Nuclear Experiment·nucl-ex

Tue·Mar 28, 2017Tuesday·March 28, 2017

9 papers—2 primary·7 cross-listed·reconstructed*

01*
Analysis of the exclusive final state npe $^{+}$ e $^{-}$ in quasi-free np reaction
J. Adamczewski-Musch (4)🇩🇪 · O. Arnold (9 and 10)🇩🇪 · E. T. Atomssa (15)🇫🇷 · C. Behnke (8)🇩🇪 · A. Belounnas (15)🇫🇷 · A. Belyaev (7)🇷🇺 · J. C. Berger-Chen (9 and 10)🇩🇪 · J. Biernat (3)🇵🇱 · A. Blanco (2)🇵🇹 · C. Blume (8)🇩🇪 · M. Böhmer (10)🇩🇪 · P. Bordalo (2)🇵🇹 and 105 other authors
We report on the investigation of dielectron production in tagged quasi-free neutron-proton collisions by using a deuteron beam of kinetic energy 1.25 GeV/u inpinging on a liquid hydrogen target. Our measurements with HADES confirm a significant excess of $e^{+} e^{-}$ pairs above the $π^{0}$ mass in the exclusive channel $d p \to n p e^{+} e^{-} (p_{s p ec t})$ as compared to the exclusive channel $pp e^{+} e^{-}$ measured in proton-proton collisions at the same energy. That excess points to different bremsstrahlung production mechanisms. Two models were evaluated for the role of the charged pion exchange between nucleons and double- $Δ$ excitation combined with intermediate $ρ$ -meson production. Differential cross sections as a function of the $e^{+} e^{-}$ invariant mass and of the angles of the virtual photon, proton and electrons provide valuable constraints and encourage further investigations on both experimental and theoretical side.
nucl-exEPJA(2017)·18 citations
02*
Cumulants of event-by-event net-strangeness distributions in Au+Au collisions at $s_{NN}$ =7.7-200 GeV from UrQMD model
Chang Zhou🇨🇳 · Ji Xu🇨🇳 · Xiaofeng Luo🇨🇳 · Feng Liu🇨🇳
Fluctuations of conserved quantities, such as baryon, electric charge and strangeness number, are sensitive observables in heavy-ion collisions to search for the QCD phase transition and critical point. In this paper, we performed a systematical analysis on the various cumulants and cumulant ratios of event-by-event net-strangeness distributions in Au+Au collisions at $s_{N N}$ =7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV from UrQMD model. We performed a systematical study on the contributions from various strange baryons and mesons to the net-strangeness fluctuations. The results demonstrate that the cumulants and cumulant ratios of net-strangeness distributions extracted from different strange particles show very different centrality and energy dependence behavior. By comparing with the net-kaon fluctuations, we found that the strange baryons play an important role in the fluctuations of net-strangeness. This study can provide useful baselines to study the QCD phase transition and search for the QCD critical point by using the fluctuations of net-strangeness in heavy-ion collisions experiment. It can help us to understand non-critical physics contributions to the fluctuations of net-strangeness.
nucl-exhep-exhep-phnucl-thPRC(2017)·28 citations
03*
Heavy-flavour measurements in p-Pb collisions with ALICE at the LHC
Jitendra Kumar (for the ALICE collaboration)🇮🇳
The measurements of open heavy-flavours, i.e. D mesons at central rapidity and leptons from charm and beauty decays at central and forward rapidity was studied in p-Pb collisions at $s_{NN}$ = 5.02 TeV using the ALICE detector. The results are presented and compared to model predictions including cold nuclear matter effects.
↳ hep-exnucl-exSpringer Proc.Phys.(2018)·0 citations
04*
Effects of Neutron-Proton Short-Range Correlation on the Equation of State of Dense Neutron-Rich Nucleonic Matter
Bao-Jun Cai🇺🇸 · Bao-An Li🇺🇸 · Lie-Wen Chen🇨🇳
The strongly isospin-dependent tensor force leads to short-range correlations (SRC) between neutron-proton (deuteron-like) pairs much stronger than those between proton-proton and neutron-neutron pairs. As a result of the short-range correlations, the single-nucleon momentum distribution develops a high-momentum tail above the Fermi surface. Because of the strongly isospin-dependent short-range correlations, in neutron-rich matter a higher fraction of protons will be depleted from its Fermi sea and populate above the Fermi surface compared to neutrons. This isospin-dependent nucleon momentum distribution may have effects on: (1) nucleon spectroscopic factors of rare isotopes, (2) the equation of state especially the density dependence of nuclear symmetry energy, (3) the coexistence of a proton-skin in momentum space and a neutron-skin in coordinate space (i.e., protons move much faster than neutrons near the surface of heavy nuclei). In this talk, we discuss these features and their possible experimental manifestations. As an example, SRC effects on the nuclear symmetry energy are discussed in detail using a modified Gogny-Hartree-Fock (GHF) energy density functional (EDF) encapsulating the SRC-induced high momentum tail (HMT) in the single-nucleon momentum distribution.
↳ nucl-thastro-ph.HEnucl-exAIP Conf.Proc.(2018)·6 citations
05*
Nucleon scalar and tensor charges using lattice QCD simulations at the physical value of the pion mass
C. Alexandrou (1, 2)🇨🇾 · M. Constantinou (3)🇺🇸 · P. Dimopoulos (4)🇮🇹 · R. Frezzotti (Rome Tor Vergata)🇮🇹 · K. Hadjiyiannakou (2)🇨🇾 · K. Jansen (5)🇩🇪 · C. Kallidonis (2)🇨🇾 · B. Kostrzewa (6)🇩🇪 · G. Koutsou (2)🇨🇾 · M. Mangin-Brinet (7)🇫🇷 · A. Vaquero Avilès-Casco (8)🇺🇸 · U. Wenger (9) ((1) Univ. of Cyprus, (2) The Cyprus Inst., (3) Temple Univ., (4) Centro Fermi & Rome Tor Vergata, (5) DESY-Zeuthen, (6) Bonn Univ., (7) Grenoble, (8) Univ. of Utah, (9) Univ. of Bern)🇨🇭
We present results on the light, strange and charm nucleon scalar and tensor charges from lattice QCD, using simulations with $N_{f} = 2$ flavors of twisted mass Clover-improved fermions with a physical value of the pion mass. Both connected and disconnected contributions are included, enabling us to extract the isoscalar, strange and charm charges for the first time directly at the physical point. Furthermore, the renormalization is computed non-perturbatively for both isovector and isoscalar quantities. We investigate excited state effects by analyzing several sink-source time separations and by employing a set of methods to probe ground state dominance. Our final results for the scalar charges are $g_{S}^{u} = 5.20 (42) (15) (12)$ , $g_{S}^{d} = 4.27 (26) (15) (12)$ , $g_{S}^{s} = 0.33 (7) (1) (4)$ , $g_{S}^{c} = 0.062 (13) (3) (5)$ and for the tensor charges $g_{T}^{u} = 0.782 (16) (2) (13)$ , $g_{T}^{d} = - 0.219 (10) (2) (13)$ , $g_{T}^{s} = - 0.00319 (69) (2) (22)$ , $g_{T}^{c} = - 0.00263 (269) (2) (37)$ in the $MS$ scheme at 2~GeV. The first error is statistical, the second is the systematic error due to the renormalization and the third the systematic arising from possible contamination due to the excited states.
↳ hep-lathep-phnucl-exnucl-thPRD(2017)·78 citations
06*
Interesting effect of the nd -> p(nn) reaction
R. A. Shindin🇷🇺 · D. K. Guriev🇷🇺 · A. N. Livanov🇷🇺 · I. P. Yudin🇷🇺
The reaction nd -> p(nn) produce two slow neutrons in the final state instead of deuteron. In the first view we can take into account the binding energy e ~ 2.23 MeV but this approach can not explain all features which are observed in the momentum spectrum of the secondaries protons. We need to suppose that two slow neutrons in the final state form the intermediate system which has own distribution of internal Fermi momentum.
↳ nucl-thnucl-ex1 citation
07*
Nuclear physics insights for new-physics searches using nuclei: Neutrinoless $β β$ decay and dark matter direct detection
Javier Menéndez🇯🇵
Experiments using nuclei to probe new physics beyond the Standard Model, such as neutrinoless $β β$ decay searches testing whether neutrinos are their own antiparticle, and direct detection experiments aiming to identify the nature of dark matter, require accurate nuclear physics input for optimizing their discovery potential and for a correct interpretation of their results. This demands a detailed knowledge of the nuclear structure relevant for these processes. For instance, neutrinoless $β β$ decay nuclear matrix elements are very sensitive to the nuclear correlations in the initial and final nuclei, and the spin-dependent nuclear structure factors of dark matter scattering depend on the subtle distribution of the nuclear spin among all nucleons. In addition, nucleons are composite and strongly interacting, which implies that many-nucleon processes are necessary for a correct description of nuclei and their interactions. It is thus crucial that theoretical studies and experimental analyses consider $β$ decays and dark matter interactions with a coupling to two nucleons, called two-nucleon currents.
↳ nucl-thastro-ph.COhep-exhep-ph+1EPJ Web Conf.(2017)·4 citations
08*
Corona effect in AA collisions at LHC
V.S. Pantuev🇷🇺
Following our earlier finding based on RHIC data on the dominant jet production from nucleus corona region, we reconsider this effect in nucleus-nucleus collisions at LHC energy. Our hypothesis was based on experimental data, which raised the idea of a finite formation time for the produced medium. At RHIC energy and in low density corona region this time reaches about 2 fm/c. All observed high p_t particles are produced in the corona region and have a chance to escape during this 2 fm/c. After that, the formed high density matter absorbs all jets. Following this hypothesis, the nuclear modification factor R_{AA} should be independent on particle momentum and be flat versus p_t. At the same time, we describe the finite azimuthal anisotropy of high p_t particles, v_2. A separate prediction held that, at LHC energy, the formation time in the corona region should be two times smaller, about 1 fm/c. New data at LHC show that R_{AA} is not flat and is rising with p_t. We add to our original hypothesis an assumption that a fast parton traversing the produced medium loses the fixed portion of its energy. A shift of about 7 GeV (I would call it as a parton binding energy) from the original power law p^{-6} production cross section in pp explains well all the observed R_{AA} dependencies. The shift of about 7 GeV is also valid at RHIC energy, where the cross section follows a power law with about p^{-8} and this shift explains a very slow rise of R_{AA} seen for neutral pions with p_t above 15 GeV/c. We also show that the observed at LHC dependence of v_2 at high p_t and our previous predictions agree.
↳ hep-phnucl-exnucl-thJETP Lett.(2017)·0 citations
09*
Structure of Exotic Nuclei: A Theoretical Review
Shan-Gui Zhou🇨🇳
The study of exotic nuclei---nuclei with the ratio of neutron number $N$ to proton number $Z$ deviating much from that of those found in nature---is at the forefront of nuclear physics research because it can not only reveal novel nuclear properties and thus enrich our knowledge of atomic nuclei, but also help us to understand the origin of chemical elements in the nucleosynthesis. With the development of radioactive ion beam facilities around the world, more and more unstable nuclei become experimentally accessible. Many exotic nuclear phenomena have been observed or predicted in nuclei far from the $β$ -stability line, such as neutron or proton halos, the shell evolution and changes of nuclear magic numbers, the island of inversion, soft-dipole excitations, clustering effects, new radioactivities, giant neutron halos, the shape decoupling between core and valence nucleons in deformed halo nuclei, etc. In this contribution, I will present a review of theoretical study of exotic nuclear structure. I will first introduce characteristic features and new physics connected with exotic nuclear phenomena: the weakly-bound feature, the large-spatial extension in halo nuclei, deformation effects in halo nuclei, the shell evolution, new radioactivities and clustering effects. Then I will highlight some recent progresses corresponding to these features.
↳ nucl-thnucl-exPoS(2017)·16 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.