Testing Saturation with Large-mass Diffraction in Dis

One of the most successful approaches to the understanding of hard diffraction in DIS is the QCD dipole picture which naturally describes both inclusive and diffractive events within the same theoretical framework1,2. It expresses the scattering of the photon through its fluctuation into a color singlet qq̄ pair (dipole) and the same dipole scattering amplitude enters in the formulation of the inclusive and diffractive proton structure functions. This approach revealed3 that unitarity and the way it is realized should be important ingredients of the description of diffractive cross-sections, making those ideal places to look for saturation effects at small-x. In this study, we analyse hard diffraction when the proton stays intact after the collision and the mass of the diffractive final state is much bigger than the virtuality of the photon. This process is called diffractive photon dissociation. We propose the measurement of the final state configuration X + jet + gap + p in virtual photon-proton collisions. We show that in the context of saturation theory, the transverse momentum distribution of the measured jet is resonant with the scale at which the contributions of large-size dipoles start to be suppressed, called the saturation scale. That exhibits the potential of the diffractive-jet measurement for testing saturation and extracting the saturation scale.