Abstract
Signals consistent with the B_{c}^{+}(2S) and B_{c}^{*+}(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 b[over ¯]c states are observed in the B_{c}^{+}π^{+}π^{-} invariant mass spectrum, with the ground state B_{c}^{+} reconstructed through its decay to J/ψπ^{+}. The two states are reconstructed as two well-resolved peaks, separated in mass by 29.1±1.5(stat)±0.7(syst) MeV. The observation of two peaks, rather than one, is established with a significance exceeding five standard deviations. The mass of the B_{c}^{+}(2S) meson is measured to be 6871.0±1.2(stat)±0.8(syst)±0.8(B_{c}^{+}) MeV, where the last term corresponds to the uncertainty in the world-average B_{c}^{+} mass.
Highlights
PffisffiS1⁄4ign1a3lsTceoVn,siisnteannt with event the Bþc ð2SÞ and BÃcþð2SÞ states are sample corresponding to an integrated observed in proton-proton collisions at luminosity of 143 fb−1, collected by the CMS experiment during the 2015–2018 LHC running periods
These excited bc states are observed in the Bþc πþπ− invariant mass spectrum, with the ground state Bþc reconstructed through its decay to J=ψπþ
The ground state was discovered in 1998 by the CDF Collaboration [1]. The spectrum of this heavy quarkonium family is predicted to be very populated [2,3,4,5,6,7,8,9,10,11,12,13], but spectroscopic observations and measurements of production properties remain scarce. Their production yields are significantly smaller than those of the charmonium and bottomonium states, the bc production cross sections being proportional to the fourth power of the strong coupling constant, αS4
Summary
(Received 1 February 2019; revised manuscript received 18 February 2019; published 2 April 2019). PffisffiS1⁄4ign1a3lsTceoVn,siisnteannt with event the Bþc ð2SÞ and BÃcþð2SÞ states are sample corresponding to an integrated observed in proton-proton collisions at luminosity of 143 fb−1, collected by the CMS experiment during the 2015–2018 LHC running periods These excited bc states are observed in the Bþc πþπ− invariant mass spectrum, with the ground state Bþc reconstructed through its decay to J=ψπþ. The invariant mass distribution of the selected Bþc → J=ψπþ candidates, shown, is fitted to the expected Bþc signal peak, modeled as a sum of two Gaussian functions with a common mean, superimposed on a background composed of three sources of events: (i) the combinatorial background resulting from associating the J=ψ with uncorrelated charged particles, parametrized by a. W3 hsehroewMsðtBhþce πMþπðB−Þþc aπnþdπM−Þð−BþcMÞðaBreþc,ÞreþspmecBtþcivdeilsy-, the reconstructed invariant masses of the Bþc πþπ− and Bþc candidates, and mBþc is the world-average Bþc mass [25]
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