The cross section for coherent J/ψ photoproduction accompanied by at least one neutron on one side of the interaction point and no neutron activity on the other side, X n 0 n , is measured with the CMS experiment in ultra-peripheral PbPb collisions at √ s NN = 2.76 TeV. The analysis is based on a data sample corresponding to an integrated luminosity of 159 µb −1 , collected during the 2011 PbPb run. The J/ψ mesons are reconstructed in the dimuon decay channel, while neutrons are detected using zero degree calorimeters. The measured cross section is dσ coh X n 0 n /dy(J/ψ) = 0.36 ± 0.04 (stat) ± 0.04 (syst) mb in the rapidity interval 1.8 < |y| < 2.3. Using a model for the relative rate of coherent photoproduction processes, this X n 0 n measurement gives a total coherent photoproduction cross section of dσ coh /dy(J/ψ) = 1.82 ± 0.22 (stat) ± 0.20 (syst) ± 0.19 (theo) mb. The data strongly disfavour the impulse approximation model prediction, indicating that nuclear effects are needed to describe coherent J/ψ photoproduction in γ + Pb interactions. The data are found to be consistent with the leading twist approximation, which includes nuclear gluon shadowing. IntroductionPhoton-induced reactions are dominant in Ultra-Peripheral Collisions (UPC) of heavy ions, which involve electromagnetic interactions at large impact parameters of the colliding nuclei. Because of the extremely high photon flux in ultra-peripheral heavy-ion collisions which is proportional to Z 2 , where Z is the charge of the nucleus, photon-nucleus collisions at the LHC are abundant [1][2][3]. Furthermore, in UPCs the LHC can reach unprecedented photon-lead and photon-proton center-of-mass energies.Vector meson photoproduction in UPCs has received recent interest [3]. Exclusive J/ψ photoproduction off protons is defined by the reaction γ + p → J/ψ + p, with the characteristic features that, apart from the vector meson in the final state, no other particles are produced and the vector meson has a mean transverse momentum significantly lower than in inclusive reactions. Another characteristic feature is that in exclusive photoproduction the quantum numbers of the final state can be studied unambiguously. The γ + p → J/ψ + p production process has been studied by H1 and ZEUS collaborations at the electron-proton collider HERA [4][5][6], by the CDF collaboration in proton-antiproton collisions at the Tevatron [7], and by the ALICE and LHCb collaborations at the LHC, in proton-lead [8] and proton-proton collisions [9], respectively. Since the cross section of photoproduced vector mesons such as J/ψ, ψ(2S), and Υ(nS), in leading order perturbative QCD, is proportional to the gluon density squared in the target [10,11], the study of such diffractive processes in high-energy collisions is expected to provide insights into the role played by gluons in hadronic matter. As an example, a J/ψ produced at rapidity y is sensitive to the gluon distribution at x = (M J/ψ / √ s)e ±y at hard scales Q 2 ∼ M 2 J/ψ /4, where M J/ψ is the J/ψ mass, The CMS detectorThe...

Rationale The microanalytical community has an outstanding need for platinum group element (PGE) reference materials, particularly for trace element analysis by laser ablation inductively coupled plasma mass spectrometry (LA‐ICPMS). National Institute of Standards and Technology (NIST) glasses contain Rh, Pd, and Pt, but lack Ru, Os, and Ir. Synthesis of silicate PGE standards has proven difficult due the tendency of PGEs to form metallic nuggets. Methods Additive manufacturing methods were used to produce PGE standards with a silica matrix. Monodispersed submicron PGE‐doped Stöber particles were used as feedstock materials for electrophoretic deposition (EPD). Two‐cm‐sized samples produced by EPD were subsequently densified by thermal processing. The homogeneity of PGEs was tested using LA‐ICPMS and concentrations were measured by laser ablation and solution ICPMS. Results The PGE concentrations ranged from 0.5 to 3 μg/g. The inhomogeneity was at the 3% RSD level for Ru, Rh, Ir, and Os throughout and 5% for Pt and Pd in the interior of the samples. Based on LA‐ICPMS analyses, the interiors of the two samples have near identical concentrations in PGEs. Conclusions The samples fabricated in this study represent the most complete and homogeneous PGE standards produced with a silicate matrix. The ability to produce multiple samples with the same composition provides opportunities for validating methods, monitoring long‐term reproducibility, and facilitating interlaboratory comparisons.

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A method is described for separating lignin from liquid solutions resulting from the pretreatment of lignocellulosic materials such as switchgrass with ammonium hydroxide. The method involves a sequence of steps including acidification, evaporation, and precipitation or centrifugation that are performed under defined conditions, and results in a relatively pure, solid lignin product. The method is tested on ammonium hydroxide solutions containing lignin extracted from switchgrass. Experimental results show that the method is capable of recovering between 66–95% of dissolved lignin as a precipitated solid. Cost estimates of pilot‐scale and industrial‐scale expressions of the process indicate that breakeven lignin prices of $2.36/kg and $0.78/kg, respectively, may be obtainable with this recovery method. © 2011 American Institute of Chemical Engineers Environ Prog, 2012