Observation of theχb1(3P)andχb

Abstract

The χ_{b1}(3P) and χ_{b2}(3P) states are observed through their ϒ(3S)γ 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 ϒ(3S) mesons are identified through their dimuon decay channel, while the low-energy photons are detected after converting to e^{+}e^{-} pairs in the silicon tracker, leading to a χ_{b}(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: 10513.42±0.41(stat)±0.18(syst) MeV and 10524.02±0.57(stat)±0.18(syst) MeV; they are determined with respect to the world-average value of the ϒ(3S) mass, which has an uncertainty of 0.5 MeV. The mass splitting is measured to be 10.60±0.64(stat)±0.17(syst) MeV.

χb(3P) multiplet revisited: Hyperfine mass splitting and radiative transitions

“…This reflects that the χ b0 (3P) has negligible radiative decay branching fraction with comparison to χ b1 (3P) and χ b2 (3P). Compared with the potential model, the suppression of the χ b0 (3P)'s radiative width in the UQM is more consistent with the non-observation of the χ b0 (3P) in the recent CMS search of χ bJ (3P) → Υ(3S )γ [1]. This indicates that our UQM predictions are more reliable than the naive quark potential models.…”

“…With the latest CMS data [1] and the P bb in Table I, our predictions of radiative decay ratios are listed in Table V. From the Table I, one can see that the small P bb [χ b0 (3P)] make the ratios in the last three rows notably larger than that of the potential model predictions, a peculiar feature of coupledchannel effects which can be tested in the upcoming experiments. Another worth noting result from Table V is the relative size of the ratios for χ b0 (3P), which from the coupled-channel calculations is roughly 1 : 6 : 12.…”

“…After the recent CMS observation [1] of χ b1 (3P) and χ b2 (3P), χ b0 (3P) is now the only missing candidate in spintriplet 3P bottomonium. With the reference of observed mass splitting of 1P, 2P and 3P multiplets, one can predict the mass of χ b0 (3P).…”

“…The excited P-wave bottomonia, χ bJ (3P), are of special interest, since they provide a laboratory to test (and model) the non-perturbative spin-spin interactions of heavy quarks. Very recently, the CMS collaboration observed two candidates of the bottomonium 3P multiplet, χ b1 (3P) and χ b2 (3P), through their decays into Υ(3S )γ [1]. Their measured masses and mass splitting are (1)…”

“…However, these measurements can not distinguish between the candidates of χ bJ (3P) multiplet. The recent CMS analysis [1] is higher resolution search, and hence, is able to distinguish between χ b1 (3P) and χ b2 (3P) for the first time.…”