Mon·Sep 30, 2019Monday·September 30, 2019

1. 01*

   On large mass $\gamma \gamma$ and $\gamma$-meson photoproduction

   L. Szymanowski🇵🇱 · B. Pire🇫🇷 · S. Wallon🇫🇷

   Enlarging the set of hard exclusive reactions to be studied in the framework of QCD collinear factorization opens new possibilities to access generalized parton distributions (GPDs). We studied the photoproduction of a large invariant mass photon-photon or photon-meson pair in the generalized Bjorken regime which may be accessible both at JLab and at the EIC.

   ↳ hep-phhep-exnucl-exnucl-th0 citations
2. 02*

   Insights into the Origin of Mass

   Craig D. Roberts🇨🇳

   Atomic nuclei are the core of everything we can see. At the first level of approximation, their atomic weights are simply the sum of the masses of all the nucleons they contain. Each nucleon has a mass $m_N\approx 1$GeV, i.e. approximately 2000-times the electron mass. The Higgs boson produces the latter, but what produces the nucleon mass? This is the crux: the vast bulk of the mass of a nucleon is lodged with the energy needed to hold quarks together inside it; and that is supposed to be explained by quantum chromodynamics (QCD), the strong-interaction piece within the Standard Model. This contribution canvasses the potential for a coherent effort in QCD phenomenology and theory, coupled with experiments at existing and planned facilities, to reveal the origin and distribution of mass by focusing on the properties of the strong-interaction Nambu-Goldstone modes. Key experiments are approved at JLab 12; planned with COMPASS++/AMBER at CERN; and could deliver far-reaching insights by exploiting the unique capabilities foreseen at an electron ion collider.

   ↳ nucl-thhep-lathep-phnucl-exJ.Phys.Conf.Ser.(2020)·11 citations
3. 03*

   Gluon polarization measurements from longitudinally polarized proton-proton collisions at STAR

   Zilong Chang (for the STAR Collaboration)🇺🇸

   Jets produced in the pseudo-rapidity range, $-1.0<\eta <1.0$, from $pp$ collisions at RHIC kinematics are dominated by quark-gluon and gluon-gluon scattering processes. Therefore the longitudinal double spin asymmetry $A_{LL}$ for jets is an effective channel to explore the longitudinal gluon polarization in the proton. At STAR, jets are reconstructed in full azimuth, from the charged-particle tracks seen by the Time Projection Chamber and electro-magnetic energy deposited in the Barrel and Endcap electro-magnetic calorimeters at both $\sqrt{s}=$ 200 and 510 GeV. Early STAR inclusive jet $A_{LL}$ results at $\sqrt{s}=$ 200 GeV provided the first evidence of the non-zero gluon polarization at $x>$ 0.05. At $\sqrt{s}=$ 510 GeV, the inclusive jet $A_{LL}$ is sensitive to the gluon polarization as low as $x\sim$ 0.015. In this talk, we will discuss recent STAR inclusive jet and dijet $A_{LL}$ results at $\sqrt{s}=$ 510 GeV and highlight the new techniques designed for this analysis, for example the underlying event correction to the jet transverse energy and its effect on the jet $A_{LL}$. Dijet $A_{LL}$ results are shown for four topologies in regions of pseudo-rapidity, effectively scanning the $x$-dependence of the gluon polarization.

   ↳ hep-exnucl-ex0 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.