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Register a new userMeasurement of the relative rate of prompt $chi_{c0}$, $chi_{c1}$ and $chi_{c2}$ production at $sqrt{s}=7$TeV
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Prompt production of charmonium $chi_{c0}$, $chi_{c1}$ and $chi_{c2}$ mesons is studied using proton-proton collisions at the LHC at a centre-of-mass energy of $sqrt{s}=7$TeV. The $chi_{c}$ mesons are identified through their decay to $J/psigamma$, with $J/psitomu^+mu^-$ using photons that converted in the detector. A data sample, corresponding to an integrated luminosity of $1.0mathrm{fb}^{-1}$ collected by the LHCb detector, is used to measure the relative prompt production rate of $chi_{c1}$ and $chi_{c2}$ in the rapidity range $2.0<y<4.5$ as a function of the $J/psi$ transverse momentum from 3 to 20 GeV$/c$. First evidence for $chi_{c0}$ meson production at a high-energy hadron collider is also presented.
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The prompt production of the charmonium $chi_{c1}$ and $chi_{c2}$ mesons has been studied in proton-proton collisions at the Large Hadron Collider at a centre-of-mass energy of $sqrt{s}=7$ TeV. The $chi_c$ mesons are identified through their decays $chi_cto J/psi,gamma$ with $J/psi to mu^+ mu^-$ using 36 $mathrm{pb^{-1}}$ of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for the two $chi_c$ spin states, $sigma(chi_{c2})/sigma(chi_{c1})$, has been determined as a function of the $J/psi$ transverse momentum, $p_{mathrm{T}}^{J/psi}$, in the range from 2 to 15 GeV/$c$. The results are in agreement with the next-to-leading order non-relativistic QCD model at high $p_{mathrm{T}}^{J/psi}$ and lie consistently above the pure leading-order colour singlet prediction.
Prompt $chi_c$ production at hadron colliders may provide a unique test for the color-octet mechanism in nonrelativistic QCD. We present an analysis for the polarization observables of $chi_{c1}$ and $chi_{c2}$ at next-to-leading order in $alpha_S$, and propose to measure them at the LHC, which is expected to be important for testing the validity of NRQCD.
This Letter reports the first measurement of prompt $chi_{c1}$ and $chi_{c2}$ charmonium production in nuclear collisions at Large Hadron Collider energies. The cross-section ratio $sigma(chi_{c2}) / sigma(chi_{c1})$ is measured in $p$Pb collisions at $sqrt{s_{NN}}$ = 8.16 TeV, collected with the LHCb experiment. The $chi_{c1,2}$ states are reconstructed via their decay to a $rm{J}/psi$ meson, subsequently decaying into a pair of oppositely charged muons, and a photon, which is reconstructed in the calorimeter or via its conversion in the detector material. The cross-section ratio is consistent with unity in the two considered rapidity regions. Comparison with a corresponding cross-section ratio previously measured by the LHCb collaboration in $pp$ collisions suggests that $chi_{c1}$ and $chi_{c2}$ states are similarly affected by nuclear effects occurring in $p$Pb collisions.
The decays $chi_{c1} rightarrow J/psi mu^+ mu^-$ and $chi_{c2} rightarrow J/psi mu^+ mu^-$ are observed and used to study the resonance parameters of the $chi_{c1}$ and $chi_{c2}$ mesons. The masses of these states are measured to be m(chi_{c1}) = 3510.71 pm 0.04(stat) pm 0.09(syst)MeV,, m(chi_{c2}) = 3556.10 pm 0.06(stat) pm 0.11(syst)MeV,, where the knowledge of the momentum scale for charged particles dominates the systematic uncertainty. The momentum-scale uncertainties largely cancel in the mass difference m(chi_{c2}) - m(chi_{c1}) = 45.39 pm 0.07(stat) pm 0.03(syst)MeV,. The natural width of the $chi_{c2}$ meson is measured to be $$Gamma(chi_{c2}) = 2.10 pm 0.20(stat) pm 0.02(syst)MeV,.$$ These results are in good agreement with and have comparable precision to the current world averages.
Using data samples of 89.5~fb$^{-1}$, 711.0~fb$^{-1}$, and 121.4~fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider at center-of-mass energies 10.52 GeV, 10.58 GeV, and 10.867 GeV, respectively, we study the exclusive reactions $e^+e^-togammachi_{cJ}$ ($J = 0,~1,~2$) and $e^+e^-togammaeta_c$. A significant $gamma chi_{c1}$ signal is observed for the first time at $sqrt{s}=10.58$ GeV with a significance of $5.1sigma$ including systematic uncertainties. No significant excesses for $gamma chi_{c0}$, $gamma chi_{c2}$, and $gamma eta_c$ final states are found, and we set 90% credibility level upper limits on the Born cross sections ($sigma_{rm B}$) at 10.52 GeV, 10.58 GeV, and 10.867~GeV. Together with cross sections measured by BESIII at lower center-of-mass energies, the energy dependency of $sigma_{rm B}(e^+e^-togammachi_{c1})$ is obtained.
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