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Citation
Aaij, R., C. Abellan Beteta, B. Adeva, M. Adinolfi, C. Adrover, A.
Affolder, Z. Ajaltouni, et al. “Determination of the X(3872) Meson
Quantum Numbers.” Physical Review Letters 110, no. 22 (May 2013).
© 2013 CERN
As Published
http://dx.doi.org/10.1103/PhysRevLett.110.222001
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American Physical Society
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Final published version
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http://hdl.handle.net/1721.1/79908
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Creative Commons Attribution 3.0
Determination of the Xð3872Þ Meson Quantum Numbers
R. Aaij et al.*(LHCb Collaboration)
(Received 25 February 2013; published 29 May 2013)
The quantum numbers of the Xð3872Þ meson are determined to be JPC¼ 1þþ based on angular correlations in Bþ! Xð3872ÞKþ decays, where Xð3872Þ ! þJ=c and J=c ! þ. The data correspond to 1:0 fb1of pp collisions collected by the LHCb detector. The only alternative assignment allowed by previous measurements JPC ¼ 2þis rejected with a confidence level equivalent to more than 8 Gaussian standard deviations using a likelihood-ratio test in the full angular phase space. This result favors exotic explanations of the Xð3872Þ state.
DOI:10.1103/PhysRevLett.110.222001 PACS numbers: 14.40.Rt, 13.25.Gv, 13.25.Hw, 14.40.Nd
It has been almost ten years since the narrow Xð3872Þ state was discovered in Bþdecays by the Belle experiment [1,2]. Subsequently, its existence has been confirmed by several other experiments [3–5]. Recently, its production has been studied at the LHC [6,7]. However, the nature of this state remains unclear. Among the open possibilities are conventional charmonium and exotic states such as D0D0 molecules [8], tetraquarks [9], or their mixtures [10]. Determination of the quantum numbers, total angular mo-mentum J, parity P, and charge-conjugation C, is impor-tant to shed light on this ambiguity. The C parity of the state is positive since the Xð3872Þ ! J=cdecay has been observed [11,12].
The CDF experiment analyzed three-dimensional (3D) angular correlations in a relatively high-background sam-ple of 2292 113 inclusively reconstructed Xð3872Þ ! þJ=c, J=c ! þ decays dominated by prompt production in p p collisions. The unknown polarization of the Xð3872Þ mesons limited the sensitivity of the measure-ment of JPC[13]. A 2fit of JPChypotheses to the binned 3D distribution of the J=c and helicity angles (J=c, ) [14–16] and the angle between their decay planes (J=c;¼ J=c ) excluded all spin-parity assignments except for 1þþ or 2þ. The Belle Collaboration observed 173 16 B ! Xð3872ÞK (K ¼ Kor K0
S), Xð3872Þ ! þJ=c, J=c ! ‘þ‘ decays [17]. The reconstruction of the full decay chain resulted in a small background and polarized Xð3872Þ mesons, making their helicity angle (X) and orientation of their decay plane (X) sensitive to JPCas well. By studying one-dimensional distributions in three different angles without exploiting correlations, they concluded that their data were equally well described by the 1þþ and 2þ hypotheses.
The BABAR experiment observed 34 7 Xð3872Þ ! !J=c, ! ! þ0events [18]. The shape of observed þ0 mass distribution favored the 2þ hypothesis, which had a confidence level (C.L.) of 62% over the 1þþ hypothesis, but the latter was not ruled out (C:L: ¼ 7%).
In this Letter, we report the first analysis of the complete five-dimensional angular correlations of the Bþ! Xð3872ÞKþ, Xð3872Þ ! þJ=c, J=c!þdecay chain usingpffiffiffis¼ 7 TeV pp collision data corresponding to 1:0 fb1collected in 2011 by the LHCb experiment. The LHCb detector [19] is a single-arm forward spectrometer covering the pseudorapidity range 2 < < 5 designed for the study of particles containing b or c quarks. The detector includes a high precision tracking system consisting of a silicon-strip vertex detector surrounding the pp interaction region, a large-area silicon-strip detector located upstream of a dipole magnet with a bending power of about 4 Tm, and three stations of silicon-strip detectors and straw drift tubes placed downstream. The combined tracking system has momentum resolution p=p that varies from 0.4% at 5 GeV to 0.6% at 100 GeV, and impact parameter resolu-tion of 20 m for tracks with high transverse momentum (pT) [20]. Charged hadrons are identified using two ring-imaging Cherenkov detectors. Photon, electron, and hadron candidates are identified by a calorimeter system consisting of scintillating-pad and preshower detectors, an electromagnetic calorimeter, and a hadronic calorimeter. Muons are identified by a system composed of alternating layers of iron and multiwire proportional chambers. The trigger [21] consists of a hardware stage based on information from the calorimeter and muon systems followed by a software stage which applies a full event reconstruction.
In the off-line analysis, J=c ! þ candidates are selected with the following criteria: pTðÞ > 0:9 GeV, pTðJ=cÞ > 1:5 GeV, 2 per degree of freedom for the two muons to form a common vertex, 2
vtxðþÞ=ndf < 9, and a mass consistent with the J=c meson. The sepa-ration of the J=c decay vertex from the nearest primary vertex (PV) must be at least 3 standard deviations.
*Full author list given at the end of the article.
Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distri-bution of this work must maintain attridistri-bution to the author(s) and the published article’s title, journal citation, and DOI.
Combinations of Kþþ candidates that are consis-tent with originating from a common vertex with 2vtxðKþþÞ=ndf < 9, with each charged hadron (h) separated from all PVs [2
IPðhÞ > 9] and having pTðhÞ > 0:25 GeV, are selected. The quantity 2
IPðhÞ is defined as the difference between the 2of the PV reconstructed with and without the considered particle. Kaon and pion candi-dates are required to satisfy ln½LðKÞ=LðÞ > 0 and <5, respectively, where L is the particle identification like-lihood [22]. If both same-sign hadrons in this combination meet the kaon requirement, only the particle with higher pT is considered a kaon candidate. We combine J=c candidates with Kþþ candidates to form Bþ candi-dates, which must satisfy 2
vtxðJ=cKþþÞ=ndf < 9, pTðBþÞ > 2 GeV and have decay time greater than 0.25 ps. The J=cKþþ mass is calculated using the known J=c mass and the B vertex as constraints.
Four discriminating variables (xi) are used in a like-lihood ratio to improve the background suppression: the minimal 2IPðhÞ, 2vtxðJ=cKþþÞ=ndf, 2IPðBþÞ, and the cosine of the largest opening angle between the J=c and the charged-hadron transverse momenta. The latter peaks at positive values for the signal, as the Bþ meson has a high transverse momentum. Background events in which particles are combined from two different B decays peak at negative values, while those due to random combi-nations of particles are more uniformly distributed. The four 1D signal probability density functions (PDFs) PsigðxiÞ are obtained from a simulated sample of Bþ !
cð2SÞKþ, cð2SÞ ! þJ=c decays, which are kine-matically similar to the signal decays. The data sample of Bþ!cð2SÞKþ events is used as a control sample for PsigðxiÞ and for systematic studies in the angular analysis. The background PDFsPbkgðxiÞ are obtained from the data in the Bþmass sidebands (4.85–5.10 and 5.45–6.50 GeV). We require 2P4i¼1ln½PsigðxiÞ=PbkgðxiÞ < 1:0, which preserves about 94% of the Xð3872Þ signal events.
About 38000 candidates are selected in a 2 mass range around the Bþ peak in the MðJ=cþKþÞ distribution, with a signal purity of 89%. The M ¼ MðþJ=cÞ MðJ=cÞ distribution is shown in Fig. 1. Fits to the cð2SÞ and Xð3872Þ signals are shown in the insets. A Crystal Ball function [23] with symmetric tails is used for the signal shapes. The background is assumed to be linear. The cð2SÞ fit is performed in the 539.2–639.2 MeV range leaving all parameters free to vary. It yields 5642 76 signal (230 21 background) candi-dates with a M resolution of M¼ 3:99 0:05 MeV, corresponding to a signal purity of 99.2% within a 2:5M region. When fitting in the 723–823 MeV range, the signal tail parameters are fixed to the values obtained in the cð2SÞ fit, which also describe well the simulated Xð3872Þ signal distribution. The fit yields 313 26 Bþ! Xð3872ÞKþ candidates with a resolution of 5:5 0:5 MeV. The number of background candidates
is 568 31 including the sideband regions. The signal purity is 68% within a2:5Msignal region. The domi-nant source of background is from Bþ ! J=cK1ð1270Þþ, K1ð1270Þþ! Kþþdecays, as found by studying the Kþþ mass distribution.
The angular correlations in the Bþ decay carry infor-mation about the Xð3872Þ quantum numbers. To discri-minate between the 1þþ and 2þ assignments, we use a likelihood-ratio test, which in general provides the most powerful discrimination between two hypotheses [24]. The PDF for each JPC hypothesis J
X is defined in the 5D angular space ðcosX; cos; X;; cosJ=c; X;J=cÞ by the normalized product of the expected decay matrix element (M) squared and of the reconstruc-tion efficiency ( ), P ðjJXÞ ¼ jMðjJXÞj2 ðÞ=IðJXÞ, where IðJXÞ ¼
R
jMðjJXÞj2 ðÞd. The efficiency is averaged over the þmass [MðÞ] using a simulation [25–29] that assumes the Xð3872Þ ! ð770ÞJ=c, ð770Þ ! þ decay [7,17,30]. The observed MðÞ distribution is in good agreement with this simulation. The line shape of the ð770Þ resonance can change slightly depending on the spin hypothesis. The effect on ðÞ is found to be very small and is neglected. We follow the approach adopted in Ref. [13] to predict the matrix ele-ments. The angular correlations are obtained using the helicity formalism, jMðjJXÞj2¼ X ¼1;þ1 X J=c; ¼1;0;þ1 A J=c; DJX 0; J=c ðX; X; XÞ D1 ;0ð; ; Þ D1 J=c; ðJ=c; J=c; J=cÞ 2 ; ) [MeV] ψ ) - M(J/ ψ J/ -π + π M( 600 800 1000 1200 1400
Number of candidates / (2.5 MeV)
0 200 400 600 800 1000 1200 LHCb 550 600 (2S) ψ 750 800 0 10 20 30 40 50 60 70 X(3872) 0 200 400 600 800 1000 1200
FIG. 1 (color online). Distribution of M for Bþ! J=c Kþþ candidates. The fits of the c ð2SÞ and Xð3872Þ signals are displayed. The solid blue, dashed red, and dotted green lines represent the total fit, signal component, and back-ground component, respectively.
where are particle helicities and DJ
1; 2 are Wigner
functions [14–16]. The helicity couplings A J=c; are
expressed in terms of the LS couplings [31,32], BLS, where L is the orbital angular momentum between the system and the J=c meson, and S is the sum of their spins. Since the energy release in the Xð3872Þ ! ð770ÞJ=c decay is small, the lowest value of L is expected to dominate, especially because the next-to-minimal value is not allowed by parity conservation. The lowest value for the 1þþhypothesis is L ¼ 0, which implies S ¼ 1. With only one LS amplitude present, the angular distribution is com-pletely determined without free parameters. For the 2þ hypothesis, the lowest value is L ¼ 1, which implies S ¼ 1 or 2. As both LS combinations are possible, the 2þ hypothesis implies two parameters, which are chosen to be the real and imaginary parts of B11=ðB11þ B12Þ. Since they are related to strong dynamics, they are difficult to predict theoretically and are treated as nuisance parameters.
We define a test statistic t ¼ 2 ln½Lð2þÞ=Lð1þþÞ, where the Lð2þÞ likelihood is maximized with respect to . The efficiency ðÞ is not determined on an event-by-event basis, since it cancels in the likelihood ratio except for the normalization integrals. A large sample of simulated events with uniform angular distributions passed through a full simulation of the detection and the data selection process is used to carry out the integration, IðJXÞ /
PNMC
i¼1 jMðijJXÞj2, where NMC is the number of reconstructed simulated events. The background in the data is subtracted in the log likelihoods using the sPlot tech-nique [33] by assigning to each candidate in the fitted M range an event weight (sWeight) wibased on its M value, 2 lnLðJXÞ ¼ sw2
PNdata
i¼1 wilnP ðijJXÞ. Here, sw is a constant scaling factor, sw¼
PNdata
i¼1 wi=
PNdata
i¼1 w2i, which accounts for statistical fluctuations in the background sub-traction. Positive (negative) values of the test statistic for the data tdata favor the 1þþ(2þ) hypothesis. The analysis procedure has been extensively tested on simulated samples for the 1þþ and 2þ hypotheses with different values of generated using theEVTGENpackage [27].
The value of that minimizes 2 lnLðJX ¼ 2þ; Þ in the data is ^ ¼ ð0:671 0:046; 0:280 0:046Þ. This is compatible with the value reported by Belle, (0.64,0.27) [17]. The value of the test statistic observed in the data is tdata ¼ þ99, thus favoring the 1þþ hypothesis. Furthermore, ^ is consistent with the value of obtained from fitting a large background-free sample of simulated 1þþevents, (0:650 0:011, 0:294 0:012). The value of tdatais compared with the distribution of t in the simulated experiments to determine a p value for the 2þhypothesis via the fraction of simulated experiments yielding a value of t > tdata. We simulate 2 million experiments with the value of , and the number of signal and background events, as observed in the data. The background is assumed to be saturated by the Bþ! J=cK1ð1270Þþdecay, which
provides a good description of its angular correlations. None of the values of t from the simulated experiments even approach tdata, indicating a p value smaller than 1=ð2 106Þ, which corresponds to a rejection of the 2þ hypothesis with greater than 5 significance. As shown in Fig.2, the distribution of t is reasonably well approximated by a Gaussian function. Based on the mean and rms spread of the t distribution for the 2þexperiments, this hypothe-sis is rejected with a significance of 8:4. The deviations of the t distribution from the Gaussian function suggest this is a plausible estimate. Using phase-space Bþ! J=cKþþ decays as a model for the background events, we obtain a consistent result. The value of tdatafalls into the region where the probability density for the 1þþ simulated experiments is high. Integrating the 1þþ distri-bution from1 to tdata gives C:L:ð1þþÞ ¼ 34%.
The value of t is the sum of the single-event likelihood ratios ln½P ðij2þ; ^ Þ=P ðij1þþÞ over the analyzed data sample and is therefore proportional to its average value. Even though this is the most effective way to discriminate between the two hypotheses, the agreement with the 1þþ hypothesis might have been coincidental if the data were inconsistent with both tested hypotheses. However, the full shape of the single-event likelihood-ratio distribution also shows good consistency between the data and the distribution expected for the 1þþ case, as illus-trated in Fig.3.
We vary the data selection criteria to probe for possible biases from the background subtraction and the efficiency corrections. The nominal selection does not bias the MðÞ distribution. By requiring Q ¼ MðJ=cÞ MðJ=cÞ MðÞ < 0:1 GeV, we reduce the background level by a factor of 4, while losing only 21% of the signal. The significance of the 2þ rejection changes very little, in agreement with the simulations. By tightening the
) ] ++ (1 L )/ -+ (2 L = -2 ln[ t -200 -100 0 100 200
Number of experiments / bin
2 10 3 10 4 10 5 10 6 10 7 10 data
t
-+ =2 PC Simulated J Simulated JPC=1++ LHCbFIG. 2 (color online). Distribution of the test statistic t for the simulated experiments with JPC¼ 2þ and ¼ ^ (black circles on the left) and with JPC¼ 1þþ (red triangles on the right). A Gaussian fit to the 2þ distribution is overlaid (blue solid line). The value of the test statistic for the data tdata is shown by the solid vertical line.
requirements on the pT of , K, and candidates, we decrease the signal efficiency by about 50% with similar reduction in the background level. In all cases, the signifi-cance of the 2þrejection is reduced by a factor consistent with the simulations.
In the analysis we use simulations to calculate the IðJXÞ integrals. In an alternative approach to the efficiency esti-mates, we use the Bþ!cð2SÞKþ events observed in the data weighted by the inverse of 1 matrix element squared. We obtain a value of tdata that corresponds to 8:2 rejection of the 2þ hypothesis.
As an additional goodness-of-fit test for the 1þþ hypot-hesis, we project the data onto five 1D and ten 2D binned distributions in all five angles and their combinations. They are all consistent with the distributions expected for the 1þþ hypothesis. Some of them are inconsistent with the distributions expected for the (2þ, ^ ) hypothesis. The most significant inconsistency is observed for the 2D projections onto cosX vs cos. The separation between the 1þþ and 2þ hypotheses increases when using correlations between these two angles, as illustrated in Fig.4.
In summary, we unambiguously establish that the values of total angular momentum, parity, and charge-conjugation eigenvalues of the Xð3872Þ state are 1þþ. This is achieved through the first analysis of the full five-dimensional angular correlations between final state particles in Bþ ! Xð3872ÞKþ, Xð3872Þ ! þJ=c, J=c ! þ decays using a likelihood-ratio test. The 2þ hypothesis is excluded with a significance of more than 8 Gaussian standard deviations. This result rules out the explanation of the Xð3872Þ meson as a conventional c2ð11D2Þ state.
Among the remaining possibilities are the c1ð23P1Þ char-monium disfavored by the value of the Xð3872Þ mass [34], and unconventional explanations such as a D0D0 mole-cule [8], tetraquark state [9], or charmonium-molecule mixture [10].
We express our gratitude to our colleagues in the CERN accelerator departments for the excellent performance of the LHC. We thank the technical and administrative staff at the LHCb institutes. We acknowledge support from CERN and from the following national agencies: CAPES, CNPq, FAPERJ, and FINEP (Brazil); NSFC (China); CNRS/ IN2P3 and Region Auvergne (France); BMBF, DFG, HGF, and MPG (Germany); SFI (Ireland); INFN (Italy); FOM and NWO (Netherlands); SCSR (Poland); ANCS/ IFA (Romania); MinES, Rosatom, RFBR, and NRC ‘‘Kurchatov Institute’’ (Russia); MinECo, XuntaGal, and GENCAT (Spain); SNSF and SER (Switzerland); NAS Ukraine (Ukraine); STFC (United Kingdom); NSF (USA). We also acknowledge the support received from the ERC under FP7. The Tier1 computing centers are ) ] ++ (1 P ) / -+ (2 P - ln[ -4 -2 0 2 4
Density of signal events
0 50 100 150 200 250 300 350 LHCb Data ++ =1 PC Simulated J -+ =2 PC Simulated J
FIG. 3 (color online). Distribution of ln½P ðij2þ; ^ Þ= P ðij1þþÞ for the data (points with error bars) compared to the distributions for the simulated experiments with JPC¼ 1þþ (red solid histogram) and with JPC¼ 2þ, ¼ ^ (blue dashed histogram) after the background subtraction using sWeights. The simulated distributions are normalized to the number of signal candidates observed in the data. Bin contents and uncertainties are divided by bin width because of unequal bin sizes. Number of candidates / 0.4 20 40 60 80 100 120 all candidates LHCb Data ++ =1 PC Simulated J -+ =2 PC Simulated J X θ cos -1 -0.5 0 0.5 1 0 10 20 30 40 50 | > 0.6 ππ θ |cos
FIG. 4 (color online). Background-subtracted distribution of cosXfor (top) all candidates and for (bottom) candidates with j cosj > 0:6 for the data (points with error bars) compared to the expected distributions for the JPC¼ 1þþ (red solid histogram) and JPC¼ 2þand ¼ ^ hypotheses (blue dashed histogram). The simulated distributions are normalized to the number of signal candidates observed in the data across the full phase space.
supported by IN2P3 (France), KIT and BMBF (Germany), INFN (Italy), NWO and SURF (Netherlands), PIC (Spain), and GridPP (United Kingdom). We are thankful for the computing resources put at our disposal by Yandex LLC (Russia), as well as to the communities behind the multiple open source software packages that we depend on.
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U. Eitschberger,9R. Ekelhof,9L. Eklund,50I. El Rifai,5Ch. Elsasser,39D. Elsby,44A. Falabella,14,eC. Fa¨rber,11 G. Fardell,49C. Farinelli,40S. Farry,12V. Fave,38D. Ferguson,49V. Fernandez Albor,36F. Ferreira Rodrigues,1
M. Ferro-Luzzi,37S. Filippov,32C. Fitzpatrick,37M. Fontana,10F. Fontanelli,19,iR. Forty,37O. Francisco,2 M. Frank,37C. Frei,37M. Frosini,17,fS. Furcas,20E. Furfaro,23A. Gallas Torreira,36D. Galli,14,cM. Gandelman,2
P. Gandini,54Y. Gao,3J. Garofoli,56P. Garosi,53J. Garra Tico,46L. Garrido,35C. Gaspar,37R. Gauld,54 E. Gersabeck,11M. Gersabeck,53T. Gershon,47,37Ph. Ghez,4V. Gibson,46V. V. Gligorov,37C. Go¨bel,57 D. Golubkov,30A. Golutvin,52,30,37A. Gomes,2H. Gordon,54M. Grabalosa Ga´ndara,5R. Graciani Diaz,35 L. A. Granado Cardoso,37E. Grauge´s,35G. Graziani,17A. Grecu,28E. Greening,54S. Gregson,46O. Gru¨nberg,58 B. Gui,56E. Gushchin,32Yu. Guz,34T. Gys,37C. Hadjivasiliou,56G. Haefeli,38C. Haen,37S. C. Haines,46S. Hall,52
T. Hampson,45S. Hansmann-Menzemer,11N. Harnew,54S. T. Harnew,45J. Harrison,53T. Hartmann,58J. He,7 V. Heijne,40K. Hennessy,51P. Henrard,5J. A. Hernando Morata,36E. van Herwijnen,37E. Hicks,51D. Hill,54 M. Hoballah,5C. Hombach,53P. Hopchev,4W. Hulsbergen,40P. Hunt,54T. Huse,51N. Hussain,54D. Hutchcroft,51
D. Hynds,50V. Iakovenko,43M. Idzik,26P. Ilten,12R. Jacobsson,37A. Jaeger,11E. Jans,40P. Jaton,38F. Jing,3 M. John,54D. Johnson,54C. R. Jones,46B. Jost,37M. Kaballo,9S. Kandybei,42M. Karacson,37T. M. Karbach,37 I. R. Kenyon,44U. Kerzel,37T. Ketel,41A. Keune,38B. Khanji,20O. Kochebina,7I. Komarov,38,31R. F. Koopman,41
P. Koppenburg,40M. Korolev,31A. Kozlinskiy,40L. Kravchuk,32K. Kreplin,11M. Kreps,47G. Krocker,11 P. Krokovny,33F. Kruse,9M. Kucharczyk,20,25,jV. Kudryavtsev,33T. Kvaratskheliya,30,37V. N. La Thi,38 D. Lacarrere,37G. Lafferty,53A. Lai,15D. Lambert,49R. W. Lambert,41E. Lanciotti,37G. Lanfranchi,18,37
C. Langenbruch,37T. Latham,47C. Lazzeroni,44R. Le Gac,6J. van Leerdam,40J. -P. Lees,4R. Lefe`vre,5 A. Leflat,31,37J. Lefranc¸ois,7S. Leo,22O. Leroy,6B. Leverington,11Y. Li,3L. Li Gioi,5M. Liles,51R. Lindner,37 C. Linn,11B. Liu,3G. Liu,37J. von Loeben,20S. Lohn,37J. H. Lopes,2E. Lopez Asamar,35N. Lopez-March,38H. Lu,3 D. Lucchesi,21,qJ. Luisier,38H. Luo,49F. Machefert,7I. V. Machikhiliyan,4,30F. Maciuc,28O. Maev,29,37S. Malde,54 G. Manca,15,dG. Mancinelli,6U. Marconi,14R. Ma¨rki,38J. Marks,11G. Martellotti,24A. Martens,8L. Martin,54
A. Martı´n Sa´nchez,7M. Martinelli,40D. Martinez Santos,41D. Martins Tostes,2A. Massafferri,1R. Matev,37 Z. Mathe,37C. Matteuzzi,20E. Maurice,6A. Mazurov,16,32,37,eJ. McCarthy,44R. McNulty,12A. Mcnab,53 B. Meadows,59,54F. Meier,9M. Meissner,11M. Merk,40D. A. Milanes,8M. -N. Minard,4J. Molina Rodriguez,57 S. Monteil,5D. Moran,53P. Morawski,25M. J. Morello,22,sR. Mountain,56I. Mous,40F. Muheim,49K. Mu¨ller,39 R. Muresan,28B. Muryn,26B. Muster,38P. Naik,45T. Nakada,38R. Nandakumar,48I. Nasteva,1M. Needham,49 N. Neufeld,37A. D. Nguyen,38T. D. Nguyen,38C. Nguyen-Mau,38,pM. Nicol,7V. Niess,5R. Niet,9N. Nikitin,31 T. Nikodem,11A. Nomerotski,54A. Novoselov,34A. Oblakowska-Mucha,26V. Obraztsov,34S. Oggero,40S. Ogilvy,50 O. Okhrimenko,43R. Oldeman,15,37,dM. Orlandea,28J. M. Otalora Goicochea,2P. Owen,52B. K. Pal,56A. Palano,13,b
M. Palutan,18J. Panman,37A. Papanestis,48M. Pappagallo,50C. Parkes,53C. J. Parkinson,52G. Passaleva,17 G. D. Patel,51M. Patel,52G. N. Patrick,48C. Patrignani,19,iC. Pavel-Nicorescu,28A. Pazos Alvarez,36
A. Pellegrino,40G. Penso,24,lM. Pepe Altarelli,37S. Perazzini,14,cD. L. Perego,20,jE. Perez Trigo,36 A. Pe´rez-Calero Yzquierdo,35P. Perret,5M. Perrin-Terrin,6G. Pessina,20K. Petridis,52A. Petrolini,19,iA. Phan,56
E. Picatoste Olloqui,35B. Pietrzyk,4T. Pilarˇ,47D. Pinci,24S. Playfer,49M. Plo Casasus,36F. Polci,8G. Polok,25 A. Poluektov,47,33E. Polycarpo,2D. Popov,10B. Popovici,28C. Potterat,35A. Powell,54J. Prisciandaro,38
V. Pugatch,43A. Puig Navarro,38G. Punzi,22,rW. Qian,4J. H. Rademacker,45B. Rakotomiaramanana,38 M. S. Rangel,2I. Raniuk,42N. Rauschmayr,37G. Raven,41S. Redford,54M. M. Reid,47A. C. dos Reis,1 S. Ricciardi,48A. Richards,52K. Rinnert,51V. Rives Molina,35D. A. Roa Romero,5P. Robbe,7E. Rodrigues,53
P. Rodriguez Perez,36S. Roiser,37V. Romanovsky,34A. Romero Vidal,36J. Rouvinet,38T. Ruf,37F. Ruffini,22 H. Ruiz,35P. Ruiz Valls,35,oG. Sabatino,24,kJ. J. Saborido Silva,36N. Sagidova,29P. Sail,50B. Saitta,15,d C. Salzmann,39B. Sanmartin Sedes,36M. Sannino,19,iR. Santacesaria,24C. Santamarina Rios,36E. Santovetti,23,k
M. Sapunov,6A. Sarti,18,lC. Satriano,24,mA. Satta,23M. Savrie,16,eD. Savrina,30,31P. Schaack,52M. Schiller,41 H. Schindler,37M. Schlupp,9M. Schmelling,10B. Schmidt,37O. Schneider,38A. Schopper,37M. -H. Schune,7 R. Schwemmer,37B. Sciascia,18A. Sciubba,24M. Seco,36A. Semennikov,30K. Senderowska,26I. Sepp,52N. Serra,39
J. Serrano,6P. Seyfert,11M. Shapkin,34I. Shapoval,42,37P. Shatalov,30Y. Shcheglov,29T. Shears,51,37 222001-6
L. Shekhtman,33O. Shevchenko,42V. Shevchenko,30A. Shires,52R. Silva Coutinho,47T. Skwarnicki,56 N. A. Smith,51E. Smith,54,48M. Smith,53M. D. Sokoloff,59F. J. P. Soler,50F. Soomro,18,37D. Souza,45 B. Souza De Paula,2B. Spaan,9A. Sparkes,49P. Spradlin,50F. Stagni,37S. Stahl,11O. Steinkamp,39S. Stoica,28
S. Stone,56B. Storaci,39M. Straticiuc,28U. Straumann,39V. K. Subbiah,37S. Swientek,9V. Syropoulos,41 M. Szczekowski,27P. Szczypka,38,37T. Szumlak,26S. T’Jampens,4M. Teklishyn,7E. Teodorescu,28F. Teubert,37 C. Thomas,54E. Thomas,37J. van Tilburg,11V. Tisserand,4M. Tobin,39S. Tolk,41D. Tonelli,37S. Topp-Joergensen,54 N. Torr,54E. Tournefier,4,52S. Tourneur,38M. T. Tran,38M. Tresch,39A. Tsaregorodtsev,6P. Tsopelas,40N. Tuning,40
M. Ubeda Garcia,37A. Ukleja,27D. Urner,53U. Uwer,11V. Vagnoni,14G. Valenti,14R. Vazquez Gomez,35 P. Vazquez Regueiro,36S. Vecchi,16J. J. Velthuis,45M. Veltri,17,gG. Veneziano,38M. Vesterinen,37B. Viaud,7 D. Vieira,2X. Vilasis-Cardona,35,nA. Vollhardt,39D. Volyanskyy,10D. Voong,45A. Vorobyev,29V. Vorobyev,33
C. Voß,58H. Voss,10R. Waldi,58R. Wallace,12S. Wandernoth,11J. Wang,56D. R. Ward,46N. K. Watson,44 A. D. Webber,53D. Websdale,52M. Whitehead,47J. Wicht,37J. Wiechczynski,25D. Wiedner,11L. Wiggers,40
G. Wilkinson,54M. P. Williams,47,48M. Williams,55F. F. Wilson,48J. Wishahi,9M. Witek,25S. A. Wotton,46 S. Wright,46S. Wu,3K. Wyllie,37Y. Xie,49,37F. Xing,54Z. Xing,56Z. Yang,3R. Young,49X. Yuan,3O. Yushchenko,34
M. Zangoli,14M. Zavertyaev,10,aF. Zhang,3L. Zhang,56W. C. Zhang,12Y. Zhang,3A. Zhelezov,11 A. Zhokhov,30L. Zhong,3and A. Zvyagin37
(LHCb Collaboration)
1Centro Brasileiro de Pesquisas Fı´sicas (CBPF), Rio de Janeiro, Brazil 2Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil 3
Center for High Energy Physics, Tsinghua University, Beijing, People’s Republic of China 4LAPP, Universite´ de Savoie, CNRS/IN2P3, Annecy-Le-Vieux, France
5Clermont Universite´, Universite´ Blaise Pascal, CNRS/IN2P3, LPC, Clermont-Ferrand, France 6CPPM, Aix-Marseille Universite´, CNRS/IN2P3, Marseille, France
7LAL, Universite´ Paris-Sud, CNRS/IN2P3, Orsay, France
8LPNHE, Universite´ Pierre et Marie Curie, Universite´ Paris Diderot, CNRS/IN2P3, Paris, France 9Fakulta¨t Physik, Technische Universita¨t Dortmund, Dortmund, Germany
10Max-Planck-Institut fu¨r Kernphysik (MPIK), Heidelberg, Germany
11Physikalisches Institut, Ruprecht-Karls-Universita¨t Heidelberg, Heidelberg, Germany 12
School of Physics, University College Dublin, Dublin, Ireland 13Sezione INFN di Bari, Bari, Italy
14Sezione INFN di Bologna, Bologna, Italy 15Sezione INFN di Cagliari, Cagliari, Italy 16Sezione INFN di Ferrara, Ferrara, Italy
17Sezione INFN di Firenze, Firenze, Italy
18Laboratori Nazionali dell’INFN di Frascati, Frascati, Italy 19Sezione INFN di Genova, Genova, Italy
20Sezione INFN di Milano Bicocca, Milano, Italy 21Sezione INFN di Padova, Padova, Italy
22Sezione INFN di Pisa, Pisa, Italy 23Sezione INFN di Roma Tor Vergata, Roma, Italy 24Sezione INFN di Roma La Sapienza, Roma, Italy
25Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, Krako´w, Poland 26AGH University of Science and Technology, Krako´w, Poland
27National Center for Nuclear Research (NCBJ), Warsaw, Poland 28
Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania 29Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia
30Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia 31Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia 32Institute for Nuclear Research of the Russian Academy of Sciences (INR RAN), Moscow, Russia 33Budker Institute of Nuclear Physics (SB RAS) and Novosibirsk State University, Novosibirsk, Russia
34Institute for High Energy Physics (IHEP), Protvino, Russia 35Universitat de Barcelona, Barcelona, Spain
36Universidad de Santiago de Compostela, Santiago de Compostela, Spain 37
European Organization for Nuclear Research (CERN), Geneva, Switzerland 38Ecole Polytechnique Fe´de´rale de Lausanne (EPFL), Lausanne, Switzerland
39Physik-Institut, Universita¨t Zu¨rich, Zu¨rich, Switzerland
40Nikhef National Institute for Subatomic Physics, Amsterdam, Netherlands
41Nikhef National Institute for Subatomic Physics and VU University Amsterdam, Amsterdam, Netherlands 42NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine
43Institute for Nuclear Research of the National Academy of Sciences (KINR), Kyiv, Ukraine 44University of Birmingham, Birmingham, United Kingdom
45H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom 46Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom
47
Department of Physics, University of Warwick, Coventry, United Kingdom 48STFC Rutherford Appleton Laboratory, Didcot, United Kingdom
49School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom 50School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom
51Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom 52Imperial College London, London, United Kingdom
53School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom 54Department of Physics, University of Oxford, Oxford, United Kingdom
55Massachusetts Institute of Technology, Cambridge, Massachusetts, USA 56Syracuse University, Syracuse, New York, USA
57Pontifı´cia Universidade Cato´lica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil [associated with Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil] 58Institut fu¨r Physik, Universita¨t Rostock, Rostock, Germany (associated with Physikalisches Institut,
Ruprecht-Karls-Universita¨t Heidelberg, Heidelberg, Germany)
59University of Cincinnati, Cincinnati, Ohio, USA (associated with Syracuse University, Syracuse, New York, USA)
a
P.N. Lebedev Physical Institute, Russian Academy of Science (LPI RAS), Moscow, Russia. bUniversita` di Bari, Bari, Italy.
cUniversita` di Bologna, Bologna, Italy. dUniversita` di Cagliari, Cagliari, Italy. eUniversita` di Ferrara, Ferrara, Italy. fUniversita` di Firenze, Firenze, Italy. gUniversita` di Urbino, Urbino, Italy.
hUniversita` di Modena e Reggio Emilia, Modena, Italy. iUniversita` di Genova, Genova, Italy.
jUniversita` di Milano Bicocca, Milano, Italy. kUniversita` di Roma Tor Vergata, Roma, Italy.
lUniversita` di Roma La Sapienza, Roma, Italy. mUniversita` della Basilicata, Potenza, Italy.
nLIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain. o
IFIC, Universitat de Valencia-CSIC, Valencia, Spain. pHanoi University of Science, Hanoi, Vietnam. qUniversita` di Padova, Padova, Italy.
rUniversita` di Pisa, Pisa, Italy.
sScuola Normale Superiore, Pisa, Italy.
