Observation of two new Ξb−\Xi_b^- baryon resonances

Two structures are observed close to the kinematic threshold in the $\Xi_b^0 \pi^-$ mass spectrum in a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb$^{-1}$ recorded by the LHCb experiment. In the quark model, two baryonic resonances with quark content $bds$ are expected in this mass region: the spin-parity $J^P = \frac{1}{2}^+$ and $J^P=\frac{3}{2}^+$ states, denoted $\Xi_b^{\prime -}$ and $\Xi_b^{*-}$. Interpreting the structures as these resonances, we measure the mass differences and the width of the heavier state to be $m(\Xi_b^{\prime -}) - m(\Xi_b^0) - m(\pi^{-}) = 3.653 \pm 0.018 \pm 0.006$ MeV$/c^2$, $m(\Xi_b^{*-}) - m(\Xi_b^0) - m(\pi^{-}) = 23.96 \pm 0.12 \pm 0.06$ MeV$/c^2$, $\Gamma(\Xi_b^{*-}) = 1.65 \pm 0.31 \pm 0.10$ MeV, where the first and second uncertainties are statistical and systematic, respectively. The width of the lighter state is consistent with zero, and we place an upper limit of $\Gamma(\Xi_b^{\prime -}) < 0.08$ MeV at 95% confidence level. Relative production rates of these states are also reported.Comment: 17 pages, 2 figure

Precision measurement of CPCP violation in Bs0→J/ψK+K−B_s^0 \to J/\psi K^+K^- decays

The time-dependent $CP$ asymmetry in $B_s^0 \to J/\psi K^+K^-$ decays is measured using $pp$ collision data, corresponding to an integrated luminosity of $3.0$fb$^{-1}$, collected with the LHCb detector at centre-of-mass energies of $7$ and $8$TeV. In a sample of 96 000 $B_s^0 \to J/\psi K^+K^-$ decays, the $CP$-violating phase $\phi_s$ is measured, as well as the decay widths $\Gamma_{L}$ and $\Gamma_{H}$ of the light and heavy mass eigenstates of the $B_s^0-\bar{B}_s^0$ system. The values obtained are $\phi_s = -0.058 \pm 0.049 \pm 0.006$ rad, $\Gamma_s \equiv (\Gamma_{L}+\Gamma_{H})/2 = 0.6603 \pm 0.0027 \pm 0.0015$ps$^{-1}$, and$\Delta\Gamma_s \equiv \Gamma_{L} - \Gamma_{H} = 0.0805 \pm 0.0091 \pm 0.0032$ps$^{-1}$, where the first uncertainty is statistical and the second systematic. These are the most precise single measurements of those quantities to date. A combined analysis with $B_s^{0} \to J/\psi \pi^+\pi^-$ decays gives $\phi_s = -0.010 \pm 0.039$rad. All measurements are in agreement with the Standard Model predictions. For the first time the phase $\phi_s$ is measured independently for each polarisation state of the $K^+K^-$ system and shows no evidence for polarisation dependence.Comment: 6 figure

Mother-to-child transmission of human immunodeficiency virus in aten years period

<p>Abstract</p> <p>Objectives</p> <p>to evaluate mother-to-child transmission (MTCT) rates and related factors in HIV-infected pregnant women from a tertiary hospital between 2000 and 2009.</p> <p>Subjects and method</p> <p>cohort of 452 HIV-infected pregnant women and their newborns. Data was collected from recorded files and undiagnosed children were enrolled for investigation. Statistical analysis: qui-square test, Fisher exact test, Student <it>t </it>test, Mann-Whitney test, ANOVA, risk ratio and confidence intervals.</p> <p>Results</p> <p>MTCT occurred in 3.74%. The study population displayed a mean age of 27 years; 86.5% were found to have acquired HIV through sexual contact; 55% were aware of the diagnosis prior to the pregnancy; 62% were not using HAART. Mean CD4 cell-count was 474 cells/ml and 70.3% had undetectable viral loads in the third trimester. HAART included nevirapine in 35% of cases and protease inhibitors in 55%; Zidovudine monotherapy was used in 7.3%. Mean gestational age at delivery was 37.2 weeks and in 92% by caesarian section; 97.2% received intravenous zidovudine. Use of AZT to newborn occurred in 100% of them. Factors identified as associated to MTCT were: low CD4 cell counts, elevated viral loads, maternal AIDS, shorter periods receiving HAART, other conditions (anemia, IUGR (intra uterine growth restriction), oligohydramnium), coinfecctions (CMV and toxoplasmosis) and the occurrence of labor. Use of HAART for longer periods, caesarian and oral zidovudine for the newborns were associated with a decreased risk. Poor adhesion to treatment was present in 13 of the 15 cases of transmission; in 7, coinfecctions were diagnosed (CMV and toxoplasmosis).</p> <p>Conclusion</p> <p>Use of HAART and caesarian delivery are protective factors for mother-to-child transmission of HIV. Maternal coinfecctions and other conditions were risk factors for MTCT.</p

Measurement of the inelastic pp cross-section at a centre-of-mass energy of √s = 7 TeV

The cross-section for inelastic proton-proton collisions, with at least one prompt long-lived charged particle of transverse momentum pT &gt; 0.2GeV/c in the pseudorapidity range 2.0 &#62; η &#62; 4.5, is measured by the LHCb experiment at a centre-ofmass energy of √ s = 7 TeV. The cross-section in this kinematic range is determined to be σ acc inel = 55.0 ± 2.4 mb with an experimental uncertainty that is dominated by systematic contributions. Extrapolation to the full phase space, using Pythia 6, yields σinel = 66.9 ± 2.9 ± 4.4 mb, where the first uncertainty is experimental and the second is due to the extrapolation

Study of η − η′ mixing from measurement of B (s) 0 → J/ψη(′) decay rates

A study of B and B0 s meson decays into J/ψη and J/ψη0 final states is performed using a data set of proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, collected by the LCHb experiment and corresponding to 3.0 fb−1 of integrated luminosity. The decay B0 → J/ψη0 is observed for the first time. The following ratios of branching fractions are measured: B(B0 → J/ψη0 ) B(B0 s → J/ψη0) = (2.28 ± 0.65 (stat) ± 0.10 (syst) ± 0.13 (fs/fd)) × 10−2 , B(B0 → J/ψη) B(B0 s → J/ψη) = (1.85 ± 0.61 (stat) ± 0.09 (syst) ± 0.11 (fs/fd)) × 10−2 , where the third uncertainty is related to the present knowledge of fs/fd, the ratio between the probabilities for a b quark to form a B0 s or a B0 meson. The branching fraction ratios are used to determine the parameters of η−η 0 meson mixing. In addition, the first evidence for the decay B0 s → ψ(2S)η 0 is reported, and the relative branching fraction is measured, B(B0 s → ψ(2S)η 0 ) B(B0 s → J/ψη0) = (38.7 ± 9.0 (stat) ± 1.3 (syst) ± 0.9(B)) × 10−2 , where the third uncertainty is due to the limited knowledge of the branching fractions of J/ψ and ψ(2S) mesons