Tue·Jun 22, 2021Tuesday·June 22, 2021

1. 01*

   Improved neutron lifetime measurement with UCN$\tau$

   F. M. Gonzalez · E. M. Fries · C. Cude-Woods · T. Bailey · M. Blatnik · L. J. Broussard · N. B. Callahan · J. H. Choi · S. M. Clayton · S. A. Currie · M. Dawid · E. B. Dees and 33 other authors

   We report an improved measurement of the free neutron lifetime ${\tau }_n$ using the UCN$\tau$ apparatus at the Los Alamos Neutron Science Center. We counted a total of approximately $38\times 10^6$ surviving ultracold neutrons (UCN) after storing in UCN$\tau$'s magneto-gravitational trap over two data acquisition campaigns in 2017 and 2018. We extract ${\tau }_n$ from three blinded, independent analyses by both pairing long and short storage-time runs to find a set of replicate ${\tau }_n$ measurements and by performing a global likelihood fit to all data while self-consistently incorporating the $\beta$-decay lifetime. Both techniques achieve consistent results and find a value ${\tau }_n=877.75\pm 0.28_{\text{ stat}}+0.22/-0.16_{\text{ syst}}$~s. With this sensitivity, neutron lifetime experiments now directly address the impact of recent refinements in our understanding of the standard model for neutron decay.

   nucl-exhep-exnucl-thPRL(2021)·194 citations
2. 02*

   Charge Radius of Neutron-deficient ${}^{54}$Ni and Symmetry Energy Constraints Using the Difference in Mirror Pair Charge Radii

   Skyy V. Pineda🇺🇸 · Kristian König🇺🇸 · Dominic M. Rossi🇩🇪 · B. Alex Brown🇺🇸 · Anthony Incorvati🇺🇸 · Jeremy Lantis🇺🇸 · Kei Minamisono🇺🇸 · Wilfried Nörtershäuser🇩🇪 · Jorge Piekarewicz🇺🇸 · Robert Powel🇺🇸 · Felix Sommer🇩🇪

   The nuclear root-mean-square charge radius of ${}^{54}$Ni was determined with collinear laser spectroscopy to be $R{(}^{54}$Ni) = 3.737\,(3)~fm. In conjunction with the known radius of the mirror nucleus ${}^{54}$Fe, the difference of the charge radii was extracted as $\Delta R_{\mathrm{ch}}$ = 0.049\,(4)~fm. Based on the correlation between $\Delta R_{\mathrm{ch}}$ and the slope of the symmetry energy at nuclear saturation density ($L$), we deduced $20\le L\le 70$\,MeV. The present result is consistent with the $L$ from the binary neutron star merger GW170817, favoring a soft neutron matter EOS, and barely consistent with the PREX-2 result within 1$\sigma$ error bands. Our result indicates the neutron-skin thickness of ${}^{48}$Ca as 0.15\,-\,0.19\,fm.

   nucl-exnucl-thPRL(2021)·80 citations
3. 03*

   Accessing Topological Fluctuations of Gauge Fields with Chiral Magnetic Effect

   Anping Huang🇨🇳 · Shuzhe Shi🇨🇦 · Shu Lin🇨🇳 · Xingyu Guo🇨🇳 · Jinfeng Liao🇺🇸

   Gauge fields provide the fundamental interactions in the Standard Model of particle physics. Gauge field configurations with nontrivial topological windings are known to play crucial roles in many important phenomena, from matter-anti-matter asymmetry of today's universe to spontaneous chiral symmetry breaking in strong interaction. Their presence is however elusive for direct detection in experiments. Here we show that measurements of the chiral magnetic effect (CME) in heavy ion collisions can be used for accessing the topological fluctuations of the non-Abelian gauge fields in the Quantum Chromodynamics (QCD). To achieve this, we implemented a key ingredient, the stochastic dynamics of gauge field topological fluctuations, into a state-of-the-art framework for simulating the CME in these collisions. This new framework provides the necessary tool to quantify initial topological fluctuations from any definitive CME signal to be extracted from experimental data. It also reveals a universal scaling relation between initial topological fluctuations and particle multiplicity produced in the corresponding collision events.

   ↳ hep-phhep-thnucl-exnucl-thPRD(2023)·3 citations
4. 04*

   Multi-messenger heavy-ion collision physics

   Charles Gale🇨🇦 · Jean-François Paquet🇺🇸 · Björn Schenke🇺🇸 · Chun Shen🇺🇸

   This work studies the production of direct photons in relativistic nuclear collisions, along with the production of hadrons. Radiation from the very first instants to the final moments of the evolution is included. The hybrid model used here describes all stages of relativistic heavy-ion collisions. Chronologically, those are an initial state reflecting the collision of nuclei described within the Color Glass Condensate effective theory; a pre-equilibrium phase based on non-equilibrium linear response; relativistic viscous hydrodynamics, and a hadronic afterburner. The effect of the pre-equilibrium phase on both photonic and hadronic observables is highlighted for the first time. The potential of photon observables -- spectrum, differential elliptic and triangular flow -- to reveal the chemical equilibration time is studied. Finally, we consider "small collision systems", including proton+nucleus collisions and collisions of light nuclei, as probed by hadronic and electromagnetic observables. We demonstrate how photon production can signal the formation of quark-gluon plasma in such small systems.

   ↳ nucl-thhep-phnucl-exPRC(2022)·122 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.