12 research outputs found
A Review of Rare Pion and Muon Decays
After a decade of no measurements of pion and muon rare decays, PIBETA, a new
experimental program is producing its first results. We report on a new
experimental study of the pion beta decay, Pi(+) -> Pi(0) e(+) Nu, the Pi(e2
gamma) radiative decay, Pi(+) -> e(+) Nu Gamma, and muon radiative decay, Mu ->
e Nu Gamma. The new results represent four- to six-fold improvements in
precision over the previous measurements. Excellent agreement with Standard
Model predictions is observed in all channels except for one kinematic region
of the Pi(e2 gamma) radiative decay involving energetic photons and
lower-energy positrons.Comment: 10 pages, 6 figures, 2 tables, invited talk presented at MESON 2004,
8th Int'l. Workshop on Meson Production, Properties and Interaction, Krakow,
Poland 4-8 June 200
Exact mass dependent two--loop in the background MOM renormalization scheme
A two-loop calculation of the renormalization group --function in a
momentum subtraction scheme with massive quarks is presented using the
background field formalism. The results have been obtained by using a set of
new generalized recurrence relations proposed recently by one of the authors
(O.V.T.). The behavior of the mass dependent effective coupling constant is
investigated in detail. Compact analytic results are presented.Comment: 20 pages, 5 figures, LaTeX, uses axodraw.sty, revised version, Sec. 5
(numerical results) changed (quark masses were not set properly) and enhance
Precise Measurement of the Pi+ -> Pi0 e+ nu Branching Ratio
Using a large acceptance calorimeter and a stopped pion beam we have made a
precise measurement of the rare Pi+ -> Pi0 e+ Nu,(pi_beta) decay branching
ratio. We have evaluated the branching ratio by normalizing the number of
observed pi_beta decays to the number of observed Pi+ -> e+ Nu, (pi_{e2})
decays. We find the value of Gamma(Pi+ -> Pi0 e+ Nu)/Gamma(total) = [1.036 +/-
0.004(stat.) +/- 0.004(syst.) +/- 0.003(pi_{e2})] x 10^{-8}$, where the first
uncertainty is statistical, the second systematic, and the third is the pi_{e2}
branching ratio uncertainty. Our result agrees well with the Standard Model
prediction.Comment: 4 pages, 5 figures, 1 table, revtex4; changed content; updated
analysi
Generalized Recurrence Relations for Two-loop Propagator Integrals with Arbitrary Masses
An algorithm for calculating two-loop propagator type Feynman diagrams with
arbitrary masses and external momentum is proposed. Recurrence relations
allowing to express any scalar integral in terms of basic integrals are given.
A minimal set consisting of 15 essentially two-loop and 15 products of one-loop
basic integrals is found. Tensor integrals and integrals with irreducible
numerators are represented as a combination of scalar ones with a higher
space-time dimension which are reduced to the basic set by using the
generalized recurrence relations proposed in Ref.[1] (Phys.Rev.D54 (1996)
6479).Comment: 28 pages, Latex, uses Axodraw.st