Showing papers by "Gianni Penso published in 2018"

Physics case for an LHCb Upgrade II - Opportunities in flavour physics, and beyond, in the HL-LHC era

Abstract: The LHCb Upgrade II will fully exploit the flavour-physics opportunities of the HL-LHC, and study additional physics topics that take advantage of the forward acceptance of the LHCb spectrometer. The LHCb Upgrade I will begin operation in 2020. Consolidation will occur, and modest enhancements of the Upgrade I detector will be installed, in Long Shutdown 3 of the LHC (2025) and these are discussed here. The main Upgrade II detector will be installed in long shutdown 4 of the LHC (2030) and will build on the strengths of the current LHCb experiment and the Upgrade I. It will operate at a luminosity up to $ 2 \times 10^{34} \rm cm^{-2}s^{-1}$, ten times that of the Upgrade I detector. New detector components will improve the intrinsic performance of the experiment in certain key areas. An Expression Of Interest proposing Upgrade II was submitted in February 2017. The physics case for the Upgrade II is presented here in more depth. $CP$-violating phases will be measured with precisions unattainable at any other envisaged facility. The experiment will probe $b\to s \ell^+\ell^-$ and $b\to d \ell^+\ell^-$ transitions in both muon and electron decays in modes not accessible at Upgrade I. Minimal flavour violation will be tested with a precision measurement of the ratio of $B(B^0\to\mu^+\mu^-)/B(B_s^0\to \mu^+\mu^-)$. Probing charm $CP$ violation at the $10^{-5}$ level may result in its long sought discovery. Major advances in hadron spectroscopy will be possible, which will be powerful probes of low energy QCD. Upgrade II potentially will have the highest sensitivity of all the LHC experiments on the Higgs to charm-quark couplings. Generically, the new physics mass scale probed, for fixed couplings, will almost double compared with the pre-HL-LHC era; this extended reach for flavour physics is similar to that which would be achieved by the HE-LHC proposal for the energy frontier.

Measurement of the Ratio of the B0→D*−τ+ντ and B0→D*−μ+νμ Branching Fractions Using Three-Prong τ -Lepton Decays

Abstract: The ratio of branching fractions R(D^{*-})≡B(B^{0}→D^{*-}τ^{+}ν_{τ})/B(B^{0}→D^{*-}μ^{+}ν_{μ}) is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb^{-1}. For the first time, R(D^{*-}) is determined using the τ-lepton decays with three charged pions in the final state. The B^{0}→D^{*-}τ^{+}ν_{τ} yield is normalized to that of the B^{0}→D^{*-}π^{+}π^{-}π^{+} mode, providing a measurement of B(B^{0}→D^{*-}τ^{+}ν_{τ})/B(B^{0}→D^{*-}π^{+}π^{-}π^{+})=1.97±0.13±0.18, where the first uncertainty is statistical and the second systematic. The value of B(B^{0}→D^{*-}τ^{+}ν_{τ})=(1.42±0.094±0.129±0.054)% is obtained, where the third uncertainty is due to the limited knowledge of the branching fraction of the normalization mode. Using the well-measured branching fraction of the B^{0}→D^{*-}μ^{+}ν_{μ} decay, a value of R(D^{*-})=0.291±0.019±0.026±0.013 is established, where the third uncertainty is due to the limited knowledge of the branching fractions of the normalization and B^{0}→D^{*-}μ^{+}ν_{μ} modes. This measurement is in agreement with the standard model prediction and with previous results.

Measurement of the Ratio of Branching Fractions B (Bc+ →j /ψτ+ντ)/ B (Bc+ →j /ψμ+νμ)

Abstract: A measurement is reported of the ratio of branching fractions R(J/ψ)=B(B_{c}^{+}→J/ψτ^{+}ν_{τ})/B(B_{c}^{+}→J/ψμ^{+}ν_{μ}), where the τ^{+} lepton is identified in the decay mode τ^{+}→μ^{+}ν_{μ}ν[over ¯]_{τ}. This analysis uses a sample of proton-proton collision data corresponding to 3.0 fb^{-1} of integrated luminosity recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. A signal is found for the decay B_{c}^{+}→J/ψτ^{+}ν_{τ} at a significance of 3 standard deviations corrected for systematic uncertainty, and the ratio of the branching fractions is measured to be R(J/ψ)=0.71±0.17(stat)±0.18(syst). This result lies within 2 standard deviations above the range of central values currently predicted by the standard model.

Observation of the decay $\Lambda^0_b\rightarrow\psi(2S)p\pi^-$

Abstract: The Cabibbo-suppressed decay Λ$_{b}^{0}$ → ψ(2S)pπ$^{−}$ is observed for the first time using a data sample collected by the LHCb experiment in proton-proton collisions corresponding to 1.0, 2.0 and 1.9 fb$^{−1}$ of integrated luminosity at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The ψ(2S) mesons are reconstructed in the μ$^{+}$μ$^{−}$ final state. The branching fraction with respect to that of the Λ$_{b}^{0}$ → ψ(2S)pK$^{−}$ decay mode is measured to be

First measurement of the $CP$-violating phase $\phi_s^{d\overline{d}}$ in $B_s^0\to(K^+\pi^-)(K^-\pi^+)$ decays

Abstract: A flavour-tagged decay-time-dependent amplitude analysis of B$_{s}^{0}$ → (K$^{+}$π$^{−}$)(K$^{−}$π$^{+}$) decays is presented in the K$^{±}$π$^{∓}$ mass range from 750 to 1600MeV/c$^{2}$. The analysis uses pp collision data collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3.0 fb$^{−1}$. Several quasi-two-body decay modes are considered, corresponding to K$^{±}$π$^{∓}$ combinations with spin 0, 1 and 2, which are dominated by the K$_{0}^{*}$ (800)$^{0}$ and K$_{0}^{*}$ (1430)$^{0}$, the K$^{*}$(892)$^{0}$ and the K$_{2}^{*}$ (1430)$^{0}$ resonances, respectively. The longitudinal polarisation fraction for the $ {B}_s^0\to {K}^{\ast }(892){}^{\circ}{\overline{K}}^{\ast }{(892)}^0 $ decay is measured as f$_{L}$ = 0.208 ± 0.032 ± 0.046, where the first uncertainty is statistical and the second is systematic. The first measurement of the mixing-induced CP-violating phase, $ {\phi}_s^{d\overline{d}} $ , in $ b\to d\overline{d}s $ transitions is performed, yielding a value of $ {\phi}_s^{d\overline{d}}=-0.10\pm 0.13\left(\mathrm{stat}\right)\pm 0.14 $ (syst) rad.

Angular moments of the decay Lambda(0)(b) -> Lambda mu(+)mu(-) at low hadronic recoil

Abstract: An analysis of the angular distribution of the decay Λ$_{b}^{0}$ → Λμ$^{+}$μ$^{−}$ is presented, using data collected with the LHCb detector between 2011 and 2016 and corresponding to an integrated luminosity of approximately 5 fb$^{−1}$. Angular observables are determined using a moment analysis of the angular distribution at low hadronic recoil, corresponding to the dimuon invariant mass squared range 15 < q$^{2}$ < 20 GeV$^{2}$/c$^{4}$. The full basis of observables is measured for the first time. The lepton-side, hadron-side and combined forward-backward asymmetries of the decay are determined to be $ \begin{array}{l}{A}_{\mathrm{FB}}^{\ell }=-0.39\pm 0.04\left(\mathrm{stat}\right)\pm 0.01\left(\mathrm{syst}\right),\hfill \\ {}{A}_{\mathrm{FB}}^h=-0.30\pm 0.05\left(\mathrm{stat}\right)\pm 0.02\left(\mathrm{syst}\right),\hfill \\ {}{A}_{\mathrm{FB}}^{\ell h}=+0.25\pm 0.04\left(\mathrm{stat}\right)\pm 0.01\left(\mathrm{syst}\right).\hfill \end{array} $

arXiv : Measurement of $\Upsilon$ production in $pp$ collisions at $\sqrt{s}$= 13 TeV

Abstract: A bstractThe production cross-sections of ϒ(1S), ϒ(2S) and ϒ(3S) mesons in proton-proton collisions at s=13$$ \\sqrt{s}=13 $$ TeV are measured with a data sample corresponding to an integrated luminosity of 277 ± 11 pb−1 recorded by the LHCb experiment in 2015. The ϒ mesons are reconstructed in the decay mode ϒ → μ+μ−. The differential production cross-sections times the dimuon branching fractions are measured as a function of the ϒ transverse momentum, pT, and rapidity, y, over the range 0 < pT< 30 GeV/c and 2.0 < y < 4.5. The ratios of the cross-sections with respect to the LHCb measurement at s=8$$ \\sqrt{s}=8 $$ TeV are also determined. The measurements are compared with theoretical predictions based on NRQCD.

Evidence for an ηc(1S)π−resonance in B0→ηc(1S)K+π−decays

Abstract: A Dalitz plot analysis of ${{B} ^0} \!\rightarrow \eta _c(1S) {{K} ^+} {{\pi } ^-} $ decays is performed using data samples of pp collisions collected with the $\text{ LHCb } $ detector at centre-of-mass energies of ${\sqrt{s}} =7,~8$ and $13{\,\mathrm {Te}\mathrm {V}} $ , corresponding to a total integrated luminosity of $4.7 \,\text{ fb }^{-1} $ . A satisfactory description of the data is obtained when including a contribution representing an exotic $\eta _c(1S) \pi ^-$ resonant state. The significance of this exotic resonance is more than three standard deviations, while its mass and width are $4096 \pm 20~^{+18-22} \,\mathrm {Me}\mathrm {V} $ and $152 \pm 58~^{+60-35} \,\mathrm {Me}\mathrm {V} $ , respectively. The spin-parity assignments $J^P=0^+$ and $J^{P}=1^-$ are both consistent with the data. In addition, the first measurement of the ${{B} ^0} \!\rightarrow \eta _c(1S) {{K} ^+} {{\pi } ^-} $ branching fraction is performed and gives $\begin{aligned} \displaystyle \mathcal {B}({{B} ^0} \!\rightarrow \eta _c(1S) {{K} ^+} {{\pi } ^-} ) = (5.73 \pm 0.24 \pm 0.13 \pm 0.66) \times 10^{-4}, \end{aligned}$ where the first uncertainty is statistical, the second systematic, and the third is due to limited knowledge of external branching fractions.

Measurement of CP asymmetries in two-body B(s)0 -meson decays to charged pions and kaons

Abstract: The time-dependent CP asymmetries in B0→π+π− and B0s→K+K− decays are measured using a data sample of p p collisions corresponding to an integrated luminosity of 3.0 fb−1, collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV. The same data sample is used to measure the time-integrated CP asymmetries in B0→K+π− and B0s→π+K− decays. The results are Cπ+π−=−0.34±0.06±0.01, Sπ+π−=−0.63±0.05±0.01, CK+K−=0.20±0.06±0.02, SK+K−=0.18±0.06±0.02, AΔΓK+K−=−0.79±0.07±0.10, AB0CP=−0.084±0.004±0.003, and AB0sCP=0.213±0.015±0.007, where the first uncertainties are statistical and the second systematic. Evidence for CP violation is found in the B0s→K+K− decay for the first time.

Search for CP violation using triple product asymmetries in Lambda(0)(b) -> pK(-) pi(+) pi(-), Lambda(0)(b) -> pK(-) K+ K- and Xi(0)(b) -> pK(-) K- pi(+) decays

Abstract: A search for CP and P violation using triple-product asymmetries is performed with Λ$_{b}^{0}$ → pK$^{−}$π$^{+}$π$^{−}$, Λ$_{b}^{0}$ → pK$^{−}$K$^{+}$K$^{−}$ and Ξ$_{b}^{0}$ → pK$^{−}$K$^{−}$π$^{+}$ decays. The data sample corresponds to integrated luminosities of 1.0 fb$^{−1}$ and 2.0 fb$^{−1}$, recorded with the LHCb detector at centre-of-mass energies of 7 TeV and 8 TeV, respectively. The CP - and P - violating asymmetries are measured both integrating over all phase space and in specific phase-space regions. No significant deviation from CP or P symmetry is found. The first observation of Λ$_{b}^{0}$ → pK$^{−}$χ$_{c0}$(1P)(→π$^{+}$π$^{−}$, K$^{+}$K$^{−}$) decay is also reported.

Search for the lepton-flavour violating decays B ( s) 0 → e±μ∓

Abstract: A search for the lepton-flavour violating decays Bs0 → e±μ∓ and B0 → e±μ∓ is performed based on a sample of proton-proton collision data corresponding to an integrated luminosity of 3 fb−1, collected with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The observed yields are consistent with the background-only hypothesis. Upper limits on the branching fraction of the Bs0 → e±μ∓ decays are evaluated both in the hypotheses of an amplitude completely dominated by the heavy eigenstate and by the light eigenstate. The results are @@ℬ(Bs0→e)<6.3(5.4)×10−9 and @@ℬ(Bs0→e)<7.2(6.0)×10−9 at 95% (90%) confidence level, respectively. The upper limit on the branching fraction of the B0 → e±μ∓ decay is also evaluated, obtaining @@ℬ(B0→e)<1.3(1.0)×10−9 at 95% (90%) confidence level. These are the strongest limits on these decays to date.[Figure not available: see fulltext.].

Evidence for the decay $ {B}_S^0\to {\overline{K}}^{\ast 0}{\mu}^{+}{\mu}^{-}

Abstract: A search for the decay $$ {B}_S^0\to {\overline{K}}^{\ast 0}{\mu}^{+}{\mu}^{-} $$ is presented using data sets corresponding to 1.0, 2.0 and 1.6 fb−1 of integrated luminosity collected during pp collisions with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, respectively. An excess is found over the background-only hypothesis with a significance of 3.4 standard deviations. The branching fraction of the $$ {B}_S^0\to {\overline{K}}^{\ast 0}{\mu}^{+}{\mu}^{-} $$ decay is determined to be $$ \mathrm{\mathcal{B}}\left({B}_s^0\to {\overline{K}}^{\ast 0}{\mu}^{+}{\mu}^{-}\right)=\left[2.9\pm 1.0\left(\mathrm{stat}\right)\pm 0.2\left(\mathrm{syst}\right)\pm 0.3\left(\mathrm{norm}\right)\right]\times {10}^{-8} $$ , where the first and second uncertainties are statistical and systematic, respectively. The third uncertainty is due to limited knowledge of external parameters used to normalise the branching fraction measurement.

Study of ϒ production in pPb collisions at√ sNN = 8.16 TeV

Abstract: The production of ϒ(nS) mesons (n = 1, 2, 3) in pPb and Pbp collisions at a centre-of-mass energy per nucleon pair $$ \sqrt{s_{\mathrm{NN}}}=8.16 $$ TeV is measured by the LHCb experiment, using a data sample corresponding to an integrated luminosity of 31.8 nb−1. The ϒ(nS) mesons are reconstructed through their decays into two opposite-sign muons. The measurements comprise the differential production cross-sections of the ϒ(1S) and ϒ(2S) states, their forward-to-backward ratios and nuclear modification factors. The measurements are performed as a function of the transverse momentum pT and rapidity in the nucleon-nucleon centre-of-mass frame y* of the ϒ(nS) states, in the kinematic range pT < 25 GeV/c and 1.5 < y* < 4.0 (−5.0 < y* < −2.5) for pPb (Pbp) collisions. In addition, production cross-sections for ϒ(3S) are measured integrated over phase space and the production ratios between all three ϒ(nS) states are determined. Suppression for bottomonium in proton-lead collisions is observed, which is particularly visible in the ratios. The results are compared to theoretical models.

Erratum to: Differential branching fraction and angular analysis of Λ b 0 → Λμ + μ − decays

Abstract: The angular distribution of the dimuon system of the decays.

Studies of the resonance structure in $D^{0} \to K^\mp \pi^\pm \pi^\pm \pi^\mp$ decays

Abstract: Amplitude models are constructed to describe the resonance structure of ${D^{0}\to K^{-}\pi^{+}\pi^{+}\pi^{-}}$ and ${D^{0} \to K^{+}\pi^{-}\pi^{-}\pi^{+}}$ decays using $pp$ collision data collected at centre-of-mass energies of 7 and 8 TeV with the LHCb experiment, corresponding to an integrated luminosity of $3.0\mathrm{fb}^{-1}$. The largest contributions to both decay amplitudes are found to come from axial resonances, with decay modes $D^{0} \to a_1(1260)^{+} K^{-}$ and $D^{0} \to K_1(1270/1400)^{+} \pi^{-}$ being prominent in ${D^{0}\to K^{-}\pi^{+}\pi^{+}\pi^{-}}$ and $D^{0}\to K^{+}\pi^{-}\pi^{-}\pi^{+}$, respectively. Precise measurements of the lineshape parameters and couplings of the $a_1(1260)^{+}$, $K_1(1270)^{-}$ and $K(1460)^{-}$ resonances are made, and a quasi model-independent study of the $K(1460)^{-}$ resonance is performed. The coherence factor of the decays is calculated from the amplitude models to be $R_{K3\pi} = 0.459\pm 0.010\,(\mathrm{stat}) \pm 0.012\,(\mathrm{syst}) \pm 0.020\,(\mathrm{model})$, which is consistent with direct measurements. These models will be useful in future measurements of the unitary-triangle angle $\gamma$ and studies of charm mixing and $C\!P$ violation.

Amplitude analysis of the decay $\overline{B}^0 \to K_{S}^0 \pi^+ \pi^-$ and first observation of the CP asymmetry in $\overline{B}^0 \to K^{*}(892)^- \pi^+$ : arXiv

Abstract: The time-integrated untagged Dalitz plot of the three-body hadronic charmless decay B[over ¯]^{0}→K_{S}^{0}π^{+}π^{-} is studied using a pp collision data sample recorded with the LHCb detector, corresponding to an integrated luminosity of 3.0 fb^{-1}. The decay amplitude is described with an isobar model. Relative contributions of the isobar amplitudes to the B[over ¯]^{0}→K_{S}^{0}π^{+}π^{-} decay branching fraction and CP asymmetries of the flavor-specific amplitudes are measured. The CP asymmetry between the conjugate B[over ¯]^{0}→K^{*}(892)^{-}π^{+} and B^{0}→K^{*}(892)^{+}π^{-} decay rates is determined to be -0.308±0.062.

Observation of B-s(0) -> (D)over-bar*(0)phi and search for B-0 -> (D)over-bar(0)phi decays

Abstract: The first observation of the Bs0→D¯*0ϕ decay is reported, with a significance of more than seven standard deviations, from an analysis of pp collision data corresponding to an integrated luminosity of 3 fb-1, collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV. The branching fraction is measured relative to that of the topologically similar decay B0→D¯0π+π- and is found to be B(Bs0→D¯*0ϕ)=(3.7±0.5±0.3±0.2)×10-5, where the first uncertainty is statistical, the second systematic, and the third from the branching fraction of the B0→D¯0π+π- decay. The fraction of longitudinal polarization in this decay is measured to be fL=(73±15±4)%. The most precise determination of the branching fraction for the Bs0→D¯0ϕ decay is also obtained, B(Bs0→D¯0ϕ)=(3.0±0.3±0.2±0.2)×10-5. An upper limit, B(B0→D¯0ϕ)<2.0 (2.3)×10-6 at 90% (95%) confidence level is set. A constraint on the ω-ϕ mixing angle δ is set at |δ|<5.2° (5.5°) at 90% (95%) confidence level.

Measurements of the branching fractions of Λ c + → pπ − π +, Λ c + → pK−K+, and Λ c + → pπ −K+

Abstract: The ratios of the branching fractions of the decays Λ + → pπ−π+, Λ + → pK−K+, and Λ + → pπ−K+ with respect to the Cabibbo-favoured Λ + → pK−π+ decay are measured using proton-proton collision data collected with the LHCb experiment at a 7 TeV centre-of-mass energy and corresponding to an integrated luminosity of 1.0 fb−1: $$ \begin{array}{l}\frac{\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{\pi}^{-}{\pi}^{+}\right)}{\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{K}^{-}{\pi}^{+}\right)}=\left(7.44\pm 0.08\pm 0.18\right)\%,\hfill \\ {}\frac{\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{K}^{-}{K}^{+}\right)}{\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{K}^{-}{\pi}^{+}\right)}=\left(1.70\pm 0.03\pm 0.03\right)\%\hfill \\ {}\frac{\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{\pi}^{-}{K}^{+}\right)}{\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{K}^{-}{\pi}^{+}\right)}=\left(0.165\pm 0.015\pm 0.005\right)\%,\hfill \end{array} $$ where the uncertainties are statistical and systematic, respectively. These results are the most precise measurements of these quantities to date. When multiplied by the world-average value for $$ \mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{K}^{-}{\pi}^{+}\right) $$ , the corresponding branching fractions are $$ \begin{array}{l}\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{\pi}^{-}{\pi}^{+}\right)=\left(4.72\pm 0.05\pm 0.11\pm 0.25\right)\times {10}^{-3},\hfill \\ {}\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{K}^{-}{K}^{+}\right)=\left(1.08\pm 0.02\pm 0.02\pm 0.06\right)\times {10}^{-3},\hfill \\ {}\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{\pi}^{-}{K}^{+}\right)=\left(1.04\pm 0.09\pm 0.03\pm 0.05\right)\times {10}^{-4},\hfill \end{array} $$ where the final uncertainty is due to $$ \mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{K}^{-}{\pi}^{+}\right) $$ .

Measurement of forward top pair production in the dilepton channel in pp collisions at √s=13 TeV

Abstract: Forward top quark pair production is studied in pp collisions in the μeb final state using a data sample corresponding to an integrated luminosity of 1.93 fb$^{−1}$ collected with the LHCb experiment at a centre-of-mass energy of 13 TeV. The cross-section is measured in a fiducial region where both leptons have a transverse momentum greater than 20 GeV and a pseudorapidity between 2.0 and 4.5. The quadrature sum of the azimuthal separation and the difference in pseudorapidities, denoted ΔR, between the two leptons must be larger than 0.1. The b-jet axis is required to be separated from both leptons by a ΔR of 0.5, and to have a transverse momentum in excess of 20 GeV and a pseudorapidity between 2.2 and 4.2. The cross-section is measured to be $ {\sigma}_{t\overline{t}}=126\pm 19\left(\mathrm{stat}\right)\pm 16\left(\mathrm{syst}\right)\pm 5\left(\mathrm{lumi}\right)\mathrm{f}\mathrm{b} $ where the first uncertainty is statistical, the second is systematic, and the third is due to the luminosity determination. The measurement is compatible with the Standard Model prediction.

A measurement of the CP asymmetry difference between Λc+ → pK−K+ and pπ−π+ decays

Abstract: The difference between the CP asymmetries in the decays Λ$_{c}^{+}$ → pK$^{−}$K$^{+}$ and Λ$_{c}^{+}$ → pπ$^{−}$π$^{+}$ is presented. Proton-proton collision data taken at centre-of-mass energies of 7 and 8 TeV collected by the LHCb detector in 2011 and 2012 are used, corresponding to an integrated luminosity of 3 fb$^{−1}$. The Λ$_{c}^{+}$ candidates are reconstructed as part of the Λ$_{b}^{0}$ → Λ$_{c}^{+}$ μ$^{−}$X decay chain. In order to maximize the cancellation of production and detection asymmetries in the difference, the final-state kinematic distributions of the two samples are aligned by applying phase-space-dependent weights to the Λ$_{c}^{+}$ → pπ$^{−}$π$^{+}$ sample. This alters the definition of the integrated CP asymmetry to A$_{CP}^{wgt}$ (pπ$^{−}$π$^{+}$). Both samples are corrected for reconstruction and selection efficiencies across the five-dimensional Λ$_{c}^{+}$ decay phase space. The difference in CP asymmetries is found to be

Observation of the decay B-s(0) -> (D)over-bar(0)phi

Abstract: First observation of the decay B-s(0) -> (D) over bar (0)phi is reported using pp collision data, corresponding to an integrated luminosity of 1.0 fb(-1), collected by the LHCb experiment at a centre-of-mass energy of 7 TeV. The significance of the signal is 6.5 standard deviations. The branching fraction is measured relative to that of the decay B-S(0) -> (D) over bar (0)phi to be beta B-S(0) -> (D) over bar (0)phi/beta B-S(0) -> (D) over bar (0)(K) over bar*(0) = 0.069 +/- 0.013 (stat) +/- 0.007 (syst). The first measurement of the ratio of branching fractions for the decays beta B-S(0) -> (D) over bar (0)(K) over bar*(0) and beta B-S(0) -> (D) over bar (0)(K) over bar*(0) is found to be beta B-S(0) -> (D) over bar (0)(K) over bar*(0/)beta B-S(0) -> (D) over bar (0)(K) over bar*(0=7.8) +/- 0.7(stat) +/- 0.3 (syst) +/- 0.6 (f(s)/f(d)) where the last uncertainty is due to the ratio of the B(s)(0)and B-0 fragmentation fractions. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved.

Studies of the resonance structure in $D^{0} \rightarrow K^\mp \pi ^\pm \pi ^\pm \pi ^\mp $ decays

Abstract: Amplitude models are constructed to describe the resonance structure of ${D^{0}\rightarrow K^{-}\pi ^{+}\pi ^{+}\pi ^{-}}$ and ${D^{0} \rightarrow K^{+}\pi ^{-}\pi ^{-}\pi ^{+}}$ decays using pp collision data collected at centre-of-mass energies of 7 and 8 TeV with the LHCb experiment, corresponding to an integrated luminosity of 3.0 $fb^{-1}$ . The largest contributions to both decay amplitudes are found to come from axial resonances, with decay modes $D^{0} \rightarrow a_1(1260)^{+} K^{-}$ and $D^{0} \rightarrow K_1(1270/1400)^{+} \pi ^{-}$ being prominent in ${D^{0}\rightarrow K^{-}\pi ^{+}\pi ^{+}\pi ^{-}}$ and $D^{0}\rightarrow K^{+}\pi ^{-}\pi ^{-}\pi ^{+}$ , respectively. Precise measurements of the lineshape parameters and couplings of the $a_1(1260)^{+}$ , $K_1(1270)^{-}$ and $K(1460)^{-}$ resonances are made, and a quasi model-independent study of the $K(1460)^{-}$ resonance is performed. The coherence factor of the decays is calculated from the amplitude models to be $R_{K3\pi } = 0.459\pm 0.010\,(\mathrm {stat}) \pm 0.012\,(\mathrm {syst}) \pm 0.020\,(\mathrm {model})$ , which is consistent with direct measurements. These models will be useful in future measurements of the unitary-triangle angle $\gamma $ and studies of charm mixing and $C\!P$ violation.

First observation of B + → Ds+ K + K − decays and a search for B + → Ds+ ϕ decays

Abstract: A search for B+ -> D-s(+) K+ K- decays is performed using pp collision data corresponding to an integrated luminosity of 48 fb(-1), collected at centre-of-mass energies of 7, 8 and 13 TeV with the LHCb experiment A significant signal is observed for the first time and the branching fraction is determined to be B(B+ -> D-s(+) K+ K-) = (71 +/- 05 +/- 06 +/- 07) x 10(-6), where the first uncertainty is statistical, the second systematic and the third due to the uncertainty on the branching fraction of the normalisation mode B+ -> D-s(+)(D) over bar (0) A search is also performed for the pure annihilation decay B+ -> D-s(+)(D) over bar (0) No significant signal is observed and a limit of B(B+ -> D-s(+) phi) < 49 x 10(-7) (42 x 10(-7)) is set on the branching fraction at 95% (90%) confidence level

Measurement of D s ± production asymmetry in pp collisions at √{s}=7 and 8 TeV

Abstract: The inclusive D$_{s}^{±}$ production asymmetry is measured in pp collisions collected by the LHCb experiment at centre-of-mass energies of $ \sqrt{s}=7 $ and 8 TeV. Promptly produced D$_{s}^{±}$ mesons are used, which decay as D$_{s}^{±}$ → ϕπ$^{±}$, with ϕ → K$^{+}$K$^{−}$. The measurement is performed in bins of transverse momentum, p$_{T}$, and rapidity, y, covering the range 2.5 < p$_{T}$ < 25.0 GeV/c and 2.0 < y < 4.5. No kinematic dependence is observed. Evidence of nonzero D$_{s}^{±}$ production asymmetry is found with a significance of 3.3 standard deviations.

Measurement of the time-integrated $CP$ asymmetry in $D^0 \rightarrow K^0_S K^0_S$ decays

Abstract: A measurement of the time-integrated $CP$ asymmetry in $D^0\rightarrow K^0_S K^0_S$ decays is reported. The data correspond to an integrated luminosity of about $2$ fb$^{-1}$ collected in 2015-2016 by the LHCb collaboration in $pp$ collisions at a centre-of-mass energy of $13$ TeV. The $D^0$ candidate is required to originate from a $D^{\ast +} \rightarrow D^0 \pi^+$ decay, allowing the determination of the flavour of the $D^0$ meson using the pion charge. The $D^0 \rightarrow K^{+}K^{-}$ decay, which has a well measured $CP$ asymmetry, is used as a calibration channel. The $CP$ asymmetry for $D^0\rightarrow K^0_S K^0_S$ is measured to be \begin{equation*} \mathcal{A}^{CP}(D^0\rightarrow K^0_S K^0_S) = (4.3\pm 3.4\pm 1.0)\%, \end{equation*} where the first uncertainty is statistical and the second is systematic. This result is combined with the previous LHCb measurement at lower centre-of-mass energies to obtain \begin{equation*} \mathcal{A}^{CP}(D^0\rightarrow K^0_S K^0_S) = (2.3\pm 2.8\pm 0.9)\%. \end{equation*}

Measurement of branching fractions of charmless four-body Λb0 and Ξb0 decays

Abstract: A search for charmless four-body decays of Λ$_{b}^{0}$ and Ξ$_{b}^{0}$ baryons with a proton and three charged mesons (either kaons or pions) in the final state is performed. The data sample used was recorded in 2011 and 2012 with the LHCb experiment and corresponds to an integrated luminosity of 3 fb$^{−1}$. Six decay modes are observed, among which Λ$_{b}^{0}$ → pK$^{−}$π$^{+}$π$^{−}$, Λ$_{b}^{0}$ → pK$^{−}$K$^{+}$K$^{−}$, Ξ$_{b}^{0}$ → pK$^{−}$π$^{+}$π$^{−}$ and Ξ$_{b}^{0}$ → pK$^{−}$π$^{+}$K$^{−}$ are established for the first time. Their branching fractions (including the ratio of hadronisation fractions in the case of the Ξ$_{b}^{0}$ baryon) are determined relative to the Λ$_{b}^{0}$ → Λ$_{c}^{+}$ π$^{−}$ decay.