Ballistic Protons in Incoherent Exclusive Vector Meson Production as a Measure of Rare Parton Fluctuations at an Electron-Ion Collider

Abstract

We argue that the proton multiplicities measured in Roman pot detectors at an electron ion collider can be used to determine centrality classes in incoherent diffractive scattering. Incoherent diffraction probes the fluctuations in the interaction strengths of multi-parton Fock states in the nuclear wavefunctions. In particular, the saturation scale that characterizes this multi-parton dynamics is significantly larger in central events relative to minimum bias events. As an application, we study the centrality dependence of incoherent diffractive vector meson production. We identify an observable which is simultaneously very sensitive to centrality triggered parton fluctuations and insensitive to details of the model. Introduction Very high multiplicity events in protonproton (p+p) and proton/deuteron-nucleus (p/d+A) collisions at LHC and RHIC have revealed that the structure of such events is more complex and interesting than previously imagined [1][2][3][4]. In particular, interpreting the results of these experiments requires a deeper understanding of event-by-event multi-parton spatial fluctuations in protons and nuclei [5][6][7][8][9]. Incoherent diffraction in deeply inelastic scattering (DIS) of electrons off nuclei (e+A collisions) has been long understood as having the potential to provide insight into event-by-event fluctuations in the spatial structure of nuclei. A significant advantage of e+A collisions relative to p+A collisions is that the former is insensitive to the final state interactions that, in the latter, can complicate the extraction of the spatial parton structure of the proton and the nucleus.

Gluon tomography from deeply virtual Compton scattering at small x

“…Refs. [10,24,[36][37][38] and references therein), if we replace the transverse wave-function of the final state real photon by the vector meson wave-function. Similar conclusions can be also applied to this process.…”

Diffractiveρproduction at smallxin future electron–ion colliders

“…[18] and used in our calculations fails to describe the vanishing of the incoherent cross section as |t| → 0. Our motivation to analyse in detail these processes is associated to the fact that the precise separation of these events will allow us to access the spatial distribution of the gluon density in the nucleus through the Fourier transform of the coherent cross section [19] as well as to study the incoherent processes which probe the fluctuations in the interaction strengths of parton configurations in the nuclear wave function with large values of the saturation scale [21]. In Fig.…”

Photoproduction of Upsilon states in ultraperipheral collisions at the LHC

“…[6], a detailed study of the incoherent cross section for the upsilon states has been done. This is quite important, as it was pointed out that incoherent diffraction probes the fluctuations in the interactions strengths of multiparton Fock states in the nuclear wavefunctions [10]. The connection between incoherent diffraction and fluctuations is a quite rich subject and the pioneering works are found in Refs.…”