Observation of the jet diffusion wake using dijets in heavy ion collisions

Abstract

Energetic quarks and gluons traversing a hot and dense quark-gluon plasma deposit energy and momentum into the medium before hadronizing to collimated sprays of particles, known as jets. This energy-momentum deposition is expected to produce medium responses, collectively known as jet wakes, with ``diffusion wake'' denoting a depletion of particles in the direction opposite to the propagating jet. These phenomena are studied by comparing dijet-hadron correlations measured in lead-lead (PbPb) and proton-proton (pp) collisions to assess jet-induced modifications of bulk particle production. The analysis uses PbPb and pp data recorded at a nucleon-nucleon center-of-mass energy $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV with the CMS detector at the CERN LHC. By exploring how the dijet-hadron correlation distributions differ for various pseudorapidity separations of the two jets in the dijet, the presence of a jet diffusion wake is firmly established. The wake has a significance greater than 5 standard deviations for charged particles in the transverse momentum range 1 $\lt$ $p_\mathrm{T}$ $\lt$ 2 GeV. The measurements are compared with various model predictions with and without jet wake effects, providing new insights into quark-gluon plasma properties and the formation of jet-induced wakes.

Figures (4)

• Figure 1: The difference of the near-side charged-particle yields $\text{R}^{\text{asym}}\xspace-\text{R}^{\text{sym}}\xspace$ as a function of $\Delta\eta\xspace^{\text{ch}, \; \text{jet}_{1}}$ in $\text{pp}$ (blue squares) and different centrality $\text{PbPb}$ collisions (red circles), with the most central (0--30%) shown in the right panels. Results are shown for two $p_{\mathrm{T}}^{\text{ch}}$ ranges: $1 < p_{\mathrm{T}}^{\text{ch}}\xspace < 2\,\text{Ge\spaceV}\xspace$ (upper) and $2 < p_{\mathrm{T}}^{\text{ch}}\xspace < 4\,\text{Ge\spaceV}\xspace$ (lower). Solid vertical lines (shaded areas) show statistical (systematic) uncertainties.
• Figure 2: The difference between $\text{PbPb}$ and $\text{pp}$ collisions for the particle yield difference observable ($\text{R}^{\text{asym}}\xspace-\text{R}^{\text{sym}}\xspace$) as a function of $\Delta\eta\xspace^{\text{ch}, \; \text{jet}_{1}}$ for central (0--30%) collisions. Results for $1 < p_{\mathrm{T}}^{\text{ch}}\xspace < 2\,\text{Ge\spaceV}\xspace$ are shown for $\text{R}^{\text{asym}}\xspace \lvert \Delta\eta\xspace^{\text{jet}_{1},\text{jet}_{2}} \rvert\xspace \in (0.5, 1.0)$ (upper panel), $\lvert \Delta\eta\xspace^{\text{jet}_{1},\text{jet}_{2}} \rvert\xspace \in (1.0, 1.5)$ (upper middle panel), and $\lvert \Delta\eta\xspace^{\text{jet}_{1},\text{jet}_{2}} \rvert\xspace \in (1.5, 2.0)$ (lower middle panel). The result for $2 < p_{\mathrm{T}}^{\text{ch}}\xspace < 4\,\text{Ge\spaceV}\xspace$ with $\text{R}^{\text{asym}}\xspace \lvert \Delta\eta\xspace^{\text{jet}_{1},\text{jet}_{2}} \rvert\xspace \in (1.0, 1.5)$ is shown in the lower panel. Predictions from the pythiapythia82pythiaCP5tunennpdf31Lokhtin:2005px, HybridCasalderrey-Solana:2014bpaHulcher:2017cpt, and CoLBT-hydro Chen:2017zte models are shown as colored bands. Solid vertical lines (shaded areas) show statistical (systematic) uncertainties. For the models, only statistical uncertainties are shown.
• Figure 3: Charged-particle yield difference integrated over $-2.4 < \Delta\eta\xspace^{\text{ch}, \; \text{jet}_{1}}\xspace < -0.6$ as a function of $\text{PbPb}$ collision centrality for $\lvert \Delta\eta\xspace^{\text{jet}_{1},\text{jet}_{2}} \rvert\xspace \in (1.0, 1.5)$ (closed markers) and $\lvert \Delta\eta\xspace^{\text{jet}_{1},\text{jet}_{2}} \rvert\xspace \in (1.5, 2.0)$ (open markers). Red markers indicate $1 < p_{\mathrm{T}}^{\text{ch}}\xspace < 2\,\text{Ge\spaceV}\xspace$, and blue markers indicate $2 < p_{\mathrm{T}}^{\text{ch}}\xspace < 4\,\text{Ge\spaceV}\xspace$. Solid vertical lines (shaded areas) show statistical (systematic) uncertainties.
• Figure A.1: Distributions of charged-particle yields with $1 < p_{\mathrm{T}}^{\text{ch}}\xspace < 2\,\text{Ge\spaceV}\xspace$ as functions of $\Delta\eta\xspace^{\text{ch}, \; \text{jet}_{1}}\xspace$ and $\Delta\varphi\xspace^{\text{ch}, \; \text{jet}_{1}}\xspace$, measured relative to the leading jet direction in $\text{pp}$ (upper panels) and 0--30% $\text{PbPb}$ (lower panels) collisions. The left (right) column shows the results for small $(\text{R}^{\text{sym}}\xspace\,\lvert \Delta\eta\xspace^{\text{jet}_{1},\text{jet}_{2}} \rvert\xspace < 0.5)$ and large $(\text{R}^{\text{asym}}\xspace\,\lvert \Delta\eta\xspace^{\text{jet}_{1},\text{jet}_{2}} \rvert\xspace \in (1.0,1.5))$ dijet configurations.