Études de production des états de charmonium avec leurs desintegration vers des hadrons dans l'experience LHCb

par Andrii Usachov

Projet de thèse en Physique des particules

Sous la direction de Sergey Barsuk.

Thèses en préparation à Paris Saclay , dans le cadre de École doctorale Particules, Hadrons, Énergie, Noyau, Instrumentation, Imagerie, Cosmos et Simulation (Orsay, Essonne) , en partenariat avec LAL - Laboratoire de l'Accélérateur Linéaire (laboratoire) et de Université Paris-Sud (établissement de préparation de la thèse) depuis le 01-10-2016 .


  • Résumé

    L'analyse vise à étudier la production de charmonium en b-hadron désintègre. Dans l'environnement LHCb, b-hadron avec une durée de vie moyenne de 1,6 ps parcourt la distance d'environ 1 cm, qui est reconstruit avec le localisateur de silicium vertex LHCb à une précision supérieure à 100 um. L'exigence d'un sommet secondaire bien reconstruit permet de réduire de manière significative fond combinatoire associée à des particules provenant du proton-proton collision vertex. En outre, la combinaison des états de charmonium reconstruits avec un ou deux hadrons chargés recherche systématique des états exotiques prédites par la théorie sera réalisée.

  • Titre traduit

    Study of charmonium production using decays to hadronic final states with the LHCb experiment


  • Résumé

    Charmonium states are copiously produced at hadron colliders, that allows systematic studies of their properties, production mechanisms and decays. The LHCb experiment at CERN deploys several analyses of charmonium states production. Recently using decays to the proton-antiproton final states, production of eta-c state in pp-collisions and from inclusive b-hadron decays has been measured. The next important task is to study production of chi-c states and eta-c(2S) state using their decays to hadrons. In addition probing production of charmonium-like states may help understanding their quantum numbers. Charmonium and charmonium-like decays to phi and f-mesons will be used. This will allow selecting pure event samples of the states with different quantum numbers. The analysis aims at studying of charmonium production in b-hadron decays. In the LHCb environment, b-hadron with an average lifetime of 1.6 ps travels the distance of about 1 cm, which is reconstructed with the LHCb silicium vertex locator to a precision of better than 100 um. The requirement of a well-reconstructed secondary vertex allows to significantly reducing combinatorial background associated to particles coming from the proton-proton collision vertex. In addition combining reconstructed charmonium states with one or two charged hadrons systematic search for exotic states predicted by theory will be performed. As a bonus of the thesis, the Ph.D. student will be able to address more challenging analysis of prompt charmonium states production at the LHC energies. The only presently available analysis of the eta-c state prompt production uses proton anti-proton final state, and the precision is limited by significant amount of the combinatorial background. The chi-c states production analysis employs low energy photon from the chi-c decay to J/psi gamma, and is thus also precision limited. Using hadronic decays will allow to provide a sample with reduced background level, while the challenge will consist in also reduced signal sample due to lower branching fractions and severe requirements at the trigger level. Track and vertex reconstruction, and particle identification using Ring Imagine CHerenkov detectors, are essential for the analysis. Measurement of production ratios allows partial cancellation of many systematic uncertainty effects. However due to difference in kinematic signature of the decays efficiency of particle identification may not completely cancel. Since Monte-Carlo simulation does not provide a proper description of the particle identification efficiency, efficiency of charged kaon identification will be studied on data in bins of kaon momenta. The Ph.D. student will perform optimisation of the event selection, and study efficiency of the trigger and event selection. In order to perform selection criteria optimization and study detector resolution and efficiencies, detailed Monte-Carlo simulation of the addressed channels should be performed. The Ph.D. student is expected to use the LHCb Monte-Carlo simulation software as well as the reconstruction and trigger related software tools. The Ph.D. student will be responsable for carrying out the entire analysis. The Ph.D. student will work in the LHCb LAL group. The group comprises 7 permanently employed physicists, a postdoc and 4 Ph.D. students. The Ph.D. student will systematically take part in the discussions with the theorists from LAL and LPT. The Ph.D. student will participate in the data taking of the LHCb experiment at CERN, taking part in shifts and ensuring data quality.