Mon·Apr 24, 2017Monday·April 24, 2017

1. 01*

   Photon and dilepton observables: An experimental overview

   S. Campbell🇺🇸

   Dilepton and direct photon measurements in heavy ion collisions provide access to the early stages of the collision. Dilepton continuum measurements at SPS and RHIC show an excess consistent with broadening of the rho meson spectral function as a result of hadronic interactions. Direct photon measurements at RHIC and the LHC show an excess of low $p_T$ photons over the expected yield. This excess has a large azimuthal anisotropy with respect to the collision plane. Understanding the direct photon excess and its anisotropy has become an outstanding question in the field of heavy ion physics. This proceeding consists of a summary of new dilepton and direct photon experimental results shown at the 2017 International Conference on Ultrarelativistic Nucleus-Nucleus Collisions and presents them in the context of our current understanding of these electromagentic probes.

   nucl-exNPA(2017)·11 citations
2. 02*

   Beam Energy Dependence of Dielectron Production in Au+Au Collisions from STAR at RHIC

   Patrick Huck🇨🇳

   Enabled by the addition of a TOF detector system in 2010, the first phase of the Beam Energy Scan (BES-I) at RHIC allows STAR to conduct an unprecedented energy-dependent study of dielectron production within a homogeneous experimental environment, and hence close the wide gap in the QCD phase diagram between SPS and top RHIC energies. This thesis concentrates on the understanding of the LMR enhancement regarding its $M_{ee}$, $p_T$ and energy dependence. It studies dielectron production in Au+Au collisions at beam energies of 19.6, 27, 39, and 62.4 GeV with sufficient statistics. In conjunction with the published STAR results at top RHIC energy, this thesis presents results on the first comprehensive energy-dependent study of dielectron production. The comparison of $M_{ee}$- and $p_T$-spectra with cocktail simulations of hadronic sources reveals a sizeable and steadily increasing excess yield in the LMR at all beam energies. The scenario of broadened in-medium $\rho$ spectral functions proves to not only serve well as dominating underlying source but also to be universal in nature since it quantitatively and qualitatively explains the LMR enhancements from SPS to top RHIC energies. It shows that most of the enhancement is governed by interactions of the $\rho$ meson with thermal resonance excitations in the late(r)-stage hot and dense hadronic phase. This conclusion is supported by the energy-dependent measurement of integrated LMR excess yields and enhancement factors. The former do not exhibit a strong dependence on beam energy as expected from the approximately constant total baryon density above 20 GeV, and the latter show agreement with the CERES measurement at SPS energy. The consistency in excess yields and agreement with model calculations over the wide RHIC energy regime makes a strong case for LMR enhancements on the order of a factor 2-3.

   nucl-exhep-ex0 citations
3. 03*

   STAR Results from Au + Au Fixed-Target Collisions at sqrt(s_NN) = 4.5 GeV

   Kathryn Meehan (for the STAR Collaboration)🇺🇸

   We present results from STAR's first dedicated fixed-target run conducted in 2015 with Au + Au collisions at sqrt(s_NN) = 4.5 GeV. Directed flow of protons and lambdas, elliptic flow of identified hadrons, HBT radii, as well as pion, K^0_s, and Lambda spectra are compared with previous results from the AGS. These results demonstrate that STAR has good event reconstruction and particle identification capabilities in the fixed-target configuration. The implications of these results on future STAR fixed-target runs are discussed.

   nucl-exNPA(2017)·38 citations
4. 04*

   Spectroscopic factor and proton formation probability for the d3/2 proton emitter 151mLu

   F. Wang🇨🇳 · B. H. Sun🇨🇳 · Z. Liu🇨🇳 · R. D. Page🇬🇧 · C. Qi🇸🇪 · C. Scholey🇫🇮 · S. F. Ashley🇬🇧 · L. Bianco🇬🇧 · I. J. Cullen🇬🇧 · I. G. Darby🇺🇸 · S. Eeckhaudt🇫🇮 · A. B. Garnsworthy🇨🇦 and 33 other authors

   The quenching of the experimental spectroscopic factor for proton emission from the short-lived $d_{3/2}$ isomeric state in ${}^{151m}$Lu was a long-standing problem. In the present work, proton emission from this isomer has been reinvestigated in an experiment at the Accelerator Laboratory of the University of Jyväskylä. The proton-decay energy and half-life of this isomer were measured to be 1295(5) keV and 15.4(8) $\mu$s, respectively, in agreement with another recent study. These new experimental data can resolve the discrepancy in the spectroscopic factor calculated using the spherical WKB approximation. Using the R-matrix approach it is found that the proton formation probability indicates no significant hindrance for the proton decay of ${}^{151m}$Lu.

   nucl-exnucl-thPLB(2017)·18 citations
5. 05*

   Antikaon Interactions with Nucleons and Nuclei - AMADEUS At Da$\Phi$ne

   J. Marton🇦🇹 · K. Piscicchia🇮🇹 · C. Curceanu🇮🇹 · M. Cargnelli🇦🇹 · R. Del Grande🇮🇹 · L. Fabbietti🇩🇪 · G. Mandaglio🇮🇹 · M. Martini🇮🇹 · P. Moskal🇵🇱 · A. Scordo🇮🇹 · D. Sirghi🇮🇹 · M. Skurzok🇵🇱 and 4 other authors

   The aim of AMADEUS is to provide unprecedented experimental information on K${}^{-}$ absorption in light nuclear targets, to face major open problems in hadron nuclear physics in the strangeness sector, namely the nature of the $\Lambda$(1405), strongly related to the possible existence of kaonic nuclear clusters, kaons and hyperon scattering cross sections on nucleons and nuclei. These issues are fundamental for a better understanding of the non-perturbative QCD in the strangeness sector. AMADEUS step 0 deals with the analysis of the 2004-2005 KLOE collected data. The interactions of the negative kaons produced by the DA$\Phi$NE collider (a unique source of monochromatic low-momentum kaons) with the materials of the KLOE detector, used as active targets, provide samples of K${}^{-}$ absorptions on H, ${}^4$He, ${}^9$Be and ${}^{12}$C, both at-rest and in-flight. A second step deals with the data from the implementation in the central region of the KLOE detector of a pure graphite target, providing a high statistic sample of K${}^{-}{}^{12}$C nuclear captures at rest. For the future a new setup, with various dedicated gaseous and solid targets, is under preparation.

   nucl-exPoS(2017)·1 citation
6. 06*

   Solar Neutrino Spectroscopy

   Michael Wurm🇩🇪

   More than forty years after the first detection of neutrinos from the Sun, the spectroscopy of solar neutrinos has proven to be an on-going success story. The long-standing puzzle about the observed solar neutrino deficit has been resolved by the discovery of neutrino flavor oscillations. Today's experiments have been able to solidify the standard MSW-LMA oscillation scenario by performing precise measurements over the whole energy range of the solar neutrino spectrum. This article reviews the enabling experimental technologies: On the one hand mutli-kiloton-scale water Cherenkov detectors performing measurements in the high-energy regime of the spectrum, on the other end ultrapure liquid-scintillator detectors that allow for a low-threshold analysis. The current experimental results on the fluxes, spectra and time variation of the different components of the solar neutrino spectrum will be presented, setting them in the context of both neutrino oscillation physics and the hydrogen fusion processes embedded in the Standard Solar Model. Finally, the physics potential of state-of-the-art detectors and a next-generation of experiments based on novel techniques will be assessed in the context of the most interesting open questions in solar neutrino physics: a precise measurement of the vacuum-matter transition curve of electron-neutrino oscillation probability that offers a definitive test of the basic MSW-LMA scenario or the appearance of new physics; and a first detection of neutrinos from the CNO cycle that will provide new information on solar metallicity and stellar physics.

   ↳ hep-exnucl-exphysics.ins-detPhys.Rept.(2017)·36 citations
7. 07*

   Refining mass formulas for astrophysical applications: a Bayesian neural network approach

   Raditya Utama · Jorge Piekarewicz🇺🇸

   Exotic nuclei, particularly those near the driplines, are at the core of one of the fundamental questions driving nuclear structure and astrophysics today: what are the limits of nuclear binding? Exotic nuclei play a critical role in both informing theoretical models as well as in our understanding of the origin of the heavy elements. Our purpose is to refine existing mass models through the training of an artificial neural network that will mitigate the large model discrepancies far away from stability. The basic paradigm of our two-pronged approach is an existing mass model that captures as much as possible of the underlying physics followed by the implementation of a Bayesian Neural Network (BNN) refinement to account for the missing physics. Bayesian inference is employed to determine the parameters of the neural network so that model predictions may be accompanied by theoretical uncertainties. Despite the undeniable quality of the mass models adopted in this work, we observe a significant improvement (of about 40%) after the BNN refinement is implemented. Indeed, in the specific case of the Duflo-Zuker mass formula, we find that the rms deviation relative to experiment is reduced from rms =0.503MeV to rms=0.286 MeV. These newly refined mass tables are used to map the neutron drip lines (or rather "drip bands") and to study a few critical r-process nuclei. The BNN approach is highly successful in refining the predictions of existing mass models. In particular, the large discrepancy displayed by the original "bare" models in regions where experimental data is unavailable is considerably quenched after the BNN refinement. This lends credence to our approach and has motivated us to publish refined mass tables that we trust will be helpful for future astrophysical applications.

   ↳ nucl-thastro-ph.SRnucl-exPRC(2017)·93 citations
8. 08*

   Hydrodynamic modeling of heavy-ion collisions

   Li Yan🇨🇦

   This contribution presents a theoretical overview of hydrodynamic modelling of heavy-ion collisions, with highlights on some recent developments. In particular, the formulation of anisotropic hydrodynamics, the role of hydrodynamic fluctuations, and the non-linear coupling of flow coefficients will be discussed.

   ↳ nucl-thhep-phnucl-exNPA(2017)·4 citations
9. 09*

   The SNO+ experiment physics goals and background mitigation

   G. Prior🇺🇸

   The main physics goal of the SNO+ experiment is the search for neutrinoless double-beta decay (0$\nu \beta \beta$), a rare process which if detected, will prove the Majorana nature of neutrinos and provide information on the absolute scale of the neutrino mass. Additional physics goals include the study of solar neutrinos, anti-neutrinos from nuclear reactors and the Earth's natural radioactivity as well as Supernovae neutrinos. Located in the SNOLAB (Canada) deep underground laboratory, it will re-use the SNO detector. A short phase with the detector completely filled with water has started at the beginning of 2017, before running the detector with scintillator. This paper describes in details the SNO+ sensitivity to 0$\nu \beta \beta$ decays, as well as the other physics goals. Crucial to these large volume liquid scintillator experiments, is the ability to constraint the low-energy background from radioactive decays. Methods to mitigate those are also presented.

   ↳ physics.ins-dethep-exnucl-ex4 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.