Wed·Nov 15, 2017Wednesday·November 15, 2017

1. 01*

   Forward-backward correlations between mean transverse momenta in Pb-Pb collisions with ALICE

   Igor Altsybeev (for the ALICE Collaboration)🇷🇺

   Forward-backward (FB) correlations are considered to be a powerful tool for the exploration of the early dynamics of hadronic interactions. The FB correlation functions can be constructed from different observables calculated event-by-event in two separated pseudorapidity regions. We report measurements of event-by-event average transverse momentum correlations for charged particles in two separated pseudorapidity regions in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ and 5.02 TeV recorded with ALICE at the LHC. The event-by-event mean transverse momenta correlations are robust against volume fluctuations and thus the centrality determination methods, which provides higher sensitivity to the properties of the initial state and evolution of the medium created in A-A collisions. The strength of the FB correlation is calculated for different centralities of the Pb-Pb collisions. Results are compared with Monte Carlo event generators, such as HIJING and AMPT.

   nucl-exKnE Energ.Phys.(2018)·9 citations
2. 02*

   The dominance of the $\nu (0d_{5/2}{)}^2$ configuration in the $N=8$ shell in ${}^{12}$Be from the breakup reaction on a proton target at intermediate energy

   Le Xuan Chung🇻🇳 · Carlos A. Bertulani🇺🇸 · Peter Egelhof🇩🇪 · Stoyanka Ilieva🇩🇪 · Dao T. Khoa🇻🇳 · Oleg A. Kiselev🇩🇪

   The momentum distribution of ${}^{11}$Be fragments produced by the breakup of ${}^{12}$Be interacting with a proton target at 700.5 MeV/$u$ energy has been measured at GSI Darmstadt. To obtain the structure information on the anomaly of the $N=8$ neutron shell, the momentum distribution of ${}^{11}$Be fragments from the one-neutron knockout ${}^{12}$Be(p,pn) reaction, measured in inverse kinematics, has been analysed in the distorted wave impulse approximation (DWIA) based on a quasi-free scattering scenario. The DWIA analysis shows a surprisingly strong contribution of the neutron $0d_{5/2}$ orbital in ${}^{12}$Be to the transverse momentum distribution of the ${}^{11}$Be fragments. The single-neutron $0d_{5/2}$ spectroscopic factor deduced from the present knock-out data is 1.39(10), which is significantly larger than that deduced recently from data of ${}^{12}$Be breakup on a carbon target. This result provides a strong experimental evidence for the dominance of the neutron $\nu (0d_{5/2}{)}^2$ configuration in the ground state of ${}^{12}$Be.

   nucl-exnucl-thPLB(2017)·9 citations
3. 03*

   Photoproduction of $\Lambda$ and ${\Sigma }^0$ hyperons off protons with linearly polarized photons at $E_{\gamma }=1.5-3.0$ GeV

   S. H. Shiu · H. Kohri · W. C. Chang · D. S. Ahn · J. K. Ahn · J. Y. Chen · S. Date · H. Ejiri · H. Fujimura · M. Fujiwara · S. Fukui · W. Gohn and 33 other authors

   We report the measurement of the $\gamma p\to K^{+}\Lambda$ and $\gamma p\to K^{+}{\Sigma }^0$ reactions at SPring-8. The differential cross sections and photon-beam asymmetries are measured at forward $K^{+}$ production angles using linearly polarized tagged-photon beams in the range of $E_{\gamma }=1.5$--3.0 GeV. With increasing photon energy, the cross sections for both $\gamma p\to K^{+}\Lambda$ and $\gamma p\to K^{+}{\Sigma }^0$ reactions decrease slowly. Distinct narrow structures in the production cross section have not been found at $E_{\gamma }=1.5$--3.0 GeV. The forward peaking in the angular distributions of cross sections, a characteristic feature of $t$-channel exchange, is observed for the production of $\Lambda$ in the whole observed energy range. A lack of similar feature for ${\Sigma }^0$ production reflects a less dominant role of $t$-channel contribution in this channel. The photon-beam asymmetries remain positive for both reactions, suggesting the dominance of $K^{\ast }$ exchange in the $t$ channel. These asymmetries increase gradually with the photon energy, and have a maximum value of +0.6 for both reactions. Comparison with theoretical predictions based on the Regge trajectory in the $t$ channel and the contributions of nucleon resonances indicates the major role of $t$-channel contributions as well as non-negligible effects of nucleon resonances in accounting for the reaction mechanism of hyperon photoproduction in this photon energy regime.

   nucl-exnucl-thPRC(2018)·25 citations
4. 04*

   Measurement of the beam asymmetry $\Sigma$ and the target asymmetry $T$ in the photoproduction of $\omega$ mesons off the proton using CLAS at Jefferson Laboratory

   P. Roy🇺🇸 · Z. Akbar🇺🇸 · S. Park🇺🇸 · V. Crede🇺🇸 · A. V. Anisovich🇩🇪 · I. Denisenko🇩🇪 · E. Klempt🇩🇪 · V. A. Nikonov🇩🇪 · A. V. Sarantsev🇩🇪 · K. P. Adhikari🇺🇸 · S. Adhikari🇺🇸 · S. Anefalos Pereira🇮🇹 and 134 other authors

   The photoproduction of $\omega$ mesons off the proton has been studied in the reaction $\gamma p\to p\omega$ using the CEBAF Large Acceptance Spectrometer (CLAS) and the frozen-spin target (FROST) in Hall B at the Thomas Jefferson National Accelerator Facility. For the first time, the target asymmetry, $T$, has been measured in photoproduction from the decay $\omega \to {\pi }^{+}{\pi }^{-}{\pi }^0$, using a transversely-polarized target with energies ranging from just above the reaction threshold up to 2.8 GeV. Significant non-zero values are observed for these asymmetries, reaching about 30-40% in the third-resonance region. New measurements for the photon-beam asymmetry, $\Sigma$, are also presented, which agree well with previous CLAS results and extend the world database up to 2.1 GeV. These data and additional $\omega$-photoproduction observables from CLAS were included in a partial-wave analysis within the Bonn-Gatchina framework. Significant contributions from $s$-channel resonance production were found in addition to $t$-channel exchange processes.

   nucl-exhep-exPRC(2018)·19 citations
5. 05*

   Constraining the ${}^7$Be($p,\gamma$)${}^8$B $S$-factor with the new precise ${}^7$Be solar neutrino flux from Borexino

   Marcell P. Takács🇩🇪 · Daniel Bemmerer🇩🇪 · Arnd R. Junghans🇩🇪 · Kai Zuber🇩🇪

   Among the solar fusion reactions, the rate of the ${}^7$Be($p,\gamma$)${}^8$B reaction is one of the most difficult to determine rates. In a number of previous experiments, its astrophysical $S$-factor has been measured at $E$ = 0.1-2.5 MeV center-of-mass energy. However, no experimental data is available below 0.1 MeV. Thus, an extrapolation to solar energies is necessary, resulting in significant uncertainty for the extrapolated $S$-factor. On the other hand, the measured solar neutrino fluxes are now very precise. Therefore, the problem of the $S$-factor determination is turned around here: Using the measured ${}^7$Be and ${}^8$B neutrino fluxes and the Standard Solar Model, the ${}^7$Be($p,\gamma$)${}^8$B astrophysical $S$-factor is determined at the solar Gamow peak. In addition, the ${}^3$He($\alpha$,$\gamma$)${}^7$Be $S$-factor is redetermined with a similar method.

   ↳ astro-ph.SRnucl-exNPA(2018)·17 citations
6. 06*

   Effect of the QCD equation of state and strange hadronic resonances on multiparticle correlations in heavy ion collisions

   Paolo Alba🇩🇪 · Valentina Mantovani Sarti🇩🇪 · Jorge Noronha🇧🇷 · Jacquelyn Noronha-Hostler🇺🇸 · Paolo Parotto🇺🇸 · Israel Portillo Vazquez🇺🇸 · Claudia Ratti🇺🇸

   The QCD equation of state at zero baryon chemical potential is the only element of the standard dynamical framework to describe heavy ion collisions that can be directly determined from first principles. Continuum extrapolated lattice QCD equations of state have been computed using 2+1 quark flavors (up/down and strange) as well as 2+1+1 flavors to investigate the effect of thermalized charm quarks on QCD thermodynamics. Lattice results have also indicated the presence of new strange resonances that not only contribute to the equation of state of QCD matter but also affect hadronic afterburners used to model the later stages of heavy ion collisions. We investigate how these new developments obtained from first principles calculations affect multiparticle correlations in heavy ion collisions. We compare the commonly used equation of state S95n-v1, which was constructed using what are now considered outdated lattice results and hadron states, to the current state-of-the-art lattice QCD equations of state with 2+1 and 2+1+1 flavors coupled to the most up-to-date hadronic resonances and their decays. New hadronic resonances lead to an enhancement in the hadronic spectra at intermediate $p_T$. Using an outdated equation of state can directly affect the extraction of the shear viscosity to entropy density ratio, $\eta /s$, of the quark-gluon plasma and results for different flow observables. The effects of the QCD equation of state on multiparticle correlations of identified particles are determined for both AuAu $\sqrt{s_{NN}}=200$ GeV and PbPb $\sqrt{s_{NN}}=5.02$ TeV collisions. New insights into the $v_2\{2\}$ to $v_3\{2\}$ puzzle in ultracentral collisions are found. Flow observables of heavier particles exhibit more non-linear behavior regardless of the assumptions about the equation of state, which may provide a new way to constrain the temperature dependence of $\eta /s$.

   ↳ nucl-thhep-lathep-phnucl-exPRC(2018)·116 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.