Searcharxiv⌕ Search

arXiv subjects

S. Fajfer

Publications and source records attributed to S. Fajfer.

53 records · Page 3Linked to original sources
arXiv1998

Radiative decays of D mesons

The short-distance contribution due to the $c\to uγ$ penguin as well as long-distance contributions are considered in an analysis of $D\to Vγ$ decays, the latter being dominant. The matrix elements for nine $D\to Vγ$ transitions are calculated using a hybrid model which combines heavy quark effective theory and the chiral Lagrangian. We present the expected range of the branching ratios for these decays, the most frequent ones $D^0\to \bar{K}^{*0}γ$ and $D^+_s \to ρ^+γ$, being a few times $10^{-4}$.

hep-ph↗
arXiv1998

The CP violating asymmetry in $B^{\pm} \to M {\bar M} π^{\pm}$ decays

We analyze the asymmetry in the partial widths for the decays $B^{\pm} \to M {\bar M} π^{\pm}$ ($ M = π^+, K ^+, π^0, η$), which results from the interference of the nonresonant decay amplitude with the resonant amplitude for $B^{\pm} \to χ_{c0} π^{\pm} $ followed by the decay $χ_{c0} \to M {\bar M} $. The CP violating phase $γ$ can be extracted from the measured asymmetry. We find that the partial width asymmetry for $B^\pm \to π^+ π^- π^\pm$ is about $0.33~sin γ$, and about $0.45~ sin γ$ for $B^\pm \to K^+ K^-π^\pm$, while it is somewhat smaller for $B^\pm \to π^0 π^0 π^\pm$ and $B^\pm \to ηηπ^\pm$. Potential sources of uncertainties in these results, primarily coming from poorly known input parameters, are discussed.

hep-ph↗
arXiv1998

Can FCNC transition $c\to ul^+l^-$ be seen in $D\to Vl^+l^-$ decays?

The decays $D\to Vl^+l^-$ present in principle the opportunity to observe the short distance FCNC transition $c\to ul^+l^-$, which is sensitive to the physics beyond the Standard Model. We analyze the $D \to V l^+ l^- $ decays within the Standard Model, where in addition to the short distance dynamics also the long distance dynamics is present. The short distance contribution due to $c\to ul^+l^-$ transition, which is present only in the Cabibbo suppressed decays, is found to be three orders of magnitude smaller than the long distance contribution. The branching ratios well above $10^{-7}$ for Cabibbo suppressed decays could signal new physics. The most frequent decays are the Cabibbo allowed decays $D_s^+\toρ^+μ^+μ^-$ and $D^0\to\bar K^{*0}μ^+μ^-$, which are expected at the branching ratios of $3\cdot 10^{-5}$ and $1.7\cdot 10^{-6}$, respectively. These rates are not much lower than the present experimental upper limit.

hep-ph↗
arXiv1998

Signal for CP violation in $B^{\pm} \to P {\bar P} π^{\pm}$ decays

We analyze the partial rate asymmetry in $B^{\pm} \to P {\bar P} π^{\pm}$ decays ($ P = π^+, K ^+, π^0, η$) which results from the interference of the nonresonant decay amplitude and the resonant amplitude for $B^{\pm} \to χ_{c0} π^{\pm} $ followed by the decay $χ_{c0} \to P {\bar P} $. The CP violating phase $γ$ can be extracted from the measured asymmetry. We find that the partial rate asymmetry for $B^\pm \to π^+ π^- π^\pm$ is $0.33~sin γ$, while for $B^\pm \to K^+ K^-π^\pm$ it amounts $0.45~ sin γ$.

hep-ph↗
arXiv1998

Resonant and nonresonant D+ -> K- pi+ l+ nu(l) semileptonic decays

We analyse the semileptonic decay D+ -> K- pi+ l+ nu(l) using an effective Lagrangian developed previously to describe the decays D -> P l nu(l) and D -> V l nu(l). Light vector mesons are included in the model which combines the heavy quark effective Lagrangian and chiral perturbation theory approach. The nonresonant and resonant contributions are compared. With no new parameters the model correctly reproduces the measured ratio Gamma(nres)/Gamma(nres + res). We also present useful nonresonant decay distributions. Finally, a similar model, but with a modified current which satisfies the soft pion theorems at the expense of introducing another parameter, is analyzed and the results of the models are compared.

hep-ph↗
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

SU(3) flavor symmetry breaking and semileptonic decays of heavy mesons

Assuming the ${\bar D}^0, D^-, D^-_s$ and $B^+, B^0, B_s^0$ mesons belong to triplets of SU(3) flavor symmetry, we analyse the form factors in the semileptonic decays of these mesons. Both quark and meson mass differences are taken into account. We find a number of relations, in agreement with the present data as well as with previous analyses, and predict certain ratios of form factors, not yet measured, most notably the D meson decay constant $f_D = 209 \pm 39$ MeV.

hep-ph↗
arXiv1996

The role of resonances in rare K decays

The decays $K \to πl^{+} l^{-}$, $K \to πγγ$ and $K \to πν{\bar ν}$ are investigated using the higher order terms of the chiral perturbation theory. The counterterms induced by strong, weak and electromagnetic interactions are determined assuming the resonance exchange. (Talk presented at the Workshop on K-Physics, Orsay, France, 30 May - 4 June, 1996)

hep-ph↗
arXiv1995

An effective model for charmed meson semileptonic decays

We analyze charm meson semileptonic decays using the measured ratios $Γ_L/Γ_T$ and $Γ_{+}/Γ_{-}$ from $D\to {\bar K}^{*}$ and the branching ratios for $D \to {\bar K}^{*}$ and $D \to {\bar K}$. First we introduce the light vector mesons in a model which combines the heavy quark effective Lagrangian and the chiral perturbation approach. We propose a method which predicts the behavior of the form factors. Using the available experimental data we determine the values of some model parameters and reproduce the observed branching ratios for $D_{s} \to Φ$, $D_{s} \to (η+ η^{\prime})$ and $D \to π$. We make predictions for the yet unmeasured branching ratios and polarization observables.

hep-ph↗
arXiv1995

$c\to u γ$ in Cabibbo suppressed D meson radiative weak decays

We investigate Cabibbo suppressed $D^{0}$, $D^{+}$ and $D^{+}_{s}$ radiative weak decays in order to find the best mode to test $c\to u γ$ decay. Combining heavy quark effective theory and the chiral Lagrangian approach we determine the decay widths. We calculate $Γ(D^{0}\to ρ^{0}/ωγ)/ Γ(D^{0}\to {\bar K}^{*0} γ)$ previously proposed to search for possible New Physics. However, we notice that there are large, unknown, corrections within the Standard Model. We propose a better alternative, the ratio $Γ(D_{s}^{+}\to K^{*+} γ)/ Γ(D_{s}^{+}\to ρ^{+} γ)$, and show that it is less sensitive to the Standard Model.

hep-ph↗
arXiv1995

Charm meson radiative decays

Combining heavy quark effective theory and the chiral Lagrangian approach we investigate D meson radiative decays. First, we reanalyse $D^{*} \rightarrow D γ$ decays using heavy quark spin symmetry, chiral symmetry Lagrangian, but including also the light vector mesons. Then, we calculate branching ratios $D \rightarrow V γ$. We make some comments on the Cabbibo suppressed decays $D \to ρ/ ωγ$ and the branching ratios of $D \rightarrow P P γ$ decays.

hep-ph↗
arXiv1995

Saturation of counterterms by resonances in $K \to πe^{+} e^{-}$ decays

The decays $K^{+} \rightarrow π^{+} e^{+} e^{-}$, $K_{S} \rightarrow π^{0} e^{+} e^{-}$ and $K_{L} \rightarrow π^{0} e^{+} e^{-}$ are reinvestigated within the framework of chiral perturbation theory. The counterterms induced by strong, electromagnetic and weak interactions are determined assuming the resonance exchange. The weak deformation model, the factorization model and the large $N_{c}$ limit are used to create a weak Lagrangian. It is found that the results of the first two approaches depend on the $H_{1}$ coupling, defined in the effective chiral Lagrangian of the ${\it O} (p^{4})$ order. The set of parameters used in the extended Nambu and Jona-Lasinio model can accommodete $K^{+} \rightarrow π^{+} e^{+} e^{-}$ decay rate within the factorization approach. The CP violating $K_{L} \rightarrow π^{0} e^{+} e^{-}$ decay rate is discussed.

hep-ph↗
arXiv1994

Vector and pseudoscalar charm meson radiative decays

Combining heavy quark effective theory and the chiral Lagrangian approach we investigate radiative decays of pseudoscalar $D$ mesons. We first reanalyse $D^{*} \rightarrow D γ$ decays within the effective Lagrangian approach using heavy quark spin symmetry, chiral symmetry Lagrangian, but including also the light vector mesons. We then investigate $D \rightarrow V γ$ decays and calculate the $D^0 \rightarrow \bar{K}^{*0} γ$ and $D^{s+} \rightarrow ρ^+ γ$ partial widths and branching ratios.

hep-ph↗