Transverse-momentum and pseudorapidity distributions of charged hadrons in pp collisions at sqrt(s) = 0.9 and 2.36 TeV


Measurements of inclusive charged-hadron transverse-momentum and pseudorapidity distributions are presented for proton-proton collisions at root(s) = 0.9 and 2.36 TeV. The data were collected with the CMS detector during the LHC commissioning in December 2009. For non-single-diff ractive interactions, the average charged-hadron transverse momentum is measured to be 0.46 +- 0.01 (stat.) +- 0.01 (syst.) GeV/c at 0.9 TeV and 0.50 +- 0.01 (stat.) +- 0.01 (syst.) GeV/c at 2.36 TeV, for pseudorapidities between -2.4 and +2.4. At these energies, the measured pseudorapidity densities in the central region, dNch/deta(abs(eta)<0.5), are 3.48+-0.02 (stat.) +- 0.13 (syst.) and 4.47 +- 0.04 (stat.) +- 0.16 (syst.), respectively. The results at 0.9 TeV are in agreement with previous measurements and confirm the expectation of near equal hadron production in ppbar and pp collisions. The results at 2.36 TeV represent the highest-energy measurements at a particle collider to date.

Approved Plots from QCD-09-010

No PAS (special approval), so the approved plots are the ones in the paper.

Figure Abbreviated Caption
Figure1a.pdf Generated multiplicity distributions of primary charged hadrons in the range abs(eta) < 2.5 for root(s) = 0.9 TeV (solid dots and histogram) and 2.36 TeV (open circles and dashed histogram) after the event selection is applied to the reconstructed events, using inelastic events from the PYTHIA (histograms) and PHOJET (symbols) event generators.
Figure1b.pdf The event selection efficiency expected for NSD events from the PYTHIA (histograms) and PHOJET (symbols) event generators as a function of generated charged hadron multiplicity in the region abs(eta) < 2.5.
Figure2a.pdf The distribution of the reconstructed z position of the primary vertex in the data (dots), compared to that from the PYTHIA simulation (histogram).
Figure2b.pdf Distribution of the cluster charge multiplied by abs(sin(Theta)) in the data (dots) and the simulation (histogram), for the clusters selected for analysis.
Figure3a.pdf Pixel cluster length along z as a function of h for the 900 GeV data. The solid line illustrates the cut applied in the cluster counting method.
Figure3b.pdf The Delta(eta) distribution of clusters on tracklets in the data (dots and circles), together with the distribution obtained from the PYTHIA simulation (solid and dotted lines), for both 0.9 and 2.36 TeV collision energy. The dashed line shows the Delta(eta) distribution of clusters for primary charged-particle tracks in the Monte Carlo simulation at 0.9 TeV. The tail of the Delta(eta) distribution comes from the combinatorial background.
Figure4a.pdf The distribution of the number of pixel hits attached to reconstructed tracks in the region of abs(eta) < 1 (closed circles), compared to the CMS detector simulation (histogram).
Figure4b.pdf The distribution of the number of hits in the SST detector attached to reconstructed tracks in the region of abs(eta) < 1 (closed circles), compared to the CMS detector simulation (histogram).
Figure5a.pdf Measured differential yield of charged hadrons in the range abs(eta) < 2.4 in 0.2-unit-wide bins of abs(eta) for the 2.36 TeV data. The measured values with systematic uncertainties (symbols) and the fit functions (Tsallis fit) are displayed. The values with increasing eta are successively shifted by four units along the vertical axis.
Figure5b.pdf Measured yield of charged hadrons for abs(eta) < 2.4 with systematic uncertainties (symbols), fit with the empirical function (Tsallis fit).
Figure6a.pdf Reconstructed dNch/deta distributions obtained from the cluster counting (dots with error bars), tracklet (squares) and tracking (triangles) methods, in pp collisions at 0.9 TeV (filled symbols) and 2.36 TeV (open symbols). The error bars include systematic uncertainties (as discussed in the text), excluding those common to all the methods.
Figure6b.pdf Reconstructed dNch/deta distributions averaged over the cluster counting, tracklet and tracking methods (circles), compared to data from the UA5 (open squares) and from the ALICE (open triangles) experiments at 0.9 TeV, and the averaged result over the three methods at 2.36 TeV (open circles). The CMS and UA5 data points are symmetrized in eta. The shaded band represents systematic uncertainties of this measurement, which are largely correlated point-to-point. The error bars on the UA5 and ALICE data points are statistical only.
Figure7a.pdf Energy dependence of the average transverse momentum of charged hadrons. The CMS data points are evaluated for the range abs(eta) < 2.4. The curve shows the fit to the data points of the form = 0.425 - 0.0197 ln(s) + 0.00156 ln^2(s) with in GeV/c and s in GeV^2. The error bars on the CMS data points include systematic uncertainties.
Figure7b.pdf Charged-hadron pseudorapidity density in the central region as a function of centre-of-mass energy in pp and ppbar collisions including lower energy data, together with various empirical parameterizations fit to the data corresponding to the inelastic (solid and dotted curves with open symbols) and to the NSD (dashed curve with solid symbols) event selection. The error bars indicate systematic uncertainties, when available.

Link to the paper in CDS

Link to the paper on the J. High Energy Physics website

Link to the paper on ArXiv

-- GaborIVeres - 04-Aug-2010

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