Mon·Aug 29, 2016Monday·August 29, 2016

1. 01*

   On the Binding Energy and the Charge Symmetry Breaking in A<=16 Lambda-hypernuclei

   E. Botta🇮🇹 · T. Bressani🇮🇹 · A. Feliciello🇮🇹

   In recent years, several experiments using magnetic spectrometers provided high precision results in the field of Hypernuclear Physics. In particular, the accurate determination of the Lambda-binding energy, B(Lambda), contributed to stimulate considerably the discussion about the Charge Symmetry Breaking effect in Lambda-hypernuclei isomultiplets. We have reorganized the results from the FINUDA experiment and we have obtained a series of B(Lambda) values for Lambda-hypernuclei with A <= 16 by taking into account data only from magnetic spectrometers implementing an absolute calibration of the energy scale (FINUDA at DAFNE and electroproduction experiments at JLab and at MaMi). We have then critically revisited the results obtained at KEK by the SKS Collaboration in order to make possible a direct comparison between data from experiments with and without such an absolute energy scale. A synopsis of recent spectrometric measurements of B(Lambda) is presented, including also emulsion experiment results. Several interesting conclusions are drawn, among which the equality within the errors of B(Lambda) for the A = 7, 12, 16 isomultiplets, based only on recent spectrometric data. This observation is in nice agreement with a recent theoretical prediction. Ideas for possible new measurements which should improve the present experimental knowledge are finally put forward.

   nucl-exNPA(2017)·65 citations
2. 02*

   Photoproduction ofeta-pi pairs off nucleons and deuterons

   A. Kaeser🇨🇭 · F. Mueller🇨🇭 · J. Ahrens🇩🇪 · J.R.M. Annand🇬🇧 · H.J. Arends🇩🇪 · K. Bantawa🇺🇸 · P.A. Bartolome🇩🇪 · R. Beck🇩🇪 · A. Braghieri🇮🇹 · W.J. Briscoe🇺🇸 · S. Cherepnya🇷🇺 · S. Costanza🇮🇹 and 57 other authors

   Quasi-free photoproduction of $\pi \eta$-pairs has been investigated from threshold up to incident photon energies of 1.4 GeV, respectively up to photon-nucleon invariant masses up to 1.9 GeV. Total cross sections, angular distributions, invariant-mass distributions of the $\pi \eta$ and meson-nucleon pairs, and beam-helicity asymmetries have been measured for the reactions $\gamma p\to p{\pi }^0\eta$, $\gamma n\to n{\pi }^0\eta$, $\gamma p\to n{\pi }^{+}\eta$, and $\gamma n\to p{\pi }^{-}\eta$ from nucleons bound inside the deuteron. For the $\gamma p$ initial state data for free protons have also been analyzed. Finally, the total cross sections for quasi-free production of ${\pi }^0\eta$ pairs from nucleons bound in ${}^3$He nuclei have been investigated in view of final state interaction (FSI) effects. The experiments were performed at the tagged photon beam facility of the Mainz MAMI accelerator using an almost $4\pi$ covering electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The shapes of all differential cross section data and the asymmetries are very similar for protons and neutrons and agree with the conjecture that the reactions are dominated by the sequential ${\Delta }^{\star }3/2^{-}\to \eta \Delta (1232)\to \pi \eta N$ decay chain, mainly with $\Delta (1700)3/2^{-}$ and $\Delta (1940)3/2^{-}$. The ratios of the magnitude of the total cross sections also agree with this assumption. However, the absolute magnitudes of the cross sections are reduced by FSI effects with respect to free proton data.

   nucl-exEPJA(2016)·24 citations
3. 03*

   Probing the hardest branching of jets in heavy ion collisions

   Yang-Ting Chien🇺🇸 · Ivan Vitev🇺🇸

   We present the first calculation of the momentum sharing and angular separation distributions between the leading subjets inside a reconstructed jet in heavy ion collisions. These observables are directly sensitive to the hardest branching in the process of jet formation and are, therefore, ideal for studying the early stage of the in-medium parton shower evolution. The modification of the momentum sharing and angular separation distributions in lead-lead relative to proton-proton collisions is evaluated using the leading-order medium-induced splitting functions obtained in the framework of soft-collinear effective theory with Glauber gluon interactions. Qualitative and in most cases quantitative agreement between theory and preliminary CMS measurements suggests that the parton shower in heavy ion collisions can be dramatically modified early in the branching history. We propose a new measurement which will illuminate the angular distribution of the hardest branching within jets in heavy ion collisions.

   ↳ hep-phhep-exnucl-exnucl-thPRL(2017)·129 citations
4. 04*

   The Majorana Demonstrator search for neutrinoless double beta decay

   C. Cuesta🇺🇸 · M. Buuck🇺🇸 · J.A. Detwiler🇺🇸 · J. Gruszko🇺🇸 · I.S. Guinn🇺🇸 · J. Leon🇺🇸 · R.G.H. Robertson🇺🇸 · N. Abgrall🇺🇸 · A.W. Bradley🇺🇸 · Y-D. Chan🇺🇸 · S. Mertens🇩🇪 · A.W.P. Poon🇺🇸 and 55 other authors

   The MAJORANA Collaboration is constructing the MAJORANA DEMONSTRATOR, an ultra-low background, modular, HPGe detector array with a mass of 44.8-kg (29.7 kg enriched >88% in Ge-76) to search for neutrinoless double beta decay in Ge-76. The next generation of tonnescale Ge-based neutrinoless double beta decay searches will probe the neutrino mass scale in the inverted-hierarchy region. The MAJORANA DEMONSTRATOR is envisioned to demonstrate a path forward to achieve a background rate at or below 1 count/tonne/year in the 4 keV region of interest around the Q-value of 2039 keV. The MAJORANA DEMONSTRATOR follows a modular implementation to be easily scalable to the next generation experiment. First data taken with the DEMONSTRATOR are introduced here.

   ↳ physics.ins-detnucl-exPoS(2017)·3 citations
5. 05*

   Directed flow in heavy-ion collisions at NICA: what is interesting to measure?

   L.V. Bravina🇳🇴 · E.E. Zabrodin🇳🇴

   We study the formation of the directed flow of hadrons in nuclear collisions at energies between AGS and SPS in Monte Carlo cascade model. The slope of the proton flow at midrapidity tends to zero (softening) with increasing impact parameter of the collision. For very peripheral topologies this slope becomes negative (antiflow). The effect is caused by rescattering of hadrons in remnants of the colliding nuclei. Since the softening of the proton flow can be misinterpreted as indication of the presence of quark-gluon plasma, we propose several measurements at NICA facility which can help one to distinguish between the cases with and without the plasma formation.

   ↳ hep-phnucl-exnucl-thEPJA(2016)·7 citations
6. 06*

   Hadronic weak charges and parity-violating forward Compton scattering

   Mikhail Gorchtein🇩🇪 · Hubert Spiesberger🇩🇪

   Parity-violating elastic electron-nucleon scattering at low momentum transfer allows one to access the nucleon's weak charge, the vector coupling of the $Z$-boson to the nucleon. In the Standard Model and at tree level, the weak charge of the proton is related to the weak mixing angle and accidentally suppressed, $Q_W^{p,\mathrm{tree}}=1-4{\sin }^2{\theta }_W\approx 0.07$. Modern experiments aim at extracting $Q_W^p$ at $\sim 1\%$ accuracy. Similarly, parity non-conservation in atoms allows to access the weak charge of atomic nuclei. We consider a novel class of radiative corrections, an exchange of two photons with parity violation in the hadronic/nuclear system. These corrections may affect the extraction of ${\sin }^2{\theta }_W$ from the experimental data at the relevant level of precision because they are affected by long-range interactions similar to other parity-violating radiative corrections, such as, e.g., the $\gamma Z$-exchange, which has obtained much attention recently. We show that the significance of this new correction increases with the beam energy in parity-violating electron scattering, but the general properties of the parity-violating forward Compton amplitude protect the formal definition of the weak charge as a limit at zero-momentum transfer and zero-energy. We also discuss the relevance of the new correction for upcoming experiments.

   ↳ nucl-thhep-phnucl-exPRC(2016)·6 citations
7. 07*

   The Algebraic Cluster Model: Structure of 16O

   R. Bijker🇲🇽 · F. Iachello🇺🇸

   We discuss an algebraic treatment of four-body clusters which includes both continuous and discrete symmetries. In particular, tetrahedral configurations with T(d) symmetry are analyzed with respect to the energy spectrum, transition form factors and B(EL) values. It is concluded that the low-lying spectrum of 16O can be described by four alpha-particles at the vertices of a regular tetrahedron, not as a rigid structure but rather a more floppy structure with relatively large rotation-vibration interactions and Coriolis forces.

   ↳ nucl-thnucl-exNPA(2017)·54 citations
8. 08*

   Precision analysis of the photomultiplier response to ultra low signals

   Pavel Degtiarenko🇺🇸

   A new computational model for the description of the photon detector response functions measured in conditions of low light is presented, together with examples of the observed photomultiplier signal amplitude distributions, successfully described using the parameterized model equation. In extension to the previously known approximations, the new model describes the underlying discrete statistical behavior of the photoelectron cascade multiplication processes in photon detectors with complex non-uniform gain structure of the first dynode. Important features of the model include the ability to represent the true single-photoelectron spectra from different photomultipliers with a variety of parameterized shapes, reflecting the variability in the design and in the individual parameters of the detectors. The new software tool is available for evaluation of the detectors' performance, response, and efficiency parameters that may be used in various applications including the ultra low background experiments such as the searches for Dark Matter and rare decays, underground neutrino studies, optimizing operations of the Cherenkov light detectors, help in the detector selection procedures, and in the experiment simulations.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2017)·10 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.