Thu·Dec 7, 2017Thursday·December 7, 2017

1. 01*

   Hadronic resonance production with ALICE at the LHC

   Sergey Kiselev (for the ALICE collaboration)🇷🇺

   We present recent results on short-lived hadronic resonances obtained by the ALICE experiment in pp, p-Pb and Pb-Pb collisions at LHC energies, including the most recent measurements of $\Lambda (1520)$ and $\Xi (1530{)}^0$ resonances.

   nucl-ex0 citations
2. 02*

   Double $K_S^0$ Photoproduction off the Proton at CLAS

   S. Chandavar🇺🇸 · J.T. Goetz🇦🇲 · K. Hicks🇺🇸 · D. Keller🇺🇸 · M.C. Kunkel🇦🇲 · M. Paolone🇺🇸 · D.P. Weygand🇦🇲 · K.P. Adhikari🇺🇸 · S. Adhikari🇺🇸 · Z. Akbar🇺🇸 · J. Ball🇫🇷 · I. Balossino🇮🇹 and 115 other authors

   The $f_0$(1500) meson resonance is one of several contenders to have significant mixing with the lightest glueball. This resonance is well established from several previous experiments. Here we present the first photoproduction data for the $f_0$(1500) via decay into the $K_S^0{K}_S^0$ channel using the CLAS detector. The reaction $\gamma p$ -> $f_{0}p$ -> $K_S^0{K}_S^{0}p$, where J = 0, 2, was measured with photon energies from 2.7 to 5.1 GeV. A clear peak is seen at 1500 MeV in the background subtracted invariant mass spectra of the two kaons. This is enhanced if the measured 4-momentum transfer to the proton target is restricted to be less than 1.0 GeV2. By comparing data with simulations, it can be concluded that the peak at 1500 MeV is produced primarily at low t, which is consistent with a t-channel production mechanism.

   nucl-exPRC(2018)·10 citations
3. 03*

   Measurement of the Two-Photon Exchange Contribution to Elastic Lepton-Proton Scattering at the OLYMPUS Experiment

   Brian S. Henderson🇺🇸

   Measurements of the ratio of the proton elastic form factors (${\mu }_p{G}_E/G_M$) using Rosenbluth separation and those using polarization-based techniques show a strong discrepancy, which increases as a function of $Q^2$. The contribution of hard two-photon exchange (TPE) to $e^{-}p$ scattering, which is neglected in the standard treatments of elastic $e^{-}p$ scattering, is the most widely-accepted hypothesis for the explanation of this discrepancy. While calculations of the hard TPE contribution are highly model dependent, the effect may be quantified experimentally by precisely measuring the ratio of the positron-proton and electron-proton elastic scattering cross sections. The OLYMPUS experiment collected approximately 4 fb${}^{-1}$ of $e^{+}p$ and $e^{-}p$ scattering data at the DORIS storage ring at DESY in 2012, with the goal of measuring the elastic ${\sigma }_{e^{+}p}/{\sigma }_{e^{-}p}$ ratio over the kinematic range $(0.4\le ϵ\le 0.9)$, $(0.6\le Q^2\le 2.2)$ GeV${}^2/c^2$ at a fixed lepton beam energy of 2.01 GeV. Initial results from OLYMPUS were presented, and subsequently results on $R_{2\gamma }={\sigma }_{e^{+}p}/{\sigma }_{e^{-}p}$ from the experiment have been publicly released and are in preparation for publication.

   nucl-ex0 citations
4. 04*

   Results from the OLYMPUS Experiment on the Contribution of Hard Two-Photon Exchange to Elastic Electron-Proton Scattering

   Brian S. Henderson🇺🇸

   Measurements of the ratio of the elastic form factors of the proton (${\mu }_p{G}_E/G_M$) exhibit a strong discrepancy. Experiments using unpolarized beams and Rosenbluth separation to determine the form factors have found values of the ratio approximately consistent with unity over a wide range of $Q^2$, while polarization transfer experiments suggest that the ratio decreases as a function of $Q^2$. The most widely-accepted hypothesis to explain this discrepancy is that hard two-photon exchange (TPE) significantly contributes to the elastic $ep$ cross section. Hard TPE has been neglected in previous analyses of electron-proton scattering scattering experiments, in part due to the fact that there exists no model independent way to calculate the contribution. The effect of hard TPE may be measured experimentally, however, via precise determination of the ratio of the electron-proton and positron-proton elastic cross sections. The OLYMPUS experiment collected more than 3 fb${}^{-1}$ of exclusive $e^{-}p$ and $e^{+}p$ elastic scattering data at DESY in 2012, and has determined the elastic ${\sigma }_{e^{+}p}/{\sigma }_{e^{-}p}$ ratio to unprecedented precision up to $Q^2\approx 2.2$ (GeV/$c$)${}^2$, $ϵ\approx 0.4$. This presentation will discuss the OLYMPUS experiment and analysis, and present the recently published results from OLYMPUS in the context of the results from the other two TPE experiments.

   nucl-exPoS(2018)·1 citation
5. 05*

   Isotopic dependence of the fragments' internal temperatures observed in multifragment emission

   S.R. Souza🇧🇷 · R. Donangelo🇧🇷

   The internal temperatures of fragments produced by an excited nuclear source are investigated using the microcanonical version of the Statistical Multifragmentation Model, with discrete energy. We focus on the fragments' properties at the breakup stage, before they have time to deexcite by particle emission. Since the adopted model provides the excitation energy distribution of these primordial fragments, it allows one to calculate the temperatures of different isotope families and infer on the sensitivity to their isospin composition. It is found that, due to the functional form of the nuclear density of states and the excitation energy distribution of the fragments, proton rich isotopes are hotter than neutron rich ones. This property has been taken to be an indication of earlier emission of the former from a source that cools down as it expands and emits fragments. Although this scenario is incompatible with the prompt breakup of a thermally equilibrated source, our results reveal that the latter framework also provides the same qualitative features just mentioned. Therefore they suggest that this property cannot be taken as evidence for non-equilibrium emission. We also found that this sensitivity to the isotopic composition of the fragments depends on the isospin composition of the source, and that it is weakened as the excitation energy of the source increases.

   ↳ nucl-thnucl-exPRC(2018)·2 citations
6. 06*

   The density- and isospin- dependent $\Delta$-formation cross section and its decay width

   Qingfeng Li🇨🇳 · Zhuxia Li🇨🇳

   The energy-, density-, and isospin-dependent $\Delta$-formation cross section ${\sigma }_{N\pi \to \Delta }^{\ast }$ and $\Delta$-decay width are calculated based on the relativistic BUU approach in which the effective mass splitting of nucleon and $\Delta$ baryons in isospin-asymmetric matter is considered by the inclusion of the $\delta$ meson exchange in the effective Lagrangian density. With the density-dependent couplings for baryons of F. Hofmann et al., the ${\sigma }_{N\pi \to \Delta }^{\ast }$ is decreased (increased) moderately with increasing density with (without) the consideration of the density dependent pion effective mass. Meanwhile, if the invariant mass of the system is not far from the $\Delta$ pole mass, the $\Delta$-decay width is also weakly dependent on density. The mass splitting effect of differently charged nucleon and $\Delta$ baryons on ${\sigma }_{N\pi \to \Delta }^{\ast }$ are found to be more obvious than that of pion mesons but much weaker than the mass splitting in the hard $\Delta$ production channel $NN\to N\Delta$. Further, the largest mass-splitting influence is seen in the ${\pi }^{-}p\to {\Delta }^0$ and ${\pi }^{+}n\to {\Delta }^{+}$ channels but not in the production of ${\Delta }^{-}$ and ${\Delta }^{++}$ isobars.

   ↳ nucl-thnucl-exSCPMA(2019)·19 citations
7. 07*

   Nuclear parton distribution functions (nPDFs) and their uncertainties in the LHC Era

   S. Atashbar Tehrani🇮🇷

   We have presented the results of our next-to-next-to-leading order (NNLO) QCD analysis of nuclear parton distribution functions (nuclear PDFs) [Phys. Rev. D 93 (2016) 014026, arXiv:1601.00939 [hep-ph]] using all available neutral current charged-lepton (${\ell }^{\pm }$ + nucleus) deeply inelastic scattering (DIS) data as well as Drell-Yan (DY) cross-section ratios ${\sigma }_{\mathrm{DY}}^A/{\sigma }_{\mathrm{DY}}^{A^{\prime }}$ for a variety of nuclear targets. We have studied in detail the parametrizations and the atomic mass (A) dependence of the nuclear PDFs at NNLO at the input scale, $Q_0^2=2\mathrm{Ge}{\mathrm{V}}^2$. Our {\tt KA15} nuclear PDFs provides a complete set of nuclear PDFs, $f_i^{(A,Z)}(x,Q^2)$, with a full functional dependence on $x$, A, $Q^2$. The uncertainties of the obtained nuclear modification factors for each parton flavour as well as the corresponding observables are estimated using the well-known Hessian method. The nuclear heavy quark contributions are also included into the analysis in the framework of zero-mass variable flavour number scheme (ZM-VFNS). We compare the results of our parametrization with all available nuclear DIS data and the results of other nuclear PDFs groups. We have found that our nuclear PDFs to be in reasonably good agreement with results in the literature. The estimates of errors provided by our global analysis ({\tt KA15}) are rather smaller than those of other groups. We have briefly reviewed different aspects of recent LHC heavy-ion collisions data including the first experimental data from the LHC proton+lead ($p-pb$) and lead+lead ($pb-pb$) run which can be used in the global fits of nuclear PDFs.

   ↳ hep-phnucl-exKnE Energ.Phys.(2018)·4 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.