1,819 research outputs found

    First observation of the decay Bs0→K*0K*0

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    The first observation of the decay B0s→K∗0K∗0 is reported using 35 pb−1 of data collected by LHCb in proton–proton collisions at a centre-of-mass energy of 7 TeV. A total of 49.8±7.5 B0s→(K+π−)(K−π+) events are observed within ±50 MeV/c2 of the B0s mass and 746 MeV/c2 < mKπ < 1046 MeV/c2, mostly coming from a resonant B0s→K∗0K∗0 signal. The branching fraction and the CP-averaged K∗0 longitudinal polarization fraction are measured to be B(B0s→K∗0K∗0)=(2.81±0.46(stat.)±0.45(syst.)±0.34(fs/ fd))×10−5 and fL =0.31±0.12(stat.)±0.04(syst.)

    Measurement of the effective B0s→K+K− lifetime

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    A measurement of the effective lifetime is presented using approximately 37 pb−1 of data collected by LHCb during 2010. This quantity can be used to put constraints on contributions from processes beyond the Standard Model in the meson system and is determined by two complementary approaches as τKK=1.440±0.096 (stat)±0.008 (syst)±0.003 (model) ps

    Measurement of the cross-section ratio σ(χc2)/σ(χc1) for prompt χc production at √s=7 TeV

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    The prompt production of the charmonium χc1 and χc2 mesons has been studied in proton–proton collisions at the Large Hadron Collider at a centre-of-mass energy of . The χc mesons are identified through their decays χc→J/ψγ with J/ψ→μ+μ− using 36 pb−1 of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for the two χc spin states, σ(χc2)/σ(χc1), has been determined as a function of the J/ψ transverse momentum, , in the range from 2 to 15 GeV/c. The results are in agreement with the next-to-leading order non-relativistic QCD model at high and lie consistently above the pure leading-order colour-singlet prediction

    Measurement of the B0–B0 oscillation frequency &#916;md with the decays B0→D−π+ and B0→ J/ψK∗0

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    The B 0 –B 0 oscillation frequency &#916;md is measured by the LHCb experiment using a dataset corresponding to an integrated luminosity of 1.0 fb−1 of proton–proton collisions at √ s = 7 TeV, and is found to be &#916;md =0.5156±0.0051 (stat.)±0.0033 (syst.) ps−1 . The measurement is based on results from analyses of the decays B 0 → D −π + (D − → K +π −π −) and B 0 → J/ψK ∗0 (J/ψ →μ +μ −,K ∗0 → K +π −) and their charge conjugated modes

    Prompt charm production in pp collisions at &#8730;<span style="text-decoration:overline">s</span>=7 TeV

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    Charm production at the LHC in pp collisions at s√=7 TeV is studied with the LHCb detector. The decays D0→K−π+, D+→K−π+π+, D⁎+→D0(K−π+)π+, D+s→ϕ(K−K+)π+, Λ+c→pK−π+, and their charge conjugates are analysed in a data set corresponding to an integrated luminosity of 15 nb−1. Differential cross-sections dσ/dpT are measured for prompt production of the five charmed hadron species in bins of transverse momentum and rapidity in the region 0&#60;pT&#60;8 GeV/c and 2.0&#60;y&#60;4.5. Theoretical predictions are compared to the measured differential cross-sections. The integrated cross-sections of the charm hadrons are computed in the above pT-y range, and their ratios are reported. A combination of the five integrated cross-section measurements gives σ(cc¯)pT&#60;8 GeV/c,2.0&#60;y&#60;4.5=1419±12(stat)±116(syst)±65(frag) μb, where the uncertainties are statistical, systematic, and due to the fragmentation functions

    Observations of Bºs→ψ(2S)η and Bº(s)→ψ(2S)π+π- decays

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    First observations of the B0s →ψ(2S)η, B0 →ψ(2S)π + π − and B0s →ψ(2S)π + π − decays are made using a dataset corresponding to an integrated luminosity of 1.0 fb−1 collected by the LHCb experiment in proton–proton collisions at a centre-of-mass energy of √ s = 7 TeV. The ratios of the branching fractions of each of the ψ(2S) modes with respect to the corresponding J/ψ decays are B(B0s →ψ(2S)η) ÷ B(B0s →J/ψη) = 0.83± 0.14 (stat)±0.12 (syst) ±0.02 (B), ; B(B0→ψ(2S)π + π − ) ÷ B(B0→J/ψπ + π − ) = 0.56± 0.07 (stat)±0.05 (syst)± 0.01 (B), ; B(B0s →ψ(2S)π + π − ) ÷ B(B0s →J/ψπ + π − ) = 0.34± 0.04 (stat)±0.03 (syst)± 0.01 (B), where the third uncertainty corresponds to the uncertainties of the dilepton branching fractions of the J/ψ and ψ(2S) meson decays

    Measurement of the polarization amplitudes and triple product asymmetries in the B0s → Φ Φ decay

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    &lt;p&gt;Using 1.0 fb−1 of pp collision data collected at a centre-of-mass energy of s√=7 TeV with the LHCb detector, measurements of the polarization amplitudes, strong phase difference and triple product asymmetries in the B0s→ϕϕ decay mode are presented. The measured values are&lt;/p&gt; &lt;p&gt;|A0|2=0.365±0.022(stat)±0.012(syst),|A⊥|2=0.291±0.024(stat)±0.010(syst),cos(δ∥)=−0.844±0.068(stat)±0.029(syst),AU=−0.055±0.036(stat)±0.018(syst),AV=0.010±0.036(stat)±0.018(syst).&lt;/p&gt

    Observation of J/ψ-pair production in pp collisions at √s=7 TeV

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    The production of J/ψ pairs in proton–proton collisions at a centre-of-mass energy of 7 TeV has been observed using an integrated luminosity of 37.5 pb−1 collected with the LHCb detector. The production cross-section for pairs with both J/ψ in the rapidity range 2 < yJ/ψ < 4.5 and transverse momentum pJ/ψ T <10 GeV/c is σJ/ψJ/ψ =5.1±1.0±1.1 nb, where the first uncertainty is statistical and the second systematic

    Measurement of the effective B_s^0 -> J/ψ K_S^0 lifetime

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    This paper reports the first measurement of the effective B_s^0 -> J/{\psi} K_S^0 lifetime and an updated measurement of its time-integrated branching fraction. Both measurements are performed with a data sample, corresponding to an integrated luminosity of 1.0 fb^{-1} of pp collisions, recorded by the LHCb experiment in 2011 at a centre-of-mass energy of 7 TeV. The results are: tau_J/{\psi}K_S^0 = 1.75 +/- 0.12 (stat) +/- 0.07 (syst) and BR(B_s^0 -> J/{\psi} K_S^0) = (1.97 +/- 0.23) X 10^{-5}. For the latter measurement, the uncertainty includes both statistical and systematic sources

    Measurement of the CP violating phase φs in Bs0→J/f0(980)

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    Measurement of mixing-induced CP violation in decays is of prime importance in probing new physics. So far only the channel has been used. Here we report on a measurement using an LHCb data sample of 0.41 fb−1, in the CP odd eigenstate J/ψf0(980), where f0(980)→π+π−. A time-dependent fit of the data with the lifetime and the difference in widths of the heavy and light eigenstates constrained to the values obtained from yields a value of the CP violating phase of −0.44±0.44±0.02 rad, consistent with the Standard Model expectation
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