π→ev, π→evγ decays and related processes

Bryman, D. A.; Depommier, P.; Leroy, C.

doi:10.1016/0370-1573(82)90162-4

Cited by 127 publications

(40 citation statements)

References 90 publications

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“…In the Standard Model the differential rate of the π + → e + νγ decay can be written in the form [1]:…”

Section: Figmentioning

confidence: 99%

“…Rd, 13.20.Cz, 14.40.Aq In the Standard Model description of radiative pion decay π + → e + νγ, where γ is a real or virtual photon (e + e − pair), the decay amplitude M depends on the vector V and axial vector A weak hadronic currents [1]. Both currents contribute to the structure-dependent terms SD V and SD A associated with virtual hadronic states, while only the axial-vector current contributes to the inner bremsstrahlung process IB.…”

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confidence: 99%

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Precise Measurement of the Pion Axial Form Factor in theπ+→e+νγDecay

et al. 2004

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We have studied radiative pion decays π + → e + νγ in three broad kinematic regions using the PIBETA detector and a stopped pion beam. Based on Dalitz distributions of 42,209 events we have evaluated absolute π → eνγ branching ratios in the three regions. Minimum χ 2 fits to the integral and differential (E e + , Eγ ) distributions result in the axial-to-vector weak form factor ratio of γ ≡ FA/FV = 0.443(15), or FA = 0.0115(4) with FV = 0.0259. However, deviations from Standard Model predictions in the high-Eγ/low-E e + kinematic region indicate the need for further theoretical and experimental work.PACS numbers: 11.30. Rd, 13.20.Cz, 14.40.Aq In the Standard Model description of radiative pion decay π + → e + νγ, where γ is a real or virtual photon (e + e − pair), the decay amplitude M depends on the vector V and axial vector A weak hadronic currents [1]. Both currents contribute to the structure-dependent terms SD V and SD A associated with virtual hadronic states, while only the axial-vector current contributes to the inner bremsstrahlung process IB. Thus, it is convenient to write the decay amplitude as a sum:where p, k and q are the pion, electron and photon fourmomenta, respectively, e and m e are the electron charge and mass, G F is the Fermi coupling constant, V ud is the CKM quark mixing matrix element, while f π is the pion decay constant. The structure-dependent amplitude is parameterized by the vector and axial vector form factors, F V and F A :The conserved vector current (CVC) hypothesis [4,5] relates F V to the π 0 lifetime yielding F V = 0.0259(5) [6], which agrees with the relativistic quark model and chiral perturbation theory [7]. Chiral symmetry calculations [7,8,9] yield F A in the range 0.010-0.014.The combined π → eνγ event count of all previously published experiments is less than 1,200 events, while the overall uncertainties of the parameter γ ≡ F A /F V extracted from data range from 12 % to 56 % [10,11,12,13,14,15].In this Letter we present a first analysis of the π + → e + νγ (πe2γ) events recorded with the PIBETA detector in the course of a new measurement of the π + → π 0 e + ν (πβ) branching ratio [16,17] from 1999 to 2001.The measurements were performed in the πE1 channel at the Paul Scherrer Institute (PSI), Villigen, Switzerland. The π + beam with p ≃ 113 MeV/c, ∆p/p ≤ 1.3 %, and 24 mr horizontal and vertical divergence, had an average intensity of 6.8 · 10 5 π + /s, and produced a σ x,y = 9 mm beam spot on target. A total of 2.2 · 10 13 π + stops were recorded during the running period.The beam particles were first registered in a 3 mm thick beam counter (BC) placed ∼395 cm upstream of the detector center. The pions were slowed in a 30 mm thick active degrader (AD) and stopped in a 50 mm long segmented active target detector (AT) positioned in the center of the PIBETA detector. The BC, AD and AT detectors are all made of plastic scintillation material.The e + and µ + beam contaminations determined by the time-of-flight method were small, 0.4 % and 0.2 %, respectively. The bac...

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“…In the Standard Model the differential rate of the π + → e + νγ decay can be written in the form [1]:…”

Section: Figmentioning

confidence: 99%

mentioning

confidence: 99%

Precise Measurement of the Pion Axial Form Factor in theπ+→e+νγDecay

et al. 2004

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“…It is customary to divide the amplitude of the latter decay into "internal bremsstrahlung" (IB) and "structure dependent"(SD) contributions (for a review of π → eνγ see e.g. 15 ). The IB contribution collects the photon radiation from the charged lepton (Fig.2 a) and from the meson (Fig.…”

Section: Radiative Leptonic Decay B → Lνγmentioning

confidence: 99%

COUNTING CONTACT TERMS IN B → Vγ DECAYS

Khodjamirian

Wyler

2002

From Integrable Models to Gauge Theories

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“…The amplitude describing the radiative pion decay can be divided into two parts, the Inner Bremsstrahlung and the Structure Dependent amplitudes [16]:…”

Section: Polarized Radiative Pion Decaymentioning

confidence: 99%