Tue·Jun 9, 2020Tuesday·June 9, 2020

1. 01*

   Quantification of the Chiral Magnetic Effect in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV

   Roy A. Lacey (1)🇺🇸 · Niseem Magdy (2) ((1) Depts. of Chemistry and Physics, Stony Brook University, Stony Brook USA, (2) Department of Physics, University of Illinois at Chicago, Chicago, Illinois, USA)🇺🇸

   The Multi-Phase Transport model, AMPT, and the Anomalous Viscous Fluid Dynamics model, AVFD, are used to assess a possible chiral-magnetically-driven charge separation ($\Delta S$) recently measured with the $R_{{\Psi }_2}(\Delta S)$ correlator in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV. The Comparison of the experimental and simulated $R_{{\Psi }_2}(\Delta S)$ distributions indicates that background-driven charge separation is insufficient to account for the measurements. The AVFD model calculations, which explicitly account for CME-driven anomalous transport in the presence of background, indicate a CME signal quantified by the $P$-odd Fourier dipole coefficient $a_1^{\prime }\approx 0.5\%$ in mid-central collisions. A similar evaluation for the $\Delta \gamma$ correlator suggests that only a small fraction of this signal ($f_{\mathrm{CME}}=\Delta {\gamma }_{\mathrm{CME}}/\Delta \gamma \approx 25\%$) is measurable with this correlator in the same collisions. The related prediction for signal detection in isobaric collisions of Ru+Ru and Zr+Zr are also presented.

   nucl-exhep-exnucl-th2 citations
2. 02*

   Charge separation measurements in $p$($d$)+Au and Au+Au collisions; implications for the chiral magnetic effect

   STAR Collaboration

   Charge separation ($\Delta S$) measurements, obtained relative to the $2^{\mathrm{nd}}$-order (${\Psi }_2$) and $3^{\mathrm{rd}}$-order (${\Psi }_3$) event planes with a new charge-sensitive correlator $R_{{\Psi }_m}(\Delta S)$, are presented for $p$($d$)+Au and Au+Au collisions at $\sqrt{s_{NN}}=200$~GeV. The correlator, which is sensitive to the hypothesized Chiral Magnetic Effect (CME), show the expected patterns of background-driven charge separation for the measurements relative to ${\Psi }_3$ and those relative to ${\Psi }_2$ for the $p$($d$)+Au systems. By contrast, the Au+Au measurements relative to ${\Psi }_2$, show event-shape-independent $R_{{\Psi }_2}(\Delta S)$ distributions consistent with a CME-driven charge separation, quantified by widths having an inverse relationship to the Fourier dipole coefficient ${\tilde{a}}_1$, which evaluates the CME. The extracted values of these widths and their dependencies on centrality and event-shape give new constraints for possible CME-driven charge separation in relativistic heavy-ion collisions.

   nucl-exhep-exhep-phnucl-th14 citations
3. 03*

   Ultracold Neutrons

   Klaus Kirch🇨🇭 · Bernhard Lauss🇨🇭

   Ultracold neutrons (UCN) are free neutrons that can be stored in experimental setups for several minutes. Some of the most important properties of the neutron, such as its tiny permanent electric dipole moment and its beta decay lifetime, are best measured with UCN. Also searches for well motivated but yet unknown, hypothetical additional interactions are being pursued with UCN. Such measurements in the field of low-energy, precision physics may have far reaching implications from particle physics to cosmology. Most experiments are statistics limited and need high-intensity UCN sources. The UCN source at PSI is at the forefront of the field and home to the international nEDM collaboration and its world-leading search for the neutron electric dipole moment. This article aims at giving an overview of the fascinating research using ultracold neutrons emphasizing on activities at PSI including various physics side-analyses which were pioneered by the nEDM collaboration.

   nucl-exhep-exphysics.ins-dethttps://sgn.web.psi.ch/sgn/snn.html, publ…·2 citations
4. 04*

   Electric field imaging using polarized neutrons

   Yuan-Yu Jau🇺🇸 · Daniel S. Hussey🇺🇸 · Thomas R. Gentile🇺🇸 · Wangchun Chen🇺🇸

   We experimentally demonstrate that electrically neutral particles, neutrons, can be used to directly visualize the electrostatic field inside a target volume that can be isolated or occupied. Electric-field images were obtained using a polychromatic, spin-polarized neutron beam with a sensitive polarimetry scheme. This work may enable new diagnostic power of the structure of electric potential, electric polarization, charge distribution, and dielectric constant by imaging spatially dependent electric fields in objects that cannot be accessed by other conventional probes.

   ↳ physics.ins-detnucl-exquant-phPRL(2020)·2 citations
5. 05*

   Level density within a micro-macroscopic approach

   A.G. Magner🇺🇦 · A.I. Sanzhur🇺🇦 · S.N. Fedotkin🇺🇦 · A.I. Levon🇺🇦 · S. Shlomo🇺🇸

   Statistical level density $\rho (E,A)$ is derived for nucleonic system with a given energy $E$, particle number $A$ and other integrals of motion in the micro-macroscopic approximation beyond the standard saddle-point method of the Fermi gas model. This level density reaches the two limits; the well-known Fermi gas grand-canonical ensemble limit for a large entropy $S$ related to large excitation energies, and the finite micro-canonical limit for a small combinatorical entropy $S$ at low excitation energies. The inverse level density parameter $K$ as function of the particle number $A$ in the semiclassical periodic orbit theory, taking into account the extended Thomas-Fermi and Strutinsky shell corrections, is calculated and compared with experimental data.

   ↳ nucl-thnucl-exNPA(2022)·8 citations
6. 06*

   Thermodynamic and Transport Properties of Matter Formed in $pp$, $p$-Pb, Xe-Xe and Pb-Pb Collisions at the Large Hadron Collider using Color String Percolation Model

   Dushmanta Sahu🇮🇳 · Raghunath Sahoo🇮🇳

   To have a better understanding of the matter formed in ultra-relativistic collisions, using the Color String Percolation Model (CSPM), we have estimated initial energy density, mean free path, squared speed of sound, shear viscosity to entropy density ratio ($\eta /s$), bulk viscosity to entropy density ratio and bulk modulus for $pp$, $p$-Pb, Xe-Xe and Pb-Pb collisions at the Large Hadron Collider (LHC). These observables are studied as a function of final state charged particle multiplicity density and initial state percolation temperature. The results from this work are compared with the results from well known QCD models and with the transport properties of matter found in day-to-day life. These observables allow us to conclude an array of important findings about the matter formed in high energy collisions at the LHC. This work gives a threshold of charged particle multiplicity $⟨d{N}_{ch}/d\eta ⟩\simeq$ 20, after which there are indications of change in the dynamics of the systems. The critical initial energy density and temperature as estimated by lattice QCD, are observed to be achieved for events with final state multiplicity $⟨d{N}_{ch}/d\eta ⟩\ge$ 20. In addition, for these high-multiplicity events, the estimated $\eta /s$ are comparable with that is observed for heavy-ion collisions, which is an indication of a strongly coupled Quark Gluon Plasma. This makes LHC high-multiplicity $pp$ collision events as probable candidates for the search of QGP droplets.

   ↳ hep-phhep-exnucl-exnucl-thJ.Phys.G(2021)·23 citations
7. 07*

   Far From Equilibrium Hydrodynamics and the Beam Energy Scan

   Travis Dore🇺🇸 · Emma McLaughlin🇺🇸 · Jacquelyn Noronha-Hostler🇺🇸

   The existence of hydrodynamic attractors in rapidly expanding relativistic systems has shed light on the success of relativistic hydrodynamics in describing heavy-ion collisions at zero chemical potential. As the search for the QCD critical point continues, it is important to investigate how out of equilibrium effects influence the trajectories on the QCD phase diagram. In this proceedings, we study a Bjorken expanding hydrodynamic system based on DMNR equations of motion with initial out of equilibrium effects and finite chemical potential in a system with a critical point. We find that the initial conditions are not unique for a specific freeze-out point, but rather the system can evolve to the same final state freeze-out point with a wide range of initial baryon chemical potential, ${\mu }_B$. For the same initial energy density and baryon density, depending on how far out of equilibrium the system begins, the initial ${\mu }_B$ can vary by $\Delta {\mu }_B\sim 350$ MeV. Our results indicate that knowledge of the out-of-equilibrium effects in the initial state provide vital information that influences the search for the QCD critical point.

   ↳ nucl-thhep-phnucl-exJ.Phys.Conf.Ser.(2020)·9 citations
8. 08*

   The anomalous magnetic moment of the muon in the Standard Model

   T. Aoyama🇯🇵 · N. Asmussen🇬🇧 · M. Benayoun🇫🇷 · J. Bijnens🇸🇪 · T. Blum🇺🇸 · M. Bruno🇨🇭 · I. Caprini🇷🇴 · C. M. Carloni Calame🇮🇹 · M. Cè🇨🇭 · G. Colangelo🇨🇭 · F. Curciarello🇮🇹 · H. Czyż🇵🇱 and 120 other authors

   We review the present status of the Standard Model calculation of the anomalous magnetic moment of the muon. This is performed in a perturbative expansion in the fine-structure constant $\alpha$ and is broken down into pure QED, electroweak, and hadronic contributions. The pure QED contribution is by far the largest and has been evaluated up to and including $\mathcal{O}({\alpha }^5)$ with negligible numerical uncertainty. The electroweak contribution is suppressed by $(m_{\mu }/M_W{)}^2$ and only shows up at the level of the seventh significant digit. It has been evaluated up to two loops and is known to better than one percent. Hadronic contributions are the most difficult to calculate and are responsible for almost all of the theoretical uncertainty. The leading hadronic contribution appears at $\mathcal{O}({\alpha }^2)$ and is due to hadronic vacuum polarization, whereas at $\mathcal{O}({\alpha }^3)$ the hadronic light-by-light scattering contribution appears. Given the low characteristic scale of this observable, these contributions have to be calculated with nonperturbative methods, in particular, dispersion relations and the lattice approach to QCD. The largest part of this review is dedicated to a detailed account of recent efforts to improve the calculation of these two contributions with either a data-driven, dispersive approach, or a first-principle, lattice-QCD approach. The final result reads $a_{\mu }^{\text{SM}}=116591810(43)\times 10^{-11}$ and is smaller than the Brookhaven measurement by 3.7$\sigma$. The experimental uncertainty will soon be reduced by up to a factor four by the new experiment currently running at Fermilab, and also by the future J-PARC experiment. This and the prospects to further reduce the theoretical uncertainty in the near future-which are also discussed here-make this quantity one of the most promising places to look for evidence of new physics.

   ↳ hep-phhep-exhep-latnucl-ex+1Phys.Rept.(2020)·1886 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.