arXiv subjects

J. Zupan

Publications and source records attributed to J. Zupan.

26 records · Page 2Linked to original sources

arXiv2002

The Radiative Leptonic Decays D^0 -> e^+ e^- gamma, mu^+ mu^- gamma in the Standard Model and Beyond

We present a calculation of the rare decay modes D^0 -> e^+ e^- gamma and D^0 -> mu^+ mu^- gamma in the framework of Standard Model. For the short distance part, we have derived QCD corrections to the Wilson coefficients involved, including C_9. The latter is found to be strongly suppressed by the corrections, leading to diminished values for the c -> u l^+l^- branching ratios in the 10^(-10) range. Within SM the exclusive decays are dominated by long distance effects. Nonresonant contributions are estimated using heavy quark and chiral symmetries to be at the level of 10%, compared to the contributions arising from D^0-> V gamma->l^+ l^- gamma, with V=rho, omega, phi. The total SM branching ratio is predicted to be in the range (1-3) x 10^(-9). We also consider contributions coming from MSSM with and without R parity conservation. Effects from MSSM are significant only for the R-parity violating case. Such contributions enhance the branching ratio D^0-> mu^+ mu^- gamma to 0.5 x 10^(-7), based on appropriately allowed values for C_9 and C_{10}. This selects D^0->mu^+ mu^- gamma as a possible probe of new physics.

hep-ph↗

arXiv2002

The rare decays of D mesons

The flavor changing transitions in the c->u gamma, c->u gamma gamma and c->u l+ l- offer the possibility to search for new physics in the charm sector. We investigate dominant decay mechanisms in the radiative decays D->V gamma, D->P(V) l+ l-, D->gamma gamma and we discuss chances to see physics beyond the standard model in these decays. In addition, we analyze Cabibbo allowed D->K pi gamma decays with nonresonant K pi, and we probe the role of light vector mesons in these decays.

hep-ph↗

arXiv2002

One loop scalar functions in the heavy quark effective theory

We find general solutions for the dimensionally regularised scalar one loop three-point and four-point functions with one heavy quark propagator. The scalar one-point function vanishes, while the expression for the two-point function has been found before. For the latter we give a detailed derivation. We also discuss some special cases and compile useful formulae.

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.

hep-ph↗

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

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.

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↗

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.

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