Publications (425)475.48 Total impact
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ABSTRACT: Using the latest LHCb measurements of timedependent CP violation in the B^0_s > K^+K^ decay, a Uspin relation between the decay amplitudes of B^0_s > K^+K^ and B^0 > \pi^+\pi^ decay processes allows constraints to be placed on the angle gamma of the unitarity triangle and on the B^0_s mixing phase 2\beta_s. Results from an extended approach, which uses additional inputs on B^0 > \pi^0\pi^0 and B^+ > \pi^+\pi^0 decays from other experiments and exploits isospin symmetry, are also presented. The dependence of the results on the maximum allowed amount of Uspin breaking is studied. At 68% probability, the value \gamma = ( 63.5 +7.2 6.7 ) degrees modulo 180 degrees is determined. In an alternative analysis, the value 2\beta_s = 0.12 +0.14 0.16 rad is found. In both measurements, the uncertainties due to Uspin breaking effects up to 50% are included.08/2014; 
Article: Measurement of the forward $W$ boson crosssection in $pp$ collisions at $\sqrt{s} = 7 {\rm \, TeV}$
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ABSTRACT: A measurement of the inclusive $W \to \mu\nu$ production crosssection using data from $pp$ collisions at a centreofmass energy of $\sqrt{s} = 7 {\rm \, TeV}$ is presented. The analysis is based on an integrated luminosity of about $1.0 {\rm \, fb}^{1}$ recorded with the LHCb detector. Results are reported for muons with a transverse momentum greater than $20 {\rm \, Ge\kern 0.1em V\!/}c$ and pseudorapidity between 2.0 and 4.5. The $W^{+}$ and $W^{}$ production crosssections are measured to be $$\sigma_{W^{+} \to \mu^{+}\nu} = 861.0 \pm 2.0 \pm 11.2 \pm 14.7 {\rm \, pb},$$ $$\sigma_{W^{} \to \mu^{}\overline{\nu}} = 675.8 \pm 1.9 \pm 8.8 \pm 11.6 {\rm \, pb},$$ where the first uncertainty is statistical, the second is systematic and the third is due to the luminosity determination. Crosssection ratios and differential distributions as functions of the muon pseudorapidity are also presented. The ratio of $W^{+}$ to $W^{}$ crosssections in the same fiducial kinematic region is determined to be $$\frac{\sigma_{W^{+} \to \mu^{+}\nu}}{\sigma_{W^{} \to \mu^{}\overline{\nu}}} = 1.274 \pm 0.005 \pm 0.009,$$ where the uncertainties are statistical and systematic, respectively. Results are in good agreement with theoretical predictions at nexttonexttoleading order in perturbative quantum chromodynamics.08/2014; 
Article: Measurement of the CKM angle \gamma using B^\pm > D K^\pm with D>K_S\pi^+\pi^, K_SK^+K^ decays
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ABSTRACT: A binned Dalitz plot analysis of $B^\pm \to D K^\pm$ decays, with $D \to K_S \pi^+\pi^$ and $D \to K_S K^+ K^$, is performed to measure the \CPviolating observables $x_{\pm}$ and $y_{\pm}$, which are sensitive to the CabibboKobayashiMaskawa angle $\gamma$. The analysis exploits a sample of protonproton collision data corresponding to 3.0\invfb collected by the LHCb experiment. Measurements from CLEOc of the variation of the stronginteraction phase of the $D$ decay over the Dalitz plot are used as inputs. The values of the parameters are found to be $x_+ = ( 7.7 \pm 2.4 \pm 1.0 \pm 0.4 )\times 10^{2}$, $x_ = (2.5 \pm 2.5 \pm 1.0 \pm 0.5) \times 10^{2}$, $y_+ = (2.2 \pm 2.5 \pm 0.4 \pm 1.0)\times 10^{2}$, and $y_ = (7.5 \pm 2.9 \pm 0.5 \pm 1.4) \times 10^{2}$. The first, second, and third uncertainties are the statistical, the experimental systematic, and that associated with the precision of the strongphase parameters. These are the most precise measurements of these observables and correspond to $\gamma = (62^{\,+15}_{\,14})^\circ$, with a second solution at $\gamma \to \gamma + 180^\circ$, and $r_B = 0.080^{+ 0.019}_{0.021}$, where $r_B$ is the ratio between the suppressed and favoured $B$ decay amplitudes.08/2014;  [Show abstract] [Hide abstract]
ABSTRACT: A search for $CP$ violation using $T$odd correlations is performed using the fourbody $D^0 \to K^+K^\pi^+\pi^$ decay, selected from semileptonic $B$ decays. The data sample corresponds to integrated luminosities of $1.0\,\text{fb}^{1}$ and $2.0\,\text{fb}^{1}$ recorded at the centreofmass energies of 7 TeV and 8 TeV, respectively. The $CP$violating asymmetry $a_{CP}^{T\text{odd}}$ is measured to be $(0.18\pm 0.29\text{(stat)}\pm 0.04\text{(syst)})\%$. Searches for $CP$ violation in different regions of phase space of the fourbody decay, and as a function of the $D^0$ decay time, are also presented. No significant deviation from the $CP$ conservation hypothesis is found.08/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The determination of track reconstruction efficiencies at LHCb using $J/\psi\rightarrow\mu^{+}\mu^{}$ decays is presented. Efficiencies above $95\%$ are found for the data taking periods in 2010, 2011, and 2012. The ratio of the track reconstruction efficiency of muons in data and simulation is compatible with unity and measured with an uncertainty of $0.8\,\%$ for data taking in 2010, and at a precision of $0.4\,\%$ for data taking in 2011 and 2012. For hadrons an additional $1.4\,\%$ uncertainty due to material interactions is assumed. This result is crucial for accurate cross section and branching fraction measurements in LHCb.08/2014;  [Show abstract] [Hide abstract]
ABSTRACT: A baryonic decay of the $B_c^+$ meson, $B_c^+\to J/\psi p\overline{p}\pi^+$, is observed for the first time, with a significance of $7.3$ standard deviations, in $pp$ collision data collected with the LHCb detector and corresponding to an integrated luminosity of $3.0$ fb$^{1}$ taken at centerofmass energies of $7$ and $8$ $\mathrm{TeV}$. With the $B_c^+\to J/\psi \pi^+$ decay as normalization channel, the ratio of branching fractions is measured to be \begin{equation*} \frac{\mathcal{B}(B_c^+\to J/\psi p\overline{p}\pi^+)}{\mathcal{B}(B_c^+\to J/\psi \pi^+)} = 0.143^{\,+\,0.039}_{\,\,0.034}\,(\mathrm{stat})\pm0.013\,(\mathrm{syst}). \end{equation*} The mass of the $B_c^+$ meson is determined as $M(B_c^+)=6274.0\pm1.8\,(\mathrm{stat})\pm0.4\,(\mathrm{syst})\,\mathrm{MeV}/c^2$, using the $B_c^+\to J/\psi p\overline{p}\pi^+$ channel.08/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The direct $C\!P$ asymmetries of the decays $B^0 \rightarrow K^{*0} \mu^+ \mu^$ and $B^+ \rightarrow K^{+} \mu^+ \mu^$ are measured using $pp$ collision data corresponding to an integrated luminosity of 3.0$\mbox{fb}^{1}$ collected with the LHCb detector. The respective control modes $B^0 \rightarrow J/\psi K^{*0}$ and $B^+ \rightarrow J/\psi K^{+}$ are used to account for detection and production asymmetries. The measurements are made in several intervals of $\mu^+ \mu^$ invariant mass squared, with the $\phi(1020)$ and charmonium resonance regions excluded. Under the hypothesis of zero $C\!P$ asymmetry in the control modes, the average values of the asymmetries are \begin{align} {\cal A}_{C\!P}(B^0 \rightarrow K^{*0} \mu^+ \mu^) &= 0.035 \pm 0.024 \pm 0.003, \cr {\cal A}_{C\!P}(B^+ \rightarrow K^{+} \mu^+ \mu^) &= \phantom{}0.012 \pm 0.017 \pm 0.001, \end{align} where the first uncertainties are statistical and the second are due to systematic effects. Both measurements are consistent with the Standard Model prediction of small $C\!P$ asymmetry in these decays.08/2014;  [Show abstract] [Hide abstract]
ABSTRACT: First observations of the rare decays $B^+\rightarrow K^+\pi^+\pi^\mu^+\mu^$ and $B^+\rightarrow \phi K^+\mu^+\mu^$ are presented using data corresponding to an integrated luminosity of $3.0\,\mbox{fb}^{1}$, collected by the LHCb experiment at centreofmass energies of $7$ and $8\mathrm{\,TeV}$. The branching fractions of the decays are \begin{eqnarray*} \mathcal{B}(B^+\rightarrow K^+\pi^+\pi^\mu^+\mu^) &=& (4.36\,^{+0.29}_{0.27}\,\mathrm{(stat)}\pm 0.21\,\mathrm{(syst)}\pm0.18\,\mathrm{(norm)})\times10^{7},\\ \mathcal{B}(B^+\rightarrow\phi K^+\mu^+\mu^) &=& (0.82 \,^{+0.19}_{0.17}\,\mathrm{(stat)}\,^{+0.10}_{0.04}\,\mathrm{(syst)}\pm0.27\,\mathrm{(norm)}) \times10^{7},\end{eqnarray*} where the uncertainties are statistical, systematic, and due to the uncertainty on the branching fractions of the normalisation modes. A measurement of the differential branching fraction in bins of the invariant mass squared of the dimuon system is also presented for the decay $B^+\rightarrow K^+\pi^+\pi^\mu^{+}\mu^{}$.08/2014; 
Article: Measurement of the B0barB0 and BsbarBs production asymmetries in pp collisions at sqrt(s)=7 TeV
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ABSTRACT: The B0barB0 and BsbarBs production asymmetries, AP(B0) and AP(Bs), are measured by means of a timedependent analysis of B0 > J/\psi K*0, B0 > D pi+ and Bs > Ds pi+ decays, using a data sample corresponding to an integrated luminosity of 1.0 fb^{1}, collected by LHCb in pp collisions at a centreofmass energy of 7 TeV. The measurements are performed as a function of transverse momentum and pseudorapidity of the B0 and Bs mesons within the LHCb acceptance. The production asymmetries, integrated over pT and eta in the range 4 < pT< 30 GeV/c and 2.5<eta<4.5, are determined to be AP(B0) = (0.35 +/ 0.76 +/ 0.28)% and AP(Bs) = (1.09 +/ 2.61 +/ 0.66)%, where the first uncertainties are statistical and the second systematic.08/2014;  [Show abstract] [Hide abstract]
ABSTRACT: An analysis of B0>D K*0 decays is presented, where D represents an admixture of D0 and D0b mesons reconstructed in four separate final states: Kpi+, piK+, K+K and pi+pi. The data sample corresponds to 3.0fb1 of protonproton collision, collected by the LHCb experiment. Measurements of several observables are performed, including CP asymmetries. The most precise determination is presented of rB(DK*0), the magnitude of the ratio of the amplitudes of the decay B0>D K+ pi with a b>u or a b>c transition, in a K pi mass region of +/50 MeV/c2 around the K*(892) mass and for an absolute value of the cosine of the K*0 helicity angle larger than 0.4.07/2014;  [Show abstract] [Hide abstract]
ABSTRACT: Measurements of the branching fractions of $B^0_{(s)} \to K^{*\pm}K^\mp$ and $B^0_{(s)} \to K^{*\pm}\pi^\mp$ decays are performed using a data sample corresponding to $1.0 \ {\rm fb}^{1}$ of protonproton collision data collected with the LHCb detector at a centreofmass energy of $7\mathrm{\,TeV}$, where the $K^{*\pm}$ mesons are reconstructed in the $K^0_{\rm S}\pi^\pm$ final state. The first observation of the $B^0_s \to K^{*\pm}K^\mp$ decay and the first evidence for the $B^0_s \to K^{*}\pi^+$ decay are reported with branching fractions \begin{eqnarray} {\cal B}\left(B^0_s \to K^{*\pm}K^\mp\right) & = & \left( 12.7\pm1.9\pm1.9 \right) \times 10^{6} \, , \\ {\cal B}\left(B^0_s \to K^{*}\pi^+\right) & = & ~\left( 3.3\pm1.1\pm0.5 \right) \times 10^{6} \, , \end{eqnarray} where the first uncertainties are statistical and the second are systematic. In addition, an upper limit of ${\cal B}\left(B^0 \to K^{*\pm}K^\mp\right) < 0.4 \ (0.5) \times 10^{6}$ is set at $90\,\% \ (95\,\%)$ confidence level.07/2014;  [Show abstract] [Hide abstract]
ABSTRACT: A study of $\chi_{b}$ meson production at LHCb is performed on protonproton collision data, corresponding to 3.0fb$^{1}$ of integrated luminosity collected at centreofmass energies $\sqrt{s}=7$ and 8TeV. The fraction of $\Upsilon(nS)$ mesons originating from $\chi_{b}$ decays is measured as a function of the $\Upsilon$ transverse momentum in the rapidity range $2.0 < y^{\Upsilon} < 4.5$. The radiative transition of the $\chi_{b}(3P)$ meson to $\Upsilon(3S)$ is observed for the first time. The $\chi_{b1}(3P)$ mass is determined to be $$m(\chi_{b1}(3P)) = 10\,511.3 \pm 1.7 \pm 2.5 MeV/c^2,$$ where the first uncertainty is statistical and the second is systematic.07/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The resonant substructure of $B_s^0 \rightarrow \overline{D}^0 K^ \pi^+$ decays is studied with the Dalitz plot analysis technique. The study is based on a data sample corresponding to an integrated luminosity of $3.0\,{\rm fb}^{1}$ of $pp$ collision data recorded by LHCb. A structure at $m(\overline{D}^0 K^) \approx 2.86 {\rm GeV}/c^2$ is found to be an admixture of spin1 and spin3 resonances. The masses and widths of these states and of the $D^*_{s2}(2573)^$ meson are measured, as are the complex amplitudes and fit fractions for all the $\overline{D}^0 K^$ and $K^\pi^+$ components included in the amplitude model. In addition, the $D^*_{s2}(2573)^$ resonance is confirmed to be spin2.07/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The resonant substructure of $B_s^0 \rightarrow \overline{D}^0 K^ \pi^+$ decays is studied using a data sample corresponding to an integrated luminosity of $3.0\,{\rm fb}^{1}$ of $pp$ collision data recorded by the LHCb detector. An excess at $m(\overline{D}^0 K^) \approx 2.86 {\rm GeV}/c^2$ is found to be an admixture of spin1 and spin3 resonances. Therefore the $D^*_{sJ}(2860)^$ state previously observed in inclusive $e^+e^ \rightarrow \overline{D}^0 K^ X$ and $pp \rightarrow \overline{D}^0 K^ X$ processes consists of at least two particles. This is the first observation of a heavy flavoured spin3 resonance, and the first time that any spin3 particle has been seen to be produced in $B$ decays. The masses and widths of the new states and of the $D^*_{s2}(2573)^$ meson are measured, giving the most precise determinations to date.07/2014;  [Show abstract] [Hide abstract]
ABSTRACT: A modeldependent amplitude analysis of $B^{\pm} \rightarrow D K^{\pm}$ with $D \rightarrow K_S^0 \pi^+ \pi^$ decays is performed using protonproton collision data, corresponding to an integrated luminosity of $1$ fb$^{1}$, recorded by LHCb at a centreofmass energy of $7$ TeV in $2011$. Values of the $CP$ violation observables $x_{\pm}$ and $y_{\pm}$, which are sensitive to the CKM angle $\gamma$, are measured to be \begin{align*} x_ &= +0.027 \pm 0.044 ^{+0.010}_{0.008} \pm 0.001, \\ y_ &= +0.013 \pm 0.048 ^{+0.009}_{0.007} \pm 0.003, \\ x_+ &= 0.084 \pm 0.045 \pm 0.009 \pm 0.005, \\ y_+ &= 0.032 \pm 0.048 ^{+0.010}_{0.009} \pm 0.008, \end{align*} where the first uncertainty is statistical, the second systematic and the third arises from the uncertainty of the $D \rightarrow K_S^0 \pi^+ \pi^$ amplitude model. The value of $\gamma$ is determined to be $(84^{+49}_{42})^\circ$, including all sources of uncertainty. Neutral $D$ meson mixing is found to have negligible effect.07/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We report on measurements of the timedependent CP violating observables in $B^0_s\rightarrow D^{\mp}_s K^{\pm}$ decays using a dataset corresponding to 1.0 fb$^{1}$ of pp collisions recorded with the LHCb detector. We find the CP violating observables $C_f=0.53\pm0.25\pm0.04$, $A^{\Delta\Gamma}_f=0.37\pm0.42\pm0.20$, $A^{\Delta\Gamma}_{\bar{f}}=0.20\pm0.41\pm0.20$, $S_f=1.09\pm0.33\pm0.08$, $S_{\bar{f}}=0.36\pm0.34\pm0.08$, where the uncertainties are statistical and systematic, respectively. We use these observables to make the first measurement of the CKM angle $\gamma$ in $B^0_s\rightarrow D^{\mp}_s K^{\pm}$ decays, finding $\gamma$ = (115$_{43}^{+28}$)$^\circ$ modulo 180$^\circ$ at 68% CL, where the error contains both statistical and systematic uncertainties.07/2014;  [Show abstract] [Hide abstract]
ABSTRACT: Threebody $B^+\to p \overline p K^+$ and $B^+\to p \overline p \pi^+$ decays are studied using a data sample corresponding to an integrated luminosity of 3.0 $fb^{1}$ collected by the LHCb experiment in protonproton collisions at centerofmass energies of $7$ and $8$ TeV. Evidence of CP violation in the $B^+\to p \overline p K^+$ decay is found in regions of the phase space, representing the first measurement of this kind for a final state containing baryons. Measurements of the forwardbackward asymmetry of the light meson in the $p\overline p$ rest frame yield $A_{\mathrm{FB}}(p \overline p K^+,~m_{p\overline p}<2.85\mathrm{\,Ge\kern 0.1em V\!/}c^2)=0.495\pm0.012~(\mathrm{stat})\pm0.007~(\mathrm{syst})$ and $A_{\mathrm{FB}}(p\overline p \pi^+,~m_{p\overline p}<2.85\mathrm{\,Ge\kern 0.1em V\!/}c^2)=0.409\pm0.033~(\mathrm{stat})\pm0.006~(\mathrm{syst})$. In addition, the branching fraction of the decay $B^+\to\kern 0.1em\overline{\kern 0.1em\Lambda}(1520)p$ is measured to be $\mathcal{B}(B^+ \to \kern 0.1em\overline{\kern 0.1em\Lambda}(1520)p)=(3.15\pm0.48~(\mathrm{stat})\pm0.07~(\mathrm{syst})\pm0.26~(\mathrm{BF}))\times 10^{7}$, where BF denotes the uncertainty on secondary branching fractions.07/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We present a measurement of the ratio of the Bs meson lifetime, in the flavorspecific decay to $D_s^+\pi^$, to that of the B0 meson. The pp collision data used correspond to an integrated luminosity of 1/fb, collected with the LHCb detector, at a centerofmass energy of 7 TeV. Combining our measured value of 1.010 +/ 0.010 +/ 0.008 for this ratio with the known lifetime, we determine the flavorspecific Bs lifetime to be tau(Bs) = 1.535 +/ 0.015 +/ 0.014 ps, where the uncertainties are statistical and systematic, respectively. This is the most precise measurement to date, and is consistent with previous measurements and theoretical predictions.07/2014;  [Show abstract] [Hide abstract]
ABSTRACT: A search is performed for the central exclusive production of pairs of charmonia produced in protonproton collisions. Using data corresponding to an integrated luminosity of $3{\rm\ fb}^{1}$ collected at centreofmass energies of 7 and 8 TeV, $J/\psi J/\psi$ and $J/\psi\psi(2S)$ pairs are observed, which have been produced in the absence of any other activity inside the LHCb acceptance that is sensitive to charged particles in the pseudorapidity ranges $(3.5,1.5)$ and $(1.5,5.0)$. Searches are also performed for pairs of Pwave charmonia and limits are set on their production. The crosssections for these processes, where the dimeson system has a rapidity between 2.0 and 4.5, are measured to be $$ \begin{array}{rl} \sigma^{J/\psi J/\psi} &= 58\pm10{(\rm stat)} \pm 6{(\rm syst)} {\rm\ pb} , \\ \sigma^{J/\psi\psi(2S)} &= 63 ^{+27}_{18}{(\rm stat)}\pm 10{(\rm syst)} {\rm\ pb} , \\ \sigma^{\psi(2S)\psi(2S)} &< 237 {\rm\ pb}, \\ \sigma^{\chi_{c0}\chi_{c0}} &< 69 {\rm\ nb}, \\ \sigma^{\chi_{c1}\chi_{c1}} &< 45 {\rm\ pb}, \\ \sigma^{\chi_{c2}\chi_{c2}} &< 141 {\rm\ pb}, \\ \end{array} $$ where the upper limits are set at the 90% confidence level. The measured $J/\psi J/\psi$ and $J/\psi\psi(2S)$ crosssections are consistent with theoretical expectations.07/2014;  [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 Ξ_{b}^{0}→Ξ_{c}^{+}π^{}, Ξ_{c}^{+}→pK^{}π^{+} signal decays are reconstructed. From this sample, the first measurement of the Ξ_{b}^{0} baryon lifetime is made, relative to that of the Λ_{b}^{0} baryon. The mass differences M(Ξ_{b}^{0})M(Λ_{b}^{0}) and M(Ξ_{c}^{+})M(Λ_{c}^{+}) are also measured with precision more than 4 times better than the current world averages. The resulting values are τ_{Ξ_{b}^{0}}/τ_{Λ_{b}^{0}}=1.006±0.018±0.010,M(Ξ_{b}^{0})M(Λ_{b}^{0})=172.44±0.39±0.17 MeV/c^{2},M(Ξ_{c}^{+})M(Λ_{c}^{+})=181.51±0.14±0.10 MeV/c^{2},where the first uncertainty is statistical and the second is systematic. The relative rate of Ξ_{b}^{0} to Λ_{b}^{0} baryon production is measured to be f_{Ξ_{b}^{0}}/f_{Λ_{b}^{0}}B(Ξ_{b}^{0}→Ξ_{c}^{+}π^{})/B(Λ_{b}^{0}→Λ_{c}^{+}π^{})B(Ξ_{c}^{+}→pK^{}π^{+})/B(Λ_{c}^{+}→pK^{}π^{+})=(1.88±0.04±0.03)×10^{2},where the first factor is the ratio of fragmentation fractions, b→Ξ_{b}^{0} relative to b→Λ_{b}^{0}. Relative production rates as functions of transverse momentum and pseudorapidity are also presented.Physical Review Letters 07/2014; 113(3):032001. · 7.73 Impact Factor
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563  Citations  
475.48  Total Impact Points  
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Institutions

2011–2013

National Institute for Subatomic Physics
Amsterdamo, North Holland, Netherlands


1994–2013

CERN
Genève, Geneva, Switzerland


1989–1991

McGill University
Montréal, Quebec, Canada


1988

Universität Heidelberg
 Institute of Physics
Heidelburg, BadenWürttemberg, Germany


1987

Lund University
Lund, Skåne, Sweden
