Soft multiple parton interactions as seen in multiplicity distributions at Tevatron and LHC

We analyze the multiplicity distributions of charged particles at Tevatron ($p\overline{p}$) and LHC ($pp$) energies in the framework of the independent pair parton interactions model. It is shown that the number of soft pair parton interactions (and therefore the density of the partonic medium) is large and increases with energy. The mean multiplicity at each parton interaction grows also with energy. This growth depends on the width of the rapidity window. Similar conclusions are obtained in the multiladder exchange model.

Figure 1

IPPI fit (dash-dotted line) of the multiplicity distribution at 1.8 TeV.

Figure 2

IPPI fit (dashed line) of the $H_q$ moments at 1.8 TeV.

Figure 3

Check-up of $q$-independence for $m$ as derived from $P_n$ and $H_q$ fits.

Figure 4

The IPPI-values of $m$ at different energies and rapidity windows; the numbers of active pairs ($j_{\max }$) are also shown near each point.

Figure 5

IPPI (dash-dotted line) and QGSM (dotted line) fits of the multiplicity distribution at 7 TeV ($|\eta |<2.4$, CMS data).

Figure 6

Extrapolation to 14 TeV of $m$-values shown in Fig. 4 for IPPI (dash-dotted line) in comparison with QGSM (dotted line) for $|\eta |<2.4$. Extrapolation for full rapidity window (straight line, non-LHC data) is also shown.

Figure 7

Corresponding extrapolation of the maximum number of pair parton interactions ($j_{\max }$) to 14 TeV.

Figure 8

Predictions of IPPI (dash-dotted lines) and QGSM (dotted line) for multiplicity distribution at 14 TeV. CMS multiplicity distribution ($|\eta |<2.4$) at 7 TeV is also shown for comparison.

Figure 9

IPPI fit (dashed line) of the $H_q$ moments at 7 TeV. The maximum rank of the moments in the fitting procedure is indicated.

Figure 10

IPPI multiplicity distributions ($P_n$) and $H_q$ moments with parameters derived from fits of $P_n$ (dash-dotted lines) and $H_q$ (dotted lines) experimental data at 1.8 TeV without $m=\mathrm{const}$ condition.

Figure 11

Check-up of $q$-independence for $m$ derived from $P_n$ (solid line) and $H_q$ (dashed line) fits at 1.8 TeV without $m=\mathrm{const}$ condition. Straight lines are the means of obtained results.