$K^{*}{\left(892\right)}^0$ and $\varphi \left(1020\right)$ production at midrapidity in $pp$ collisions at $\sqrt{s}=8$ TeV

The production of $K^{*}{\left(892\right)}^0$ and $\varphi \left(1020\right)$ in $pp$ collisions at $\sqrt{s}=8$ TeV was measured by using Run 1 data collected by the ALICE collaboration at the CERN Large Hadron Collider (LHC). The $p_{\mathrm{T}}$-differential yields $d^{2}N/dyd{p}_{\mathrm{T}}$ in the range $0<p_{\mathrm{T}}<20$ GeV/$c$ for $K^{*0}$ and $0.4<p_{\mathrm{T}}<16$ GeV/$c$ for $\varphi$ have been measured at midrapidity, $\left|y\right|<0.5$. Moreover, improved measurements of the $K^{*0}\left(892\right)$ and $\varphi \left(1020\right)$ at $\sqrt{s}=7$ TeV are presented. The collision energy dependence of $p_{\mathrm{T}}$ distributions, $p_{\mathrm{T}}$-integrated yields, and particle ratios in inelastic $pp$ collisions are examined. The results are also compared with different collision systems. The values of the particle ratios are found to be similar to those measured at other LHC energies. In $pp$ collisions a hardening of the particle spectra is observed with increasing energy, but at the same time it is also observed that the relative particle abundances are independent of the collision energy. The $p_{\mathrm{T}}$-differential yields of $K^{*0}$ and $\varphi$ in $pp$ collisions at $\sqrt{s}=8$ TeV are compared with the expectations of different Monte Carlo event generators.

Figure 1

(Upper panels) Invariant-mass distributions (closed black point) for the $K^{*0}$ (left) and $\varphi$ (right) in $pp$ collisions at 8 TeV in the $p_{\mathrm{T}}$ range $0<p_{\mathrm{T}}<0.2\mathrm{GeV}/c$ and $0.6<p_{\mathrm{T}}<0.7\mathrm{GeV}/c$, respectively. The combinatorial background (open red circles) is estimated by using unlike-sign pairs from different events (mixed events). The statistical uncertainties are shown as bars. (lower panels) $K\pi$ (left) and $KK$ (right) invariant-mass distributions in the same $p_{\mathrm{T}}$ ranges after combinatorial background subtraction together with the fits to the signal and background contribution.

Figure 2

Upper panels shows the $p_{\mathrm{T}}$ spectra of $K^{*0}$ and $\varphi$ in inelastic $pp$ collisions at 7 TeV (left) and 8 TeV (right) and fit with the Lévy-Tsallis distribution [23, 24]. The normalization uncertainty in the spectra is ${}_{-3.5}^{+7.3}$% for 7 TeV and 2.69% for 8 TeV. The vertical bars show statistical uncertainties and the boxes show systematic uncertainties. The lower panels show the ratio of data to the Lévy-Tsallis fit. Here, the bars show the systematic uncertainty.

Figure 3

Ratios of transverse-momentum spectra of $K^{*0}$ and $\varphi$ in inelastic events at $\sqrt{s}=7$ and 8 TeV to the transverse-momentum spectra in $pp$ collisions at $\sqrt{s}=2.76$ TeV. The statistical and systematic uncertainties are shown as vertical error bars and boxes, respectively. The normalization uncertainties are indicated by boxes around unity.

Figure 4

Particle ratios of $K^{*0}/\pi$ (left) and $\varphi /\pi$ (right) are presented for $pp$ collisions as a function of collision energy. Bars (when present) represent statistical uncertainties. Boxes represent the total systematic uncertainties or the total uncertainties for cases when separate statistical uncertainties were not reported [10, 11, 12, 13, 26, 28, 29, 30, 31, 32].

Figure 5

Particle ratios of $K^{*0}/K$ (left) and $\varphi /K$ (right) are presented for $pp$, high-multiplicity $p$-Pb, central $d$-Au, and central $A-A$ collisions [10, 11, 12, 13, 28, 29, 30, 31, 33, 34, 35, 36, 37, 38, 39, 40, 41] as a function of the collision energy. Bars (when present) represent statistical uncertainties. Boxes represent the total systematic uncertainties or the total uncertainties for cases when separate statistical uncertainties were not reported. The value given by a grand-canonical thermal model with a chemical freeze-out temperature of 156 MeV [27] is also shown.

Figure 6

Particle ratio $\varphi /K^{*0}$ presented for $pp$ collisions [13, 26, 28, 29] as a function of collision energy. Bars (when present) represent statistical uncertainties. Boxes represent the total systematic uncertainties or the total uncertainties for cases when separate statistical uncertainties were not reported.

Figure 7

Comparison of the $K^{*0}$ (left) and $\varphi$ (right) $p_{\mathrm{T}}$ spectra measured in inelastic $pp$ collisions with those obtained from pythia8 (Monash tune) [7], phojet [8, 9] and epos-lhc [6]. The bottom plots show the ratios of the $p_{\mathrm{T}}$ spectra from the models to the measured $p_{\mathrm{T}}$ spectra by ALICE. The total fractional uncertainties of the data are shown as shaded boxes.