Fri·Dec 4, 2015Friday·December 4, 2015

1. 01*

   Interplay of fission modes in mass distribution of light actinide nuclei 225,227Pa

   R.Dubey · P.Sugathan🇧🇪 · A.Jhingan · Gurpreet Kaur🇮🇳 · Ish Mukul🇮🇱 · G.Mohanto · D.Siwal · N.Saneesh · T.Banerjee · Meenu Thakur · Ruchi Mahajan · N.Kumar🇺🇸 · M.B. Chatterjee

   Fission-fragment mass distributions were measured for 225,227Pa nuclei formed in fusion reactions of 19F + 206, 208Pb around fusion barrier energies. Mass-angle correlations do not indicate any quasi-fission like events in this bombarding energy range. Mass distributions were fitted by Gaussian distribution and mass variance extracted. At below-barrier energies, the mass variance was found to increase with decrease in energy for both nuclei. Results from present work were compared with existing data for induced fission of 224, 226Th and 228U around barrier energies. Enhancement in mass variance of 225, 227Pa nuclei at below-barrier energies shows evidence for presence of asymmetric fission events mixed with symmetric fission events. This is in agreement with the results of mass distributions of nearby nuclei 224, 226Th and 228U where two-mode fission process was observed. Two-mode feature of fission arises due to the shell effects changing the landscape of the potential energy surfaces at low excitation energies. The excitation-energy dependence of the mass variance gives strong evidence for survival of microscopic shell effects in fission of light actinide nuclei 225, 227Pa with initial excitation energy ~30 - 50 MeV.

   nucl-exnucl-thPLB(2016)·16 citations
2. 02*

   Charm production in Pb+Pb collisions at the Large Hadron Collider energy

   Taesoo Song🇩🇪 · Hamza Berrehrah🇩🇪 · Daniel Cabrera🇩🇪 · Wolfgang Cassing🇩🇪 · Elena Bratkovskaya🇩🇪

   We study charm production in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=$2.76 TeV in the Parton-Hadron-String-Dynamics transport approach and the charm dynamics in the partonic and hadronic medium. The charm quarks are produced through initial binary nucleon-nucleon collisions by using the PYTHIA event generator taking into account the (anti-)shadowing incorporated in the EPS09 package. The produced charm quarks interact with off-shell massive partons in the quark-gluon plasma and are hadronized into $D$ mesons through coalescence or fragmentation close to the critical energy density, and then interact with hadrons in the final hadronic stage with scattering cross sections calculated in an effective Lagrangian approach with heavy-quark spin symmetry. The PHSD results show a reasonable $R_{\mathrm{AA}}$ and elliptic flow of $D$ mesons in comparison to the experimental data for Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV from the ALICE Collaboration. We also study the effect of temperature-dependent off-shell charm quarks in relativistic heavy-ion collisions. We find that the scattering cross sections are only moderately affected by off-shell charm degrees of freedom. However, the position of the peak of $R_{\mathrm{AA}}$ for $D$ mesons depends on the strength of the scalar partonic forces which also have an impact on the $D$ meson elliptic flow. The comparison with experimental data on the $R_{\mathrm{AA}}$ suggests that the repulsive force is weaker for off-shell charm quarks as compared to that for light quarks. Furthermore, the effects from radiative charm energy loss appear to be low compared to the collisional energy loss up to transverse momenta of $\sim$ 15 GeV/c.

   ↳ nucl-thnucl-exPRC(2016)·189 citations
3. 03*

   Systematic study of complete fusion suppression in reactions involving weakly bound nuclei at energies above the Coulomb barrier

   Bing Wang🇨🇳 · Wei-Juan Zhao🇨🇳 · Alexis Diaz-Torres🇮🇹 · En-Guang Zhao🇨🇳 · Shan-Gui Zhou🇨🇳

   Complete fusion excitation functions of reactions involving breakup are studied by using the empirical coupled-channel (ECC) model with breakup effects considered. An exponential function with two parameters is adopted to describe the prompt-breakup probability in the ECC model. These two parameters are fixed by fitting the measured prompt-breakup probability or the complete fusion cross sections. The suppression of complete fusion at energies above the Coulomb barrier is studied by comparing the data with the predictions from the ECC model without the breakup channel considered. The results show that the suppression of complete fusion are roughly independent of the target for the reactions involving the same projectile.

   ↳ nucl-thnucl-exPRC(2016)·30 citations
4. 04*

   Pion-induced production of the $Z_c(3900)$ off a nuclear target

   Yin Huang🇨🇳 · Jun He🇨🇳 · Xiang Liu🇨🇳 · Hong Fei Zhang🇨🇳 · Ju Jun Xie🇨🇳 · Xu Rong Chen🇨🇳

   We investigate the possibility to study the charmoniumlike state $Z_c(3900)$ through the pion-induced production off a nuclear target. By using a high-energy pion beam, the $Z_c(3900)$ can be produced off a proton or nucleus though the Primakoff effect. The production amplitude is calculated in an effective Lagrangian approach combined with the vector dominance model. The total cross sections of the $p({\pi }^{-},Z_c^{-}(3900))$ and $p({\pi }^{-},Z_c^{-}(3900)\to J/\psi {\pi }^{-})$ reactions are calculated, and their order of magnitude is about 0.1 and 0.01nb, respectively, with an assumption of branch ratio 10\% for the $Z_c(3900)$ decay in $J/\psi \pi$ channel. If the proton target is replaced by a nuclear target, the production of the $Z_c(3900)$ enhances obviously. The predicted total cross sections for the $A({\pi }^{-},Z_c^{-}(3900))$ and $A({\pi }^{-},Z_c^{-}(3900)\to J/\psi {\pi }^{-})$ reactions with $A{=}^{12}$C or ${}^{208}$Pb are on the order of magnitude of 100 and 10 nb, respectively, which is about one thousand times larger than the cross sections off a proton target. Based on these the results, we suggest the experimental study of the $Z_c(3900)$ by using high-energy pion beams with a nuclear target at facilities such as COMPASS and J-PARC.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2016)·8 citations
5. 05*

   Ab-initio calculations of charge symmetry breaking in the A=4 hypernuclei

   Daniel Gazda🇸🇪 · Avraham Gal🇮🇱

   We report on ab-initio NCSM calculations of the A=4 mirror Lambda hypernuclei Lambda-4H and Lambda-4He, using the Bonn-Juelich LO chiral EFT YN potentials plus a CSB Lambda0--Sigma0 mixing vertex. In addition to reproducing rather well the 0+ (g.s.) and 1+ (exc.) binding energies, these four-body calculations demonstrate for the first time that the observed CSB splitting of mirror levels, reaching hundreds of keV for 0+ (g.s.), can be reproduced using realistic theoretical interaction models, although with a non-negligible momentum cutoff dependence. Our results are discussed in relation to recent measurements of the Lambda-4H (0+ g.s.) binding energy [MAMI A1 Collaboration, Phys. Rev. Lett. 114, 232501 (2015)] and the Lambda-4He (1+ exc.) excitation energy [J-PARC E13 Collaboration, Phys. Rev. Lett. 115, 222501 (2015)].

   ↳ nucl-thhep-phnucl-exPRL(2016)·72 citations
6. 06*

   Performance of Several Solid State Photomultipliers with CLYC Scintillator

   Katherine E. Mesick🇺🇸 · Laura C. Stonehill · Jonathan T. Morrell · Daniel D.S. Coupland

   $C{s}_{2}LiYC{l}_6:C{e}^{3+}$ (CLYC) is an inorganic scintillator that has recently garnered attention for its ability to detect and discriminate between gammas and thermal neutrons. We investigate several important performance parameters of three different solid state photomultipliers (SSPMs) when reading out CLYC crystals: linearity, energy resolution, and pulse shape and discrimination ability. These performance parameters are assessed at a variety of temperatures between -20${}^{\circ }$C and +50${}^{\circ }$C.

   ↳ physics.ins-detnucl-ex2 citations
7. 07*

   Axial form factors of the octet baryons in a covariant quark model

   G. Ramalho🇧🇷 · K. Tsushima🇧🇷

   We study the weak interaction axial form factors of the octet baryons, within the covariant spectator quark model, focusing on the dependence of four-momentum transfer squared, Q^2. In our model the axial form factors G_A(Q^2) (axial-vector form factor) and G_P(Q^2) (induced pseudoscalar form factor), are calculated based on the constituent quark axial form factors and the octet baryon wave functions. The quark axial current is parametrized by the two constituent quark form factors, the axial-vector form factor g_A^q(Q^2), and the induced pseudoscalar form factor g_P^q(Q^2). The baryon wave functions are composed of a dominant S-state and a P-state mixture for the relative angular momentum of the quarks. First, we study in detail the nucleon case. We assume that the quark axial-vector form factor g_A^q(Q^2) has the same function form as that of the quark electromagnetic isovector form factor. The remaining parameters of the model, the P-state mixture and the Q^2-dependence of g_P^q(Q^2), are determined by a fit to the nucleon axial form factor data obtained by lattice QCD simulations with large pion masses. In this lattice QCD regime the meson cloud effects are small, and the physics associated with the valence quarks can be better calibrated. Once the valence quark model is calibrated, we extend the model to the physical regime, and use the low Q^2 experimental data to estimate the meson cloud contributions for G_A(Q^2) and G_P(Q^2). Using the calibrated quark axial form factors, and the generalization of the nucleon wave function for the other octet baryon members, we make predictions for all the possible weak interaction axial form factors G_A(Q^2) and G_P(Q^2) of the octet baryons. The results are compared with the corresponding experimental data for G_A(0), and with the estimates of baryon-meson models based on SU(6) symmetry.

   ↳ hep-phhep-exhep-latnucl-ex+1PRD(2016)·32 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.