Thu·Nov 12, 2015Thursday·November 12, 2015

1. 01*

   The pi0, eta, eta' -> gamma gamma*(Q^2) Decay Rates and Radii

   A.M.Bernstein🇺🇸

   The low $Q^2$ slopes of the the transition form factors provide a unique method to measure the sizes of the neutral pseudo-scalar mesons, since they do not have electromagnetic form factors. From the slope one obtains the "axial transition RMS radius" $R_{PS,A}=\sqrt{<r^2>}$ for each PS meson. The present status of theory and experiment for these quantities are presented. A comparison of the $R_{PS,A}$ is presented along with the electromagnetic and scalar radii of the ${\pi }^{\pm }$ mesons and the proton. We observe the striking similarity of the values of axial transition radii of all of the pseudoscalar mesons to each other and to the charge radius of the ${\pi }^{\pm }$. In the $Q^2$ = 0 limit the transition form factor is a measure of the pseudo-scalar meson radiative width (lifetime) and is a possible fourth (unexploited) method to perform such a measurement. The ${\pi }^0\to \gamma \gamma$ decay rate is a test of QCD at the confinement scale. There is a firm QCD prediction with a theoretical uncertainty of $\simeq$ 1 \% which calls for an experimental test at the same level of accuracy. There are three methods that have been utilized to perform this measurement and the present status of the experimental tests are outlined. The current accuracy is significantly less than the theoretical uncertainty. The efforts to improve this are briefly summarized.

   nucl-exhep-exhep-phnucl-thPoS(2016)·2 citations
2. 02*

   Target and Double Spin Asymmetries of Deeply Virtual ${\pi }^0$ Production with a Longitudinally Polarized Proton Target and CLAS

   A. Kim · H. Avakian · V. Burkert · K. Joo · W. Kim · K.P. Adhikari · Z. Akbar · S. Anefalos Pereira · R.A. Badui · M. Battaglieri · V. Batourine · I. Bedlinskiy and 117 other authors

   The target and double spin asymmetries of the exclusive pseudoscalar channel $\vec{e}\vec{p}\to ep{\pi }^0$ were measured for the first time in the deep-inelastic regime using a longitudinally polarized 5.9 GeV electron beam and a longitudinally polarized proton target at Jefferson Lab with the CEBAF Large Acceptance Spectrometer (CLAS). The data were collected over a large kinematic phase space and divided into 110 four-dimensional bins of $Q^2$, $x_B$, $-t$ and $\varphi$. Large values of asymmetry moments clearly indicate a substantial contribution to the polarized structure functions from transverse virtual photon amplitudes. The interpretation of experimental data in terms of generalized parton distributions (GPDs) provides the first insight on the chiral-odd GPDs ${\tilde{H}}_T$ and $E_T$, and complement previous measurements of unpolarized structure functions sensitive to the GPDs $H_T$ and ${\bar{E}}_T$. These data provide necessary constraints for chiral-odd GPD parametrizations and will strongly influence existing theoretical handbag models.

   nucl-exPLB(2017)·24 citations
3. 03*

   Investigating the scaling of higher-order flows in relativistic heavy-ion collisions

   Chun-Jian Zhang🇨🇳 · Jun Xu🇨🇳

   The modified number of constituent quark (NCQ) scaling $v_n/n_q^{n/2}\sim K{E}_T/n_q$ for mesons and baryons and the scaling relation $v_n\sim v_2^{n/2}$ for higher-order anisotropic flows, which were observed experimentally, have been investigated at top RHIC energy. It has been found that the modified NCQ scaling can not be obtained from the naive coalescence even by taking into account event-by-event fluctuations but may be due to hadronic afterburner or thermal freeze-out. In addition, we observed that the behavior of the $v_n/v_2^{n/2}$ ratio is sensitive to the partonic interaction, and it is different for mesons and baryons from the naive coalescence but is expected to be almost the same experimentally.

   ↳ nucl-thhep-exnucl-exPRC(2016)·7 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.