arXiv subjects

G. Eilam

Publications and source records attributed to G. Eilam.

23 records · Page 2Linked to original sources

arXiv1995

Radiative Decay $ B \to l νγ$ in the Light Cone QCD Approach

We calculate to the leading twist 2 accuracy the rate for the decay $ B_{u} \rightarrow l νγ$ using the light cone QCD sume rules. We find $ Br( B_{u} \rightarrow l νγ) \simeq 2 \cdot 10^{-6} $. The results are used to test the applicability of the constituent quark model approximation to the same process.The latter estimate is proportional to $ 1/m_{u}^{2} $, where $ m_{u} \simeq \barΛ_{u} $ is the "constituent quark mass", indicating that the process is of long distance type. We find that the two approaches yield similar results for the rate with the choice $ m_{u} \simeq 430-480 \;MeV $. This indicates that the constituent quark model may be used for estimates of the radiative "annihilation" contribution to this and other radiative decays. We point out that this decay may be useful for the measurement of $ |V_{ub}|$.

hep-ph↗

arXiv1995

Long Distance Contribution to $s \to dγ$ and Implications for $Ω^-\to Ξ^-γ, B_s \to B_d^*γ$ and $b \to sγ$

We estimate the long distance (LD) contribution to the magnetic part of the $s \to dγ$ transition using the Vector Meson Dominance approximation $(V=ρ,ω,ψ_i)$. We find that this contribution may be significantly larger than the short distance (SD) contribution to $s \to dγ$ and could possibly saturate the present experimental upper bound on the $Ω^-\to Ξ^-γ$ decay rate, $Γ^{\rm MAX}_{Ω^-\to Ξ^-γ} \simeq 3.7\times10^{-9}$eV. For the decay $B_s \to B^*_dγ$, which is driven by $s \to dγ$ as well, we obtain an upper bound on the branching ratio $BR(B_s \to B_d^*γ)<3\times10^{-8}$ from $Γ^{\rm MAX}_{Ω^-\to Ξ^-γ}$. Barring the possibility that the Quantum Chromodynamics coefficient $a_2(m_s)$ be much smaller than 1, $Γ^{\rm MAX}_{Ω^-\to Ξ^-γ}$ also implies the approximate relation $\frac{2}{3} \sum_i \frac{g^2_{ψ_i}(0)}{m^2_{ψ_i}} \simeq \frac{1}{2} \frac{g^2_ρ(0)}{m^2_ρ} + \frac{1}{6}\frac{g^2_ω(0)}{m^2_ω}$. This relation agrees quantitatively with a recent independent estimate of the l.h.s. by Deshpande et al., confirming that the LD contributions to $b \to sγ$ are small. We find that these amount to an increase of $(4\pm2)\%$ in the magnitude of the $b \to s γ$ transition amplitude, relative to the SD contribution alone.

hep-ph↗

arXiv1995

Energy Distribution of $ϕ$ in Pure Penguin Induced $B$ Decays

We study the energy distribution of $ϕ$ in pure penguin induced $B\rightarrow X_s ϕ$ taking into account the fermi motion of b inside $B$ meson for $b\rightarrow sϕ$ and also modification due to gluon bremsstrahlung process $b\rightarrow sϕg$. We find that the contribution to $B\rightarrow X_sϕ$ from $b\rightarrow sϕg$ is less than 3\%. This study provides a criterion for including most of the $ϕ$'s produced in a penguin process.

hep-ph↗

arXiv1995

LONG DISTANCE EFFECTS AND CP VIOLATION in $B^{\pm}\toρ^{\pm}γ$

We demonstrate that the long distance contribution to $B^{\pm} \to ρ^{\pm} γ$ may have a large effect on the decay rate and through it on the CP violating partial rate asymmetry. The change in the asymmetry can be between a factor of 0.4 and 1.4 with respect to the effect of the short distance contribution alone, depending on the values of the CKM parameters $ρ$ and $η$ .

hep-ph↗

arXiv1994

Pure Leptonic Radiative Decays $B^\pm, D_s\to\ellνγ$ and the Annihilation Graph

Pure leptonic radiative decays of heavy-light mesons are calculated using a very simple non-relativistic model. Dominant contribution originates from photon emission from light initial quark. We find $BR(B^\pm\to\ellνγ)\sim3.5\times10^{-6}$ and $BR(D_s\to \ellνγ)\sim1.7 \times10^{-4}$. The importance of these reactions to clarify the dynamics of the annihilation graph is emphasized.

hep-ph↗