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  • Mäntysaari, Heikki; Mueller, Niklas; Schenke, Björn (2019)
    Experimental processes that are sensitive to partonWigner distributions provide a powerful tool to advance our understanding of proton structure. In this work, we compute gluon Wigner and Husimi distributions of protons within the color glass condensate framework, which includes a spatially dependent McLerran-Venugopalan initial configuration and the explicit numerical solution of the Jalilian-Marian-IancuMcLerran-Weigert-Leonidov-Kovner equations. We determine the leading anisotropy of the Wigner and Husimi distributions as a function of the angle between the impact parameter and transverse momentum. We study experimental signatures of these angular correlations at a proposed electron-ion collider by computing coherent diffractive dijet production cross sections in e + p collisions within the same framework. Specifically, we predict the elliptic modulation of the cross section as a function of the relative angle between the nucleon recoil and dijet transversemomentumfor a wide kinematical range. We further predict its dependence on the collision energy, which is dominated by the growth of the proton with decreasing x.
  • Goharipour, Muhammad; Khanpour, Hamzeh; Guzey, Vadim (2018)
    We present GKG18-DPDFs, a next-to-leading order (NLO) QCD analysis of diffractive parton distribution functions (diffractive PDFs) and their uncertainties. This is the first global set of diffractive PDFs determined within the xFitter framework. This analysis is motivated by all available and most up-to-date data on inclusive diffractive deep inelastic scattering (diffractive DIS). Heavy quark contributions are considered within the framework of the Thorne-Roberts (TR) general mass variable flavor number scheme (GM-VFNS). We form a mutually consistent set of diffractive PDFs due to the inclusion of high-precision data from H1/ZEUS combined inclusive diffractive cross sections measurements. We study the impact of the H1/ZEUS combined data by producing a variety of determinations based on reduced data sets. We find that these data sets have a significant impact on the diffractive PDFs with some substantial reductions in uncertainties. The predictions based on the extracted diffractive PDFs are compared to the analyzed diffractive DIS data and with other determinations of the diffractive PDFs.
  • Adare, A.; Kim, D. J.; Krizek, F.; Novitzky, N.; Rak, J.; PHENIX Collaboration (2017)
    Dihadron and isolated direct photon-hadron angular correlations are measured in p + p collisions at root s = 510 GeV. Correlations of charged hadrons of 0.7 <p(T) <10 GeV/c with pi(0) mesons of 4 <p(T) <15 GeV/c or isolated direct photons of 7 <p(T) <15 GeV/c are used to study nonperturbative effects generated by initial-state partonic transverse momentum and final-state transverse momentum from fragmentation. The nonperturbative behavior is characterized by measuring the out-of-plane transverse momentum component p(out) perpendicular to the axis of the trigger particle, which is the high-p(T) direct photon or pi(0). Nonperturbative evolution effects are extracted from Gaussian fits to the away-side inclusive-charged-hadron yields for different trigger-particle transverse momenta (p(T)(trig)). The Gaussian widths and root mean square of p(out) are reported as a function of the interaction hard scale p(T)(trig) to investigate possible transverse-momentum-dependent evolution differences between the pi(0)-h(+/-) and direct photon-h(+/-) correlations and factorization breaking effects. The widths are found to decrease with p(T)(trig) , which indicates that the Collins-Soper-Sterman soft factor is not driving the evolution with the hard scale in nearly back-to-back dihadron and direct photon-hadron production in p + p collisions. This behavior is in contrast to Drell-Yan and semi-inclusive deep-inelastic scattering measurements.
  • Aschenauer, E. C.; Fazio, S.; Lamont, M. A. C.; Paukkunen, H.; Zurita, P. (2017)
    The quantitative knowledge of heavy nuclei's partonic structure is currently limited to rather large values of momentum fraction x-robust experimental constraints below x similar to 10(-2) at low resolution scale Q(2) are particularly scarce. This is in sharp contrast to the free proton's structure which has been probed in Deep Inelastic Scattering (DIS) measurements down to x similar to 10(-5) at perturbative resolution scales. The construction of an electron-ion collider (EIC) with a possibility to operate with a wide variety of nuclei, will allow one to explore the low-x region in much greater detail. In the present paper we simulate the extraction of the nuclear structure functions from measurements of inclusive and charm reduced cross sections at an EIC. The potential constraints are studied by analyzing simulated data directly in a next-toleading order global fit of nuclear Parton Distribution Functions based on the recent EPPS16 analysis. A special emphasis is placed on studying the impact an EIC would have on extracting the nuclear gluon parton distribution function, the partonic component most prone to nonlinear effects at low Q(2). In comparison to the current knowledge, we find that the gluon parton distribution function can be measured at an EIC with significantly reduced uncertainties.
  • Brambilla, N.; Eidelman, S.; Foka, P.; Gardner, S.; Kronfeld, A. S.; Alford, M. G.; Alkofer, R.; Butenschoen, M.; Cohen, T. D.; Erdmenger, J.; Fabbietti, L.; Faber, M.; Goity, J. L.; Ketzer, B.; Lin, H. W.; Llanes-Estrada, F. J.; Meyer, H. B.; Pakhlov, P.; Pallante, E.; Polikarpov, M. I.; Sazdjian, H.; Schmitt, A.; Snow, W. M.; Vairo, A.; Vogt, R.; Vuorinen, Aleksi; Wittig, H.; Arnold, P.; Christakoglou, P.; Di Nezza, P.; Fodor, Z.; Garcia i Tormo, X.; Hoellwieser, R.; Janik, M. A.; Kalweit, A.; Keane, D.; Kiritsis, E.; Mischke, A.; Mizuk, R.; Odyniec, G.; Papadodimas, K.; Pich, A.; Pittau, R.; Qiu, J. -W.; Ricciardi, G.; Salgado, C. A.; Schwenzer, K.; Stefanis, N. G.; von Hippel, G. M.; Zakharov, V. I. (2014)
    We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.