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Measurement of charged particle multiplicities in $pp$ collisions at $\sqrt{s}$ = 7 TeV in the forward region

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Abstract

The charged particle production in proton-proton collisions is studied with the LHCb detector at a centre-of-mass energy of ${\sqrt{s} =7}$TeV in different intervals of pseudorapidity $\eta$. The charged particles are reconstructed close to the interaction region in the vertex detector, which provides high reconstruction efficiency in the $\eta$ ranges $-2.5<\eta<-2.0$ and $2.0<\eta<4.5$. The data were taken with a minimum bias trigger, only requiring one or more reconstructed tracks in the vertex detector. By selecting an event sample with at least one track with a transverse momentum greater than 1 GeV/c a hard QCD subsample is investigated. Several event generators are compared with the data; none are able to describe fully the multiplicity distributions or the charged particle density distribution as a function of $\eta$. In general, the models underestimate the charged particle production.

Figures and captions

The multiplicity distribution in $\eta$ bins (shown as points with statistical error bars) with predictions of different event generators. The inner error bar represents the statistical uncertainty and the outer error bar represents the systematic and statistical uncertainty on the measurements. The data in both figures are identical with predictions from Pythia 6, Phojet and Pythia 8 in (a) and predictions of the Pythia 6 Perugia tunes with and without diffraction in (b).

newsys[..].eps [42 KiB]
HiDef png [397 KiB]
Thumbnail [91 KiB]
*.C file
newsyst1_noptcut_log_bw.eps
newsys[..].eps [42 KiB]
HiDef png [428 KiB]
Thumbnail [89 KiB] *.C file
newsyst1_noptcut_nodiff_log_bw.eps

The multiplicity distribution in the forward $\eta$ range (shown as points with error bars) with predictions of different event generators. The shaded bands represent the total uncertainty on the measurements. The data in both figures are identical with predictions from Pythia 6, Phojet and Pythia 8 in (a) and predictions of the Pythia 6 Perugia tunes with and without diffraction in (b).

newsys[..].eps [16 KiB]
HiDef png [199 KiB]
Thumbnail [42 KiB]
*.C file
newsyst2_noptcut_log_bw.eps
newsys[..].eps [17 KiB]
HiDef png [217 KiB]
Thumbnail [45 KiB] *.C file
newsyst2_noptcut_nodiff_log_bw.eps

The KNO distributions in different bins of $\eta$. Only the the statistical uncertainties are shown.

kno.eps [12 KiB]
HiDef png [102 KiB]
Thumbnail [25 KiB]
*.C file
kno.eps

The charged particle densities as a function of $\eta$ (shown as points with statistical error bars) and comparisons with predictions of event generators, as indicated in the key. The shaded bands represent the total uncertainty. The events are selected by requiring at least one charged particle in the range $2.0<\eta<4.5$. The data in both figures are identical with predictions from Pythia 6, Phojet and Pythia 8 in (a) and predictions of the Pythia 6 Perugia tunes with and without diffraction in (b).

MCrap.eps [13 KiB]
HiDef png [117 KiB]
Thumbnail [27 KiB]
*.C file
MCrap.eps
MCrap_[..].eps [13 KiB]
HiDef png [131 KiB]
Thumbnail [29 KiB] *.C file
MCrap_nodiff.eps

The multiplicity distribution in $\eta$ bins (shown as points with error bars) with predictions of different event generators. The inner error bar represents the statistical uncertainty and the outer error bar represents the systematic and statistical uncertainty on the measurements. The events have at least one track with a $ p_{\rm T} >1.0$ $ {\mathrm{\,GeV\!/}c}$ in the pseudorapidity range $2.5 < \eta < 4.5$. The data in both figures are identical with predictions from Pythia 6, Phojet and Pythia 8 in (a) and predictions of the Pythia 6 Perugia tunes in (b).

newsys[..].eps [43 KiB]
HiDef png [388 KiB]
Thumbnail [86 KiB]
*.C file
newsyst1_ptcut_log_bw.eps
newsys[..].eps [39 KiB]
HiDef png [310 KiB]
Thumbnail [76 KiB] *.C file
newsyst1_ptcut_nodiff_log_bw.eps

The multiplicity distribution in the forward $\eta$ range (shown as points with statistical error bars) with predictions of different event generators. The shaded bands represent the total uncertainty. The events have at least one track with a $ p_{\rm T} >1.0$ $ {\mathrm{\,GeV\!/}c}$ in the pseudorapidity range $2.5 < \eta < 4.5$. The data in both figures are identical with predictions from Pythia 6, Phojet and Pythia 8 in (a) and predictions of the Pythia 6 Perugia tunes in (b).

newsys[..].eps [17 KiB]
HiDef png [215 KiB]
Thumbnail [44 KiB]
*.C file
newsyst2_ptcut_log_bw.eps
newsys[..].eps [15 KiB]
HiDef png [173 KiB]
Thumbnail [35 KiB] *.C file
newsyst2_ptcut_nodiff_log_bw.eps

The data charged particle densities as a function of $\eta$ (shown as points with statistical error bars) and comparisons with predictions of event generators, as indicated in the key. The events have at least one track with a $ p_{\rm T} >1.0$ $ {\mathrm{\,GeV\!/}c}$ in the pseudorapidity range $2.5 < \eta < 4.5$. The shaded bands represent the total uncertainty.

MCrap_[..].eps [13 KiB]
HiDef png [119 KiB]
Thumbnail [27 KiB]
*.C file
MCrap_ptcut.eps
MCrap_[..].eps [10 KiB]
HiDef png [91 KiB]
Thumbnail [21 KiB] *.C file
MCrap_nodiff_ptcut.eps

Animated gif made out of all figures.

PAPER-2011-011.gif
Thumbnail
thumbnail_PAPER-2011-011.gif

Tables and captions

Charged particle multiplicity distribution in the pseudorapidity range $-2.5<\eta<-2.0$ for minimum bias events and for hard QCD events (see text). The first quoted uncertainty is statistical and the second is systematic.

Table_1.pdf [38 KiB]
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tex code
Table_1.pdf

Charged particle multiplicity distribution in the pseudorapidity range $2.0<\eta<2.5$ for minimum bias events and for hard QCD events (see text). The first quoted uncertainty is statistical and the second is systematic.

Table_2.pdf [38 KiB]
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tex code
Table_2.pdf

Charged particle multiplicity distribution in the pseudorapidity range $2.5<\eta<3.0$ for minimum bias events and for hard QCD events (see text). The first quoted uncertainty is statistical and the second is systematic.

Table_3.pdf [38 KiB]
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tex code
Table_3.pdf

Charged particle multiplicity distribution in the pseudorapidity range $3.0<\eta<3.5$ for minimum bias events and for hard QCD events (see text). The first quoted uncertainty is statistical and the second is systematic.

Table_4.pdf [38 KiB]
HiDef png [283 KiB]
Thumbnail [48 KiB]
tex code
Table_4.pdf

Charged particle multiplicity distribution in the pseudorapidity range $3.5<\eta<4.0$ for minimum bias events and for hard QCD events (see text). The first quoted uncertainty is statistical and the second is systematic.

Table_5.pdf [38 KiB]
HiDef png [286 KiB]
Thumbnail [48 KiB]
tex code
Table_5.pdf

Charged particle multiplicity distribution in the pseudorapidity range $4.0<\eta<4.5$ for minimum bias events and for hard QCD events (see text). The first quoted uncertainty is statistical and the second is systematic.

Table_6.pdf [38 KiB]
HiDef png [277 KiB]
Thumbnail [47 KiB]
tex code
Table_6.pdf

Charged particle multiplicity distribution in the pseudorapidity range $2.0<\eta<4.5$ for minimum bias events and for hard QCD events (see text). The first quoted uncertainty is statistical and the second is systematic.

Table_7.pdf [38 KiB]
HiDef png [575 KiB]
Thumbnail [94 KiB]
tex code
Table_7.pdf

Created on 09 December 2018.Citation count from INSPIRE on 09 December 2018.