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Register a new userObservation of a new baryon state in the $Lambda_b^0pi^+pi^-$ mass spectrum
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A new baryon state is observed in the $Lambda_b^0pi^+pi^-$ mass spectrum with high significance using a data sample of $pp$ collisions, collected with the LHCb detector at centre-of-mass energies $sqrt{s}=7, 8$ and 13TeV, corresponding to an integrated luminosity of 9fb$^{-1}$. The mass and natural width of the new state are measured to be begin{eqnarray*} m & = & 6072.3 pm 2.9 pm 0.6 pm 0.2 MeV,, Gamma & = & 72 pm 11 pm 2 MeV,, end{eqnarray*} where the first uncertainty is statistical and the second systematic. The third uncertainty for the mass is due to imprecise knowledge of the $Lambda_b^0$ baryon mass. The new state is consistent with the first radial excitation of the $Lambda_b^0$ baryon, the $Lambda_b(2S)^0$ resonance. Updated measurements of the masses and the upper limits on the natural widths of the previously observed $Lambda_b(5912)^0$ and $Lambda_b(5920)^0$ states are also reported.
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The decays $ Lambda_b^0 to psi(2S)pK^-$ and $ Lambda_b^0 to J/psi pi^+ pi^- pK^-$ are observed in a data sample corresponding to an integrated luminosity of 3fb$^{-1}$, collected in proton-proton collisions at 7 and 8TeV centre-of-mass energies by the LHCb detector. The $psi(2S)$ mesons are reconstructed through the decay modes $psi(2S)tomu^+mu^-$ and $psi(2S)to J/psipi^+pi^-$. The branching fractions relative to that of $ Lambda_b^0 to J/psi pK^-$ are measured to be begin{eqnarray*} frac{mathcal{B}(Lambda_b^0 to psi(2S) pK^-)} {mathcal{B}(Lambda_b^0 to J/psi pK^-)} & = & (20.70pm 0.76pm 0.46pm 0.37)times10^{-2} ,, frac{mathcal{B}(Lambda_b^0 to J/psi pi^+ pi^- pK^-)} {mathcal{B}(Lambda_b^0 to J/psi pK^-)} & = & (20.86pm 0.96pm 1.34)times10^{-2} ,, end{eqnarray*} where the first uncertainties are statistical, the second are systematic and the third is related to the knowledge of $J/psi$ and $psi(2S)$ branching fractions. The mass of the $Lambda_b^0$ baryon is measured to be $$ M(Lambda_b^0) = 5619.65 pm 0.17 pm 0.17mathrm{MeV}/c^2,$$ where the uncertainties are statistical and systematic.
We report the observation of a new structure in the $Lambda_b^0 pi^+pi^-$ spectrum using the full LHCb data set of $pp$ collisions, corresponding to an integrated luminosity of $9,mathrm{fb}^{-1}$, collected at $sqrt{s}=7$, 8 and $13,mathrm{TeV}$. A study of the structure suggests its interpretation as a superposition of two almost degenerate narrow states. The masses and widths of these states are measured to be begin{eqnarray*} m_{Lambda_{b}mathrm{(6146)}^0} &=&6146.17 pm 0.33 pm 0.22 pm 0.16,mathrm{MeV} ,, m_{Lambda_{b}mathrm{(6152)}^0} &=&6152.51 pm 0.26 pm 0.22 pm 0.16,mathrm{MeV} ,, Gamma_{Lambda_{b}mathrm{(6146)}^0}&=&phantom{615}2.9phantom{0}pm 1.3phantom{0} pm 0.3phantom{0},mathrm{MeV},, Gamma_{Lambda_{b}mathrm{(6152)}^0} &=&phantom{615}2.1phantom{0}pm 0.8phantom{0} pm 0.3phantom{0},mathrm{MeV},, end{eqnarray*} with a mass splitting of $Delta m = 6.34 pm 0.32 pm 0.02,mathrm{MeV}$, where the first uncertainty is statistical, the second systematic and the third derives from the knowledge of the mass of the $Lambda_b^0$ baryon. The measured masses and widths of these new excited states suggest their possible interpretation as a doublet of $Lambda_{b}mathrm{(1D)}^0$ states.
The first observation of the Cabibbo-suppressed decay $Lambda_b^0rightarrow J/psi p pi^-$ is reported using a data sample of proton-proton collisions at 7 and 8 TeV, corresponding to an integrated luminosity of 3 $rm fb^{-1}$. A prominent signal is observed and the branching fraction relative to the decay mode $Lambda_b^0rightarrow J/psi p K^-$ is determined to be $$ frac{{cal B}(Lambda_b^0rightarrow J/psi p pi^-)}{{cal B}(Lambda_b^0rightarrow J/psi p K^-)}=0.0824pm0.0025:(text{stat})pm0.0042:(text{syst}). $$ A search for direct CP violation is performed. The difference in the CP asymmetries between these two decays is found to be $$ {cal A}_{CP}(Lambda_b^0rightarrow J/psi p pi^-)-{cal A}_{CP}(Lambda_b^0rightarrow J/psi p K^-)=(+5.7pm 2.4:(text{stat})pm1.2:(text{syst}))%, $$ which is compatible with CP symmetry at the $2.2sigma$ level.
With a sample of 225.3 million $J/psi$ events taken with the BESIII detector, the decay $J/psirightarrow gamma 3(pi^+pi^-)$ is analyzed. A structure at 1.84 GeV/c$^2$ is observed in the $3(pi^+pi^-)$ invariant mass spectrum with a statistical significance of 7.6$sigma$ . The mass and width are measured to be $M=1842.2pm 4.2^{+7.1}_{-2.6}$ MeV/c$^2$ and $Gamma=83pm 14 pm 11$ MeV. The product branching fraction is determined to be $B(J/psirightarrowgamma X(1840))times B(X(1840)rightarrow 3(pi^+pi^-))=(2.44pm0.36^{+0.60}_{-0.74})times 10^{-5}$. No $eta^prime$ signals are observed in the $3(pi^+pi^-)$ invariant mass spectrum, and the upper limit of the branching fraction for the decay $eta^primerightarrow 3(pi^+pi^-)$ is set to be $3.1times10^{-5}$ at a 90% confidence level.
Using $1.09times10^{9}$ $J/psi$ events collected by the BESIII experiment in 2012, we study the $J/psirightarrowgammaeta^{prime}pi^{+}pi^{-}$ process and observe a significant abrupt change in the slope of the $eta^{prime}pi^{+}pi^{-}$ invariant mass distribution at the proton-antiproton ($pbar{p}$) mass threshold. We use two models to characterize the $eta^{prime}pi^{+}pi^{-}$ line shape around $1.85~text{GeV}/c^{2}$: one which explicitly incorporates the opening of a decay threshold in the mass spectrum (Flatt{e} formula), and another which is the coherent sum of two resonant amplitudes. Both fits show almost equally good agreement with data, and suggest the existence of either a broad state around $1.85~text{GeV}/c^{2}$ with strong couplings to $pbar{p}$ final states or a narrow state just below the $pbar{p}$ mass threshold. Although we cannot distinguish between the fits, either one supports the existence of a $pbar{p}$ molecule-like state or bound state with greater than $7sigma$ significance.
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