Wed·Jul 15, 2015Wednesday·July 15, 2015

1. 01*

   Beam-Energy Dependence of Charge Balance Functions from Au+Au Collisions at RHIC

   STAR Collaboration

   Balance functions have been measured in terms of relative pseudorapidity ($\Delta \eta$) for charged particle pairs at the Relativistic Heavy-Ion Collider (RHIC) from Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 7.7 GeV to 200 GeV using the STAR detector. These results are compared with balance functions measured at the Large Hadron Collider (LHC) from Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV by the ALICE Collaboration. The width of the balance function decreases as the collisions become more central and as the beam energy is increased. In contrast, the widths of the balance functions calculated using shuffled events show little dependence on centrality or beam energy and are larger than the observed widths. Balance function widths calculated using events generated by UrQMD are wider than the measured widths in central collisions and show little centrality dependence. The measured widths of the balance functions in central collisions are consistent with the delayed hadronization of a deconfined quark gluon plasma (QGP). The narrowing of the balance function in central collisions at $\sqrt{s_{\mathrm{NN}}}$ = 7.7 GeV implies that a QGP is still being created at this relatively low energy.

   nucl-exhep-exnucl-thPRC(2016)·31 citations
2. 02*

   Splitting of ISGMR strength in the light-mass nucleus ${}^{24}$Mg due to ground-state deformation

   Y. K. Gupta🇺🇸 · U. Garg🇺🇸 · J. T. Matta🇺🇸 · D. Patel🇺🇸 · T. Peach🇺🇸 · J. Hoffman🇺🇸 · K. Yoshida🇯🇵 · M. Itoh🇯🇵 · M. Fujiwara🇯🇵 · K. Hara🇯🇵 · H. Hashimoto🇯🇵 · K. Nakanishi🇯🇵 and 10 other authors

   The isoscalar giant monopole resonance (ISGMR) strength distribution in ${}^{24}$Mg has been determined from background-free inelastic scattering of 386-MeV $\alpha$ particles at extreme forward angles, including 0${}^{\circ }$. The ISGMR strength distribution has been observed for the first time to have a two-peak structure in a light-mass nucleus. This splitting of ISGMR strength is explained well by microscopic theory in terms of the prolate deformation of the ground state of ${}^{24}$Mg.

   nucl-exnucl-thPLB(2015)·44 citations
3. 03*

   Collinear laser spectroscopy of atomic cadmium

   Nadja Frömmgen🇩🇪 · Dimiter L. Balabanski🇷🇴 · Mark L. Bissell🇧🇪 · Jacek Bieroń🇵🇱 · Klaus Blaum🇩🇪 · Bradley Cheal🇬🇧 · Kieran Flanagan🇬🇧 · Stephan Fritzsche🇩🇪 · Christopher Geppert🇩🇪 · Michael Hammen🇩🇪 · Magdalena Kowalska🇨🇭 · Kim Kreim🇩🇪 and 7 other authors

   Hyperfine structure $A$ and $B$ factors of the atomic $5s5p{}^3{\mathrm{P}}_2\to 5s6s{}^3{\mathrm{S}}_1$ transition are determined from collinear laser spectroscopy data of ${}^{107-123}$Cd and ${}^{111m-123m}$Cd. Nuclear magnetic moments and electric quadrupole moments are extracted using reference dipole moments and calculated electric field gradients, respectively. The hyperfine structure anomaly for isotopes with $s_{1/2}$ and $d_{5/2}$ nuclear ground states and isomeric $h_{11/2}$ states is evaluated and a linear relationship is observed for all nuclear states except $s_{1/2}$. This corresponds to the Moskowitz-Lombardi rule that was established in the mercury region of the nuclear chart but in the case of cadmium the slope is distinctively smaller than for mercury. In total four atomic and ionic levels were analyzed and all of them exhibit a similar behaviour. The electric field gradient for the atomic $5s5p{}^3{\mathrm{P}}_2$ level is derived from multi-configuration Dirac-Hartree-Fock calculations in order to evaluate the spectroscopic nuclear quadrupole moments. The results are consistent with those obtained in an ionic transition and based on a similar calculation.

   nucl-exphysics.atom-phEur.Phys.J.D(2015)·17 citations
4. 04*

   Strengths of the resonances at 436, 479, 639, 661, and 1279 keV in the ${}^{22}$Ne(p,$\gamma$)${}^{23}$Na reaction

   Rosanna Depalo · Francesca Cavanna🇮🇹 · Federico Ferraro🇮🇹 · Alessandra Slemer · Tariq Al-Abdullah · Shavkat Akhmadaliev🇩🇪 · Michael Anders🇩🇪 · Daniel Bemmerer🇩🇪 · Zoltán Elekes🇩🇪 · Giovanni Mattei · Stefan Reinicke🇩🇪 · Konrad Schmidt🇩🇪 · Carlo Scian · Louis Wagner🇩🇪

   The ${}^{22}$Ne(p,$\gamma$)${}^{23}$Na reaction is included in the neon-sodium cycle of hydrogen burning. A number of narrow resonances in the Gamow window dominates the thermonuclear reaction rate. Several resonance strengths are only poorly known. As a result, the ${}^{22}$Ne(p,$\gamma$)${}^{23}$Na thermonuclear reaction rate is the most uncertain rate of the cycle. Here, a new experimental study of the strengths of the resonances at 436, 479, 639, 661, and 1279 keV proton beam energy is reported. The data have been obtained using a tantalum target implanted with ${}^{22}$Ne. The strengths $\omega \gamma$ of the resonances at 436, 639, and 661 keV have been determined with a relative approach, using the 479 and 1279 keV resonances for normalization. Subsequently, the ratio of resonance strengths of the 479 and 1279 keV resonances was determined, improving the precision of these two standards. The new data are consistent with, but more precise than, the literature with the exception of the resonance at 661 keV, which is found to be less intense by one order of magnitude. In addition, improved branching ratios have been determined for the gamma decay of the resonances at 436, 479, and 639 keV.

   nucl-exPRC(2015)·40 citations
5. 05*

   Test for exotic isoscalar resonance dominating $D^0\to {\pi }^{+}{\pi }^{-}{\pi }^0$ decays

   Michael Gronau🇮🇱 · Jonathan L. Rosner🇺🇸

   The decay $D^0\to {\pi }^{+}{\pi }^{-}{\pi }^0$ appears to be dominated by $\rho \pi$ states in a configuration of zero total isotopic spin. The spin $J$, parity $P$, and charge-conjugation eigenvalue $C$ of this final state are therefore $J^{PC}=0^{--}$, which cannot be formed of a quark $q$ and antiquark $\bar{q}$. If a resonance near $M(D^0)$ dominates the final state, it must be a {\it hybrid} composed of a quark-antiquark pair and a constituent gluon, or a {\it tetraquark} $qq\bar{q}\bar{q}$. A test for this resonance in electroproduction is proposed.

   ↳ hep-phhep-exnucl-exPRD(2015)·3 citations
6. 06*

   Identifying exotic hidden-charm pentaquarks

   Rui Chen🇨🇳 · Xiang Liu🇨🇳 · Xue-Qian Li🇨🇳 · Shi-Lin Zhu🇨🇳

   The LHCb Collaboration at the Large Hadron Collider at CERN discovered two pentaquark states $P_c(4380)$ and $P_c(4450)$. These two hidden-charm states are interpreted as the loosely bound ${\Sigma }_c(2455)D^{\ast }$ and ${\Sigma }_c^{\ast }(2520)D^{\ast }$ molecular states in the boson exchange interaction model, which provides an explanation for why the experimental width of $P_c(4450)$ is much narrower than that of $P_c(4380)$. The discovery of the new resonances $P_c(4380)$ and $P_c(4450)$, indeed, opens a new page for hadron physics. The partners of $P_c(4380)$ and $P_c(4450)$ should be pursued in future experiments.

   ↳ hep-phhep-exhep-latnucl-ex+1PRL(2015)·341 citations
7. 07*

   Parton Distribution Functions properties of the statistical model

   Claude Bourrely🇫🇷

   We show that the parton distribution functions (PDF) described by the statistical model have very interesting physical properties which help to understand the structure of partons. The role of the quark helicity components is emphasized as they represent the building blocks of the PDF. In the model the sign of the polarized quarks PDF comes out in a quite natural way once the thermodynamical potentials with a given helicity are known. Introducing the concept of entropy we study the states madeof |2u + d >, |u +d +s > and $|2\bar{u}+\bar{d}>$, for a fixed Q^2, the variation with x shows that the first state has a dominant entropy due to the effect of u quark. We prove that the PDF parameters obtained from experiments give in fact an optimal solution of an entropy equation subject to constraints. We develop a new approach of the polarized gluon density based on a neural model which explains its property, in particular, a large positivity value and an agreement with the positvity constraint. An extension of this neural approach is applied to quarks giving a coherent description of the partons structure.

   ↳ hep-phhep-exnucl-ex9 citations
8. 08*

   Moments of $\varphi$ meson spectral functions in vacuum and nuclear matter

   Philipp Gubler🇮🇹 · Wolfram Weise🇩🇪

   Moments of the $\varphi$ meson spectral function in vacuum and in nuclear matter are analyzed, combining a model based on chiral SU(3) effective field theory (with kaonic degrees of freedom) and finite-energy QCD sum rules. For the vacuum we show that the spectral density is strongly constrained by a recent accurate measurement of the $e^{+}{e}^{-}\to K^{+}{K}^{-}$ cross section. In nuclear matter the $\varphi$ spectrum is modified by interactions of the decay kaons with the surrounding nuclear medium, leading to a significant broadening and an asymmetric deformation of the $\varphi$ meson peak. We demonstrate that both in vacuum and nuclear matter, the first two moments of the spectral function are compatible with finite-energy QCD sum rules. A brief discussion of the next-higher spectral moment involving strange four-quark condensates is also presented.

   ↳ hep-phhep-exnucl-exnucl-thPLB(2015)·51 citations
9. 09*

   An Electron-Tracking Compton Telescope for a Survey of the Deep Universe by MeV gamma-rays

   T. Tanimori🇯🇵 · H. Kubo🇯🇵 · A. Takada🇯🇵 · S. Iwaki🇯🇵 · S. Komura🇯🇵 · S. Kurosawa🇯🇵 · Y. Matsuoka🇯🇵 · K. Miuchi🇯🇵 · S. Miyamoto🇯🇵 · T. Mizumoto🇯🇵 · Y. Mizumura🇯🇵 · K. Nakamura🇯🇵 and 8 other authors

   Photon imaging for MeV gammas has serious difficulties due to huge backgrounds and unclearness in images, which are originated from incompleteness in determining the physical parameters of Compton scattering in detection, e.g., lack of the directional information of the recoil electrons. The recent major mission/instrument in the MeV band, Compton Gamma Ray Observatory/COMPTEL, which was Compton Camera (CC), detected mere $\sim 30$ persistent sources. It is in stark contrast with $\sim$2000 sources in the GeV band. Here we report the performance of an Electron-Tracking Compton Camera (ETCC), and prove that it has a good potential to break through this stagnation in MeV gamma-ray astronomy. The ETCC provides all the parameters of Compton-scattering by measuring 3-D recoil electron tracks; then the Scatter Plane Deviation (SPD) lost in CCs is recovered. The energy loss rate (dE/dx), which CCs cannot measure, is also obtained, and is found to be indeed helpful to reduce the background under conditions similar to space. Accordingly the significance in gamma detection is improved severalfold. On the other hand, SPD is essential to determine the point-spread function (PSF) quantitatively. The SPD resolution is improved close to the theoretical limit for multiple scattering of recoil electrons. With such a well-determined PSF, we demonstrate for the first time that it is possible to provide reliable sensitivity in Compton imaging without utilizing an optimization algorithm. As such, this study highlights the fundamental weak-points of CCs. In contrast we demonstrate the possibility of ETCC reaching the sensitivity below $1\times 10^{-12}$ erg cm${}^{-2}$ s${}^{-1}$ at 1 MeV.

   ↳ astro-ph.IMastro-ph.COastro-ph.HEhep-ex+1ApJ(2015)·41 citations
10. 10*

    A search for baryon- and lepton-number violating decays of $\Lambda$ hyperons using the CLAS detector at Jefferson Laboratory

    M.E. McCracken🇺🇸 · M. Bellis🇺🇸 · K.P. Adhikari🇺🇸 · D. Adikaram🇺🇸 · Z. Akbar🇺🇸 · S. Anefalos Pereira🇮🇹 · R.A. Badui🇺🇸 · J. Ball🇫🇷 · N.A. Baltzell🇺🇸 · M. Battaglieri🇮🇹 · V. Batourine🇺🇸 · I. Bedlinskiy🇷🇺 and 119 other authors

    We present a search for ten baryon-number violating decay modes of $\Lambda$ hyperons using the CLAS detector at Jefferson Laboratory. Nine of these decay modes result in a single meson and single lepton in the final state ($\Lambda \to m\ell$) and conserve either the sum or the difference of baryon and lepton number ($B\pm L$). The tenth decay mode ($\Lambda \to \bar{p}{\pi }^{+}$) represents a difference in baryon number of two units and no difference in lepton number. We observe no significant signal and set upper limits on the branching fractions of these reactions in the range $(4-200)\times 10^{-7}$ at the $90\%$ confidence level.

    ↳ hep-exnucl-exPRD(2015)·31 citations
11. 11*

    Collision Geometry and Flow in Uranium+Uranium Collisions

    Andy Goldschmidt🇺🇸 · Zhi Qiu🇺🇸 · Chun Shen🇨🇦 · Ulrich Heinz🇺🇸

    Using event-by-event viscous fluid dynamics to evolve fluctuating initial density profiles from the Monte-Carlo Glauber model for U+U collisions, we report a "knee"-like structure in the elliptic flow as a function of collision centrality, located around the 0.5% most central collisions as measured by the final charged multiplicity. This knee is due to the preferential selection of tip-on-tip collision geometries by a high-multiplicity trigger. Such a knee structure is not seen in the STAR data. This rules out the two-component MC-Glauber model for initial energy and entropy production. Hence an enrichment of tip-tip configurations by triggering solely on high-multiplicity in the U+U collisions does not work. On the other hand, by using the Zero Degree Calorimeters (ZDCs) coupled with event-shape engineering such a selection is possible. We identify the selection purity of body-body and tip-tip events in full-overlap U+U collisions. By additionally constraining the asymmetry of the ZDC signals we can further increase the probability of selecting tip-tip events in U+U collisions.

    ↳ nucl-thnucl-exPRC(2015)·53 citations
12. 12*

    Bottomonia suppression in 2.76 TeV Pb-Pb collisions

    Brandon Krouppa🇺🇸 · Radoslaw Ryblewski🇵🇱 · Michael Strickland🇺🇸

    We compute the QGP suppression of Upsilon(1s), Upsilon(2s), Upsilon(3s), chi_b1, and chi_b2 states in sqrt(s_NN)=2.76 TeV Pb-Pb collisions. Using the suppression of each of these states, we estimate the inclusive R_AA for the Upsilon(1s) and Upsilon(2s) states as a function of N_part, y, and p_T including the effect of excited state feed down. We find that our model provides a reasonable description of preliminary CMS results for the N_part-, y-, and p_T-dependence of R_AA for both the Upsilon(1s) and Upsilon(2s). Comparing to our previous model predictions, we find a flatter rapidity dependence, thereby reducing some of the tension between our model and ALICE forward-rapidity results for Upsilon(1s) suppression.

    ↳ hep-phnucl-exnucl-thPRC(2015)·98 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.