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13:30 - 13:45 Overview of the LHCb activities (Arneau Romeu Joan)
13:45 - 14:15 PhD Student présentation
Study of the Bs->eta_cPhi channel with the LHCb experiment at Cern
Morgan Martin
The LHCb experiment is designed to carry out precision measurements in beauty and charm sectors. One of the core physics program at LHCb is the determination of CP-violating phase phi_s in the transition b to c \bar{c} s. The existence of the CP-violation permits unambiguous discrimination between matter and antimatter. However CP-violation in the Standard Model is too small to explain the matter/antimatter asymmetry in the universe. On the other hand, some new physics models predict additionnal sources of CP-violation, in particular in loop mediated processes. The interference between Bs meson decay amplitudes to CP final state directly or via mixing gives rise to a measurable CP-violating phase phi_s, which is predicted to be phi_s^{SM}= (0.03764 +/- 0.0008) rad in the Standard Model. However, such process may receive contributions from new physics and change the value of phi_s. At present, the most precise measurement of phi_s is given by the LHCb experiment, using the decay Bs to J/psi phi, with J/psi is reconstructed in mu^+ mu^- and phi is reconstructed in K^+K^-. The measured phi_s is phi_s^{exp} = (0.058 +/- 0.049 +/- 0.006) rad, which is still dominated by the statistical uncertainty. Study of other decays that are sensitive to phi_s would be very useful.
The Bs to eta_c phi decay is such process, and has never been studied before. A multivariate analysis based pre-selection has been developed for Bs to eta_c phi, with eta_c is reconstructed in 4 charged hadrons (pion or kaon), and phi is reconstructed in K^+K^-. The normalization channel is Bs to J/psi phi, which is also study. We measured for the first time the branching fraction of Bs ->eta_c phi.
Search for the Lepton Flavour Violating decay $B_{(s)}\rightarrow\tau\mu$ in the LHCb experiment.
Arneau Romeu Joan
Lepton Flavour Violation is heavily supressed in the Standard Model of particle physics, nevertheless it is allowed in different models describing physics beyond our current knowledge. The goal of this thesis is to find evidence of physics beyond the Standard Model by searching for this rare decay decay in the data collected by the LHCb detector at CERN.
14:15 - 14:30 Overview of the RENOIR activities ()
14:30 - 15:00 PhD Student présentation
On-ground tests of the NISP infrared spectrometer instrument for Euclid
Jomni Ciryl
Euclid is an ESA mission dedicated to understand the acceleration of the expansion of the Universe. The mission will measure hundred of millions of galaxies in spectrophotometry and photometry in the near infrared thanks to a spectro-photometer called NISP. This instrument will be assembled and tested in Marseille. To prepare the on-ground test plan and develop the test procedure, we have used simulated PSF images, based on a Zemax (Optical design software) optical design of the instrument. We have developed the analysis tools that will be further used to build the procedure verification. We present here the method and analysis results to adjust the focus of the instrument. We will in particular show that because of the sampling of the PSF, a dithering strategy should be adapted and will constraint the development of the test plan.
Astronomical image processing from large all-sky photometric surveys for the detection and the measurement of transients
Juan-Pablo Reyes Gomez
As part of the next large photometric survey of the Large Synoptique Survey Telescope (LSST), development of a specific software is underway to process massive batch of images that will be collected during 10 years from 2020. One of the major challenges of this project is to discover and follow hundreds of millions of objects that appear and then disappear from the image: the transients, among tens of petabytes of images that will be observed. Among these transients, Type Ia supernovae are one of the main probes that will help determine the parameters of the cosmological model and specify the nature of dark energy.
The purpose of the thesis is, from an existing framework, to suggest optimizations or new numerical methods for the discovery of transient objects and selection of type Ia supernovae on time-series images. In its current state, the developed framework has been tested on a dataset from the CFHT Legacy Survey. By using a subtraction algorithm based on PSF-matching different images, several transient candidates have been extracted and studied. These results allow for a thorough analysis of the current of the algorithmm, necessary improvements and future developments for other kind of data, including the images that will be obtained from the telescope.
