The physics of $Z^0/γ^*$-tagged jets at the LHC

TL;DR

The paper develops LO and NLO predictions for $Z^0/\gamma^*$+jet production at the LHC, establishing a high-precision baseline in proton-proton and heavy-ion collisions. It formulates and applies a GLV-based description of medium-induced energy loss for parton showers in a dynamically evolving QGP, linking the in-medium gluon bremsstrahlung spectrum to observable jet suppression and energy redistribution. A key contribution is the first NLO treatment of tagged jets in heavy-ion collisions and the prediction of a sharp transition from suppression to enhancement as a function of the tagged jet $p_T$, reflecting the underlying gluon bremsstrahlung spectrum. The work lays the groundwork for jet tomography with electroweak-tagged jets and offers concrete predictions for LHC measurements that can constrain QGP properties.

Abstract

Electroweak bosons produced in conjunction with jets in high-energy collider experiments is one of the principle final-state channels that can be used to test the accuracy of perturbative Quantum Chromodynamics calculations and to assess the potential to uncover new physics through comparison between data and theory. In this paper we present results for the $Z^0/γ^*$+jet production cross sections at the LHC at leading and next-to-leading orders. In proton-proton reactions we elucidate up to ${\cal O}(G_Fα_s^2)$ the constraints that jet tagging via the $Z^0/γ^*$ decay dileptons provides on the momentum distribution of jets. In nucleus-nucleus reactions we demonstrate that tagged jets can probe important aspects of the dynamics of quark and gluon propagation in hot and dense nuclear matter and characterize the properties of the medium-induced parton showers in ways not possible with more inclusive measurements. Finally, we present specific predictions for the anticipated suppression of the $Z^0/γ^*$+jet production cross section in the quark-gluon plasma that is expected to be created in central lead-lead collisions at the LHC relative to the naive superposition of independent nucleon-nucleon scatterings.

Figures (13)

• Figure 1: (Color online) Experimental results from the Fermi Lab Tevatron Collider Abazov:2008ez for the cross section of jets associated with $Z^0$/$\gamma^*\rightarrow \mu^++\mu^-$ in $p+\bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV are compared to tree level pQCD. The left panel shows this cross section versus $p_{T\,(\rm jet)}$, whereas the right panel shows it versus $y_{(\rm jet)}$. The (red) lines indicate our LO result. The (yellow) bands indicate the variation from the choice of scale. The experimental cuts are discussed in the text.
• Figure 2: (Color online) Same as in Figure \ref{['tevdata']} but with a comparison of the Tevatron data to the MCFM LO result (blue) dotted line and the MCFM NLO result (green) solid line. Note that experimental error bars are statistical only.
• Figure 3: (Color online) Transverse momentum distributions of a jet associated with $Z^0/\gamma^*(\rightarrow \mu^++\mu^-)$ tag to ${\cal O}(G_F\alpha_s)$ and ${\cal O}(G_F\alpha_s^2)$. Left and right panels show results for two transverse momentum cuts $92.5\;{\rm GeV} < p_T < 112.5$ GeV and $7\;{\rm GeV} < p_T < 13$ GeV on the tagging particle, respectively.
• Figure 4: (Color online) The left panel shows the binary collision density in central Pb+Pb collisions at the LHC from an optical Glauber model with $\sigma_{in} =65$ mb. The right panel shows the transverse density of soft partons/particles, which is proportional to the participant density.
• Figure 5: (Color online) Fractional energy $\Delta E / E$ lost by 100 GeV quark and gluon jets inside a cone of radius $R$ via gluon emission of $\omega > \omega_{\rm min}$ as a result of final-state interactions in the QGP created in central Pb+Pb reactions at the LHC.