Wed·Sep 11, 2019Wednesday·September 11, 2019

1. 01*

   Background evaluations for the chiral magnetic effect with normalized correlators using a multiphase transport model

   Subikash Choudhury🇨🇳 · Gang Wang🇺🇸 · Wanbing He🇨🇳 · Yu Hu🇨🇳 · Huan Zhong Huang🇺🇸

   The chiral magnetic effect (CME) induces an electric charge separation in a chiral medium along the magnetic field that is mostly produced by spectator protons in heavy-ion collisions. The experimental searches for the CME, based on the charge-dependent angular correlations ($\gamma$), however, have remained inconclusive, because the non-CME background contributions are not well understood. Experimentally, the $\gamma$ correlators have been measured with respect to the second-order (${\Psi }_2$) and the third-order (${\Psi }_3$) symmetry planes, defined as ${\gamma }_{112}$ and ${\gamma }_{123}$, respectively. The expectation was that with a proper normalization, ${\gamma }_{123}$ would provide a data-driven estimate for the background contributions in ${\gamma }_{112}$. In this work, we calculate different harmonics of the $\gamma$ correlators using a charge-conserving version of a multiphase transport (AMPT) model to examine the validity of the said assumption. We find that the pure-background AMPT simulations do not yield an equality in the normalized ${\gamma }_{112}$ and ${\gamma }_{123}$, quantified by ${\kappa }_{112}$ and ${\kappa }_{123}$, respectively. Furthermore, we test another correlator, ${\gamma }_{132}$, within AMPT, and discuss the relation between different $\gamma$ correlators.

   ↳ hep-phhep-exnucl-exEPJC(2020)·16 citations
2. 02*

   Barium Tagging with Selective, Dry-Functional, Single Molecule Sensitive On-Off Fluorophores for the NEXT Experiment

   N.K. Byrnes🇺🇸 · A. A. Denisenko🇺🇸 · F.W. Foss Jr.🇺🇸 · B.J.P. Jones🇺🇸 · A.D. McDonald🇺🇸 · D.R. Nygren🇺🇸 · P. Thapa🇺🇸 · K. Woodruff🇺🇸

   In the search for neutrinoless double beta decay, understanding and reducing backgrounds is crucial for success. An advance that could drive backgrounds to negligible levels would be the ability to efficiently detect the barium daughter in ${}^{136}$Xe to ${}^{136}$Ba double beta decay, since no conventional radioactive process can produce barium ions or atoms in xenon at significant rates. In xenon gas, the barium daughter most likely survives as a dication. An approach under development by the NEXT collaboration involves transporting this ion from the active medium onto a coated transparent plane supporting a barium-sensitive fluorescent dye, monitored via fluorescence microscopy. Upon exposure to a barium dication, the dye will begin fluorescing, which, when correlated with the detection of a double electron signal at the anode, would confirm double beta decay.Our results have shown that a single barium ion can be resolved via Single Molecule Fluorescent Imaging (SMFI). The next challenge is a realization of this technique within in a large volume of xenon gas. Significant advances have recently been made: custom barium-tagging molecules that fluoresce strongly in the dry state when exposed to barium have been demonstrated, and devices constructed that can observe fluorescence via in-vacuum or in-gas Total Internal Reflection Fluorescence Microscopy. We present the status of this technique and the outlook for barium tagging with On-Off switchable fluorophores, including new results with a Ba${}^{2+}$-selective dye that functions under our desired conditions in the visible region and with single ion sensitivity.

   ↳ physics.ins-dethep-exnucl-ex8 citations
3. 03*

   Statistics of the Charge Spectrum of Photo-Multipliers and Methods for Absolute Calibration

   Milind V. Diwan🇺🇸

   We derive the full expression for the shape of the charge spectrum that results from the illumination of a photo-multiplier tube. The derivation is for low intensity illumination with constant gain, a common condition for most nuclear and particle physics applications. Under these conditions, it is shown that an analytic expression can be formulated that describes details of the spectrum including the pedestal and dark noise with excellent fidelity to allow statistical fits to data. The derivation and full formula using either Gaussian or Poisson models for gain, and its limiting forms under various simplifying assumptions are presented with strategies on their use. The analytic description can be used to formulate data acquisition strategies to perform precise absolute calibration of photo-multipliers, the digitizers, and the data acquisition system.

   ↳ physics.ins-dethep-exnucl-exJINST(2020)·7 citations
4. 04*

   A Hierarchical Bayesian Approach to Neutron Spectrum Unfolding with Organic Scintillators

   Haonan Zhu · Yoann Altmann · Angela Di Fulvioand Stephen McLaughlin🇮🇹 · Sara Pozzi🇮🇹 · Alfred Hero

   We propose a hierarchical Bayesian model and state-of-art Monte Carlo sampling method to solve the unfolding problem, i.e., to estimate the spectrum of an unknown neutron source from the data detected by an organic scintillator. Inferring neutron spectra is important for several applications, including nonproliferation and nuclear security, as it allows the discrimination of fission sources in special nuclear material (SNM) from other types of neutron sources based on the differences of the emitted neutron spectra. Organic scintillators interact with neutrons mostly via elastic scattering on hydrogen nuclei and therefore partially retain neutron energy information. Consequently, the neutron spectrum can be derived through deconvolution of the measured light output spectrum and the response functions of the scintillator to monoenergetic neutrons. The proposed approach is compared to three existing methods using simulated data to enable controlled benchmarks. We consider three sets of detector responses. One set corresponds to a 2.5 MeV monoenergetic neutron source and two sets are associated with (energy-wise) continuous neutron sources (${}^{252}$Cf and ${}^{241}$AmBe). Our results show that the proposed method has similar or better unfolding performance compared to other iterative or Tikhonov regularization-based approaches in terms of accuracy and robustness against limited detection events, while requiring less user supervision. The proposed method also provides a posteriori confidence measures, which offers additional information regarding the uncertainty of the measurements and the extracted information.

   ↳ physics.ins-detnucl-exphysics.comp-phstat.APIEEE Trans.Nucl.Sci.(2019)·4 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.