N-jet event shapes as probes of nuclear dynamics

We propose the use of N-jettiness (tau(N)), a global event shape, 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 give a new factorization formula for the 1-jettiness (tau(1)) distribution for the production of a single hard jet (J) in lepton-nucleus collisions: l + A(P) -> J(P-J) + X. Each nuclear target gives rise to a unique pattern of radiation, affected by nuclear dynamics, that can be quantified by the tau(1) distribution. Up to power corrections, the tau(1) distribution allows for a direct measurement of the nuclear parton distribution functions. Additional nuclear-dependent effects will be dominated through power corrections of size similar to Q(s)(2) (A)/(tau P-1(JT)), where Q(s)(A) is a dynamical nuclear scale and P-JT is the transverse momentum of the jet. Such nuclear-dependent effects can be studied through a dedicated program to measure tau(1) distributions for a range of 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.