arXiv subjects

Emi Kou

Publications and source records attributed to Emi Kou.

25 records · Page 2Linked to original sources

arXiv2009

Soft Photon Problem in Leptonic B-decays

We point out at the peculiarity of B --> mu nu decay, namely the enhancement of the soft photon events which originate from the structure dependent part of the B --> mu nu gamma amplitude. This may be a dominant source of systematic uncertainty and compromise the projected experimental uncertainty on Gamma(B --> mu nu). We show that the effect of these soft photons can be controlled if the experimental cut on identification of soft photons is lowered and especially if the better resolution in identifying the momentum of muon emerging from B --> mu nu, is made. A lattice QCD computation of the relevant form factors would be highly helpful for a better numerical control over the structure dependent soft photon emission.

hep-ph↗

arXiv2003

B->gamma e nu Transitions from QCD Sum Rules

B->gamma e nu transitions have recently been studied in the framework of QCD factorization. The attractiveness of this channel for such an analysis lies in the fact that, at least in the heavy quark limit, the only hadron involved is the B meson itself, so one expects a very simple description of the form factor in terms of a convolution of the B meson distribution amplitude with a perturbative kernel. This description, however, does not include contributions suppressed by powers of the b quark mass. In this letter, we calculate corrections to the factorized expression which are induced by the ``soft'' hadronic component of the photon. We demonstrate that the power-suppression of these terms is numerically not effective for physical values of the $b$ quark mass and that they increase the form factor by about 30% at zero momentum transfer. We also derive a sum rule for lambda_B, the first negative moment of the B meson distribution amplitude, and find lambda_B = 0.6 GeV (to leading order in QCD).

hep-ph↗

arXiv2000

On the $η'$ Gluonic Admixture

The $η'$ which is an $SU(3)_F$ singlet state can contain a pure gluon component, gluonium. We examine this possibility by analysing all available experimental data. It is pointed out that the $η'$ gluonic component may be as large as 26%. We also show that the amplitude for $J/ψ-> η'γ$ decay obtains a notable contribution from gluonium.

hep-ph↗

arXiv1998

Possible large direct CP asymmetry in hadronic B+- -> π+- η' decays

We calculate the branching ratio and direct CP asymmetry in nonleptonic two body B decays B^+- ->π^+- η'. It is shown that the tree diagram and gluon fusion mechanism via penguin diagram have comparable contributions to these decays which, as a result, could provide an interesting venue for investigating CP violation. Our estimate shows that the direct CP asymmetry in the above decays could be as large as 75% which along with a branching ratio B(B^- ->π^- η')=3.4 X 10^{-6} should be accessible to experiment in the near future.

hep-ph↗

arXiv1998

Nonperturbative QCD contribution to gluon-gluon-eta' vertex

We investigate the momentum dependence of the g*-g-eta' vertex form factor in the presence of the nonperturbative QCD vacuum condensate. The behaviour of this form factor is crucial for, among other things, some proposed mechanisms devised to explain the large branching ratio for fast eta' production in charmless B decays observed by CLEO. We show that the leading momentum dependence of this vertex form factor is not altered when the contribution of nonperturbative quark condensate is considered.

hep-ph↗

arXiv1997

Intermediate psuedoscalar resonance contributions to B->X_s photon photon

We calculate the decay rate B-> X_s photon photon via intermediate psuedoscalar charmonium eta_c. This process is thought to be the main long-distance contribution which dominates the corresponding inclusive rare B decay. We point out that once the momentum dependence of eta_c-> photon photon conversion strength, due to off-shellness of the intermediate eta_c, is taken into account, the rate of this decay mode is reduced. The change in differential decay rate in region of spectrum immediately below m_{eta_c} is more significant. On the other hand, we point out that the unexpectedly large branching ratio for B-> X_s eta' which is recently observed by CLEO could indicate a potentially larger long-distance contribution via eta' resonance.

hep-ph↗

arXiv1997

Combined B->X_sψand B-> X_sη_c decays as a test of factorization

We calculate the inclusive decays $B\to X_sψ$ and $B\to X_sη_c$ using factorization assumption. To investigate the bound state effect of the decaying B meson in these inclusive decays we take into account the motion of the $b$ quark using a Gaussian momentum distribution model. The resulting correction to free quark decay approximation is around 6% at most. Utilizing a potential model evaluation of the ratio of the decay constants $f^2_{η_c}/f^2_ψ$, it is shown that the ratio $R=Γ(B\to X_sη_c )/Γ(B\to X_sψ)$ can be used as a possible test of factorization assumption.

hep-ph↗