New measurements on physics of B -hadrons in ATLAS experiment
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ew Measurements on Physics of B-Hadrons in ATLAS Experiment1 V. Nikolaenko State Research Center of Russian Federation—Institute for High Energy Physics of National Research Center Kurchatov Institute, Protvino, Moscow oblast, 142281 Russia e-mail: [email protected] Abstract⎯Recent results on B -hadron physics in ATLAS are reviewed. A new measurement of CP-violating parameters in B s → J ψϕ decay is performed on full Run 1 statistics. Branching fraction
BR(B s → μ +μ − ) = (0 . 9 −+ 10.. 18 ) × 10 − 9 is measured, below the Standard Model (SM) prediction. DOI: 10.1134/S1063779617060454
1. RECENT ATLAS RESULTS The following results on production processes, spectroscopy, CP -violation and rare decays are published or presented at Conferences in 2015–2016: • J ψ and ψ(2S ) production at 7 and 8 TeV. • J ψ non-prompt fraction at 13 TeV. • D -meson production at 7 TeV. • f s f d fragmentation fraction ratio at 7 TeV. • Observation of Λ b → J ψ (2S ) decay. • Study of Bc → J ψ D s+(∗) decays. • CP Violation analysis in B s → J ψ ϕ(1020) decay on Run 1 data. • B -hadron reconstruction at 13 TeV. • Search of rare B s → μ +μ − and B 0 → μ +μ − decays using the LHC Run 1 data with the ATLAS detector. Experimental statistics was acquired mainly with a dimuon trigger on opposite-sign muons from J ψ or ψ(2S ) decays. Requirements on muon pT were tighten with the rise of instantaneous luminosity in the course of data taking campaign. No lifetime requirement was applied. Recent B -physics measurements in ATLAS which can be compared with SM predictions are discussed below. 1 The article is published in the original.
2. CP VIOLATION IN B s → J ψ ϕ DECAY A channel that is possibly sensitive to new physics contributions is the decay B s0 → J ψ ϕ . CP violation in this decay occurs due to interference between direct decays and decays with B s0 − B s0 mixing. In the SM the CP -violating phase ϕ s is small and can be related to Cabibbo–Kobayashi–Maskawa (CKM) quark mixing matrix elements via the relation ϕ s ≈ − 2β s (see details in [1, 2]). Assuming no physics beyond the SM contributions, a value of ϕ s = − 0 . 0363 +−00..0016 0015 rad can be predicted [3]. Decay B s → J ψ ϕ occurs in 3 waves. S- and D-waves lead to CP-even final state, while P-wave corresponds to CP-odd system. A 4-th wave was included to the Partial Wave Analysis (PWA), with (K + K − ) system is S-wave. It worse mentioning that a b -meson tagging at the production time was performed, which significantly increases the precision of the ϕ s measurement. An opposite side tagging was applied, which looks for lepton charge or jet charge associated with 2-nd B -hadron in the event. Results of mass and time-dependent PWA with 4 waves are shown at Fig. 1 (left panel), and also results from other experiments and the SM prediction. ATLAS measurement is consistent with other experiments and with SM prediction. 3. B s → μ +μ − DECAY CMS and LHCb experiments reveal new rare particle decay B s → μ +μ − and measured the Branching Ratios BR(B s → μ +μ − ) = (2 . 8 +−10..19 ) × 10
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