arXiv subjects

Paul Singer

Publications and source records attributed to Paul Singer.

17 recordsLinked to original sources

arXiv2004

The hidden strangeness mechanism in Ds^+ -> omega pi^+ and Ds^+ -> rho^0 pi^+ decays

We study possible contributions to the Ds^+ -> omega pi^+ and Ds^+ -> rho^0 pi^+ decay amplitudes. The Ds^+ -> omega pi^+ decay amplitude vanishes when the naive factorization is used, while the Ds^+ -> rho^0 pi^+ decay amplitude arises due to the annihilation contribution. We find that amplitudes for both decays might be a result of the internal K, K^* exchange. The Ds^+ -> omega pi^+ amplitude might obtain additional contribution from Ds^+ -> rho^0 eta (eta') re-scattering. The low experimental bound on the Ds^+ -> rho^0 pi^+ rate can be understood as a result of combination of the pi(1300) pole dominated annihilation contribution and the K,K^* internal exchanges. The calculated branching fractions for Ds^+ -> omega pi^+ and Ds^+ -> rho^0 pi^+ are in agreement with the current experimental results.

hep-ph↗

arXiv2003

Final State Interactions in the Ds+ --> omega pi+ and Ds+ --> rho0 pi+ Decays

We investigate the decay mechanisms in the Ds+ --> omega pi+ and Ds+ --> rho0 pi+ transitions. The naive factorization ansatz predicts vanishing amplitude for the Ds+ --> omega pi+ decay, while the Ds+ --> rho0 pi+ decay amplitude does have an annihilation contribution also in this limit. Both decays can proceed through intermediate states of hidden strangeness, e.g. K, K*, which we estimate in this paper. These contributions can explain the experimental value for the Ds+ --> omega pi+ decay rate, which no longer can be viewed as a clean signature of the annihilation decay of Ds+. The combination of the π(1300) pole dominated annihilation contribution and the internal K, K* exchange can saturate present experimental upper bound on Ds+ --> rho0 pi+ decay rate, which is therefore expected to be within the experimental reach. Finally, the proposed mechanism of hidden strangeness FSI constitutes only a small correction to the Cabibbo allowed decay rates Ds--> K K*, phi pi, which are well described already in the factorization approximation.

hep-ph↗

arXiv2002

Charm Radiative Decays with Neutral Mesons D^0 -> K^0(bar) pi^0 gamma, D^0 -> K^0(bar) eta (eta') gamma

The radiative decays D^0 -> K^0(bar) P^0 gamma with nonresonant K^0(bar) P^0 (P^0 = pi^0, eta, eta') are considered within the framework which combines heavy quark effective theory and the chiral Lagrangian. Due to neutral mesons the amplitudes do not have bremsstrahlung contributions. We assume factorization for the weak matrix elements. Light (virtual) vector mesons are found to give the main contribution to the decay amplitudes. The decay D^0 -> K^0(bar) pi^0 gamma is predicted to have a branching ratio of 3 x 10^(-4), with comparable contributions from parity-conserving and parity-violating parts of the amplitude. The decays with eta (eta') in the final state are expected with branching ratios of 1.1 x 10^(-5) and 0.4x10^(-7) respectively and are mainly parity conserving.

hep-ph↗

arXiv2002

Cabibbo Allowed D -> K pi gamma Decays

The weak radiative Cabibbo allowed decays D^+ -> anti K^0 pi^+ gamma and D^0 -> K^- pi^+ gamma with nonresonant K pi are investigated by relying on the factorization approximation for the nonleptonic weak transitions and the model which combines the heavy quark effective theory and the chiral Lagrangian approach. The dominant contributions to the amplitudes come from the long distance effects. The decay amplitude has both parity violating and parity conserving parts. The parity violating part includes also a bremsstrahlung contribution. The branching ratio obtained for the parity conserving part is of the order 10^-4 for the D^0 -> K^- pi^+ gamma decay and 10^-5 for the D^+ -> anti K^0 pi^+ gamma, when the effect of light vector mesons is included, and smaller otherwise. The branching ratio for the parity violating part with a photon energy cut of 50 MeV, is close to 10^-3 for the D^0 decay and 4x10^-4 for the D^+ decay. We present Dalitz plots and energy spectra for both transitions as derived from our model and we probe the role of light vector mesons in these decays.

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arXiv2000

Determination of the strong g-coupling and of the $μ_{B^*Bγ}-$ strength from two-photon decays of heavy vector mesons

We describe a calculation of the two-photon decays of heavy vector-mesons, $B^*\to Bγγ$ and $D^*\to Dγγ$, by using the ``heavy meson chiral Lagrangian''. The decay amplitudes are expressed in terms of the strong coupling $g$ of the Lagrangian at various powers and the strength of the anomalous magnetic dipole $μ_{B^*Bγ}$ (respectively $μ_{D^*D}γ$). In the charm case we are able to express the branching ratio $Γ(D^{*0}\to D^0γγ)/Γ(D^{*0})$ as a function of $g$ only and we expect it to be in the $10^{-6}-10^{-5}$ range, depending on the value of $g$. The determination of $μ_{B^{*0}B^{0}γ},μ_{B^{*+}B^+}γ$ requires a more involved analysis, including the consideration of bremsstrahlung radiation for the $B^{*+}\to B^+γγ$ case.

hep-ph↗

arXiv2000

$ω-ρ$ Mixing and the $ω\toππγ$ Decay

We reexamine the $ω\to π^{0} π^{0} γ$ decay, adding the effect of $ω-ρ$ mixing to the amplitude calculated with the aid of chiral perturbation theory and vector meson dominance. We predict the neutral decay to occur with a width of $Γ($ω\to π^{0} π^{0} γ$) =(390\pm96) {\rm eV}$ and also analyze the effect of the $ω-ρ$ mixing on the $Γ($ω\to π^{0} π^{0} γ$)/ Γ($ω\to π^{+} π^{-} γ$)$ ratio. Several remarks on the effect of $ω-ρ$ mixing on certain radiative decays of vector mesons are presented.

hep-ph↗

arXiv1999

Rare Decays of Heavy Quarks - Searching Ground for New Physics

The search for new physics beyond the standard model is proceeding nowadays intensively along experimental and theoretical lines. We review here the sector of charm radiative decays in this context. The calculation of $D\to Vγ$, $D\to \ell^+\ell^-γ$ transitions reveals their unequivocal dominance by long-distance contributions. On the other hand, the beauty-conserving charm-changing electroweak transition $B_c\to B_u^*γ$ is shown to have unique properties which make it a promising avenue in the search for new physics. We describe a calculation of short- and long-distance contributions to this decay which finds them to be of comparable size. The branching ratio of this decay in the standard model is estimated to be $\simeq 10^{-8}$.

hep-ph↗

arXiv1999

Radiative Decays of Heavy Mesons and the Determination of the Strong g-Coupling

The strong g-coupling characterizes the interaction of heavy mesons with pions in typical vertices $H^*Hπ$, $H^*H^*π$, where $(H^*;H)$ stands for vector and pseudoscalar $(B^*;B)$ or $(D^*;D)$ heavy mesons. Its estimation by different theoretical methods has led to a wide range of possible values. We describe a new approach to the determination of g, which exploits the rare radiative decays $B^*\to Bγγ$ and $D^*\to Dγγ$. It is shown that the branching ratio of $D^*\to Dγγ$ can be expressed as a function of a single unknown $g$ and we calculate it to be in the measurable range between $1.6\times 10^{-6}$ and $3.3\times 10^{-5}$ for 0.25 < g < 1.

hep-ph↗

arXiv1999

Two photon decays of heavy vector mesons, $B^{}\to Bγγ$,$D^{}\to Dγγ$, and the possible determination of the $g_{B^{}(D^{})B(D)π}$ and $g_{B^{*}^0B^0γ}$ couplings

We study the novel decays $B^{*}\to Bγγ$ and $D^{*}\to Dγγ$ using the framework of the Heavy Meson Chiral Lagrangian (HM$χ$L) to leading order in chiral perturbation theory. The branching ratios of these decays are expressed in terms of the strong $g_{B^{*}(D^{*})B(D)π}$ and the electromagnetic $g_{B^{*}(D^*)B(D)γ}$ couplings, thus providing a possible tool for their determination. In the charm case, using the experimentally determined ratios $({D^*}^{0,+}\to Dπ)/({D^*}^{0,+}\to Dγ),$ we are able to express the branching ratio as a function of the strong coupling only. We thus find $1.6\times 10^{-6}<{\rm Br} ({D^{*}}^{0}\to D^0γγ)<3.3\times 10^{-5}$ for $0.25 0.6.$ The expected two-photon differential distributions are presented for both ${B^{*}}^{0} \to B^0 γγ$ and ${D^{*}}^{0}\to D^0γγ,$ for different values of the couplings involved.

hep-ph↗

arXiv1998

$b\to s s \bar d$ Decay in Two Higgs Doublet Models

In the Standard Model, the box-diagram mediated decay $b\to s s \bar d$ is predicted to occur with an extremely small branching ratio of below $10^{-11}$, thus providing a safe testing ground for exposing new physics. We study this process in several Two Higgs Doublet Models and explore their parameter space, indicating where this process becomes observable.

hep-ph↗

arXiv1998

Searching for new physics in $b\to s s \bar d$ decays

For any new physics possibly emerging in the future B experiments, the problem is how to extract the signals from the SM background. We consider the decay $b\to s s\bar d$ which is very small in the SM. In the MSSM this decay is possibly accessible in the future experiments. In the supersymmetric models with R-parity violating couplings, this channel is not strictly constrained, thus being useful in obtaining bounds on the lepton-number violating couplings. A typical candidate for the suggested search is the $B^-\to K^-K^-π^+$ mode.

hep-ph↗

arXiv1997

Two-photon exclusive decays $B_s \to η(η') γγ$ and $B \to K γγ$

The exclusive decay modes $B \to K γγ$ and $B_s \to η(η') γγ$ are shown to have significant branching ratios of approximately $0.5\times 10^{-7}$. This first calculation of these modes employs a model based on a cascade transition $B\to Vγ\to Pγγ$ for estimating the long-distance contribution and the process $b\to sγγ$ for the short distance one.

hep-ph↗

arXiv1996

The Long Distance Contribution to $D\toπl^+l^-$

We calculate the long distance contribution to $D^{+,0}\toπ^{+,0}l^+l^-$ decays by the use of a vector meson dominance model, in which the $ϕ$-meson plays the central role. The branching ratios obtained are $10^{-6}$ and a few times $10^{-7}$ for the resonance and non-resonance regions respectively. The analysis includes a calculation of $D^+\toπ^+ϕ$, consistent with the experimental value.

hep-ph↗

arXiv1996

The $s \to d γ$ Transition in Kaon and Hyperon Decays

We survey the possibilities of detecting the $s \rightarrow d γ$ transition in kaon and hyperon radiative decays. In the more frequent decays, like $K^+ \rightarrow π^+ π^o γ$, $K^+ \rightarrow π^+ \ell^+ \ell^-$, the short-distance contribution is obscured by various long-distance transitions. Among the hyperon radiative decays, $Ξ^- \rightarrow Σ^- γ$ and $Ω^- \rightarrow Ξ^- γ$ are the leading candidates for providing a window to the short-distance $s \rightarrow d γ$. The long-distance $s \rightarrow d γ$ transitions are also analyzed; their magnitude depends on the size of the deviation from a sum-rule among couplings of vector mesons to photons. The measurement of $Ω^- \rightarrow Ξ^- γ$ could provide information on the relative size of the short and long-distance contributions to the magnetic component of $s \rightarrow d γ$.

hep-ph↗

arXiv1996

Weak Radiative Decays of Beauty Baryons

Weak radiative decays of beauty baryons into strange baryons, induced by the electroweak penguin, are estimated by using a quark model approach. Relations between formfactors in the semileptonic and in the weak radiative decays are derived within the heavy quark effective theory. The partial decay widths are found to be of the order of $10^{-15}{\rm MeV}$ for $Λ_b\rightarrowΛγ$ and $Ξ_b\rightarrowΞγ$ and of the oder of $10^{-13}{\rm MeV}$ for $Ω_b\rightarrowΩγ$. The $Ω_b$ radiative decay is thus expected at the sizable branching ratio of approximately $10^{-4}$.

hep-ph↗

arXiv1996

Two-body Cabibbo-suppressed Decays of Charmed Baryons into Vector Mesons and into Photons

The heavy quark effective theory and the factorization approximation are used to treat the Cabibbo-suppressed decays of charmed baryons to vector mesons, $Λ_C\rightarrow p{ρ^0}, pω$, $Ξ_C^{+,0}\rightarrowΣ^{+,0}ϕ, Σ^{+,0}{ρ^0}, Σ^{+,0}ω$ and $Ξ_C^{0}\rightarrowΛϕ, Λρ, Λω$. The input from two recent experimental results on $Λ_C$ decays allows the estimation of the branching ratios for these modes, which turn out to be between $10^{-4}$ and $10^{-3}$. The long distance contribution of these transitions via vector meson dominance to the radiative weak processes $Λ_C\rightarrow pγ$, $Ξ_C\rightarrowΣγ$ and $Ξ_C^0\rightarrowΛγ$ leads to quite small branching ratios, $10^{-6}-10^{-9}$; the larger value holds if a sum rule between the coupling constants of the vector mesons is broken.

hep-ph↗

arXiv1995

Weak Radiative Decays of Hyperons and of Charm and Beauty Baryons

A review is presented of the weak radiative decays of baryons.It includes an anlysis of the possible contributions of electromagnetic penguins to these decays,a survey of the difficulties still encountered in the sector of hyperon decays and a short account on some new developments on this topic. The theoretical treatments on charm and beauty baryon decays are summarized,with a good outlook for their detection.

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