Mon·Sep 3, 2018Monday·September 3, 2018

1. 01*

   Global and local polarization of $\Lambda$ hyperons in Au+Au collisions at 200 GeV from STAR

   Takafumi Niida (for the STAR Collaboration)🇺🇸

   New results on global polarization of $\Lambda$ hyperons in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV reveal non-zero signal on the order of a few tenths of a percent. Compared with lower energy results, the current measurement shows that the polarization decreases at higher collision energy, the trend being well reproduced by theoretical calculations. The polarization is found to be larger in more peripheral collisions, as well as in the in-plane than in the out-of-plane direction. The signal seems to depend on the asymmetry between positive and negative charge in each event, which may indicate an influence of the axial current induced by the magnetic field. In addition, the first measurement of a local polarization along the beam direction was performed. The results show a quadrupole modulation relative to the second-order event plane, as expected from the elliptic flow.

   nucl-exNPA(2019)·117 citations
2. 02*

   Strangeness photoproduction at extremely forward angles at the BGO-OD experiment

   T. C. Jude🇩🇪

   The BGO-OD experiment at the ELSA accelerator facility uses an energy tagged bremstrahlung photon beam to investigate the internal structure of the nucleon. The setup consists of a highly segmented BGO calorimeter surrounding the target, with a particle tracking magnetic spectrometer at forward angles. BGO-OD is ideal for investigating low momentum transfer processes due to the acceptance and high momentum resolution at forward angles. This enables the investigation of strangeness photoproduction where $t$-channel exchange mechanisms play a dominant role. A detailed understanding of this low-momentum transfer region is also crucial for constraints in hypernuclei electroproduction, and sensitive to any extended, molecular-like interactions that may contribute to reaction mechanisms. Progress in the study of $K^{+}\Lambda$(1405) differential cross sections and line shapes, $K^0$ photoproduction, and differential cross section measurements for $K^{+}\Lambda$ and $K^{+}{\Sigma }^0$ photoproduction at extremely forward angles is presented. Opportunities for hypernuclei studies are also discussed.

   nucl-exAIP Conf.Proc.(2019)·1 citation
3. 03*

   Hidden charm pentaquarks: mass spectrum, magnetic moments, and photocouplings

   Emmanuel Ortiz-Pacheco🇲🇽 · Roelof Bijker🇲🇽 · César Fernández-Ramírez🇲🇽

   We develop an extension of the usual three flavor quark model to four flavors (u, d, s and c), and discuss the classification of pentaquark states with hidden charm. We fit our model to the known baryon spectrum and we predict the double and triple charm baryons, finding good agreement with the most recent lattice QCD calculations. We compute the the ground state of hidden charm pentaquarks and their associated magnetic moments and electromagnetic couplings, of interest to pentaquark photoproduction experiments.

   ↳ nucl-thhep-exhep-phnucl-exJ.Phys.G(2019)·52 citations
4. 04*

   Two-particle angular correlations in pp and p-Pb collisions at LHC energies from a multi-phase transport model

   Liuyao Zhang🇨🇳 · Jinhui Chen🇨🇳 · Ziwei Lin🇺🇸 · Yugang Ma🇨🇳 · Song Zhang🇨🇳

   We apply a multi-phase transport (AMPT) model to study two-particle angular correlations in $pp$ collisions at $\sqrt{s}=7$ TeV. Besides being able to describe the angular correlation functions of meson-meson pairs, a large improvement for the angular correlations of baryon-baryon and antibaryon-antibaryon is achieved. We further find that the AMPT model with new quark coalescence provides an even better description on the anti-correlation feature of baryon-baryon correlations observed in the experiments. We also extend the study to p-Pb collisions at $\sqrt{s}=5.02$ TeV and obtained similar results. These results help us better understand the particle production mechanism in $pp$ and p-Pb collisions at LHC energies.

   ↳ nucl-thnucl-exPRC(2018)·21 citations
5. 05*

   Accessing gluon parton distributions in large momentum effective theory

   Jian-Hui Zhang🇩🇪 · Xiangdong Ji🇺🇸 · Andreas Schäfer🇩🇪 · Wei Wang🇨🇳 · Shuai Zhao🇨🇳

   Gluon parton distribution functions (PDFs) in the proton can be calculated directly on Euclidean lattices using large momentum effective theory (LaMET). To realize this goal, one has to find renormalized gluon quasi-PDFs in which power divergences and operator mixing are thoroughly understood. For the unpolarized distribution, we identify four independent quasi-PDF correlators that can be multiplicatively renormalized on the lattice. Similarly, the helicity distribution can be derived from three independent multiplicatively renormalizable quasi-PDFs. We provide a LaMET factorization formula for these renormalized quasi-PDFs from which one can extract the gluon PDFs.

   ↳ hep-phhep-exhep-latnucl-ex+1PRL(2019)·122 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.