We present a dynamical explanation of the hollowness effect observed in proton-proton scattering at √ s = 7 TeV. This phenomenon, not observed at lower energies, consists in a depletion of the inelasticity density at zero impact parameter of the collision. Our analysis is based on three main ingredients: we rely gluonic hot spots inside the proton as effective degrees of freedom for the description of the scattering process. Next we assume that some non-trivial correlation between the transverse positions of the hot spots inside the proton exists. Finally we build the scattering amplitude from a multiple scattering, Glauber-like series of collisions between hot spots. In our approach, the onset of the hollowness effect is naturally explained as due to the diffusion or growth of the hot spots in the transverse plane with increasing collision energy.The analysis of experimental data on the elastic proton-proton differential cross-section at collision energy √ s = 7 TeV measured by the TOTEM Collaboration[1] has revealed a new, intriguing feature of hadronic interactions: at high energies, the inelasticity density of the collision does not reach a maximum at zero impact parameter. Rather, peripheral collisions, where the effective geometric overlap of the colliding protons is smaller, are more inelastic or, equivalently, are more effective in the production of secondary particles than central ones. This phenomenon, not observed before at lower collision energies, has been referred to as hollowness [2] or grayness [3-5] of proton-proton collisions by the authors of the first analyses where it was identified.Our own independent analysis of LHC and ISR data, to be described below, confirms that the inelasticity density of the collisionwhere T el (s, b) is the scattering amplitude in the impact parameter representation, reaches a maximum at b = 0 for a collision energy √ s = 7 TeV, as shown in Fig. 1.The hollowness effect challenges the standard geometric interpretations of proton-proton collisions. In particular, it precludes models where the scattering amplitude is built in terms of a positive dependence on the convolution of the density profiles of the two colliding protons. Indeed, it can be shown that the inelasticity density associated to any elastic scattering amplitude thus constructed presents a maximum at zero impact parameter, regardless how intricate the internal structure of one individual proton may be [2]. These observations suggest that the scattering problem may be best formulated in terms of sub nucleonic degrees of freedom which internal dynamics and correlations should be non-trivial with increasing collision energy. Such is the view adopted in this work, where we consider hot spots to be the effective degrees of freedom in terms of which to discuss the properties of the scattering amplitude.The idea that the gluon content of the proton is con-× 2 |t|[GeV 2 ] dσ/dt [GeV −4 ]

We propose a new class of infrared-collinear (IRC) and Sudakov safe observables with an associated jet grooming technique that removes dynamically soft and large angle branches. It is based on identifying the hardest branch in the Cambridge/Aachen re-clustering sequence and discarding prior splittings that occur at larger angles. This leads to a dynamically generated cut-off on the phase space of the tagged splitting that is encoded in a Sudakov form factor. In this exploratory study we focus on the mass and momentum sharing distributions of the tagged splitting which we analyze analytically to modified leading logarithmic accuracy and compare to Monte-Carlo simulations. * mehtartani@bnl.gov † ontoso@bnl.gov ‡ konrad.tywoniuk@uib.no

We present a quantitative study of the νN cross section in the neutrino energy range 10 4 < E ν < 10 14 GeV within two transversal QCD approaches: NLO DGLAP evolution using different sets of PDFs and BK small-x evolution with running coupling and kinematical corrections. We show that the non-linear effects embodied in the BK equation yield a slower raise in the cross section for E ν 10 8 GeV than the usual DGLAP based calculation. Finally, we translate this theoretical uncertainty into upper bounds for the ultra-high-energy neutrino flux for different experiments.

We present a systematic study of the normalized symmetric cumulants, NSC(n,m), at the eccentricity level in proton-proton interactions at √ s = 13 TeV within a wounded hot spot approach. We focus our attention on the influence of spatial correlations between the proton constituents, in our case gluonic hot spots, on this observable. We notice that the presence of short-range repulsive correlations between the hot spots systematically decreases the values of NSC(2,3) and NSC(2,4) in midto ultra-central collisions while increases them in peripheral interactions. In the case of NSC(2,3) we find that, as suggested by data, an anti-correlation of ε2 and ε3 in ultra-central collisions, i.e. NSC(2,3) < 0, is possible within the correlated scenario while it never occurs without correlations when the number of gluonic hot spots is set to three. We attribute this fact to the decisive role of correlations on enlarging the probability of interaction topologies that reduce the value of NSC(2,3) and, eventually, make it negative. Further, we explore the dependence of our conclusions on the number of hot spots, the values of the hot spot radius and the repulsive core distance. Our results add evidence to the idea that considering spatial correlations between the subnucleonic degrees of freedom of the proton may have a strong impact on the initial state properties of proton-proton interactions [1].