Wed·Jun 10, 2020Wednesday·June 10, 2020

1. 01*

   Pair invariant mass to isolate background in the search for the chiral magnetic effect in Au+Au collisions at $\sqrt{s_{{}_{\mathrm{NN}}}}$= 200 GeV

   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 352 other authors

   Quark interactions with topological gluon configurations can induce local chirality imbalance and parity violation in quantum chromodynamics, which can lead to the chiral magnetic effect (CME) -- an electric charge separation along the strong magnetic field in relativistic heavy-ion collisions. The CME-sensitive azimuthal correlator observable ($\Delta \gamma$) is contaminated by background arising, in part, from resonance decays coupled with elliptic anisotropy ($v_2$). We report here differential measurements of the correlator as a function of the pair invariant mass ($m_{\mathrm{inv}}$) in 20-50\% centrality Au+Au collisions at $\sqrt{s_{{}_{\mathrm{NN}}}}$= 200 GeV by the STAR experiment at RHIC. Strong resonance background contributions to $\Delta \gamma$ are observed. At large $m_{\mathrm{inv}}$ where this background is significantly reduced, the $\Delta \gamma$ value is found to be significantly smaller. An event-shape-engineering technique is deployed to determine the $v_2$ background shape as a function of $m_{\mathrm{inv}}$. We extract a $v_2$-independent and $m_{\mathrm{inv}}$-averaged signal $\Delta {\gamma }_{\mathrm{sig}}$ = (0.03 $\pm$ 0.06 $\pm$ 0.08) $\times 10^{-4}$, or $(2\pm 4\pm 5)\%$ of the inclusive $\Delta \gamma (m_{\mathrm{inv}}>0.4$ GeV/$c^2$)$=(1.58\pm 0.02\pm 0.02)\times 10^{-4}$, within pion $p_T$ = 0.2 - 0.8~\gevc and averaged over pseudorapidity ranges of $-1<\eta <-0.05$ and $0.05<\eta <1$. This represents an upper limit of $0.23\times 10^{-4}$, or $15\%$ of the inclusive result, at $95\%$ confidence level for the $m_{\mathrm{inv}}$-integrated CME contribution.

   nucl-exhep-exnucl-thPRC(2022)·36 citations
2. 02*

   Constraining isovector nuclear interactions with giant resonances within a Bayesian approach

   Jun Xu🇨🇳 · Jia Zhou🇺🇸 · Zhen Zhang🇨🇳 · Wen-Jie Xie🇨🇳 · Bao-An Li🇺🇸

   We put a stringent constraint on the isovector nuclear interactions in the Skyrme-Hartree-Fock model from the centroid energy $E_{-1}$ of the isovector giant dipole resonance in ${}^{208}$Pb as well as its electric polarizability ${\alpha }_D$. Using the Bayesian analysis method, $E_{-1}$ and ${\alpha }_D$ are found to be mostly determined by the nuclear symmetry energy $E_{sym}$ at about ${\rho }^{\star }=0.05$ fm${}^{-3}$ and the isovector nucleon effective mass $m_v^{\star }$ at the saturation density. At $90\%$ confidence level, we obtain $E_{sym}({\rho }^{\star })=16.4_{-0.9}^{+1.0}$ MeV and $m_v^{\star }/m=0.79_{-0.06}^{+0.06}$.

   ↳ nucl-thnucl-exPLB(2020)·27 citations
3. 03*

   Report from the A.I. For Nuclear Physics Workshop

   Paulo Bedaque🇺🇸 · Amber Boehnlein🇺🇸 · Mario Cromaz🇺🇸 · Markus Diefenthaler🇺🇸 · Latifa Elouadrhiri🇺🇸 · Tanja Horn🇺🇸 · Michelle Kuchera🇺🇸 · David Lawrence🇺🇸 · Dean Lee🇺🇸 · Steven Lidia🇺🇸 · Robert McKeown🇺🇸 · Wally Melnitchouk🇺🇸 and 6 other authors

   This report is an outcome of the workshop "AI for Nuclear Physics" held at Thomas Jefferson National Accelerator Facility on March 4-6, 2020. The workshop brought together 184 scientists to explore opportunities for Nuclear Physics in the area of Artificial Intelligence. The workshop consisted of plenary talks, as well as six working groups. The report includes the workshop deliberations and additional contributions to describe prospects for using AI across Nuclear Physics research.

   ↳ physics.comp-phnucl-exnucl-th6 citations
4. 04*

   The J-PET detector -- a tool for precision studies of ortho-positronium decays

   K. Dulski🇵🇱 · S.D. Bass🇵🇱 · J. Chhokar🇵🇱 · N. Chug🇵🇱 · C. Curceanu🇮🇹 · E. Czerwiński🇵🇱 · M. Dadgar · J. Gajewski · A. Gajos🇵🇱 · M. Gorgol🇵🇱 · R. Del Grande🇮🇹 · B.C. Hiesmayr🇦🇹 and 32 other authors

   The J-PET tomograph is constructed from plastic scintillator strips arranged axially in concentric cylindrical layers. It enables investigations of positronium decays by measurement of the time, position, polarization and energy deposited by photons in the scintillators, in contrast to studies conducted so far with crystal and semiconductor based detection systems where the key selection of events is based on the measurement of the photons energies. In this article we show that the J-PET tomograph system is capable of exclusive measurements of the decays of ortho-positronium atoms. We present the first positronium production results, its lifetime distribution measurements and discuss estimation of the influence of various background sources. The tomograph s performance demonstrated here makes it suitable for precision studies of positronium decays including entanglement of the final state photons, positron annihilation lifetime spectroscopy plus molecular imaging diagnostics.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2021)·30 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.