Transverse-momentum and pseudorapidity distributions of charged hadrons in pp collisions at sqrt(s) = 7 TeV

Abstract

Charged-hadron transverse-momentum and pseudorapidity distributions in proton-proton collisions at sqrt(s) = 7 TeV are measured with the inner tracking system of the CMS detector at the LHC. The charged-hadron yield is obtained by counting the number of reconstructed hits, hit-pairs, and fully reconstructed charged-particle tracks. The combination of the three methods gives a charged-particle multiplicity per unit of pseudorapidity, dN(charged)/d(eta), for |eta| < 0.5, of 5.78 +/- 0.01 (stat) +/- 0.23 (syst) for non-single-diffractive events, higher than predicted by commonly used models. The relative increase in charged-particle multiplicity from sqrt(s) = 0.9 to 7 TeV is 66.1% +/- 1.0% (stat) +/- 4.2% (syst). The mean transverse momentum is measured to be 0.545 +/- 0.005 (stat) +/- 0.015 (syst) GeV/c. The results are compared with similar measurements at lower energies.

Figures (5)

• Figure 1: Differential yield of charged hadrons in the range $|\eta| < 2.4$ in $0.2$-unit-wide bins of $|\eta|$ in NSD events. The solid curves represent fits of Eq. \ref{['eq:tsallis']} to the data. The measurements with increasing $\eta$ are successively shifted by six units along the vertical axis.
• Figure 2: Charged-hadron yield in the range $|\eta| < 2.4$ in NSD events as a function of $p_{\mathrm{T}}$; the systematic uncertainties are smaller than the symbols. The measurements at $\sqrt{s}=0.9$ and 2.36 TeV 1stpaper are also shown. The solid lines represent fits of Eq. \ref{['eq:tsallis']} to the data.
• Figure 3: Distributions of $dN_{ch}/d\eta$, averaged over the three measurement methods and compared with data from UA5 Alner:1986xu ($p\bar{p}$, with statistical errors only) and ALICE alice (with systematic uncertainties). The shaded band shows systematic uncertainties of the CMS data. The CMS and UA5 data are averaged over negative and positive values of $\eta$.
• Figure 4: Average $p_{\mathrm{T}}$ of charged hadrons as a function of the centre-of-mass energy. The CMS measurements are for $|\eta|<2.4$. Also shown are measurements from the ISR Rossi:1974if ($pp$), E735 Alexopoulos:1988na ($p\bar{p}$), and CDF Abe:1988yu ($p\bar{p}$) for $|\eta|<0.5$, and from UA1 Albajar:1989an ($p\bar{p}$) for $|\eta|<2.5$. The solid line is a fit of the functional form $\langle p_{\mathrm{T}}\xspace \rangle=0.413-0.0171\ln s + 0.00143\ln^2 s$ to the data. The error bars on the CMS data include the systematic uncertainties.
• Figure 5: Average value of $dN_{\mathrm{ch}}/d\eta$ in the central $\eta$ region as a function of centre-of-mass energy in $pp$ and $\hbox{$p\bar{p}$}$ collisions. Also shown are NSD and inelastic measurements from the NAL Bubble Chamber Whitmore:1973ri ($p\bar{p}$), ISR Thome:1977ky ($pp$), UA1 Albajar:1989an ($p\bar{p}$), UA5 Alner:1986xu ($p\bar{p}$), CDF Abe:1989td ($p\bar{p}$), STAR star:2008ez ($pp$), PHOBOS Nouicer:2004ke ($pp$), and ALICE alice ($pp$). The curves are second-order polynomial fits for the inelastic (solid) and NSD event selections (dashed). The error bars include systematic uncertainties, when available. Data points at 0.9 and 2.36 TeV are slightly displaced horizontally for visibility.