Jet quenching from QCD evolution

Recent advances in soft-collinear effective theory with Glauber gluons have led to the development of a new method that gives a unified description of inclusive hadron production in reactions with nucleons and heavy nuclei. We show how this approach, based on the generalization of the DGLAP evolution equations to include final-state medium-induced parton shower corrections for large $Q^2$ processes, can be combined with initial-state effects for applications to jet quenching phenomenology. We demonstrate that the traditional parton energy loss calculations can be regarded as a special soft-gluon emission limit of the general QCD evolution framework. We present phenomenological comparison of the ${\mathrm{SCET}}_{\mathrm{G}}$-based results on the suppression of inclusive charged hadron and neutral pion production in $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$ lead-lead collisions at the Large Hadron Collider to experimental data. We also show theoretical predictions for the upcoming $\sqrt{s_{\mathrm{NN}}}\simeq 5.1\mathrm{TeV}$ $\mathrm{Pb}+\mathrm{Pb}$ run at the LHC.

Figure 1

The nuclear modification factor $R_{AA}$ for charged hadrons is calculated in central $\mathrm{Pb}+\mathrm{Pb}$ collisions at the LHC $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$, and compared with the ATLAS experimental data [21]. Top left panel: Central collisions without CNM energy loss, and bands represent the variation of the coupling strength $g=2.0\pm 0.1$. Top right panel: Central collisions with CNM energy loss, and bands represent the variation of the coupling strength $g=1.9\pm 0.1$. Middle panels are the same as the top panels but calculated in midperipheral $\mathrm{Pb}+\mathrm{Pb}$ collisions. Bottom panels: The comparison of our calculations with ATLAS charged hadron suppression measurements in central (left) as well as midperipheral (right) $\mathrm{Pb}+\mathrm{Pb}$ collisions. The dashed cyan curves are for the coupling strength $g=2.0$ without CNM energy loss, while the solid magenta curves are for the coupling strength $g=1.9$ with CNM energy loss.

Figure 2

Same as in Fig. 1 except the comparison is made to ALICE charged hadron data for the $R_{AA}$ for $\mathrm{Pb}+\mathrm{Pb}$ collisions at the LHC $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$.

Figure 3

Same as in Fig. 1 except the comparison is made to CMS charged hadron data for the $R_{AA}$ for $\mathrm{Pb}+\mathrm{Pb}$ collisions at the LHC $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$.

Figure 4

Same as in Fig. 1 except the comparison is made to ALICE neutral pions data for the $R_{AA}$ for $\mathrm{Pb}+\mathrm{Pb}$ collisions at the LHC $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$.

Figure 5

Comparison of calculations of the nuclear modification factor of charged hadrons (left) and neutral pions (right) with and without cold nuclear matter energy loss. Results for central and midperipheral $\mathrm{Pb}+\mathrm{Pb}$ collisions are shown for $g=1.9$.

Figure 6

The predicted nuclear modification factor $R_{AA}$ for charged hadrons (left) and neutral pions (right) in central (magenta) and midperipheral (cyan) $\mathrm{Pb}+\mathrm{Pb}$ collisions at the LHC $\sqrt{s_{\mathrm{NN}}}=5.1\mathrm{TeV}$ is plotted as a function of hadron transverse momentum $p_T$. In top panels the bands represent a variation of the coupling strength $g=2.0\pm 0.1$ and we do not include CNM energy loss effects. In the middle panels the coupling is varied $g=1.9\pm 0.1$ and we do include CNM energy loss effects. In the bottom we present the combined results. For the coupling strength $g=2.0$, we again do not include the CNM energy loss effects. For the coupling strength $g=1.9$, we include the usual CNM energy loss constrained at RHIC, as well as an additional calculation where we assume 50% larger CNM energy loss effects.