arXiv subjects

Oleg Yakovlev

Publications and source records attributed to Oleg Yakovlev.

11 recordsLinked to original sources

arXiv2001

Top quark mass definition and top quark pair production near threshold at the NLC

We suggest an infrared-insensitive quark mass, defined by subtracting the soft part of the quark self energy from the pole mass. We demonstrate the deep relation of this definition with the static quark-antiquark potential. At leading order in 1/m this mass coincides with the PS mass which is defined in a completely different manner. Going beyond static limit, the small normalization point introduces recoil corrections which are calculated here as well. Using this mass concept and other concepts for the quark mass we calculate the cross section of e+ e- -> t t-bar near threshold at NNLO accuracy adopting three alternative approaches, namely (1) fixing the pole mass, (2) fixing the PS mass, and (3) fixing the new mass which we call the PS-bar mass. We demonstrate that perturbative predictions for the cross section become much more stable if we use the PS or the PS-bar mass for the calculations. A careful analysis suggests that the top quark mass can be extracted from a threshold scan at NLC with an accuracy of about 100-200 MeV.

hep-ph↗

arXiv2000

On Higgs Production in Photon Photon Collisions

I review recent progress on the Higgs production in gamma gamma collisions at the photon mode of the Next Linear Collider (NLC). I mainly focus on two particular topics. The first topic is the Higgs-two photon vertex, which is sensitive to new physics, and can be considered a counter of the number of new heavy particles. I recall the results on QCD and electroweak two loop radiative corrections. The second topic is the heavy quark anti-quark pair production in gamma gamma collisions, which is the dominant background process for the Higgs production at m_H <150 GeV. We suggest a procedure for the resummation of double (DL) and single (SL) logarithms in the process gamma gamma -> b anti-b.

hep-ph↗

arXiv2000

On t anti-t threshold and top quark mass definition

In this talk we discuss the process e^+e^-\to t\bar t near threshold, calculated with NNLO accuracy as well as top quark mass definitions adequate for the threshold. As new definition we suggest the PS-bar mass which allows to calculate recoil corrections to the static PS mass. Using this result we calculate the cross section of e^+e^-\to t\bar t near threshold at NNLO accuracy adopting three alternative approaches, namely (1) fixing the pole mass, (2) fixing the PS mass, and (3) fixing the new mass which we call the PS-bar mass. We demonstrate that perturbative predictions for the cross section become much more stable if we use the PS or the PS-bar mass for the calculations. A careful analysis suggests that the top quark mass can be extracted from a threshold scan at NLC with an accuracy of about 100 MeV.

hep-ph↗

arXiv2000

Top quark production near threshold at NLC

In this talk we discuss the process e+e- -> t t-bar near threshold. In particular we discuss a quark mass definition which is a generalization of the static PS mass. The new definition allows us to calculate recoil corrections to the static PS mass. Using this result we calculate the cross section of e+e- -> t t-bar near threshold at NNLO accuracy adopting three alternative approaches, namely (1) fixing the pole mass, (2) fixing the PS mass, and (3) fixing the new mass which we call the PS-bar mass. We demonstrate that perturbative predictions for the cross section become much more stable if we use the PS or the PS-bar mass for the calculations. A careful analysis suggests that the top quark mass can be extracted from a threshold scan at NLC with an accuracy of about 100-200 MeV.

hep-ph↗

arXiv2000

A dynamic mass definition near the t t-bar threshold

Starting from general considerations about the different concepts which exist for the definition of the quark mass near the pair production threshold, we introduce the definition of a mass with a dynamic degree of freedom that extends the previously given concept of the static PS mass.

hep-ph↗

arXiv2000

New approach for calculating heavy-to-light form factors with QCD sum rules on the light-cone

We suggest a new approach for calculating heavy-to-light form factors. The method is based on light cone sum rules (LCSR) and covers the whole kinematical range of momentum transfer. The derivation of the new sum rule uses a suitable combination of double and single dispersion integrals. As an example we give numerical results for the form factor f^+ for the B -> pion transition.

hep-ph↗

arXiv2000

Perturbative Effects in the Form Factor γγ^*\to πand Extraction of the Pion Wave Function from CLEO Data

We study the pion form factor F^{πγγ^*}(Q^2) in the light-cone sum rule approach, accounting for radiative corrections and higher twist effects. Comparing the results to the CLEO experimental data on F^{πγγ^*}(Q^2), we extract the the pion distribution amplitude of twist-2. The deviation of the distribution amplitude from the asymptotic one is small and is estimated to be a_2(μ) = 0.12 \pm 0.03 at μ=2.4 GeV, in the model with one non-asymptotic term. The ansatz with two non-asymptotic terms gives some region of a_2 and a_4, which is consistent with the asymptotic distribution amplitude, but does not agree with some old models.

hep-ph↗

arXiv1999

QCD sum rules on the light cone and B -> pi form factors

The semileptonic decay B -> pi l nu is one of the most important reactions for the determination of the CKM matrix element |V_{ub}|. However, in order to extract |V_{ub}| from data one needs an accurate theoretical calculation of the hadronic matrix element describing the B to pi transition. QCD sum rules, based on operator-product expansion on the light-cone, provide a reliable approach to this aim. QCD corrections and higher twist contributions can be taken systematically into account.

hep-ph↗

arXiv1999

Top quark production near threshold: NNLO QCD correction

We calculate the cross section of the process e^+e^- \to t\bar t near threshold by resumming Coulomb-like terms with next-to-next-to-leading (NNLO) accuracy. The nonrelativistic Green function formalism and the method of ``direct matching'' are used. The NNLO correction turns out to be large, of the same size as the NLO correction. It changes the position and the normalization of the 1S-peak. The obtained results are compared with results existing in the literature.

hep-ph↗

arXiv1998

Top quark production near threshold: on resummation of O( (β_0α_s)^n) QCD corrections

We discuss the resummation of the potentially large O((β_0α_s)^n) QCD corrections to the total cross section of the process e^+e^- \to t \bar t near the threshold. In this approximation, the cross section factorization into the short- and long-distance parts is valid. The short-distance correction is reduced to the production vertex renormalization. It amounts to -9.5% and is well under control. The long distance corrections are accounted for as the effect of the coupling's running in the QCD potential. We argue that the accuracy of present predictions for the cross section in the scheme with the running QCD coupling is about 10%.

hep-ph↗

arXiv1994

Threshold Effects in Two--Photon Decays of Higgs Particles

The couplings of Higgs particles to two photons are analyzed in the threshold region, where the Higgs mass is about twice the loop--particle mass leading to possible bound state formation. The amplitude of the pseudoscalar decay $A\to γγ$ for pseudoscalar masses in the range of $(t\bar t)$--bound state masses is calculated in leading and next--to--leading order in $α_s$. It is shown that the real and imaginary parts of the form factor are significantly different from the lowest order perturbative one.

hep-ph↗