Measurement of the total and differential b cross sections at HERA and CMS tracker alignment at LHC

This thesis is logically divided into two main parts. The first part present a ZEUS analysis which was performed on the data obtained from electron-proton collisions measured by the ZEUS detector for the 2003-2007 running period. The full HERA-II integrated luminosity of 376 $pb^{−1}$ is used. The ZEUS detector is sensitive to the full phase space of beauty production, since it has cylindrical geometry, covers a wide rapidity range and was able to measure low transverse momentum muons. In this part a measurement of beauty production was studied via the process $ep \rightarrow {e}'b \bar{b} \rightarrow {e}'\mu \mu X$. Making full use of the HERA-II detector upgrade, $bX$ secondary vertex information was used to constrain the beauty and charm contribution to this process. The result of this analysis is the measurement of the total, visible and differential cross sections for beauty production. The cross sections are compared to next-to-leading order QCD calculations. Similar to the beauty events, instanton or instanton-induced events involving heavy flavour can also be a source for non-isolated, both like- and unlike-sign muon pairs. In this analysis, instantons were studied with using QCDINS predictions. The data show no indication for instanton-induced events. The second part is related to CMS tracker alignment. It uses collision and cosmic data samples obtained by the CMS detector at the Large Hadron Collider in 2012. This part consists of studies of the CMS tracker alignment weak modes and a detailed study of the “z-rescaling” weak mode. The CMS tracker alignment weak mode study includes the simulation of the weak modes, and the alignment implementation on top of such simulation. This study shows that the alignment procedure of the CMS tracker is stable with regard to the three weak modes: “Twist, Sagitta and Telescope” which stand for three types of systematic shifts of the CMS tracker. The “z-rescaling” weak mode shows a strong and unexpected shift of some tracker detector components in the z direction. To study the issue, a significant number of tests such as “high level structure” alignment only, alignment with fixed end caps, impact of the $p_T$ dependence of the tracks on the alignment procedure, the simulation of cosmic data as collision data, introducing TID, TEC end cap disk constraints and other important tests were performed. Even though this issue was not yet fully solved, the studies performed in this thesis show consistent and detailed steps that help to better understand the issue and solve it in the future. The track helix parametrisation of both the ZEUS and CMS experiments was studied. A checked, detailed description of such parametrisation as well as its transformation from the CMS format into the ZEUS format is performed. In addition, a CMS physics analyses of $B \rightarrow J/ψK$ decays was started. These studies were performed with the CMS “open data” for the 2010 time period. Logically this can be seen as a first step towards a measurement of the total beauty cross section in CMS in the same spirit as the one performed with the ZEUS data.