arXiv subjects

P. Singer

Publications and source records attributed to P. Singer.

21 records · Page 2Linked to original sources

arXiv1997

Long distance $c \to u γ$ effects in weak radiative decays of D-mesons

We present a detailed analysis of the $D \to V γ$ transitions, using a model which combines heavy quark effective theory and the chiral Lagrangian approach and includes symmetry breaking. We notice that in addition to the previously considered s - channel annihilation and t - channel W - exchange, there is a long distance penguin - like $ c \to u γ$ contribution in the t - channel of Cabibbo - suppressed modes. Its magnitude is determined by the size of symmetry breaking which we calculate with a vector dominance approach. Although smaller in magnitude, the penguin - like contribution would lead to sizeable effects in case of cancellations among the other contributions to the amplitude. Thus, it may invalidate suggested tests for beyond the standard model effects in these decays. We also indicate the range of expectations for the branching ratios of various $D \to V γ$ modes.

hep-ph↗

arXiv1996

Asymmetry in the decay $Ω^-\toΞ^-γ$

We consider the asymmetry in the decay $Ω^-\rightarrowΞ^-γ$ assuming that a Vector Meson Dominance approach for the $s\rightarrow dγ$ transition gives the dominant contribution. Since in this long-distance approximation the decay is due to a single quark transition $s\rightarrow dγ$, the angular distribution asymmetry is given by the single positive asymmetry parameter $α_h = \frac{M^2_s-M^2_d}{M^2_s+M^2_d} = 0.4\pm0.1$. We also discuss the asymmetry in $Ξ\rightarrow Σ^-γ$, which is expected to be between -0.2 and 0.3.

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↗