Decision number: DIR/WK/2016/16

Title: The LHCb experiment at CERN

Aim of the project The LHCb [1] experiment (Large Collider beauty) is one of the large high physics (HEP) experiments collecting data at the LHC [2] () at the CERN research center near Geneva. The research work conducted in the LHCb experiment belongs to the category of basic research. The experiment is designed for precise measurements of the effects related to breaking the symmetry between matter and antimatter, observed in the Universe, and searching for the so-called New Physics, i.e. physics beyond the scope of the , the model which collects the current knowledge about elementary particles and the interactions between them. The fact of the domination of matter over antimatter, confirmed by astrophysical observations, can be described theoretically by breaking one of the fundamental symmetries, which is the combined CP symmetry - charge conjugation parity symmetry [3]. Within the Standard Model, this phenomenon can be attributed to the weak force. The problem of the Standard Model is that the description of CP symmetry breaking requires the introduction of a number of constants (e.g. the parameters of the Cabibbo-Kobayashi-Maskawa unitarity triangle). The values of these constants cannot be predicted theoretically and require experimental measurements. The measured values of these parameters are insufficient to explain observed matter-antimatter . In addition to measuring CP symmetry breaking, the LHCb experiment performs checks for invariance of the combined CPT symmetry (where T stands for inversion of time direction) and Lorentz transformations. It is also important when looking for physics beyond the Standard Model.

Apart from measurements in the heavy sector, the LHCb experiment - thanks to the use of the sophisticated event reconstruction and systems, performed a number of measurements related to hadron spectroscopy to study behavior of - the building blocks of compound particles such as or neutron which form nuclei of atoms. The LHCb collaboration has published a number of results concerning the study of the properties of exotic states containing beauty and charmed quarks, as well as the discovery of the so-called [4], the existence of which was predicted by the Gell- Mann-Zweig quark model.

The capabilities of each experiment are related to its electronic data acquisition system. Such real-time systems have a direct impact on the quality of physical data that will be analyzed in the next stages of scientific research. The LHCb collaboration, thanks to its unique approach to the implementation of the trigger system, has set new directions for the future HEP experiments. The new LHCb trigger, prepared especially for the second phase of data collection (Run II), performs the final, full reconstruction of tracks and vertices using real-time calibration. Thanks to this, the size of recorded data can be significantly reduced by saving only reconstructed objects (i.e. tracks and vertices) [5]. This way unprecedented high statistics samples can be collected and analysed.

The LHCb detector can perform measurements complementary to those performed by ATLAS and CMS experiments. The LHCb collaboration has published around 500 publications, a significant number of which contain world’s best precision measurements in the field of flavor physics. During the first data collection period (2009-2012 Run I), the physics program of the LHCb experiment was significantly extended beyond the original plans to accurately measure CP symmetry breaking and to search for New Physics among heavy quarks. As a result, the LHCb experiment can now be regarded as a universal "forward physics" experiment.

References: [1] The LHCb Collaboration, “The LHCb Detector at LHC”, Journal of Instrumentation, 2008 JINST 3 S08005 [2] Materiały opublikowane na stronie internetowej .ch/lhc [3] A. D. Sakharov. "Violation of CP invariance, C asymmetry, and asymmetry of the universe". Journal of Experimental and Theoretical Physics 5 (1967) [4] The LHCb Collaboration, “Observation of J/ψp resonances consistent with states in Λb0→J/ψK- p decays”, Phys. Rev. Lett. 115 (2015) 072001 [5] R. Aaij et al., “Tesla : an application for real-time data analysis in High Energy Physics”, arXiv:1604.05596