Single Hadronic-Spin Asymmetries in Weak Interaction Processes

We show that measurements of single-spin asymmetries (SSAs) in charged current weak interaction processes such as deep inelastic neutrino scattering on a polarized target and inclusive $W$ production in polarized hadron-hadron collisions discriminate between the two fundamental QCD mechanisms (the Sivers and Collins effects) which have been proposed to explain such time-reversal-odd asymmetries. It has recently been shown that QCD final-state interactions due to gluon exchange between the struck quark and the proton spectators in semi-inclusive deep inelastic lepton scattering will produce non-zero Sivers-type single-spin asymmetries which survive in the Bjorken limit. We show that this QCD final-state interaction produces identical SSAs in charged and neutral current reactions. Furthermore, the contribution of each quark to the SSA from this mechanism is proportional to the contribution of that quark to the polarized baryon's anomalous magnetic moment. In contrast, the Collins effect contribution to SSAs depends on the transversity distribution of quarks in the polarized target. Since the charged current only couples to quarks of one chirality, it cannot sense the transversity distribution of the target, and thus it gives no Collins-type contribution to single-spin correlations.Comment: 12 pages, 1 figur

q→Λq \to \Lambda Fragmentation Function and Nucleon Transversity Distribution in a Diquark Model

Based on a simple quark-diquark model, we propose a set of unpolarized, longitudinally polarized and transversely polarized fragmentation functions for the $\Lambda$ by fitting the unpolarized $\Lambda$ production data in $e^+ e ^-$ annihilation. It is found that the helicity structure of the obtained $\Lambda$ fragmentation functions is supported by the all available experimental data on the longitudinal $\Lambda$ polarization. Within the same framework of the diquark model, the nucleon transversity distributions are presented and consistent descriptions of the available HERMES data on the azimuthal spin asymmetries in pion electroproduction are obtained. Furthermore, the spin transfers to the transversely polarized $\Lambda$ in the charged lepton DIS on a transversely polarized nucleon target are predicted for future experiments.Comment: Talk given in a seminar of U. Santa Mari

Single spin asymmetry in πp\pi p Drell-Yan process

We study the single spin asymmetries for the $\pi p^\uparrow\rightarrow\mu^+\mu^-X$ process. We consider the asymmetries contributed by the coupling of the Boer-Mulders function with the transversity distribution and the pretzelosity distribution, characterized by the $\sin(\phi+\phi_S)$ and $\sin(3\phi-\phi_S)$ azimuthal angular dependence, respectively. We estimate the magnitude of these asymmetries at COMPASS by using proper weighting functions. We find that the $\sin(\phi+\phi_S)$ asymmetry is of the size of a few percent and can be measured through the experiment. The $\sin(3\phi-\phi_S)$ asymmetry is smaller than the $\sin(\phi+\phi_S)$ asymmetry. After a cut on $q_T$, we succeed in enhancing the asymmetry.Comment: 11 pages, 2 figures, final version to appear in PL

Angular dependences in electroweak semi-inclusive leptoproduction

We present the leading order unpolarized and polarized cross sections in electroweak semi-inclusive deep inelastic leptoproduction. The azimuthal dependences in the cross section differential in the transverse momentum of the vector boson arise due to intrinsic transverse momenta of the quarks. However, the presented asymmetries are not suppressed by inverse powers of the hard scale. We discuss the different opportunities to measure specific asymmetries as offered by neutral compared to charged current processes and point out the optimal kinematical regions. The present and (proposed) future HERA collider experiments would be most suitable for measuring some of the asymmetries discussed here, especially in case of Lambda production.Comment: 10 pages, Revtex, 5 Postscript figures, uses aps.sty, epsfig.st

SU(5) Completion of the Dark Scalar Doublet Model of Radiative Neutrino Mass

Adding a second scalar doublet (eta^+,eta^0) and three neutral singlet fermions N_{1,2,3} to the Standard Model of particle interactions with a new Z_2 symmetry, it has been shown that eta^0_R or eta^0_I is a good dark-matter candidate and seesaw neutrino masses are generated radiatively. A minimal extension of this new idea is proposed to allow for its SU(5) completion. Supersymmetric unification is then possible, and leptoquarks of a special kind are predicted at the TeV scale.Comment: 6 pages, 2 figures, 1 tabl

Azimuthal asymmetry in unpolarized πN\pi N Drell-Yan process

Taking into account the effect of final state interaction, we calculate the non-zero (na\"{i}ve) $T$-odd transverse momentum dependent distribution h_1^{\perp}(x,\kp^2) of the pion in a quark-spectator-antiquark model with effective pion-quark-antiquark coupling as a dipole form factor. Using the model result we estimate the $\cos 2\phi$ asymmetries in the unpolarized $\pi^- N$ Drell-Yan process which can be expressed as $h_1^{\perp}\times\bar{h}_1^{\perp}$. We find that the resulting h_{1\pi}^\p(x,\kp^2) has the advantage to reproduce the asymmetry that agrees with the experimental data measured by NA10 Collaboration. We estimate the $\cos2\phi$ asymmetries averaged over the kinematics of NA10 experiments for 140, 194 and 286 GeV $\pi^-$ beam and compare them with relevant experimental data.Comment: 11 pages, 4 figures, to appear in PL

Triplicity of Quarks and Leptons

Quarks come in three colors and have electric charges in multiples of one-third. There are also three families of quarks and leptons. Whereas the first two properties can be understood in terms of unification symmetries such as SU(5), SO(10), or E_6, why there should only be three families remains a mystery. I propose how all three properties involving the number three are connected in a fivefold application of the gauge symmetry SU(3).Comment: 10 pages, including 2 figure

Single Spin Asymmetry in Lepton Angular Distribution of Drell-Yan Processes

We study the single spin asymmetry in the lepton angular distribution of Drell-Yan processes in the frame work of collinear factorization. The asymmetry has been studied in the past and different results have been obtained. In our study we take an approach different than that used in the existing study. We explicitly calculate the transverse-spin dependent part of the differential cross-section with suitable parton states. Because the spin is transverse, one has to take multi-parton states for the purpose. Our result agrees with one of the existing results. A possible reason for the disagreement with others is discussed.Comment: Typos corrected. Conclusions unchange

New observables in longitudinal single-spin asymmetries in semi-inclusive DIS

We analyze longitudinal beam and target single-spin asymmetries in semi-inclusive deep inelastic scattering and in jet deep inelastic scattering, including all possible twist-3 contributions as well as quark mass corrections. We take into account the path-ordered exponential in the soft correlators and show that it leads to the introduction of a new distribution and a new fragmentation function contributing to the asymmetries.Comment: 8 page

Sivers function in light-cone quark model and azimuthal spin asymmetries in pion electroproduction

We perform a calculation of Sivers function in a light-cone SU(6) quark-diquark model with both scalar diquark and vector diquark spectators. We derive the transverse momentum dependent light-cone wave function of the proton by taking into account the Melosh-Wigner rotation. By adopting one-gluon exchange, we obtain a non-vanishing Sivers function of $down$ quark from interference of proton spin amplitudes. We analyze the $\frac{|P_{h\perp}|}{M}$ weighted Sivers asymmetries in $\pi^+$, $\pi^-$ and $\pi^0$ electroproduction off transverse polarized proton target, averaged and not averaged by the kinematics of HERMES experiment.Comment: 17 LaTex pages, 2 figures. Final version for journal publicatio