arXiv subjects

S. Fajfer

Publications and source records attributed to S. Fajfer.

At least 37 records · Page 2Linked to original sources

arXiv2001

Constraints on heavy Z' couplings from ΔS = 2 B^- -> K^- K^- π^+ decay

The heavy Z' boson with family nonuniversal couplings can introduce flavour changing effects. Constraints on nondiagonal Z' couplings coming from the μ-e conversion in a muonic atom, K^0 - \bar{K^0} and B - \bar{B} mixing, epsilon and epsilon'/ εCP- violating coefficients have been already established. By using the OPAL upper bound of the branching ratio for the B^- -> K^- K^- π^+ decay, we indicate additional constraints on the Z' couplings. We comment also on the constraints of Z' couplings coming from the b->d d \bar{s} transition. The constraint obtained here from the upper bound of the B^- -> K^- K^- π^+ decay involves a different combination of couplings than those previously presented, but is much weaker.

hep-ph↗

arXiv2001

The D^0 -> K^0 \bar{K^0} decay beyond factorization

The decay mode D^0 -> K^0 \bar{K^0} has no factorizable contribution. We calculate the nonfactorizable chiral loop contributions of order O(p^3)and then we use a heavy-light type chiral quark model to calculate nonfactorizable tree level terms, also of order O(p^3), proportional to the gluon condensate. Calculated chiral loops and the gluon condensate contributions are of the same order of magnitude as the experimental amplitude.

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arXiv2001

The Rare Decay D^0 -> gamma gamma

We present a calculation of the rare decay mode D^0 -> gamma gamma, in which the long distance contributions are expected to be dominant. Using the Heavy Quark Chiral Perturbation Theory Lagrangian with a strong g coupling as recently determined by CLEO from the D^* -> D pi width, we consider both the anomaly contribution which relates to the annihilation part of the weak Lagrangian and the one-loop pi, K diagrams. The loop contributions which are proportional to g and contain the a_1 Wilson coefficient are found to dominate the decay amplitude, which turns out to be mainly parity violating. The branching ratio is then calculated to be (1.0+-0.5)x10^(-8). Observation of an order of magnitude larger branching ratio could be indicative of new physics.

hep-ph↗

arXiv2001

Rare charm meson decays D->Pl^+l^- and c->ul^+l^- in SM and MSSM

We study the nine possible rare charm meson decays D->Pl^+l^- (P=pi,K,eta,eta') using the Heavy Meson Chiral Lagrangians and find them to be dominated by the long distance contributions. The decay D^+ -> pi^+l^+l^- with the branching ratio 1*10^(-6) is expected to have the best chances for an early experimental discovery. The short distance contribution in the five Cabibbo suppressed channels arises via the c->ul^+l^- transition; we find that this contribution is detectable only in the D->pi l^+l^- decay, where it dominates the differential spectrum at high-q^2. The general Minimal Supersymmetric Standard Model can enhance the c->ul^+l^- rate by up to an order of magnitude; its effect on the D->Pl^+l^- rates is small since the c->ul^+l^- enhancement is sizable in low-q^2 region, which is inhibited in the hadronic decay.

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arXiv2001

The Search for New Physics in D^0 --> gamma gamma Decay

We present main results of the investigation of the rare decay mode D^0 -->gamma gamma, in which the long distance contributions are expected to be dominant. Using the Heavy Quark Chiral Lagrangian we have considered the anomaly contribution which relates to the annihilation part of the weak Lagrangian and the one - loop pi, K diagrams. The loop contributions which are proportional to g and contain the a_1 Wilson coefficient are found to dominate the decay amplitude. The branching ratio is then calculated to be (1.0+-0.5)x 10^{-8}. Observation of an order of magnitude larger branching ratio could signal new physics.

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arXiv2001

$ΔS = 2$ decays of $B^-$ meson in MSSM and two Higgs doublet model

In view of the extreme smallness of $ΔS = 2$ transitions of $B$ meson in the Standard Model, we consider their occurence in several extensions of it. Thus, we analyze the three - body $B^- \to K^- K^- π^+$ and two - body $B^- \to K^{*-} \barK^{*0}$, $B^- \to K^- \bar K^{0}$, $B^- \to K^{*-} \bar K^{0}$, $B^- \to K^{-} \bar K^{*0}$ decay modes both in the Standard Model and in the Minimal Supersymmetric Model with and without ${\cal R}$ parity conservation and in two Higgs doublet models. All five modes are found to have a branching ratio of the order of $10^{-13}$ in the Standard Model, while the expected branching ratio in the different extensions vary between $10^{-9} - 10^{-6}$, for a given reasonable choice of parameters.

hep-ph↗

arXiv2001

Nonfactorizable contributions to the decay mode D^0 -> K^0 \bar{K^0}

We point out that the decay mode D^0 -> K^0 \bar{K^0} has no factorizable contribution. In the chiral perturbation language, treating D^0 as heavy, the O(p) contribution is zero. We calculate the nonfactorizable chiral loop contributions of order O(p^3). Then, we use a heavy-light type chiral quark model to calculate nonfactorizable tree level terms, also of order O(p^3), proportional to the gluon condensate. We find that both the chiral loops and the gluon condensate contributions are of the same order of magnitude as the experimental amplitude.

hep-ph↗

arXiv2000

Search for new physics in $ΔS = 2$ two - body (VV, PP, VP) decays of the B^- - meson

The $ΔS = 2$ $b \to \bar d ss$ transition proceeds via the box - diagram in the Standard Model with a branching ratio calculated to be below $10^{-11}$, thus providing an appropriate testing ground for physics beyond the Standard Model. We analyze the $ΔS = 2$ two - body $B^- \to K^{*-} \bar K^{*0}$, $B^- \to K^- \bar K^{0}$, $B^- \to K^{*-} \bar K^{0}$ and $B^- \to K^{-} \bar K^{*0}$ exclusive decays which are driven by the $b \to \bar d ss$ transition, both in the Standard Model and in several extensions of it. The models considered are the minimal supersymmetric model with and without ${\cal R}$ parity conservation and two Higgs doublet models. All four modes are found to have a branching ratio of the order of $10^{-13}$ in the Standard Model, while the expected branching ratio in the different extensions vary between $10^{-9} - 10^{-6}$.

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arXiv2000

A Possible Arena for Searching New Physics - the $Γ(D^0 \to ρ^0 γ)/Γ(D^0 \to ωγ)$ Ratio

We propose to investigate flavour changing neutral currents in the $c \to u γ$ transition through the measurement of the difference between $Γ(D^0 \to ρ^0 γ)$ and $Γ(D^0 \to ωγ)$. This is based on the observation that $D^0 \to (d \bar d) γ$ is due to long distance physics while $D^0 \to (u \bar u) γ$ arises from the $c \to u γ$ transition. The effect of $ρ- ω$ mixing is included. A difference in the decay widths of more than about 30% would be indicative of new physics.

hep-ph↗

arXiv2000

Long distance contribution to $B^- \to K^- K^- π^+$, - a searching ground mode for new physics

The decay $B^- \to K^- K^- π^+$ has been sugested as a test for minimal supersymmetric standard model and for supersymmetric models with R-parity violating couplings, in view of its extreme smallnesss in the standard model. We calculate two long distance contributions to this decay, that associated with $DD$ and $Dπ$ intermediate states and that induced by virtual $D$, $π$ mesons. The branching ratio due to these contributions is $6 \times 10^{-12}$, which is somewhat smaller than the standard model short distance result, leaving this decay free for the search of new physics.

hep-ph↗

arXiv1999

FCNC transition $c\to uγ$ in $B_c\to B_u^*γ$ decay

We propose the $B_c\to B_u^*γ$ decay as the most suitable probe for the flavour changing neutral transition $c\to uγ$. We estimate the short and long distance contributions to this decay within the standard model and we find them to be comparable; this is in contrast to radiative decays of $D$ mesons, that are completely dominated by the long distance contributions. Since the $c\to uγ$ transition is very sensitive to the physics beyond the standard model, the standard model prediction $Br(B_c\to B_u^*γ)\sim 10^{-8}$ obtained here opens a new window for future experiments. The detection of $B_c\to B_u^*γ$ decay at branching ratio well above $10^{-8}$ would signal new physics.

hep-ph↗

arXiv1999

The role of K^*_0(1430) in D->PK and τ->KPν_τdecays

We consider the scalar form factor in the weak current matrix element , P =π,η,η'. It obtains the contributions from the scalar meson resonance K^*_0(1430) and from the scalar projection of the vector meson K^*(892) resonance. We analyze decay amplitudes of the Cabibbo suppressed decays D->K P, P =π,η,η' using the factorization approach. The form factors of the relevant matrix elements are described by assuming the dominance of nearby resonances. The annihilation contribution in these decays arises from the matrix element . All the required parameters are experimentally known except the scalar meson K^*_0(1430) decay constant. We fit the decay amplitudes and we find that final state interaction improves the agreement with the experimental data. Then we extract bounds on scalar form factor parameters and compare them with the experimental data obtained in the analyses of K->πeν_e and K->πμν_μ. The same scalar form factor is present in the τ-> K P ν_τdecay, with P =π,η,η'. Using the obtained bounds we investigate the significance of the scalar meson form factor in the τ-> K P ν_τ, P = π, η, η' decay rates and spectra. We find that the K^*_0(1430) scalar meson dominates in the τ-> K η'ν_τdecay spectrum.

hep-ph↗

arXiv1999

Probing $c\to uγ$ in $B_c\to B_u^*γ$ decay

Flavour changing neutral current (FCNC) transitions $c\to uγ$ and $c\to ul^+l^-$ are very rare in the standard model and present an interesting probe for the physics beyond it. We study long distance contamination to these short distance processes in different hadron decays. As the most suitable probe for $c\to uγ$ transition we propose $B_c\to B_u^*γ$ decay. Its detection at the branching ratio well above $10^{-8}$ would signal new physics. The $c\to ul^+l^-$ transition may be probed at high $m_{ll}$ in $D\to πl^+l^-$. The decays $D\to Vγ$ and $D\to Vl^+l^-$ ($V$ is a light vector meson) are less suitable, since they are dominated by the long distance effects.

hep-ph↗

arXiv1999

Two photon decays of scalar mesons in a covariant quark model

Two photon decay widths of the $J^P = O^+$ scalar mesons $a_{0} (980)$, $f_{0}(980)$, $f_{0}(1370)$ and $χ_{c0}$ are calculated in a covariant model which is characterized by the quark - antiquark structure. Previously such models were used to calculate current form factors. Here a different application is tried. A simple version of the model uses adjusted nonrelativistic model parameters with small quark masses. The results seem to prefer nonideal mixing of $f_0(980)$ and $f_0(1370)$. The calculated decay rate of $χ_{c0}$ agrees with the experimental results.

hep-ph↗

arXiv1999

FCNC transitions $c\to uγ$ and $s\to dγ$ in $B_c\to B_u^γ$ and $B_s\to B_d^γ$ decays

hep-ph↗

arXiv1998

The penguin operators in nonresonant $B^- \to M \bar M π^-$ $(M =π^-, K^-, K^0)$ decays

We investigate the contributions coming from the penguin operators in the nonresonant $B^- \to M \bar M π^-$ ($M =π^-, K^-, K^0$) decays. The effective Wilson coefficients of the the strong penguin operators $O_{4,6}$ are found to be relatively larger. We calculate the contributions arising from the $O_4$ and $O_6$ operators in the nonresonant decays $B^- \to M \bar Mπ^-$ ($M = π^-, K^-, \bar K^0$) using a model combining heavy quark symmetry and the chiral symmetry, developed previously. We find that the forbidden nonresonant $B^- \to K^0 \bar K^0 π^-$ decay occurs through the strong penguin operators. These penguin contributions affect the branching ratios for $B^- \to M \bar Mπ^-$ ($M = π^-, K^-$) by only a few percent. The branching ratio for $B^- \to K^0 \bar K^0 π^-$ is estimated to be of the order $ 10^{-6}$.

hep-ph↗

arXiv1998

Resonant and nonresonant contributions to the weak $D\to Vl^+l^-$ decays

The Cabibbo suppressed decays $D\to Vl^+l^-$ (V is light vector meson) present in principle the opportunity to observe the short distance FCNC transition $c\to ul^+l^-$, which is sensitive to physics beyond the Standard Model. We analyze these as well as the Cabibbo allowed $D \to V l^+ l^-$ decays within the Standard Model, where in addition to the short distance dynamics also the long distance dynamics is present. The long distance contribution is induced by the effective nonleptonic weak Lagrangian accompanied by the emission of a virtual photon, which occurs resonantly via conversion from a vector meson $ρ^0, ω$ or $ϕ$ or nonresonantly as direct emission from a $D$ meson. We calculate the branching ratios for all $D\to Vl^+l^-$ decays using the model, which combines heavy quark symmetry and chiral perturbation theory. 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, which are expected at the rates, that are not much lower than the present experimental upper limit: $D_s^+\to ρ^+μ^+μ^-$ is expected at the branching ratio of approximately $3\cdot 10^{-5}$, while $D^0\to\bar K^{*0}μ^+μ^-$ is expected at $1.7\cdot 10^{-6}$.

hep-ph↗

arXiv1998

Long distance contributions in $D \to V γ$ decays

Using the factorization scheme for the nonleptonic $D \to V V_0$ weak amplitudes, we classify all diagrams which arise in $D \to V γ$ decays and calculate them with the help of the hybrid model which combines the heavy quark effective theory and the chiral Lagrangian approach. Thus we determine the long distance contribution to the amplitudes of Cabibbo allowed and Cabibbo suppressed $D \to Vγ$ decays. The calculation of the expected range of the branching ratios of nine different $D \to V γ$ channels is compared with results of other approaches. The present work establishes an increase of the parity violating contribution in these decays in comparison with previous analyses.

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