Wed·Oct 7, 2015Wednesday·October 7, 2015

1. 01*

   The Proton Radius from Electron Scattering Data

   Douglas W. Higinbotham🇺🇸 · Al Amin Kabir · Vincent Lin🇹🇼 · David Meekins🇺🇸 · Blaine Norum🇺🇸 · Brad Sawatzky🇺🇸

   [Background] The proton charge radius extracted from recent muonic hydrogen Lamb shift measurements is significantly smaller than that extracted from atomic hydrogen and electron scattering measurements. [Purpose] In an attempt to understand the discrepancy, we review high-precision electron scattering results from Mainz, Jefferson Lab, Saskatoon and Stanford. [Method] We make use of stepwise regression techniques using the $F$-test as well as the Akaike information criterion to systematically determine the predictive variables to use for a given set and range of electron scattering data as well as to provide multivariate error estimates. [Results] Starting with the precision, low four-momentum transfer ($Q^2$) data from Mainz (1980) and Saskatoon (1974), we find that a stepwise regression of the Maclaurin series using the $F$-test as well as the Akaike information criterion justify using a linear extrapolation which yields a value for the proton radius that is consistent with the result obtained from muonic hydrogen measurements. Applying the same Maclaurin series and statistical criteria to the 2014 Rosenbluth results on $G_E$ from Mainz, we again find that the stepwise regression tends to favor a radius consistent with the muonic hydrogen radius but produces results that are extremely sensitive to the range of data included in the fit. Making use of the high-$Q^2$ data on $G_E$ to select functions which extrapolate to high $Q^2$, we find that a Padé ($N=M=1$) statistical model works remarkably well, as does a dipole function with a 0.84 fm radius, $G_E(Q^2)=(1+Q^2/0.66{\mathrm{GeV}}^2{)}^{-2}$. [Conclusions] From this statistical analysis, we conclude that the electron scattering result and the muonic hydrogen result are consistent. It is the atomic hydrogen results that are the outliers.

   nucl-exmath-phmath.MPnucl-thPRC(2016)·94 citations
2. 02*

   Strangeness Photoproduction at the BGO-OD Experiment

   T. C. Jude🇩🇪 · S. Alef🇩🇪 · D. Bayadilov🇩🇪 · R. Beck🇩🇪 · M. Becker🇩🇪 · A. Bella🇩🇪 · P. Bielefeldt🇩🇪 · S. Boese🇩🇪 · A. Braghieri🇮🇹 · K. Brinkmann🇩🇪 · P. Cole🇺🇸 · F. Curciarello🇮🇹 and 52 other authors

   BGO-OD is a newly commissioned experiment to investigate the internal structure of the nucleon, using an energy tagged bremsstrahlung photon beam at the ELSA electron facility. The setup consists of a highly segmented BGO calorimeter surrounding the target, with a particle tracking magnetic spectrometer at forward angles. BGO-OD is ideal for investigating meson photoproduction. The extensive physics programme for open strangeness photoproduction is introduced, and preliminary analysis presented.

   nucl-exJPS Conf.Proc.(2016)·4 citations
3. 03*

   Mass Measurements Demonstrate a Strong N =28 Shell Gap in Argon

   Z. Meisel🇺🇸 · S. George🇩🇪 · S. Ahn🇺🇸 · J. Browne🇺🇸 · D. Bazin🇺🇸 · B. A. Brown🇺🇸 · J. F. Carpino🇺🇸 · H. Chung🇺🇸 · R. H. Cyburt🇺🇸 · A. Estradé🇬🇧 · M. Famiano🇺🇸 · A. Gade🇺🇸 and 19 other authors

   We present results from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. We report the first mass measurements of 48Ar and 49Ar and find atomic mass excesses of -22.28(31) MeV and -17.8(1.1) MeV, respectively. These masses provide strong evidence for the closed shell nature of neutron number N=28 in argon, which is therefore the lowest even-Z element exhibiting the N=28 closed shell. The resulting trend in binding-energy differences, which probes the strength of the N=28 shell, compares favorably with shellmodel calculations in the sd-pf shell using SDPF-U and SDPF-MU Hamiltonians.

   nucl-exPRL(2015)·40 citations
4. 04*

   Mass measurement of 56Sc reveals a small A=56 odd-even mass staggering, implying a cooler accreted neutron star crust

   Z. Meisel🇺🇸 · S. George🇩🇪 · S. Ahn🇺🇸 · D. Bazin🇺🇸 · B.A. Brown🇺🇸 · J. Browne🇺🇸 · J.F. Carpino🇺🇸 · H. Chung🇺🇸 · A.L. Cole🇺🇸 · R.H. Cyburt🇺🇸 · A. Estradé🇬🇧 · M. Famiano🇺🇸 and 20 other authors

   We present the mass excesses of 52-57Sc, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The masses of 56Sc and 57Sc were determined for the first time with atomic mass excesses of -24.85(59)(+0 -54) MeV and -21.0(1.3) MeV, respectively, where the asymmetric uncertainty for 56Sc was included due to possible contamination from a long-lived isomer. The 56Sc mass indicates a small odd-even mass staggering in the A = 56 mass-chain towards the neutron drip line, significantly deviating from trends predicted by the global FRDM mass model and favoring trends predicted by the UNEDF0 and UNEDF1 density functional calculations. Together with new shell-model calculations of the electron-capture strength function of 56Sc, our results strongly reduce uncertainties in model calculations of the heating and cooling at the 56Ti electron-capture layer in the outer crust of accreting neutron stars. We found that, in contrast to previous studies, neither strong neutrino cooling nor strong heating occurs in this layer. We conclude that Urca cooling in the outer crusts of accreting neutron stars that exhibit superbursts or high temperature steady-state burning, which are predicted to be rich in A=56 nuclei, is considerably weaker than predicted. Urca cooling must instead be dominated by electron capture on the small amounts of adjacent odd-A nuclei contained in the superburst and high temperature steady-state burning ashes. This may explain the absence of strong crust Urca cooling inferred from the observed cooling light curve of the transiently accreting x-ray source MAXI J0556-332.

   nucl-exnucl-thPRL(2015)·31 citations
5. 05*

   Soft photon yield in nuclear interactions

   E. Kokoulina🇷🇺

   First results of study of a soft photon yield at Nuclotron (LHEP, JINR) in nucleus-nucleus collisions at 3.5 GeV per nucleon are presented. These photons are registered by an BGO electromagnetic calorimeter built by SVD-2 Collaboration. The obtained spectra confirm the excessive yield in the energy region less than 50 MeV in comparison with theoretical estimations and agree with previous experiments at high-energy interactions.

   nucl-exphysics.ins-detEPJ Web Conf.(2016)·1 citation
6. 06*

   Accessing the Elastic Form-Factors of the $\Delta (1232)$ Using the Beam-Normal Asymmetry

   Mark Macrae Dalton🇺🇸

   The beam-normal single-spin asymmetry, $B_n$, exists in the scattering of high energy electrons, polarized transverse to their direction of motion, from nuclear targets. To first order, this asymmetry is caused by the interference of the one-photon exchange amplitude with the imaginary part of the two-photon exchange amplitude. Measurements of $B_n$, for the production of a $\Delta (1232)$ resonance from a proton target, will soon become available from the Qweak experiment at Jefferson Lab and the A4 experiment at Mainz. The imaginary part of two-photon exchange allows only intermediate states that are on-shell, including the $\Delta$ itself. Therefore such data is sensitive to $\gamma \Delta \Delta$, the elastic form-factors of the $\Delta$. This article will introduce the form-factors of the $\Delta$, discuss what might be learned about the elastic form-factors from these new data, describe ongoing efforts in calculation and measurement, and outline the possibility of future measurements.

   nucl-ex1 citation
7. 07*

   Strangeness Photoproduction on Quasifree Neutrons

   Dominik Werthmüller🇬🇧

   Strangeness photoproduction in the elementary reactions $\gamma N\to KY$ offers the possibility to study nucleon resonances in the mass region above 1.7 GeV, where the number of states and their properties are still under debate. These reactions could allow the first 'complete' experiment in pseudoscalar meson photoproduction due to the easier access to recoil polarization observables in experiments. In addition to measurements on proton targets, a full isospin decomposition of the $I=1/2$ electromagnetic amplitudes requires also data obtained from quasifree neutron targets. This contribution shows first preliminary results on feasibility studies for such measurements at the A2 experiment at MAMI.

   nucl-exhep-exnucl-thJPS Conf.Proc.(2016)·3 citations
8. 08*

   Initial conditions from the shadowed Glauber model

   Sandeep Chatterjee🇮🇳 · Sushant K. Singh🇮🇳 · Snigdha Ghosh🇮🇳 · Md Hasanujjaman🇮🇳 · Jane Alam🇮🇳 · Sourav Sarkar🇮🇳

   The two component Monte-Carlo Glauber model predicts a knee-like structure in the centrality dependence of elliptic flow $v_2$ in Uranium+Uranium collisions at $\sqrt{s_{NN}}=193$ GeV. It also produces a strong anti-correlation between $v_2$ and $d{N}_{ch}/dy$ in the case of top ZDC events. However, none of these features have been observed in data. We address these discrepancies by including the effect of nucleon shadowing to the two component Monte-Carlo Glauber model. Apart from addressing successfully the above issues, we find that the nucleon shadow suppresses the event by event fluctuation of various quantities, e.g. ${\epsilon }_2$ which is in accordance with expectation from the dynamical models of initial condition based on gluon saturation physics.

   ↳ nucl-thhep-phnucl-exPLB(2016)·26 citations
9. 09*

   Theoretical study of the elastic breakup of weakly bound nuclei at near barrier energies

   D. R. Otomar🇧🇷 · P. R. S. Gomes🇧🇷 · J. Lubian🇧🇷 · L. F. Canto🇧🇷 · M. S. Hussein🇧🇷

   We have performed CDCC calculations for collisions of ${}^7$Li projectiles on ${}^{59}$Co, ${}^{144}$Sm and ${}^{208}$Pb targets at near-barrier energies, to assess the importance of the Coulomb and the nuclear couplings in the breakup of ${}^7$Li, as well as the Coulomb-nuclear interference. We have also investigated scaling laws, expressing the dependence of the cross sections on the charge and the mass of the target. This work is complementary to the one previously reported by us on the breakup of ${}^6$Li. Here we explore the similarities and differences between the results for the two Lithium isotopes. The relevance of the Coulomb dipole strength at low energy for the two-cluster projectile is investigated in details.

   ↳ nucl-thnucl-exPRC(2015)·9 citations
10. 10*

    Diffractive $\rho$ production at small $x$ in future Electron - Ion Colliders

    V. P. Goncalves🇧🇷 · F. S. Navarra🇧🇷 · D. Spiering🇧🇷

    The future Electron - Ion ($eA$) Collider is expected to probe the high energy regime of the QCD dynamics, with the exclusive vector meson production cross section being one of the most promising observables. In this paper we complement previous studies of exclusive processes presenting a comprehensive analysis of diffractive $\rho$ production at small $x$. We compute the coherent and incoherent cross sections taking into account non-linear QCD dynamical effects and considering different models for the dipole - proton scattering amplitude and for the vector meson wave function. The dependence of these cross sections with the energy, photon virtuality, nuclear mass number and squared momentum transfer is analysed in detail. Moreover, we compare the non-linear predictions with those obtained in the linear regime. Finally, we also estimate the exclusive photon, $J/\Psi$ and $\varphi$ production and compare with the results obtained for $\rho$ production. Our results demonstrate that the analysis of diffractive $\rho$ production in future electron - ion colliders will be important to understand the non-linear QCD dynamics.

    ↳ hep-phhep-exnucl-exnucl-thJ.Phys.G(2016)·13 citations
11. 11*

    Overview of new results from ATLAS heavy ion physics program

    Martin Spousta🇨🇿

    In this short paper we provide an overview of new results from the ATLAS physics program at the LHC as of spring 2015. We separately summarize the results from p+Pb collisions and Pb+Pb collisions along with some of their interpretations.

    ↳ hep-exnucl-exNucl.Part.Phys.Proc.(2016)·1 citation

* 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.