Measurement of forward jet suppression in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$$ TeV with the ATLAS detector

Abstract

Inclusive jet production is measured with the ATLAS detector at the LHC at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV in Pb+Pb and $pp$ collisions, using data samples corresponding to integrated luminosities of 1.72 nb${}^{-1}$ and 255 pb${}^{-1}$, respectively. The jet nuclear modification factor, $R_{\mathrm{AA}}$, is reported for anti-$k_t$ jets with radius parameter $R=0.4$ in the forward-rapidity intervals $2.8<|y|<3.2$ and $3.2<|y|<3.6$, probing transverse momenta $p_{\mathrm{T}}>74$ GeV. The observed $R_{\mathrm{AA}}$ values show a significant suppression of jet yields in Pb+Pb collisions relative to those measured in $pp$ collisions. The suppression increases monotonically from peripheral to central collisions and exhibits a mild jet $p_{\mathrm{T}}$ dependence. A comparison with previous ATLAS measurements indicates stronger jet suppression in the $2.8<|y|<3.2$ region than in the $|y|<2.8$ region. In the $3.2<|y|<3.6$ region, the precision of the measurement does not allow a conclusive comparison with the $|y|<2.8$ region. These results constitute the first measurement of inclusive jet suppression at forward rapidity in heavy-ion collisions and provide new constraints on flavor, geometric, and medium-density dependence of parton energy loss.

37 pages in total, author list starting page 20, 2 tables, 6 figures, submitted to Phys. Lett. B. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2023-11