The CMS pixel detector consists of approximately 66 million silicon pixels whose analog signals are read out by 15,840 programmable Readout Chips. With the recent startup of the LHC, the detector is ...now collecting data used for precise vertexing and track-finding. In preparation for data taking, the detector's Readout Chips and their supporting readout and control electronics were calibrated. The calibration that has taken place since the detector's installation in the summer of 2008 will be described. These calibrations focused on the optimization of the Readout Chips’ thresholds and analog response. The operation of the detector during the early running of the LHC will also be discussed. The calibrations that are performed on a regular basis and a mechanism to handle the readout of large beam background events will be described.
Shallow crystalline groundwater in the semi-arid hinterland of Ceará is brackish or saline with mixed chloride or sodium chloride facies. Very few hydrochemical data are available for the area and ...the drivers behind this salinity are not clearly identified. In this study, extensive field data collection was performed to provide new information about the hydrogeological functioning and the salinization processes, through the implementation of piezometric, hydrogeochemical, isotopic (
18
O,
2
H) and multitracer dating (
14
C,
3
H, CFC, SF
6
) monitoring. Piezometric and isotopic data evidence fast flow circulation processes and a high contribution of evaporated surface water to aquifer recharge. Multitracer dating shows the groundwater is essentially composed of seasonal vertical infiltration flows that mix with older waters stored in the aquifer. Chemical analyses suggest the groundwater, originally low mineralized, has become progressively saltier due to leaching of salts that were evapoconcentrated in either surface waters or the unsaturated zone during drier periods.
The observation of the standard model (SM) Higgs boson decay to a pair of bottom quarks is presented. The main contribution to this result is from processes in which Higgs bosons are produced in ...association with a W or Z boson (VH), and are searched for in final states including 0, 1, or 2 charged leptons and two identified bottom quark jets. The results from the measurement of these processes in a data sample recorded by the CMS experiment in 2017, comprising 41.3 fb^{-1} of proton-proton collisions at sqrts=13 TeV, are described. When combined with previous VH measurements using data collected at sqrts=7, 8, and 13 TeV, an excess of events is observed at m_{H}=125 GeV with a significance of 4.8 standard deviations, where the expectation for the SM Higgs boson is 4.9. The corresponding measured signal strength is 1.01±0.22. The combination of this result with searches by the CMS experiment for H→bbover ¯ in other production processes yields an observed (expected) significance of 5.6 (5.5) standard deviations and a signal strength of 1.04±0.20.
New sets of parameters (“tunes”) for the underlying-event (UE) modelling of the
pythia
8,
pythia6
and
herwig++
Monte Carlo event generators are constructed using different parton distribution ...functions. Combined fits to CMS UE proton–proton (
p
p
) data at
s
=
7
TeV
and to UE proton–antiproton (
p
p
¯
) data from the CDF experiment at lower
s
, are used to study the UE models and constrain their parameters, providing thereby improved predictions for proton–proton collisions at 13
TeV
. In addition, it is investigated whether the values of the parameters obtained from fits to UE observables are consistent with the values determined from fitting observables sensitive to double-parton scattering processes. Finally, comparisons are presented of the UE tunes to “minimum bias” (MB) events, multijet, and Drell–Yan (
q
q
¯
→
Z
/
γ
∗
→
lepton-antilepton+jets) observables at 7 and 8
TeV
, as well as predictions for MB and UE observables at 13
TeV
.
Results are presented from searches for the standard model Higgs boson in proton–proton collisions at s=7 and 8 TeV in the Compact Muon Solenoid experiment at the LHC, using data samples ...corresponding to integrated luminosities of up to 5.1 fb−1 at 7 TeV and 5.3 fb−1 at 8 TeV. The search is performed in five decay modes: γγ, ZZ, W+W−, τ+τ−, and bb¯. An excess of events is observed above the expected background, with a local significance of 5.0 standard deviations, at a mass near 125 GeV, signalling the production of a new particle. The expected significance for a standard model Higgs boson of that mass is 5.8 standard deviations. The excess is most significant in the two decay modes with the best mass resolution, γγ and ZZ; a fit to these signals gives a mass of 125.3±0.4(stat.)±0.5(syst.) GeV. The decay to two photons indicates that the new particle is a boson with spin different from one.
A measurement of the mass of the Higgs boson in the diphoton decay channel is presented. This analysis is based on 35.9fb−1 of proton-proton collision data collected during the 2016 LHC running ...period, with the CMS detector at a centre-of-mass energy of 13 TeV. A refined detector calibration and new analysis techniques have been used to improve the precision of this measurement. The Higgs boson mass is measured to be mH=125.78±0.26GeV. This is combined with a measurement of mH already performed in the H→ZZ→4ℓ decay channel using the same data set, giving mH=125.46±0.16GeV. This result, when further combined with an earlier measurement of mH using data collected in 2011 and 2012 with the CMS detector, gives a value for the Higgs boson mass of mH=125.38±0.14GeV. This is currently the most precise measurement of the mass of the Higgs boson.
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