Schmidt, Ivan

2019-02-25, Kopeliovich, Boris, Nemchik, J., Potashnikova, I. K., Schmidt, Ivan

Production of heavy flavored hadrons from fragmentation of heavy quarks represents an alternative probe for a medium created after heavy ion collisions. We demonstrate that observed strong suppression of heavy flavored D and B mesons, produced with high transverse momenta pT, is caused by final state interactions with such a medium. The space-time pattern of hadronization of a highly virtual heavy quark is controlled predominantly by intensive gluon radiation, which is ceased at a short time scale in accordance with perturbative QCD calculations and LEP measurements of the fragmentation functions. However, production of heavy flavored hadrons lasts a long time due to prompt multiple breakups of produced colorless (pre)hadrons in the medium. This fact together with the specific shape of heavy quark fragmentation function, peaked at large z, allows to explain the observed strong suppression of D and B mesons in a good accord with data.

2018-03-01, Arbelaéz, Carolina, DIB VENTURELLI, CLAUDIO OMAR, SCHMIDT, IVAN, Vasquez, Juan Carlos

We propose a strategy for distinguishing the Dirac / Majorana character of heavy neutrinos with masses below the W boson mass, using purely leptonic decays at the LHC. The strategy makes use of a forward-backward asymmetry of the opposite charge lepton in the W+→l+l+l′−ν decay. In order to check the experimental feasibility of the model, we show, through a numerical analysis, that in the decay W+→e+e+μ−ν the two positrons in the final state can be distinguished for different ranges of the heavy neutrino masses. Finally, we estimated the number of events of W+→e+e+μ−ν for a Dirac and Majorana N neutrino. For an integrated luminosity of 120 fb−1 at LHC RUN II, signals can be found if heavy-to-light neutrino mixings are |UNμ|^2,|UNe|^2≳10−6.

2019-02-01, DIB VENTURELLI, CLAUDIO OMAR, Gutsche, Thomas, Kovalenko, Sergey G., Lyubovitskij, Valery E., SCHMIDT, IVAN

We study two- and three-body lepton flavor violating (LFV) decays involving leptons and neu- tral vector bosons V = ρ0, ω, φ, J/ψ, Υ, Z0, as well as pseudoscalar P = π0, η, η′, ηc and scalar S = f0(500), f0(980), a0(980), χc0(1P ) mesons, without referring to a specific mechanism of LFV realization. In particular, we relate the rates of the three-body LFV decays τ (μ) → 3`, where ` = μ or e, to the two-body LFV decays (V, P ) → τ μ(τ e, μe), where V and P play the role of intermediate resonances in the decay process τ (μ) → 3`. From the experimental upper bounds for the branching ratios of τ (μ) → 3` decays, we derive upper limits for the branching ratios of (V, P ) → τ μ(τ e, μe). We compare our results to the available experimental data and known theoretical upper limits from previous studies of LFV processes and find that some of our limits are several orders of magnitude more stringent. Using the idea of quark-hadron duality, we extract limits on various quark-lepton dimension-six LFV operators from data on lepton decays. Some of these limits are either new or stronger than those existing in the literature.