Production of K$^{*}$(892)$^{0}$ and $φ$(1020) in pp collisions at $\sqrt{s}=7$ TeV

The production of K$^{*}$(892)$^{0}$ and $\phi$(1020) in pp collisions at $\sqrt{s}=7$ TeV was measured by the ALICE experiment at the LHC. The yields and the transverse momentum spectra d$^{2}$N/d$y$d$p_{\rm T}$ at midrapidity $|y|<~0.5$ in the range $0<~p_{\rm T}<~6$ GeV/$c$ for K$^{*}$(892)$^{0}$ and $0.4<~p_{\rm T}<~6$ GeV/$c$ for $\phi$(1020) are reported and compared to model predictions. Using the yield of pions, kaons, and Omega baryons measured previously by ALICE at $\sqrt{s}=7$ TeV, the ratios K$^{*}$/K$^{-}$, $\phi$/K$^{*}$, $\phi$/K$^{-}$, $\phi/\pi^{-}$, and ($\Omega$ + $\overline{\Omega}$)/$\phi$ are presented. The values of the K$^{*}$/K$^{-}$, $\phi$/K$^{*}$ and $\phi$/K$^{-}$ ratios are similar to those found at lower centre-of-mass energies. In contrast, the $\phi/\pi^{-}$ ratio, which has been observed to increase with energy, seems to saturate above 200 GeV. The ($\Omega$ + $\overline{\Omega}$)/$\phi$ ratio in the $p_{\rm T}$ range $1$-$5$ GeV/$c$ is found to be in good agreement with the prediction of the HIJING/BB v2.0 model with a strong colour field.

Figures

Figure 1

Specific ionization energy loss $\dedx$ vs. momentum for tracks measured with the ALICE TPC The solid lines are parametrizations of the Bethe-Bloch function.
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Figure 2

Velocity $\beta$ of particles measured by TOF vs. momentum.
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Figure 3

(Upper panel) The $\pi^{\pm}$K$^{\mp}$ invariant mass distribution in $|y|$$< $0.5 for the bin 0.4 $< ~\pt~< $ 0.5 GeV/$c$ (left) and 0.9 $< ~\pt~< $ 1.0 GeV/$c$ (right), in pp collisions at 7 TeV. The background shape estimated using unlike-sign pairs from different events (event mixing) and like-sign pairs from the same event are shown as open red squares and full green squares, respectively (Lower panel). The $\pi^{\pm}$K$^{\mp}$ invariant mass distribution after like-sign background subtraction for 0.4 $< ~\pt~< $0.5 GeV/$c$ (left) and 0.9 $< ~\pt~< $ 1.0 GeV/$c$ (right). The solid curve is the result of the fit by Eq. 1, the dashed line describes the residual background.
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Figure 4

(Upper panel) The K$^+$K$^-$ invariant mass distribution in $|y|$< 0.5, for the bin 0.5 $< ~\pt~< $ 0.6 GeV/$c$ (left) and 1.1 $< ~\pt~< $ 1.2 GeV/$c$ (right) in pp collisions at 7 TeV. The solid curve is the fit result (Eq. 2), while the dashed line describes the background. The background shape estimated using unlike-sign pairs from different events (event mixing) or like-sign pairs from the same event are shown as open red squares and full green squares, respectively (Lower panel). The K$^+$K$^-$ invariant mass distribution after mixed-event background subtraction for 0.5 $< ~\pt~< $ 0.6 GeV/$c$ (left) and 1.1 $< ~\pt~< $ 1.2 GeV/$c$ (right). The solid curve is the fit result (Eq. 2), while the dashed line describes the residual background.
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Figure 5

The product of acceptance and efficiency of K$^*$ and $\phi$ detection as a function of $\pt$ in $|y|< $0.5. Statistical uncertainties are reported. Contributions to the point-to-point systematic uncertainties are listed in Tab. 1.
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Figure 6

Transverse momentum spectra for K$^*$ and $\phi$(1020) in pp collisions at $\sqrt{s}$= 7 TeV. The statistical and systematic uncertainties are added in quadratureand the uncertainty due to normalization is shown separately. The statistical uncertainty is smaller than the symbol size. Each spectrum is fitted with a Lévy-Tsallis function (dashed line).
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Figure 7

Energy dependence of $\langle{\pt}\rangle$ for K$^*$ (triangles) and $\phi$ (squares) in pp collisions. The points at lower energies are from STAR and PHENIX ($\sqrt{s}$=200 GeV), ALICE ($\sqrt{s}$=0.9 TeV) and E735 ($\sqrt{s}$=1.8 TeV). The STAR data have been slightly displaced to separate the K$^*$ and the $\phi$. The data point at 1.8 TeV represents the mean of the two values quoted from the E735 collaboration in [33], obtained from two different fit functions of the $\phi$ $\pt$ distribution.
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Figure 8

Comparison of the K$^*$ $\pt$ spectra in inelastic pp collisions with PHOJET and PYTHIA tunes D6T (109), ATLAS-CSC (306), Perugia 0 (320), and Perugia 2011 (350).
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Figure 9

Comparison of the $\phi$(1020) $\pt$ spectra in inelastic pp collisions with PHOJET and PYTHIA tunes D6T (109), ATLAS-CSC (306), Perugia 0 (320), and Perugia 2011 (350).
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Figure 10

Energy dependence of the K$^*$/K$^-$ (upper panel) and $\phi$/K$^{*}$ (lower panel) ratio in e$^+$e$^-$ (diamonds), and pp (triangles) collisions. Red squares represent the data from the ALICE experiment for 7 TeV pp collisions, K$^-$ yields are from. Open circles represent the same ratios in central nucleus-nucleus collisions from. Some points have been displaced horizontally for better visibility. Ratios are calculated from yields at mid-rapidity or in full phase space.
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Figure 11

Energy dependence of the $\phi/\pi^{-}$ (upper panel) and $\phi/$K$^-$ ratio (bottom panel) in nuclear (open circles) [4, 5, 50, 52, 53, 54, 55], e$^+$e$^-$ (diamonds) [2, 41, 42, 46, 60], and pp (triangles) [1, 3, 5, 28, 45, 47, 52, 53, 54, 57] collisions. Other $\pi^{-}$ and K$^-$ yields are from [56, 57, 58, 59]. Red squares represent the ALICE data at 0.9 and 7 TeV. The pion and kaon yields at 7 TeV are from [11]. The $\phi$, $\pi^-$, and K$^-$ yields at 0.9 TeV are from [24, 32]. Some points have been displaced horizontally for better visibility. Ratios are calculated from yields at mid-rapidity or in full phase space, except the data at $\sqrt{s}$ = 4.87 GeV [52].
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Figure 12

($\Omega$ + $\overline{\Omega}$)/$\phi$ ratio as a function of transverse momentum for pp collisions at $\sqrt{s}$ = 7 TeV $\Omega$ data are from [12]. The dashed line represents the prediction of HIJING/B$\overline{\rm B}$ v2.0 model with a SCF for pp collisions at $\sqrt{s}$ = 5.5 TeV with a string tension of 2 GeV/fm [13]. The same calculation at 7 TeV yields a $\sim$ 10% higher ratio. The full line represents the prediction of the PYTHIA Perugia 2011 tune [14] for pp collisions at $\sqrt{s}$ = 7 TeV.
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