Thu·Apr 1, 2021Thursday·April 1, 2021

1. 01*

   Linear polarization-direction correlations in $\gamma$-ray scattering experiments

   Christian Iliadis🇺🇸 · Udo Friman-Gayer🇺🇸

   Scattering measurements with incident linearly polarized $\gamma$ rays provide information on spins, parities, and $\gamma$-ray multipolarity mixing coefficients, and, therefore, on the nuclear matrix elements involved in the transitions. We present the general formalism for analyzing the observed angular correlations. The expressions are used to compute three-dimensional radiation patterns, which are important tools for optimizing experimental setups. Frequently, $\gamma$-ray transitions can proceed via two multipolarities that mix coherently. In such cases, the relative phases of the nuclear matrix elements are important when comparing results from different measurements. We discuss different phase conventions that have been used in the literature and present their relationships. Finally, we propose a basic experimental geometry consisting of detectors located at four different spatial locations. For this geometry, we present the measured anisotropies of the emitted $\gamma$ rays in graphical format as an aid in the data analysis.

   nucl-exEPJA(2021)·10 citations
2. 02*

   Mapping the Electromagnetic Fields of Heavy-Ion Collisions with the Breit-Wheeler Process

   James Daniel Brandenburg🇺🇸 · Wangmei Zha🇨🇳 · Zhangbu Xu🇺🇸

   Ultra-relativistic heavy-ion collisions are expected to produce the strongest electromagnetic fields in the known Universe. These highly-Lorentz contracted fields can manifest themselves as linearly polarized quasi-real photons that can interact via the Breit-Wheeler process to produce lepton anti-lepton pairs. The energy and momentum distribution of the produced dileptons carry information about the strength and spatial distribution of the colliding fields. Recently it has been demonstrated that photons from these fields can interact even in heavy-ion collisions with hadronic overlap, providing a purely electromagnetic probe of the produced medium. In this review we discuss the recent theoretical progress and experimental advances for mapping the ultra-strong electromagnetic fields produced in heavy-ion collisions via measurement of the Breit-Wheeler process.

   ↳ hep-phnucl-exEPJA(2021)·71 citations
3. 03*

   Spinning Gluons from the QCD Light-Ray OPE

   Hao Chen🇨🇳 · Ian Moult🇺🇸 · Hua Xing Zhu🇨🇳

   We study the transverse spin structure of the squeezed limit of the three-point energy correlator, $⟨\mathcal{E}({\vec{n}}_1)\mathcal{E}({\vec{n}}_2)\mathcal{E}({\vec{n}}_3)⟩$. To describe its all orders perturbative behavior, we develop the light-ray operator product expansion (OPE) in QCD. At leading twist the iterated OPE of $\mathcal{E}({\vec{n}}_i)$ operators closes onto light-ray operators ${\mathbb{O}}^{[J]}(\vec{n})$ with spin $J$, and transverse spin $j=0,2$. We compute the $\mathcal{E}({\vec{n}}_1)\mathcal{E}({\vec{n}}_2)$, $\mathcal{E}({\vec{n}}_1){\mathbb{O}}^{[J]}({\vec{n}}_2)$ and ${\mathbb{O}}^{[J_1]}({\vec{n}}_1){\mathbb{O}}^{[J_2]}({\vec{n}}_2)$ OPEs as analytic functions of $J$, which allows for the description of arbitrary squeezed limits of $N$-point correlators in QCD. We use these results with $J=3$ to reproduce the perturbative expansion in the squeezed limit of the three-point correlator, as well as to resum the leading twist singular structure for both quark and gluon jets, including transverse spin contributions, as required for phenomenological applications. Finally, we briefly comment on the transverse spin structure at higher twists, and show that to all orders in the twist expansion the highest transverse spin contributions are universal between quark and gluon jets, and are descendants of the leading twist transverse spin-2 operator, allowing their resummation into a simple two-dimensional Euclidean conformal block. Due to the general applicability of our results to arbitrary correlation functions of energy flow operators, we anticipate that they can be widely applied to improving our understanding of jet substructure at the LHC.

   ↳ hep-phhep-exhep-thnucl-ex+1JHEP(2022)·84 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.