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Jiro Kodaira

Publications and source records attributed to Jiro Kodaira.

At least 19 recordsLinked to original sources
arXiv2008

Double-spin asymmetries for small-Q_T Drell-Yan pair production in transversely polarized p\bar{p} collisions

We discuss the Drell-Yan process at a measured transverse-momentum $Q_T$ of the produced lepton pair in collisions of transversely polarized protons and antiprotons, to be observed at the proposed spin experiments at GSI. The large logarithmic contributions from multiple soft gluon emission, accompanying the Drell-Yan mechanism at small $Q_T$, are resummed to all orders in QCD perturbation theory up to next-to-leading logarithmic (NLL) accuracy. Numerical evaluation shows the impact of the NLL as well as LL effect on the dilepton $Q_T$ spectra. For the corresponding $Q_T$-dependent spin asymmetry $\aqt$, the LL effect gives significant modification while the NLL effect is marginal, leading to QCD prediction that $\aqt$ at GSI is flat at small and moderate $Q_T$ and almost equals the conventional asymmetry $A_{TT}$ associated with the $Q_T$-integrated cross sections. This flat behavior in turn allows us to use analytic saddle-point evaluation of the resummation formula in the limit $Q_T\to 0$, not only to obtain quantitative estimate of $\aqt$, but also to clarify mechanisms behind the relation $\aqt \simeq A_{TT}$ characteristic of $p\bar{p}$ collisions at GSI.

hep-ph↗
arXiv2008

The OPE of the B-meson light-cone wavefunction for exclusive B decays: radiative corrections and higher-dimensional operators

We discuss the B-meson light-cone wavefunction relevant for QCD factorization approach for exclusive B-meson decays. We derive the operator product expansion for the B-meson light-cone wavefunction, taking into account the local composite operators of dimension less than 6 and calculating the radiative corrections at order α_s for the corresponding Wilson coefficients. The result embodies peculiar UV and IR behaviors of the B-meson light-cone wavefunction, the Sudakov-type double logarithmic effects and the mixing of the multiparticle states with additional gluons inside the B meson. The former effects are induced from the cusp singularity in the radiative corrections, while the latter is manifested by the participation of the higher-dimensional operators associated with the nonperturbative structure of the B meson.

hep-ph↗
arXiv2008

Soft gluon resummation in Drell-Yan dilepton production at small transverse momentum: spin asymmetry and a novel asymptotic formula

We discuss the double-spin asymmetry \aqt in the transversely polarized Drell-Yan process at small transverse-momentum Q_T of the produced dilepton. The soft gluon corrections relevant for small Q_T are resummed to all orders in α_s, up to the next-to-leading logarithmic accuracy. We show that the soft gluon corrections largely cancel in the spin asymmetry, but the significant corrections still remain.The asymmetries \aqt are calculated for pp collision at RHIC and J-PARC, and for p\bar{p} collision at GSI. A novel asymptotic formula for \aqt at small Q_T is presented, which provides a new approach to extract the transversity δq(x) from the experimental data.

hep-ph↗
arXiv2007

Transversely Polarized Drell-Yan Process and Soft Gluon Resummation in QCD

We calculate the transverse-momentum $Q_T$ spectrum of the dilepton in the transversely polarized Drell-Yan process on the basis of the factorization theorem in QCD. We take into account universal logarithmically enhanced corrections in edge region of phase space by resumming multiple soft-gluon emissions to all orders in the small $Q_T$ region.

hep-ph↗
arXiv2007

Soft gluon corrections to double transverse-spin asymmetries for small-$Q_T$ dilepton production at RHIC and J-PARC

We calculate the double transverse-spin asymmetries, $\aqt$, in transversely polarized Drell-Yan process at the transverse-momentum $Q_T$ of the produced lepton pair. We perform all-order resummation of the logarithmically enhanced contributions in the relevant Drell-Yan cross sections at small $Q_T$, which are due to multiple soft gluon emission in QCD, up to the next-to-leading logarithmic accuracy. The asymmetries $\aqt$ to be observed in polarized experiments at RHIC and J-PARC are studied numerically as a function of $Q_T$. We show that the effects of the soft gluon resummation to the polarized and unpolarized cross sections largely cancel in $\aqt$, but the significant corrections still remain and are crucial for making a reliable QCD prediction of $\aqt$. In particular, the soft gluon corrections enhance $\aqt$ considerably in the small $Q_T$ region compared with the asymmetry in the fixed-order $α_s$ perturbation theory. We also derive a novel asymptotic formula which embodies those remarkable features of $\aqt$ at small $Q_T$ in a compact analytic form and is useful to extract the transversity $δq(x)$ from the experimental data.

hep-ph↗
arXiv2006

QCD Prediction of $A_{TT}$ for Small $Q_T$ Dimuon Production in $pp$ and $p\bar{p} Collisions

We present QCD prediction of double-spin asymmetries ($A_{TT}$) in transversely polarized Drell-Yan process at small transverse momentum $Q_T$ of dimuon. Resummation of large logarithmic corrections, relevant in small $Q_T$ region, is performed up to next-to-leading logarithmic (NLL) accuracy. $A_{TT}$ at RHIC, J-PARC and GSI are studied numerically in the corresponding kinematic regions.We show that the large $A_{TT}$ is obtained for small $Q_T$ and moderate energies.

hep-ph↗
arXiv2005

The Dilepton Q_T Spectrum in Transversely Polarized Drell-Yan Process in QCD

We discuss the transverse momentum Q_T distribution of Drell-Yan pair, produced in collisions of transversely polarized protons. We calculate the transversely polarized Drell-Yan cross section up to order α_s in the dimensional regularization scheme, which gives QCD prediction at large Q_T. For small Q_T region, we include all-orders resummation of large logarithms due to emission of soft gluons up to next-to-leading logarithmic accuracy. At intermediate Q_T region, the resummation formula is matched with the fixed-order α_s perturbative results in a systematic way, so that we derive the cross section with uniform accuracy over the entire range of Q_T.

hep-ph↗
arXiv2005

Unravelling soft components in the shape function for inclusive B decays

In the heavy-quark limit, the decay spectrum for radiative and semileptonic inclusive B-meson decays is determined by a universal structure function, i.e. the shape function. We study the constraints on the bilocal heavy-quark operator for the shape function from the QCD equations of motion and heavy-quark symmetry, and we obtain a new basis of nonlocal operators that reveals relevant soft components in the shape function. Those nonlocal operators represent the ``kinetic energy distribution'' of the b-quark inside the B-meson and the four-parton correlations with additional quarks and gluons. A corresponding local operator basis relevant for relating the shape function to HQET parameters is also given, and novel effects of the quark-gluon correlations are discussed.

hep-ph↗
arXiv2003

Detect ΔG at BNL-RHIC via Double Quarkonium Production

The double spin asymmetry for exclusive $J/ψ$ pair production in the polarized $p-p$ collisions at RHIC is investigated. Our study shows that the asymmetry in this process is measurable at RHIC-SPIN experiments in the near future, and, hence it can be used to determine the gluon distribution function $ΔG (x)$ in the polarized nucleon.

hep-ph↗
arXiv2003

Lepton Helicity Distributions in Polarized Drell-Yan Process

The lepton helicity distributions in the polarized Drell-Yan process at RHIC energy are investigated. For the events with relatively low invariant mass of lepton pair in which the weak interaction is negligible, only the measurement of lepton helicity can prove the antisymmetric part of the hadronic tensor. Therefore it might be interesting to consider the helicity distributions of leptons to obtain more information on the structure of nucleon from the polarized Drell-Yan process. We estimate the QCD corrections at O(alpha_s) level to the hadronic tensor including both intermediate gamma and Z bosons. We present the numerical analyses for different invariant masses and show that the u (bar{u}) and d (bar{d}) quarks give different and characteristic contributions to the lepton helicity distributions. We also estimate the lepton helicity asymmetry for the various proton's spin configurations.

hep-ph↗
arXiv2002

B meson light-cone wavefunctions in the heavy quark limit

We present a systematic study of the B meson light-cone wavefunctions in QCD in the heavy-quark limit. We construct model-independent formulae for the light-cone wavefunctions in terms of independent dynamical degrees of freedom, which exactly satisfy the QCD equations of motion and constraints from heavy-quark symmetry. The results demonstrate novel behaviors of longitudinal as well as transverse momentum distribution in the B mesons.

hep-ph↗
arXiv2002

Transverse Momentum Distribution in the B Mesons in the Heavy-quark Limit: the Wandzura-Wilczek Part

In the heavy-quark limit, the valence Fock-state components in the B mesons are described by a set of two light-cone wavefunctions. We show that these two wavefunctions obey simple coupled differential equations, which are based on the equations of motion in the Heavy Quark Effective Theory (HQET), and the analytic solutions for them are obtained. The results generalize the recently obtained longitudinal-momentum distribution in the Wandzura-Wilczek approximation by including the transverse momenta. We find that the transverse momentum distribution depends on the longitudinal momentum of the constituents, and that the wavefunctions damp very slowly for large transverse separation between quark and antiquark.

hep-ph↗
arXiv2002

Lepton Asymmetry in Polarized Drell-Yan

The lepton helicity distributions in the polarized Drell-Yan process at RHIC energy are investigated. In the absence of the weak interaction, only the measurement of lepton helicity can prove the antisymmetric part of the hadronic tensor. Therefore it might be interesting to consider the helicity distributions of leptons to obtain more information on the structure of nucleon from the polarized Drell-Yan process. We estimate the QCD corrections at ${\cal O} (α_s)$ level to the hadronic tensor including both intermediate $γ$ and $Z$ bosons. We report the numerical analyses on the $Z$ pole and show that the $u (\bar{u})$ and $d (\bar{d})$ quarks give different and characteristic contributions to the lepton helicity distributions. We also estimate the lepton helicity asymmetry for the various proton's spin configurations.

hep-ph↗
arXiv2002

B meson light-cone distribution amplitudes in the heavy-quark limit

We investigate the B meson light-cone distribution amplitudes in the heavy-quark limit which are relevant for the QCD factorization approach for the exclusive B meson decays. We derive exact relations between two- and three-particle distribution amplitudes from the QCD equations of motion and heavy-quark symmetry constraint. As solution of these relations, we give representations for the quark-antiquark distribution amplitudes in terms of independent dynamical degrees of freedom. In particular, we find that the Wandzura-Wilczek-type contributions are determined uniquely in analytic form in terms of \barΛ, a fundamental mass parameter of heavy-quark effective theory, and that both leading- and higher-twist distribution amplitudes receive the contributions of multi-particle states with additional gluons.

hep-ph↗
arXiv2001

B meson light-cone distribution amplitudes and heavy-quark symmetry

We present a systematic study of the B meson light-cone distribution amplitudes which are relevant for the QCD factorization approach for the exclusive B meson decays. We construct representations for the quark-antiquark distribution amplitudes in terms of independent dynamical degrees of freedom, which exactly satisfy the QCD equations of motion and constraints from heavy-quark symmetry.

hep-ph↗