Jet peak shapes based on two-particle angular correlations in lead-lead collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

Abstract

The longitudinal invariance of jet-induced peaks in two-particle correlation functions from relativistic lead-lead collisions is experimentally explored. The data were collected at a center-of-mass energy per nucleon pair of 5.02 TeV in 2018 using the CMS detector. The dataset corresponds to an integrated luminosity of 0.607 nb$^{-1}$. Long- and short-range correlations are studied through two-dimensional distributions of the separations in pseudorapidity and azimuth between particles in an event. Jets manifest as a well-defined peak at small angular separations, and the shape of this peak provides insight into jet medium interactions. This Letter examines the evolution of the jet peak shape, focusing on the dependence of its width and longitudinal asymmetry on the transverse momentum, collision centrality, and pseudorapidity of the associated charged particles. The jet-peak distributions of lower transverse momentum particles broaden in both pseudorapidity and azimuth with increasing collision overlap, with the broadening in pseudorapidity being more pronounced. The longitudinal asymmetry of the peaks is also found to increase as the average pseudorapidity increases. These results are compared to proton-proton collision data that were obtained at the same nucleon-nucleon collision center-of-mass energy with an integrated luminosity of 252 nb$^{-1}$.

Figures (6)

• Figure 1: Average signal (left), mixed-event (middle), and pair-acceptance corrected per-trigger associated yield (right) distributions for 0--10% centrality events, with $4 < p_\text{T,trig}\xspace < 8\,\text{Ge\spaceV}\xspace$ and $2 < p_\text{T,asso}\xspace < 3\,\text{Ge\spaceV}\xspace$, in $\text{PbPb}$ collision data at 5.02$\,\text{Te\spaceV}$.
• Figure 2: (Upper) One-dimensional $\Delta\eta$ projection and (lower) One-dimensional $\Delta\phi$ projection.
• Figure 3: Two-dimensional correlation distributions in the 0--10% centrality interval for $\text{PbPb}$ (upper) and ${ \mathup{{{p}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{p}}{} _{ {}} ^{ {}}} }\xspace$ (lower) collisions are shown, with $1.5 < \lvert \eta_\text{trig}\xspace \rvert < 2$, $12 < p_\text{T,trig}\xspace < 16\,\text{Ge\spaceV}\xspace$, and $2 < p_\text{T,asso}\xspace < 3\,\text{Ge\spaceV}\xspace$.
• Figure 4: One-dimensional $\Delta\eta$ projection from the long-range background-subtracted averaged 2D correlation, combining $1.5 < \eta_\text{trig}\xspace < 2$ (original) and $-2 < \eta_\text{trig}\xspace < -1.5$ (mirror). Three vertical lines correspond to a $\Delta\eta$ value of --0.7, 0 and 0.7 from left to right. The dashed line indicates the zero level on the y-axis.
• Figure 5: Centrality dependence of the longitudinal $\sigma_{\Delta\eta}$ (left panel) and transverse $\sigma_{\Delta\phi}$ (right panel) values are presented in different $p_{\mathrm{T}}$ ranges for $\text{PbPb}$ collisions and ${ \mathup{{{p}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{p}}{} _{ {}} ^{ {}}} }\xspace$ collisions (rightmost points in each panel). The same symbols are used for the same $p_{\text{T,asso}}$ selections, with open markers representing high $p_{\text{T,trig}}$ and closed markers for low $p_{\text{T,trig}}$. The statistical uncertainties of the data points are smaller than the marker size, and rectangular boxes indicate the systematic uncertainties. Expected values from hydjet 1.9 are represented by bands: hatched for low $p_{\text{T,trig}}$ and solid-filled for high $p_{\text{T,trig}}$.