Blazenka Melic | Karlsruhe Institute of Technology (KIT) (original) (raw)
Papers by Blazenka Melic
Physics Letters B, 2000
The preasymptotic effects originating from the four-quark operators are disentangled from the oth... more The preasymptotic effects originating from the four-quark operators are disentangled from the other contributions by considering appropriate combinations of inclusive decay rates. Under the assumption of the isospin and heavy-quark symmetry, a set of relations connecting charmed and beauty decays is obtained without invoking specific models. The results are compared with other approaches and confronted with experiment.
Physics Letters B, 1999
We extend Voloshin's recent analysis of charmed and beauty hyperon decays based on SU (3) symmetr... more We extend Voloshin's recent analysis of charmed and beauty hyperon decays based on SU (3) symmetry and heavy quark effective theory, by introducing a rather moderate model-dependence, in order to obtain more predictive power, e.g. the values of lifetimes of the (Λ b , Ξ b) hyperon triplet and the lifetime of Ω b. In this way we obtain an improvement of the ratio τ (Λ b)/τ (B 0 d) ∼ 0.9 and the hierarchy of lifetimes τ (Λ b) ≃ τ (Ξ 0 b) < τ (Ξ − b) < τ (Ω b) with lifetimes of Ξ − b and Ω b exceeding the lifetime of Λ b by 22% and 35%, respectively.
Physical Review D, 2003
We evaluate the next-to-next-to-leading order corrections to the hard-scattering amplitude of the... more We evaluate the next-to-next-to-leading order corrections to the hard-scattering amplitude of the photon-topion transition form factor. Our approach is based on the predictive power of the conformal operator product expansion, which is valid for a vanishing  function in the so-called conformal scheme. The Wilson coefficients appearing in the nonforward kinematics are then entirely determined from those of the polarized deep inelastic scattering known to next-to-next-to-leading order accuracy. We propose different schemes to include explicitly also the conformal symmetry breaking term proportional to the  function and discuss numerical predictions calculated in different kinematical regions. It is demonstrated that the photon-to-pion transition form factor can provide a fundamental testing ground for our QCD understanding of exclusive reactions.
Nuclear Physics B - Proceedings Supplements, 2001
In this talk we present theoretical evidence that the exclusive/inclusive ratio of semileptonic Λ... more In this talk we present theoretical evidence that the exclusive/inclusive ratio of semileptonic Λ b-decays exceeds that of semileptonic B-decays, where the experimental exclusive/inclusive ratio amounts to about 66%. We start from the observation that the spectator quark model provides a lower bound on the leading order Isgur-Wise function of the Λ b → Λ c transition in terms of the corresponding B → D, D * mesonic Isgur-Wise function. Using experimental data for the B → D, D * mesonic Isgur-Wise functions this bound is established. Applying a QCD sum rule estimate of the Λ b → Λ c transition form factor which satisfy the spectator quark model bound we predict the exclusive/inclusive ratio of semileptonic Λ b decay rates to lie in a range between 0.81 and 0.89. We also provide an upper bound on the baryonic Isgur-Wise function which is determined from the requirement that the exclusive rate should not exceed the inclusive rate. Our pre-Osaka results are discussed in the light of new recent preliminary experimental results on the pertinent mesonic and baryonic form factors presented at the Osaka ICHEP 2000 Conference.
The European Physical Journal C, 2004
We briefly review the calculational procedure for the PQCD prediction for hard exclusive quantiti... more We briefly review the calculational procedure for the PQCD prediction for hard exclusive quantities and reconsider the problem of the factorization scale dependence.
The European Physical Journal C, 2005
We consider the Standard Model on a non-commutative space and expand the action in the non-commut... more We consider the Standard Model on a non-commutative space and expand the action in the non-commutativity parameter θ µν. No new particles are introduced, the structure group is SU (3) × SU (2) × U (1). We derive the leading order action. At zeroth order the action coincides with the ordinary Standard Model. At leading order in θ µν we find new vertices which are absent in the Standard Model on commutative space-time. The most striking features are couplings between quarks, gluons and electroweak bosons and many new vertices in the charged and neutral currents. We find that parity is violated in non-commutative QCD. The Higgs mechanism can be applied. QED is not deformed in the minimal version of the NCSM to the order considered.
The European Physical Journal C, 2005
In this article we review the electroweak charged and neutral currents in the Non-Commutative Sta... more In this article we review the electroweak charged and neutral currents in the Non-Commutative Standard Model (NCSM) and compute the Higgs and Yukawa parts of the NCSM action. With the aim to make the NCSM accessible to phenomenological considerations, all relevant expressions are given in terms of physical fields and Feynman rules are provided. *
The European Physical Journal C, 1999
We extract the B, D, and D * meson wave functions from the CLEO data of the decays B → K * γ and ... more We extract the B, D, and D * meson wave functions from the CLEO data of the decays B → K * γ and B → D (*) π in the perturbative QCD framework. In this formalism, various logarithmic corrections are organized to give the Wilson evolution from the W boson mass down to the characteristic scale of a decay process, which is of order of the b quark mass, and the Sudakov evolution from the characteristic scale to a lower factorization scale of order Λ QCD. With large logarithms organized, the b quark decay amplitudes are evaluated reliably in perturbation theory. Below the factorization scale, QCD dynamics is regarded as being nonperturbative, and absorbed into meson wave functions. Because of their universality, the heavy-meson wave functions determined in this work, can be employed to make predictions of other decay modes.
Physics Letters B, 2000
The preasymptotic effects originating from the four-quark operators are disentangled from the oth... more The preasymptotic effects originating from the four-quark operators are disentangled from the other contributions by considering appropriate combinations of inclusive decay rates. Under the assumption of the isospin and heavy-quark symmetry, a set of relations connecting charmed and beauty decays is obtained without invoking specific models. The results are compared with other approaches and confronted with experiment.
Physics Letters B, 1999
We extend Voloshin's recent analysis of charmed and beauty hyperon decays based on SU (3) symmetr... more We extend Voloshin's recent analysis of charmed and beauty hyperon decays based on SU (3) symmetry and heavy quark effective theory, by introducing a rather moderate model-dependence, in order to obtain more predictive power, e.g. the values of lifetimes of the (Λ b , Ξ b) hyperon triplet and the lifetime of Ω b. In this way we obtain an improvement of the ratio τ (Λ b)/τ (B 0 d) ∼ 0.9 and the hierarchy of lifetimes τ (Λ b) ≃ τ (Ξ 0 b) < τ (Ξ − b) < τ (Ω b) with lifetimes of Ξ − b and Ω b exceeding the lifetime of Λ b by 22% and 35%, respectively.
Physical Review D, 2003
We evaluate the next-to-next-to-leading order corrections to the hard-scattering amplitude of the... more We evaluate the next-to-next-to-leading order corrections to the hard-scattering amplitude of the photon-topion transition form factor. Our approach is based on the predictive power of the conformal operator product expansion, which is valid for a vanishing  function in the so-called conformal scheme. The Wilson coefficients appearing in the nonforward kinematics are then entirely determined from those of the polarized deep inelastic scattering known to next-to-next-to-leading order accuracy. We propose different schemes to include explicitly also the conformal symmetry breaking term proportional to the  function and discuss numerical predictions calculated in different kinematical regions. It is demonstrated that the photon-to-pion transition form factor can provide a fundamental testing ground for our QCD understanding of exclusive reactions.
Nuclear Physics B - Proceedings Supplements, 2001
In this talk we present theoretical evidence that the exclusive/inclusive ratio of semileptonic Λ... more In this talk we present theoretical evidence that the exclusive/inclusive ratio of semileptonic Λ b-decays exceeds that of semileptonic B-decays, where the experimental exclusive/inclusive ratio amounts to about 66%. We start from the observation that the spectator quark model provides a lower bound on the leading order Isgur-Wise function of the Λ b → Λ c transition in terms of the corresponding B → D, D * mesonic Isgur-Wise function. Using experimental data for the B → D, D * mesonic Isgur-Wise functions this bound is established. Applying a QCD sum rule estimate of the Λ b → Λ c transition form factor which satisfy the spectator quark model bound we predict the exclusive/inclusive ratio of semileptonic Λ b decay rates to lie in a range between 0.81 and 0.89. We also provide an upper bound on the baryonic Isgur-Wise function which is determined from the requirement that the exclusive rate should not exceed the inclusive rate. Our pre-Osaka results are discussed in the light of new recent preliminary experimental results on the pertinent mesonic and baryonic form factors presented at the Osaka ICHEP 2000 Conference.
The European Physical Journal C, 2004
We briefly review the calculational procedure for the PQCD prediction for hard exclusive quantiti... more We briefly review the calculational procedure for the PQCD prediction for hard exclusive quantities and reconsider the problem of the factorization scale dependence.
The European Physical Journal C, 2005
We consider the Standard Model on a non-commutative space and expand the action in the non-commut... more We consider the Standard Model on a non-commutative space and expand the action in the non-commutativity parameter θ µν. No new particles are introduced, the structure group is SU (3) × SU (2) × U (1). We derive the leading order action. At zeroth order the action coincides with the ordinary Standard Model. At leading order in θ µν we find new vertices which are absent in the Standard Model on commutative space-time. The most striking features are couplings between quarks, gluons and electroweak bosons and many new vertices in the charged and neutral currents. We find that parity is violated in non-commutative QCD. The Higgs mechanism can be applied. QED is not deformed in the minimal version of the NCSM to the order considered.
The European Physical Journal C, 2005
In this article we review the electroweak charged and neutral currents in the Non-Commutative Sta... more In this article we review the electroweak charged and neutral currents in the Non-Commutative Standard Model (NCSM) and compute the Higgs and Yukawa parts of the NCSM action. With the aim to make the NCSM accessible to phenomenological considerations, all relevant expressions are given in terms of physical fields and Feynman rules are provided. *
The European Physical Journal C, 1999
We extract the B, D, and D * meson wave functions from the CLEO data of the decays B → K * γ and ... more We extract the B, D, and D * meson wave functions from the CLEO data of the decays B → K * γ and B → D (*) π in the perturbative QCD framework. In this formalism, various logarithmic corrections are organized to give the Wilson evolution from the W boson mass down to the characteristic scale of a decay process, which is of order of the b quark mass, and the Sudakov evolution from the characteristic scale to a lower factorization scale of order Λ QCD. With large logarithms organized, the b quark decay amplitudes are evaluated reliably in perturbation theory. Below the factorization scale, QCD dynamics is regarded as being nonperturbative, and absorbed into meson wave functions. Because of their universality, the heavy-meson wave functions determined in this work, can be employed to make predictions of other decay modes.