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| CMS-BPH-17-008 ; CERN-EP-2018-134 | ||
| Observation of the $ \chi_{\mathrm{b}1}(\mathrm{3P}) $ and $ \chi_{\mathrm{b}2}(\mathrm{3P}) $ and measurement of their masses | ||
| CMS Collaboration | ||
| 29 May 2018 | ||
| Phys. Rev. Lett. 121 (2018) 092002 | ||
| Abstract: The $ \chi_{\mathrm{b}1}(\mathrm{3P}) $ and $ \chi_{\mathrm{b}2}(\mathrm{3P}) $ states are observed through their $ \Upsilon(\mathrm{3S}) \gamma$ decays, using an event sample of proton-proton collisions collected by the CMS experiment at the CERN LHC. The data were collected at a center-of-mass energy of 13 TeV and correspond to an integrated luminosity of 80.0 fb$^{-1}$. The $ \Upsilon(\mathrm{3S}) $ mesons are identified through their dimuon decay channel, while the low-energy photons are detected after converting to $ \mathrm{ e^+e^- } $ pairs in the silicon tracker, leading to a $ \chi_{\mathrm{b}}(\mathrm{3P}) $ mass resolution of 2.2 MeV. This is the first time that the $J = $ 1 and 2 states are well resolved and their masses individually measured: 10 513.42 $\pm$ 0.41 (stat) $\pm$ 0.18 (syst) MeV and 10 524.02 $\pm$ 0.57 (stat) $\pm$ 0.18 (syst) MeV; they are determined with respect to the world-average value of the $ \Upsilon(\mathrm{3S}) $ mass, which has an uncertainty of 0.5 MeV. The mass splitting is measured to be 10.60 $\pm$ 0.64 (stat) $\pm$ 0.17 (syst) MeV. | ||
| Links: e-print arXiv:1805.11192 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
The dimuon invariant mass distribution, in two equidistant $ | y |$ ranges. The midrapidity dimuons have a significantly better mass resolution. |
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Figure 2:
The PES as a function of the measured photon energy, obtained using $ {\chi _{{{\mathrm {c}}}1}}\to {\mathrm {J}/\psi} \, \gamma $ decays from the 2015-2016 (open circles) and 2017 (filled circles) data samples. The points are drawn at the average $E_{\gamma}$ in each bin. The curve represents the parametrization mentioned in the text. |
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Figure 3:
The invariant mass distributions of the $ {\chi _{{{\mathrm {b}}}J}}\to {\Upsilon} \mathrm {(nS)} \, \gamma $ candidates ($ \mathrm {n} =$ 1, 2, 3), after the PES correction. The inset shows the ${\chi _\mathrm {\mathrm{b}1}\mathrm {(1P)}}$ and ${\chi _\mathrm {\mathrm{b}1}\mathrm {(2P)}}$ masses fitted before (open squares) and after (filled circles) the PES correction, with vertical bars representing the statistical uncertainties. The world-average values [33] are shown by the horizontal bands, with dashed lines representing their total uncertainties. |
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Figure 4:
The invariant mass distribution of the $ {\chi _{{{\mathrm {b}}}J} \mathrm {(3P)}}\to {\Upsilon \mathrm {(3S)}}\, \gamma $ candidates. The vertical bars are the statistical uncertainties. The curves represent the fitted contributions of the two signal peaks, the background, and their sum. |
| Summary |
| In summary, data samples of pp collisions at $\sqrt{s} = $ 13 TeV,collected by CMS in the years 2015-2017, corresponding to an integrated luminosity of 80.0 fb$^{-1}$, were used to measure the invariant mass distribution of the $\chi_{\mathrm{b}}(\mathrm{3P}) \to \Upsilon(\mathrm{3S}) \gamma $ candidates, with the $ \Upsilon(\mathrm{3S}) $ mesons detected in the dimuon decay channel and the photons reconstructed through conversions to $ \mathrm{ e^+e^- } $ pairs. The measured distribution is well reproduced by the superposition of the $ \chi_{\mathrm{b}1}(\mathrm{3P}) $ and $ \chi_{\mathrm{b}2}(\mathrm{3P}) $ quarkonium states, overlaid on a smooth continuum. This is the first time that the two states are individually observed. Their mass difference is $\Delta M = $ 10.60 $\pm$ 0.64 (stat) $\pm$ 0.17 (syst) MeV, and their masses, assuming that the $J = $ 1 state is the lighter one, are $M(\chi_{\mathrm{b}1}(\mathrm{3P})) = $ 10 513.42 $\pm$ 0.41 (stat) $\pm$ 0.18 (syst) and $M(\chi_{\mathrm{b}2}(\mathrm{3P})) = $ 10 524.02 $\pm$ 0.57 (stat) $\pm$ 0.18 (syst) MeV, having an additional 0.5 MeV uncertainty reflecting the present precision of the world-average $ \Upsilon(\mathrm{3S}) $ mass. This measurement fills a gap in the spin-dependent bottomonium spectrum below the open-beauty threshold and should significantly contribute to an improved understanding of the nonperturbative spin-orbit interactions affecting quarkonium spectroscopy. |
| References | ||||
| 1 | Quarkonium Working Group Collaboration, N. Brambilla et al. | Heavy Quarkonium Physics | CERN Yellow Reports: Monographs. CERN, Geneva | |
| 2 | N. Brambilla et al. | Heavy quarkonium: progress, puzzles, and opportunities | EPJC 71 (2011) 1534 | 1010.5827 |
| 3 | N. Brambilla et al. | QCD and strongly coupled gauge theories: Challenges and perspectives | EPJC 74 (2014) 2981 | 1404.3723 |
| 4 | G. C. Nayak, J.-W. Qiu, and G. F. Sterman | Fragmentation, factorization and infrared poles in heavy quarkonium production | PLB 613 (2005) 45 | hep-ph/0501235 |
| 5 | G. Nayak, J.-W. Qiu, and G. Sterman | Fragmentation, NRQCD and NNLO factorization analysis in heavy quarkonium production | PRD 72 (2005) 114012 | hep-ph/0509021 |
| 6 | G. C. Nayak, J.-W. Qiu, and G. F. Sterman | NRQCD factorization and velocity-dependence of NNLO poles in heavy quarkonium production | PRD 74 (2006) 074007 | hep-ph/0608066 |
| 7 | N. Brambilla, A. Pineda, J. Soto, and A. Vairo | Potential NRQCD: An effective theory for heavy quarkonium | NPB 566 (2000) 275 | hep-ph/9907240 |
| 8 | N. Brambilla, A. Pineda, J. Soto, and A. Vairo | The QCD potential at O(1/m) | PRD 63 (2000) 014023 | hep-ph/0002250 |
| 9 | N. Brambilla, A. Pineda, J. Soto, and A. Vairo | Effective field theories for heavy quarkonium | Rev. Mod. Phys. 77 (2005) 1423 | hep-ph/0410047 |
| 10 | G. Bodwin, E. Braaten, and P. Lepage | Rigorous QCD analysis of inclusive annihilation and production of heavy quarkonium | PRD 51 (1995) 1125 | hep-ph/9407339 |
| 11 | G. Bodwin et al. | Fragmentation contributions to hadroproduction of prompt $ \mathrm{J}/\psi, \chi_{{\mathrm{c}}J} $, and $ \psi $(2S) states | PRD 93 (2016) 034041 | 1509.07904 |
| 12 | P. Faccioli et al. | Quarkonium production at the LHC: A data-driven analysis of remarkably simple experimental patterns | PLB 773 (2017) 476 | 1702.04208 |
| 13 | P. Faccioli et al. | From identical S- and P-wave $ {p_{\mathrm{T}}} $ spectra to maximally distinct polarizations: Probing NRQCD with $ \chi $ states | EPJC 78 (2018) 268 | 1802.01106 |
| 14 | P. Faccioli, C. Louren\cco, M. Ara\'ujo, and J. Seixas | Universal kinematic scaling as a probe of factorized long-distance effects in high-energy quarkonium production | EPJC 78 (2018) 118 | 1802.01102 |
| 15 | ATLAS Collaboration | Observation of a new $ \chi_{\mathrm{b}} $ state in radiative transitions to $ \Upsilon\text{1S} $ and $ \Upsilon\text{2S} $ at ATLAS | PRL 108 (2012) 152001 | 1112.5154 |
| 16 | D0 Collaboration | Observation of a narrow mass state decaying into $ \Upsilon\text{1S}\ + \gamma $ in $ {\mathrm{p}}\overline{{\mathrm{p}}} $ collisions at $ \sqrt{s} = $ 1.96 TeV | PRD 86 (2012) 031103 | 1203.6034 |
| 17 | LHCb Collaboration | Study of $ \chi_{\mathrm{b}}\ $ meson production in pp collisions at $ \sqrt{s}= $ 7 and 8 TeV and observation of the decay $ \chi_{\mathrm{b}}(\text{3P}) \to \Upsilon\text{3S} \gamma $ | EPJC 74 (2014) 3092 | 1407.7734 |
| 18 | LHCb Collaboration | Measurement of the $ \chi_{\mathrm{b}}(\text{3P})\ $ mass and of the relative rate of $ \chi_{\mathrm{b}1}(\text{1P}) $ and $ \chi_{\mathrm{b}2}(\text{1P}) $ production | JHEP 10 (2014) 088 | 1409.1408 |
| 19 | Belle Collaboration | Observation of a narrow charmonium-like state in exclusive $ \mathrm{B}^{\pm} \to \mathrm{K}^{\pm} \pi^+ \pi^- \mathrm{J}/\psi $ decays | PRL 91 (2003) 262001 | hep-ex/0309032 |
| 20 | M. Karliner, J. L. Rosner, and T. Skwarnicki | Multiquark states | 1711.10626 | |
| 21 | A. Esposito, A. Pilloni, and A. D. Polosa | Multiquark resonances | PR 668 (2016) 1 | 1611.07920 |
| 22 | S. L. Olsen | A new hadron spectroscopy | Front. Phys. 10 (2015) 121 | 1411.7738 |
| 23 | E. J. Eichten, K. Lane, and C. Quigg | New states above charm threshold | PRD 73 (2006) 014014 | hep-ph/0511179 |
| 24 | E. J. Eichten, K. Lane, and C. Quigg | Charmonium levels near threshold and the narrow state $ \mathrm{X}Belle \to \pi^{+}\pi^{-} \mathrm{J}/\psi $ | PRD 69 (2004) 094019 | hep-ph/0401210 |
| 25 | M. Karliner and J. L. Rosner | $ \mathrm{X}(3872)$, $\mathrm{X}_{\mathrm{b}}, $ and the $ \chi_{\mathrm{b}1}(\text{3P}) $ state | PRD 91 (2015) 014014 | 1410.7729 |
| 26 | CMS Collaboration | CMS luminosity measurement for the 2015 data-taking period | CMS-PAS-LUM-15-001 | CMS-PAS-LUM-15-001 |
| 27 | CMS Collaboration | CMS luminosity measurements for the 2016 data taking period | CMS-PAS-LUM-17-001 | CMS-PAS-LUM-17-001 |
| 28 | CMS Collaboration | CMS luminosity measurements for the 2017 data taking period | CMS-PAS-LUM-17-004 | |
| 29 | CMS Collaboration | The CMS experiment at the CERN LHC | JINST 3 (2008) S08004 | CMS-00-001 |
| 30 | CMS Collaboration | The CMS trigger system | JINST 12 (2017) P01020 | CMS-TRG-12-001 1609.02366 |
| 31 | CMS Collaboration | Measurement of the relative prompt production rate of $ \chi_{\mathrm{c}2} $ and $ \chi_{\mathrm{c}1} $ in pp collisions at $ \sqrt{s}= $ 7 TeV | EPJC 72 (2012) 2251 | CMS-BPH-11-010 1210.0875 |
| 32 | CMS Collaboration | Measurement of the production cross section ratio $ \sigma(\chi_{\mathrm{b}2}(\text{1P})) / \sigma(\chi_{\mathrm{b}2}(\text{1P})) $ in pp collisions at $ \sqrt{s} = $ 8 TeV | PLB 743 (2015) 383 | CMS-BPH-13-005 1409.5761 |
| 33 | Particle Data Group, C. Patrignani et al. | Review of particle physics | CPC 40 (2016) 100001 | |
| 34 | M. J. Oreglia | A study of the reactions $\psi' \to \gamma\gamma \psi$ | PhD thesis, Stanford University, 1980 SLAC Report SLAC-R-236, see Appendix D | |
| 35 | T. Sjostrand et al. | An introduction to PYTHIA 8.2 | CPC 191 (2015) 159 | 1410.3012 |
| 36 | D. J. Lange | The EVTGEN particle decay simulation package | NIMA 462 (2001) 152 | |
| 37 | E. Barberio and Z. W\cas | PHOTOS: A universal Monte Carlo for QED radiative corrections. Version 2.0 | CPC 79 (1994) 291 | |
| 38 | GEANT4 Collaboration | GEANT4--a simulation toolkit | NIMA 506 (2003) 250 | |
| 39 | B.-Q. Li and K.-T. Chao | Bottomonium spectrum with screened potential | Commun. Theor. Phys. 52 (2009) 653 | 0909.1369 |
| 40 | C. O. Dib and N. A. Neill | $ \chi_{\mathrm{b}}(\text{3P})\ $ splitting predictions in potential models | PRD 86 (2012) 094011 | 1208.2186 |
| 41 | J.-F. Liu and G.-J. Ding | Bottomonium spectrum with coupled-channel effects | EPJC 72 (2012) 1981 | 1105.0855 |
| 42 | Bhaghyesh and K. B. Vijaya Kumar | Properties of bottomonium in a semi-relativistic model | CPC 37 (2013) 023103 | |
| 43 | W.-Z. Tian, L. Cao, Y.-C. Yang, and H. Chen | Bottomonium states versus recent experimental observations in the QCD-inspired potential model | CPC 37 (2013) 083101 | 1308.0960 |
| 44 | W. W. Repko, M. D. Santia, and S. F. Radford | Three-loop static QCD potential in heavy quarkonia | NP A 924 (2014) 65 | 1211.6373 |
| 45 | J. Ferretti, G. Galat\`a, and E. Santopinto | Quark structure of the $ \mathrm{X}Belle\ $ and $ \chi_{\mathrm{b}}(\text{3P})\ $ resonances | PRD 90 (2014) 054010 | 1401.4431 |
| 46 | J. Ferretti and E. Santopinto | Higher mass bottomonia | PRD 90 (2014) 094022 | 1306.2874 |
| 47 | S. Godfrey and K. Moats | Bottomonium mesons and strategies for their observation | PRD 92 (2015) 054034 | 1507.00024 |
| 48 | J. Segovia, P. G. Ortega, D. R. Entem, and F. Fern\'andez | Bottomonium spectrum revisited | PRD 93 (2016) 074027 | 1601.05093 |
| 49 | Y. Lu, M. N. Anwar, and B.-S. Zou | Coupled-channel effects for the bottomonium with realistic wave functions | PRD 94 (2016) 034021 | 1606.06927 |
| 50 | W.-J. Deng, H. Liu, L.-C. Gui, and X.-H. Zhong | Spectrum and electromagnetic transitions of bottomonium | PRD 95 (2017) 074002 | 1607.04696 |
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