrelativistic reduction of the scheme is performed and applied to the Isgur-Karl model of hadron structure. The results obtained are consistent with a sizable Sivers effect and the signs for the u and d flavor contributions turn out to be opposite. This pattern is in agreement with the one found analyzing, in the same model, the impact parameter dependent generalized parton distributions. The Burkardt sum rule turns out to be fulfilled to a large extent. We estimate the QCD evolution of our results from the momentum scale of the model to the experimental one and obtain reasonable agreement with the available data.

We argue that due to Parity constraints, the helicity combination of the purely momentum space counterparts of the Wigner distributions -the generalized transverse momentum distributionsthat describes the configuration of an unpolarized quark in a longitudinally polarized nucleon, can enter the deeply virtual Compton scattering amplitude only through matrix elements involving a final state interaction. The relevant matrix elements in turn involve light cone operators projections in the transverse direction, or they appear in the deeply virtual Compton scattering amplitude at twist three. Orbital angular momentum or the spin structure of the nucleon was a major reason for these various distributions and amplitudes to have been introduced. We show that the twist three contributions associated to orbital angular momentum are related to the target-spin asymmetry in deeply virtual Compton scattering, already measured at HERMES.PACS numbers: 13.60.Hb, 13.40.Gp, 24.85.+p 1. Considerable attention has been devoted to the partons' Transverse Momentum Distributions (TMDs), to the Generalized Parton Distributions (GPDs), and to finding a connection between the two [1-3]. TMDs are distributions of different spin configurations of quarks and gluons within the nucleon whose longitudinal and transverse momenta can be accessed in Semi-Inclusive Deep Inelastic Scattering (SIDIS). GPDs are real amplitudes for quarks or gluons being probed in a hard process and then returning to reconstitute a scattered nucleon. They are accessed through exclusive electroproduction of vector bosons along with the nucleon. In each case there is a nucleon matrix element of bilinear, non-local quark or gluon field operators. In principle both TMDs and GPDs are different limits of Wigner distributions, i.e. the phase space distributions in momenta and impact parameters. The purely momentum space form of those are the Generalized TMDs (GTMDs). GTMDs correlate hadronic states with same parton longitudinal momentum, x (assuming zero skewness), different relative transverse distance, z T = b in − b out , between the struck parton's initial and final (out) states, and same average transverse distance, b = (b in + b out )/2, of the struck parton with respect to the center of momentum [4] (Figure 1a).Understanding the angular momentum or spin structure of the nucleon is a major reason for these various distri-FIG. 1: (a) Left: Correlation function for a GTMD; (b) quark-proton scattering in the u-channel.

We define the pion-photon transition distribution amplitudes (TDA) in a field theoretic formalism from a covariant Bethe-Salpeter approach for the determination of the bound state. We apply our formalism to the Nambu-Jona-Lasinio model, as a realistic theory of the pion. The obtained vector and axial TDAs satisfy all features required by general considerations. In particular, sum rules and the polynomiality condition are explicitly verified. We have numerically proved that the odd coefficients in the polynomiality expansion of the vector TDA vanish in the chiral limit. The role of PCAC and the presence of a pion pole are explicitly shown.