Measurement of the lifetime of the Bc+B_c^+ meson using the Bc+→J/ψπ+B_c^+\rightarrow J/\psi\pi^+ decay mode

The difference in total widths between the $B_c^+$ and $B^+$ mesons is measured using 3.0fb$^{-1}$ of data collected by the LHCb experiment in 7 and 8 TeV centre-of-mass energy proton-proton collisions at the LHC. Through the study of the time evolution of $B_c^+ \rightarrow J/\psi \pi^+$ and $B^+\rightarrow J/\psi K^+$ decays, the width difference is measured to be $$\Delta\Gamma \equiv \Gamma_{B_c^+} - \Gamma_{B^+} = 4.46 \pm 0.14 \pm 0.07mm^{-1}c,$$ where the first uncertainty is statistical and the second systematic. The known lifetime of the $B^+$ meson is used to convert this to a precise measurement of the $B_c^+$ lifetime, $$\tau_{B_c^+} = 513.4 \pm 11.0 \pm 5.7fs,$$ where the first uncertainty is statistical and the second systematic.Comment: 19 pagers, 3 figure

Optical coherence tomography in the evaluation of retinal changes associated with suspicious choroidal melanocytic tumors

Subretinal fluid (SRF) is a strong risk factor for growth of choroidal melanocytic tumors. However, subtle SRF can be difficult to assess clinically and to distinguish from chronic retinal changes overlying a dormant lesion. This study investigates optical coherence tomography (OCT) in evaluating SRF in suspicious choroidal melanocytic tumors. Interventional case series. Review of 33 patients with untreated choroidal melanocytic tumors who underwent OCT for suspicion of subtle SRF. Fluorescein angiography was performed in 26 of the patients. The main outcome was tumor growth. No retinal separation was found in 12 tumors, of which 1 (8%) grew on follow-up and 3 (25%) were treated. Chronic retinal changes (localized retinal separation with retinal atrophy or intraretinal cysts) were found in nine tumors: one (11%) grew on follow-up and none were treated. Active SRF (localized retinal separation with normal retinal appearance) was found in 12 tumors: 6 (50%) grew on follow-up, and 7 (58%) were treated. The active OCT pattern was associated with fluorescein angiography hotspots (P =.041), documented tumor growth (P =.033), and tumor treatment (P =.014), and inversely associated with drusen (P =.024), atrophic retinal pigment epithelium changes surrounding the tumor (P =.048), and intraretinal cysts by OCT (P =.002). Optical coherence tomography is useful in distinguishing active subretinal fluid from chronic retinal changes overlying a choroidal melanocytic tumor. Optical coherence tomography findings may have predictive value in identifying tumors that are likely to grow and require treatment