untitled University of Birmingham Study of beauty hadron decays into Pairs of charm hadrons LHCb Collaboration DOI: 10.1103/PhysRevLett.112.202001 License: Creative Commons: Attribution (CC BY) Document Version Publisher's PDF, also known as Version of record Citation for published version (Harvard): LHCb Collaboration 2014, 'Study of beauty hadron decays into Pairs of charm hadrons', Physical Review Letters, vol. 112, no. 20, 202001. https://doi.org/10.1103/PhysRevLett.112.202001 Link to publication on Research at Birmingham portal General rights Unless a licence is specified above, all rights (including copyright and moral rights) in this document are retained by the authors and/or the copyright holders. 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Aaij et al.* (LHCb Collaboration) (Received 17 March 2014; published 21 May 2014) First observations of the decays Λ0b → Λ þ c D − ðsÞ are reported using data corresponding to an integrated luminosity of 3 fb−1 collected at 7 and 8 TeV center-of-mass energies in proton-proton collisions with the LHCb detector. In addition, the most precise measurement of the branching fraction BðB0s → DþD−s Þ is made and a search is performed for the decays B0ðsÞ → Λ þ c Λ − c . The results obtained are BðΛ0b → Λþc D−Þ=BðΛ0b → Λþc D−s Þ ¼ 0.042 � 0.003ðstatÞ � 0.003ðsystÞ;� BðΛ0b → Λþc D−s Þ BðB̄0 → DþD−s Þ � = � BðΛ0b → Λþc π−Þ BðB̄0 → Dþπ−Þ � ¼ 0.96 � 0.02ðstatÞ � 0.06ðsystÞ; BðB0s → DþD−s Þ=BðB̄0 → DþD−s Þ ¼ 0.038 � 0.004ðstatÞ � 0.003ðsystÞ; BðB̄0 → Λþc Λ−c Þ=BðB̄0 → DþD−s Þ < 0.0022½95% C.L.�; BðB0s → Λþc Λ−c Þ=BðB0s → DþD−s Þ < 0.30½95% C.L.�: Measurement of the mass of the Λ0b baryon relative to the B̄ 0 meson gives MðΛ0bÞ − MðB̄0Þ ¼ 339.72 � 0.24ðstatÞ � 0.18ðsystÞ MeV=c2. This result provides the most precise measurement of the mass of the Λ0b baryon to date. DOI: 10.1103/PhysRevLett.112.202001 PACS numbers: 14.20.Mr, 13.30.−a Hadrons are systems of quarks bound by the strong interaction, described at the fundamental level by quantum chromodynamics (QCD). Low-energy phenomena, such as the binding of quarks and gluons within hadrons, lie in the nonperturbative regime of QCD and are difficult to calculate. Much progress has been made in recent years in the study of beauty mesons [1]; however, many aspects of beauty baryons are still largely unknown. Many decays of beauty mesons into pairs of charm hadrons have branching fractions at the percent level [2]. Decays of beauty baryons into pairs of charm hadrons are expected to be of compa- rable size, yet none have been observed to date. If such decays do have sizable branching fractions, they could be used to study beauty-baryon properties. For example, a comparison of beauty meson and baryon branching frac- tions can be used to test factorization in these decays [3]. Many models and techniques have been developed that attempt to reproduce the spectrum of the measured hadron masses, such as constituent-quark models or lattice QCD calculations [4]. Precise measurements of ground-state beauty-baryon masses are required to permit precision tests of a variety of QCD models [5–11]. The Λ0b baryon mass is particularly interesting in this context, since several ground-state beauty-baryon masses are measured relative to that of the Λ0b [12]. This Letter reports the first observation of the decays Λ0b → Λ þ c D − s and Λ 0 b → Λ þ c D −. The decay Λ0b → Λ þ c D − s is used to make the most precise measurement to date of the mass of the Λ0b baryon. Improved measurements of the branching fraction BðB0s → DþD−s Þ and stringent upper limits on BðB0ðsÞ → Λþc Λ−c Þ are also reported. Charge con- jugated decay modes are implied throughout this Letter. The data used correspond to an integrated luminosity of 1 and 2 fb−1 collected at 7 and 8 TeV center-of-mass energies in pp collisions, respectively, with the LHCb detector. The LHCb detector is a single-arm forward spectrometer covering the pseudorapidity range 2 < η < 5, described in detail in Refs. [13–18]. Samples of simulated events are used to determine selection efficiencies, to model candidate distributions, and to investigate possible background con- tributions. In the simulation, pp collisions are generated using PYTHIA [19] with a specific LHCb configuration [20]. Decays of hadronic particles are described by EVTGEN [21], in which final-state radiation is generated using PHOTOS [22]. The interaction of the generated particles with the detector and its response are implemented using the GEANT4 toolkit [23] as described in Ref. [24]. In this analysis, signal beauty-hadron candidates are formed by combining charm-hadron candidate pairs recon- structed in the following decay modes: Dþ → K−πþπþ, Dþs → K −Kþπþ, and Λþc → pK −πþ. The measured invari- ant mass of each charm-hadron candidate, the resolution on * 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 attribution to the author(s) and the published articles title, journal citation, and DOI. PRL 112, 202001 (2014) P H Y S I C A L R E V I E W L E T T E R S week ending 23 MAY 2014 0031-9007=14=112(20)=202001(9) 202001-1 © 2014 CERN, for the LHCb Collaboration http://dx.doi.org/10.1103/PhysRevLett.112.202001 http://dx.doi.org/10.1103/PhysRevLett.112.202001 http://dx.doi.org/10.1103/PhysRevLett.112.202001 http://dx.doi.org/10.1103/PhysRevLett.112.202001 http://creativecommons.org/licenses/by/3.0/ http://creativecommons.org/licenses/by/3.0/ which is about 6 − 8 MeV=c2 , is required to be within 25 MeV=c2 of the nominal value [2]. To improve the resolution of the beauty-hadron mass, the decay chain is fit imposing kinematic and vertex constraints [25]; this includes constraining the charm-hadron masses to their nominal values. To suppress contributions from noncharm decays, the reconstructed charm-hadron decay vertex is required to be downstream of, and significantly displaced from, the reconstructed beauty-hadron decay vertex. A boosted decision tree (BDT) [26] is used to select each type of charm-hadron candidate. These BDTs use five variables for the charm hadron and 23 for each of its decay products. The variables include kinematic quantities, track and vertex qualities, and particle identification (PID) infor- mation. The signal samples used to train the BDTs are obtained from large data sets of B̄0→Dþπ−, B̄0s →D þ s π −, and Λ0b → Λ þ c π − decays that are background subtracted using weights [27] obtained from fits to the beauty-hadron invariant mass distributions. The background data samples are taken from the charm-hadron and high-mass beauty- hadron sidebands in the same data sets. To obtain the BDT efficiency in a given signal decay mode, the kinematical properties and correlations between the two charm hadrons are taken from simulation. The BDT response distributions are obtained from independent data samples of the decays used in the BDT training, weighted to match the kinematics of the signal. Because of the kinematic similarity of the decays Dþ → K−πþπþ, Dþs → K −Kþπþ, and Λþc → pK −πþ, cross feed may occur among beauty-hadron decays into pairs of charm hadrons. For example, cross feed between Dþ and Dþs mesons occurs when a K −hþπþ candidate is reconstructed in the Dþ mass region under the hþ ¼ πþ hypothesis and in the Dþs mass region under the h þ ¼ Kþ hypothesis. In such situations, an arbitration is performed: if the ambiguous track (hþ) can be associated to an oppositely charged track to form a ϕð1020Þ → KþK− candidate, the kaon hypothesis is taken, resulting in a Dþs assignment to the charm-hadron candidate; otherwise, stringent PID requirements are applied to hþ to choose which hypothesis to take. The efficiency of these arbitra- tions, which is found to be about 90% per charm hadron, is obtained using simulated signal decays to model the kinematical properties and D�þ → D0πþ calibration data for the PID efficiencies. The misidentification probability is roughly 1% per charm hadron. Signal yields are determined by performing unbinned extended likelihood fits to the beauty-hadron invariant- mass spectra observed in the data. The signal distributions are modeled using a so-called Apollonios function, which is the exponential of a hyperbola combined with a power- law low-mass tail [28]. The peak position and resolution parameters are allowed to vary while fitting the data, while the low-mass tail parameters are taken from simulation and fixed in the fits. Four categories of background contributions are consid- ered: partially reconstructed decays of beauty hadrons where at least one final-state particle is not reconstructed; decays into a single charm hadron and three light hadrons; reflections, defined as cases where the cross-feed arbitra- tion fails to remove a misidentified particle; and combi- natorial background. The only partially reconstructed decays that contribute in the mass region studied are those where a single pion or photon is not reconstructed; thus, only final states comprised of D�þðsÞ or Σ þ c and another charm hadron are considered (e.g., Λ0b → Λ þ c D �− s ). These back- ground contributions are modeled using kernel probability density functions (PDFs) [29] obtained from simulation; their yields are free to vary in the fits. Single-charm back- grounds are studied using data that are reconstructed outside of a given charm-hadron mass region. These backgrounds are found to be Oð1%Þ of the size of the signal yield for signal decays containing a D−s (e.g., B̄ 0 → DþK−Kþπ−) and are negligible otherwise. The only non-negligible reflection is found to be Λ0b → Λ þ c D − s decays misidentified as Λþc D − candidates. The invariant-mass distribution for this reflection is obtained from simulation, while the normali- zation is fixed using simulation and the aforementioned PID calibration sample to determine the fraction of Λ0b → Λ þ c D − s decays that are not removed by the cross-feed criteria. Reflections of B̄0 → DþD−s decays misidentified as final states containing Λþc particles do not have a peaking structure in the beauty-hadron invariant mass and, therefore, are absorbed into the combinatorial backgrounds, which are modeled using exponential distributions. Figure 1 shows the invariant mass spectra for the Λ0b → Λ þ c D − s and Λ 0 b → Λ þ c D − candidates. The signal yields obtained are 4633 � 69 and 262 � 19 for Λ0b → Λþc D−s and Λ0b → Λ þ c D − , respectively. This is the first observation of each of these decays. The ratio of branching fractions determined using the nominal D−s [2] and D − [30] meson branching fractions and the ratio of efficiencies is BðΛ0b → Λþc D−Þ BðΛ0b → Λþc D−s Þ ¼ 0.042 � 0.003ðstatÞ � 0.003ðsystÞ: The similarity of the final states and the shared parent particle result in many cancellations of uncertainties in the determination of the ratio of branching fractions. The remaining uncertainties include roughly equivalent contri- butions from determining the efficiency-corrected yields and from the ratio of charm-hadron branching fractions (see Table I). The dominant contribution to the uncertainty of the fit PDF is due to the low-mass background contribu- tions, which are varied in size and shape to determine the effect on the signal yield. The uncertainty due to signal model is found to be negligible. The efficiencies of the cross feed and BDT criteria are determined in a data-driven manner that produces small uncertainties. The observed ratio is approximately the ratio of the relevant quark-mixing PRL 112, 202001 (2014) P H Y S I C A L R E V I E W L E T T E R S week ending 23 MAY 2014 202001-2 factors and meson decay constants, jVcd=Vcsj2× ðfD=fDsÞ2 ≈ 0.034, as expected assuming nonfactorizable effects are small. The branching fraction of the decay Λ0b → Λ þ c D − s is determined relative to that of the B̄0 → DþD−s decay. Using DþD−s BDT criteria optimized to maximize the expected B̄0 significance, 19 395 � 145 B̄0 → DþD−s decays are obs- erved (see Fig. 2). The measurement of BðΛ0b → Λþc D−s Þ= BðB̄0 → DþD−s Þ is complicated by the fact that the ratio of the Λ0b and B̄ 0 production cross sections, σðΛ0bÞ=σðB̄0Þ, dependson the pT ofthe beauty hadrons [32].Figure 3 shows the ratio of efficiency-corrected yields, NðΛ0b → Λþc D−s Þ= NðB̄0 → DþD−s Þ, as a function of beauty-hadron pT. The ratio of branching-fraction ratios is obtained using a fit with the shape of the pT dependence measured in BðΛ0b → Λþc π−Þ=BðB̄0 → Dþπ−Þ [33] and found to be � BðΛ0b → Λþc D−s Þ BðB̄0 → DþD−s Þ � = � BðΛ0b → Λþc π−Þ BðB̄0 → Dþπ−Þ � ¼ 0.96 � 0.02ðstatÞ � 0.06ðsystÞ: This result does not depend on the absolute ratio of production cross sections or on any charm-hadron branching fractions.The systematicuncertaintiesonthisresultarelisted in Table I. The uncertainty in the fit model is due largely to the sizable single-charm background contributions to these modes and to contributions from the fits described in Ref. [33]. The BðΛ0b → Λþc π−Þ=BðB̄0 → Dþπ−Þ result was obtained only using data collected at ffiffiffi s p ¼ 7 TeV. The ratio NðΛ0b → Λþc D−s Þ=NðB̄0 → DþD−s Þ is observed to be con- sistent in data collected at ffiffiffi s p ¼ 7 and 8 TeV. The statistical uncertainty on this comparison is assigned as the systematic uncertainty on the energy dependence of the Λ0b and B̄ 0 production fractions. The ratio of branching ratios is con- sistent with unity, as expected assuming small nonfactoriz- able effects. The kinematic similarity of the decay modes Λ0b → Λþc D − s and B̄ 0 → DþD−s permits a precision measurement of the mass difference of the Λ0b and B̄ 0 hadrons. The relatively small value of ½MðΛ0bÞ − MðΛþc Þ − MðD−s Þ� − ½MðB̄0Þ − MðDþÞ − MðD−s Þ� means that the uncertainty due to momentum scale, the dominant uncertainty in absolute-mass measurements, mostly cancels; however, it is still important to determine accurately the momenta of the final-state particles. The momentum-scale calibration of the spectrometer, which accounts for imperfect knowledge of the magnetic field and alignment, is discussed in detail in Refs. [12,34]. The uncertainty on the calibrated momentum scale is estimated to be 0.03% by comparing various particle masses measured at LHCb to their nominal values [34]. The kinematic and vertex constraints used in the fits described previously reduce the statistical uncertainty on MðΛ0bÞ − MðB̄0Þ by improving the resolution. These ]2 Mass [MeV/cs - D+cΛ 5400 5600 5800 ) 2 C a n d id a te s / (5 M e V /c 0 500 1000 LHCb - s D + cΛ→ 0 bΛ - s D + cΣ→ 0 bΛ -*s D + cΛ→ 0 bΛ -π-K+ K+cΛ→ 0 bΛ Combinatorial ]2 Mass [MeV/c - D+cΛ 5400 5500 5600 5700 5800 5900 ) 2 C a n d id a te s / (1 0 M e V /c 0 50 100 - D+cΛ→ 0 bΛ - D+cΣ + - D*+cΛ→ 0 bΛ - sD + cΛ→ 0 bΛ Combinatorial LHCb - D+cΛ→ 0 bΛ - D+cΣ + - D*+cΛ→ 0 bΛ - sD + cΛ→ 0 bΛ Combinatorial FIG. 1 (color online). Invariant mass distributions for (left) Λ0b → Λ þ c D − s and (right) Λ 0 b → Λ þ c D − candidates with the fits described in the text overlaid. TABLE I. Relative systematic uncertainties on branching fraction measurements (%). The production ratio σðB0sÞ=σðB̄0Þ is taken from Ref. [31]. The numbers in parentheses in the last column are for the B0s decay mode. Source BðΛ0b → Λþc D−Þ= BðΛ0b → Λþc D−s Þ ð½BðΛ0b → Λþc D−s Þ=BðB̄0 → DþD−s Þ�Þ= ð½BðΛ0b → Λþc π−Þ=BðB̄0 → Dþπ−Þ�Þ BðB0s → DþD−s Þ= BðB̄0 → DþD−s Þ BðB0ðsÞ → Λþc Λ−c Þ= BðB0ðsÞ → DþD−s Þ Efficiency 3.5 5.2 1.0 3.9 (5.0) Fit model 3.0 2.6 3.0 � � � BðDþðsÞ; Λþc Þ 5.2 � � � � � � 8.8 σðB0sÞ=σðB̄0Þ � � � � � � 5.8 � � � σðΛ0bÞ=σðB̄0Þ � � � 2.0 � � � � � � Total 6.9 6.1 6.6 9.6 (10.1) PRL 112, 202001 (2014) P H Y S I C A L R E V I E W L E T T E R S week ending 23 MAY 2014 202001-3 constraints also increase the systematic uncertainty by introducing a dependence on the precision of the nominal charm-hadron masses. These constraints are not imposed in the mass measurement, as it is found that this approach produces a smaller total uncertainty. The mass difference obtained is MðΛ0bÞ − MðB̄0Þ ¼ 339.72 � 0.24ðstatÞ � 0.18ðsystÞ MeV=c2: The dominant systematic uncertainty (see Table II) arises due to a correlation between the reconstructed beauty- hadron mass and reconstructed charm-hadron flight dis- tance. The large difference in the Λþc and D þ hadron lifetimes [2] could lead to only a partial cancellation of the biases induced by the charm-lifetime selection criteria. This effect is studied in simulation and a 0.16 MeV=c2 uncer- tainty is assigned. The 0.03% uncertainty in the momentum scale results in an uncertainty on the mass difference of 0.08 MeV=c2. Many variations in the fit model are consid- ered, and none produce a significant shift in the mass difference. Thesystematic uncertainty in themass difference due to the uncertainty in the amount of detector material in which charged particles lose energy is negligible [34]. Furthermore, the uncertainty on MðΛ0bÞ − MðB̄0Þ due to differences in beauty-hadron production kinematics, as seen in Fig. 3, is also found to be negligible. Using the nominal value for MðB̄0Þ[2] gives MðΛ0bÞ ¼ 5619.30 � 0.34 MeV=c2, where the uncertainty includes both statistical and systematic contributions. This is the most precise result to date. The total uncertainty is dominated by statistics and charm-hadron lifetime effects; thus, this result can be treated as being uncorrelated with the previous LHCb result obtained using the Λ0b → J=ψΛ 0 decay [35]. A weighted average of the LHCb results gives MðΛ0bÞ ¼ 5619.36 � 0.26 MeV=c2. This value may then be used to improve the precision of the Ξ−b and Ω − b baryon masses using their mass differences with respect to the Λ0b baryon, as reported in Ref. [35]. Using BDT criteria optimized for maximizing the expected significance of B0s → D þD−s , 14 608 � 121 B̄0 and 143 � 14 B0s decays are observed (see Fig. 2), from which the ratio extracted is BðB0s → DþD−s Þ BðB̄0 → DþD−s Þ ¼ 0.038 � 0.004ðstatÞ � 0.003ðsystÞ: This is the most precise measurement to date of BðB0s → DþD−s Þ and supersedes Ref. [36]. Since the two decay modes sharethesamefinal state,many systematic unc- ertainties cancel. The dominant contribution to the uncer- tainty comes from the beauty-hadron production fractions. ]2 Mass [MeV/cs - D+D 5200 5400 5600 ) 2 C a n d id a te s / (5 M e V /c 0 1000 2000 3000 4000 LHCb s - D+ D→ 0 B s - D+ D→s 0B - sD +* D→ 0 B -* s D + D→ 0 B -π-K+ K+ D→ 0 B Combinatorial ]2 Mass [MeV/cs - D+D 5200 5400 5600 ) 2 C a n d id a te s / (5 M e V /c 0 20 40 60 80 100 LHCb s - D+ D→ 0 B s - D+ D→s 0B - sD +* D→ 0 B -* s D + D→ 0 B -π-K+ K+ D→ 0 B Combinatorial FIG. 2 (color online). Invariant mass distributions for DþD−s candidates selected using BDT criteria optimized for the (left) B̄0 → DþD−s and (right) B 0 s → D þD−s decay modes with the fits described in the text overlaid. [MeV/c] T p 0 10000 20000 30000 40000 ) s- D + D → 0 B )/ N ( s- D + c Λ → 0 b Λ N ( 0 0.2 0.4 0.6 0.8 1 LHCb FIG. 3 (color online). Efficiency-corrected ratio of the yields of Λ0b → Λ þ c D − s and B̄ 0 → DþD−s vs pT. The points are located at the mean pT value of the Λ 0 b in each bin. The curve shows the data fit with the shape of the pT dependence measured in Ref. [33]. TABLE II. Systematic uncertainties for MðΛ0bÞ − MðB̄0Þ. Description Value (MeV=c2) Λþc − Dþ lifetime difference 0.16 Momentum scale 0.08 Fit model 0.02 Total 0.18 PRL 112, 202001 (2014) P H Y S I C A L R E V I E W L E T T E R S week ending 23 MAY 2014 202001-4 A small additional uncertainty on the efficiency arises due to theuncertaintyontheB0s lifetime.Uncertaintyinthefitmodel is largely due to the size of the combinatorial background neartheB0s peak.Themeasuredratioofbranchingfractionsis approximately the ratio of quark-mixing factors, as expected assuming nonfactorizable effects are small. A search is also performed for the decay modes B0ðsÞ → Λ þ c Λ − c . Regions centered around the nominal B 0 ðsÞ meson masses with boundaries defined such that each region contains 95% of the corresponding signal are determined using simulation. The expected background contribution in each of these regions is obtained from the charm-hadron mass sidebands. Applying this technique to the B̄0 → DþD−s and Λ 0 b → Λ þ c D − ðsÞ decays produces back- ground estimates consistent with those obtained by fitting the invariant mass spectra for those modes. The number of observed candidates in each signal region is then compared to the expected background contribution; no significant excess is observed in either Λþc Λ − c signal region. The limits obtained using the method of Ref. [37] and the known D−s [2], D− [30], and Λþc [38] hadron branching fractions are BðB̄0 → Λþc Λ−c Þ BðB̄0 → DþD−s Þ < 0.0022½95% C.L.�; BðB0s → Λþc Λ−c Þ BðB0s → DþD−s Þ < 0.30½95% C.L.�: For these results the lifetime of the light-mass B0s eigenstate is assumed, as this produces the most conservative limits [1]. This is the best limit to date for the B̄0 decay mode and the first limit for the B0s decay mode. In summary, first observations and relative branching- fraction measurements have been made for the decays Λ0b → Λ þ c D − ðsÞ. The most precise measurements of the Λ 0 b baryon mass and of BðB0s → DþD−s Þ have been presented and the most stringent upper limits have been placed on BðB0ðsÞ → Λþc Λ−c Þ. Using BðB̄0 → DþD−s Þ ¼ ð7.2 � 0.8Þ × 10−3 [2] and BðΛ0b → Λþc π−Þ=BðB̄0 → Dþπ−Þ from Ref. [33], the absolute branching fractions obtained are BðΛ0b → Λþc D−s Þ ¼ ð1.1 � 0.1Þ × 10−2; BðΛ0b → Λþc D−Þ ¼ ð4.7 � 0.6Þ × 10−4; BðB0s → DþD−s Þ ¼ ð2.7 � 0.5Þ × 10−4; BðB̄0 → Λþc Λ−c Þ < 1.6 × 10−5½95% C.L.�; BðB0s → Λþc Λ−c Þ < 8.0 × 10−5½95% C:L:�: These results are all consistent with expectations that assume small nonfactorizable effects. 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 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 (The Netherlands); SCSR (Poland); MEN/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 acknowl- edge the support received from EPLANET and the ERC under FP7. The Tier1 computing centers are supported by IN2P3 (France), KIT and BMBF (Germany), INFN (Italy), NWO and SURF (The Netherlands), PIC (Spain), GridPP (United Kingdom). We are indebted to the communities behind the multiple open-source software packages we depend on. We are also thankful for the computing resources and the access to software R&D tools provided by Yandex LLC (Russia). [1] Y. Amhis et al. 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Stone,59 B. Storaci,40 S. Stracka,23,38 M. Straticiuc,29 U. Straumann,40 R. Stroili,22 V. K. Subbiah,38 L. Sun,57 W. Sutcliffe,53 K. Swientek,27 S. Swientek,9 V. Syropoulos,42 M. Szczekowski,28 P. Szczypka,39,38 D. Szilard,2 T. Szumlak,27 S. T’Jampens,4 M. Teklishyn,7 G. Tellarini,16,c E. Teodorescu,29 F. Teubert,38 C. Thomas,55 E. Thomas,38 J. van Tilburg,41 V. Tisserand,4 M. Tobin,39 S. Tolk,42 L. Tomassetti,16,c D. Tonelli,38 S. Topp- Joergensen,55 N. Torr,55 E. Tournefier,4 S. Tourneur,39 M. T. Tran,39 M. Tresch,40 A. Tsaregorodtsev,6 P. Tsopelas,41 N. Tuning,41 M. Ubeda Garcia,38 A. Ukleja,28 A. Ustyuzhanin,63 U. Uwer,11 V. Vagnoni,14 G. Valenti,14 A. Vallier,7 R. Vazquez Gomez,18 P. Vazquez Regueiro,37 C. Vázquez Sierra,37 S. Vecchi,16 J. J. Velthuis,46 M. Veltri,17,t G. Veneziano,39 M. Vesterinen,11 B. Viaud,7 D. Vieira,2 M. Vieites Diaz,37 X. Vilasis-Cardona,36,h A. Vollhardt,40 D. Volyanskyy,10 PRL 112, 202001 (2014) P H Y S I C A L R E V I E W L E T T E R S week ending 23 MAY 2014 202001-7 D. Voong,46 A. Vorobyev,30 V. Vorobyev,34 C. Voß,62 H. Voss,10 J. A. de Vries,41 R. Waldi,62 C. Wallace,48 R. Wallace,12 J. Walsh,23 S. Wandernoth,11 J. Wang,59 D. R. Ward,47 N. K. Watson,45 A. D. Webber,54 D. Websdale,53 M. Whitehead,48 J. Wicht,38 D. Wiedner,11 G. Wilkinson,55 M. P. Williams,45 M. Williams,56 F. F. Wilson,49 J. Wimberley,58 J. Wishahi,9 W. Wislicki,28 M. Witek,26 G. Wormser,7 S. A. Wotton,47 S. Wright,47 S. Wu,3 K. Wyllie,38 Y. Xie,61 Z. Xing,59 Z. Xu,39 Z. Yang,3 X. Yuan,3 O. Yushchenko,35 M. Zangoli,14 M. Zavertyaev,10,u F. Zhang,3 L. Zhang,59 W. C. Zhang,12 Y. Zhang,3 A. Zhelezov,11 A. Zhokhov,31 L. Zhong3 and A. Zvyagin38 (LHCb Collaboration) 1Centro Brasileiro de Pesquisas Físicas (CBPF), Rio de Janeiro, Brazil 2Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil 3Center for High Energy Physics, Tsinghua University, Beijing, China 4LAPP, Université de Savoie, CNRS/IN2P3, Annecy-Le-Vieux, France 5Clermont Université, Université Blaise Pascal, CNRS/IN2P3, LPC, Clermont-Ferrand, France 6CPPM, Aix-Marseille Université, CNRS/IN2P3, Marseille, France 7LAL, Université Paris-Sud, CNRS/IN2P3, Orsay, France 8LPNHE, Université Pierre et Marie Curie, Université Paris Diderot, CNRS/IN2P3, Paris, France 9Fakultät Physik, Technische Universität Dortmund, Dortmund, Germany 10Max-Planck-Institut für Kernphysik (MPIK), Heidelberg, Germany 11Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany 12School 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 Milano, Milano, Italy 22Sezione INFN di Padova, Padova, Italy 23Sezione INFN di Pisa, Pisa, Italy 24Sezione INFN di Roma Tor Vergata, Roma, Italy 25Sezione INFN di Roma La Sapienza, Roma, Italy 26Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, Kraków, Poland 27AGH - University of Science and Technology, Faculty of Physics and Applied Computer Science, Kraków, Poland 28National Center for Nuclear Research (NCBJ), Warsaw, Poland 29Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania 30Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia 31Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia 32Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia 33Institute for Nuclear Research of the Russian Academy of Sciences (INR RAN), Moscow, Russia 34Budker Institute of Nuclear Physics (SB RAS) and Novosibirsk State University, Novosibirsk, Russia 35Institute for High Energy Physics (IHEP), Protvino, Russia 36Universitat de Barcelona, Barcelona, Spain 37Universidad de Santiago de Compostela, Santiago de Compostela, Spain 38European Organization for Nuclear Research (CERN), Geneva, Switzerland 39Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland 40Physik-Institut, Universität Zürich, Zürich, Switzerland 41Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherlands 42Nikhef National Institute for Subatomic Physics and VU University Amsterdam, Amsterdam, The Netherlands 43NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine 44Institute for Nuclear Research of the National Academy of Sciences (KINR), Kyiv, Ukraine 45University of Birmingham, Birmingham, United Kingdom 46H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom 47Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom 48Department of Physics, University of Warwick, Coventry, United Kingdom 49STFC Rutherford Appleton Laboratory, Didcot, United Kingdom PRL 112, 202001 (2014) P H Y S I C A L R E V I E W L E T T E R S week ending 23 MAY 2014 202001-8 50School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom 51School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom 52Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom 53Imperial College London, London, United Kingdom 54School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom 55Department of Physics, University of Oxford, Oxford, United Kingdom 56Massachusetts Institute of Technology, Cambridge, Massachusetts, USA 57University of Cincinnati, Cincinnati, Ohio, USA 58University of Maryland, College Park, Maryland, USA 59Syracuse University, Syracuse, New York, USA 60Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil (associated with Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil) 61Institute of Particle Physics, Central China Normal University, Wuhan, Hubei, China (associated with Center for High Energy Physics, Tsinghua University, Beijing, China) 62Institut für Physik, Universität Rostock, Rostock, Germany (associated with Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany) 63National Research Centre Kurchatov Institute, Moscow, Russia (associated with Institute of Theoretical and Experimental Physics [ITEP], Moscow, Russia) 64Instituto de Fisica Corpuscular (IFIC), Universitat de Valencia-CSIC, Valencia, Spain (associated with Universitat de Barcelona, Barcelona, Spain) 65KVI-University of Groningen, Groningen, The Netherlands (associated with Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherlands) 66Celal Bayar University, Manisa, Turkey (associated with European Organization for Nuclear Research [CERN], Geneva, Switzerland) aAlso at Politecnico di Milano, Milano, Italy. bAlso at Università di Firenze, Firenze, Italy. cAlso at Università di Ferrara, Ferrara, Italy. dAlso at Università della Basilicata, Potenza, Italy. eAlso at Università di Modena e Reggio Emilia, Modena, Italy. fAlso at Università di Padova, Padova, Italy. gAlso at Università di Milano Bicocca, Milano, Italy. hAlso at LIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain. iAlso at Università di Bologna, Bologna, Italy. jAlso at Università di Roma Tor Vergata, Roma, Italy. kAlso at Università di Genova, Genova, Italy. lAlso at Universidade Federal do Triângulo Mineiro (UFTM), Uberaba-MG, Brazil. mAlso at Università di Cagliari, Cagliari, Italy. nAlso at Scuola Normale Superiore, Pisa, Italy. oAlso at Hanoi University of Science, Hanoi, Viet Nam. pAlso at Università di Bari, Bari, Italy. qAlso at Università degli Studi di Milano, Milano, Italy. rAlso at Università di Pisa, Pisa, Italy. sAlso at Università di Roma La Sapienza, Roma, Italy. tAlso at Università di Urbino, Urbino, Italy. uAlso at P.N. Lebedev Physical Institute, Russian Academy of Science (LPI RAS), Moscow, Russia. PRL 112, 202001 (2014) P H Y S I C A L R E V I E W L E T T E R S week ending 23 MAY 2014 202001-9