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| CMS-HIN-25-012 ; CERN-EP-2026-017 | ||
| Observation of the jet diffusion wake using dijets in heavy ion collisions | ||
| CMS Collaboration | ||
| 23 February 2026 | ||
| Submitted to Phys. Rev. Lett. | ||
| 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 ($ \text{pp} $) collisions to assess jet-induced modifications of bulk particle production. The analysis uses PbPb and $ \text{pp} $ data recorded at a nucleon-nucleon center-of-mass energy $ \sqrt{\smash[b]{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 $ < p_{\mathrm{T}} < $ 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. | ||
| Links: e-print arXiv:2602.19431 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
The difference of the near-side charged-particle yields $ \text{R}^{\text{asym}}-\text{R}^{\text{sym}} $ as a function of $ \Delta\eta^{\text{ch}, \; \text{jet}_{1}} $ in $ \text{pp} $ (blue squares) and different centrality 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}} < $ 2 GeV (upper) and 2 $ < p_{\mathrm{T}}^{\text{ch}} < $ 4 GeV (lower). Solid vertical lines (shaded areas) show statistical (systematic) uncertainties. |
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Figure 2:
The difference of the near-side charged-particle yields $ \text{R}^{\text{asym}}-\text{R}^{\text{sym}} $ as a function of $ \Delta\eta^{\text{ch}, \; \text{jet}_{1}} $ in $ \text{pp} $ (blue squares) and different centrality 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}} < $ 2 GeV (upper) and 2 $ < p_{\mathrm{T}}^{\text{ch}} < $ 4 GeV (lower). Solid vertical lines (shaded areas) show statistical (systematic) uncertainties. |
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Figure 3:
The difference between PbPb and $ \text{pp} $ collisions for the particle yield difference observable ($ \text{R}^{\text{asym}}-\text{R}^{\text{sym}} $) as a function of $ \Delta\eta^{\text{ch}, \; \text{jet}_{1}} $ for central (0--30%) collisions. Results for 1 $ < p_{\mathrm{T}}^{\text{ch}} < $ 2 GeV are shown for $ \text{R}^{\text{asym}} |\Delta\eta^{\text{jet}_{1},\text{jet}_{2}}| \in (0.5, 1.0) $ (upper panel), $ |\Delta\eta^{\text{jet}_{1},\text{jet}_{2}}| \in (1.0, 1.5) $ (upper middle panel), and $ |\Delta\eta^{\text{jet}_{1},\text{jet}_{2}}| \in (1.5, 2.0) $ (lower middle panel). The result for 2 $ < p_{\mathrm{T}}^{\text{ch}} < $ 4 GeV with $ \text{R}^{\text{asym}} |\Delta\eta^{\text{jet}_{1},\text{jet}_{2}}| \in (1.0, 1.5) $ is shown in the lower panel. Predictions from the PYTHIA [56,57,58,59], HYBRID [64,65], and CoLBT-hydro [66] models are shown as colored bands. Solid vertical lines (shaded areas) show statistical (systematic) uncertainties. For the models, only statistical uncertainties are shown. |
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Figure 4:
Charged-particle yield difference integrated over $ -2.4 < \Delta\eta^{\text{ch}, \; \text{jet}_{1}} < - $ 0.6 as a function of PbPb collision centrality for $ |\Delta\eta^{\text{jet}_{1},\text{jet}_{2}}| \in (1.0, 1.5) $ (closed markers) and $ |\Delta\eta^{\text{jet}_{1},\text{jet}_{2}}| \in (1.5, 2.0) $ (open markers). Red markers indicate 1 $ < p_{\mathrm{T}}^{\text{ch}} < $ 2 GeV, and blue markers indicate 2 $ < p_{\mathrm{T}}^{\text{ch}} < $ 4 GeV. Solid vertical lines (shaded areas) show statistical (systematic) uncertainties. |
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Figure B1:
Distributions of charged-particle yields with 1 $ < p_{\mathrm{T}}^{\text{ch}} < $ 2 GeV as functions of $ \Delta\eta^{\text{ch}, \; \text{jet}_{1}} $ and $ \Delta\varphi^{\text{ch}, \; \text{jet}_{1}} $, measured relative to the leading jet direction in $ \text{pp} $ (upper panels) and 0--30% PbPb (lower panels) collisions. The left (right) column shows the results for small $ (\text{R}^{\text{sym}} |\Delta\eta^{\text{jet}_{1},\text{jet}_{2}}| < 0.5) $ and large $ (\text{R}^{\text{asym}} |\Delta\eta^{\text{jet}_{1},\text{jet}_{2}}| \in (1.0,1.5)) $ dijet configurations. |
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Figure B1-a:
Distributions of charged-particle yields with 1 $ < p_{\mathrm{T}}^{\text{ch}} < $ 2 GeV as functions of $ \Delta\eta^{\text{ch}, \; \text{jet}_{1}} $ and $ \Delta\varphi^{\text{ch}, \; \text{jet}_{1}} $, measured relative to the leading jet direction in $ \text{pp} $ (upper panels) and 0--30% PbPb (lower panels) collisions. The left (right) column shows the results for small $ (\text{R}^{\text{sym}} |\Delta\eta^{\text{jet}_{1},\text{jet}_{2}}| < 0.5) $ and large $ (\text{R}^{\text{asym}} |\Delta\eta^{\text{jet}_{1},\text{jet}_{2}}| \in (1.0,1.5)) $ dijet configurations. |
png pdf |
Figure B1-b:
Distributions of charged-particle yields with 1 $ < p_{\mathrm{T}}^{\text{ch}} < $ 2 GeV as functions of $ \Delta\eta^{\text{ch}, \; \text{jet}_{1}} $ and $ \Delta\varphi^{\text{ch}, \; \text{jet}_{1}} $, measured relative to the leading jet direction in $ \text{pp} $ (upper panels) and 0--30% PbPb (lower panels) collisions. The left (right) column shows the results for small $ (\text{R}^{\text{sym}} |\Delta\eta^{\text{jet}_{1},\text{jet}_{2}}| < 0.5) $ and large $ (\text{R}^{\text{asym}} |\Delta\eta^{\text{jet}_{1},\text{jet}_{2}}| \in (1.0,1.5)) $ dijet configurations. |
png pdf |
Figure B1-c:
Distributions of charged-particle yields with 1 $ < p_{\mathrm{T}}^{\text{ch}} < $ 2 GeV as functions of $ \Delta\eta^{\text{ch}, \; \text{jet}_{1}} $ and $ \Delta\varphi^{\text{ch}, \; \text{jet}_{1}} $, measured relative to the leading jet direction in $ \text{pp} $ (upper panels) and 0--30% PbPb (lower panels) collisions. The left (right) column shows the results for small $ (\text{R}^{\text{sym}} |\Delta\eta^{\text{jet}_{1},\text{jet}_{2}}| < 0.5) $ and large $ (\text{R}^{\text{asym}} |\Delta\eta^{\text{jet}_{1},\text{jet}_{2}}| \in (1.0,1.5)) $ dijet configurations. |
png pdf |
Figure B1-d:
Distributions of charged-particle yields with 1 $ < p_{\mathrm{T}}^{\text{ch}} < $ 2 GeV as functions of $ \Delta\eta^{\text{ch}, \; \text{jet}_{1}} $ and $ \Delta\varphi^{\text{ch}, \; \text{jet}_{1}} $, measured relative to the leading jet direction in $ \text{pp} $ (upper panels) and 0--30% PbPb (lower panels) collisions. The left (right) column shows the results for small $ (\text{R}^{\text{sym}} |\Delta\eta^{\text{jet}_{1},\text{jet}_{2}}| < 0.5) $ and large $ (\text{R}^{\text{asym}} |\Delta\eta^{\text{jet}_{1},\text{jet}_{2}}| \in (1.0,1.5)) $ dijet configurations. |
| Summary |
| In summary, we report the first observation of the diffusion wake using dijets in heavy ion collisions. The measurements use pseudorapidity-separated dijets in lead-lead (PbPb) and proton-proton (pp) collisions at a center-of-mass energy per nucleon pair of 5.02 TeV. Charged-particle correlations were studied relative to the highest transverse momentum ($p_{\mathrm{T}}$) jet of each dijet. Correlations are measured for dijets with different pseudorapidity separations, and the difference between correlations from large and small separation samples is used for the jet diffusion wake extraction. When isolating medium modifications by examining the difference between PbPb and pp collisions, a pronounced depletion of charged-particle yields is observed in the region where a wake signal is expected. The integrated signal for low-$p_{\mathrm{T}}$ charged particles ($1 < p_{\mathrm{T}}^{ch} < 2$ GeV) in central collisions deviates from zero with a significance exceeding 5 standard deviations. The depletion is less pronounced in more peripheral collisions and when examining a higher $ p_{\mathrm{T}}^{ch}$ selection. Theoretical models incorporating jet energy loss and medium response show qualitatively similar trends with magnitudes that are larger than what is seen in the data, whereas models without jet-medium interactions do not show any depletion. This observation of the diffusion wake offers new insights into quark-gluon plasma properties and jet-induced medium response. |
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