arXiv subjects

Kazuhiro Tanaka

Publications and source records attributed to Kazuhiro Tanaka.

At least 37 records · Page 2Linked to original sources

arXiv2011

Single Transverse-Spin Asymmetry in Open Charm Production in SIDIS

We discuss the single transverse-spin asymmetry (SSA) to be observed in the $D$-meson production with large transverse-momentum in semi-inclusive DIS (SIDIS), $e p^\uparrow \rightarrow e D X$. This contribution is embodied as a twist-3 mechanism in the collinear factorization, which is induced by purely gluonic correlation inside the transversely-polarized nucleon, in particular, by the three-gluon correlation effects. We derive the first complete formula for the corresponding SSA in the leading-order QCD, revealing the five independent structures with respect to the dependence on the azimuthal angle for the produced $D$-meson. Our result obeys universal structure behind the SSAs in a variety of hard processes. We present the numerical calculations of our SSA formula for the $D$-meson production at the kinematics relevant to a future Electron Ion Collider.

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arXiv2011

Master Formula for the Three-Gluon Contribution to Single Spin Asymmetry in Semi-Inclusive Deep Inelastic Scattering

We derive a "master formula" for the contribution of the three-gluon correlation function in the nucleon to the twist-3 single-spin-dependent cross section for semi-inclusive deep-inelastic scattering, ep^\uparrow\to eDX. This is an extension of the similar formula known for the so-called soft-gluon-pole contribution induced by the quark-gluon correlation function in a variety of processes. Our master formula reduces the relevant interfering partonic subprocess with the participation of the three gluons to the Born cross sections for the γ^*g\to c\bar{c} scattering, which reveals the new structure behind the twist-3 single spin asymmetry and simplifies the actual calculation greatly. A possible extension to higher order corrections is also discussed.

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arXiv2010

On the contribution of twist-3 multi-gluon correlation functions to single transverse-spin asymmetry in SIDIS

We study the single spin asymmetry (SSA) induced by purely gluonic correlation inside a nucleon, in particular, by the three-gluon correlation functions in the transversely polarized nucleon, $p^\uparrow$. This contribution is embodied as a twist-3 mechanism in the collinear factorization framework and controls the SSA to be observed in the $D$-meson production with large transverse-momentum in semi-inclusive DIS (SIDIS), $ep^\uparrow \rightarrow eDX$. We define the relevant three-gluon correlation functions in the nucleon, and determine their complete set at the twsit-3 level taking into account symmetry constraints in QCD. We derive the single-spin-dependent cross section for the $D$-meson production in SIDIS, taking into account all the relevant contributions at the twist-3 level. The result is obtained in a manifestly gauge-invariant form as the factorization formula in terms of the three-gluon correlation functions and reveals the five independent structures with respect to the dependence on the azimuthal angle for the produced $D$ meson. We also demonstrate the remarkable relation between the twist-3 single-spin-dependent cross section and twist-2 cross sections for the $D$-meson production, as a manifestation of universal structure behind the SSA in a variety of hard processes.

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arXiv2010

Contribution of Twist-3 Multi-Gluon Correlation Functions to Single Spin Asymmetry in Semi-Inclusive Deep Inelastic Scattering

As a possible source of the single transverse spin asymmetry, we study the contribution from purely gluonic correlation represented by the twist-3 ``three-gluon correlation" functions in the transversely polarized nucleon. We first define a complete set of the relevant three-gluon correlation functions, and then derive its contribution to the twist-3 single-spin-dependent cross section for the $D$-meson production in semi-inclusive deep inelastic scattering, which is relevant to determine the three-gluon correlations. Our cross-section formula differs from the corresponding result in the literature, and the origin of the discrepancy is clarified.

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arXiv2010

Evolution equation for the B-meson distribution amplitude in the heavy-quark effective theory in coordinate space

The B-meson distribution amplitude (DA) is defined as the matrix element of a quark-antiquark bilocal light-cone operator in the heavy-quark effective theory, corresponding to a long-distance component in the factorization formula for exclusive B-meson decays. The evolution equation for the B-meson DA is governed by the cusp anomalous dimension as well as the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi-type anomalous dimension, and these anomalous dimensions give the "quasilocal" kernel in the coordinate-space representation. We show that this evolution equation can be solved analytically in the coordinate-space, accomplishing the relevant Sudakov resummation at the next-to-leading logarithmic accuracy. The quasilocal nature leads to a quite simple form of our solution which determines the B-meson DA with a quark-antiquark light-cone separation $t$ in terms of the DA at a lower renormalization scale $μ$ with smaller interquark separations $zt$ ($z \leq 1$). This formula allows us to present rigorous calculation of the B-meson DA at the factorization scale $\sim \sqrt{m_b Λ_{\rm QCD}}$ for $t$ less than $\sim 1$ GeV^{-1}, using the recently obtained operator product expansion of the DA as the input at $μ\sim 1$ GeV. We also derive the master formula, which reexpresses the integrals of the DA at $μ\sim \sqrt{m_b Λ_{\rm QCD}}$ for the factorization formula by the compact integrals of the DA at $μ\sim 1$ GeV.

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arXiv2009

Theoretical Update of Twist-3 Single-Spin Asymmetry in Semi-Inclusive DIS

We discuss the single-spin asymmetry in semi-inclusive DIS, $e p^\uparrow \to e πX$, based on the twist-3 mechanism in the collinear factorization relevant for the pion production with the large transverse-momentum. This updates our previous study by including, in particular, the contributions induced by the novel partonic subprocesses, and allows us to derive the entire formula for the corresponding single-spin asymmetry associated with a complete set of the twist-3 quark-gluon correlation functions in the transversely polarized nucleon. We discuss the correspondence with the results obtained by the transverse-momentum-dependent factorization relevant for the pion production with the low transverse-momentum.

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arXiv2009

OPE for B-meson distribution amplitude and dimension-5 HQET operators

The $B$-meson light-cone distribution amplitude (LCDA) is defined as the matrix element of a quark-antiquark bilocal light-cone operator in the heavy-quark effective theory (HQET) and is a building block of QCD factorization formula for exclusive $B$-meson decays. When the corresponding bilocal HQET operator has a light-like distance $t$ between the quark and antiquark fields, the scale $\sim 1/t$ separates the UV and IR regions, which induce the cusp singularity in radiative corrections and the mixing of multiparticle states in nonperturbative corrections, respectively. We treat the bilocal HQET operator based on the operator product expansion (OPE), disentangling the singularities from the IR and UV regions systematically. The matching at the next-to-leading order $α_s$ is performed in the $\overline{\rm MS}$ scheme with a complete set of local operators of dimension $d \le 5$, through a manifestly gauge-invariant calculation organizing all contributions in the coordinate space. The result exhibits the Wilson coefficients with Sudakov-type double logarithms and the higher-dimensional operators with additional gluons. This OPE yields the $B$-meson LCDA for $t$ less than $\sim 1$ GeV$^{-1}$, in terms of $\barΛ= m_B - m_b$ and the two additional HQET parameters as matrix elements of dimension-5 operators. The impact of these novel HQET parameters on the integral relevant to exclusive $B$ decays, $λ_B$, is also discussed.

hep-ph↗

arXiv2009

Operator product expansion for B-meson distribution amplitude and dimension-5 HQET operators

When the bilocal heavy-quark effective theory (HQET) operator for the B-meson distribution amplitude has a light-like distance t between the quark and antiquark fields, the scale \sim 1/t separates the UV and IR regions, which induce the cusp singularity in radiative corrections and the mixing of multiparticle states in nonperturbative corrections, respectively. We treat these notorious UV and IR behaviors simultaneously using the operator product expansion, with the local operators of dimension $d \le 5$ and radiative corrections at order α_s for the corresponding Wilson coefficients. The result is derived in the coordinate space, which manifests the Wilson coefficients with Sudakov-type double logarithms and the higher-dimensional operators with additional gluons. This result yields the B-meson distribution amplitude for t less than \sim 1 GeV^{-1}, in terms of $\barΛ=m_B - m_b$ and the two additional HQET parameters as matrix elements of dimension-5 operators. The impact of these novel HQET parameters on the integral relevant to exclusive B decays, λ_B, is also discussed.

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arXiv2009

Twist-3 Single-Spin Asymmetry for SIDIS and its Azimuthal Structure

We derive the complete twist-3 single-spin-dependent cross section for semi-inclusive DIS, $ep^\uparrow\to eπX$, associated with the complete set of the twist-3 quark-gluon correlation functions in the transversely polarized nucleon, extending our previous study. The cross section consists of five independent structure functions with different azimuthal dependences, consistently with the transverse-momentum-dependent (TMD) factorization approach in the low $q_T$ region. Correspondence with the inclusive DIS limit and comparison with the TMD approach are briefly discussed.

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arXiv2009

Double-Spin Asymmetry A_{LT} for Polarized Drell-Yan Process in p\bar{p} Collisions: Wandzura-Wilczek Contribution

The longitudinal-transverse spin asymmetry $A_{LT}$ in the polarized Drell-Yan process depends on twist-3 quark distributions of nucleon. In addition to the contributions associated with the twist-3 operators, these distributions contain the "Wandzura-Wilczek (WW)" part, which is determined by a certain integral of twist-2 distributions. The recently obtained empirical information on the transversity allows a realistic estimate of the WW contribution to $A_{LT}$ for the polarized $p\bar{p}$ collisions. Our results indicate that rather large $A_{LT}$ ($\sim 10$%) can be observed in the proposed spin experiments at GSI, with novel pattern as a function of dilepton mass compared with $A_{TT}$ and $A_{LL}$.

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arXiv2009

Double Transverse-Spin Asymmetries for Small-Q_T Drell-Yan Pair Production in p\bar{p} Collisions

We discuss the double-spin asymmetries in transversely polarized Drell-Yan process, calculating all-order gluon resummation corrections up to the next-to-leading logarithmic accuracy. This resummation is relevant when the transverse-momentum $Q_T$ of the produced lepton pair is small, and reproduces the (fixed-order) next-to-leading QCD corrections upon integrating over $Q_T$. The resummation corrections in $p\bar{p}$-collision behave differently compared with $pp$-collision cases, and are small at the kinematics in the proposed GSI experiments. This fact allows us to predict large value of the double-spin asymmetries at GSI, using recent empirical information on the transversity.

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arXiv2008

Master Formula for Twist-3 Soft-Gluon-Pole Mechanism to Single Transverse-Spin Asymmetry

Perturbative QCD relates the single transverse-spin asymmetries (SSAs) for hard processes at large transverse-momentum of produced particle to partonic matrix elements that describe interference between scattering from a coherent quark-gluon pair and from a single quark, generated through twist-3 quark-gluon correlations inside a hadron. When the coherent gluon is soft at the gluonic poles, its coupling to partonic subprocess can be systematically disentangled, so that the relevant interfering amplitude can be derived entirely from the Born diagrams for the scattering from a single quark. We establish a new formula that represents the exact rules to derive the SSA due to soft-gluon poles from the knowledge of the twist-2 cross section formula for unpolarized processes. This single master formula is applicable to a range of processes like Drell-Yan and direct-photon production, and semi-inclusive deep inelastic scattering, and is also useful to manifest the gauge invariance of the results.

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arXiv2008

Drell-Yan double-spin asymmetry A_{LT} in polarized p\bar{p} collisions: Wandzura-Wilczek contribution

The longitudinal-transverse spin asymmetry A_{LT} in the polarized Drell-Yan process depends on the twist-3 spin-dependent distributions of nucleon. In addition to the contributions expressed as matrix element of the twist-3 operators, these distributions contain the so-called Wandzura-Wilczek part, which is completely determined by a certain integral of the twist-2 spin-dependent parton distributions. We demonstrate that the recently obtained empirical information on the transversity distribution allows a realistic estimate of the Wandzura-Wilczek contribution to A_{LT} for the case of polarized proton-antiproton collisions. In particular, our results in the Wandzura-Wilczek approximation indicate that rather large A_{LT} can be observed in the proposed spin experiments at GSI, and its behavior as a function of dilepton mass obeys novel pattern, compared with the other double-spin asymmetries A_{TT} and A_{LL}. Our results provide a guide for testing a signal of effects originating from the twist-3 operators associated with quark-gluon correlation.

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arXiv2008

Double Transverse-Spin Asymmetries for Drell-Yan Process in pp and p\bar{p} Collisions: Role of Nonleading QCD Corrections at Small Transverse Momentum

We discuss the double-spin asymmetries in transversely polarized Drell-Yan process, calculating all-order gluon resummation corrections up to the next-to-leading logarithmic accuracy. This resummation is relevant when the transverse-momentum Q_T of the produced lepton pair is small, and reproduces the (fixed-order) next-to-leading QCD corrections upon integrating over Q_T. The resummation corrections behave differently between pp- and p\bar{p}-collision cases and are small for the latter case at the kinematics in the proposed GSI experiments. This fact allows us to predict large value of the double-spin asymmetries at GSI, using the recent empirical information on the transversity.

hep-ph↗

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.

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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.

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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.

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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.

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