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T. Yamanishi

Publications and source records attributed to T. Yamanishi.

16 recordsLinked to original sources
arXiv2007

F and D Values with Explicit Flavor Symmetry Breaking and Δs Contents of Nucleons

We propose a new model for describing baryon semi-leptonic decays for estimating $F$ and $D$ values with explicit breaking effects of both SU(3) and SU(2) flavor symmetry, where all possible SU(3) and SU(2) breaking effects are induced from an effective interaction. An overall fit including the weak magnetism form factor yields $F=0.477\pm 0.001$ and $D=0.835\pm 0.001$ with $χ^2=4.43/5$ d.o.f. with $V_{ud}=0.975\pm 0.002$ and $V_{us}=0.221\pm 0.002$. The spin content of strange quarks $Δs$ is estimated from the obtained values $F$ and $D$, and the nucleon spin problem is re-examined. Furthermore, the unmeasured values of $(g_1/f_1)$ and $(g_1)$ for other hyperon semi-leptonic decays are predicted from this new formula.

hep-ph↗
arXiv2003

Polarized light-flavor antiquarks from Drell-Yan processes of h+\vec{N}\to\vec{l^{+-}} + l^{-+} + X

We propose a formula to determine the first moment of difference between the polarized $\bar u$- and $\bar d$-quarks in the nucleon, {\it i.e.} $Δ\bar u-Δ\bar d$ from the Drell-Yan processes in collisions of unpolarized hadrons with longitudinally polarized nucleons by measuring outgoing lepton helicities. As coefficients in the differential cross section depend on the $u$- and $d$-quark numbers in the unpolarized hadron beam, the difference $Δ\bar u-Δ\bar d$ can be independently tested by changing the hadron beam. Moreover, a formula for estimating the $K$-factor in Drell-Yan processes is also suggested.

hep-ph↗
arXiv2002

Semi-inclusive large-$p_T$ light hadron pair production as a probe of polarized gluons

We propose a new formula for extracting the polarized gluon distribution $Δg$ in the proton from the large--$p_T$ light hadron pair production in deep inelastic semi-inclusive reactions. Though the process dominantly occurs via photon--gluon fusion(PGF) and QCD Compton, we can remove an effect of QCD Compton from the combined cross section of light hadron pair production by using symmetry relation among fragmentation functions and thus, rather clearly extract information of $Δg$.

hep-ph↗
arXiv2001

Extraction of Polarized Gluon Distributions from Large-pt Light Hadron Pair Production

We propose a new formula for extracting the polarized gluon distribution from the large-$p_T$ light hadron pair production for semi-inclusive processes in polarized deep inelastic scattering. In general, a large-$p_T$ hadron pair is produced via photon-gluon fusion(PGF) and QCD Compton at the lowest order of QCD. The PGF gives us a direct information on $Δg$ in the nucleon, while QCD Compton becomes background to the signal process for extracting $Δg$. We show that the contribution from this background, i.e. the QCD Compton process, can be removed by using symmetry relation among fragmentation functions and taking an appropriate combination of various light hadron pair production processes, and thus the double spin asymmetry can be described in terms of $Δg/g$ alone.

hep-ph↗
arXiv2000

Polarized Parton Distribution Functions in the Nucleon

Polarized parton distribution functions are determined by using world data from the longitudinally polarized deep inelastic scattering experiments. A new parametrization of the parton distribution functions is adopted by taking into account the positivity and the counting rule. From the fit to the asymmetry data A_1, the polarized distribution functions of u and d valence quarks, sea quarks, and gluon are obtained. The results indicate that the quark spin content is ΔΣ=0.20 and 0.05 in the leading order (LO) and the next-to-leading-order (NLO) MS-bar scheme, respectively. However, if x dependence of the sea-quark distribution is fixed at small x by "perturbative QCD" and Regge theory, it becomes ΔΣ=0.24 ~ 0.28 in the NLO. The small-x behavior cannot be uniquely determined by the existing data, which indicates the importance of future experiments. From our analysis, we propose one set of LO distributions and two sets of NLO ones as the longitudinally-polarized parton distribution functions.

hep-ph↗
arXiv1999

Polarized light flavor sea-quark asymmetry in polarized semi-inclusive processes

We propose new formulas for extracting a difference of the polarized light sea-quark density, $Δ\bar d(x)-Δ\bar u(x)$, from polarized deep-inelastic semi-inclusive data. We have estimated the value of it from the present experimental data measured by SMC and HERMES groups. Although the data might suggest a violation of polarized light flavor sea-quark symmetry, the precision of the present data is not enough for confirming it.

hep-ph↗
arXiv1997

$ψ'$ productions as a test of color-octet mechanism

To test the color-octet model of heavy quarkonium productions, we propose $ψ'$-productions at small-$p_T$ regions in polarized $pp$ collisions for the forthcoming RHIC polarized experiments, whose experimental test at $\sqrt s=50$ GeV might be very promising.

hep-ph↗
arXiv1997

Hard Processes with Spin-Dependent Parton Distributions

To test a possible color-octet contribution of heavy quarkonium productions, we propose $ψ$'-productions for small-$p_T$ regions, where the color-singlet $ψ$' state cannot be produced by the gluon-gluon fusion owing to charge conjugation. We also point out that these processes are very useful to deduce informations of spin-dependent gluon distributions $Δg$.

hep-ph↗
arXiv1997

Semi-inclusive Lambda_c^+ Leptoproductions and Polarized Gluon Distributions

In order to extract the behavior and magnitude of the spin-dependent gluon distribution, we propose a semi-inclusive $Λ_c^+$ production using unpolarized lepton beams and polarized proton targets. The correlation between the target proton spin and the spin of $Λ_c^+$ produced in the target fragmentation region might be very effective for testing various models of polarized gluons.

hep-ph↗
arXiv1996

Delta s density in a proton and unpolarized lepton - polarized proton scatterings

It is shown that the parity--violating deep--inelastic scatterings of unpolarized charged leptons on polarized protons, $\ell^{\mp} + \vec P\to \stackrel{\scriptscriptstyle(-)}{ν_{\ell}} + X$, could provide a sensitive test for the behavior and magnitude of the polarized strange--quark density in a proton. Below charm threshold these processes are also helpful to uniquely determine the magnitude of individual polarized parton distributions.

hep-ph↗
arXiv1995

Polarized Gluons in the Nucleon

QCD suggests that gluons in the nucleon play an important role in {\it so-called} ``the proton spin problem''. In this talk, the behavior of the polarized gluon distribution in the nucleon is discussed by using the positivity condition of distribution functions together with the unpolarized and polarized experimental data.

hep-ph↗
arXiv1995

TWO--SPIN ASYMMETRY OF HEAVY QUARKONIA PRODUCTIONS AT RHIC ENERGY

Hadroproductions of charmonium and bottomonium $χ_J$ in polarized $pp$ collisions at RHIC energies are studied. Two--spin asymmetries $A_{LL}^{χ_J}(pp)$ for these reactions are very good parameters for examining the polarized gluon distributions in a proton.

hep-ph↗
arXiv1994

The Shape of Polarized Gluon Distributions

The recent high precision SMC data on polarized $μp$ scatterings have again confirmed that very little of the proton spin is carried by quarks. To unravel the mystery of the proton spin structure, it is quite important to know the behavior of the polarized gluon distribution. By using the positivity condition of distribution functions together with the unpolarized and polarized experimental data, we restrict the $x$ dependence of the polarized gluon distribution.

hep-ph↗
arXiv1994

A Way to Measure Polarized Gluon Distributions

Effects of the spin-dependent gluon distributions on J/$ψ$ productions in polarized ep and pp collisions are investigated. These productions serve as a very clean probe of the spin-dependent gluon distributions in a proton.

hep-ph↗
arXiv1994

How to probe the spin-dependent gluon distributions

Two-spin asymmetries $A_{LL}^{π^0}$ are calculated for various types of spin-dependent gluon distributions. It is concluded that the E581/704 data on $A_{LL}^{π^0}$ do not necessarily rule out the large gluon polarization but restrict severely the $x$ dependence of its distribution. Moreover, $A_{LL}^{J/ψ}$ are calculated for the forthcoming test of spin-dependent gluon distributions.

hep-ph↗