Thu·Jul 31, 2014Thursday·July 31, 2014

1. 01*

   Dielectron measurements in pp, p-Pb and Pb-Pb collisions with ALICE at the LHC

   Markus K. Koehler (for the ALICE Collaboration)🇩🇪

   Electromagnetic probes are excellent messengers from the hot and dense medium created in high-energy heavy-ion collisions. Since leptons do not interact strongly, their spectra reflect the entire space-time evolution of the collision. The surrounding medium can lead to modifications of the dielectron production with respect to the vacuum rate. To quantify modifications in heavy-ion collisions, measurements in pp collisions serve as a reference, while the analysis of p-A collisions allows for the disentanglement of cold nuclear matter effects from those of the hot and dense medium. In this proceedings, dielectron measurements with the ALICE central barrel detectors are presented. The invariant mass distributions in the range $0<m_{ee}<3$ GeV/$c^2$ are compared to the expected yields from hadronic sources for pp collisions at $\sqrt{s}=7$ TeV, and for p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. The cross section of direct photons measured via virtual photons in pp collisions is compared to predictions from NLO pQCD calculations as a function of the transverse momentum. The status of the analysis of Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV is presented.

   nucl-exNPA(2014)·15 citations
2. 02*

   Measurement of D-meson production in pp, p-Pb, and Pb-Pb collisions at the LHC with the ALICE detector

   Chitrasen Jena (for the ALICE Collaboration)🇮🇹

   Heavy quarks are a powerful probe for investigating the properties of the Quark-Gluon Plasma created in heavy-ion collisions, since they are produced in initial hard scattering processes and experience all the stages of the medium evolution. ALICE has measured the production of ${\mathrm{D}}^0$, ${\mathrm{D}}^{+}$, ${\mathrm{D}}^{\ast +}$, and ${\mathrm{D}}_{\mathrm{s}}^{+}$ mesons at central rapidity in their hadronic decay channels in various collision systems and energies. We present recent results for D-meson production measured by the ALICE Collaboration in pp collisions at $\sqrt{s}=7$ and 2.76 TeV, Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV and p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV.

   nucl-exhep-exhep-phJ.Phys.Conf.Ser.(2014)·6 citations
3. 03*

   Role of the possible ${\Sigma }^{\ast }({\frac{1}{2}}^{-})$ state in the $\Lambda p\to \Lambda p{\pi }^0$ reaction

   Ju-Jun Xie🇨🇳 · Jia-Jun Wu🇺🇸 · Bing-Song Zou🇨🇳

   The $\Lambda p\to \Lambda p{\pi }^0$ reaction near threshold is studied within an effective Lagrangian method. The production process is described by single-pion and single-kaon exchange. In addition to the role played by the ${\Sigma }^{\ast }(1385)$ resonance of spin-parity $J^P=3/2^{+}$, the effects of a newly proposed ${\Sigma }^{\ast }$ ($J^P=1/2^{-}$) state with mass and width around $1380$ MeV and $120$ MeV are investigated. We show that our model leads to a good description of the experimental data on the total cross section of the $\Lambda p\to \Lambda p{\pi }^0$ reaction by including the contributions from the possible ${\Sigma }^{\ast }({\frac{1}{2}}^{-})$ state. However, the theoretical calculations by considering only the ${\Sigma }^{\ast }(1385)$ resonance fail to reproduce the experimental data, especially for the enhancement close to the reaction threshold. On the other hand, it is found that the single-pion exchange is dominant. Furthermore, we also demonstrate that the angular distributions provide direct information of this reaction, hence could be useful for the investigation of the existence of the ${\Sigma }^{\ast }({\frac{1}{2}}^{-})$ state and may be tested by future experiments.

   ↳ nucl-thhep-exhep-phnucl-exPRC(2014)·33 citations
4. 04*

   Constraining the density slope of nuclear symmetry energy at subsaturation densities using electric dipole polarizability in ${}^{208}$Pb

   Zhen Zhang🇨🇳 · Lie-Wen Chen🇨🇳

   Nuclear structure observables usually most effectively probe the properties of nuclear matter at subsaturation densities rather than at saturation density. We demonstrate that the electric dipole polarizibility ${\alpha }_{\text{D}}$ in ${}^{208}$Pb is sensitive to both the magnitude $E_{\text{sym}}({\rho }_{\text{c}})$ and density slope $L({\rho }_{\text{c}})$ of the symmetry energy at a subsaturation cross density ${\rho }_{\text{c}}=0.11$ fm${}^{-3}$. Using the experimental data of ${\alpha }_{\text{D}}$ in ${}^{208}$Pb from RCNP and the recent accurate constraint of $E_{\text{sym}}({\rho }_{\text{c}})$ from the binding energy difference of heavy isotope pairs, we extract a value of $L({\rho }_{\text{c}})=47.3\pm 7.8$ MeV. The implication of the present constraint of $L({\rho }_{\text{c}})$ to the symmetry energy at saturation density, the neutron skin thickness of ${}^{208}$Pb and the core-crust transition density in neutron stars is discussed.

   ↳ nucl-thastro-ph.SRnucl-exPRC(2014)·69 citations
5. 05*

   Determination of electron-nucleus collision geometry with forward neutrons

   L. Zheng🇨🇳 · E.C. Aschenauer🇺🇸 · J.H. Lee🇨🇳

   There are a large number of physics programs one can explore in electron-nucleus collisions at a future electron-ion collider. Collision geometry is very important in these studies, while the measurement for an event-by-event geometric control is rarely discussed in the prior deep inelastic scattering experiments off a nucleus. This paper seeks to provide some detailed studies on the potential of tagging collision geometries through forward neutron multiplicity measurements with a zero degree calorimeter. This type of geometry handle, if achieved, can be extremely beneficial in constraining nuclear effects for the electron-nucleus program at an electron-ion collider.

   ↳ hep-exhep-phnucl-exphysics.ins-detEPJA(2014)·24 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.