We have developed a model in which the quantum fluctuations of the proton structure are characterised by hot spots, whose number grows with decreasing Bjorken-x. Our model reproduces the F2(x,Q2) ...data from HERA at the relevant scale, as well as the exclusive and dissociative J/ψ photoproduction data from H1 and ALICE. Our model predicts that for Wγp≈500 GeV, the dissociative J/ψ cross section reaches a maximum and then decreases steeply with energy, which is in qualitatively good agreement to a recent observation that the dissociative J/ψ background in the exclusive J/ψ sample measured in photoproduction by ALICE decreases as energy increases. Our prediction provides a clear signature for gluon saturation at LHC energies.
We study the photoproduction of vector mesons off proton and off nuclear targets. We work within the colour dipole model in an approach that includes subnucleon degrees of freedom, so-called hot ...spots, whose positions in the impact-parameter plane change event-by-event. The key feature of our model is that the number of hot spots depends on the energy of the photon–target interaction. Predictions are presented for exclusive and dissociative production of ρ0, J/ψ, and ϒ(1S) off protons, as well as for coherent and incoherent photoproduction of ρ0 off nuclear targets, where Xe, Au, and Pb nuclei are considered. We find that the mass dependence of dissociative production off protons as a function of the energy of the interaction provides a further handle to search for saturation effects at HERA, the LHC and future colliders. We also find that the coherent photonuclear production of ρ0 is sensitive to fluctuations in the subnucleon degrees of freedom at RHIC and LHC energies.
Quantum tomography is a method to experimentally extract all that is observable about a quantum mechanical system. We introduce quantum tomography to collider physics with the illustration of the ...angular distribution of lepton pairs. The tomographic method bypasses much of the field-theoretic formalism to concentrate on what can be observed with experimental data. We provide a practical, experimentally driven guide to model-independent analysis using density matrices at every step. Comparison with traditional methods of analyzing angular correlations of inclusive reactions finds many advantages in the tomographic method, which include manifest Lorentz covariance, direct incorporation of positivity constraints, exhaustively complete polarization information, and new invariants free from frame conventions. For example, experimental data can determine the entanglement entropy of the production process. We give reproducible numerical examples and provide a supplemental standalone computer code that implements the procedure. We also highlight a property of complex positivity that guarantees in a least-squares type fit that a local minimum of a
χ
2
statistic will be a global minimum: There are no isolated local minima. This property with an automated implementation of positivity promises to mitigate issues relating to multiple minima and convention dependence that have been problematic in previous work on angular distributions.
In this paper, we will discuss results on coherent and incoherent J/ψ photoproduction in ultra-peripheral Pb-Pb collisions at 2.76, as well as preliminary results on exclusive J/ψ and two-photon ...production in ultra-peripheral p-Pb collisions at 5.02 TeV. Results on four-pion production in ultra-peripheral Pb-Pb collisions will also be given. Finally, the prospects for other UPC measurements in ALICE will be briefly mentioned.
This report describes the physics case, the resulting detector requirements, and the evolving detector concepts for the experimental program at the Electron-Ion Collider (EIC). The EIC will be a ...powerful new high-luminosity facility in the United States with the capability to collide high-energy electron beams with high-energy proton and ion beams, providing access to those regions in the nucleon and nuclei where their structure is dominated by gluons. Moreover, polarized beams in the EIC will give unprecedented access to the spatial and spin structure of the proton, neutron, and light ions. The studies leading to this document were commissioned and organized by the EIC User Group with the objective of advancing the state and detail of the physics program and developing detector concepts that meet the emerging requirements in preparation for the realization of the EIC. The effort aims to provide the basis for further development of concepts for experimental equipment best suited for the science needs, including the importance of two complementary detectors and interaction regions.
This report consists of three volumes. Volume I is an executive summary of our findings and developed concepts. In Volume II we describe studies of a wide range of physics measurements and the emerging requirements on detector acceptance and performance. Volume III discusses general-purpose detector concepts and the underlying technologies to meet the physics requirements. These considerations will form the basis for a world-class experimental program that aims to increase our understanding of the fundamental structure of all visible matter.
The pT-differential production cross sections of the prompt charmed mesons D0, D+, D*+, and D+s and their charge conjugate in the rapidity interval –0.96 < ycms < 0.04 were measured in p–Pb ...collisions at a center-of-mass energy √sNN = 5.02 TeV with the ALICE detector at the LHC. The nuclear modification factor RpPb, quantifying the D-meson yield in p–Pb collisions relative to the yield in pp collisions scaled by the number of binary nucleon-nucleon collisions, is compatible within the 15%–20% uncertainties with unity in the transverse momentum interval 1 < pT < 24 GeV/c. No significant difference among the RpPb of the four D-meson species is observed. The results are described within uncertainties by theoretical calculations that include initial-state effects. In conclusion, the measurement adds experimental evidence that the modification of the momentum spectrum of D mesons observed in Pb-Pb collisions with respect to pp collisions is due to strong final-state effects induced by hot partonic matter.
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