Jet momentum dependence of jet quenching in PbPb collisions at sqrt(sNN)=2.76 TeV

TL;DR

This CMS study analyzes dijet production in PbPb collisions at √sNN = 2.76 TeV to quantify jet quenching through dijet momentum balance and angular correlations. Using a large PbPb dataset and reference PYTHIA+HYDJET simulations, the work shows pronounced dijet momentum imbalance in central events without notable broadening of the azimuthal opening, indicating differential parton energy loss in the quark-gluon plasma. The imbalance persists across leading-jet pT up to at least 350 GeV, with peripheral collisions aligning with pp references, thereby tightening constraints on energy-loss mechanisms. Overall, the results extend the observed jet-quenching phenomena across centrality and pT, reinforcing the picture of medium-induced parton energy loss without large angular decorrelation.

Abstract

Dijet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV is studied with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 150 inverse microbarns is analyzed. Jets are reconstructed using combined information from tracking and calorimetry. The dijet momentum balance and angular correlations are studied as a function of collision centrality and leading jet transverse momentum. For the most peripheral PbPb collisions, good agreement of the dijet momentum balance distributions with pp data and reference calculations at the same collision energy is found, while more central collisions show a strong imbalance of leading and subleading jet transverse momenta attributed to the jet-quenching effect. The dijet momentum imbalance in central collisions is found to persist for leading jet transverse momenta up to the highest values studied.

Figures (6)

• Figure 1: Distribution of the angle $\Delta\phi_{1,2}$ between the leading and subleading jets in bins of leading jet transverse momentum from 120 $< p_{\text{T},1} < 150$${\,\text{Ge\spaceV\space/\space}c}$ to $p_{\text{T},1} > 300$${\,\text{Ge\spaceV\space/\space}c}$ for subleading jets of $p_{\text{T},2}> 30$${\,\text{Ge\spaceV\space/\space}c}$. Results for 0--20% central PbPb events are shown as points while the histogram shows the results for pythia dijets embedded into hydjet PbPb simulated events. The error bars represent the statistical uncertainties.
• Figure 2: Fraction of events with a genuine subleading jet with $\Delta\phi_{1,2} > 2\pi/3$, as a function of leading jet $p_{\text{T},1}$ (left) and $N_\text{part}$ (right). The background due to underlying event fluctuations is estimated from $\Delta\phi_{1,2} < \pi/3$ events and subtracted from the number of dijets. The fraction of the estimated background is shown in the bottom panels. The error bars represent the statistical uncertainties.
• Figure 3: Dijet asymmetry ratio, $A_{J}$, for leading jets of $p_{\text{T},1}> 120$${\,\text{Ge\spaceV\space/\space}c}$ and subleading jets of $p_{\text{T},2}> 30$${\,\text{Ge\spaceV\space/\space}c}$ with a selection of $\Delta\phi_{1,2}>2\pi/3$ between the two jets. Results are shown for six bins of collision centrality, corresponding to selections of 70--100% to 0--10% of the total inelastic cross section. Results from data are shown as points, while the histogram shows the results for pythia dijets embedded into hydjet PbPb simulated events. Data from pp collisions at 2.76$\,\text{Te\spaceV}$ are shown as open points in comparison to PbPb results of 70--100% centrality. The error bars represent the statistical uncertainties.
• Figure 4: Dijet asymmetry ratio, $A_{J}$, in bins of leading jet transverse momentum from 120 $< p_{\text{T},1} < 150$${\,\text{Ge\spaceV\space/\space}c}$ to $p_{\text{T},1} > 300$${\,\text{Ge\spaceV\space/\space}c}$ for subleading jets of $p_{\text{T},2}> 30$${\,\text{Ge\spaceV\space/\space}c}$ and $\Delta\phi_{1,2}>2\pi/3$ between leading and subleading jets. Results for 0--20% central PbPb events are shown as points, while the histogram shows the results for pythia dijets embedded into hydjet PbPb simulated events. The error bars represent the statistical uncertainties.
• Figure 5: Subleading jet transverse momentum fraction ($p_{\text{T},2}/p_{\text{T},1}$), in bins of leading jet transverse momentum from 120 $< p_{\text{T},1} < 150$${\,\text{Ge\spaceV\space/\space}c}$ to $p_{\text{T},1} > 300$${\,\text{Ge\spaceV\space/\space}c}$ for subleading jets of $p_{\text{T},2}> 30$${\,\text{Ge\spaceV\space/\space}c}$ and $\Delta\phi_{1,2}>2\pi/3$ between leading and subleading jets. Results for 0--20% central PbPb events are shown as points, while the histogram shows the results for pythia dijets embedded into hydjet PbPb simulated events. The arrows show the mean values of the distributions and the error bars represent the statistical uncertainties.