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Register a new userMeasurement of the cross-section ratio $sigma(chi_{c2})/sigma(chi_{c1})$ for prompt $chi_c$ production at $sqrt{s}=7$ TeV
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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.
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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.
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.
The prompt production of charmonium $chi_{c}$ and $J/psi$ states is studied in proton-proton collisions at a centre-of-mass energy of $sqrt{s}=7$ TeV at the Large Hadron Collider. The $chi_{c}$ and $J/psi$ mesons are identified through their decays $chi_{c}rightarrow J/psi gamma$ and $J/psirightarrow mu^+mu^-$ using 36 pb$^{-1}$ of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for $chi_{c}$ and $J/psi$, $sigma (chi_{c}rightarrow J/psi gamma)/ sigma (J/psi)$, is determined as a function of the $J/psi$ transverse momentum in the range $2 < p_{mathrm T}^{J/psi} < 15$ GeV/$c$. The results are in excellent agreement with next-to-leading order non-relativistic expectations and show a significant discrepancy compared with the colour singlet model prediction at leading order, especially in the low $p_{mathrm T}^{J/psi}$ region.
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.
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