Abstract
Using pp collision data corresponding to an integrated luminosity of 8.5 fb^{-1} recorded by the LHCb experiment at center-of-mass energies of sqrt[s]=7, 8, and 13TeV, the observation of an excited B_{c}^{+} state in the B_{c}^{+}π^{+}π^{-} invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(B_{c}^{+}) MeV/c^{2}, where the last uncertainty is due to the limited knowledge of the B_{c}^{+} mass. It is consistent with expectations of the B_{c}^{*}(2^{3}S_{1})^{+} state reconstructed without the low-energy photon from the B_{c}^{*}(1^{3}S_{1})^{+}→B_{c}^{+}γ decay following B_{c}^{*}(2^{3}S_{1})^{+}→B_{c}^{*}(1^{3}S_{1})^{+}π^{+}π^{-}. Asecond state is seen with a global (local) statistical significance of 2.2σ (3.2σ) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(B_{c}^{+}) MeV/c^{2}, and is consistent with the B_{c}(2^{1}S_{0})^{+} state. These mass measurements are the most precise to date.
Highlights
6841.2 Æ 0.6ðstatÞ Æ 0.1ðsystÞ Æ 0.8ðBþc Þ MeV=c2, where the last uncertainty is due to the limited knowledge of the Bþc mass
The Bc meson family is unique in the standard model as its states are formed from two heavy quarks of different flavors
The Bc mesons are much less explored compared to quarkonia due to the small production rate, since their predominant production mechanism requires the production of both ccand bbpairs
Summary
Large Hadron Collider, the ATLAS Collaboration first reported the observation of a signal in the Bþc πþπ− mass distribution peaking 5ðsystÞ MeV=c2 using at a pp value collision of 6842pÆffiffi data at s. To reconstruct the BðcÃÞð2SÞþ candidates, Bþc candidates with MðJ=ψπþÞ ∈ 1⁄26200; 6320 MeV=c2 are combined with a pair of oppositely charged particles identified as pions. These pion candidates are required to originate from the PV, and each have pT > 300 MeV=c, p > 1500 MeV=c, and a good track-fit quality. The masses and yields of the BðcÃÞð2SÞþ peaks are determined using an unbinned maximum-likelihood fit to the distribution of the mass difference ΔM ≡ MðBþc πþπ−Þ − MðBþc Þ to eliminate the dependence on the reconstructed Bþc mass. The uncertainty of the momentum calibration is estimated using other particles, such as
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
