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Register a new userMeasurement of prompt hadron production ratios in $pp$ collisions at $sqrt{s} = $ 0.9 and 7 TeV
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The charged-particle production ratios $bar{p}/p$, $K^-/K^+$, $pi^-/pi^+$, $(p + bar{p})/(pi^+ + pi^-)$, $(K^+ + K^-)/(pi^+ + pi^-)$ and $(p + bar{p})/(K^+ + K^-)$ are measured with the LHCb detector using $0.3 {rm nb^{-1}}$ of $pp$ collisions delivered by the LHC at $sqrt{s} = 0.9$ TeV and $1.8 {rm nb^{-1}}$ at $sqrt{s} = 7$ TeV. The measurements are performed as a function of transverse momentum $p_{rm T}$ and pseudorapidity $eta$. The production ratios are compared to the predictions of several Monte Carlo generator settings, none of which are able to describe adequately all observables. The ratio $bar{p}/p$ is also considered as a function of rapidity loss, $Delta y equiv y_{rm beam} - y$, and is used to constrain models of baryon transport.
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The $bar{Lambda} / Lambda$ and $bar{Lambda} / K^0_mathrm{S}$ production ratios are measured by the LHCb detector from $0.3,mathrm{nb}^{-1}$ of $pp$ collisions delivered by the LHC at $sqrt{s} = 0.9$,TeV and $1.8,mathrm{nb}^{-1}$ at $sqrt{s} = 7$,TeV. Both ratios are presented as a function of transverse momentum, $p_mathrm{T}$, and rapidity, $y$, in the ranges {$0.15 < p_mathrm{T} < 2.50,mathrm{GeV}/c$} and {$2.0<y<4.5$}. Results at the two energies are in good agreement as a function of rapidity loss, $Delta y = y_mathrm{beam} - y$, and are consistent with previous measurements. The ratio $bar{Lambda} / Lambda$, measuring the transport of baryon number from the collision into the detector, is smaller in data than predicted in simulation, particularly at high rapidity. The ratio $bar{Lambda} / K^0_mathrm{S}$, measuring the baryon-to-meson suppression in strange quark hadronisation, is significantly larger than expected.
The production of K_short mesons in pp collisions at a centre-of-mass energy of 0.9 TeV is studied with the LHCb detector at the Large Hadron Collider. The luminosity of the analysed sample is determined using a novel technique, involving measurements of the beam currents, sizes and positions, and is found to be 6.8 +/- 1.0 microbarn^-1. The differential prompt K_short production cross-section is measured as a function of the K_short transverse momentum and rapidity in the region 0 < pT < 1.6 GeV/c and 2.5 < y < 4.0. The data are found to be in reasonable agreement with previous measurements and generator expectations.
Charm production at the LHC in pp collisions at sqrt(s)=7 TeV is studied with the LHCb detector. The decays D0 -> K- pi+, D+ -> K- pi+ pi+, D*+ -> D0(K- pi+) pi+, D_s+ -> phi(K- K+) pi+, Lambda_c+ -> p K- pi+, and their charge conjugates are analysed in a data set corresponding to an integrated luminosity of 15 nb^{-1}. Differential cross-sections dsigma/dp_T are measured for prompt production of the five charmed hadron species in bins of transverse momentum and rapidity in the region 0 < p_T < 8 GeV/c and 2.0 < y < 4.5. Theoretical predictions are compared to the measured differential cross-sections. The integrated cross-sections of the charm hadrons are computed in the above p_T-y range, and their ratios are reported. A combination of the five integrated cross-section measurements gives sigma(cbar{c})_{p_T < 8 GeV/c, 2.0 < y < 4.5} = 1419 +/- 12 (stat) +/- 116 (syst) +/- 65 (frag) microbarn, where the uncertainties are statistical, systematic, and due to the fragmentation functions.
The production of Upsilon(1S), Upsilon(2S) and Upsilon(3S) mesons in proton-proton collisions at the centre-of-mass energy of sqrt(s)=7 TeV is studied with the LHCb detector. The analysis is based on a data sample of 25 pb-1 collected at the Large Hadron Collider. The Upsilon mesons are reconstructed in the decay mode Upsilon -> mu+ mu- and the signal yields are extracted from a fit to the mu+ mu- invariant mass distributions. The differential production cross-sections times dimuon branching fractions are measured as a function of the Upsilon transverse momentum pT and rapidity y, over the range pT < 15 GeV/c and 2.0 < y < 4.5. The cross-sections times branching fractions, integrated over these kinematic ranges, are measured to be sigma(pp -> Upsilon(1S) X) x B(Upsilon(1S)->mu+ mu-) = 2.29 {pm} 0.01 {pm} 0.10 -0.37 +0.19 nb, sigma(pp -> Upsilon(2S) X) x B(Upsilon(2S)->mu+ mu-) = 0.562 {pm} 0.007 {pm} 0.023 -0.092 +0.048 nb, sigma(pp -> Upsilon(3S) X) x B(Upsilon(3S)->mu+ mu-) = 0.283 {pm} 0.005 {pm} 0.012 -0.048 +0.025 nb, where the first uncertainty is statistical, the second systematic and the third is due to the unknown polarisation of the three Upsilon states.
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 rapidity 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.
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