Publications (840)339.39 Total impact
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ABSTRACT: A search for \CP violation in Cabibbosuppressed $D^{\pm}\rightarrow K^0_{\mathrm{S}} K^{\pm}$ and $D^{\pm}_{s}\rightarrow K^0_{\mathrm{S}} \pi^{\pm}$ decays is performed using $pp$ collision data, corresponding to an integrated luminosity of 3~fb$^{1}$, recorded by the LHCb experiment. The individual $CP$violating asymmetries are measured to be \begin{eqnarray*} \mathcal{A}_{CP}^{D^{\pm}\rightarrow K^0_{\mathrm{S}} K^{\pm}} & = & (+0.03 \pm 0.17 \pm 0.14) \% \mathcal{A}_{CP}^{D^{\pm}_{s}\rightarrow K^0_{\mathrm{S}} \pi^{\pm}} & = & (+0.38 \pm 0.46 \pm 0.17) \%, \end{eqnarray*} assuming that $CP$ violation in the Cabibbofavoured decays is negligible. A combination of the measured asymmetries for the four decay modes $D^{\pm}_{(s)}\rightarrow K^0_{\mathrm{S}} K^{\pm}$ and $D^{\pm}_{(s)}\rightarrow K^0_{\mathrm{S}} \pi^{\pm}$ gives the sum \[ \mathcal{A}_{CP}^{D^{\pm}\rightarrow K^0_{\mathrm{S}} K^{\pm}} + \mathcal{A}_{CP}^{D^{\pm}_{s}\rightarrow K^0_{\mathrm{S}} \pi^{\pm}} = (+0.41 \pm 0.49 \pm 0.26) \%. \] In all cases, the first uncertainties are statistical and the second systematic. The results represent the most precise measurements of these asymmetries to date and show no evidence for CP violation.06/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The first observation of the Cabibbosuppressed decay $\Lambda_b^0\rightarrow J/\psi p \pi^$ is reported using a data sample of protonproton collisions at 7 and 8 TeV, corresponding to an integrated luminosity of 3 $\rm fb^{1}$. A prominent signal is observed and the branching fraction relative to the decay mode $\Lambda_b^0\rightarrow J/\psi p K^$ is determined to be $$ \frac{{\cal B}(\Lambda_b^0\rightarrow J/\psi p \pi^)}{{\cal B}(\Lambda_b^0\rightarrow J/\psi p K^)}=0.0824\pm0.0025\:(\text{stat})\pm0.0042\:(\text{syst}). $$ A search for direct CP violation is performed. The difference in the CP asymmetries between these two decays is found to be $$ {\cal A}_{CP}(\Lambda_b^0\rightarrow J/\psi p \pi^){\cal A}_{CP}(\Lambda_b^0\rightarrow J/\psi p K^)=(+5.7\pm 2.3\:(\text{stat})\pm1.2\:(\text{syst}))\%, $$ which is compatible with CP symmetry at the $2.2\sigma$ level.06/2014;  [Show abstract] [Hide abstract]
ABSTRACT: Using a protonproton collision data sample corresponding to an integrated luminosity of 3 fb$^{1}$ collected by LHCb at centerofmass energies of 7 and 8 TeV, about 3800 $\Xi_b^0\to\Xi_c^+\pi^$, $\Xi_c^+\to pK^\pi^+$ signal decays are reconstructed. From this sample, the first measurement of the $\Xi_b^0$ baryon lifetime is made, relative to that of the $\Lambda_b^0$ baryon. The mass differences $M(\Xi_b^0)M(\Lambda_b^0)$ and $M(\Xi_c^+)M(\Lambda_c^+)$ are also measured with precision more than four times better than the current world averages. The resulting values are $\frac{\tau_{\Xi_b^0}}{\tau_{\Lambda_b^0}} = 1.006\pm0.018\pm0.010$, $M(\Xi_b^0)  M(\Lambda_b^0) = 172.44\pm0.39\pm0.17 MeV/c^2$, $M(\Xi_c^+)  M(\Lambda_c^+) = 181.51\pm0.14\pm0.10 MeV/c^2$, where the first uncertainty is statistical and the second is systematic. The relative rate of $\Xi_b^0$ to $\Lambda_b^0$ baryon production is measured to be $\frac{f_{\Xi_b^0}}{f_{\Lambda_b^0}}\frac{{\cal{B}}(\Xi_b^0\to\Xi_c^+\pi^)}{{\cal{B}}(\Lambda_b^0\to\Lambda_c^+\pi^)}\frac{{\cal{B}}(\Xi_c^+\to pK^\pi^+)}{{\cal{B}}(\Lambda_c^+\to pK^\pi^+)} = (1.88\pm0.04\pm0.03)\times10^{2}$, where the first factor is the ratio of fragmentation fractions, $b\to\Xi_b^0$ relative to $b\to\Lambda_b^0$. Relative production rates as functions of transverse momentum and pseudorapidity are also presented.05/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The kinematic dependences of the relative production rates, $f_{\Lambda_b^0}/f_d$, of $\Lambda_b^0$ baryons and $\bar{B}^0$ mesons are measured using $\Lambda_b^0 \rightarrow \Lambda_c^+ \pi^$ and $\bar{B}^0 \rightarrow D^+ \pi^$ decays. The measurements use protonproton collision data, corresponding to an integrated luminosity of 1 fb$^{1}$ at a centreofmass energy of 7 TeV, recorded in the forward region with the LHCb experiment. The relative production rates are observed to depend on the transverse momentum, $p_T$, and pseudorapidity, $\eta$, of the beauty hadron, in the studied kinematic region $1.5 < p_T < 40$ GeV/$c$ and $2 < \eta < 5$. Using a previous LHCb measurement of $f_{\Lambda_b^0}/f_d$ in semileptonic decays, the branching fraction $\mathcal{B}(\Lambda_b^0 \rightarrow \Lambda_c^+ \pi^) = \Big( 4.30 \pm 0.03 \,\, ^{+0.12}_{0.11} \pm 0.26 \pm 0.21 \Big) \times 10^{3}$ is obtained, where the first uncertainty is statistical, the second is systematic, the third is from the previous LHCb measurement of $f_{\Lambda_b^0}/f_d$ and the fourth is due to the $\bar{B}^0 \rightarrow D^+ \pi^$ branching fraction. This is the most precise measurement of a $\Lambda_b^0$ branching fraction to date.05/2014;  [Show abstract] [Hide abstract]
ABSTRACT: Production of $\Upsilon$ mesons in protonlead collisions at a nucleonnucleon centreofmass energy $\sqrt{s_{NN}}=5 \mathrm{TeV}$ is studied with the LHCb detector. The analysis is based on a data sample corresponding to an integrated luminosity of $1.6 \mathrm{nb}^{1}$. The $\Upsilon$ mesons of transverse momenta up to $15 \mathrm{GeV}/c$ are reconstructed in the dimuon decay mode. The rapidity coverage in the centreofmass system is $1.5<y<4.0$ (forward region) and $5.0<y<2.5$ (backward region). The forwardbackward production ratio and the nuclear modification factor for $\Upsilon(1S)$ mesons are determined. The data are compatible with the predictions for a suppression of $\Upsilon(1S)$ production with respect to protonproton collisions in the forward region, and an enhancement in the backward region. The suppression is found to be smaller than in the case of prompt $J/\psi$ mesons.05/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The mixinginduced CPviolating phase $\phi_s$ in ${B}^0_s$ and $\overline{B}^0_s$ decays is measured using the $J/\psi \pi^+\pi^$ final state in data, taken from 3\,fb$^{1}$ of integrated luminosity, collected with the LHCb detector in 7 and 8 TeV centreofmass $pp$ collisions at the LHC. A timedependent flavourtagged amplitude analysis, allowing for direct \CP violation, yields a value for the phase $\phi_s=70\pm 68\pm 8$\,mrad. This result is consistent with the Standard Model expectation and previous measurements.05/2014;  [Show abstract] [Hide abstract]
ABSTRACT: Decays of the form $B^{0}_{(s)}\rightarrow J/\psi K_{{\rm S}}^{0} h^+ h^{\left(\prime\right) }$ ($h^{(\prime)} = K, \pi$) are searched for in protonproton collision data corresponding to an integrated luminosity of $1.0 \, {\rm fb}^{1}$ recorded with the LHCb detector. The first observation of the $B^{0}_{s}\rightarrow J/\psi K_{{\rm S}}^{0} K^{\pm} \pi^{\mp}$ decay is reported, with significance in excess of 10 standard deviations. The $B^{0}\rightarrow J/\psi K_{{\rm S}}^{0} K^{+} K^{}$ decay is also observed for the first time. The branching fraction of $B^{0}\rightarrow J/\psi K_{{\rm S}}^{0} \pi^{+} \pi^{}$ is determined, to significantly better precision than previous measurements, using $B^0 \rightarrow J/\psi K_{{\rm S}}^{0}$ as a normalisation channel. Branching fractions and upper limits of the other $B^{0}_{(s)}\rightarrow J/\psi K_{{\rm S}}^{0} h^+ h^{\left(\prime\right) }$ modes are determined relative to that of the $B^{0}\rightarrow J/\psi K_{{\rm S}}^{0} \pi^{+} \pi^{}$ decay.05/2014; 
Article: Measurement of $CP$ asymmetry in $D^0 \rightarrow K^ K^+$ and $D^0 \rightarrow \pi^ \pi^+$ decays
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ABSTRACT: Timeintegrated $CP$ asymmetries in $D^0$ decays to the final states $K^ K^+$ and $\pi^ \pi^+$ are measured using protonproton collisions corresponding to $3\mathrm{\,fb}^{1}$ of integrated luminosity collected at centreofmass energies of $7\mathrm{\,Te\kern 0.1em V}$ and $8\mathrm{\,Te\kern 0.1em V}$. The $D^0$ mesons are produced in semileptonic $b$hadron decays, where the charge of the accompanying muon is used to determine the initial flavour of the charm meson. The difference in $CP$ asymmetries between the two final states is measured to be \begin{align} \Delta A_{CP} = A_{CP}(K^K^+)A_{CP}(\pi^\pi^+) = (+0.14 \pm 0.16\mathrm{\,(stat)} \pm 0.08\mathrm{\,(syst)})\% \ . \nonumber \end{align} A measurement of $A_{CP}(K^K^+)$ is obtained assuming negligible $CP$ violation in charm mixing and in Cabibbofavoured $D$ decays. It is found to be \begin{align} A_{CP}(K^K^+) = (0.06 \pm 0.15\mathrm{\,(stat)} \pm 0.10\mathrm{\,(syst)}) \% \ ,\nonumber \end{align} where the correlation coefficient between $\Delta A_{CP}$ and $A_{CP}(K^K^+)$ is $\rho=0.28$. By combining these results, the $CP$ asymmetry in the $D^0\rightarrow\pi^\pi^+$ channel is $A_{CP}(\pi^\pi^+)=(0.20\pm0.19\mathrm{\,(stat)}\pm0.10\mathrm{\,(syst)})\%$.05/2014;  [Show abstract] [Hide abstract]
ABSTRACT: Using a data sample of pp collisions corresponding to an integrated luminosity of $3~ \rm fb^{1}$, the $\Xi_b^$ and $\Omega_b^$ baryons are reconstructed in the $\Xi_b^ \rightarrow J/\psi \Xi^$ and $\Omega_b^ \rightarrow J/\psi \Omega^$ decay modes and their lifetimes measured to be $\tau (\Xi_b^) = 1.55\, ^{+0.10}_{0.09}~{\rm(stat)} \pm 0.03\,{\rm(syst)}$ ps, $\tau (\Omega_b^) = 1.54\, ^{+0.26}_{0.21}~{\rm(stat)} \pm 0.05\,{\rm(syst)}$ ps. These are the most precise determinations to date. Both measurements are in good agreement with previous experimental results and with theoretical predictions.05/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The resonant structure of the reaction $\overline{B}^0\rightarrow J/\psi \pi^+\pi^$ is studied using data from 3 fb$^{1}$ of integrated luminosity collected by the LHCb experiment, onethird at 7 Tev centerofmass energy and the remainder at 8 Tev. The invariant mass of the $\pi^+\pi^$ pair and three decay angular distributions are used to determine the fractions of the resonant and nonresonant components. Six interfering $\pi^+\pi^$ states: $\rho(770)$, $f_0(500)$, $f_2(1270)$, $\rho(1450)$, $\omega(782)$ and $\rho(1700)$ are required to give a good description of invariant mass spectra and decay angular distributions. The positive and negative CP fractions of each of the resonant final states are determined. The $f_0(980)$ meson is not seen and the upper limit on its presence, compared with the observed $f_0(500)$ rate, is inconsistent with a model of tetraquark substructure for these scalar mesons at the eight standard deviation level. In the $q\overline{q}$ model, the absolute value of the mixing angle between the $f_0(980)$ and the $f_0(500)$ scalar mesons is limited to be less than $17^{\circ}$ at 90% confidence level.04/2014;  [Show abstract] [Hide abstract]
ABSTRACT: Evidence for the decay mode $X(3872)\rightarrow\psi(2S)\gamma$ in $B^+\rightarrow X(3872)K^+$ decays is found with a significance of 4.4 standard deviations. The analysis is based on a data sample of protonproton collisions, corresponding to an integrated luminosity of 3fb$^{1}$ collected with the LHCb detector, at centreofmass energies of 7 and 8TeV. The ratio of the branching fraction of the $X(3872)\to\psi(2S)\gamma$ decay to that of the $X(3872)\rightarrow J/\psi \gamma$ decay is measured to be $$ \frac{Br(X(3872)\rightarrow\psi(2S)\gamma)}{Br(X(3872)\rightarrow J/\psi\gamma)} = 2.46\pm0.64\pm0.29, %\pm0.06,$$ where the first uncertainty is statistical and the second is systematic. The measured value agrees with expectations for a pure charmonium interpretation of the $X(3872)$ state and a mixture of charmonium and molecular interpretations. However, it does not support a pure $D\bar{D}^{*}$ molecular interpretation of the $X(3872)$state.04/2014;  [Show abstract] [Hide abstract]
ABSTRACT: Evidence is presented for the decay $B_c+\rightarrow J/\psi 3\pi^+2\pi^$ using protonproton collision data, corresponding to an integrated luminosity of 3fb$^{1}$, collected with the LHCb detector. A signal yield of $32\pm8$ decays is found with a significance of 4.5 standard deviations. The ratio of the branching fraction of the $B_c^+\rightarrow J/\psi 3\pi^+ 2\pi^$ decay to that of the $B_c^+ \rightarrow J/\psi \pi^+$ decay is measured to be $$ \frac{Br (B_c^+ \rightarrow J/\psi 3\pi^+2\pi^)}{Br (B_c^+ \rightarrow J/\psi \pi^+)} = 1.74\pm0.44\pm0.24, $$ where the first uncertainty is statistical and the second is systematic.04/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The angular distributions of the rare decays $B^+ \to K^+\mu^+\mu^$ and $B^0 \to K^0_{\rm\scriptscriptstyle S}\mu^+\mu^$ are studied with data corresponding to 3$~$fb$^{1}$ of integrated luminosity, collected in protonproton collisions at 7 and 8$~$TeV centreofmass energies with the LHCb detector. The angular distribution is described by two parameters, $F_{\rm H}$ and the forwardbackward asymmetry of the dimuon system $A_{\rm FB}$, which are determined in bins of the dimuon mass squared. The parameter $F_{\rm H}$ is a measure of the contribution from (pseudo)scalar and tensor amplitudes to the decay width. The measurements of $A_{\rm FB}$ and $F_{\rm H}$ reported here are the most precise to date and are compatible with predictions from the Standard Model.03/2014; 
Article: Differential branching fractions and isospin asymmetries of $B \to K^{(*)}\mu^{+}\mu^{}$ decays
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ABSTRACT: The isospin asymmetries of $B \to K\mu^+\mu^$ and $B \to K^{*}\mu^+\mu^$ decays and the partial branching fractions of the $B^0 \to K^0\mu^+\mu^$, $B^+ \to K^+\mu^+\mu^$ and $B^+ \to K^{*+}\mu^+\mu^$ decays are measured as functions of the dimuon mass squared, $q^2$. The data used correspond to an integrated luminosity of 3$~$fb$^{1}$ from protonproton collisions collected with the LHCb detector at centreofmass energies of 7$\,$TeV and 8$\,$TeV in 2011 and 2012, respectively. The isospin asymmetries are both consistent with the Standard Model expectations. The three measured branching fractions, while individually consistent, all favour lower values than their respective Standard Model predictions.03/2014;  [Show abstract] [Hide abstract]
ABSTRACT: First observations of the decays $\Lambda_b^0 \to \Lambda_c^+ D_{(s)}^$ are reported using data corresponding to an integrated luminosity of $3\,{\rm fb}^{1}$ collected at 7 and 8 TeV centerofmass energy in protonproton collisions with the LHCb detector. In addition, the most precise measurement of the branching fraction ${\mathcal{B}(B_s^0 \to D^+D_s^)}$ is made and a search is performed for the decays $B^0_{(s)} \to \Lambda_c^+ \Lambda_c^$. The results obtained are \begin{eqnarray*} \mathcal{B}(\Lambda_b^0 \to \Lambda_c^+ D^)/\mathcal{B}(\Lambda_b^0 \to \Lambda_c^+ D_{s}^) &=& 0.042 \pm 0.003({\rm stat}) \pm 0.003({\rm syst}), \left[\frac{\mathcal{B}(\Lambda_b^0 \to \Lambda_c^+ D_{s}^)}{\mathcal{B}({\kern 0.2em}\overline{\kern 0.2em B}_d^0 \to D^+D_s^)}\right]\big/\left[\frac{\mathcal{B}(\Lambda_b^0 \to \Lambda_c^+\pi^)}{\mathcal{B}({\kern 0.2em}\overline{\kern 0.2em B}_d^0 \to D^+\pi^)}\right] &=& 0.96 \pm 0.02({\rm stat}) \pm 0.06({\rm syst}), \mathcal{B}(B_s^0 \to D^+D_s^)/\mathcal{B}({\kern 0.2em}\overline{\kern 0.2em B}_d^0 \to D^+D_s^) &=& 0.038\pm0.004({\rm stat})\pm0.003({\rm syst}), \mathcal{B}({\kern 0.2em}\overline{\kern 0.2em B}^0 \to \Lambda_c^+ \Lambda_c^)/\mathcal{B}({\kern 0.2em}\overline{\kern 0.2em B}_d^0 \to D^+D_s^) & < & 0.0022\; [95\% \; {\rm C.L.}], \mathcal{B}(B^0_{s} \to \Lambda_c^+ \Lambda_c^)/\mathcal{B}(B_s^0 \to D^+D_s^) & < & 0.30\; [95\% \; {\rm C.L.}]. \end{eqnarray*} Measurement of the mass of the $\Lambda_b^0$ baryon relative to the $B^0$ meson gives ${M(\Lambda_b^0) M(B^0) = 339.72\pm 0.24({\rm stat}) \pm 0.18({\rm syst})}$ MeV$/c^2$. This result provides the most precise measurement of the mass of the $\Lambda_b^0$ baryon to date.03/2014;  [Show abstract] [Hide abstract]
ABSTRACT: An angular analysis of the decay $B^0 \to \phi K^*(892)^0$ is reported based on a $pp$ collision data sample, corresponding to an integrated luminosity of 1.0 fb$^{1}$, collected at a centreofmass energy of $\sqrt{s} = 7$ TeV with the LHCb detector. The Pwave amplitudes and phases are measured with a greater precision than by previous experiments, and confirm about equal amounts of longitudinal and transverse polarization. The Swave $K^+ \pi^$ and $K^+K^$ contributions are taken into account and found to be significant. A comparison of the $B^0 \to \phi K^*(892)^0$ and $\bar{B}^0 \to \phi \bar{K}^*(892)^0$ results shows no evidence for direct CP violation in the rate asymmetry, in the tripleproduct asymmetries or in the polarization amplitudes and phases.03/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The polarisation of prompt $\psi(2S)$ mesons is measured by performing an angular analysis of $\psi(2S)\rightarrow \mu^{+} \mu^{}$ decays using protonproton collision data, corresponding to an integrated luminosity of 1.0 fb$^{1}$, collected by the LHCb detector at a centreofmass energy of 7 TeV. The polarisation is measured in bins of transverse momentum $p_\mathrm{T}$ and rapidity $y$ in the kinematic region $3.5<p_\mathrm{T}<15$ GeV$/c$ and $2.0<y<4.5$, and is compared to theoretical models. No significant polarisation is observed.03/2014;  [Show abstract] [Hide abstract]
ABSTRACT: This Letter presents a study of the flavorchanging neutral current radiative $B^{\pm} \to K^{\pm}\pi^{\mp}\pi^{\pm}\gamma$ decays performed using data collected in protonproton collisions with the LHCb detector at $7$ and $8\,$TeV centerofmass energies. In this sample, corresponding to an integrated luminosity of $3\,\text{fb}^{1}$, nearly $14\,000$ signal events are reconstructed and selected, containing all possible intermediate resonances with a $K^{\pm}\pi^{\mp}\pi^{\pm}$ final state in the $[1.1, 1.9]\,$GeV/$c^{2}$ mass range. The distribution of the angle of the photon direction with respect to the plane defined by the finalstate hadrons in their rest frame is studied in intervals of $K^{\pm}\pi^{\mp}\pi^{\pm}$ mass and the asymmetry between the number of signal events found on each side of the plane is obtained. The first direct observation of the photon polarization in the $b \to s\gamma$ transition is reported with a significance of $5.2\,\sigma$.02/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The resonant structure of the decay $\overline{B}_s^0\to J/\psi\pi^+\pi^$ is studied using data corresponding to 3 fb$^{1}$ of integrated luminosity from $pp$ collisions by the LHC and collected by the LHCb detector. Five interfering $\pi^+\pi^$ states are required to describe the decay: $f_0(980),f_0(1500),f_0(1790),f_2(1270)$, and $f_2^{\prime}(1525)$. An alternative model including these states and a nonresonant $J/\psi \pi^+\pi^$ component also provides a good description of the data. Based on the different transversity components measured for the spin2 intermediate states, the final state is found to be compatible with being entirely $CP$odd. The $CP$even part is found to be $<2.3$% at 95% confidence level. The $f_0(500)$ state is not observed, allowing a limit to be set on the absolute value of the mixing angle with the $f_0(980)$ of $<7.7^{\circ}$ at 90% confidence level, consistent with a tetraquark interpretation of the $f_0(980)$ substructure.02/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The LHCb measurement of the lifetime ratio of the $\Lambda^0_b$ to the $\overline{B}^0$ meson is updated using data corresponding to an integrated luminosity of 3.0 fb$^{1}$ collected using 7 and 8 TeV centreofmass energy $pp$ collisions at the LHC. The decay modes used are $\overline{B}^0\to J/\psi p K^$ and $\overline{B}^0\to J/\psi \pi^+ K^$, where the $\pi^+K^$ mass is consistent with that of the $\overline{K}^{*0}(892)$ meson. The lifetime ratio is determined with unprecedented precision to be $0.974\pm0.006\pm0.004$, where the first uncertainty is statistical and the second systematic. This result is in agreement with original theoretical predictions based on the heavy quark expansion. Using the current world average of the $\overline{B}^0$ lifetime, the $\Lambda^0_b$ lifetime is found to be $1.479 \pm 0.009 \pm 0.010$ ps.02/2014;
Publication Stats
1k  Citations  
339.39  Total Impact Points  
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Institutions

2006–2013

Université de Savoie
Chambéry, RhôneAlpes, France
