Status on the transversity parton distribution: the dihadron fragmentation functions way

in PoS (2012), QNP2012

We report on the extraction of dihadron fragmentation functions (DiFF) from the semiinclusive production of two hadron pairs in back-to-back jets in e+e- annihilation. A nonzero asymmetry in the ... [more ▼]

We report on the extraction of dihadron fragmentation functions (DiFF) from the semiinclusive 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 DiFF. A combined analysis of this asymmetry and the spin asymmetry in the SIDIS process ep↑→e′(π+π−)X has led to the first extraction of the u and d-flavor transversity parton distribution function in the framework of collinear factorization. [less ▲]

First extraction of interference fragmentation functions from e+e- data

in Physical Review D - Particles, Fields, Gravitation and Cosmology (2012), 85(11),

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 ... [more ▼]

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. © 2012 American Physical Society. [less ▲]

Dihadron fragmentation functions and their relevance for transverse spin studies

in Journal of Physics: Conference Series [=JPCS] (2011), 295(1),

Dihadron fragmentation functions describe the probability that a quark fragments into two hadrons plus other undetected hadrons. In particular, the so-called interference fragmentation functions describe ... [more ▼]

Dihadron fragmentation functions describe the probability that a quark fragments into two hadrons plus other undetected hadrons. In particular, the so-called interference fragmentation functions describe the azimuthal asymmetry of the dihadron distribution when the quark is transversely polarized. They can be used as tools to probe the quark transversity distribution in the nucleon. Recent studies on unpolarized and polarized dihadron fragmentation functions are presented, and we discuss their role in giving insights into transverse spin distributions. [less ▲]

Enhancement effects in exclusive ππ and ρπ production in γ* γ scattering

in Physics Letters B (2009), 675(1), 38-42

The exclusive ππ and ρπ production in hard γ* γ scattering in the forward kinematical region where the virtual photon is highly off-shell is studied using the γ → π- Transition Distribution Amplitudes ... [more ▼]

The exclusive ππ and ρπ production in hard γ* γ scattering in the forward kinematical region where the virtual photon is highly off-shell is studied using the γ → π- Transition Distribution Amplitudes obtained in realistic models for the pion. For ρπ production we confirm the previous estimates before QCD evolution. Nevertheless, once evolution is taken into account this cross section grows one order of magnitude. In the case of ππ production we have evaluated the cross section including the pion pole contribution. We observe that this contribution is responsible for an enhancement of two orders of magnitude with respect to the cross section evaluated without the pion pole term. © 2009 Elsevier B.V. All rights reserved. [less ▲]

Model calculations of the Sivers function satisfying the Burkardt sum rule

in Physical Review D - Particles, Fields, Gravitation and Cosmology (2009), 79(7),

It is shown that, at variance with previous analyses, the MIT bag model can explain the available data of the Sivers function and satisfies the Burkardt sum rule to a few percent accuracy. The agreement ... [more ▼]

It is shown that, at variance with previous analyses, the MIT bag model can explain the available data of the Sivers function and satisfies the Burkardt sum rule to a few percent accuracy. The agreement is similar to the one recently found in the constituent quark model. Therefore, these two model calculations of the Sivers function are in agreement with the present experimental and theoretical wisdom. © 2009 The American Physical Society. [less ▲]

Sivers asymmetry for the proton and the neutron

in AIP Conference Proceedings (2008), 1056

A formalism is presented to evaluate the Sivers function in constituent quark models. A non-relativistic reduction of the scheme is performed and applied to the Isgur-Karl model. The results obtained are ... [more ▼]

A formalism is presented to evaluate the Sivers function in constituent quark models. A non-relativistic reduction of the scheme is performed and applied to the Isgur-Karl model. 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. The Burkardt Sum Rule is fulfilled to a large extent. After the estimate of the QCD evolution of the results from the momentum scale of the model to the experimental one, a reasonable agreement with the available data is obtained. A calculation of nuclear effects in the extraction of neutron single spin asymmetries in semi-inclusive deep inelastic scattering off 3He is also described. In the kinematics of forth-coming experiments at JLab, it is found that the nuclear effects arising within an Impulse Approximation approach are under control. © American Institute of Physics. [less ▲]

Quark model analysis of the Sivers function

in Physical Review D - Particles, Fields, Gravitation and Cosmology (2008), 78(3),

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 ... [more ▼]

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. © 2008 The American Physical Society. [less ▲]

Pion-photon transition distribution amplitudes in the Nambu-Jona-Lasinio model

in Physical Review D - Particles, Fields, Gravitation and Cosmology (2007), 76(9),

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 ... [more ▼]

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. © 2007 The American Physical Society. [less ▲]