cern.ch

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

[to restricted-access page]

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]
HiDef png [299 KiB]
Thumbnail [97 KiB]
*.C file
DLLKpiVsDLLPpi_Protons.eps
DLLKpi[..].eps [58 KiB]
HiDef png [352 KiB]
Thumbnail [109 KiB] *.C file
DLLKpiVsDLLPpi_Kaons.eps
DLLKpi[..].eps [65 KiB]
HiDef png [365 KiB]
Thumbnail [106 KiB] *.C file
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.

K0S_Mass.eps [24 KiB]
HiDef png [159 KiB]
Thumbnail [56 KiB]
*.C file
K0S_Mass.eps
Lambda[..].eps [25 KiB]
HiDef png [167 KiB]
Thumbnail [63 KiB] *.C file
Lambda_Mass.eps
Phi_Mass.eps [25 KiB]
HiDef png [194 KiB]
Thumbnail [70 KiB] *.C file
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.

MC_Pro[..].eps [7 KiB]
HiDef png [150 KiB]
Thumbnail [52 KiB]
*.C file
MC_Proton_eff.eps
MC_Kao[..].eps [8 KiB]
HiDef png [154 KiB]
Thumbnail [54 KiB] *.C file
MC_Kaon_eff.eps
MC_Pio[..].eps [10 KiB]
HiDef png [188 KiB]
Thumbnail [70 KiB] *.C file
MC_Pion_eff.eps

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

Public[..].eps [15 KiB]
HiDef png [218 KiB]
Thumbnail [90 KiB]
*.C file
Public_FP_450GeV_proton_v3_ptbin3_average.eps
Public[..].eps [17 KiB]
HiDef png [231 KiB]
Thumbnail [98 KiB] *.C file
Public_FP_3500GeV_proton_v3_ptbin3_average.eps

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

Public[..].eps [16 KiB]
HiDef png [210 KiB]
Thumbnail [87 KiB]
*.C file
Public_FP_450GeV_kaon_v3_ptbin3_average.eps
Public[..].eps [17 KiB]
HiDef png [216 KiB]
Thumbnail [97 KiB] *.C file
Public_FP_3500GeV_kaon_v3_ptbin3_average.eps

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

Public[..].eps [18 KiB]
HiDef png [233 KiB]
Thumbnail [104 KiB]
*.C file
Public_FP_450GeV_pion_v3_ptbin3_average.eps
Public[..].eps [17 KiB]
HiDef png [225 KiB]
Thumbnail [92 KiB] *.C file
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).

Public[..].eps [18 KiB]
HiDef png [253 KiB]
Thumbnail [111 KiB]
*.C file
Public_FP_450GeV_ppi_v3_ptbin3_average.eps
Public[..].eps [17 KiB]
HiDef png [235 KiB]
Thumbnail [99 KiB] *.C file
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).

Public[..].eps [18 KiB]
HiDef png [246 KiB]
Thumbnail [107 KiB]
*.C file
Public_FP_450GeV_Kpi_v3_ptbin3_average.eps
Public[..].eps [18 KiB]
HiDef png [244 KiB]
Thumbnail [105 KiB] *.C file
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).

Public[..].eps [16 KiB]
HiDef png [212 KiB]
Thumbnail [89 KiB]
*.C file
Public_FP_450GeV_pK_v3_ptbin3_average.eps
Public[..].eps [16 KiB]
HiDef png [223 KiB]
Thumbnail [93 KiB] *.C file
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]
HiDef png [150 KiB]
Thumbnail [53 KiB]
*.C file
Deltay_4paper_withfit.eps

Animated gif made out of all figures.

PAPER-2011-037.gif
Thumbnail
thumbnail_PAPER-2011-037.gif

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_0.pdf [37 KiB]
HiDef png [68 KiB]
Thumbnail [10 KiB]
tex code
Table_0.pdf

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

Table_1.pdf [37 KiB]
HiDef png [78 KiB]
Thumbnail [12 KiB]
tex code
Table_1.pdf

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

Table_2.pdf [46 KiB]
HiDef png [60 KiB]
Thumbnail [10 KiB]
tex code
Table_2.pdf

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

Table_3.pdf [46 KiB]
HiDef png [62 KiB]
Thumbnail [10 KiB]
tex code
Table_3.pdf

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

Table_4.pdf [46 KiB]
HiDef png [46 KiB]
Thumbnail [7 KiB]
tex code
Table_4.pdf

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

Table_5.pdf [46 KiB]
HiDef png [46 KiB]
Thumbnail [7 KiB]
tex code
Table_5.pdf

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

Table_6.pdf [30 KiB]
HiDef png [110 KiB]
Thumbnail [18 KiB]
tex code
Table_6.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_7.pdf [36 KiB]
HiDef png [101 KiB]
Thumbnail [16 KiB]
tex code
Table_7.pdf

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

Table_8.pdf [36 KiB]
HiDef png [101 KiB]
Thumbnail [16 KiB]
tex code
Table_8.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_9.pdf [36 KiB]
HiDef png [103 KiB]
Thumbnail [16 KiB]
tex code
Table_9.pdf

Created on 09 December 2018.Citation count from INSPIRE on 09 December 2018.