Tue·Nov 24, 2015Tuesday·November 24, 2015

1. 01*

   Scattering cross sections of liquid deuterium for ultracold neutrons: Experimental results and a calculation model

   Stefan Döge🇫🇷 · Christian Herold🇹🇭 · Stefan Müller · Christoph Morkel · Erwin Gutsmiedl · Peter Geltenbort🇫🇷 · Thorsten Lauer🇩🇪 · Peter Fierlinger🇩🇪 · Winfried Petry · Peter Böni

   We present scattering cross sections ${\sigma }_{\text{scatt}}$ of ultracold neutrons (UCN) in liquid deuterium at T = 20.6 K, as recently measured by means of a transmission experiment. The indispensable thorough raw data treatment procedure is explained. A calculation model for coherent and incoherent scattering in liquid deuterium in the hydrodynamic limit based on appropriate physical concepts is provided and shown to fit the data well. The applicability of the incoherent approximation for UCN scattering in liquid deuterium was tested and found to deliver acceptable results.

   nucl-exphysics.flu-dynphysics.ins-detPRB(2015)·5 citations
2. 02*

   Measuring the Th-229 nuclear isomer transition with U-233 doped crystals

   Simon Stellmer · Matthias Schreitl · Georgy Kazakov · Johannes Sterba · Thorsten Schumm

   We propose a simple approach to measure the energy of the few-eV isomeric state in Th-229. To this end, U-229 nuclei are doped into VUV-transparent crystals, where they undergo alpha decay into Th-229, and, with a probability of 2%, populate the isomeric state. These Th-229m nuclei may decay into the nuclear ground state under emission of the sought-after VUV gamma, whose wavelength can be determined with a spectrometer. Based on measurements of the optical transmission of U:CaF2 crystals in the VUV range, we expect a signal at least 2 orders of magnitude larger compared to current schemes using surface-implantation of recoil nuclei. The signal background is dominated by Cherenkov radiation induced by beta decays of the thorium decay chain. We estimate that, even if the isomer undergoes radiative de-excitation with a probability of only 0.1%, the VUV gamma can be detected within a reasonable measurement time.

   nucl-exphysics.ins-detquant-phPRC(2016)·19 citations
3. 03*

   Excited Baryon Structure Using Exclusive Reactions with CLAS12

   Daniel S. Carman (for the CLAS Collaboration)🇺🇸

   Studying excited nucleon structure through exclusive electroproduction reactions is an important avenue for exploring the nature of the non-perturbative strong interaction. Electrocouplings for $N^{\ast }$ states in the mass range below 1.8~GeV have been determined from analyses of CLAS $\pi N$, $\eta N$, and $\pi \pi N$ data. This work made it clear that consistency of independent analyses of exclusive channels with different couplings and non-resonant backgrounds but the same $N^{\ast }$ electro-excitation amplitudes, is essential to have confidence in the extracted results. In terms of hadronic coupling, many high-lying $N^{\ast }$ states preferentially decay through the $\pi \pi N$ channel instead of $\pi N$. Data from the $KY$ channels will therefore be critical to provide an independent analysis to compare the extracted electrocouplings for the high-lying $N^{\ast }$ states against those determined from the $\pi N$ and $\pi \pi N$ channels. A program to study excited $N^{\ast }$ decays to non-strange and strange exclusive final states using CLAS12 will measure differential cross sections to be used as input to extract the ${\gamma }_{v}N{N}^{\ast }$ transition form factors for the most prominent $N^{\ast }$ states in the range of invariant energy $W$ up 3~GeV in the virtually unexplored domain of momentum transfers $Q^2$ up to 12~GeV${}^2$.

   nucl-exnucl-thAIP Conf.Proc.(2016)·0 citations
4. 04*

   Jet Hadronization via Recombination of Parton Showers in Vacuum and in Medium

   Rainer J. Fries🇺🇸 · Kyongchol Han🇺🇸 · Che Ming Ko🇺🇸

   We have studied the hadronization of jet parton showers based on the quark recombination model. This is achieved by letting gluons at the end of the perturbative shower evolution undergo a non-perturbative splitting into quark and antiquark pairs, then applying a Monte-Carlo version of instantaneous quark recombination, and finally subjecting remnant quarks (those which have not found a recombination partner) to Lund string fragmentation. When applied to parton showers from the PYTHIA Monte Carlo generator, the final hadron spectra from our calculation compare quite well to PYTHIA jets that have been hadronized with the default Lund string fragmentation. Modeling the quark gluon plasma produced in heavy ion collisions by a blast wave model, we have further studied medium effects on the hadronization of jet shower partons by also including their recombination with the thermal partons from the quark gluon plasma. We find that the latter leads to a significant enhancement of intermediate transverse momentum pions and protons at both RHIC and LHC. Our results thus suggest that medium modification of jet fragmentation provides a plausible explanation for the enhanced production of intermediate transverse momentum hadrons observed in experiments.

   ↳ nucl-thnucl-exNucl.Part.Phys.Proc.(2016)·1 citation
5. 05*

   Spin asymmetries for vector boson production in polarized p+p collisions

   Jin Huang🇺🇸 · Zhong-Bo Kang🇺🇸 · Ivan Vitev🇺🇸 · Hongxi Xing🇺🇸

   We study the cross section for vector boson ($W^{\pm }/Z^0/{\gamma }^{\ast }$) production in polarized nucleon-nucleon collisions for low transverse momentum of the observed vector boson. For the case where one measures the transverse momentum and azimuthal angle of the vector bosons, we present the cross sections and the associated spin asymmetries in terms of transverse momentum dependent parton distribution functions (TMDs) at tree level within the TMD factorization formalism. To assess the feasibility of experimental measurements, we estimate the spin asymmetries for $W^{\pm }/Z^0$ boson production in polarized proton-proton collisions at the Relativistic Heavy Ion Collider (RHIC) by using current knowledge of the relevant TMDs. We find that some of these asymmetries can be sizable if the suppression effect from TMD evolution is not too strong. The $W$ program at RHIC can, thus, test and constrain spin theory by providing unique information on the universality properties of TMDs, TMD evolution, and the nucleon structure. For example, the single transverse spin asymmetries could be used to probe the well-known Sivers function $f_{1T}^{\perp q}$, as well as the transversal helicity distribution $g_{1T}^q$ via the parity-violating nature of $W$ production.

   ↳ hep-phhep-exnucl-exPRD(2016)·17 citations
6. 06*

   Searching for minimum in dependence of squared speed-of-sound on collision energy

   Fu-Hu Liu🇨🇳 · Li-Na Gao🇨🇳 · Roy A. Lacey🇺🇸

   Experimental results of the rapidity distributions of negatively charged pions produced in proton-proton ($p$-$p$) and beryllium-beryllium (Be-Be) collisions at different beam momentums, measured by the NA61/SHINE Collaboration at the super proton synchrotron (SPS), are described by a revised (three-source) Landau hydrodynamic model. The squared speed-of-sound parameter $c_s^2$ is then extracted from the width of rapidity distribution. There is a local minimum (knee point) which indicates a softest point in the equation of state (EoS) appearing at about 40$A$ GeV/$c$ (or 8.8 GeV) in $c_s^2$ excitation function [the dependence of $c_s^2$ on incident beam momentum (or center-of-mass energy)]. This knee point should be related to the searching for the onset of quark deconfinement and the critical point of quark-gluon plasma (QGP) phase transition.

   ↳ hep-phhep-exnucl-exnucl-thAdv.High Energy Phys.(2016)·5 citations
7. 07*

   The $K^{\ast 0}\Lambda$ photoproduction off a neutron

   Xiao-Yun Wang🇨🇳 · Jun He🇨🇳

   Inspired by the preliminary experimental data by the CLAS Collaboration, the $K^{\ast 0}\Lambda$ photoproduction off a neutron is studied within an effective Lagrangian approach. The contributions from the Born terms including $s$, $u$, and $t$ channels are considered to calculate the amplitude, with which the cross sections are calculated and compared with preliminary CLAS data. The theoretical results indicate that the contribution from the $K$-exchange $t$ channel plays a dominant role for the $K^{\ast 0}\Lambda$ photoproduction. The contribution from the $\kappa$ exchange is found one order of magnitude smaller than that from the $K$ exchange. Both the Regge model and the Feynman model are applied to treat the $t$-channel contribution. The discrepancy between two models is found small in the energy range of CLAS data and predicted to become obvious at energies higher than 3 GeV. More precise experimental data especially at backward angles will be helpful to further understand the interaction mechanism of the $K^{\ast 0}\Lambda$ photoproduction.

   ↳ nucl-thhep-phnucl-exPRC(2016)·17 citations
8. 08*

   Effect of correlations on cumulants in heavy-ion collisions

   D. K. Mishra🇮🇳 · P. Garg🇮🇳 · P. K. Netrakanti🇮🇳

   We study the effects of correlations on cumulants and their ratios of net-proton multiplicity distributions which have been measured for central (0\%-5\%) Au + Au collisions at the Relativistic Heavy Ion Collider (RHIC). This effect has been studied assuming individual proton and anti-proton distributions as a Poisson or Negative Binomial Distribution (NBD). In-spite of significantly correlated production due to baryon number, electric charge conservation and kinematical correlations of protons and anti-protons, the measured cumulants of the net-proton distribution follow the independent production model. In the present work we demonstrate how the introduction of the correlations will affect the cumulants and their ratios for the difference distributions. We have also demonstrated this study using the proton and anti-proton distributions obtained from the HIJING event generator.

   ↳ nucl-thnucl-exPRC(2016)·5 citations
9. 09*

   An homeopathic cure to pure Xenon large diffusion

   C. D. R. Azevedo🇵🇹 · L.M.P. Fernandes🇵🇹 · E. D. C. Freitas🇵🇹 · D. Gonzalez-Diaz🇩🇪 · F. Monrabal🇺🇸 · C. M. B. Monteiro🇵🇹 · J. M. F. Dos Santos🇵🇹 · J.F.C.A. Veloso🇵🇹 · J. J Gomez-Cadenas🇪🇸

   The NEXT neutrinoless double beta decay experiment will use a high- pressure gas electroluminescence-based TPC to search for the decay of Xe-136. One of the main advantages of this technology is the possibility to reconstruct the topology of events with energies close to Qbb. The rejection potential associated to the topology reconstruction is limited by our capacity to prop- erly reconstruct the original path of the electrons in the gas. This reconstruction is limited by different factors that include the geometry of the detector, the density of the sensors in the tracking plane and the separation among them, etc. Ultimately, the resolution is limited by the physics of electron diffusion in the gas. In this paper we present a series of molecular additives that can be used in Xenon gas at very low partial pressure to reduce both longitudinal and transverse diffusion. We will show the results of different Monte-Carlo simulations of electron transport in the gas mixtures from wich we have extracted the value of some important parameters like diffusion, drift velocity and light yields. These results show that there is a series of candidates that can reduce diffusion without affecting the energy resolution of the detector and they should be studied experimentally. A comparison with preliminary results from such an ongoing experimental effort is given.

   ↳ physics.ins-dethep-exnucl-exJINST(2016)·21 citations
10. 10*

    Hydrodynamical noise and Gubser flow

    Li Yan🇫🇷 · Hanna Grönqvist🇫🇷

    Hydrodynamical noise is introduced on top of Gubser's analytical solution to viscous hydrodynamics. With respect to the ultra-central collision events of Pb-Pb, p-Pb and p-p at the LHC energies, we solve the evolution of noisy fluid systems and calculate the radial flow velocity correlations. We show that the absolute amplitude of the hydrodynamical noise is determined by the multiplicity of the collision event. The evolution of azimuthal anisotropies, which is related to the generation of harmonic flow, receives finite enhancements from hydrodynamical noise. Although it is strongest in the p-p systems, the effect of hydrodynamical noise on flow harmonics is found to be negligible, especially in the ultra-central Pb-Pb collisions. For the short-range correlations, hydrodynamical noise contributes to the formation of a near-side peak on top of the correlation structure originated from initial state fluctuations. The shape of the peak is affected by the strength of hydrodynamical noise, whose height and width grow from the Pb-Pb system to the p-Pb and p-p systems.

    ↳ nucl-thhep-phnucl-exJHEP(2016)·31 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.