52 research outputs found

    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

    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.)

    Measurements of the Lambda_b0 -> J/psi Lambda decay amplitudes and the Lambda_b0 polarisation in pp collisions at sqrt(s) = 7 TeV

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    An angular analysis of View the Λb0→J/ψΛ decays is performed using a data sample corresponding to 1.0 fb−11.0 fb−1 collected in pp collisions at s=7 TeV with the LHCb detector at the LHC. A parity violating asymmetry parameter characterising the View the Λb0→J/ψΛ decay of 0.05±0.17±0.070.05±0.17±0.07 and a View the Λb0 transverse production polarisation of 0.06±0.07±0.020.06±0.07±0.02 are measured, where the first uncertainty is statistical and the second systematic

    Measurement of the ratio of prompt χ c to J / ψ production in pp collisions at √s = 7 TeV

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    The prompt production of charmonium χ c and J / ψ states is studied in proton-proton collisions at a centre-of-mass energy of √s = 7 TeV at the Large Hadron Collider. The χ c and J / ψ mesons are identified through their decays χ c → J / ψ γ and 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 χ c and J / ψ, σ (χ c → J / ψ γ) / σ (J / ψ), is determined as a function of the J / ψ transverse momentum in the range 2 < p T J / ψ < 15 GeV / c. The results are in excellent agreement with next-to-leading order non-relativistic expectations and show a significant discrepancy compared with the colour singlet model prediction at leading order, especially in the low p T J / ψ region

    Measurement of the CKM angle gamma from a combination of B->Dh analyses

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    A combination of three LHCb measurements of the CKM angle gamma is presented. The decays B->DK and B->Dpi are used, where D denotes an admixture of D0 and D0-bar mesons, decaying into K+K-, pi+pi-, K+-pi-+, K+-pi-+pi+-pi-+, KSpi+pi-, or KSK+K- final states. All measurements use a dataset corresponding to 1.0 fb-1 of integrated luminosity. Combining results from B->DK decays alone a best-fit value of gamma = 72.0 deg is found, and confidence intervals are set gamma in [56.4,86.7] deg at 68% CL, gamma in [42.6,99.6] deg at 95% CL. The best-fit value of gamma found from a combination of results from B->Dpi decays alone, is gamma = 18.9 deg, and the confidence intervals gamma in [7.4,99.2] deg or [167.9,176.4] deg at 68% CL, are set, without constraint at 95% CL. The combination of results from B->DK and B->Dpi decays gives a best-fit value of gamma = 72.6 deg and the confidence intervals gamma in [55.4,82.3] deg at 68% CL, gamma in [40.2,92.7] deg at 95% CL are set. All values are expressed modulo 180 deg, and are obtained taking into account the effect of D0-D0bar mixing

    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 inclusive φ cross-section in pp collisions at √s=7 TeV

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    The cross-section for inclusive φ meson production in pp collisions at a centre-of-mass energy of √s = 7 TeV has been measured with the LHCb detector at the Large Hadron Collider. The differential cross-section is measured as a function of the φ transverse momentum pT and rapidity y in the region 0.6< pT <5.0 GeV/c and 2.44< y <4.06. The cross-section for inclusive φ production in this kinematic range is σ(pp→φX)=1758±19(stat) +43−14(syst)±182(scale) μb, where the first systematic uncertainty depends on the pT and y region and the second is related to the overall scale. Predictions based on the Pythia 6.4 generator underestimate the cross-section

    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

    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

    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
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