N-Jettiness as a probe of nuclear dynamics

We propose the use of N-jettiness (τ_N), a global event shape variable, as a probe of nuclear dynamics in lepton-nucleus collisions. It characterizes the amount of soft radiation between the jet and nuclear beam directions. We write down the factorization for the 1-jettiness ($τ_1$) distribution for the production of a single hard jet (J) in lepton-nucleus collisions: \ell+A(P) \to J(P_{J})+X. Each nuclear target gives rise to a unique pattern radiation, determined by nuclear dynamics, that can be quantified by the τ_1-distribution. Up to power corrections, the τ_1-distribution allows for a direct measurement of the nuclear PDFs. Additional nuclear-dependent effects will be dominated through power corrections of size $\sim Q_s^2(A)/(P_{JT}τ_1)$ where $Q_s(A)$ is a dynamical scale sensitive to nuclear medium effects. Such nuclear-dependent effects and the dependence of Q_s(A) on the nuclear atomic number $A$ can be probed through a dedicated program of precision measurements of τ_1-distributions for various nuclei and kinematics. We give numerical results for the 1-jettiness distribution for the simplest case of a proton target at next-to-leading-log accuracy.

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