Publications (436)1232.6 Total impact
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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.  [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.  [Show abstract] [Hide abstract]
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  [Show abstract] [Hide abstract]
ABSTRACT: The resonant substructures of B[superscript 0] → [bar over D][superscript 0]π[superscript +]π[superscript ] decays are studied with the Dalitz plot technique. In this study a data sample corresponding to an integrated luminosity of 3.0 fb[superscript 1] of pp collisions collected by the LHCb detector is used. The branching fraction of the B[superscript 0] → [bar over D][superscript 0]π[superscript +]π[superscript ] decay in the region m([bar over D][superscript 0]π[superscript ±]) > 2.1 GeV/c[superscript 2] is measured to be (8.46 ± 0.14 ± 0.29 ± 0.40) × 10[superscript 4], where the first uncertainty is statistical, the second is systematic and the last arises from the normalization channel B[superscript 0] → D[superscript *](2010)[superscript ]π[superscript +]. The π[superscript +]π[superscript ] Swave components are modeled with the isobar and Kmatrix formalisms. Results of the Dalitz plot analyses using both models are presented. A resonant structure at m([bar over D][superscript 0]π[superscript ]) ≈ 2.8 GeV/c[superscript 2] is confirmed and its spinparity is determined for the first time as J[superscript P] = 3[superscript ]. The branching fraction, mass and width of this structure are determined together with those of the D[* over 0](2400)[superscript ] and D[* over 2](2460)[superscript ] resonances. The branching fractions of other B[superscript 0] → [bar over D][superscript 0]h[superscript 0] decay components with h[superscript 0] → π[superscript +]π[superscript ] are also reported. Many of these branching fraction measurements are the most precise to date. The first observation of the decays B[superscript 0] → [bar over D][superscript 0]f[subscript 0](500), B[superscript 0] → [bar over D][superscript 0]f[subscript 0](980), B[superscript 0] → [bar over D][superscript 0][subscript p](1450), B[superscript 0] → D[* over 3](2760)[superscript ]π[superscript +] and the first evidence of B[superscript 0] → [bar over D][superscript 0]f[subscript 0](2020) are presented.  [Show abstract] [Hide abstract]
ABSTRACT: Using a dataset corresponding to an integrated luminosity of 3.0 fb$^{1}$ collected in $pp$ collisions at centreofmass energies of 7 and 8 TeV, the $B_s^0 \to \phi \phi$ branching fraction is measured to be \[ \mathcal{B}(B_s^0 \to \phi \phi) = ( 1.84 \pm 0.05 (\text{stat}) \pm 0.07 (\text{syst}) \pm 0.11 (f_s/f_d) \pm 0.12 (\text{norm}) ) \times 10^{5}, \] where $f_s/f_d$ represents the ratio of the $B_s^0$ to $B^0$ production crosssections, and the $B^0 \to \phi K^*(892)^0$ decay mode is used for normalization. This is the most precise measurement of this branching fraction to date, representing a factor five reduction in the statistical uncertainty compared with the previous best measurement. A search for the decay $B^0 \to \phi \phi$ is also made. No signal is observed, and an upper limit on the branching fraction is set as \[ \mathcal{B}(B^0 \to \phi \phi) < 2.8 \times 10^{8} \] at 90% confidence level. This is a factor of seven improvement compared to the previous best limit.  [Show abstract] [Hide abstract]
ABSTRACT: Measurements are presented of the CP violation observables S and C in the decays of B^{0} and B[over ¯]^{0} mesons to the J/ψK_{S}^{0} final state. The data sample corresponds to an integrated luminosity of 3.0 fb^{1} collected with the LHCb experiment in protonproton collisions at centerofmass energies of 7 and 8 TeV, and contains a total of 41 560 selected B^{0} and B[over ¯]^{0} decays. The analysis of the time evolution of these decays yields S=0.731±0.035(stat)±0.020(syst) and C=0.038±0.032(stat)±0.005(syst). In the standard model, S equals sin(2β) to a good level of precision. The values are consistent with the current world averages and with the standard model expectations.Physical Review Letters 08/2015; 115(3):031601. · 7.51 Impact Factor 
Article: Quantum numbers of the X(3872) state and orbital angular momentum in its p[superscript 0]J/ψ decay
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ABSTRACT: Angular correlations in B[superscript +] → X(3872)K[superscript +] decays, with X(3872) → ρ[superscript 0]J/ψ, ρ[superscript 0] → π[superscript +]π[superscript ] and J/ψ → μ[superscript +]μ[superscript ], are used to measure orbital angular momentum contributions and to determine the J[superscript PC] value of the X(3872) meson. The data correspond to an integrated luminosity of 3.0 fb[superscript 1] of protonproton collisions collected with the LHCb detector. This determination, for the first time performed without assuming a value for the orbital angular momentum, confirms the quantum numbers to be J[superscript PC] = 1[superscript ++]. The X(3872) is found to decay predominantly through an S wave and an upper limit of 4% at 95% C.L. is set on the Dwave contribution.  [Show abstract] [Hide abstract]
ABSTRACT: Proton–proton collision data recorded in 2011 and 2012 by the LHCb experiment, corresponding to an integrated luminosity of , are analysed to search for the charmless decay. More than 600 signal decays are selected and used to perform an amplitude analysis, under the assumption of no CP violation in the decay, from which the decay is observed for the first time with 7.1 standard deviations significance. The fraction of decays yielding a longitudinally polarised final state is measured to be . The branching fraction, using the decay as reference, is also reported as .  [Show abstract] [Hide abstract]
ABSTRACT: The decay B0s → ψ(2S)K+π is observed using a data set corresponding to an integrated luminosity of 3.0fb1 collected by the LHCb experiment in pp collisions at centreofmass energies of 7 and 8 TeV. The branching fraction relative to the B0 → ψ(2S)K+π decay mode is measured to be, where fs/fd indicates the uncertainty due to the ratio of probabilities for a b quark to hadronise into a B0s or B0 meson. Using an amplitude analysis, the fraction of decays proceeding via an intermediate K*(892)0 meson is measured to be 0.645±0.049(stat)±0.049(syst) and its longitudinal polarisation fraction is 0.524±0.056(stat)±0.029(syst). The relative branching fraction for this component is determined to be. In addition, the mass splitting between the B0s and B0 mesons is measured as M(B0s)M(B0)=87.45±0.44(stat)±0.09(syst)MeV/c2.  [Show abstract] [Hide abstract]
ABSTRACT: The first observation of the B[s over 0] → η[superscript ′]η[superscript ′] decay is reported. The study is based on a sample of protonproton collisions corresponding to 3.0 fb[superscript 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[superscript 5], where the third uncertainty comes from the B[superscript ±] → η[superscript ′]K[superscript ±] branching fraction that is used as a normalization. In addition, the charge asymmetries of B[superscript ±] → η[superscript ′]K[superscript ±] and B[superscript ±] → ϕK[superscript ±], 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.
Publication Stats
3k  Citations  
1,232.60  Total Impact Points  
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Institutions

2010–2014

CERN
Genève, Geneva, Switzerland


2011–2013

National Institute for Subatomic Physics
Amsterdamo, North Holland, Netherlands 
Tsinghua University
 Center for High Energy Physics
Peping, Beijing, China
