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Register a new userMeasurements of $phi_s$ at the LHCb experiment
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Greig A. Cowan
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These proceedings present the current status of measurements of the CP-violating phase $phi_s$ by the LHCb collaboration, reviewing the measurements in channels such as $B_s^0to J/psiphi$, $B_s^0to J/psi pi^+pi^-$ and $B_s^0 to psi(2S)phi$. The observation of the $B_s^0toeta_cphi$ decay mode is presented for the first time, which can be used to measure $phi_s$ with larger data samples that will be collected over the coming years by the LHCb experiment. Finally, the expected increase in precision from LHCb measurements of $phi_s$ over the next decade is presented.
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A time dependent angular analysis of the decay mode $B_s rightarrow J/psi phi$ allows for the measurement of the mixing induced CP-violating phase $phi_s$. Within the Standard Model $phi_s$ is theoretically precisely predicted to be very small, however many Standard Model extensions predict sizeable contributions to this phase. The current experimental knowledge of $phi_s$ has very larger uncertainties. However already with the data expected to be delivered within the next year, the LHCb experiment at the Large Hadron Collider at CERN, has the potential to improve significantly existing measurements. In a data set of up to 37.5 pb$^{-1}$ taken in 2010, first physics signals in the LHCb detector are reconstructed and their properties are compared to Monte Carlo predictions. Based on recently published measurements of $bbar{b}$ cross-sections from the LHCb collaboration, the sensitivity on the $CP$ violating phase $phi_s$ in the decay $B_s rightarrow J/psi phi$ is evaluated. Additionally an alternative method to potentially extract complementary information on $phi_s$ from the measurement of the asymmetry in semileptonic final states is presented.
The LHCb experiment is designed to study the decays and properties of heavy flavoured hadrons produced in the forward region from proton-proton collisions at the CERN Large Hadron Collider. During Run 1, it has recorded the worlds largest data sample of beauty and charm hadrons, enabling precise studies into the spectroscopy of such particles, including discoveries of new states and measurements of their masses, widths and quantum numbers. An overview of recent LHCb results in the area of exotic hadron spectroscopy is presented, focussing on the discovery of the first pentaquark states in the $Lambda_b^0 to J/psi p K^-$ channel and a search for them in the related $Lambda_b^0 to J/psi ppi^-$ mode. The LHCb non-confirmation of the D0 tetraquark candidate in the $B_s^0pi^+$ invariant mass spectrum is presented.
Measuring cross-sections at the LHC requires the luminosity to be determined accurately at each centre-of-mass energy $sqrt{s}$. In this paper results are reported from the luminosity calibrations carried out at the LHC interaction point 8 with the LHCb detector for $sqrt{s}$ = 2.76, 7 and 8 TeV (proton-proton collisions) and for $sqrt{s_{NN}}$ = 5 TeV (proton-lead collisions). Both the van der Meer scan and beam-gas imaging luminosity calibration methods were employed. It is observed that the beam density profile cannot always be described by a function that is factorizable in the two transverse coordinates. The introduction of a two-dimensional description of the beams improves significantly the consistency of the results. For proton-proton interactions at $sqrt{s}$ = 8 TeV a relative precision of the luminosity calibration of 1.47% is obtained using van der Meer scans and 1.43% using beam-gas imaging, resulting in a combined precision of 1.12%. Applying the calibration to the full data set determines the luminosity with a precision of 1.16%. This represents the most precise luminosity measurement achieved so far at a bunched-beam hadron collider.
The calibration and performance of the opposite-side flavour tagging algorithms used for the measurements of time-dependent asymmetries at the LHCb experiment are described. The algorithms have been developed using simulated events and optimized and calibrated with B+ -> J/psi K+, B0 -> J/psi K*0 and B0 -> D*- mu+ nu_mu decay modes with 0.37 fb^-1 of data collected in pp collisions at sqrt(s) = 7 TeV during the 2011 physics run. The opposite-side tagging power is determined in the B+ -> J/psi K+ channel to be (2.10 +- 0.08 +- 0.24) %, where the first uncertainty is statistical and the second is systematic.
An evolved real-time data processing strategy is proposed for high-energy physics experiments, and its implementation at the LHCb experiment is presented. The reduced event model allows not only the signal candidate firing the trigger to be persisted, as previously available, but also an arbitrary set of other reconstructed or raw objects from the event. This allows for higher trigger rates for a given output data bandwidth, when compared to the traditional model of saving the full raw detector data for each trigger, whilst accommodating inclusive triggers and preserving data mining capabilities. The gains in physics reach and savings in computing resources already made possible by the model are discussed, along with the prospects of employing it more widely for Run 3 of the Large Hadron Collider.
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