Schematic of a photon-tagged jet (γ+jet) in heavy-ion collisions. (IMAGE)
Caption
In high-energy heavy-ion collisions, jets serve as penetrating probes of the quark-gluon plasma (QGP) because their structure is modified as they traverse this hot, dense medium. A fundamental challenge is that we observe only the final, medium-modified jets, lacking direct knowledge of their initial state. Figure 1 illustrates a photon-tagged jet (γ+jet). Unlike an inclusive jet, a γ+jet originates from a parton-photon pair produced back-to-back. The photon escapes the collision unaffected by the QGP, thereby providing a precise reference for the jet's initial energy and direction. This makes photon-tagging a powerful method to mitigate experimental biases in studying jet quenching.
Credit
Sa Wang
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