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The pi° --> gamma gamma decay width is analyzed within the combined framework of Chiral Perturbation Theory and the 1/N{sub c} expansion up to order(p6) and order(p4 x 1/N{sub c}) in the decay amplitude. The eta' is explicitly included in the analysis. It is found that the decay width is enhanced by about 4% due to the isospin-breaking induced mixing of the pure U(3) states. This effect, which is of leading order in the low energy expansion, is shown to persist nearly unchanged at next to leading order. The chief prediction Gamma{sub pi}0{sub {yields}gamma gamma} = 8.10 eV is estimated to have an uncertainty of less than 1%. Observations on the eta and eta' can also be made, especially about their mixing, which is shown to be significantly affected by next to leading order corrections.
Chiral dynamics provides a rigorous and model-independent methodology for making QCD predictions at the confinement scale. This helps particularly in the testing of the standard model. The workshop reported here was focused on theoretical predictions and the measurements of physical processes, analyzing carefully the phenomenology needed to bridge the gap between the two. Besides the lectures, this volume also contains summaries of the working groups on Â-Â-scattering, ÂN-interaction, photo/electro-pion-production, and on chiral anomaly. This book is a thorough review of the state of the art and it addresses researchers as well as graduate students.
On September 27 – October 3, 2008 the NATO Advanced Research Workshop (ARW) on progress in high-energy physics and nuclear safety was held in Yalta, Crimea (see: http://crimea.bitp.kiev.ua and http://arw.bitp.kiev.ua). Nearly 50 leading experts in high-energy and nuclear physics from Eastern and Western Europe as well as from North America participated at the Workshop. The topics of the ARW covered recent results of theoretical and experimental studies in high-energy physics, accelerator, detection and nuclear technologies, as well as problems of nuclear safety in high-energy experimentation and in nuclear - dustry. The forthcoming experiments at the Large Hadron Collider (LHC) at CERN and cosmic-ray experiments were among the topics of the ARW. An important aspect of the Workshop was the scienti?c collaboration between nuclear physicists from East and West, especially in the ?eld of nuclear safety. The present book contains a selection of invited talks presented at the ARW. The papers are grouped in two parts.
This book provides an authoritative, up to date, overview of the field of chiral dynamics, and also provides an excellent introduction to the field. The workshop is known for the interplay of theory and experiment and as a meeting place for most of the leading researchers in the field.
This thesis describes a search for the rare decay K{sub L} {yields} {pi}{sup 0}{pi}{sup 0}{gamma} using data from the KTeV experiment, using the topology K{sub L} {yields} {pi}{sup 0}{pi}{sub D}{sup 0}{gamma} (where {pi}{sub D}{sup 0} {yields} {gamma}e{sup +}e{sup -}). Due to Bose statistics and the real nature of the photon, the K{sub L} {yields} {pi}{sup 0}{pi}{sup 0}{gamma} decay can proceed at lowest order only by the Cp conserving direct emission of an E2 photon. The decay vanishes to O(p{sup 4}) in chiral perturbation theory and is a probe of the theory to the sixth order. The primary background to this decay consists of K{sub L} {yields} {pi}{sup 0}{pi}{sup 0}{pi}{sub D}{sup 0} events with one lost photon. The upper limit for the decay K{sub L} {yields} {pi}{sup 0}{pi}{sup 0}{gamma} presented in this thesis is 2.32 x 10{sup -7} at the 90% confidence level. This upper limit was derived from both 1997 and 1999 data, using a blind analysis. The upper limit was derived from a Feldman-Cousins method, based on a weighted total of 0.53 data events in the signal region with an expected K{sub L} {yields} {pi}{sup 0}{pi}{sup 0}{pi}{sub D}{sup 0} background of 0.37 {+-} 0.28 events. The previous upper limit for this decay was 5.6 x 10{sup -6} at the 90% confidence level.
The pi 0 {yields} gamma gamma width is determined to next to leading order in the combined chiral and 1/Nc expansions. It is shown that corrections driven by chiral symmetry breaking produce an enhancement of about 4.5% with respect to the width calculated in terms of the chiral-limit amplitude leading to Gamma{sub {pi}}{sup 0} {yields} {gamma}{gamma} = 8.1 +/- 0.08 MeV. This theoretical prediction will be tested via pi 0 Primakoff production by the PRIMEX experiment at Jefferson Lab.