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Andrzej Czarnecki

Publications and source records attributed to Andrzej Czarnecki.

8 recordsLinked to original sources
PubMed2006

Enhancement of hadronic b quark decays.

A class of previously unknown strong-interaction corrections is found to enhance the rate of nonleptonic decays of the quark by 5%-8%. This effect decreases the predicted fraction of semileptonic decays and brings it into fair agreement with experimental results. As well as solving a long-standing puzzle of measurements disagreeing with the standard model prediction, our work suggests a way for future precise studies of nonleptonic quark decays and their application to searching for "new physics."

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PubMed2005

Calculation of the one- and two-loop lamb shift for arbitrary excited hydrogenic states.

General expressions for quantum electrodynamic corrections to the one-loop self-energy [of order alpha(Zalpha)6] and for the two-loop Lamb shift [of order alpha2(Zalpha)6] are derived. The latter includes all diagrams with closed fermion loops. The general results are valid for arbitrary excited non-S hydrogenic states and for the normalized Lamb shift difference of states, defined as Delta N = n3deltaE(nS) - delta E(1S). We present numerical results for one-loop and two-loop corrections for excited S, P, and D states. In particular, the normalized Lamb shift difference of states is calculated with an uncertainty of order 0.1 kHz.

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PubMed2004

Heavy-to-light-quark decays with two-loop accuracy.

We present a determination of a new class of three-loop Feynman diagrams describing heavy-to-light transitions. We apply it to find the O(alpha2(s)) corrections to the top quark decay t --> bW and to the distribution of lepton invariant mass in the semileptonic b quark decay b --> ulnu. We also confirm the previously determined total rate of that process as well as the O(alpha2) corrections to the muon lifetime.

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PubMed2002

Semileptonic b-->u decays: lepton invariant mass spectrum.

We compute O(alpha(2)(s)) QCD corrections to the lepton invariant mass spectrum in the decay b-->ulnu(l), relevant for the determination of the Cabibbo-Kobayashi-Maskawa matrix element /V(ub)/. Our method can also be used to evaluate moments of the lepton energy distribution with an O(alpha(2)(s)) accuracy. The Abelian part of our result gives the neutrino invariant mass spectrum in the muon decay and, upon integration, the O(alpha(2)) correction to the muon lifetime.

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