The production of $\pi^+$, $\pi^-$, $K^+$, $K^-$, p, and $\rm\overline{p}$ at mid-rapidity has been measured in proton-proton collisions at $\sqrt{s} = 900$ GeV with the ALICE detector. Particle identification is performed using the specific energy loss in the inner tracking silicon detector and the time projection chamber. In addition, time-of-flight information is used to identify hadrons at higher momenta. Finally, the distinctive kink topology of the weak decay of charged kaons is used for an alternative measurement of the kaon transverse momentum ($p_{\rm T}$) spectra. Since these various particle identification tools give the best separation capabilities over different momentum ranges, the results are combined to extract spectra from $p_{\rm T}$ = 100 MeV/$c$ to 2.5 GeV/$c$. The measured spectra are further compared with QCD-inspired models which yield a poor description. The total yields and the mean $p_{\rm T}$ are compared with previous measurements, and the trends as a function of collision energy are discussed.
Eur. Phys. J. C 71 (2011) 1655
HEP Data
e-Print: arXiv:1101.4110 | PDF | inSPIRE
CERN-PH-EP-2010-085
Figure 2
Distribution of ln[d$E$/d$x$]$_{\rm meas}-$ln[d$E$/d$x$(K)]$_{\rm calc}$ measured with the ITS in the two $\pt$-ranges, 300-350 MeV/$c$ (upper panels) and 400-450 MeV/$c$ (lower panels), using the kaon mass hypothesis. The left panels show the result for ITS-TPC combined tracks, while the right panels show the ITS stand-alone result. The lines indicate fits as described in the text. |  |
Figure 10
(a) $q_{\rm t}$ distribution of the daughter tracks with respect to mother momentum for all reconstructed kinks inside the analyzed sample. The dashed(solid)histograms show the distribution before (after) applying the $q_{\rm t}> 40$ MeV/$c$ cut (b) Invariant mass of the two-body decays $\rm{K^\pm}/{\pi^\pm}\rightarrow\mu^\pm +\nu_{\mu}$ for candidate kaon kinks. Solid curve: after applying $q_{\rm t}>$40 MeV/$c$; dashed curve: without this selection (hence also showing the pion decays) (c) d$E$/d$x$ of kinks as a function of the mother momentum, after applying the full list of selection criteria for their identification. |  |
Figure 11
Upper panel: The acceptance of kaons decaying in the fiducial volume of the TPC as a function of thekaon $\pt$ for $\rm{K}^+$ (full-triangles) and $\rm{K}^-$(open-squares). Lower panel: The efficiency of reconstructed kaons from kinks as a function of the $\pt$ (mother), separately for $\rm{K}^+$ (full-triangles) and $\rm{K}^-$ (open-squares). The contamination from wrongly associated kinks is also plotted for both charges (lower set of points). |  |
Figure 14
Transverse momentum spectra of positive(top) and negative (bottom) hadrons from pp collisions at $\sqrt{s} = 900 $GeV. Grey bands: total $\pt$-dependent error (systematic plus statistical); normalization systematic error (3.6%) not shown The curves represent fits using a $L\grave{e}vy$ function. |  |
Figure 15
Mean $\pt$ as a function of the mass of the emitted particle in pp collisions at 900 GeV (ALICE, red solid circles, statistical and systematic errors) compared to results at $\sqrt{s} = 200 $GeV (star markers, average values of the results from the STAR and the PHENIX Collaborations [32,33]) and $\rm\overline{p}$p reactions at $\sqrt{s} = 900 $GeV (open squares). Some data points are displaced for clarity. |  |
Figure 16
Ratios ($K^+$ + $K^-$) / ($\pi^+$ + $\pi^-$) and K$^0/\pi$ as a function of $\sqrt{s}$. Data (full symbols) are from pp collisions, (at $\sqrt{s}$ = 17.9 GeV by NA49 [34,35], at $\sqrt{s}$ = 200 GeV by STAR [32] and at $\sqrt{s}$ = 900 ALICE, present work) and(open symbols) from $\rm\overline{p}$p interaction (at $\sqrt{s}$ = 560 GeV by UA5 [37] and at the TEVATRON by E735 [36,38]). |  |
Figure 18
Ratios of ($K^+$ + $K^-$) / ($\pi^+$ + $\pi^-$)(upper panel) and (p + $\rm\overline{p}$) / ($\pi^+$ + $\pi^-$) (lower panel) as a function of $\pt$ from pp collisions at $\sqrt{s}$ = 900 GeV (statistical errors only). Values from the E735Collaboration [36] and the STAR Collaboration [32] (upper part) and from the PHENIX Collaboration [41] (lower part) also are given. The dashed and dotted curves refer to calculations using PYTHIA and PHOJET at $\sqrt{s}$ = 900 GeV. |  |
