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Reference : UMR7585-MARGUY-005
Workplace : PARIS 05
Date of publication : Tuesday, February 09, 2021
Scientific Responsible name : Francesco POLCI
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2021
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
Title: Search for lepton flavor violating b-decays with the LHCb experiment
Observation of neutrino oscillations implies that lepton flavor is not a conserved quantity. Nevertheless, charge lepton flavor violating processes have never been observed so far. In fact, in the Standard Model, they should be extremely suppressed, beyond the sensitivity of current detectors. However, a New Physics could increase their rate: these processes, rare in the Standard Model, are among the most powerful probes for searching new physics!
Interest in these decays has increased since the publication of the lepton flavor universality tests performed by the LHCb, RK and RK*. In the Standard Model, these ratios should be equal to unity, while LHCb observed discrepancies amounting to 2.6 and 2.4 standard deviations, respectively. If confirmed, these results would imply lepton flavor universality violation, necessarily associated with a new interaction violating the conservation of the lepton flavor, which could significantly increase the rates of b-decay processes with an s quark and two leptons of different flavors in the final state.
Observing these decays would be a remarkable sign of the existence of new physics, with many possible implications: on the seesaw mechanism of neutrinos and on models with heavy neutrinos, natural candidates for dark matter; on the great unified theories involving lepto-quarks; on understanding the matter-antimatter asymmetry of the Universe.
The LHCb experiment has made it possible to collect an unprecedented amount of B mesons produced during proton-proton collisions at the LHC, CERN's Large Hadron Collider, allowing searching for these decays. The LHCb group at LPNHE has made significant contributions in lepton flavor universality tests and to early searches of lepton flavor violating b-decays.
LHCb will resume its data taking in 2022, with detector completely renewed in its tracking system and with an innovative completely software triggering system. The doctoral student will thus have the opportunity to analyze not only all the data already collected by LHCb, but also those that will be collected in the years to come, which will significantly increase the sensitivity of lepton flavor violating searches. He or she will deepen his or her knowledge of how particle physics detectors work, thanks to the rare opportunity to actively participate in the start of data taking in a major LHC experiment, among other things through studies of the performance of the new detector. In addition, he or she will learn sophisticated analytical techniques, and help unravel one of the most fascinating puzzles in particle physics today.
LPNHE (Laboratoire de Physique Nucléaire et des Hautes Energies, https://lpnhe.in2p3.fr/) is a laboratory of the IN2P3 (Institut National de Physique Nucléaire et de Physique de Particules), a CNRS institute, and of the universities « Sorbonne Université » and « Université de Paris ». The laboratory is located in Paris (France). It is involved in major particle physics, astroparticle physics and cosmology international collaborations. 130 permanent agents work at LPNHE.
Currently, the LHCb group at LPNHE is involved in the analysis of the data of the experiment, in particular in the tests of lepton universality and in B decays without charm quark in the final state. It is active in the electronic back-end of the scintillating fiber tracker detector and in the tuning of the trigger system of the experiment, in particular for the aspects of real-time reconstruction.
Constraints and risks
The COVID-19 sanitary situation permitting, trips are to be planned in France and abroad, in particular to CERN to participate to collaboration meetings and data taking activities.
The successful candidate will contribute to lepton flavor violation searches with LHCb data and to detector performance studies.
The candidate should hold an M.Sc. degree (or equivalent) in fundamental physics or particle physics. Previous experience in particle physics is an asset, although not mandatory. A solid experience in C++ and Python programming is highly desirable.
The doctoral position is funded by IN2P3 for 36 months through the “Fellowhsips of the Two Infinites” program. The starting date is October 1st, 2021.
Applications will include a CV and a covering letter.
The position is funded by IN2P3 for 36 months. The starting date is October 1st , 2021.
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