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Measurement of prompt hadron production ratios in $pp$ collisions at $\sqrt{s} = $ 0.9 and 7 TeV

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Abstract

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.

Figures and captions

Two-dimensional distribution of the change in log likelihood DLL($p-K$) and DLL($p-\pi$) for (a) protons, (b) kaons and (c) pions (here shown for negative tracks and one magnet polarity) in the calibration sample with $p_{\rm T} > 1.2$ GeV/$c$ and $3.5 < \eta \le 4.0$. The region indicated by the dotted lines in the top right corner of each plot is that which is selected in the analysis to isolate the proton sample. The selection of the calibration sample is discussed in Sect. ???.

DLLKpi[..].eps [44 KiB]
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DLLKpiVsDLLPpi_Protons.eps
DLLKpi[..].eps [58 KiB]
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DLLKpiVsDLLPpi_Kaons.eps
DLLKpi[..].eps [65 KiB]
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DLLKpiVsDLLPpi_Pions.eps

Invariant mass distributions reconstructed for one magnet polarity from the $\sqrt{s}=7 \mathrm{TeV}$ data in the analysis bin for which the positive final-state particle has $ p_{\rm T} \ge 1.2 {\rm GeV}$ and $3.5\le \eta<4.0$ for (a) $K^0_{\rm S} \rightarrow \pi^+\pi^-$, (b) $\Lambda \rightarrow p \pi^-$ and (c) $\phi \rightarrow K^+K^-$. The results of unbinned maximum likelihood fits to the data are superimposed.

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K0S_Mass.eps
Lambda[..].eps [25 KiB]
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Lambda_Mass.eps
Phi_Mass.eps [25 KiB]
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Phi_Mass.eps

Monte Carlo PID efficiency study for protons (a), kaons (b) and pions (c). Shown is a comparison of measured efficiencies from a Monte Carlo calibration sample, after background subtraction and reweighting, with the true values in the Monte Carlo analysis sample. The diagonal line on each plot is drawn with unit gradient.

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MC_Proton_eff.eps
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MC_Kaon_eff.eps
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MC_Pion_eff.eps

Results for the $\bar{p}/p$ ratio at 0.9 TeV (a) and 7 TeV (b).

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Public_FP_450GeV_proton_v3_ptbin3_average.eps
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Public_FP_3500GeV_proton_v3_ptbin3_average.eps

Results for the $K^{-}/K^{+}$ ratio at 0.9 TeV (a) and 7 TeV (b).

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Public_FP_450GeV_kaon_v3_ptbin3_average.eps
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Public_FP_3500GeV_kaon_v3_ptbin3_average.eps

Results for the $\pi^{-}/\pi^{+}$ ratio at 0.9 TeV (a) and 7 TeV (b).

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Public_FP_450GeV_pion_v3_ptbin3_average.eps
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Public_FP_3500GeV_pion_v3_ptbin3_average.eps

Results for the $(p + \bar{p})/(\pi^+ + \pi^-)$ ratio at 0.9 TeV (a) and 7 TeV (b).

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Public_FP_450GeV_ppi_v3_ptbin3_average.eps
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Public_FP_3500GeV_ppi_v3_ptbin3_average.eps

Results for the $(K^+ + K^-)/(\pi^+ + \pi^-)$ ratio at 0.9 TeV (a) and 7 TeV (b).

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Public_FP_450GeV_Kpi_v3_ptbin3_average.eps
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Public_FP_3500GeV_Kpi_v3_ptbin3_average.eps

Results for the $(p + \bar{p})/(K^+ + K^-)$ ratio at 0.9 TeV (a) and 7 TeV (b).

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Public_FP_450GeV_pK_v3_ptbin3_average.eps
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Public_FP_3500GeV_pK_v3_ptbin3_average.eps

Results for the $\bar{p}/p$ ratio against the rapidity loss $\Delta y$ from LHCb. Results from other experiments are also shown \cite{ALICEPBARP,ISR,BRAHMS, PHENIX,PHOBOS,STAR}. Superimposed is a fit to the LHCb and ALICE \cite{ALICEPBARP} measurements that is described in the text.

Deltay[..].eps [13 KiB]
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Deltay_4paper_withfit.eps

Animated gif made out of all figures.

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Tables and captions

Number of particle candidates in the analysis sample at $\sqrt{s}=0.9$ TeV, separated into positive and negative charge ($Q$).

Table_1.pdf [37 KiB]
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Table_1.pdf

Number of particle candidates in the analysis sample at $\sqrt{s}=7.0$ TeV, separated into positive and negative charge ($Q$).

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Table_2.pdf

Range of systematic uncertainties, in percent, for same-particle ratios at $\sqrt{s}=0.9$ TeV.

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Table_3.pdf

Range of systematic uncertainties, in percent, for same-particle ratios at $\sqrt{s}=7$ TeV.

Table_4.pdf [46 KiB]
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Table_4.pdf

Range of systematic uncertainties, in percent, for different-particle ratios at $\sqrt{s}=0.9$ TeV.

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Table_5.pdf

Range of systematic uncertainties, in percent, for different-particle ratios at $\sqrt{s}=7$ TeV.

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Table_6.pdf

Results for $\bar{p}/p$ ratio integrated over $p_{\rm T}$ in $\eta$ bins as a function of the rapidity loss $\Delta y$.

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Table_7.pdf

Results for the $\bar{p}/p$ ratio with statistical and systematic uncertainties, as a function of $p_{\rm T}$ and $\eta$. Also shown is the mean rapidity, $y$, and RMS spread for the sample in each $\eta$ bin.

Table_8.pdf [38 KiB]
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Table_8.pdf

Results for the $K^-/K^+$ ratio with statistical and systematic uncertainties, as a function of $p_{\rm T}$ and $\eta$. Also shown is the mean rapidity, $y$, and RMS spread for the sample in each $\eta$ bin.

Table_9.pdf [38 KiB]
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Table_9.pdf

Results for the $\pi^-/\pi^+$ ratio with statistical and systematic uncertainties, as a function of $p_{\rm T}$ and $\eta$. Also shown is the mean rapidity, $y$, and RMS spread for the sample in each $\eta$ bin.

Table_10.pdf [38 KiB]
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Table_10.pdf

Results for the $(p + \bar{p})/(\pi^+ + \pi^-)$ ratio with statistical and systematic uncertainties, as a function of $p_{\rm T}$ and $\eta$.

Table_11.pdf [36 KiB]
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Table_11.pdf

Results for the $(K^+ + K^-)/(\pi^+ + \pi^-)$ ratio with statistical and systematic uncertainties, as a function of $p_{\rm T}$ and $\eta$.

Table_12.pdf [36 KiB]
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Table_12.pdf

Results for the $(p + \bar{p})/(K^+ + K^-)$ ratio with statistical and systematic uncertainties, as a function of $p_{\rm T}$ and $\eta$.

Table_13.pdf [36 KiB]
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Table_13.pdf

Created on 11 July 2020.