Double parton scatterings in high-energy proton-nucleus collisions and partonic correlations

The joint study of double-parton scattering (DPS) in high-energy proton-proton and proton-nucleus collisions can provide a lot of information on multiparton correlations. The multiparton structure is in fact probed in different ways by DPS in $p\text{−}p$ and in $p\text{−}A$ collisions. In $p\text{−}A$ collisions, the interpretation of the experimental results may be complicated, however, by the presence of interference terms, which are missing in $p\text{−}p$ collisions. A suitable reaction channel, where interference terms are absent, is $WJJ$ production. By studying $WJJ$ production in $p\text{−}Pb$ collisions, we estimate that the fraction of events due to DPS may be larger by a factor 3 or 4 as compared to $p\text{−}p$, while the amount of the increased fraction can give information on the importance of different correlation terms.

Figure 1

Double-parton scattering contributions to the discontinuity of the forward $p\text{−}A$ interaction amplitude: (a) diagonal term, (b) interference term.

Figure 2

Configuration in transverse space corresponding to the DPS cross section in Eq. (11).

Figure 3

Upper part of the figure: Configurations in transverse space of the left-hand (A) and right-hand (A*) site amplitudes in the off-diagonal contribution to the cross section in Eq. (12). Lower part of the figure: Nucleons’ fractional momentum flow in the off-diagonal contribution to the cross section in Eq. (12).

Figure 4

Distribution in $p_t$ of the leading jet in $p\text{−}p$ collisions (left panel) and in $p\text{−}Pb$ collisions (right panel). The pink histograms refer to the single scattering contribution, the green ones to the DPS contribution, and the black histograms to the sum of the two contributions. We used ${\sigma }_{\text{eff}}=15\mathrm{mb}$ and $K^2=2$.

Figure 5

Distribution in $p_t$ of the leading jet in $p\text{−}Pb$ collisions in the cases ${\sigma }_{\text{eff}}=15\mathrm{mb}$ (ATLAS) and ${\sigma }_{\text{eff}}=20.7\mathrm{mb}$ (CMS [28]) for $K^2=1$ (left panel) and $K^2=2$ (right panel).

Figure 6

Distribution in $p_t$ of the charged lepton from the $W^{+}$ decay, in $p\text{−}p$ collisions (left panel) and in $p\text{−}Pb$ collisions in the case of ${\sigma }_{\text{eff}}=15\mathrm{mb}$ and $K^2=2$ (right panel).

Figure 7

Rapidity distribution of the charged lepton from the $W^{+}$ decay, in $p\text{−}Pb$ collisions in the case of ${\sigma }_{\text{eff}}=15\mathrm{mb}$ (ATLAS) and ${\sigma }_{\text{eff}}=20.7\mathrm{mb}$ (CMS) for $K^2=1$ (left panel) and $K^2=2$ (right panel).

Figure 8

Discontinuity of the forward amplitude in Eq. (a1).

Figure 9

Discontinuity of the forward amplitude in Eq. (a2).