Two photon decay of the pseudoscalars, the chiral symmetry breaking corrections

The extrapolation of the decay amplitudes of the pseudoscalar mesons into two photons from the soft meson limit where it is obtained from the axial-anomaly to the mass shell involves the contribution of the 0^ - continuum. These chiral symmetry breaking corrections turn out to be large. The effects of these corrections on the calculated pi ^0 decay rate, on the values of the singlet-octet mixing angle and on the ratios f_8 / f_pi and f_0 / f_pi are discussed. The implications for the transition form factors gamma gamma* --> pseudoscalars are also evaluated and confronted with the available experimental data.Comment: Computational errors straightened and study of the implications on the form factors of the transitions gamma gamma* --> pseudoscalars adde

Quark-hadron duality, axial anomaly and mixing

Interplay between axial anomaly and quark-hadron duality in the presence of strong mixing is considered. The anomaly sum rule for meson transition form factors based on the dispersive representation of axial anomaly and quark-hadron duality in octet channel is analyzed. The comparison of this sum rule to the experimental data on $\eta$ and $\eta'$ mesons transition form factors shows that the interval of duality in this channel is rather small, contradicting the usual understanding of quark-hadron duality. The same values of interval of duality are supported by considering the two-point correlator in the local duality limit. This contradiction may be resolved by introducing of some nonperturbative non-OPE correction to the relevant spectral density. The form and value of this correction are discussed.Comment: 9 pages, 1 figure, reference adde

On the NLO Power Correction to Photon-Pion Transition Form Factor

We propose a perturbative evaluation for the next-to-leading-order (NLO) $O(1/Q^4)$ power correction to the photon-pion transition form factor. The effects of the NLO power correction are analyzed.Comment: 4 pages, 3 figures, Revtex, revised versio

Eddy current studies from the undulator-based positron source target wheel prototype

The ef­fi­cien­cy of fu­ture positron sources for the next gen­er­a­tion of high-en­er­gy par­ti­cle col­lid­ers (e.g. ILC, CLIC, LHeC) can be im­proved if the positron-pro­duc­tion tar­get is im­mersed in the mag­net­ic field of ad­ja­cent cap­ture op­tics. If the tar­get is also ro­tat­ing due to heat de­po­si­tion con­sid­er­a­tions then eddy cur­rents may be in­duced and lead to ad­di­tion­al heat­ing and stress­es. In this paper we pre­sent data from a ro­tat­ing tar­get wheel pro­to­type for the base­line ILC positron source. The wheel has been op­er­at­ed at rev­o­lu­tion rates up to 1800rpm in fields of the order of 1 Tesla. Com­par­isons are made be­tween torque data ob­tained from a trans­duc­er on the tar­get drive shaft and the re­sults of fi­nite-el­e­ment sim­u­la­tions. Ro­tor­dy­nam­ics is­sues are pre­sent­ed and fu­ture ex­per­i­ments on other as­pects of the positron source tar­get sta­tion are con­sid­ered

Detecting and Studying Higgs Bosons at a Photon-Photon Collider

We examine the potential for detecting and studying Higgs bosons at a photon-photon collider facility associated with a future linear collider. Our study incorporates realistic \gam\gam luminosity spectra based on the most probable available laser technology. Results include detector simulations. We study the cases of: a) a SM-like Higgs boson; b) the heavy MSSM Higgs bosons; c) a Higgs boson with no $WW/ZZ$ couplings from a general two Higgs doublet model.Comment: 52 pages, 26 figures, revised version with new appendi

Quantifying an aquifer nitrate budget and future nitrate discharge using field data from streambeds and well nests

Novel groundwater sampling (age, flux, and nitrate) carried out beneath a streambed and in wells was used to estimate (1) the current rate of change of nitrate storage, dSNO3 /dt, in a contaminated unconfined aquifer, and (2) future [NO3–]FWM (the flow-weighted mean nitrate concentration in groundwater discharge) and fNO3 (the nitrate flux from aquifer to stream). Estimates of dSNO3 /dt suggested that at the time of sampling (2013) the nitrate storage in the aquifer was decreasing at an annual rate (mean = –9 mmol/m2yr) equal to about one-tenth the rate of nitrate input by recharge. This is consistent with data showing a slow decrease in the [NO3–] of groundwater recharge in recent years. Regarding future [NO3–]FWM and fNO3 , predictions based on well data show an immediate decrease that becomes more rapid after ~5 years before leveling out in the early 2040s. Predictions based on streambed data generally show an increase in future [NO3–]FWM and fNO3 until the late 2020s, followed by a decrease before leveling out in the 2040s. Differences show the potential value of using information directly from the groundwater—surface water interface to quantify the future impact of groundwater nitrate on surface water quality. The choice of denitrification kinetics was similarly important; compared to zero-order kinetics, a first-order rate law levels out estimates of future [NO3–]FWM and fNO3 (lower peak, higher minimum) as legacy nitrate is flushed from the aquifer. Major fundamental questions about nonpoint-source aquifer contamination can be answered without a complex numerical model or long-term monitoring program

Twist-3 contribution to the γ∗γ→ππ\gamma^*\gamma\to \pi\pi amplitude in the Wandzura-Wilczek approximation

We have calculated the Wandzura-Wilczek contribution to the twist-3 part of $\gamma^*\gamma\to 2\pi$ amplitude. It describes interaction of the longitudinally polarized virtual photon with the real one, and it is suppressed by 1/Q, where $Q^2$ is the virtuality of the $\gamma^*$, as compared to the twist-2 contribution. We have found that, in the Wandzura-Wilczek approximation, factorization applies to the twist-3 amplitude.Comment: 13 pages, 4 figure

Pion-photon and photon-pion transition form factors in light-cone formalism

We derive the minimal Fock-state expansions of the pion and the photon wave functions in light-cone formalism, then we calculate the pion-photon and the photon-pion transition form factors of $\gamma ^{\ast}\pi ^{0}\to \gamma$ and $\gamma ^{\ast}\gamma \to \pi ^{0}$ processes by employing these quark-antiquark wave functions of the pion and the photon. We find that our calculation for the $\gamma ^{\ast}\gamma \to \pi ^{0}$ transition form factor agrees with the experimental data at low and moderately high energy scale. Moreover, the physical differences and inherent connections between the transition form factors of $\gamma ^{\ast}\pi ^{0}\to \gamma$ and $\gamma ^{\ast}\gamma \to \pi ^{0}$ have been illustrated, which indicate that these two physical processes are intrinsically related. In addition, we also discuss the $\pi ^{0}\to \gamma \gamma$ form factor and the decay width $\mathit{\Gamma}(\pi \to \gamma \gamma)$ at $Q^{2}=0$.Comment: 20 pages, 2 figure