arXiv subjects

Kazumasa Ohkuma

Publications and source records attributed to Kazumasa Ohkuma.

25 records · Page 2Linked to original sources

arXiv2002

Charmed Hadron Production in Polarized pp Collisions

To extract information about polarized gluons in the proton, production of charmed hadrons, in particular, Λ_c^+ baryon in pp collisions was studied. We calculated the transverse momentum distribution and the pseudo-rapidity distribution of the spin correlation asymmetry A_{LL} between the initial proton and the produced Λ_c^+. Those statistical sensitivities were also calculated under the condition of RHIC experiment. We found that the pseudo-rapidity distribution of A_{LL} is promising for testing the model of polarized gluons in the proton and also the spin-dependent fragmentation model of a charm quark decaying into Λ_c^+ baryon.

hep-ph↗

arXiv2002

Lambda_c^+ production in polarized pp scattering and polarized gluon distribution

To extract information about the polarized gluon distribution, $\dg$, in the nucleons, we propose Lambda_c^+ productions in polarized pp scattering, p + \vec{p} \to \vec{Lambda_c^+} + X, which will be observed at RHIC experiment starting soon. For this process, we have calculated the spin correlation differential cross section, dΔσ/d\pt, and the spin correlation asymmetry defined by \A_ll \equiv [ d Δσ/ d \pt ] / [ d σ/ d\pt ]. We have found that the \A_ll is sensitive to the polarized gluon distribution in the nucleon and thus the process is promising for testing ΔG(x,Q^2).

hep-ph↗

arXiv2002

Single Diffractive Lambda_c^+ Production in Polarized pp Scattering with Polarized Gluon Distribution in the Proton

Based on the hard-scattering factorization which decomposes the diffractive structure function into a pomeron flux and a pomeron structure function, we study the single diffractive Lambda_c^+ production in polarized pp scattering: p + p -> p + Lambda_c^+ + X, which will be observed at forthcoming RHIC experiment. By analyzing the cross section and correlation of the spin polarization between the initial proton and produced Lambda_c^+, we found that the process is quite effective for testing both hard-scattering factorization and models of the polarized gluon distribution in the proton.

hep-ph↗

arXiv2002

Effects of Top-Quark Anomalous Decay Couplings at γγColliders

Most general tbW couplings were investigated in the process γγ-> ttbar -> l^{+-} X for unpolarized photon beams. The double angular and energy distribution of the lepton was calculated and an optimal-observable analysis on it was carried out for the SM ttbar production mechanism. It was also shown that the leptonic angular distribution is insensitive to non-standard tbW vertex. That means that observation of non-standard effects indicates existence of some new physics in the production part.

hep-ph↗

arXiv2002

Charmed Hadron Production at RHIC

To extract information about polarized gluon distribution in the proton, charmed hadron, actually Λ_c^+, productions at RHIC experiment are studied. We found that the spin correlation asymmetry between the initial proton and the produced Λ_c^+ is enable us to distinguish parameterization models of polarized gluons.

hep-ph↗

arXiv2001

CP Violation via Top Quark Anomalous Interaction at the Fermilab Tevatron

Expecting the forthcoming experiment at the upgraded Fermilab Tevatron, we calculated CP-violating polarization asymmetry of t t-bar, A_{CP}= [sigma(p p-bar --> t(-) t-bar(-) X) - sigma(p p-bar --> t(+) t-bar(+) X)]/ sigma(p p-bar --> t t-bar X), due to possible anomalous chromomagnetic (kappa) and chromoelectric (tilde{kappa}) couplings of the gluon to the top quark. Since kappa and tilde{kappa} are sensitive to a contribution from new physics beyond standard model, this observable is useful to search for a signal of new physics. It was seen that the magnitude of A_{CP} depends only on Im(tilde{kappa) and Im(kappa^* tilde{kappa}). Futhermore, we found that when |Im(kappa^* tilde{kappa})|>0.5, one can possibly detect the CP-violation effect as a signal of new physics even if the magnitude of Im(tilde{kappa) is zero.

hep-ph↗

arXiv1998

Remark on CP-violating Polarization Asymmetry of tt-bar via Anomalous Couplings to gamma and Z

We calculate the CP-violating polarization asymmetry of tt-bar, delta =[ sigma(ee-bar --> t(-)t-bar(-))-sigma(ee-bar --> t(+)t-bar(+)) ]/ sigma(ee-bar --> tt-bar), for the most general tt-bar gamma/Z couplings without dropping any non-standard contribution. We find that one term which is usually neglected increases with s and will eventually become non-negligible at very high energy.

hep-ph↗