The central component of the CMS detector is the largest silicon tracker ever built. The precise alignment of this complex device is a formidable challenge, and only achievable with a significant extension of the technologies routinely used for tracking detectors in the past. This article describes the full-scale alignment procedure as it is used during LHC operations. Among the specific features of the method are the simultaneous determination of up to 200 000 alignment parameters with tracks, the measurement of individual sensor curvature parameters, the control of systematic misalignment effects, and the implementation of the whole procedure in a multiprocessor environment for high execution speed. Overall, the achieved statistical accuracy on the module alignment is found to be significantly better than 10 µm.

Pair production of Υ(1S) mesons is observed at the LHC in proton-proton collisions at √ s = 8 TeV by the CMS experiment in a data sample corresponding to an integrated luminosity of 20.7 fb −1 . Both Υ(1S) candidates are fully reconstructed via their decays to µ + µ − . The fiducial acceptance region is defined by an absolute Υ(1S) rapidity smaller than 2.0. The fiducial cross section for the production of Υ(1S) pairs, assuming that both mesons decay isotropically, is measured to be 68.8 ± 12.7 (stat) ± 7.4 (syst) ± 2.8 (B) pb, where the third uncertainty comes from the uncertainty in the branching fraction of Υ(1S) decays to µ + µ − . Assuming instead that the Υ(1S) mesons are produced with different polarizations leads to variations in the measured cross section in the range from −38% to +36%.Quarkonium pair production in pp collisions via DPS is assumed to result from two independent SPS occurrences [7,13]. Several DPS production processes, including final states with associated jets, are commonly described by an effective cross section (σ eff ) that characterizes the transverse area of the hard partonic interactions [14,15]. It is estimated as the product of single quarkonium production cross sections divided by the corresponding DPS quarkonium pair cross section [16]. Assuming the parton distribution functions are not correlated, σ eff is expected to be independent of the final state and the center-of-mass energy. Recent measurements of σ eff in final states with jets are in the range 12−20 mb [17][18][19][20]. However, measurements of J/ψ pair [21] and J/ψ +Υ(1S) [22] production in ppcollisions yield values of 4.8 and 2.2 mb, respectively. From a fit to differential cross section measurements of J/ψ pair production with CMS [23], Lansberg and Shao [24] estimate an effective cross section of 8.2 mb. In this paper, we report the first observation of Υ(1S) pair production and estimate σ eff using this result, along with theoretical predictions.

Within fluvial networks, lakes can be sinks or sources of dissolved organic carbon (DOC) and nutrients, yet the controls over sink‐source behavior remain unclear. We investigated the influence that an in‐network lake exerted on DOC and nutrient export. Our investigation consisted of: (1) injecting a conservative tracer to determine lake travel times and flow paths; (2) sampling lake inflow, outflow, and surrounding groundwater to determine water and nutrient budgets; and, (3) sampling internal lake profiles to ascertain in‐lake physico‐chemical patterns through time. Conservative tracer data indicated considerable in‐lake retention and combined with inflow‐outflow discharge measurements revealed a decoupling of kinematic and solute pulses. Nitrate (NO3) was the dominant form of dissolved inorganic nitrogen (DIN) at lake inflow whereas ammonium (NH4) became the dominant component at lake outflow. The lake was a sink for NO3‐N and PO4, but a source for NH4‐N, DON, TDN, and DOC. We observed hydrologic controls on DOC concentrations and export patterns, but redox controls on DIN dynamics. Our results indicate that lakes within fluvial networks can be sources of dissolved organic material and reduced nitrogen (NH4) while simultaneously being sinks for NO3‐N and PO4‐P. Determining controls on sink‐source behavior and the cumulative effect of lakes on DOC and nutrient budgets is a necessary first step toward improved understanding of the role of lakes in network‐ to regional‐scale dynamics.

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