Measurement of V0 production ratios in pp collisions at √s = 0.9 and 7 TeV

The preprint is available here.

More detailed informations: ANA note 2011-026

Eur. Phys. J. C 72 (2012) 2168

arXiv:1107.0882

Abstract

The Λˉ/Λ and Λˉ/K0S production ratios are measured by the LHCb detector from 0.3nb−1 of pp collisions delivered by the LHC at √s=0.9\,TeV and 1.8nb−1 at √s=7\,TeV. Both ratios are presented as a function of transverse momentum, pT, and rapidity, y, in the ranges {0.15<pT<2.50GeV/c} and {2.0<y<4.5}. Results at the two energies are in good agreement as a function of rapidity loss, Δy=ybeam−y, and are consistent with previous measurements. The ratio Λˉ/Λ, 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 Λˉ/K0S, measuring the baryon-to-meson suppression in strange quark hadronisation, is significantly larger than expected.

Figures

(Note, eps versions are available under attachments).

Caption	Figure
The Fisher discriminant FIP in 0.5 million Monte Carlo simulated minimum bias events at √s = 7 TeV for KS0.
The Fisher discriminant FIP in 0.5 million Monte Carlo simulated minimum bias events at √s = 7 TeV for Λ.
Invariant mass peaks for Λ in the range 0.25 < pT < 2.50 GeV/c & 2.5 < y < 3.0 at √s = 0.9TeV with field up. Signal yields, N, are found from fits (solid curves) with a double Gaussian peak with common mean, μ, over a linear background (dashed lines). The width, σ, is computed as the quadratic average of the two Gaussian widths weighted by their signal fractions.
Invariant mass peaks for KS0 in the range 0.65 < pT < 1.00GeV/c & 3.5 < y < 4.0 at √s = 0.9TeV with field up. Signal yields, N, are found from fits (solid curves) with a double Gaussian peak with common mean, μ, over a linear background (dashed lines). The width, σ, is computed as the quadratic average of the two Gaussian widths weighted by their signal fractions.
Transverse momentum for KS0 in data and Monte Carlo at sqrt(s) = 7 TeV. The difference between data and Monte Carlo is reduced by weighting the simulated candidates.
Rapidity distributions for KS0 in data and Monte Carlo at sqrt(s) = 7 TeV. The difference between data and Monte Carlo is reduced by weighting the simulated candidates.
The double ratio (Λ/Λ)Data/(Λ/Λ)MC is shown as a function of the material traversed, in units of radiation length. Flat line fits, shown together with their respective χ2 probabilities, give no evidence of a bias.
The double ratio (Λ/KS0)Data/(Λ/KS0)MC is shown as a function of the material traversed, in units of radiation length. Flat line fits, shown together with their respective χ2 probabilities, give no evidence of a bias.
The ratio Λ/Λ from the full analysis procedure at √s = 0.9 TeV, shown as a function of rapidity, compared across intervals of transverse momentum. Vertical lines show the combined statistical and systematic uncertainties and the short horizontal bars (where visible) show the statistical component.
The ratio Λ/Λ from the full analysis procedure at √s = 7 TeV, shown as a function of rapidity, compared across intervals of transverse momentum. Vertical lines show the combined statistical and systematic uncertainties and the short horizontal bars (where visible) show the statistical component.
The ratio Λ/KS0 from the full analysis procedure at √s = 0.9 TeV, shown as a function of rapidity, compared across intervals of transverse momentum. Vertical lines show the combined statistical and systematic uncertainties and the short horizontal bars (where visible) show the statistical component.
The ratio Λ/KS0 from the full analysis procedure at √s = 7 TeV, shown as a function of rapidity, compared across intervals of transverse momentum. Vertical lines show the combined statistical and systematic uncertainties and the short horizontal bars (where visible) show the statistical component.
The ratio Λ/Λ at √s = 0.9 TeV compared with the predictions of the LHCb MC, Perugia 0 and Perugia NOCR as a function of rapidity. Vertical lines show the combined statistical and systematic uncertainties and the short horizontal bars (where visible) show the statistical component.
The ratio Λ/Λ at √s = 0.9 TeV compared with the predictions of the LHCb MC, Perugia 0 and Perugia NOCR as a function of transverse momentum. Vertical lines show the combined statistical and systematic uncertainties and the short horizontal bars (where visible) show the statistical component.
The ratio Λ/KS0 at √s = 0.9 TeV compared with the predictions of the LHCb MC, Perugia 0 and Perugia NOCR as a function of rapidity. Vertical lines show the combined statistical and systematic uncertainties and the short horizontal bars (where visible) show the statistical component.
The ratio Λ/KS0 at √s = 0.9 TeV compared with the predictions of the LHCb MC, Perugia 0 and Perugia NOCR as a function of transverse momentum. Vertical lines show the combined statistical and systematic uncertainties and the short horizontal bars (where visible) show the statistical component.
The ratio Λ/Λ at √s = 7 TeV compared with the predictions of the LHCb MC, Perugia 0 and Perugia NOCR as a function of rapidity. Vertical lines show the combined statistical and systematic uncertainties and the short horizontal bars (where visible) show the statistical component.
The ratio Λ/Λ at √s = 7 TeV compared with the predictions of the LHCb MC, Perugia 0 and Perugia NOCR as a function of transverse momentum. Vertical lines show the combined statistical and systematic uncertainties and the short horizontal bars (where visible) show the statistical component.
The ratio Λ/KS0 at √s = 7 TeV compared with the predictions of the LHCb MC, Perugia 0 and Perugia NOCR as a function of rapidity. Vertical lines show the combined statistical and systematic uncertainties and the short horizontal bars (where visible) show the statistical component.
The ratio Λ/KS0 at √s = 7 TeV compared with the predictions of the LHCb MC, Perugia 0 and Perugia NOCR as a function of transverse momentum. Vertical lines show the combined statistical and systematic uncertainties and the short horizontal bars (where visible) show the statistical component.
The ratio Λ/Λ from LHCb is compared at both √s = 0.9TeV (triangles) and 7TeV (circles) with the published results from STAR[1] (squares) as a function of rapidity loss, ∆y = ybeam − y. Vertical lines show the combined statistical and systematic uncertainties and the short horizontal bars (where visible) show the statistical component.
The ratio Λ/KS0 from LHCb is compared at both √s = 0.9TeV (triangles) and 7TeV (circles) with the published results from STAR[1] (squares) as a function of rapidity loss, ∆y = ybeam − y. Vertical lines show the combined statistical and systematic uncertainties and the short horizontal bars (where visible) show the statistical component.

-- TaraShears - 18-Sep-2012