Tue·Nov 28, 2017Tuesday·November 28, 2017

1. 01*

   Measurement of polarization-transfer to bound protons in carbon and its virtuality dependence

   A1 Collaboration: D. Izraeli (1)🇮🇱 · T. Brecelj (2)🇸🇮 · P. Achenbach (3)🇩🇪 · A. Ashkenazi (1)🇮🇱 · R. Böhm (3)🇩🇪 · E. O. Cohen (1)🇮🇱 · M. O. Distler (3)🇩🇪 · A. Esser (3)🇩🇪 · R. Gilman (4)🇺🇸 · T. Kolar (2)🇸🇮 · I. Korover (1 and 5)🇮🇱 · J. Lichtenstadt (1)🇮🇱 and 16 other authors

   We measured the ratio $P_x/P_z$ of the transverse to longitudinal components of polarization transferred from electrons to bound protons in ${}^{12}\mathrm{C}$ by the ${}^{12}\mathrm{C}(\vec{e},e^{\prime }\vec{p})$ process at the Mainz Microtron (MAMI). We observed consistent deviations from unity of this ratio normalized to the free-proton ratio, $(P_x/P_z{)}_{{}^{12}\mathrm{C}}/(P_x/P_z{)}_{{}^1\mathrm{H}}$, for both $s$- and $p$-shell knocked out protons, even though they are embedded in averaged local densities that differ by about a factor of two. The dependence of the double ratio on proton virtuality is similar to the one for knocked out protons from ${}^2\mathrm{H}$ and ${}^4\mathrm{He}$, suggesting a universal behavior. It further implies no dependence on average local nuclear density.

   nucl-exPLB(2018)·20 citations
2. 02*

   Study of jet quenching with isolated-photon+jet correlations in PbPb and pp collisions at $\sqrt{s_{{}_{\mathrm{NN}}}}=$ 5.02 TeV

   CMS Collaboration

   Measurements of azimuthal angle and transverse momentum ($p_{\mathrm{T}}$) correlations of isolated photons and associated jets are reported for pp and PbPb collisions at $\sqrt{s_{{}_{\mathrm{NN}}}}=$ 5.02 TeV. The data were recorded with the CMS detector at the CERN LHC. For events containing a leading isolated photon with $p_{\mathrm{T}}^{\gamma }>$ 40 GeV$/c$ and an associated jet with $p_{\mathrm{T}}^{\text{jet}}>$ 30 GeV$/c$, the photon+jet azimuthal correlation and $p_{\mathrm{T}}$ imbalance in PbPb collisions are studied as functions of collision centrality and $p_{\mathrm{T}}^{\gamma }$. The results are compared to pp reference data collected at the same collision energy and to predictions from several theoretical models for parton energy loss. No evidence of broadening of the photon+jet azimuthal correlations is observed, while the ratio $p_{\mathrm{T}}^{\text{jet}}/p_{\mathrm{T}}^{\gamma }$ decreases significantly for PbPb data relative to the pp reference. All models considered agree within uncertainties with the data. The number of associated jets per photon with $p_{\mathrm{T}}^{\gamma }>$ 80 GeV$/c$ is observed to be shifted towards lower $p_{\mathrm{T}}^{\text{jet}}$ values in central PbPb collisions compared to pp collisions.

   nucl-exhep-exPLB(2018)·119 citations
3. 03*

   Polarization Observables using Positron Beams

   Axel Schmidt🇺🇸

   The discrepancy between polarized and unpolarized measurements of the proton's electromagnetic form factors is striking, and suggests that two-photon exchange (TPE) may be playing a larger role in elastic electron-proton scattering than is estimated in standard radiative corrections formulae. While TPE is difficult to calculate in a model-independent way, it can be determined experimentally from asymmetries between electron-proton and positron-proton scattering. The possibility of a polarized positron beam at Jefferson Lab would open the door to measurements of TPE using polarization observables. In these proceedings, I examine the feasibility of measuring three such observables with positron scattering. Polarization-transfer, specifically the $ϵ$-dependence for fixed $Q^2$, is an excellent test of TPE, and the ability to compare electrons and positrons would lead to a drastic reduction of systematics. However, such a measurement would be severely statistically limited. Normal single-spin asymmetries (SSAs) probe the imaginary part of the TPE amplitude and can be improved by simultaneous measurements with electron and positron beams. Beam-normal SSAs are too small to be measured with the proposed polarized positron beam, but target-normal SSAs could be feasibly measured with unpolarized positrons in the spectrometer halls. This technique should be included in the physics case for developing a positron source for Jefferson Lab.

   nucl-exAIP Conf.Proc.(2018)·1 citation
4. 04*

   Measurement of J/$\psi$ production as a function of multiplicity in pp and p-Pb collisions with ALICE

   Anisa Khatun (for the ALICE Collaboration)🇮🇳

   The increase of hard probe production as a function of the charged particle multiplicity in proton-proton and proton-lead collisions is considered to be an interesting observable for the study of multiple parton interactions. In the present work, the correlation between J/$\psi$ production and charged particle multiplicity has been reviewed in pp collisions at $\sqrt{s}=7$ and 13 TeV and p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV at mid- and forward rapidities. The J/$\psi$ measurement in pp collisions at $\sqrt{s}$ = 13 TeV using events triggered by the ALICE electromagnetic calorimeter at midrapidity is discussed in this report, too. An increment of the relative J/$\psi$ yields has been observed as a function of the multiplicity. The results have also been compared to theoretical model predictions.

   nucl-exEPJ Web Conf.(2018)·2 citations
5. 05*

   Measuring the lepton sign asymmetry in elastic electron-proton scattering with OLYMPUS

   Axel Schmidt🇺🇸

   OLYMPUS is a particle physics experiment that collected data in 2012 at DESY, in Hamburg, Germany, on the asymmetry between positron-proton and electron-proton elastic scattering cross sections. A non-zero asymmetry is evidence of hard two-photon exchange, which has been hypothesized to cause the discrepancy in measurements of the proton's electromagnetic form factors. Alternating electron and positron beams, accelerated to 2 GeV, were directed through a windowless, gaseous, hydrogen target, and the scattered lepton and recoiling proton were detected in coincidence using a large acceptance magnetic spectrometer. Determining the relative integrated luminosity between the electron and positron data sets was critical, and a new technique, involving multi-interaction events, was developed to achieve the desired sub-percent accuracy. A detailed Monte Carlo simulation was built in order to reproduce the convolution of systematic effects at every stage of the experiment. The first stage in the simulation was new radiative event generator, which permitted the full simulation of the non-trivial, radiative corrections to the measurement. The analysis of the data and simulation showed that the lepton sign asymmetry rises by several percent between a momentum transfer of 0.5 GeV${}^2/c^2$ and 2.25 GeV${}^2/c^2$. This rise as a function of increasing momentum transfer confirms that two photon exchange at least partially contributes to the proton form factor discrepancy.

   nucl-ex10 citations
6. 06*

   Femtoscopy of stopped protons

   Andrzej Bialas🇵🇱 · Adam Bzdak🇵🇱 · Volker Koch🇺🇸

   The longitudinal proton-proton femtoscopy (HBT) correlation function, based on the idea that in a heavy ion collision at $\sqrt{s}\lesssim 20$ GeV stopped protons are likely to be separated in configuration space, is evaluated. It shows a characteristic oscillation which appears sufficiently pronounced to be accessible in experiment. The proposed measurement is essential for estimating the baryon density in the central rapidity region, and can be also viewed as an (almost) direct verification of the Lorentz contraction of the fast-moving nucleus.

   ↳ hep-phhep-exnucl-exnucl-thPRC(2019)·1 citation
7. 07*

   Signatures of octupole correlations in neutron-rich odd-mass barium isotopes

   K. Nomura🇫🇷 · T. Nikšić🇭🇷 · D. Vretenar🇭🇷

   Octupole deformation and the relevant spectroscopic properties of neutron-rich odd-mass barium isotopes are investigated in a theoretical framework based on nuclear density functional theory and the particle-core coupling scheme. The interacting-boson Hamiltonian that describes the octupole-deformed even-even core nucleus, as well as the single-particle energies and occupation probabilities of an unpaired nucleon, are completely determined by microscopic axially-symmetric $({\beta }_2,{\beta }_3)$-deformation constrained self-consistent mean-field calculations for a specific choice of the energy density functional and pairing interaction. A boson-fermion interaction that involves both quadrupole and octupole degrees of freedom is introduced, and their strength parameters are determined to reproduce selected spectroscopic data for the odd-mass nuclei. The model reproduces recent experimental results both for the even-even and odd-mass Ba isotopes. In particular, for ${}^{145,147}$Ba our results indicate, in agreement with recent data, that octupole deformation does not determine the structure of the lowest states in the vicinity of the ground state, and only becomes relevant at higher excitation energies.

   ↳ nucl-thnucl-exPRC(2018)·36 citations
8. 08*

   New baryonic and mesonic observables from NA61/SHINE

   Antoni Marcinek (for the NA49 and NA61/SHINE collaborations)🇵🇱

   One of the main objectives of the NA61/SHINE experiment at the CERN SPS is to study properties of strongly interacting matter. This paper presents new results on observables relevant for this part of the NA61/SHINE programme. These include the first ever measurements of $\varphi$ meson production in p+p collisions at 40 and 80 GeV, and most detailed ever experimental data at 158 GeV. This contribution demonstrates the superior accuracy of the present dataset with respect to existing measurements. The comparison of p+p to Pb+Pb collisions shows a non-trivial system size dependence of the longitudinal evolution of hidden strangeness production, contrasting with that of other mesons. Furthermore, proton density fluctuations are investigated as a possible order parameter of the second order phase transition in the neighbourhood of the critical point (CP) of strongly interacting matter. An intermittency analysis is performed of the proton second scaled factorial moments in transverse momentum space. A previous analysis of this sort revealed significant power-law fluctuations for the "Si"+Si system at 158A GeV measured by the NA49 experiment. The fitted power-law exponent was consistent within errors with the theoretically expected critical value, a result suggesting a baryochemical potential in the vicinity of the CP of about 250 MeV. The analysis will now be extended to NA61/SHINE systems of similar size, Be+Be and Ar+Sc, at 150A GeV. Finally, spectator-induced electromagnetic (EM) effects on charged meson production are being studied and bring information on the space-time position of the pion formation zone, which appears to be much closer to the spectator system for faster pions than for slower ones. On that basis, we demonstrate that the longitudinal evolution of the system at CERN SPS energies may be interpreted as a pure consequence of local energy-momentum conservation.

   ↳ hep-exnucl-exEPJ Web Conf.(2018)·4 citations
9. 09*

   $\varphi$ meson in nuclear matter and nuclei

   J. J. Cobos-Martínez🇲🇽 · K.Tsushima🇧🇷 · G. Krein🇧🇷 · A. W. Thomas🇦🇺

   The mass and decay width of the $\varphi$ meson in cold nuclear matter are computed in an effective Lagrangian approach, with the medium dependence of these properties obtained by evaluating kaon-antikaon loop contributions to the $\varphi$ self-energy. At normal nuclear matter density, we find a downward shift of the $\varphi$ mass by a few percent, while the decay width is enhanced by an order of magnitude. We also present $\varphi$--nucleus bound state energies and absorption widths for some selected nuclei, using complex optical potentials obtained in the local density approximation. Our results suggest that the $\varphi$ should form bound states with all the nuclei considered. However, the identification of the signal for these predicted bound states will need careful investigation because of their sizable absorption widths.

   ↳ nucl-thhep-phnucl-exPoS(2018)·3 citations
10. 10*

    Vector boson tagged jets and jet substructure

    Ivan Vitev🇺🇸

    In these proceedings, we report on recent results related to vector boson-tagged jet production in heavy ion collisions and the related modification of jet substructure, such as jet shapes and jet momentum sharing distributions. $Z^0$-tagging and $\gamma$-tagging of jets provides new opportunities to study parton shower formation and propagation in the quark-gluon plasma and has been argued to provide tight constrains on the energy loss of reconstructed jets. We present theoretical predictions for isolated photon-tagged and electroweak boson-tagged jet production in Pb+Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV at the LHC, addressing the modification of their transverse momentum and transverse momentum imbalance distributions. Comparison to recent ATLAS and CMS experimental measurements is performed that can shed light on the medium-induced radiative corrections and energy dissipation due to collisional processes of predominantly quark-initiated jets. The modification of parton splitting functions in the QGP further implies that the substructure of jets in heavy ion collisions may differ significantly from the corresponding substructure in proton-proton collisions. Two such observables and the implication of tagging on their evaluation is also discussed.

    ↳ hep-phnucl-exnucl-thEPJ Web Conf.(2018)·1 citation
11. 11*

    FSQP nuclear matrix elements for two neutrino double beta decays

    Hiroyasu Ejiri🇯🇵

    Nuclear matrix elements (NMEs) for two neutrino double beta decays are discussed in terms of the Fermi Surface Quasi-Particle (FSQP) Model. The evaluated NMEs agree with the observed NMEs . The new NMEs for two neutrino double beta decays from Kr78, Cd106, Ba130, and Pd110 were evaluated by FSQP. The NMEs show shell configuration dependence. Impacts of the FSQP NMEs for two neutrino double beta decays on the NMEs for neutrino less double beta decays are discussed.

    ↳ nucl-thnucl-exJ.Phys.G(2017)·17 citations
12. 12*

    Lithium-loaded scintillators coupled to a custom-designed silicon photomultiplier array for neutron and gamma-ray detection

    Felix Liang · Hartmut Brands · Les Hoy · Jeff Preston · Jason Smith

    Scintillators capable of detecting both neutrons and gamma-rays have generated considerable interest. In particular, the use of such scintillators with silicon photomultipliers (SiPMs) enables low-power and compact-geometry applications. Three types of Li-loaded scintillators, CLYC, CLLB, and NaIL, have been tested with a custom-designed SiPM array for temperatures between --20 and 50${}^{\circ }$C. The array consists of four 6x6~mm${}^2$ SiPMs arranged in a 2x2 configuration. Pulse shape discrimination is used for neutron and gamma identification. Because the pulse shape changes with temperature, the quality of neutron and gamma discrimination varies with temperature. Furthermore, the larger dark current in SiPMs at high temperatures results in poorer energy resolution and neutron-gamma discrimination. Comparison of the energy resolution and the neutron-gamma discrimination for the three scintillators coupled to the custom SiPM array will be discussed.

    ↳ physics.ins-detnucl-exIEEE Trans.Nucl.Sci.(2018)·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.