Exclusive photoproduction of π0 up to large values of Mandelstam variables s,t, and u with CLAS

Abstract

Exclusive photoproduction cross sections have been measured for the process γp → pπ 0 [e + e − (γ )] with the Dalitz decay final state using tagged photon energies in the range of E γ = 1.275-5.425 GeV. The complete angular distribution of the final state π 0 , for the entire photon energy range up to large values of t and u, has been measured for the first time. The data obtained show that the cross section dσ/dt, at mid to large angles, decreases with energy as s −6.89±0.26 . This is in agreement with the perturbative QCD quark counting rule prediction of s −7 . Paradoxically, the size of angular distribution of measured cross sections is greatly underestimated by the QCD-based generalized parton distribution mechanism at highest available invariant energy s = 11 GeV 2 . At the same time, the Regge-exchange-based models for π 0 photoproduction are more consistent with experimental data.

High Energy Behaviour of Light Meson Photoproduction

“…The light meson photoproduction was examined in terms of the counting rule in Refs. [8][9][10][11][12][13][14][15][16][17]. As has been observed, first of all at SLAC by Anderson et al, the reaction γp → π + n (s = 8.4 − 15 GeV 2 ) shows agreement with constituent counting rules that predict the cross section should vary as s −7 and (n -2) = 7.3 ± 0.4 [8].…”

“…The new CLAS high statistical cross sections, for instance, obtained recently for γp → π 0 p [17] are compared in Fig. 1 (top left) with previous data from CLAS measurements [25].…”

Global analysis of charge exchange meson production at high energies

“…In η photoproduction, the PWA models are less constrained by the available low-energy data and we have shown how the high-energy data can help reducing uncertainties, specifically those related to unnatural exchanges [11,13]. Our prediction for the π 0 photopro-duction cross section [10] compares favorably with the CLAS data [24], and our results on π 0 , η and η photoproduction beam asymmetries [14,15] are in agreement with the GlueX results [6,25]. The main conclusion one can draw from these comparisons is that, at forward scattering angles, the natural Regge poles dominate over the unnatural ones and over the non-pole contributions.…”

It Takes Two to Tango: Activation of Protein Kinase D by Dimerization

“…Deletion of the ULD modestly accelerates membrane translocation, suggesting that it also contributes to the stability of the autoinhibited state [14] (Figure 4b). Similar to Akt and PKC, small molecule inhibitors that bind to the active site paradoxically lead to activation loop phosphorylation as well as re-localization of PKD to basal DAG pools, [67] indicating that inhibitors can dramatically alter the conformational landscape of protein kinases and that phosphorylation should be treated cautiously as a proxy for kinase activity. In summary, the regulatory domains maintain the kinase domain in an inactive conformation in the absence of DAG, analogous to what has been observed for PKC.…”