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Register a new userStrange Particle Production in pp Collisions at sqrt(s) = 0.9 and 7 TeV measured with the ALICE Experiment
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H. Oeschler
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Hadrons measured in proton-proton collisions at sqrt(s) = 0.9 and 7 TeV with the ALICE detector have been identified using various techniques: the specific energy loss and the time-of flight information for charged pions, kaons and protons, the displaced vertex resulting from their weak decay for K0, Lambda and Xi and the kink topology of decaying charged kaons. These various particle identification tools give the best separation at different momentum ranges and the results are combined to obtain spectra from pt = 100 MeV/c to 2.5 GeV/c. This allows to extract total yields. In detail we discuss the K/pi ratio together with previous measurements and we show a fit using a statistical approach.
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Proton-proton (pp) collisions have been used extensively as a reference for the study of interactions of larger colliding systems at the LHC. Recent measurements performed in high-multiplicity pp and proton-lead (p-Pb) collisions have shown features that are reminiscent of those observed in lead-lead (Pb-Pb) collisions. In this context, the study of identified particle spectra and yields as a function of multiplicity is a key tool for the understanding of similarities and differences between small and large systems. We report on the production of pions, kaons, protons, $K^{0}_{rm S}$, $Lambda$, $Xi$, $Omega$ and $K^{*0}$ as a function of multiplicity in pp collisions at $sqrt{s}=$ 7 TeV measured with the ALICE experiment. The work presented here represents the most comprehensive set of results on identified particle production in pp collisions at the LHC. Spectral shapes, studied both for individual particles and via particle ratios as a function of $p_{rm T}$, exhibit an evolution with charged particle multiplicity that is similar to the one observed in larger systems. In addition, results on the production of light flavour hadrons in pp collisions at $sqrt{s}=$ 13 TeV, the highest centre-of-mass energy ever reached in the laboratory, are also presented and compared with previous, lower energy results.
The production of K_short mesons in pp collisions at a centre-of-mass energy of 0.9 TeV is studied with the LHCb detector at the Large Hadron Collider. The luminosity of the analysed sample is determined using a novel technique, involving measurements of the beam currents, sizes and positions, and is found to be 6.8 +/- 1.0 microbarn^-1. The differential prompt K_short production cross-section is measured as a function of the K_short transverse momentum and rapidity in the region 0 < pT < 1.6 GeV/c and 2.5 < y < 4.0. The data are found to be in reasonable agreement with previous measurements and generator expectations.
The $bar{Lambda} / Lambda$ and $bar{Lambda} / K^0_mathrm{S}$ production ratios are measured by the LHCb detector from $0.3,mathrm{nb}^{-1}$ of $pp$ collisions delivered by the LHC at $sqrt{s} = 0.9$,TeV and $1.8,mathrm{nb}^{-1}$ at $sqrt{s} = 7$,TeV. Both ratios are presented as a function of transverse momentum, $p_mathrm{T}$, and rapidity, $y$, in the ranges {$0.15 < p_mathrm{T} < 2.50,mathrm{GeV}/c$} and {$2.0<y<4.5$}. Results at the two energies are in good agreement as a function of rapidity loss, $Delta y = y_mathrm{beam} - y$, and are consistent with previous measurements. The ratio $bar{Lambda} / Lambda$, 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 $bar{Lambda} / K^0_mathrm{S}$, measuring the baryon-to-meson suppression in strange quark hadronisation, is significantly larger than expected.
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.
Vector mesons are key probes of the hot and dense state of strongly interacting matter produced in heavy ion collisions. Their dileptonic decay channel is particularly suitable for these studies, since dileptons have negligible final state interactions in hadronic matter. A preliminary measurement of the $phi$ and $omega$ differential cross sections was performed by the ALICE experiment in pp collisions at $sqrt{s}=7$ TeV, through their decay in muon pairs. The $p_{rm T}$ and rapidity regions covered in this analysis are $p_{rm T}>1$ GeV$/c$ and $2.5 < y < 4$.
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