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].

We investigate the effect of non-trivial spatial correlations between proton constituents, considered in this work to be gluonic hot spots, on the initial conditions of proton-proton collisions from ISR to LHC energies, i.e. $\sqrt s\!=\!52.6,7000,13000$ GeV. The inclusion of these correlations is motivated by their fundamental role in the description of a recently observed new feature of $pp$ scattering at $\sqrt s\!=\!7$ TeV, the hollowness effect. Our analysis relies on a Monte-Carlo Glauber approach including fluctuations in the hot spot positions and their entropy deposition in the transverse plane. We explore both the energy dependence and the effect of spatial correlations on the number of wounded hot spots, their spatial distribution and the eccentricities, $\varepsilon_n$, of the initial state geometry of the collision. In minimum bias collisions we find that the inclusion of short range repulsive correlations between the hot spots reduces the value of the eccentricity ($\varepsilon_2$) and the triangularity ($\varepsilon_3$). In turn, upon considering only the events with the highest entropy deposition i.e. the ultra-central ones, the probability of having larger $\varepsilon_{2,3}$ increases significantly in the correlated scenario. Finally, the eccentricities show a quite mild energy dependence.Comment: Manuscript restructured and extended to include a centrality study and probability distributions instead of averages . Accepted for publication in Phys. Rev.

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The unambiguous observation of a Chiral Magnetic Effect (CME)-driven charge separation is the core aim of the isobar program at RHIC consisting of 96 40 Zr+ 96 40 Zr and 96 44 Ru+ 96 44 Ru collisions at √ sNN = 200 GeV. We quantify the role of the spatial distributions of the nucleons in the isobars on both eccentricity and magnetic field strength within a relativistic hadronic transport approach (SMASH, Simulating Many Accelerated Strongly-interacting Hadrons). In particular, we introduce isospin-dependent nucleon-nucleon spatial correlations in the geometric description of both nuclei, deformation for 96 44 Ru and the so-called neutron skin effect for the neutron-rich isobar i.e. 96 40 Zr. The main result of this study is a reduction of the magnetic field strength difference between 96 44 Ru+ 96 44 Ru and 96 40 Zr+ 96 40Zr by a factor of 2, from 10% to 5% in peripheral collisions when the neutron-skin effect is included. Further, we find an increase of the eccentricity ratio between the isobars by up to 10% in ultra-central collisions as due to the deformation of 96 44 Ru while neither the neutron skin effect nor the nucleon-nucleon correlations result into a significant modification of this observable with respect to the traditional Woods-Saxon modeling. Our results suggest a significantly smaller CME signal to background ratio for the experimental charge separation measurement in peripheral collisions with the isobar systems than previously expected.

In this work, we analyse the all-orders resummation structure of the momentum sharing fraction, zg, opening angle, θg, and relative transverse momentum, kt,g, of the splitting tagged by the Dynamical Grooming procedure in hadronic collisions. We demonstrate that their resummation does non-exponentiate and it is free of clustering logarithms. Then, we analytically compute the probability distributions of (zg, θg, kt,g) up to next-to-next-to-double logarithm accuracy (N2DL) in the narrow jet limit, including a matching to leading order in αs. On the phenomenological side, we perform an analytic-to-parton level comparison with Pythia and Herwig. We find that differences between the analytic and the Monte-Carlo results are dominated by the infra-red regulator of the parton shower. Further, we present the first analytic comparison to preliminary ALICE data and highlight the role of non-perturbative corrections in such low-pt regime. Once the analytic result is corrected by a phenomenologically determined non-perturbative factor, we find very good agreement with the data.