Publications (804)837.13 Total impact
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ABSTRACT: Associated production of bottomonia and open charm hadrons in $pp$ collisions at $\sqrt{s}=7$ and $8$TeV is observed using data corresponding to an integrated luminosity of 3$fb^{1}$ accumulated with the LHCb detector. The observation of five combinations, $\Upsilon(1S)D^0$, $\Upsilon(2S)D^0$, $\Upsilon(1S)D^+$, $\Upsilon(2S)D^+$ and $\Upsilon(1S)D^+_{s}$, is reported. Production crosssections are measured for $\Upsilon(1S)D^0$ and $\Upsilon(1S)D^+$ pairs in the forward region. The measured crosssections and the differential distributions indicate the dominance of double parton scattering as the main production mechanism. This allows a precise measurement of the effective crosssection for double parton scattering.  [Show abstract] [Hide abstract]
ABSTRACT: A search for the rare decay of a $B^{0}$ or $B^{0}_{s}$ meson into the final state $J/\psi\gamma$ is performed, using data collected by the LHCb experiment in $pp$ collisions at $\sqrt{s}=7$ and $8$ TeV, corresponding to an integrated luminosity of 3 fb$^{1}$. The observed number of signal candidates is consistent with a backgroundonly hypothesis. Branching fraction values larger than $1.7\times 10^{6}$ for the $B^{0}\to J/\psi\gamma$ decay mode are excluded at 90% confidence level. For the $B^{0}_{s}\to J/\psi\gamma$ decay mode, branching fraction values larger than $7.4\times 10^{6}$ are excluded at 90% confidence level; this is the first branching fraction limit for this decay.  [Show abstract] [Hide abstract]
ABSTRACT: Using a $pp$ collision data sample corresponding to an integrated luminosity of 3.0~fb$^{1}$, collected by the LHCb detector, we present the first search for the strangenesschanging weak decay $\Xi_b^\to\Lambda_b^0\pi^$. No $b$ hadron decay of this type has been seen before. A signal for this decay, corresponding to a significance of 3.2 standard deviations, is reported. The relative rate is measured to be ${{f_{\Xi_b^}}\over{f_{\Lambda_b^0}}}{\cal{B}}(\Xi_b^\to\Lambda_b^0\pi^) = (5.7\pm1.8^{+0.8}_{0.9})\times10^{4}$, where $f_{\Xi_b^}$ and $f_{\Lambda_b^0}$ are the $b\to\Xi_b^$ and $b\to\Lambda_b^0$ fragmentation fractions, and ${\cal{B}}(\Xi_b^\to\Lambda_b^0\pi^)$ is the branching fraction. Assuming $f_{\Xi_b^}/f_{\Lambda_b^0}$ is bounded between 0.1 and 0.3, the branching fraction ${\cal{B}}(\Xi_b^\to\Lambda_b^0\pi^)$ would lie in the range from $(0.57\pm0.21)\%$ to $(0.19\pm0.07)\%$.  [Show abstract] [Hide abstract]
ABSTRACT: The decay $B^0\to \psi(2S) K^+\pi^$ is analyzed using $\rm 3~fb^{1}$ of $pp$ collision data collected with the LHCb detector. A modelindependent description of the $\psi(2S) \pi$ mass spectrum is obtained, using as input the $K\pi$ mass spectrum and angular distribution derived directly from data, without requiring a theoretical description of resonance shapes or their interference. The hypothesis that the $\psi(2S)\pi$ mass spectrum can be described in terms of $K\pi$ reflections alone is rejected with more than 8$\sigma$ significance. This provides confirmation, in a modelindependent way, of the need for an additional resonant component in the mass region of the $Z(4430)^$ exotic state.  [Show abstract] [Hide abstract]
ABSTRACT: The first modelindependent measurement of the charm mixing parameters in the decay $D^0 \to K_S \pi^+ \pi^$ is reported, using a sample of $pp$ collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 1.0 fb$^{1}$ at a centreofmass energy of 7 TeV. The measured values are \begin{eqnarray*} x &=& (+0.86 \pm 0.53 \pm 0.17) \times 10^{2}, \\ y &=& (+0.03 \pm 0.46 \pm 0.13) \times 10^{2}, \end{eqnarray*} where the first uncertainties are statistical and include small contributions due to the external input for the strong phase measured by the CLEO collaboration, and the second uncertainties are systematic. The results are consistent with the current world averages.  [Show abstract] [Hide abstract]
ABSTRACT: Production crosssections of prompt charm mesons are measured with the first data from $pp$ collisions at the LHC at a centreofmass energy of $13\,\mathrm{TeV}$. The data sample corresponds to an integrated luminosity of $4.98 \pm 0.19\,\mathrm{pb}^{1}$ collected by the LHCb experiment. The production crosssections of $D^{0}$, $D^{+}$, $D_{s}^{+}$, and $D^{*+}$ mesons are measured in bins of charm meson transverse momentum, $p_{\mathrm{T}}$, and rapidity, $y$, and cover the range $0 < p_{\mathrm{T}} < 15\,\mathrm{GeV}/c$ and $2.0 < y < 4.5$. The ratios of the integrated crosssections between charm mesons agree with previously measured fragmentation fractions. The inclusive $c\overline{c}$ crosssection within the range of $0 < p_{\mathrm{T}} < 8\,\mathrm{GeV}/c$ is found to be \[ \sigma(pp \to c\overline{c}X) = 2940 \pm 3 \pm 180 \pm 160\,\mu\mathrm{b} \] where the uncertainties are due to statistical, systematic and fragmentation fraction uncertainties, respectively.  [Show abstract] [Hide abstract]
ABSTRACT: The forwardbackward charge asymmetry for the process $q\bar{q} \rightarrow Z/\gamma^{\ast} \rightarrow \mu^{+}\mu^{}$ is measured as a function of the invariant mass of the dimuon system. Measurements are performed using proton proton collision data collected with the LHCb detector at $\sqrt{s} = 7$ and 8\tev, corresponding to integrated luminosities of $1$fb$^{1}$ and $2$fb$^{1}$ respectively. Within the Standard Model the results constrain the effective electroweak mixing angle to be $$sin^{2}\theta_{W}^{eff} = 0.23142 \pm 0.00073 \pm 0.00052 \pm 0.00056 $$ where the first uncertainty is statistical, the second systematic and the third theoretical. This result is in agreement with the current world average, and is one of the most precise determinations at hadron colliders to date.  [Show abstract] [Hide abstract]
ABSTRACT: Amplitude models are applied to studies of resonance structure in $D^0\to K^0_S K^ \pi^+$ and $D^0\to K^0_S K^+ \pi^$ decays using $pp$ collision data corresponding to an integrated luminosity of $3.0\,\mathrm{fb}^{1}$ collected by the LHCb experiment. Relative magnitude and phase information is determined, and coherence factors and related observables are computed for both the whole phase space and a restricted region of $100\,\mathrm{MeV/}c^2$ around the $K^{*}(892)^{\pm}$ resonance. Two formulations for the $K\pi$ $S$wave are used, both of which give a good description of the data. The ratio of branching fractions $\mathcal{B}(D^0\to K^0_S K^+ \pi^)/\mathcal{B}(D^0\to K^0_S K^ \pi^+)$ is measured to be $0.655\pm0.004\,(\textrm{stat})\pm0.006\,(\textrm{syst})$ over the full phase space and $0.370\pm0.003\, (\textrm{stat})\pm0.012\,(\textrm{syst})$ in the restricted region. A search for $CP$ violation is performed using the amplitude models and no significant effect is found. Predictions from $SU(3)$ flavor symmetry for $K^{*}(892)K$ amplitudes of different charges are compared with the amplitude model results.  [Show abstract] [Hide abstract]
ABSTRACT: The branching fraction ratio R(D*) ≡ B([bar over B][superscript 0] → D[superscript *+]τ[superscript ][bar over ν][subscript τ])/B([bar over B][superscript 0] → D[superscript *+]μ[superscript ][bar over ν][subscript μ]) is measured using a sample of protonproton collision data corresponding to 3.0 fb[superscript 1] of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode τ[superscript ] → μ[superscript ][bar over ν][subscript μ]ν[subscript τ]. The semitauonic decay is sensitive to contributions from nonstandardmodel particles that preferentially couple to the third generation of fermions, in particular, Higgslike charged scalars. A multidimensional fit to kinematic distributions of the candidate [bar over B][superscript 0] decays gives R(D*) = 0.336 ± 0.027(stat) ± 0.030(syst). This result, which is the first measurement of this quantity at a hadron collider, is 2.1 standard deviations larger than the value expected from lepton universality in the standard model.  [Show abstract] [Hide abstract]
ABSTRACT: The production of $\Upsilon$ mesons in $pp$ collisions at $\sqrt=7$ and $8\,\mathrm{TeV}$ is studied with the LHCb detector using data samples corresponding to an integrated luminosity of $1\,\mathrm{fb}^{1}$ and $2\,\mathrm{fb}^{1}$ respectively. The production crosssections and ratios of crosssections are measured as functions of the meson transverse momentum $p_T$ and rapidity $y$, for $p_T<30\,\mathrm{GeV}/c$} and $2.0<y<4.5$. 
Article: Measurement of forward $J/\psi$ production crosssections in $pp$ collisions at $\sqrt{s}=13$ TeV
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ABSTRACT: The production of $J/\psi$ mesons in protonproton collisions at a centreofmass energy of $\sqrt{s}=13$ TeV is studied with the LHCb detector. Crosssection measurements are performed as a function of the transverse momentum $p_\mathrm{T}$ and the rapidity $y$ of the $J/\psi$ meson in the region $p_\mathrm{T}<14 \mathrm{GeV}/c$ and $2.0<y<4.5$, for both prompt $J/\psi$ mesons and $J/\psi$ mesons from $b$hadron decays. The production crosssections integrated over the kinematic coverage are $15.30\pm 0.03\pm 0.86$ $\mu$b for prompt $J/\psi$ and $2.34\pm 0.01\pm 0.13$ $\mu$b for $J/\psi$ from $b$hadron decays, assuming zero polarization of the $J/\psi$ meson. The first uncertainties are statistical and the second systematic. The crosssection reported for $J/\psi$ mesons from $b$hadron decays is used to extrapolate to a total $b\bar{b}$ crosssection. The ratios of the crosssections with respect to $\sqrt{s}=8$ TeV are also determined.Journal of High Energy Physics 09/2015; 2015(10). DOI:10.1007/JHEP10(2015)172 · 6.11 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The first measurement of ${C\!P}$ asymmetries in the decay ${B_s^0\to J/\psi \overline{K}^{*}(892)^{0}}$ and an updated measurement of its branching fraction and polarisation fractions are presented. The results are obtained using data corresponding to an integrated luminosity of $3.0\,fb^{1}$ of protonproton collisions recorded with the LHCb detector at centreofmass energies of $7$ and $8\,\mathrm{TeV}$. Together with constraints from ${B^0\to J/\psi \rho^0}$, the results are used to constrain additional contributions due to penguin diagrams in the ${C\!P}$violating phase ${{\phi}_{s}}$, measured through ${B_s^0}$ decays to charmonium.  [Show abstract] [Hide abstract]
ABSTRACT: The product of the $\Lambda_b^0$ ($\overline{B}^0$) differential production crosssection and the branching fraction of the decay $\Lambda_b^0\rightarrow J/\psi pK^$ ($\overline{B}^0\rightarrow J/\psi\overline{K}^*(892)^0$) is measured as a function of the beauty hadron transverse momentum, $p_{\rm T}$, and rapidity, $y$. The kinematic region of the measurements is $p_{\rm T}<20~{\rm GeV}/c$ and $2.0<y<4.5$. The measurements use a data sample corresponding to an integrated luminosity of $3~{\rm fb}^{1}$ collected by the LHCb detector in $pp$ collisions at centreofmass energies $\sqrt{s}=7~{\rm TeV}$ in 2011 and $\sqrt{s}=8~{\rm TeV}$ in 2012. Based on previous LHCb results of the fragmentation fraction ratio, $f_{\Lambda_B^0}/f_d$, the branching fraction of the decay $\Lambda_b^0\rightarrow J/\psi pK^$ is measured to be \begin{equation*} \mathcal{B}(\Lambda_b^0\rightarrow J/\psi pK^)= (3.04\pm0.04\pm0.06\pm0.33^{+0.43}_{0.27})\times10^{4}, \end{equation*} where the first uncertainty is statistical, the second is systematic, the third is due to the uncertainty on the branching fraction of the decay $\overline{B}^0\rightarrow J/\psi\overline{K}^*(892)^0$, and the fourth is due to the knowledge of $f_{\Lambda_b^0}/f_d$. The sum of the asymmetries in the production and decay between $\Lambda_b^0$ and $\overline{\Lambda}_b^0$ is also measured as a function of $p_{\rm T}$ and $y$. The previously published branching fraction of $\Lambda_b^0\rightarrow J/\psi p\pi^$, relative to that of $\Lambda_b^0\rightarrow J/\psi pK^$, is updated. The branching fractions of $\Lambda_b^0\rightarrow P_c^+(\rightarrow J/\psi p)K^$ are determined.  Journal of High Energy Physics 09/2015; 2015(9). DOI:10.1007/JHEP09(2015)006 · 6.11 Impact Factor
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ABSTRACT: The differential branching fraction with respect to the dimuon invariant mass squared, and the $C\!P$ asymmetry of the $B^\pm\to\pi^\pm\mu^+\mu^$ decay are measured for the first time. The CKM matrix elements $V_{td}$ and $V_{ts}$, and the ratio $V_{td}/V_{ts}$ are determined. The analysis is performed using protonproton collision data corresponding to an integrated luminosity of 3.0 fb$^{1}$, collected by the LHCb experiment at centreofmass energies of 7 and 8 TeV. The total branching fraction and $C\!P$ asymmetry of $B^\pm\to\pi^\pm\mu^+\mu^$ decays are measured to be \begin{eqnarray} \mathcal{B}(B^\pm\to\pi^\pm\mu^+\mu^) &=& (1.83 \pm 0.24 \pm 0.05) \times 10^{8}\,\,\,\mathrm{and} \nonumber\\ \mathcal{A}_{C\!P}(B^\pm\to\pi^\pm\mu^+\mu^) &=& 0.11 \pm 0.12 \pm 0.01\,, \nonumber \end{eqnarray} where the first uncertainties are statistical and the second are systematic. These are the most precise measurements of these observables to date, and they are compatible with the predictions of the Standard Model. 
Article: Observation of J/ψp Resonances Consistent with Pentaquark States in Λ_{b}^{0}→J/ψK^{}p Decays
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ABSTRACT: Observations of exotic structures in the J/ψp channel, which we refer to as charmoniumpentaquark states, in Λ_{b}^{0}→J/ψK^{}p decays are presented. The data sample corresponds to an integrated luminosity of 3 fb^{1} acquired with the LHCb detector from 7 and 8 TeV pp collisions. An amplitude analysis of the threebody final state reproduces the twobody mass and angular distributions. To obtain a satisfactory fit of the structures seen in the J/ψp mass spectrum, it is necessary to include two BreitWigner amplitudes that each describe a resonant state. The significance of each of these resonances is more than 9 standard deviations. One has a mass of 4380±8±29 MeV and a width of 205±18±86 MeV, while the second is narrower, with a mass of 4449.8±1.7±2.5 MeV and a width of 39±5±19 MeV. The preferred J^{P} assignments are of opposite parity, with one state having spin 3/2 and the other 5/2.Physical Review Letters 08/2015; 115(7):072001. · 7.51 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The timeintegrated $CP$ asymmetry in the decay $D^0 \to K^0_S K^0_S$ is measured using $3 fb^{1}$ of protonproton collision data collected by the LHCb experiment at centreofmass energies of 7 and 8 TeV. The flavour of the $D^0$ meson is determined by use of the decay $D^{*+} \to D^0 \pi^+$ and its charge conjugate mode. The result is \[ {\cal A}_{CP} = 0.029 \pm 0.052 \pm 0.022, \] where the first uncertainty is statistical and the second systematic. The result is consistent with Standard Model expectations and improves the uncertainty with respect to the only previous measurement of this quantity by more than a factor of three.  [Show abstract] [Hide abstract]
ABSTRACT: Observations of exotic structures in the J/ψp channel, which we refer to as charmoniumpentaquark states, in Λ[0 over b] → J/ψK[superscript ]p decays are presented. The data sample corresponds to an integrated luminosity of 3 fb[superscript 1] acquired with the LHCb detector from 7 and 8 TeV pp collisions. An amplitude analysis of the threebody final state reproduces the twobody mass and angular distributions. To obtain a satisfactory fit of the structures seen in the J/ψp mass spectrum, it is necessary to include two BreitWigner amplitudes that each describe a resonant state. The significance of each of these resonances is more than 9 standard deviations. One has a mass of 4380 ± 8 ± 29 MeV and a width of 205 ± 18 ± 86 MeV, while the second is narrower, with a mass of 4449.8 ± 1.7 ± 2.5 MeV and a width of 39 ± 5 ± 19 MeV. The preferred J[superscript P] assignments are of opposite parity, with one state having spin 3/2 and the other 5/2.  [Show abstract] [Hide abstract]
ABSTRACT: A search is presented for hiddensector bosons, $\chi$, produced in the decay ${B^0\!\to K^*(892)^0\chi}$, with $K^*(892)^0\!\to K^{+}\pi^{}$ and $\chi\!\to\mu^+\mu^$. The search is performed using $pp$collision data corresponding to 3.0 fb$^{1}$ collected with the LHCb detector. No significant signal is observed in the accessible mass range $214 \leq m({\chi}) \leq 4350$ MeV, and upper limits are placed on the branching fraction product $\mathcal{B}(B^0\!\to K^*(892)^0\chi)\times\mathcal{B}(\chi\!\to\mu^+\mu^)$ as a function of the mass and lifetime of the $\chi$ boson. These limits are of the order of $10^{9}$ for $\chi$ lifetimes less than 100 ps over most of the $m(\chi)$ range, and place the most stringent constraints to date on many theories that predict the existence of additional lowmass bosons.  [Show abstract] [Hide abstract]
ABSTRACT: The first observation of the B_{s}^{0}→η^{'}η^{'} decay is reported. The study is based on a sample of protonproton collisions corresponding to 3.0 fb^{1} of integrated luminosity collected with the LHCb detector. The significance of the signal is 6.4 standard deviations. The branching fraction is measured to be [3.31±0.64(stat)±0.28(syst)±0.12(norm)]×10^{5}, where the third uncertainty comes from the B^{±}→η^{'}K^{±} branching fraction that is used as a normalization. In addition, the charge asymmetries of B^{±}→η^{'}K^{±} and B^{±}→ϕK^{±}, which are control channels, are measured to be (0.2±1.3)% and (+1.7±1.3)%, respectively. All results are consistent with theoretical expectations.Physical Review Letters 08/2015; 115(5):051801. · 7.51 Impact Factor
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2k  Citations  
837.13  Total Impact Points  
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Institutions

20022012

University of Valencia
 Atomic, Molecular and Nuclear Physics
Valenza, Valencia, Spain


20072009

University of Ljubljana
 Department of Physics
Ljubljana, Ljubljana, Slovenia 
Lancaster University
 Department of Physics
Lancaster, England, United Kingdom


2006

Università degli Studi di Trieste
 Department of Physics
Trst, Friuli Venezia Giulia, Italy
