The LHCb Outer Tracker is a gaseous detector covering an area of 5 × 6 m 2 with 12 double layers of straw tubes. The detector with its services are described together with the commissioning and calibration procedures. Based on data of the first LHC running period from 2010 to 2012, the performance of the readout electronics and the single hit resolution and efficiency are presented.The efficiency to detect a hit in the central half of the straw is estimated to be 99.2%, and the position resolution is determined to be approximately 200 µm. The Outer Tracker received a dose in the hottest region corresponding to 0.12 C/cm, and no signs of gain deterioration or other ageing effects are observed.

The first moments of the polarized valence parton distribution functions (PDFs) truncated to the wide Bjorken x region 0.004 < x < 0.7 are directly (without any fitting procedure) extracted in the next to leading order (NLO) QCD from both COMPASS and HERMES data on pion production in polarized semi-inclusive DIS (SIDIS) experiments. The COMPASS and HERMES data are combined in two ways and two scenarios for the fragmentation functions (FFs) are considered. Two procedures are proposed for an estimation of light sea quark contributions to the proton spin. Both of them lead to the conclusion that these contributions are compatible with zero within the errors.

Theˇrst moments of polarized valence PDFs, responsible for the respective contributions to the nucleon spin, are extracted in NLO QCD from the data of COMPASS and HERMES Collaborations on the semi-inclusive difference asymmetries. To this end, the new method of QCD analysis (alternative to the usual globalˇt analysis) is applied. Using the obtained results on valence PDFs, theˇrst moments of polarized sea PDFs are reconstructed. They occur surprisingly small: compatible with zeros within the errors.

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