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تسجيل مستخدم جديدMeasurement of the prompt J/psi and psi(2S) polarizations in pp collisions at sqrt(s) = 7 TeV
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The CMS Collaboration
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The polarizations of prompt J/psi and psi(2S) mesons are measured in proton-proton collisions at sqrt(s) = 7 TeV, using a dimuon data sample collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 4.9 inverse femtobarns. The prompt J/psi and psi(2S) polarization parameters lambda[theta], lambda[phi], and lambda[theta,phi], as well as the frame-invariant quantity lambda(tilde), are measured from the dimuon decay angular distributions in three different polarization frames. The J/psi results are obtained in the transverse momentum range 14 < pt < 70 GeV, in the rapidity intervals abs(y) < 0.6 and 0.6 < abs(y) < 1.2. The corresponding psi(2S) results cover 14 < pt < 50 GeV and include a third rapidity bin, 1.2 < abs(y) < 1.5. No evidence of large transverse or longitudinal polarizations is seen in these kinematic regions, which extend much beyond those previously explored.
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Exclusive $J/psi$ and $psi(2S)$ vector meson production has been observed in the dimuon channel using the LHCb detector. The cross-section times branching fractions to two muons with pseudorapidities between 2.0 and 4.5 are measured to be $ sigma_{pp
rightarrow J/psi (rightarrow mu^{+} mu^{-})} (2.0 <eta_{mu^{pm}}< 4.5) = 307 pm 21 pm 36 text{pb}, sigma_{pprightarrow psi(2S) (rightarrow mu^{+} mu^{-})} (2.0 <eta_{mu^{pm}}< 4.5) = 7.8 pm 1.3 pm 1.0 text{pb}, $ where the first uncertainties are statistical and the second are systematic. The measurements are found to be in good agreement with results from previous experiments and theoretical predictions. The $J/psi$ photoproduction cross-section has been measured as a function of the photon-proton centre-of-mass energy. The results are consistent with measurements obtained at HERA and confirm a similar power law behaviour for the photoproduction cross-section.
The polarisation of prompt $psi(2S)$ mesons is measured by performing an angular analysis of $psi(2S)rightarrow mu^{+} mu^{-}$ decays using proton-proton collision data, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected by the LHC
b detector at a centre-of-mass energy of 7 TeV. The polarisation is measured in bins of transverse momentum $p_mathrm{T}$ and rapidity $y$ in the kinematic region $3.5<p_mathrm{T}<15$ GeV$/c$ and $2.0<y<4.5$, and is compared to theoretical models. No significant polarisation is observed.
The production of J/psi mesons in proton-proton collisions at sqrt(s)=7 TeV is studied with the LHCb detector at the LHC. The differential cross-section for prompt J/psi production is measured as a function of the J/psi transverse momentum pT and rap
idity y in the fiducial region 0<pT<14 GeV/c and 2.0<y<4.5. The differential cross-section and fraction of J/psi from b-hadron decays are also measured in the same pT and y ranges. The analysis is based on a data sample corresponding to an integrated luminosity of 5.2pb-1. The measured cross-sections integrated over the fiducial region are 10.52 +/- 0.04 +/- 1.40 +1.64/-2.20 mub for prompt J/psi production and 1.14 +/- 0.01 +/- 0.16 mub for J/psi from b-hadron decays, where the first uncertainty is statistical and the second systematic. The prompt J/psi production cross-section is obtained assuming no J/psi polarisation and the third error indicates the acceptance uncertainty due to this assumption.
An angular analysis of the decay $J/psi rightarrow mu^{+} mu^{-}$ is performed to measure the polarization of prompt $J/psi$ mesons produced in $pp$ collisions at $sqrt{s}=7; mathrm{TeV}$. The dataset corresponds to an integrated luminosity of 0.37 f
b$^{-1}$ collected with the LHCb detector. The measurement is presented as a function of transverse momentum, $p_mathrm{T}$, and rapidity, $y$, of the $J/psi$ meson, in the kinematic region $2 < p_mathrm{T} < 15; mathrm{GeV}/c$ and $2.0<y<4.5$.
The differential cross-section for the inclusive production of psi(2S) mesons in pp collisions at sqrt(s)=7 TeV has been measured with the LHCb detector. The data sample corresponds to an integrated luminosity of 36 pb-1. The psi(2S) mesons are recon
structed in the decay channels psi(2S) -> mu+ mu- and psi(2S) -> J/psi pi+ pi-, with the J/psi meson decaying into two muons. Results are presented both for promptly produced psi(2S) mesons and for those originating from b-hadron decays. In the kinematic range pT(psi(2S)) <= 16 GeV/c and 2 < y(psi(2S)) <= 4.5 we measure 1.44 +- 0.01 +- 0.12+0.2-0.4 mub for prompt psi(2S) production and 0.25 +- 0.01 +- 0.02 mub for psi(2S) from b-hadron decays, where the last uncertainty on the prompt cross-section is due to the unknown psi(2S) polarization. Recent QCD calculations are found to be in good agreement with our measurements. Combining the present result with the LHCb J/psi measurements we determine the inclusive branching fraction B(b -> psi(2S) X) = (2.73 +- 0.06 +- 0.16 +- 0.24) x 10^(-3), where the last uncertainty is due to the B(b -> J/psi X), B(J/psi -> mu+ mu-) and B(psi(2S) -> e+ e-) branching fraction uncertainties. All above results are corrected by an erratum included as an appendix.
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