We test the hypothesis that configurations of a proton with a large-x parton, xp ≳ 0.1, have a smaller than average transverse size. The application of the QCD Q2 evolution equations shows that these ...small configurations also have a significantly smaller interaction strength, which has observable consequences in proton-nucleus collisions. We perform a global analysis of jet production data in proton- and deuteronnucleus collisions at RHIC and the LHC. Using a model which takes a distribution of interaction strengths into account, we quantitatively extract the xp dependence of the average interaction strength, σðxpÞ, over a wide kinematic range. By comparing the RHIC and LHC results, our analysis finds that the interaction strength for small configurations, while suppressed, grows faster with collision energy than does that for average configurations. We check that this energy dependence is consistent with the results of a method which, given σðxpÞ at one energy, can be used to quantitatively predict that at another. This finding further suggests that at even lower energies, nucleons with a large-xp parton should interact much more weakly than those in an average configuration, a phenomenon in line with explanations of the EMC effect for largexp quarks in nuclei based on color screening.
Here, several methods of generating three constituent quarks in a nucleon are evaluated which explicitly maintain the nucleon's center of mass and desired radial distribution and can be used within ...Monte Carlo Glauber frameworks. The geometric models provided by each method are used to generate distributions over the number of constituent quark participants (Nqp) in p+p,d+Au, and Au+Au collisions. The results are compared with each other and to a previous result of Nqp calculations, without this explicit constraint, used in measurements of √SNN = 200 GeV p+p,d+Au, and Au+Au collisions at the BNL Relativistic Heavy Ion Collider.
QCD challenges from pp to A–A collisions Adolfsson, J.; Andronic, A.; Bierlich, C. ...
The European physical journal. A, Hadrons and nuclei,
2020, Letnik:
56, Številka:
11
Journal Article
Recenzirano
Odprti dostop
This paper is a write-up of the ideas that were presented, developed and discussed at the third International Workshop on QCD Challenges from pp to A–A, which took place in August 2019 in Lund, ...Sweden (Workshop link:
https://indico.lucas.lu.se/event/1214/
). The goal of the workshop was to focus on some of the open questions in the field and try to come up with concrete suggestions for how to make progress on both the experimental and theoretical sides. The paper gives a brief introduction to each topic and then summarizes the primary results.
Measurements of reconstructed jets in high-energy proton–nucleus collisions over a wide rapidity and transverse momentum range are a fundamental probe of the partonic structure of nuclei. Inclusive ...jet production is sensitive to the modification of parton distribution functions (PDF) in the high-density nuclear environment. Furthermore, any modification of jet production in p+A collisions has implications for understanding the strong suppression seen in central A + A collisions. The latest results on inclusive jet production in 29/nb of proton–lead collisions at 5.02 TeV with the ATLAS detector at the LHC are presented. The centrality of p+Pb events is characterized through the sum of the transverse energy in the Pb-going forward calorimeter. In minimum bias p+Pb collisions, the jet yields are seen to be consistent with calculations incorporating nuclear PDF effects. However, the jet yields in central and peripheral p+Pb collisions are found to be strongly suppressed and enhanced, respectively, relative to geometric expectations. Furthermore, the modifications at forward rapidities are seen to be consistent with a scaling in the total jet energy, suggesting that the modifications may depend on the initial kinematics of the hard parton–parton scattering.
Experimental studies of the collisions of heavy nuclei at relativistic energies have established the properties of the quark–gluon plasma (QGP), a state of hot, dense nuclear matter in which quarks ...and gluons are not bound into hadrons1–4. In this state, matter behaves as a nearly inviscid fluid5 that efficiently translates initial spatial anisotropies into correlated momentum anisotropies among the particles produced, creating a common velocity field pattern known as collective flow. In recent years, comparable momentum anisotropies have been measured in small-system proton–proton (p+p) and proton–nucleus (p+A) collisions, despite expectations that the volume and lifetime of the medium produced would be too small to form a QGP. Here we report on the observation of elliptic and triangular flow patterns of charged particles produced in proton–gold (p+Au), deuteron–gold (d+Au) and helium–gold (3He+Au) collisions at a nucleon–nucleon centre-of-mass energy \\sqrt {s_{{\mathrm{NN}}}\ = 200 GeV. The unique combination of three distinct initial geometries and two flow patterns provides unprecedented model discrimination. Hydrodynamical models, which include the formation of a short-lived QGP droplet, provide the best simultaneous description of these measurements.
Jet reconstruction in heavy ion collisions at RHIC and the LHC is becoming a popular tool to explore medium effects including the energy loss and modified fragmentation of hard-scattered partons. In ...p + A and d + A collisions, reconstructed jets are important for evaluating cold nuclear matter effects such as the impact parameter dependence of nuclear parton distribution functions and initial state energy loss. We present current PHENIX results from p + p, d + Au, and Cu + Cu collisions at 200 GeV using the Gaussian filter and anti-kT algorithms. The systematic study of direct jet reconstruction across a variety of collisions systems at PHENIX will help to tell a coherent story of jet physics at RHIC.
sPHENIX is a new experiment under construction for the Relativistic Heavy Ion Collider at Brookhaven National Laboratory which will study the quark-gluon plasma to further the understanding of ...quantum chromodynamics (QCP) matter and interactions. A prototype of the sPHENIX electromagnetic calorimeter (EMCal) was tested at the Fermilab Test Beam Facility in Spring 2018 as experiment T-1044. The EMCal prototype corresponds to a solid angle of <inline-formula> <tex-math notation="LaTeX">\Delta \eta \times \Delta \phi = 0.2 \times 0.2 </tex-math></inline-formula> centered at pseudo-rapidity <inline-formula> <tex-math notation="LaTeX">\eta = 1 </tex-math></inline-formula>. The prototype consists of scintillating fibers embedded in a mix of tungsten powder and epoxy. The fibers project back approximately to the center of the sPHENIX detector, giving 2-D projectivity. The energy response of the EMCal prototype was studied as a function of position and input energy. The energy resolution of the EMCal prototype was obtained after applying a position-dependent energy correction and a beam profile correction. Two separate position-dependent corrections were considered. The EMCal energy resolution was found to be <inline-formula> <tex-math notation="LaTeX">\sigma (E)/\langle E\rangle = 3.5(0.1) \oplus 13.3(0.2)/\sqrt {E} </tex-math></inline-formula> based on the hodoscope position-dependent correction, and <inline-formula> <tex-math notation="LaTeX">\sigma (E)/\langle E\rangle = 3.0(0.1) \oplus 15.4(0.3)/\sqrt {E} </tex-math></inline-formula> based on the cluster position-dependent correction. These energy resolution results meet the requirements of the sPHENIX physics program.
The centrality dependence of forward jet production in pA collisions at the Large Hadron Collider (LHC) has been found to grossly violate the Glauber model prediction in a way that depends on the x ...in the proton. In this paper, we argue that this modification pattern provides the first experimental evidence for x-dependent proton color fluctuation effects. On average, parton configurations in the projectile proton containing a parton with large x interact with a nuclear target with a significantly smaller than average cross section and have smaller than average size. We implement the effects of fluctuations of the interaction strength and, using the ATLAS analysis of how hadron production at backward rapidities depends on the number of wounded nucleons, make quantitative predictions for the centrality dependence of the jet production rate as a function of the x-dependent interaction strength σ(x). We find that σ(x) ~ 0.6(σ) gives a good description of the data at x = 0.6. Finally, these findings support an explanation of the European Muon Collaboration effect as arising from the suppression of small-size nucleon configurations in the nucleus.
Recently, multiparticle-correlation measurements of relativistic p/d/^{3}He+Au, p+Pb, and even p+p collisions show surprising collective signatures. Here, we present beam-energy-scan measurements of ...two-, four-, and six-particle angular correlations in d+Au collisions at sqrts_{NN}=200, 62.4, 39, and 19.6 GeV. We also present measurements of two- and four-particle angular correlations in p+Au collisions at sqrts_{NN}=200 GeV. We find the four-particle cumulant to be real valued for d+Au collisions at all four energies. We also find that the four-particle cumulant in p+Au has the opposite sign as that in d+Au. Further, we find that the six-particle cumulant agrees with the four-particle cumulant in d+Au collisions at 200 GeV, indicating that nonflow effects are subdominant. These observations provide strong evidence that the correlations originate from the initial geometric configuration, which is then translated into the momentum distribution for all particles, commonly referred to as collectivity.
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