Compact Muon Solenoid
LHC, CERN
Visit us: CMS Public Website, CMS Physics ;
Contact us: CMS Publications Committee
| CMS-BPH-18-007 ; CERN-EP-2019-014 | ||
| Observation of two excited $ \mathrm{B^{+}_{c}} $ states and measurement of the ${\mathrm{B^{+}_{c}} \mathrm{(2S)}}$ mass in pp collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 1 February 2019 | ||
| Phys. Rev. Lett. 122 (2019) 132001 | ||
| Abstract: Signals consistent with the ${\mathrm{B^{+}_{c}} \mathrm{(2S)}}$ and ${\mathrm{B^{*+}_{c}} \mathrm{(2S)}}$ states are observed in proton-proton collisions at $\sqrt{s} = $ 13 TeV, in an event sample corresponding to an integrated luminosity of 143 fb$^{-1}$, collected by the CMS experiment during the 2015-2018 LHC running periods. These excited $\mathrm{\bar{b}c} $ states are observed in the ${\mathrm{B^{+}_{c}} \pi^{+} \pi^{-}}$ invariant mass spectrum, with the ground state $ \mathrm{B^{+}_{c}} $ reconstructed through its decay to ${\mathrm{J}/\psi \pi^{+}} $. The two states are well resolved from each other and are observed with a significance exceeding five standard deviations. The mass of the ${\mathrm{B^{+}_{c}} \mathrm{(2S)}}$ meson is measured to be 6871.0 $\pm$ 1.2 (stat) $\pm$ 0.8 (syst) $\pm$ 0.8 ($\mathrm{B^{+}_{c}} $) MeV, where the last term corresponds to the uncertainty in the world-average $ \mathrm{B^{+}_{c}} $ mass. | ||
| Links: e-print arXiv:1902.00571 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
png pdf |
Figure 1:
Transitions between the lightest ${\mathrm {B_{c}}}$ states, with solid and dashed lines indicating the emission of photons and pion pairs, respectively [2]. |
png pdf |
Figure 2:
The invariant mass distribution of the ${{\mathrm {B_{c}}} ^{+}}$ candidates. The vertical dashed lines indicate the mass window retained for the reconstruction of the ${{{\mathrm {B_{c}}} ^{+} \mathrm {(2S)}}}$ and ${{{\mathrm {B_{c}}} ^{*+}} \mathrm {(2S)}}$ candidates. The vertical bars on the points represent the statistical uncertainty in the data. The contributions from various sources are shown by the stacked distributions. The solid line represents the result of the fit. |
png pdf |
Figure 3:
The $M({\mathrm{B^{+}_{c}} \pi^{+} \pi^{-}} ) - M({{\mathrm {B_{c}}} ^{+}}) + m_{{{\mathrm {B_{c}}} ^{+}}}$ distribution. The ${{{\mathrm {B_{c}}}} ^{+} \mathrm {(2S)}}$ is assumed to be the right-most peak. The vertical bars on the points represent the statistical uncertainty in the data. The contributions from the various sources are shown by the stacked distributions. The solid line represents the result of the fit. |
| Summary |
| In summary, signals consistent with the ${\mathrm{B^{+}_{c}} \mathrm{(2S)}}$ and ${\mathrm{B^{*+}_{c}} \mathrm{(2S)}}$ states have been separately observed for the first time by investigating the ${\mathrm{B^{+}_{c}}} \pi^{+}\pi^{-}$ invariant mass spectrum measured by CMS. The analysis is based on the entire LHC sample of proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to a total integrated luminosity of 143 fb$^{-1}$. The two peaks are well resolved, with a measured mass difference of $\Delta M = $ 29.1 $\pm$ 1.5 (stat) $\pm$ 0.7 (syst) MeV. The ${\mathrm{B^{+}_{c}} \mathrm{(2S)}}$ mass is measured to be 6871.0 $\pm$ 1.2 (stat) $\pm$ 0.8 (syst) $\pm$ 0.8 (${\mathrm{B^{+}_{c}}}$) MeV, where the last term is the uncertainty in the world-average ${\mathrm{B^{+}_{c}}}$ mass. Because the low-energy photon emitted in the ${\mathrm{B^{*+}_{c}} \to {\mathrm{B^{+}_{c}}} \gamma}$ radiative decay is not reconstructed, the observed ${\mathrm{B^{*+}_{c}} \mathrm{(2S)}}$ peak has a mass lower than the true value, which remains unknown. These measurements contribute significantly to the detailed characterization of heavy meson spectroscopy and provide a rich source of information on the nonperturbative QCD processes that bind heavy quarks into hadrons. |
| References | ||||
| 1 | CDF Collaboration | Observation of the ${\mathrm{B^{+}_{c}}}$ meson in $ {\mathrm{p}}\mathrm{\bar{p}}\ $ collisions at $ \sqrt{s} = $ 1.8 TeV | PRL 81 (1998) 2432 | hep-ex/9805034 |
| 2 | E. J. Eichten and C. Quigg | Mesons with beauty and charm: Spectroscopy | PRD 49 (1994) 5845 | hep-ph/9402210 |
| 3 | S. S. Gershtein, V. V. Kiselev, A. K. Likhoded, and A. V. Tkabladze | ${\mathrm{B^{+}_{c}}}$ spectroscopy | PRD 51 (1995) 3613 | hep-ph/9406339 |
| 4 | J. Zeng, J. W. Van Orden, and W. Roberts | Heavy mesons in a relativistic model | PRD 52 (1995) 5229 | hep-ph/9412269 |
| 5 | S. N. Gupta and J. M. Johnson | ${\mathrm{B^{+}_{c}}}$ spectroscopy in a quantum chromodynamic potential model | PRD 53 (1996) 312 | hep-ph/9511267 |
| 6 | C. T. H. Davies et al. | ${\mathrm{B^{+}_{c}}}$ spectroscopy from lattice QCD | PLB 382 (1996) 131 | hep-lat/9602020 |
| 7 | L. P. Fulcher | Phenomenological predictions of the properties of the ${\mathrm{B^{+}_{c}}}$ system | PRD 60 (1999) 074006 | hep-ph/9806444 |
| 8 | D. Ebert, R. N. Faustov, and V. O. Galkin | Properties of heavy quarkonia and ${\mathrm{B^{+}_{c}}}$ mesons in the relativistic quark model | PRD 67 (2003) 014027 | hep-ph/0210381 |
| 9 | S. Godfrey | Spectroscopy of ${\mathrm{B^{+}_{c}}}$ mesons in the relativized quark model | PRD 70 (2004) 054017 | hep-ph/0406228 |
| 10 | A. Berezhnoy and A. Likhoded | The observation possibility of ${\mathrm{B^{+}_{c}}}$ excitations at LHC | PoS QFTHEP2013 (2013) 051 | 1307.5993 |
| 11 | E. B. Gregory et al. | A prediction of the ${\mathrm{B^{*}_{c}}}$ mass in full lattice QCD | PRL 104 (2010) 022001 | 0909.4462 |
| 12 | R. J. Dowdall, C. T. H. Davies, T. C. Hammant, and R. R. Horgan | Precise heavy-light meson masses and hyperfine splittings from lattice QCD including charm quarks in the sea | PRD 86 (2012) 094510 | 1207.5149 |
| 13 | N. Mathur, M. Padmanath, and S. Mondal | Precise predictions of charmed-bottom hadrons from lattice QCD | PRL 121 (2018) 202002 | 1806.04151 |
| 14 | ATLAS Collaboration | Observation of an excited ${\mathrm{B^{*\pm}_{c}}}$ meson state with the ATLAS detector | PRL 113 (2014) 212004 | 1407.1032 |
| 15 | LHCb Collaboration | Search for excited ${\mathrm{B^{+}_{c}}}$ states | JHEP 01 (2018) 138 | 1712.04094 |
| 16 | CMS Collaboration | The CMS experiment at the CERN LHC | JINST 3 (2008) S08004 | CMS-00-001 |
| 17 | CMS Collaboration | The CMS trigger system | JINST 12 (2017) P01020 | CMS-TRG-12-001 1609.02366 |
| 18 | CMS Collaboration | Performance of the CMS muon detector and muon reconstruction with proton-proton collisions at $ \sqrt{s}= $ 13 TeV | JINST 13 (2018) P06015 | CMS-MUO-16-001 1804.04528 |
| 19 | C.-H. Chang, X.-Y. Wang, and X.-G. Wu | BCVEGPY2.2: A newly upgraded version for hadronic production of the meson ${\mathrm{B^{+}_{c}}}$ and its excited states | CPC 197 (2015) 335 | 1507.05176 |
| 20 | T. Sjostrand, S. Mrenna, and P. Skands | A brief introduction to PYTHIA 8.1 | Comp. Phys. Comm. 178 (2008) 852 | 0710.3820 |
| 21 | D. J. Lange | The EvtGen particle decay simulation package | NIMA 462 (2001) 152 | |
| 22 | E. Barberio and Z. W\c as | PHOTOS - a universal Monte Carlo for QED radiative corrections: version 2.0 | CPC 79 (1994) 291 | |
| 23 | GEANT4 Collaboration | GEANT4--a simulation toolkit | NIMA 506 (2003) 250 | |
| 24 | CMS Collaboration | Description and performance of track and primary-vertex reconstruction with the CMS tracker | JINST 9 (2014) P10009 | CMS-TRK-11-001 1405.6569 |
| 25 | Particle Data Group, M. Tanabashi et al. | Review of Particle Physics | PRD 98 (2018) 030001 | |
| 26 | R. Fruhwirth, W. Waltenberger, and P. Vanlaer | Adaptive vertex fitting | JPG 34 (2007) N343 | |
| 27 | CMS Collaboration | Measurement of the ratio of the production cross sections times branching fractions of $ \mathrm{B}_{\mathrm{c}}^{\pm} \to \mathrm{J}/\psi \pi^{\pm} $ and $ \mathrm{B^{\pm}} \to \mathrm{J}/\psi \mathrm{K^{\pm}} $ and $ \mathcal{B}(\mathrm{B}_{\mathrm{c}}^{\pm} \to \mathrm{J}/\psi \pi^{\pm}\pi^{\pm} {\pi^\mathrm{\mp}})/\mathcal{B}(\mathrm{B}_{\mathrm{c}}^{\pm} \to \mathrm{J}/\psi \pi^{\pm}) $ in $ {\mathrm{p}}{\mathrm{p}} $ collisions at $ \sqrt{s} = $ 7 TeV | JHEP 01 (2015) 063 | CMS-BPH-12-011 1410.5729 |
| 28 | CMS Collaboration | Measurement of b hadron lifetimes in pp collisions at $ \sqrt{s} = $ 8 TeV | EPJC 78 (2018) 457 | CMS-BPH-13-008 1710.08949 |
| 29 | ARGUS Collaboration | Search for hadronic $ \mathrm{b} \to \mathrm{u} $ decays | PLB 241 (1990) 278 | |
| 30 | LHCb Collaboration | Measurement of the ratio of branching fractions $ \mathcal{B} ({\mathrm{B^{+}_{c}}} \to \mathrm{J}/\psi \mathrm{K}^{+}) / \mathcal{B}({\mathrm{B^{+}_{c}}} \to \mathrm{J}/\psi \pi^{+}) $ | JHEP 09 (2016) 153 | 1607.06823 |
| 31 | CMS Collaboration | Search for the X(5568) state decaying into $ \mathrm{B_s}^0 \pi^{\pm} $ in proton-proton collisions at $ \sqrt{s}= $ 8 TeV | PRL 120 (2018) 202005 | CMS-BPH-16-002 1712.06144 |
| 32 | CMS Collaboration | Studies of $ \mathrm{B}^*_{\mathrm{s2}}(5840)^0 $ and $ \mathrm{B}_{\mathrm{s1}}(5830)^0 $ mesons including the observation of the $ \mathrm{B}^*_{\mathrm{s2}}(5840)^0 \rightarrow \mathrm{B}^0 \mathrm{K}^0_{\mathrm{S}} $ decay in proton-proton collisions at $ \sqrt{s} = $ 8 TeV | EPJC 78 (2018) 939 | CMS-BPH-16-003 1809.03578 |
| 33 | S. S. Wilks | The large-sample distribution of the likelihood ratio for testing composite hypotheses | Annals Math. Statist. 9 (1938) 60 | |
| 34 | G. Cowan, K. Cranmer, E. Gross, and O. Vitells | Asymptotic formulae for likelihood-based tests of new physics | EPJC 71 (2011) 1554 | 1007.1727 |
|
|
Compact Muon Solenoid LHC, CERN |
|
|
|
|
|
|