Measurements of the Nuclear Modification Factor for Jets in Pb+Pb Collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV with the ATLAS Detector

TL;DR

Inclusive jet production is found to be suppressed by approximately a factor of 2 in central collisions compared to pp collisions, and the nuclear modification factor R(AA) shows a slight increase with p(T) and no significant variation with rapidity.

Abstract

Measurements of inclusive jet production are performed in $pp$ and Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV with the ATLAS detector at the LHC, corresponding to integrated luminosities of 4.0 $\mathrm{pb}^{-1}$ and 0.14 $\mathrm{nb}^{-1}$, respectively. The jets are identified with the anti-$k_t$ algorithm with $R=0.4$, and the spectra are measured over the kinematic range of jet transverse momentum $32 < p_{\mathrm{T}} < 500$ GeV, and absolute rapidity $|y| < 2.1$ and as a function of collision centrality. The nuclear modification factor, $R_{\mathrm{AA}}$, is evaluated and jets are found to be suppressed by approximately a factor of two in central collisions compared to $pp$ collisions. The $R_{\mathrm{AA}}$ shows a slight increase with $p_{\mathrm{T}}$ and no significant variation with rapidity.

Figures (4)

• Figure 1: The double differential jet cross section in $pp$ collisions as a function of $p_{\mathrm{T}}$ in different rapidity bins (scaled by successive powers of $10^{2}$). The statistical and systematic uncertainties are indicated by the error bars (too small to be seen on this scale) and shaded bands, respectively. The points and horizontal error bars indicate the $p_{\mathrm{T}}$ bin center and width, respectively.
• Figure 2: The per-event jet yield in Pb+Pb collisions, multiplied by $1/ \hbox{$\langle T_{\mathrm{AA}} \rangle$}$, as a function of $p_{\mathrm{T}}$ (scaled by successive powers of $10^{2}$). The upper panel shows the 0--2.1 rapidity range in different centrality intervals. The lower panel shows the 0--10% centrality interval in different rapidity ranges. The statistical and systematic uncertainties are indicated by the error bars (too small to be seen on this scale) and shaded bands, respectively. The points and horizontal error bars indicate the $p_{\mathrm{T}}$ bin center and width, respectively. The solid and dashed lines represent the $pp$ jet cross section for the same rapidity interval scaled by the same factor.
• Figure 3: Jet $R_{\mathrm{AA}}$ as a function of $p_{\mathrm{T}}$ in different centrality bins with each panel showing a different range in $|y|$. The fractional luminosity and $\langle T_{\mathrm{AA}} \rangle$ uncertainties are indicated separately as shaded boxes centered at one. The boxes, bands and error bars indicate uncorrelated systematic, correlated systematic and statistical uncertainties, respectively.
• Figure 4: The $R_{\mathrm{AA}}$ for jets with $80 < p_{\mathrm{T}} < 100$Ge V as a function of $|y|$ for different centrality bins (top) and as a function of $\langle N_{\mathrm{part}}\rangle$ for the $|y| < 2.1$ range (bottom). The fractional luminosity and $\langle T_{\mathrm{AA}} \rangle$ uncertainties are indicated separately as shaded boxes centered at one. The boxes, bands and error bars indicate uncorrelated systematic, correlated systematic and statistical uncertainties, respectively.