Observation of medium-induced yield enhancement and acoplanarity broadening of low-$p_\mathrm{T}$ jets from measurements in pp and central Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV

The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high transverse momentum (high $p_{\rm T}$) hadron trigger in proton$-$proton and central Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV. A data-driven statistical method is used to mitigate the large uncorrelated background in central Pb$-$Pb collisions. Recoil jet distributions are reported for jet resolution parameter $R=0.2$, 0.4, and 0.5 in the range $7 <~ p_{\rm T,jet} <~ 140$ GeV$/c$ and trigger$-$recoil jet azimuthal separation $\pi/2 <~ \Delta\varphi <~ \pi$. The measurements exhibit a marked medium-induced jet yield enhancement at low $p_{\rm T}$ and at large azimuthal deviation from $\Delta\varphi\sim\pi$. The enhancement is characterized by its dependence on $\Delta\varphi$, which has a slope that differs from zero by 4.7$\sigma$. Comparisons to model calculations incorporating different formulations of jet quenching are reported. These comparisons indicate that the observed yield enhancement arises from the response of the QGP medium to jet propagation.


Accepted by: PRL
HEP Data
e-Print: arXiv:2308.16131 | PDF | inSPIRE
Figure group

Figure 1

Distributions of recoil jets with $\rr=0.2$, 0.4, and 0.5 in \pp\ and central \PbPb\ collisions at $\sqrtsNN=5.02$ TeV Upper panels: corrected \DrecoilpTch\ distributions. Lower panels: \IAApT\ (see text). Also shown are calculations based on JETSCAPE , JEWEL , and the Hybrid model .

Figure 2

Upper panels: Corrected \Drecoilphi\ distributions for $\rr=0.4$ in \PbPb\ and \pp\ collisions at $\sqrtsNN=5.02$ TeV, for intervals in recoil \pTjetch:[10,20] (left), [20,30] (middle), and [30,50] (right) \gev. Lower panels: \IAAphi. Predictions from JETSCAPE , JEWEL , and the LO pQCD calculation  are also shown.

Figure 3

\IAAphi\ for $\rr=0.2$, 0.4 and 0.5, for intervals in recoil \pTjetch:[10,20], [20,30], and [30,50] \gev. The central points and systematic uncertainties are offset from the center of the \dphi\ intervals for clarity. The vertical dashed grey lines represent the \dphi\ interval edges. Predictions from JEWEL are also shown.