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A. Pineda

Publications and source records attributed to A. Pineda.

24 records · Page 2Linked to original sources
arXiv1997

Calculation of Quarkonium Spectrum and $m_b, m_c$ to Order $α_s^4$

We include two loop, relativistic one loop and second order relativistic tree level corrections, plus leading nonperturbative contributions, to obtain a calculation of the lower states in the heavy quarkonium spectrum correct up to, and including, $O(α_s^4)$ and leading $Λ^4/m^4$ terms. This allows us, in particular, to obtain a model independent determination of the pole masses of the $b, c$ quarks, $$m_b=5 015^{+110}_{-70} mev; m_c=1 884^{+222}_{-133} mev$$ to which correspond the $\bar{\hbox{MS}}$ masses, $$\bar{m}_b(\bar{m}_b^2)=4 453^{+50}_{-32} mev; \bar{m}_c(\bar{m}_c^2)=1 547^{+169}_{-102} mev.$$ The decay $Γ(Υ\to e^+e^-)$ is found in agreement with experiment, $$Γ(Υ\to e^+e^-)=1.135^{+0.27}_{-0.29} kev (\hbox{exp.}=1.320\pm0.04 kev),$$ and the hyperfine splitting is predicted to be $$M(Υ)-M(η)=48.5^{+15.7}_{-12.2} mev.$$

hep-ph↗
arXiv1997

Next-to-leading nonperturbative calculation in heavy quarkonium

The next-to-leading nonperturbative contributions to heavy quarkonium systems are calculated. The applicability of the Voloshin-Leutwyler approach to heavy quarkonia systems for the physical cases of Bottomonium and Charmonium is investigated. We study whether the background gluon field correlation time can be considered to be infinity or not, by calculating the leading correction to this assumption and checking whether the expansion is under control. A phenomenological analysis of our results is also performed. The results make us feel optimistic about the $Υ(1S)$ and to a lesser extent about the $J/ψ$ but do not about higher levels. We also briefly discuss the connection with different models where a finite gluon correlation time is introduced.

hep-ph↗
arXiv1996

Heavy Quarkonium and nonperturbative corrections

We analyse the possible existence of non-perturbative contributions in heavy $\bar Q Q$ systems ($\bar Q$ and $Q$ need not have the same flavour) which cannot be expressed in terms of local condensates. Starting from QCD, with well defined approximations and splitting properly the fields into large and small momentum components, we derive an effective lagrangian where hard gluons (in the non-relativistic aproximation) have been integrated out. The large momentum contributions (which are dominant) are calculated using Coulomb type states. Besides the usual condensate corrections, we see the possibility of new non-perturbative contributions. We parametrize them in terms of two low momentum correlators with Coulomb bound state energy insertions $E_n$. We realize that the Heavy Quark Effective lagrangian can be used in these correlators. We calculate the corrections that they give rise to in the decay constant, the bound state energy and the matrix elements of bilinear currents at zero recoil. We study the cut-off dependence of the new contributions and we see that it matches perfectly with that of the large momentum contributions. We consider two situations in detail: i) $E_n>> Λ_{QCD}$ ($M_Q \rightarrow \infty$) and ii) $E_n << Λ_{QCD}$, and briefly discuss the expected size of the new contributions in $Υ$ , $J/Ψ$ and $B_{c}^{\ast}$ systems.

hep-ph↗
arXiv1996

Heavy Quark Hadronic Lagrangian for S-wave Quarkonium

We use Heavy Quark Effective Theory (HQET) techniques to parametrize certain non-perturbative effects related to quantum fluctuations that put both heavy quark and antiquark in quarkonium almost on shell. The large off-shell momentum contributions are calculated using Coulomb type states. The almost on-shell momentum contributions are evaluated using an effective 'chiral' lagrangian which incorporates the relevant symmetries of the HQET for quarks and antiquarks. The cut-off dependence of both contributions matches perfectly. The decay constants and the matrix elements of bilinear currents at zero recoil are calculated. The new non-perturbative contributions from the on-shell region are parametrized by a single constant. They turn out to be $O(α^2/Λ_{QCD} a_{n})$, $a_{n}$ being the Bohr radius and $α$ the strong coupling constant, times the non-perturbative contribution coming from the multipole expansion (gluon condensate). We discuss the physical applications to $Υ$, $J/Ψ$ and $B_{c}$ systems.

hep-ph↗
arXiv1995

Matching the HQET to Coulomb Type Bound States

We show that the infinite imaginary anomalous dimensions of certain heavy quark-antiquark currents in the HQET arise due to an inappropriate commutation of two limits, namely coinciding velocities and infinite cut-off. This commutation is not apparent when dimensional regularization is used, but it can be made manifest in a cut-off regularization. We argue that operators containing heavy quark and antiquark fields with the same velocity in the HQET must not be matched to perturbative QCD but to Coulomb-type bound state contributions. We show how to do so at one loop level.

hep-ph↗