Measurement of sigma(pp'bar' → W) x BF(W → eν) in the CDF experiment, and single photoelectron analysis of light signals

In this work, I present a measurement of the cross section of W production at collider Tevatron times branching fraction for W → eν (sigma(pp'bar' → W) x BF(W → eν)) with electron reconstructed in the forward region of the detector CDF, using combined calorimetric and tracking information. This is the first CDF measurement in the forward rapidity range and is the first step for study of W properties at large η. For the period Run II, started from autumn 2001, was made upgrade of CDF detector. The forward region (for pseudorapidity |η| > 1) was strongly affected by this upgrade. Mainly due to new silicon tracking system and new forward calorimeter. With combination of tracking detectors SVXII and ISL it is now possible to reconstruct '3D' tracks. The analysis starts from calorimeter-based selection criteria finished with sample of W candidates. This selection is followed by matching '3D' tracks (to remove remaining background) with reconstructed cluster in electromagnetic calorimeter, which is measuring not only energy, but also position of electromagnetic object by Preshower detector (part of calorimeter). Besides MET PEM trigger and tracking efficiencies were established as a helpful numbers for other analysis in forward region. The measured value of the σ x BF(W → eν) is 2.874 ± 0.034(stat) ± 0.167(sys) ± 0.172(lum)nb for data sample of integrated luminosity 64 pb-1, taken from February 2002 until the January 2003 shutdown. Presented value is in agreement with measurements performed by CDF in the central region and with theoretical estimates. Analysis of the photomultiplier (PMT) pulse height spectra from faint light sources (usually called the single-photoelectron spectra) is of a great importance because it reveals many features and can be used to find relevant parameters of PMTs. A deconvolution method is based on a sophisticated photomultiplier response function, which takes into account also photoeffect on first dynode and non-Gaussian response of dynode system for light source less then 3 photoelectrons. The method was used to analyze the photo-multiplier spectra taken in single photoelectron mode. The spectra taken by Hamamatsu R5600 and R5900 photomultipliers with metal channel dynode system have been analyzed. The detailed analysis shows that the method appropriately describes the process of charge multiplication in these photomultipliers in a wide range of operating modes. We demonstrated that the single photoelectron analysis presented in this work can be used for: - calibration and monitoring of the PMT-based spectrometric channels; - finding of the PMT noise characteristics, especially so called excess factor. (author)