Neutral Pion Decay

Published on Oct 26, 2011in Annual Review of Nuclear and Particle Science14.219
· DOI :10.1146/ANNUREV-NUCL-102010-130426
R. Miskimen1
Estimated H-index: 1
(UMass: University of Massachusetts Amherst)
Sources
Abstract
The study of π0 decay has played an important role in the development of particle physics: The π0→γγ decay provides key insights into the anomaly sector of quantum chromodynamics. In this review, the historical progression of π0 discovery, lifetime measurements, and theory are presented. A new measurement of the π0 radiative width via the Primakoff effect has been made at JLab. The result, Γ(π0→γγ)=7.82±0.14(stat.)±0.17(syst.) eV, is a factor of 2.1 more precise than the currently accepted value, and it is in agreement with the chiral anomaly prediction and with next-to-leading-order chiral perturbation theory calculations. Primakoff experiments at higher energies to measure the η and η′ radiative widths are also discussed.
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References51
Newest
#2D. McNulty (MIT: Massachusetts Institute of Technology)H-Index: 21
#2A. M. BernsteinH-Index: 29
Last. A. Teymurazyan (UK: University of Kentucky)H-Index: 6
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High precision measurements of the differential cross sections for \pi^0photoproduction at forward angles for two nuclei, ^{12} and ^{208}b, have been performed for incident photon energies of 4.9 - 5.5 GeV to extract the {\pi^0 \to \gamma\gamma}decay width. The experiment was done at Jefferson Lab using the Hall B photon tagger and a high-resolution multichannel calorimeter. The {\pi^0 \to \gamma\gamma}decay width was extracted by fitting the measured cross sections using recentl...
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The mechanism of incoherent {pi}{sup 0} and {eta} photoproduction from complex nuclei is investigated from 4 to 12 GeV with an extended version of the multicollisional Monte Carlo (MCMC) intranuclear cascade model. The calculations take into account the elementary photoproduction amplitudes via a Regge model and the nuclear effects of photon shadowing, Pauli blocking, and meson-nucleus final-state interactions. The results for {pi}{sup 0} photoproduction reproduced for the first time the magnitu...
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#2E. Clinton (UMass: University of Massachusetts Amherst)H-Index: 6
#4D. Lawrence (UMass: University of Massachusetts Amherst)H-Index: 10
Abstract A technique is presented for precision measurements of the area densities, ρT , of approximately 5% radiation length carbon and 208 Pb targets used in an experiment at Jefferson Laboratory to measure the neutral pion radiative width. The precision obtained in the area density for the carbon target is ±0.050%, and that obtained for the lead target through an X-ray attenuation technique is ±0.43%.
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With the advent of new photon-tagging facilities and novel experimental technologies, it has become possible to perform photoproduction cross-sectional measurements of pseudoscalar mesons on nuclei with percent-level accuracy. The extraction of the radiative decay widths from these measurements at forward angles is done by the Primakoff method, which requires theoretical treatment of all processes participating in these reactions at the same percent level. In this work, we review the theoretical...
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#1M. Bychkov (UVA: University of Virginia)H-Index: 9
#2Dinko PocanicH-Index: 64
Last. A. S. KorenchenkoH-Index: 13
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We have measured the \pi^+\to {\rm e}^+\nu\gammabranching ratio over a wide region of phase space, based on a total of 65,460 events acquired using the PIBETA detector. Minimum-\chi^2fits to the measured (E_{e^+},E_\gamma)energy distributions result in the weak form factor value of F_A=0.0119(1)with a fixed value of F_V=0.0259 An unconstrained fit yields F_V=0.0258(17)and F_A=0.0117(17) In addition, we have measured a=0.10(6)for the dependence of F_Von q^2 the ${\rm...
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#1Karol Kampf (Paul Scherrer Institute)H-Index: 1
#2Bachir Moussallam (University of Paris-Sud)H-Index: 17
The corrections induced by light quark masses to the current algebra result for the {\ensuremath{\pi}}^{0}lifetime are reexamined. We consider next-to-next-to-leading order corrections and we compute all the one-loop and the two-loop diagrams which contribute to the decay amplitude at this order in the two-flavor chiral expansion. We show that the result is renormalizable, as Weinberg consistency conditions are satisfied. We find that chiral logarithms are present at this order unlike the cas...
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(Received 26 April 2007; revised manuscript received 28 January 2008; published 3 July 2008) Incoherentphotoproduction in nuclei is evaluated at forward angles within 4 to 9 GeV using a multiple scattering Monte Carlo cascade calculation with full � -nucleus final-state interactions. The Primakoff, nuclear coherent and nuclear incoherent components of the cross sections fit remarkably well previous measurements for Be and Cu from Cornell, suggesting a destructive interference between the Coulomb...
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The Jefferson Lab Hall B PrimEx Collaboration is using tagged photons to perform a 1.4% level measurement of the absolute cross section for the photo-production of neutral pions in the Coulomb field of a nucleus as a test of Chiral Perturbation Theory. Such a high precision pushes the limits of the photon tagging technique in regards to the determination of the absolute photon flux. A multifaceted approach to this problem has included measuring the absolute tagging ratios with a Total Absorption...
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Abstract The anomaly in the vacuum expectation value of the product of axial and two vector currents (AVV) in QCD is investigated. The goal is to determine from its value the π 0 → 2 γ decay width with high precision. The sum rule for AVV formfactor is studied. The difference f π 0 − f π + caused by strong interaction is calculated and appears to be small. The π 0 – η mixing is accounted. The π 0 → 2 γ decay width determined theoretically from the axial anomaly is found to be Γ ( π 0 → 2 γ ) = 7...
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#1Jean Laget (JLab: Thomas Jefferson National Accelerator Facility)H-Index: 1
The Primakoff effect offers us a way to determine the radiative decay width of pseudoscalar mesons when they are photoproduced in the electromagnetic field of hadronic systems. Taking advantage of recent developments in the Regge description of the production of mesons in the strong hadronic field, this paper evaluates the relative importance of the electromagnetic and the strong amplitudes and assesses the possibilities that have become opened because of modern experimental facilities.
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A fundamental property of QCD is the presence of the chiral anomaly, which is the primary component of the \pi^0\rightarrow\gamma\gammadecay amplitude. Based on this anomaly and its small (\simeq4.5%) chiral correction, a firm prediction of the \pi^0lifetime can be used as a test of QCD at confinement scale energies. The interesting experimental and theoretical histories of the \pi^0meson are reviewed, from discovery to the present era. Experimental results are in agreement with the ...
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Recent advances in the photon tagging facilities together with the novel, high-resolution fast calorimetry make it possible to perform photoproduction cross section measurements of pseudoscalar mesons on nuclei with a percent level accuracy. The extraction of the radiative decay widths, needed for testing the symmetry breaking effects in QCD, from these measurements at small angles is done by the Primakoff method. This method requires theoretical treatment of all processes participating in these...
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