Mon·Jan 20, 2020Monday·January 20, 2020

1. 01*

   First direct measurement of ${}^{22}$Mg($\alpha$,p)${}^{25}$Al and implications for X-ray burst model-observation comparisons

   J. S. Randhawa🇨🇦 · Y. Ayyad🇪🇸 · W. Mittig🇺🇸 · Z. Meisel🇺🇸 · T. Ahn🇺🇸 · S. Aguilar · H. Alvarez-Pol🇪🇸 · D. W. Bardayan🇺🇸 · D. Bazin🇺🇸 · S. Beceiro-Novo🇪🇸 · L. Carpenter🇺🇸 · M. Cortesi🇺🇸 and 17 other authors

   Type-I X-ray burst (XRB) light curves are sensitive to the model's nuclear input and consequently affects the model-observation comparisons. ${}^{22}$Mg($\alpha$,p)${}^{25}$Al is among the most important reactions which directly impact the XRB light curve. We report the first direct measurement of ${}^{22}$Mg($\alpha$,p)${}^{25}$Al using the Active Target Time Projection Chamber. XRB light curve model-observation comparison for the source $GS1826-24$ using new reaction rate implies a less-compact neutron star than previously inferred. Additionally, our result removes an important uncertainty in XRB model calculations that previously hindered extraction of the neutron star compactness.

   nucl-exPRL(2020)·32 citations
2. 02*

   First search for $2\epsilon$ and $\epsilon {\beta }^{+}$ decay of ${}^{174}$Hf

   F.A. Danevich🇺🇦 · M. Hult🇧🇪 · D.V. Kasperovych🇺🇦 · G.P. Kovtun🇺🇦 · K.V. Kovtun🇺🇦 · G. Lutter🇧🇪 · G. Marissens🇧🇪 · O.G. Polischuk🇺🇦 · S.P. Stetsenko🇺🇦 · V.I. Tretyak🇺🇦

   The first ever search for $2\epsilon$ and $\epsilon {\beta }^{+}$ decay of ${}^{174}$Hf was realized using a high-pure sample of hafnium (with mass 179.8 g) and the ultra low-background HPGe-detector system located 225 m underground. After 75 days of data taking no indication of the double beta decay transitions could be detected but lower limits for the half-lives of the different channels and modes of the decays were set on the level of $\lim T_{1/2}\sim 10^{16}-10^{18}$ a.

   nucl-exNPA(2020)·6 citations
3. 03*

   Beam energy dependence of net-$\Lambda$ fluctuations measured by the STAR experiment at RHIC

   STAR Collaboration: J. Adam🇺🇸 · L. Adamczyk🇵🇱 · J. R. Adams🇺🇸 · J. K. Adkins🇺🇸 · G. Agakishiev🇷🇺 · M. M. Aggarwal🇮🇳 · Z. Ahammed🇮🇳 · I. Alekseev🇷🇺 · D. M. Anderson🇺🇸 · A. Aparin🇷🇺 · E. C. Aschenauer🇺🇸 · M. U. Ashraf🇨🇳 and 346 other authors

   The measurements of particle multiplicity distributions have generated considerable interest in understanding the fluctuations of conserved quantum numbers in the Quantum Chromodynamics (QCD) hadronization regime, in particular near a possible critical point and near the chemical freeze-out. We report the measurement of efficiency and centrality bin width corrected cumulant ratios ($C_2/C_1$, $C_3/C_2$) of net-$\Lambda$ distributions, in the context of both strangeness and baryon number conservation, as a function of collision energy, centrality and rapidity. The results are for Au + Au collisions at five beam energies ($\sqrt{s_{NN}}$ = 19.6, 27, 39, 62.4 and 200 GeV) recorded with the Solenoidal Tracker at RHIC (STAR). We compare our results to the Poisson and negative binomial (NBD) expectations, as well as to Ultra-relativistic Quantum Molecular Dynamics (UrQMD) and Hadron Resonance Gas (HRG) model predictions. Both NBD and Poisson baselines agree with data within the statistical and systematic uncertainties. The ratios of the measured cumulants show no features of critical fluctuations. The chemical freeze-out temperatures extracted from a recent HRG calculation, which was successfully used to describe the net-proton, net-kaon and net-charge data, indicate $\Lambda$ freeze-out conditions similar to those of kaons. However, large deviations are found when comparing to temperatures obtained from net-proton fluctuations. The net-$\Lambda$ cumulants show a weak, but finite, dependence on the rapidity coverage in the acceptance of the detector, which can be attributed to quantum number conservation.

   nucl-exhep-exhep-phnucl-thPRC(2020)·32 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.