Two particle differential transverse momentum and number density correlations in p-Pb and Pb-Pb at the LHC

Measurements of two-particle differential number correlation functions $R_{2}$ and transverse momentum correlation functions $P_{2}$, obtained from p-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV and Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV, are presented. Measurements are reported for charged particles in the pseudorapidity range |$\eta$| < 1.0, and transverse momentum range 0.2 < $p_{T}$ < 2.0 GeV/$c$ as a function of pair separation in pseudorapidity, |$\Delta\eta$|, azimuthal angle, $\Delta\phi$, and for several charged-particle multiplicity classes. The correlation measurements are carried out for like-sign (LS) and unlike-sign (US) charged-particle pairs separately. The LS and US correlation functions are combined to obtain charge-independent (CI) and charge-dependent (CD) correlation functions. The correlation functions $R_{2}^{(CI)}$ and $P_{2}^{(CI)}$ both feature a prominent and relatively narrow peak centered at $\Delta\phi$ = 0, |$\Delta\eta$| = 0 (called near-side peak in the remainder of this work) in peripheral Pb-Pb collisions and the emergence of large $\Delta\phi$ modulations in more central collisions. However, $P_{2}^{(CI)}$ is characterized, in 5% most central collisions, by a strong third harmonic that gives rise to a dip-like structure at $\Delta\phi \sim \pi$. The correlation functions $R_{2}^{(CD)}$ and $P_{2}^{(CD)}$ also feature a dominant near-side peak but are devoid of flow-like $\Delta\phi$ modulations. Projections of $R_{2}^{(CI)}$, $P_{2}^{(CI)}$, $R_{2}^{(CD)}$ and $P_{2}^{(CD)}$ onto |$\Delta\eta$| and $\Delta\phi$ axes are studied to extract the dependence of the width of the near-side peak of these correlation functions on multiplicity classes in Pb-Pb and p-Pb collisions. The widths of CD correlation functions are observed to monotonically decrease with increasing multiplicity. The widths of the $P_{2}$ correlator are notably smaller than those of $R_{2}$ in both collision systems and all multiplicity classes. The $\Delta\phi$ widths exhibit a non-monotonic dependence on the longitudinal particle pair separation, |∆η|, that may be related to the transport properties of the system and the magnitude of radial flow. Additionally, Fourier decompositions of the $R_{2}$ and $P_{2}$ correlators in $\Delta\phi$ are studied as a function of the pair separation |$\Delta\eta$|. Significant differences in the dependence of their harmonic coefficients on multiplicity classes were found. These differences can be exploited, in theoretical models, to obtain further insight into charged-particle production and transport in heavy-ion collisions. Moreover, an upper limit of non-flow contributions to flow coefficients $v_{n}$ measured in Pb-Pb collisions based on the relative strength of Fourier coefficients measured in p-Pb interactions is estimated.